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Degraded inland and coastal water quality is a critical statewide concern in Florida and other states. Nutrients released from land-based human activities are present in water bodies resulting in algal blooms and increased eutrophication that impairs water bodies for their intended uses. There are differing approaches to addressing eutrophication, including voluntary adoption of current best management practices (BMPs) for nutrients, state regulation, or local county or municipal ordinances. The local ordinance, some including a summer (or so-called “wet season”) fertilizer ban or “blackout,” has been the chosen approach in some Florida counties and municipalities to address local water quality issues. Many components of these ordinances follow published BMPs, and there is agreement in the literature on the effectiveness of these practices for preventing nutrient losses from the landscape. However, there has been disagreement among stakeholders regarding the inclusion of a total fertilizer ban in a local ordinance. Regulators are asking about the best approach to controlling urban pollution and if banning fertilizer in the growing season would achieve the desired environmental protection and whether there are any potential unintended consequences associated with removing fertilizer from turfgrass growing in the summer months. The scientific literature documents the nature and scope of the water pollution problem, and numerous research reports have addressed fertilizer BMPs to prevent nutrient losses from the landscape. This article discusses the increased rate of eutrophication and reviews the pertinent national literature regarding managing urban landscape fertilization to protect water quality. Particular attention is given to fertilization practices during the active landscape plant (especially turfgrass) growth period that corresponds to the summer fertilizer bans in some Florida local ordinances. Therefore, special attention is paid to the question of what information is in the scientific literature and whether a fertilizer ban is the best way of achieving the goal of improving urban water quality. Research summarized in this review points to potential unintended consequences of increased nutrient losses from urban landscapes, particularly turfgrass, when proper, recommended fertilization and irrigation practices are not followed.
Increasing eutrophication or nutrient enrichment of fresh and coastal waters is a serious and growing concern (Diaz and Rosenberg, 2008; Heisler et al., 2008). Eutrophication is largely the result of human activities in managing land, plants, and wastes (Selman and Greenhaugh, 2009). Contribution of urban nutrient sources is becoming a widespread question as officials try to deal with urban water quality problems. In the UnitedStates, during the decade of 1982–92, there were 1.4 million acres converted for urban development and there were 2.2 million acres converted from 1992–97 (U.S. Department of Agriculture, 2005). It is well documented that urbanization changes land cover and hydrology leading to “unintended consequences” on urban ecosystems, including altered nutrient flows (Roach et al., 2008).
Coastal and urban water quality is a major concern of federal, state, and local governments and agencies; university turf and environmental scientists; and the citizens of states like Florida. Point and nonpoint source nutrient pollution of water bodies causes degradation or impairment of the water bodies for their intended uses, such as recreation, fishing, drinking water, irrigation, etc. Nitrate–nitrogen (NO3–N) pollution of water bodies has been associated with methemoglobinemia (blue-baby syndrome) and a limit of 10 ppm NO3–N was set (Knobeloch et al., 2000; U.S. Environmental Protection Agency, 2012a). In addition, N and phosphorus (P) can be involved in increasing the rate of eutrophication of a water body leading to impairment of intended uses. Earlier research reports of eutrophication focused on N or P separately, but Paerl (2009) pointed out that N and P should now be managed together to control eutrophication rates in the freshwater–marine water continuum.
Cleanup of impaired water bodies is required by the total maximum daily load (TMDL) program (Florida Department of Environmental Protection, 2009a; U.S. Environmental Protection Agency, 2010). The required cleanup of impaired waters puts severe economic burdens on local governments (Baker, 2007). In addition to the direct costs to local governments, harmful and toxic algal blooms were determined to result in greater revenue losses for local businesses on the panhandle of Florida than other environmental events such as tropical storms and rains (Larkin and Adams, 2007). Nutrient enrichment of waters is an ecologically damaging and costly issue and must be addressed in a science-based comprehensive process. While this review focuses on the urban eutrophication issue in Florida, we draw on relevant research reported in the national scientific literature to learn what is being done in the country for reducing urban nutrient pollution.
Research has pointed to many sources of nutrients contributing to increased nutrient loads and algal growth in surface waters throughout the world (Alcock, 2007; Baker, 2007; Carey et al., 2012; Glibert et al., 2005; Heisler et al., 2008). Impairment of water bodies in Florida includes increases in algal growth (blooms), especially those algae that produce toxins (harmful algae) that can potentially impact aquatic wildlife and humans (Anderson et al., 2002; Paerl et al., 2010). Understanding the myriad of pollutant sources will help develop management approaches to reduce pollution from these sources. In the next part of this review article, we present information on the various sources of nutrients in the urban environment that may lead to eutrophication of water bodies.
Land-based sewage sources were implicated in algal blooms off the southeast coast of Florida (Lapointe et al., 2005). Paerl et al. (2010) found that toxic cyanobacteria (e.g., Cylindrospermopsis sp., Lyngbya sp.) associated with red tide respond to iron, N, and P from sewage outfalls, urban wastewater, urban development runoff, and nutrients in groundwater. Lapointe et al. (2006) determined that large algal blooms of a planktonic freshwater cyanobacterium (Microcystis aeruginosa) in the Caloosahatchee estuary in 2005 were likely related to sewage effluent as were red tide blooms offshore of Sanibel Island in 2004. There are examples where the removal of sewage-based nutrient sources was related to a reduction in algal blooms (Anderson et al., 2002). Green and Janicki (2006) showed that quantity of Tampa Bay desirable seagrasses [e.g., turtle grass (Thalassia sp.), shoal grass (Halodule ruppia)] increased an estimated 13.8% from 1998–2004 due initially to regulation of wastewater treatment plant discharges. Land-based N discharges from Lake Okeechobee and the Caloosahatchee River following the hurricanes of 2004 and 2005 were implicated in algal blooms in southwest Florida. In addition to specific sewage and hurricane-driven storm water events, continuous nonpoint nutrient loads from inland surface waters that enter coastal waters have also been observed to influence algal blooms. Likewise, nutrient flux from bays, harbors, and rivers along the west coast of Florida were shown to provide a significant nutrient load to support high-biomass blooms of a toxic algae (Karenia brevis), the organism responsible for red tide outbreaks in Florida (Vargo et al., 2008).
Land-based N and P sources can vary from location to location and this variability can lead to a gradient of P- and N-limited phytoplankton communities (Heil et al., 2007). Although the ultimate source of nutrient enrichment may be land-based, there can be considerable cycling, transport, and mineralization of N and P from phytoplankton already in the water bodies, and these cycled quantities can be greater than external loadings (Wang et al., 1999). These authors suggested that, while nutrient load reductions are needed, time will be required before observing impacts of those reductions because cycling of already imported nutrients plays a role in algal blooms. Furthermore, the impacts of eutrophication differ depending on the algal species (Anderson et al., 2002).
While nearby land-based sources contribute to the total nutrient load, studies have also implicated long-distance transported nutrients in Florida red tides. For example, depositions of Saharan dust, containing iron, could relieve iron deficiency in certain aquatic organisms (Walsh and Steidinger, 2001). Stumpf et al. (2007) used thermal and ocean color satellite data to suggest the possible involvement of nutrients from the Mississippi River that travel in a plume to the west Florida shelf. Eutrophication of water bodies is a complex problem, requiring timely, and comprehensive, understanding of its causal factors and adaptive management approaches (Alcock, 2007).
Industrial (e.g., smoke) and fossil fuel combustion (e.g., automobiles) emit N oxides to the air, which can be deposited onto land or water bodies during rainfalls. For example, in 1996, the Tampa Bay Estuary Program predicted that as much as 33% of nutrient contribution to Tampa Bay by 2010 would result from atmospheric deposition (Zarbock et al., 1996). An updated report (Janicki et al., 2001) using the methods of Zarbock et al. (1996) predicted that for 2010 conditions atmospheric deposition would be 20% and nonpoint contributions of N to Tampa Bay would be 49%. The total annual N load predicted for 2010 in the latter report was 2950 tons, down from the predicted value of 3670 tons in the Zarbock et al. (1996) report. Predicted total quantities of nonpoint N loses in both estimates were similar. The percent loads because of nonpoint sources increased because material losses and atmospheric deposition were predicted to be lower in the later model. A recent planning and management document from the Tampa Bay Estuary Program claimed that the two largest contributors of nutrients to Tampa Bay were atmospheric deposition and storm water runoff (Tampa Bay Estuary Program, 2006).
Fertilizers used on urban landscapes and turf may be a source of nutrients in aquatic eutrophication (Baker, 2007). A study was conducted in the Wekiva River Basin (central Florida) to determine if residential fertilizers were contributing to NO3–N found in the river (MACTEC, 2009). Groundwater sampling wells were placed in the surficial aquifer in residential areas (not impacted by septic systems) and in natural areas. Groundwater samples from the residential wells averaged 2.0 mg·L−1 NO3–N, significantly greater than the 0.3 mg·L−1 NO3–N from the wells in the natural areas. Isotopic analyses for N and oxygen supported the conclusion that NO3–N in the residential wells did not come from organic sources and was likely from fertilizers. High proportions of lawns being fertilized were confirmed in a companion study in the Wekiva Basin, which found that 80% of residents in the study area applied fertilizer to their lawns (Souto et al., 2009). Determining rates of application was made difficult by availability of data as 41% of residents did not apply fertilizer themselves; rather the fertilizer was applied by hired applicators.
In a Baltimore, MD, study, Groffman et al. (2004) measured greater NO3–N losses from urban and suburban watersheds (≈2 to 7 lb/acre per year N) compared with a forested watershed (less than 1 lb/acre per year N). These researchers, however, also noted high retention (75%) of N inputs in the urban watersheds mostly consisting of fertilizer and atmospheric deposition. In other studies of urban turf and forested landscapes in Baltimore, researchers noted that grasslands exported more N than forests, but the urban grasslands (turf) had significant ability to retain N (Groffman et al., 2009). The authors found, in some instances, that unfertilized urban turfgrass lands had more leaching losses than fertilized grasslands. The authors emphasized that changing from agricultural land to urban grasslands would have a benefit of reducing N losses. In a study of urbanization impacts on water quality in small coastal watersheds, Tufford et al. (2003) found that dissolved organic nitrogen (DON) and P-containing particulates were the dominant sources of these nutrients and there was variation in location and season. DON dominated in the summer and from forested wetland creeks, while particulate P dominated in the summer from urban ponds. These authors concluded that broad land use or land cover classes should not be used to predict nutrient concentrations in streams of small watersheds. Losses of nutrients from the urban landscape can be reduced by improving irrigation management, using slow-release fertilizers, and modifying sandy soils for better nutrient and water-holding capacities (Petrovic, 1990; Soldat and Petrovic, 2008). Fertilizer as a source of nutrients leaving residential areas cannot be assumed to be negligible. More information on specific lawn fertilization practices is presented later in this article.
Decaying pet waste transported to water bodies in storm water can consume oxygen and release nutrients. Low oxygen levels and ammonia can damage the health of fish and other aquatic life (U.S. Environmental Protection Agency, 2009). Pet waste carries bacteria, viruses, and parasites that can threaten the health of humans and wildlife. Pet waste also contains nutrients that promote aquatic weed and algae growth (eutrophication). A 45-lb dog can excrete ≈9 lb of N and 2 lb of P per year, while a human produces 13 lb of N and 1.5 lb of P per year (Baker, 2007). Most of the pet N is in the urine and the P is in the solids. Consequently “pooper scooper” ordinances requiring pet owners to collect the pet waste when walking their pets can be effective in P control but less so for N (Wood et al., 2004). Baker et al. (2001) suggested that ≈15 lb/acre per year of N could be added to the Glyndon (Baltimore, MD) watershed from pet waste.
In urban communities, nutrients can come from native and introduced landscape plants, such as tree leaf-fall and grass clippings (Cowen and Lee, 1973; Dorney, 1986; Strynchuk et al., 2004). Some communities have yard waste (e.g., tree limbs, hedge clippings, grass clippings) collection programs where homeowners are told to place their yard waste curbside or at the edge of the street for collection. Without collection, the potential for this yard waste to enter storm drains is high, especially in regions having frequent rain events.
Using a time-series analysis of decomposition of leaf and st. augustinegrass (Stenotaphrum secundatum) clippings in Brevard County, FL, Strynchuk et al. (2004) determined that quick removal of street organic debris is needed to avoid the rapid loss of pollutants from the debris. Phosphorus from leaf litter in Milwaukee, WI, was determined to be a major source of P and the amount of leachable P per whole leaf varied by tree species, but not by tree diameter (Dorney, 1986). As much as 9% of the total leaf-P could be leached from leaves within 2 h. In an early article on leaf-P, Cowen and Lee (1973) found up to 230 μg·g −1 of P in oak (Quercus sp.) and poplar (Populus sp.) leaves in Madison, WI. Leaves that were in the littoral zone of Lake Mendota (Madison, WI) had less P than leaves collected from the ground surface near the shore. In heavily canopied communities, leaves can be greater sources of P than lawns (Baker, 2007). Lawns and streets were the largest sources of P in runoff in two urban residential basins in Madison, WI (Waschbusch et al., 1999). These two sources combined to account for 80% of the total and dissolved P in runoff. Streets contributed P from soil and organic matter.
These few studies on the subject of nutrients from plant debris point to two conclusions: First, there is considerable potential nutrient load from plant debris in the urban environment that can be a significant source of nutrients in the storm water. Second, plant debris should be removed (street sweeping) as soon as possible because water (rain) can easily and rapidly extract nutrients from the debris.
The literature review above documents the complexity of eutrophication of inland and coastal water bodies. Land-based nutrient (N and P) sources are important components in the nutrient loads to the water bodies, and furthermore, there are many distinct nutrient sources. These sources undergo complex changes and interactions with the environment en route to a water body, and once in the water body they play a role in complex nutrient cycling that maintains nutrients in forms suitable for algal growth. Controlling nutrients at the source is a sound approach to reducing nutrient loading to water bodies, but nutrient fates are complex processes. As a result of the myriad of sources and their complex interactions, source reduction requires a comprehensive and adaptive approach that avoids unintended consequences because of misunderstanding of the complete and complex nutrient source and fate process. Clearly, nutrients from land-based activities are being added to water bodies. The challenge is finding the best approach to reducing the level of pollution.
The scientific literature points to various nutrient sources and a complex process behind urban water pollution, which leads to the question, “how can we best mitigate water quality problems, manage nutrient sources, and limit losses to the environment?” State and federal rules and guidelines and scientifically based university recommendations have been developed to encourage improved nutrient management practices in the urban landscape (especially turfgrass) environment that have nutrient source reduction as their main goal. BMPs have been proposed as an effective, science-based approach to address the water quality issue. However, some counties and municipalities in Florida have instituted rules more stringent than the research-based BMPs. These jurisdictions believe that fertilizer applied to turf and landscape plants is a major cause of eutrophication and that BMPs alone are not effective enough to resolve serious water pollution problems. In these cases, counties and municipalities have chosen the local ordinance approach as a means to control urban fertilizer application (Evans et al., n.d.; Florida Department of Agriculture and Consumer Services, 2007, 2008; Hartman et al., 2008). The severe Florida red tide blooms in 2005 and 2006 precipitated local governmental action in Florida (Hartman et al., 2008). Examples of county and local ordinances in Florida are summarized in Table 1.
A fertilizer use ban for turf and landscape plants was part of a recommendation of a workgroup for a model ordinance from the Tampa Bay Estuary Program (2008a). This workgroup was composed of members from most of the important stakeholders (public, private, turf and fertilizer industry, and nongovernmental organizations) involved personally or professionally in the urban water quality issue for the Tampa Bay area. The ban or restricted period, or “fertilizer blackout” part of the Tampa Bay Model Ordinance was not supported unanimously by the workgroup (Tampa Bay Estuary Program, 2008a). The model ordinance including the summer ban was passed and was proposed as a model for counties and municipalities in Florida, especially those around Tampa Bay to follow in developing their own ordinances.
A number of counties and municipalities in Florida have chosen the local landscape ordinance as a means to control fertilizer use (Table 1). Most ordinances contain certain fertilization guidelines that are supported by research and are consistent with the University of Florida and Florida Department of Environmental Protection nutrient BMPs (Florida Department of Environmental Protection, 2008). These practices include, following recommended fertilizer application rates, timing, and methods, and keeping grass clippings and fertilizer from impervious surfaces since these materials can be moved into water bodies via storm water. Certain ordinances go a step further with a ban on fertilizer use and/or sales during the period from 1 June through 30 Sept. The rationale for these summer fertilizer bans is that heavy rainfall events are common in the summer months, which increase the likelihood of leaching and runoff of fertilizer (Tampa Bay Estuary Program, 2008a, 2008b). However, the summer months also are the months when landscape plants such as turfgrass grow most actively and require nutrients for healthy development. Therefore, the fertilizer ban appeared to be at odds with most fertilizer BMPs for urban turfgrass landscapes.
In 2007, the Florida Department of Agriculture and Consumer Services created the Urban Turf Fertilizer Rule [5E-1.003(2) Florida Administrative Code] to help protect water quality in Florida by controlling the application of N and P fertilizers for urban turf and lawns (Florida Department of Agriculture and Consumer Services, 2007). This rule was designed to help guide Florida’s citizens to apply fertilizers in the urban environment at rates that sustain turfgrass growth and development yet minimize potential nonpoint source pollution from nutrient loss.
The rule requires that all fertilizers in packages less than 50 lb and sold for urban turf use have labels specifying the amount of N and P needed to sustain healthy turfgrass along with several cautionary statements above fertilizer use. The allowable annual N use rates follow the University of Florida guidelines for turfgrass maintenance across three geographic regions in Florida and are turfgrass species specific. The use rates are predicted on a maximum application rate of 0.7 lb/1000 ft2 readily available N at any one time in the year. The total per-application N rate cannot exceed 1.0 lb/1000 ft2. Additionally, the application rate for P shall not exceed 0.11 lb/1000 ft2 per application and not exceed 0.22 lb/1000 ft2 annually.
The Florida Consumer Fertilizer Task Force was created by the Florida Legislature in 2007 to review and provide recommendations on the state’s policies and programs addressing consumer fertilizers. After reviewing the relevant research literature on urban landscape leaching and runoff, the Consumer Fertilizer Task Force chose not to include a fertilizer-restricted period (ban or blackout) in their report to the Florida Legislature. The task force did recommend adoption of a “Florida-Friendly Fertilizer Use on Urban Landscapes Model Ordinance” that contained a “Prohibited and Restricted Application Period” defined as “the time period during which a Flood Watch or Warning, or a Tropical Storm Watch or Warning, or a Hurricane Watch or Warning, or a 3-day Cone of Uncertainty is in effect for any portion of (CITY/COUNTY), issued by the National Weather Service, or if heavy rain is expected” (Florida Department of Agriculture and Consumer Services, 2008). The approach to fertilization during the summer months sets the Legislative Task Force Model Ordinance apart from that of the Tampa Bay Estuary Program. The state Task Force encouraged BMPs, while the Tampa Bay Estuary Program suggested full fertilizer bans. Evans et al. (n.d.) from the Conservation Clinic of the University of Florida, College of Law, summarized the arguments for and against BMPs or fertilizer bans. These authors suggested that bans should be considered after mandated or voluntary BMPs have been tried and found ineffective.
Florida is not the only state with local fertilizer ordinances. Several other states enacted ordinances before Florida. Ann Arbor, MI, is one municipality in the United States with an ordinance controlling P fertilization (Ann Arbor, 2011). The ordinance was developed in conjunction with a statewide U.S. Environmental Protection Agency TMDL-driven P fertilizer reduction effort. The ordinance went into effect in 2007. Manufactured fertilizers cannot be applied before 1 April or after 15 Nov., coinciding with the colder part of the year when the turf is not actively growing and runoff from frozen ground is most likely. P fertilizer cannot be used except where establishing new turfgrass or where a soil test indicates a deficiency in soil-P.
Michigan researchers established water quality sampling stations in the Huron River watershed in southeastern Michigan (Lehman et al., 2009). Sampling was conducted under the jurisdiction of the Ann Arbor, MI, fertilizer ordinance and upstream in a geographic area not addressed by the city ordinance. P concentrations in the water samples were compared for 2008 data against older data collected before the ordinance was enacted. P concentrations in the river water were lower in 2008 compared with the period before the ordinance and lower for the Ann Arbor sampling sites compared with upstream sites. The ordinance not only restricted P fertilization but also included strong education programs about proper fertilizer management. The study showed a positive relationship between the reduction in P pollution in the water and the implementation of the ordinance BMPs, but the authors acknowledged that it was impossible to determine if the restriction on fertilizer alone led to the reductions in P. Other components of the comprehensive program, such as fertilizer management education, may have also played a role.
Madison, WI, is another municipality having a similar P ordinance to that of Ann Arbor addressing P loads to Lake Mendota (Dane County Office of Lakes and Watersheds, n.d.). The Madison and Ann Arbor programs had the goal of improvement in water quality by following the BMPs in the ordinance and implementing a strong public education program.
Minnesota enacted in 2002 the first state regulation on P in urban fertilizers. Minnesota Department of Agriculture reported to the Minnesota Legislature on the effectiveness of the Minnesota Phosphorus Lawn Fertilizer Law over the first years (Minnesota Department of Agriculture, 2007). The findings included: P-free fertilizer was widely available in Minnesota, amount of P applied was reduced 48%, and the law created a “teachable” moment for fertilizer management. Also the report pointed out that additional research was needed to ensure avoidance of negative “unintended” consequences of P-free fertilizers on turf health and water quality.
Several states and municipalities have enacted laws to help manage fertilizer in the urban environment with the goals of reducing nutrient losses to water bodies. The literature on local ordinances and state laws in the country appears to favor enacting laws that embody the state researched BMPs. Most states, including Florida, have soil testing, following proper fertilizer rates, keeping nutrients from impermeable surfaces, and including controlled-release fertilizers as a source of nutrients in the ordinances. However, at this time, only Florida appears to have laws banning fertilizer application and fertilizer sales during the summer growing period for turfgrass.
The growth in fertilizer ordinances demonstrates an interest in controlling fertilizer as a source of nutrients potentially degrading urban water bodies. Further, there are differences in approaches taken by states and municipalities to manage urban fertilization practices. This result shows a strong interest in knowledge about fertilizer pollution and leads to another question: “what is known about fertilizer management in the urban landscape and its relationship to aquatic pollution.” In the next section, we discuss research results with fertilizer management on urban landscape and turfgrass and the relationships with nutrient losses. This information is important to know when considering if a regulation containing a fertilizer ban would likely meet its intended goal of reducing nutrient losses from the landscape.
Fertilizer is a common input for managing landscape plants, especially turfgrass. Amounts of fertilizers sold and used in nonfarm areas in Florida (nurseries, golf courses, and retail establishments) have declined over recent years (Florida Department of Agriculture and Consumer Services, 2012). For example, N sales increased from 2002–06, but sales declined from 2006–10. In 2005, the nonfarm sales of N fertilizer was 69,523 tons but declined to 29,816 tons in 2010, a 57% reduction in urban fertilizer sales. The nonfarm sale of P fertilizer declined from 14,169 tons in 2005 to 5144 tons in 2010, a 64% reduction (Florida Department of Agriculture and Consumer Services, 2012). Although the negative economy may have influenced this trend toward the latter part of the period, this overall reduction in fertilizer use is significant in light of fertilizer limitations imposed by passage of the Urban Turf Fertilizer Rule in 2007 and its potential positive environmental impacts.
Fertilizer is necessary for the health and aesthetic value of urban turf, yet fertilizer could be a water pollutant if it is transported to a water body. Considerable research has been conducted nationally on BMPs for turf fertilization to address the question of the role turfgrass may play in protecting water quality. The literature on the fate and transport of P in turfgrass systems was reviewed by Soldat and Petrovic (2008). They found that soil properties had greater impacts on P runoff than did plant growth. Greatest P runoff and leaching occurred when P was applied close to heavy rainfall. P inputs slightly exceeded the P uptake in grass clippings. Rate, timing, and source for P fertilization were critical factors for P losses. The same result has been found for Florida. P fertilization is not needed when the soil already is high in P content as determined by a soil test (Sartain, 2007).
Published books (Beard and Green, 1994; Beard and Kenna, 2008; Nett et al., 2008) have summarized the research literature on turfgrass systems with attention to environmental impacts. Turfgrass benefits (Beard and Green, 1994) can be grouped into functional (e.g., preventing erosion, preventing weeds), recreational (sports fields), and aesthetic (beauty and value-added for homes and properties). Beard and Green (1994) have described the functional and nonfunctional benefits of properly maintained lawns and landscapes to include benefits such as soil erosion control and improved aquifer water recharge and water quality protection.
In this review article, we focused on the nutrient BMPs for achieving and maximizing benefits of turf directed at water pollution prevention. Little research of this type has been published for other landscape plants. Properly managed turfgrass systems absorb the majority of nutrients when applied at recommended rates, thus minimizing leaching and runoff from landscape surfaces (Brown et al., 1977; Easton and Petrovic, 2004; Frank 2008; Gross et al., 1990; Harrison, 1992; Hull and Liu, 2005; Shuman, 2001). Petrovic and Easton (2005) reviewed the literature on the role of properly managed turfgrass and urban water quality. Numerous research studies show that turfgrass has a lower impact on groundwater N levels than other land uses. However, small-scale research results “do not exonerate or implicate turfgrass as a contributor to water quality degradation in urban/suburban watersheds” and that more work is needed to clearly define a source of pollutants. Raciti et al. (2008) outlined N flows in an urban environment where lawns, under low to moderate management, can be nutrient sinks rather than sources. These authors found high retention of atmospheric N in the soil organic matter pools of urban lawns. Eighty to 90% of N was assimilated in the transition fall and spring months for bermudagrass (Cynodon dactylon) in North Carolina (Wherley et al., 2009). The potential for nutrient retention can be great for urban soils, especially for lawns. This high retention is because lawns are typically managed with irrigation and fertilizer to encourage plant growth and development (Pouyat et al., 2010). Plant biomass is converted to soil organic matter, especially in lawns and this organic matter retains nutrients and water. Conversely, research suggests that lawns may decrease in their N-retention capacity as they age (Frank et al., 2006; Porter et al., 1980).
Several environmental benefits of turfgrass have been described in research from various sites around the country. In a study in Minnesota with kentucky bluegrass (Poa pratensis), zero, low, medium, and high P fertilization programs were imposed during the year (Bierman et al., 2010). The researchers measured runoff volume and nutrient loads moving off the research site plots. Where N and potassium (K) were supplied, P in the runoff increased as the P rate increased. P runoff from the unfertilized (no N or K) plots was greater than from fertilized turf. The researchers attributed the increased P runoff to the poorer growth of the turfgrass in the unfertilized plots. P runoff was greater when P was applied in the fall, when plant growth slowed and plants entered dormancy. These researchers concluded that P should not be applied in the fall or when soils already are high in P content, and that P runoff was reduced in properly managed, fertilized turf.
In a 6-year study in Wisconsin, Kussow (2008) evaluated management practices that affect N and P losses from upper midwestern U.S. lawns. Annual NO3–N leachate concentrations were typically between 2 and 4 ppm and the quantity of N leached was ≈3 lb/acre, which was intermediate between losses from agricultural and natural areas in the upper Midwest. The most important factor for increasing runoff loss of N and P was depth of runoff water. Next in importance was failure to fertilize.
In another Wisconsin study (U.S. Geological Survey, 2002) of lakefront home lawns, NO3–N plus nitrite–N concentrations in runoff were low. Fertilization did not affect N concentrations in the runoff. Total P concentrations in runoff were related to the P level in the soils. P in runoff from sites receiving non-P fertilizers was similar to P in runoff from nonfertilized sites indicating that non-P fertilizers may be an effective method to reduce P in surface runoff.
In Florida with st. augustinegrass, leaching of NO3–N increased as fertilizer rates increased above the recommended rate (Trenholm et al., 2012a). However, even though leaching of N increased with rates greatly exceeding those recommended, the total N mass leached was small (less than 1%) in studies with healthy st. augustinegrass.
Seasonal variation in nutrient uptake is widely reported for cool-season grasses (Frank, 2008; Miltner et al., 1996), but is less well understood for warm-season grasses. The most active growth period for warm-season grasses is during the long, warm days of late spring and summer (Turgeon, 2008), and this is the time of greatest growth and nutrient requirements for these grasses. ‘Tifway’ hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) captured more N during the active growing summer season (>90% uptake within 3 d) and the system was inefficient (<20% uptake within 16 d) in winter when bermudagrass was dormant (Wherley et al., 2009). Large amounts of N also were captured in a summer kentucky bluegrass system (Frank, 2008). Trenholm et al. (2012a, 2012b) reported that with the exception of the first year when grasses had recently been sodded, greatest NO3–N leaching from st. augustinegrass and zoysiagrass (Zoysia japonica) typically occurred in the winter and spring months before spring green-up rather than in the fall months. Trenholm et al. (2012a) found that annual NO3–N leaching was greater with zoysiagrass compared with st. augustinegrass. Importantly, total NO3–N leaching with st. augustinegrass was less than 3 kg·ha−1 (≈2%) with the recommended rate (4 lb/1000 ft2 per year) of N and even with 2X recommended rate. Recommended rates for N for turfgrass in Florida range from 3 to 6 lb/1000 ft2 per year, depending on turfgrass species and location in the state (Sartain, 2007). NO3–N loading during the summer months from st. augustinegrass grown with a commercial fertilizer comprised of a mixture of 62% soluble and 38% controlled-release N at the currently recommended rate of 1.0 lb/1000 ft2 of N was negligible (Erickson et al., 2001). In well-established and maintained st. augustinegrass turfgrass, inorganic N leachate was lower in concentrations of NH4–N (ammonium–nitrogen) and NO3–N than that reported for rain water in southern Florida (Erickson et al., 2008).
Recovery of leached N averaged 0.23% of the total N applied over a 2-year period for kentucky bluegrass (Miltner et al., 1996). Total recovery of N was 64% and 81% for spring and fall, respectively, pointing to potential gaseous losses of N.
Root biomass of warm-season grasses declines in the fall (Sartain, 2002). Sifers et al. (1985) reported that warm-season turfgrasses undergo spring root decline (i.e., severe browning of the entire root system) just after spring green-up. Bushoven and Hull (2001) showed that the NO3–N assimilative capacity of roots correlates with greater dry matter allocation to root mass by the whole plant. This greater NO3–N assimilative capacity was correlated with increased N uptake efficiency in one of the two grass species studied. Bermudagrass roots were more competitive than the soil microbial population for assimilating nutrients (Wherley et al., 2009). Grass [annual bluegrass (Poa annua) and creeping bentgrass (Agrostis palustris)] with greater aboveground biomass also had greater root biomass that, in turn, led to more N uptake (Pare et al., 2006). These authors suggested that management practices that lead to better root development can be important in reducing fertilizer N leaching with these grasses. Additionally, following recommended fertilization practices will help maintain a strong, expansive root system capable of absorbing nutrients, especially during periods of active growth.
There are many other published scientific studies demonstrating the advantages of well-managed turfgrass for reducing fertilizer losses from the landscape. Returning clippings to the lawn was shown to have a large effect on nutrient distribution in the turf system (Starr and DeRoo, 1981). One-half of the N was derived from fertilizer in the system where clippings were not returned, while one-third of the N came from fertilizer where clippings were returned to the system. These authors hypothesized that the microbiologically active turf thatch system may be responsible for N losses such as denitrification and volatilization. Cultivation practices may be effective in reducing nutrient losses from turf. For example, runoff volume and amounts of soluble P, and ammonium and NO3–N from golf fairway turf was reduced with hollow-tine core cultivation (Rice and Horgan, 2011). Although these practices are common in golf course turf management, they may be adaptable for residential areas.
In an early review of the fate of N in turfgrass systems, Petrovic (1990) analyzed the literature on N uptake, leaching, runoff, atmospheric losses (volatilization and denitrification), and immobilization. The research showed that proper fertilizer management minimizes impacts to the environment. These strategies would include proper irrigation management, using slow-release fertilizers, and modifying sandy soils for better nutrient and water-holding capacities. Easton and Petrovic (2004) stated that following recommended fertilization rates leads to dense turf growth that prevents erosion and slows overland transport of water and nutrients. The scientific literature clearly documents the advantages of having well-managed and carefully fertilized turfgrass in the urban landscape for reducing nutrient losses.
Fertilizers can be supplied in soluble and slow- or controlled-release forms. Controlled-release fertilizers have been shown to be effective for producing healthy turfgrass (Petrovic, 1990; Sartain, 1981, 2007, 2008) and reducing the potential for nutrient losses (Saha et al., 2007) from lawn grasses. Research on NO3–N loading because of N source from st. augustinegrass and zoysiagrass found no difference in NO3–N loading because of N treatments from either water soluble, controlled release, or biosolid N sources when N was applied at recommended or slightly higher than recommended rates (Trenholm et al., 2009).
Nitrogen rate had little effect in NO3–N loading in established st. augustinegrass, even when applied at annual rates 2.5 times greater than the current recommended rates (Trenholm et al., 2012a). Zoysiagrass NO3–N loading was greater at the higher rates of applied N. Recent research in Florida shows that NO3–N loading was dependent on turfgrass species, with greater NO3–N loading from zoysiagrass than from st. augustinegrass (Trenholm et al., 2012a). Similar results for these two species were found by Bowman et al. (2002), who reported lowest NO3–N loading from st. augustinegrass compared with other warm-season turf species. Erickson et al. (2001) reported annual inorganic-N loss of 3.7 lb/acre from st. augustinegrass compared with 43 lb/acre from a mixed landscape species in the first year of the study. The studies above show that N losses from the turfgrass system can be influenced by several variables, not the least of which is the type of turfgrass.
Buffer strips planted to turfgrass are used to capture, filter, and reduce nutrient runoff (Cole et al., 1997; Steinke et al., 2007). Buffer strips as small as 2 ft wide have reduced runoff compared with no buffer strips. Dense turf vegetation reduces runoff by creating “tortuous pathways,” which reduce runoff rate and enhance soil infiltration. Thus, water can be filtered of sediment and nutrients by turf roots. Easton and Petrovic (2004) reported that doubling the number of turfgrass shoots in a lawn reduced the amount of runoff by 67%. Weedy, less dense lawns had three times more N runoff than a healthy, dense turf (Easton, 2004, 2006).
Reducing the velocity of runoff water with dense, healthy turfgrass increased infiltration and resulted in groundwater recharge (Blanco-Canqui et al., 2004; 2006; Easton and Petrovic, 2004) and increased nutrient uptake by turfgrass. Turfgrass captured runoff-carrying nutrients and displaced soil from a 10% sloped site and reduced the N concentration in that runoff to a level similar to rain water (Erickson et al., 2001).
Research summarized above shows that turfgrass can play a positive role in absorbing nutrients, especially during active growth. Trenholm and Sartain (2010) pointed out that factors leading to increased leaching losses of N included application of fertilizer at higher than recommended rates, application too near a rainfall event or irrigation, and fertilization when the turfgrass is not growing actively. Use of poor management practices such as overfertilization or excessive irrigation can lead to nutrient losses. Further, research shows that nutrient-deficient, less dense turfgrass will lead to increased runoff volume and nutrient losses. Bare-soil areas are most prone to soil erosion and transport nutrients with the displaced soil.
The research shows that the mass of the healthy turfgrass root system plays a large role in removing nutrients from the soil. The scientific evidence points to potential unintended consequences of increases in nutrient losses from the landscape when recommended fertilizer and irrigation practices are not followed.
Soils serve several functions in the urban landscape including absorbing rainfall and releasing water and nutrients for plants (U.S. Department of Agriculture, 2005). The soil used for landscape planting is critical for proper nutrient management. There may be no definition for a “typical” urban soil (Pouyat et al., 2010) since there are so many soil types, many types of urban fill-soils, and many ways to impact soils during construction and landscape installation. Soils can have direct effects on ecosystems such as soil disturbance and soils can also have an indirect impact such as pollution resulting from inappropriate soil management practices. Pouyat et al. (2010) showed how these direct and indirect effects can contribute to a “mosaic” of soil conditions in their study in Baltimore, MD. They found that urban soils, even though disturbed, can have a high capacity to deliver positive effects on the ecosystems relative to the native soils they replaced. McKinney (2008) also noted a particularly high degree of plant species richness in urban areas. This species diversity suggests that the mosaic of urban soils offer potential for using the richness for the development of sustainable management practices for improving the capacity of the urban landscape to deliver environmental benefits.
Urban landscapes can have sloped lawn areas that may be prone to runoff. Nutrient runoff losses were greater at the bottom of a sloped turf area than from the upper part (Easton and Petrovic, 2005). Soil infiltration was greater at the top of the slope and the soil moisture content was greater at the bottom of the slope, leading to increased runoff at the bottom. The authors cautioned that landscape sites should be evaluated carefully for suitability for nutrient applications. Special caution should be given to nutrient application near the bottom of slopes especially if they are near water bodies.
Urban soils can be highly disturbed because of the excavation, grading, soil moving, and construction processes and fill-soils can take many forms (U.S. Department of Agriculture, 2005). Urban soils can be highly compacted during the construction period and the water infiltration rate is reduced in these compacted soils (Gregory et al., 2006). These authors found that construction activity reduced infiltration rates 70% to 99% and infiltration rates were typically lower than design storm infiltration rate (10 inches/h) used in northern Florida. Understanding these soil formation and transformation processes is needed for developing (after construction) and maintaining landscapes that achieve the desired aesthetic properties yet also do not result in degradation of nearby water bodies. Paving and compacted soils can be facilitators of urban runoff and pollution. In a meta-analysis of research studies on the relationship between impervious surface and stream water quality, Schueler et al. (2009) found the impervious cover model was supported; stream water quality can be predicted from impervious cover percentage. The relative proportion of open urban turf and landscape areas and impervious areas should be considered to minimize runoff impacts on stream water quality (U.S. Department of Agriculture, 2005). Municipalities considering regulations regarding limits to impervious cover should first conduct a comprehensive evaluation of receiving water bodies and environmental assessments such as sources and mitigation because one-size-fits-all approaches may lead to increased environmental problems (Jones et al., 2005).
Plant growth and health are related to soil properties (U.S. Department of Agriculture, 2005). In Florida, undisturbed urban soils include sandy soils of low organic matter, sandy soils of >3% organic matter, and sandy clay soils. Most soils have low nutrient-supplying capacity, but some urban soils have long-term nutrient-supplying capacity for P or N, including soils that have high (>3%) organic matter content. These soils would require reduced fertilizer inputs. Soils that have been amended with P-containing organic matter may have increased risk for P runoff (Soldat et al., 2009). Urban soils that test high in P content would be unlikely to require additional P fertilization for several years, and then a well-calibrated soil test could predict when P fertilization should resume for healthy turfgrass. The majority of soils in a North Carolina study did not need P fertilization (Osmond and Hardy, 2004).
Gaseous losses of N from urban soils are much less studied. Urban soil systems can be responsible for significant N losses because of denitrification (Groffman and Crawford, 2003). Their studies in an urban riparian zone in Baltimore, MD, showed strong positive relationships among soil moisture, organic matter, and denitrification. These authors suggested taking advantage of these soil properties in storm water treatment in urban environments. Raciti et al. (2011) reported that denitrification is an important means of removing reactive N in suburban lawn soils. They calculated annual denitrification to be 12.5 ± 3.2 lb/acre per year of N and they noted that 5% of the growing season accounted for >80% of the annual denitrification activity. Additionally, they noted that factors affecting soil saturation (texture, structure, and compaction) and NO3–N availability (fertilization) influenced the process.
In summary, research shows that urban soils can be highly disturbed, yet maintain a high degree of capacity to benefit the environment. Urban soils are highly variable in nutrient-supplying and retention capacities. Urban landscape management especially for soil disturbance, fertilization, and irrigation are critical factors in whether a soil/landscape system will be a nutrient sink or source and the degree of either. Soils with actively growing turfgrass leading to increased organic matter are associated with high levels of nutrient retention. There is much variability in urban soils suggesting that a one-size-fits-all approach to reducing nutrient losses in an urban environment would not be supported by the science-based literature.
The unpredictable nature of rainfall is one reason cited for the need for fertilizer bans in the rainy summer season. Rainfall frequency, duration, and intensity influence nutrient movement from the landscape. Regulators often ask how fertilizer should be managed during the wet season of the year.
Florida receives more rain than nearly all other states, but the rain often falls in large amounts over short periods of time (Purdum, 2007). This rainfall pattern presents problems, for example, erosion, especially where soils are on slopes and where groundcover is poor.
Florida may receive significant rainfall at any time of the year, but particularly in the summer months (all of Florida) and winter months in northern Florida (National Oceanic and Atmospheric Administration, 2004). The potential for fertilizer leaching and runoff increases when the soil becomes saturated during a heavy rain or after several successive rains. The World Meteorological Society and National Weather Service have established a 2-inch rainfall as a “heavy rain”—when soil saturation is most likely to occur for most soils in Florida. There can be two or three rainfall events yielding more than 1 inch each month, considered to be a significant rainfall (National Oceanic and Atmospheric Administration, 2004). About 10% to15% of rainfall events (during the period from 1942–2005) in Florida were 1 inch or more; that is, those most likely to result in nutrient leaching or runoff (Harper and Baker, 2007). Leaching or runoff occurs not simply because of “heavy” rainfall, but because the rainfall is in excess of the soil’s water-holding capacity or from situations where the soil is already saturated. There are several factors that affect how fast the soil will become saturated leading to leaching or runoff (Brady and Weil, 2002; Zotarelli et al., 2010). These factors include the soil texture, natural soil bulk density, compaction, and how much of the water-holding capacity is already filled by prior rain or irrigation events. Sandy soils that are present in most urban areas in Florida only hold from 0.7 to 1.0 inches of water per foot of soil. Therefore, rain events in excess of this may force leaching events or water may runoff of the site carrying nutrients with it.
There are few research reports in the literature addressing the impacts of rain and irrigation amounts on nutrient losses. Linde and Watschke (1997) reported that up to 25% of P fertilizer was lost in runoff and leaching when applied to saturated soils. Runoff volume from bermudagrass was related to simulated rainfall amounts and soil moisture level before rain (Shuman, 2002). Runoff was 24% to 44% of applied 50 mm (2.0 inches) rain and 3% to 27% for the 25 mm rainfall. The greatest mass loss of P was from the first 4 h after the first rainfall. The P loss decreased after 24 h and for later rain events. Loss of N increased with rate of N application. The author suggested that runoff losses of N and P could be minimized with small applications of irrigation after fertilizer application and by not applying fertilizer before heavy rainfall or when the soil is already moist. These research results illustrate the importance of careful irrigation so as not to keep the soil saturated. Fertilization events should be scheduled to avoid predicted heavy rainfall.
Irrigation is recommended to supplement rainfall in supplying needed water for plant growth. Nutrient losses to water bodies from the urban landscape are mostly mediated by water movement. Therefore, any attempt to minimize N or P pollution from the urban landscape will be negated if best irrigation management practices are not included in fertilizer guidelines. Nutrient and water management are tightly linked for maintaining healthy turfgrass (Dukes, 2008; Dukes et al., 2009). Proper irrigation management is needed for healthy turf and to prevent nutrient losses. The University of Florida has an urban irrigation scheduler tool available on the Florida Automated Weather Network (University of Florida Cooperative Extension Service, 2012). This tool allows a user to determine irrigation controller runtimes with three clicks of the computer mouse. Research has shown that using guidelines such as this tool can reduce irrigation by as much as 30% (Haley et al., 2007).
In an early study in Florida, scheduling irrigation by using a moisture sensor device that inhibited irrigation when the soil contained adequate moisture led to more efficient irrigation and to negligible loss of the soluble N (ammonium nitrate) applied (Snyder et al., 1984). Irrigation at 125% of evapotranspiration (ET) plus rainfall resulted in loss of 50% of the applied soluble N (Snyder et al., 1984). Proper irrigation management is critical to preventing nutrient losses.
New technology is available in the irrigation arena known as “smart irrigation.” New controllers typically monitor soil moisture status and allow or bypass irrigation based on soil moisture levels. These irrigation controllers use inputs such as soil moisture from the irrigated area to determine or regulate irrigation. Research in Florida on soil moisture sensor controllers has shown that irrigation savings can exceed 70% of automatic, clock-scheduled irrigations with a variety of controllers under normal rainfall conditions (Cardenas-Lailhacar et al., 2008; McCready et al., 2009). Savings during dry periods were less than during wet periods but still were as much as 30% to 40% (McCready et al., 2009). ET controllers have also been shown to result in savings of 43% during dry conditions (Davis et al., 2009).
In a study in North Carolina, Osmond and Hardy (2004) found that residents with movable sprinklers used about one-half the water as residents with fixed systems. Apparently, the ease of operation of fixed systems led to more irrigation. Automatic operation of irrigation systems during rainfall, or when the soil is saturated, or overirrigating in a single irrigation event, intensifies leaching and runoff potential (Hull and Liu, 2005).
Morton et al. (1988) studied N losses from kentucky bluegrass in Rhode Island. Nitrogen mass losses because of leaching were 2 lb/acre with the managed-irrigation treatment (tensiometer) and 30 lb/acre with the excessively irrigated treatment. The N loss with the managed-irrigation treatment was the same as the N loss with the nonirrigated control treatment. Leaching and not runoff was the main avenue of loss of N. Runoff occurred on two occasions, once when rain fell on frozen ground and once when rain fell on already saturated soil.
Current trends in Florida point to greater mandated water restrictions, such as even/odd day watering, even during nondrought periods, to help conserve potable water supplies. Homeowners should be educated about proper irrigation and how excessive irrigation on their assigned irrigation day could result in nutrient leaching and runoff. For irrigation recommendations to have maximum benefit, other recommended practices must be followed. For example, the irrigation system should be properly designed and installed to achieve a high degree of uniformity of water application (Baum et al., 2005). The research clearly shows that proper irrigation management and timing of fertilizer application in relation to rain or irrigation is critical for minimizing leaching of nutrients from the urban landscape, irrespective of the time of year.
Increasingly, home irrigation systems apply reclaimed water when the utility supplies reclaimed water to a new community. Reclaimed water can be used for lawn irrigation thus conserving potable water supplies. Florida is a leading state for the use of reclaimed water in irrigation (Association of California Water Agencies, 2009; Florida Department of Environmental Protection, 2009c). Many new residential developments have made reclaimed water available for irrigating lawns and landscapes as a means to preserve potable water for direct human use (drinking and food preparation, etc.). In addition to the water for irrigation, reclaimed water is a source of nutrients (Martinez and Clark. 2009a, 2009b; Martinez et al., 2011) and these nutrients may be beneficial for plants. Where reclaimed water is used for irrigation, these nutrients could be leached if nutrient levels in the reclaimed water are high and if irrigation is excessive. Thomas et al. (2006) used reclaimed water from San Antonio, TX, to irrigate bermudagrass and zoysiagrass. The reclaimed water contained 12.6 ppm NO3–N. Concentrations of NO3–N in leachate exceeded 10 ppm on 6 of 27 sampling dates and most of those events were when the turf growth was inactive. Proper irrigation management with reclaimed water is required to prevent N leaching from overapplication of reclaimed water. Although many municipalities recognize the benefits from using reclaimed water in urban landscapes, concerns have been raised that nutrient criteria for water bodies used by environmental agencies may hinder the use of reclaimed water for irrigation (Arrington and Melton, 2010).
Nutrients such and N and P move from the urban landscape with water either as leachate or runoff. The research points to increases in losses of nutrients when excessive rainfall occurs or when homeowners apply excessive irrigation. The likelihood of nutrient losses is associated with the soil moisture level. Irrigating or receiving rainfall when the soil is saturated will lead to leaching or runoff. Runoff is increased when the groundcover is poor and on slopes. Homeowners should pay attention to the local weather conditions and avoid fertilizing or irrigating when rains are forecast. The research clearly illustrates how fertilizer management and irrigation practices should be linked through proper timing of either. New “smart irrigation” technologies have been shown to improve irrigation management and thus reduce the potential for nutrient losses.
Humans play a role in minimizing nutrient losses from their landscapes because humans make decisions about nutrient and irrigation management. Preventing nutrient losses in the urban environment depends on knowing the BMPs for the local urban area. However, having widespread understanding and adoption of these BMPs is critical and this depends on human education. Fertilizers and pesticides are used by most homeowners in the United States (Robbins et al., 2001; Templeton et al., 1998). In eastern Nebraska, a survey of homeowner practices found that 91% of homeowners fertilized their lawns at least once annually, yet only 3% had ever tested their soil (Sewell et al., 2010). Soil tests, however, showed that the soils in the study area were high in P, above the level where a response in turf growth was expected. The authors concluded that increased efforts in homeowner education would be a key factor leading to better understanding of the impacts of lawn practices on the environment.
Researchers found that 75% of Georgia homeowners were engaged in home landscape management and that 80% reported applying fertilizers to their landscapes (Varlamoff et al., 2001). Fertilization appeared to be related to a perceived homeowner need (54% of homeowners) to have a lawn of comparable quality to those of their neighbors. Greenness of the lawn also was important for 56% of the homeowners surveyed. Varlamoff et al. (2001) found that homeowners were receptive to education about landscape practices that reduced the threat to the environment. This proportion of residents applying fertilizer in Georgia was confirmed for Florida by Souto et al. (2009) who found that 84% of homeowners applied fertilizer to their lawns either themselves or through commercial applicator. Homeowners were found to lack knowledge about amounts of fertilizer applied by hired applicators or amounts applied by the homeowners themselves.
Few reports exist in the scientific literature on the relationship between human behavior in landscape management and urban water quality. Raciti et al. (2011) noted that current homeowner management practices (fertilizer addition and irrigation) did not predict NO3–N availability or production in residential soils in the metropolitan area of Baltimore, MD. Zhou et al. (2009) found that lifestyle was a good predictor of lawn-care expenditures, but while the relationship between socioeconomic status and lawn greenness was statistically significant, the correlation was weak. Law et al. (2004) surveyed homeowner lawn fertilization practices in two watersheds in Baltimore County, MD. Fertilizer use rates in the Glyndon watershed averaged 110 lb/acre per year N, but the standard deviation was 100 lb/acre N, meaning that the application rates were extremely variable in the watershed. The rate varied from 2 to 4 lb/1000 ft2 per year. Homeowner application rates were more related to the soil type than to socioeconomic variables. More fertilizer was applied to turf on nutritionally poorer soils. These findings pointed to more “hot spots” for nutrient losses and suggested the need for more soil-based testing to predict fertilizer needs and nutrient loss potential.
Water quality in Roberts Bay within the Sarasota Bay–Peace–Myakka Watershed in Sarasota County, FL, improved from 1998 to 2007 and was removed from the states impaired water list in 2010 (U.S. Environmental Protection Agency, 2012b). Water quality improvements and reductions in chlorophyll-a were attributed to implementation of BMPs by homeowners, monitoring postconstruction loading from nutrient separating baffle boxes, and implementation of educational components by a broad range of stakeholders and the Florida-Friendly Landscaping Program™. Five other water bodies in nearby Sarasota Bay, Little Sarasota Bay, and Blackburn Bay were delisted for chlorophyll-a or historical chlorophyll-a between 2005 and 2010. These results confirmed the observations of Green and Janicki (2006) that declines in water quality in estuaries are reversible especially if BMPs are implemented and followed.
The authors mentioned above and others (Grove et al., 2006) suggest comprehensive and detailed environmental testing and education programs, rather than “one-size-fits-all” approaches. History indicates that homeowners may be willing to change practices. For example, one-third of municipal waste is recycled today, an increase from 7% in the 1970s (U.S. Environmental Protection Agency, 2005, 2007). Further, studies in North Carolina have shown one-half of residents now sweep fertilizer from impervious surfaces back onto the lawn (Osmond and Hardy, 2004). Education will be critical to the success of pollution prevention efforts. Baker (2007) studied literature on the question of whether fertilizer laws would work and concluded that programs most likely to result in behavioral change include a mix of components including education, incentives (subsidies), disincentives, and marketing. Further, programs may need to be spatially and socially targeted.
There is an increasing amount of research-based information for nutrient management in urban environments. Our review of the literature shows that there is considerable scientific information available for development and adoption of BMPs. BMPs can be complex requiring the integration of several nutrient and water management factors, and importantly the human behavior factor plays a role in the success of a BMP. The research literature shows that adoption of BMPs is the single-most factor minimizing potential unintended consequences of increasing nutrient losses in the urban environment. While much is known about BMPs for preventing nutrient losses, there are still areas in need of further work that can be identified from this literature review. Some of these areas are described below.
There is an inadequate level of knowledge about nutrient sources and fates in the urban environment. Large-scale water quality studies similar to those conducted in Baltimore, MD, and Phoenix, AZ, are needed for other regions of the United States. Before specific control measures can be determined, more information is needed about the particular nutrient sources, their relative amounts, and how they potentially could impact water quality. This quantification of nutrient mass balance is needed for N and P. Fertilizer recommendations should be evaluated for turfgrass health and for impacts on water quality from leaching or runoff. These studies should include the relationship of healthy or unhealthy turfgrass and landscape plants with nutrient losses from the landscape. New fertilizer materials such as controlled-release fertilizers should be included in leaching and runoff studies of the impacts of fertilizer practices on water quality. Nutrient release curves will be needed for each type of controlled-release fertilizer. There is the possibility that controlled-release fertilizers applied at the onset of the restricted period may help keep turfgrass from excessive decline during the summer when fertilizer is reduced or banned. Further, nutrient release rates are needed for various organic materials used to amend urban soils. Where fertilizer bans have been implemented, research is needed on their effectiveness for maintaining healthy turfgrass and landscapes and whether nutrient losses for the landscape are avoided. No reports were found in the literature demonstrating environmental benefits of total fertilization bans during the active growing period of turfgrass.
Most of the research studies addressing nutrient fates in the urban environment have been with turfgrass. Similar research with landscape plants, such as trees, shrubs, and perennial plants needs to be conducted. Currently, the fertilizer ordinance bans are for general landscape fertilization, but there may be differences in risks to nutrient losses among the various landscape plants.
Human behavior plays a large role in the success of environmental programs, voluntary or regulatory. More research is needed in the social sciences to determine what individuals know about water quality and the relationship their landscape management activities may have on water quality. BMP manuals should consider conflicting goals and preferences of homeowners (Varlamoff et al., 2001). The homeowners’ desire for convenience, improved appearance, and concern for the environment are factors that should be considered in any landscape BMP manual. Educational programs such as The Florida-Friendly LandscapingTM program (Florida Department of Environmental Protection, 2008, 2009b; Hansen et al., 2009) can therefore be effective in educating the public about conserving water and protecting water quality through sustainable landscaping practices.
Additional information is needed on the interaction of irrigation and N fertilization to determine the optimum fertilizer and irrigation combinations for various turfgrasses and landscape plants. More information is needed on the specific nutrient and water requirements of common and new landscape plants. This research should include native and nonnative plants. Research is needed on reclaimed water use in urban environments for supplying water and nutrients. Determining if there is a fertilizer offset when using reclaimed water is essential.
Finally, challenges in addressing nutrient management in the urban landscape may be related to underlying soil problems from the home construction process. Research is needed on optimum construction site management for best soil preparation for landscape installation, with attention to minimizing negative environmental impacts.
From this literature review and analysis, the following conclusions were drawn:
Coastal and urban eutrophication is an increasing problem and is related to land-based activities. Sources of nutrients involved with eutrophication are numerous and the interactions with harmful algal blooms are complex.
The research literature documents that an unintended consequence of increased nutrient loss may occur with summer fertilizer bans on turfgrass. Healthy, well-managed (fertilizer and irrigation) turfgrass has been shown to minimize nutrient loses to leaching and runoff. Practices that reduce turfgrass health and groundcoverage may lead to increased nutrient losses. Before adoption of a fertilizer ban, research should be conducted to demonstrate any potential benefits to the environment of fertilizer bans.
BMPs when followed correctly can reduce the losses of N and P from urban turf areas, such as home lawns. The research is especially clear on this for P where inadequately fertilized turf (N or K deficiency) leads to more P losses. Weedy nondense turf resulted in more losses of nutrients than healthy, dense turfgrass. The following BMPs are supported by the scientific research:
○ Soil testing can inform the homeowner about amounts of P needed.
○ Very little nutrient losses occur when turfgrass is fertilized according to BMPs; therefore, excessive nutrient amounts are to be avoided.
○ Vigorous, dense turfgrass should be maintained because healthy turfgrass reduces nutrient runoff and turfgrass with dense root systems reduces nutrient leaching.
○ Recommended irrigation should be followed because excessive irrigation or irrigation when the soil is already saturated leads to nutrient losses.
Research identifies continued education efforts as key to informing homeowners about how landscape practices impact water quality. Continuing the effort to educate the public about the best landscape maintenance practices, as determined by scientific research, is critical to minimizing nutrient losses.
Contributor Notes
Corresponding author. E-mail: hoch@ufl.edu.
