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Donald J. Merhaut, Lea Corkidi, Maren Mochizuki, Toan Khuong, Julie Newman, Ben Faber, Oleg Daugovish, and Sonya Webb

. 2009 and Oct. 2009, respectively. These priority drainage areas were classified as first, second, or third tier based on the total number of benchmark exceedances, the number of classes of pollutants, the number of total maximum daily loads effective at

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Sarah A. White

is uncertain. In the two most recent cases in which regulations were imposed in an effort to protect water resources, the Florida numeric nutrient criterion used concentration-based end points, whereas the Chesapeake Bay used total maximum daily loads

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John C. Majsztrik and John D. Lea-Cox

applied to suburban areas. WHAT IS A TOTAL MAXIMUM DAILY LOAD? A TMDL is a numeric scientific estimate of the maximum daily amount of any pollutant that a body of water can receive and still meet water quality standards. Pollutant loads can be established

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Luther C. Carson and Monica Ozores-Hampton

percentage of total nutrients. For instance, a PCF (N–P–K) incubated in free water for 60 d at 30 °C released 82% NO 3 , 79% K, and 42% P. This relative order remained for all the three water levels. Similarly, Huett and Gogel (2000) measured nutrient

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Roger Kjelgren*, Thayne Montague, and Richard Beeson

We investigated water use and a water needs index multiplier relative to reference evapotranspiration for a sweetgum cultivar (Liquidambar styraciflua `Moraine') in Logan, Utah, Lubbock, Texas, and Orlando Fla. Three individual trees with ≈80-mm trunk diameter, were potted in to large containers with organic media at each location. Sweetgum water use (Tsw) was measured over the season at each location with load cells and dataloggers, concurrent with measurement of reference evapotranspiration (ETo) from adjacent weather stations. Dawn-to-dusk stomatal conductance (Gs) was measured several times during the season at all locations. Trees were watered daily. At the end of the season, total tree leaf area was collected and used to normalize volumetric water use data to depth units. Tsw was highest in Florida, up to 4 mm/day, as was maximum daily Gs. Tsw only reached 2.5 mm/day in Texas and Utah due in part to stomatal sensitivity to high vapor pressure deficits that moderated transpiration. There was no relationship between Tsw and ETo at ETo levels above 4 mm/day in Texas and Utah, resulting in substantial scatter in the water needs index multiplier relative to ETo that centered on 0.3 in Texas and 0.4 in Utah. Tsw in Florida showed an upper boundary relationship with ETo, under which it varied considerably, resulting in a values relative to ETo centered on 0.6. During a partial dry down in Utah, morning Gs was unaffected while afternoon Gs declined progressively under mild water stress, resulting multiplier values of 0.15-2. The study shows that regional climate affects tree water use independent of effects measured in ETo, increasing the uncertainty of sweetgum water use estimated as a function of ETo.

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J.M. Tarara and J.C. Ferguson

Management strategies like “deficit irrigation” in wine grapes require accurate, reliable information on vine water use, making direct measurements of vine transpiration highly desirable. The heat-balance sap flow method has the advantages of being non-invasive and requiring no other calibration beyond a zero-flow set. Potential violations of the method's assumptions were dealt with and the heat balance method successfully applied to mature grape vines under conditions of extremely high sap flow. Greenhouse studies suggested that vines transpire at night, up to 9.5% of the total 24-h water loss, thus violating the zero-flow assumption for setting the gauge constant. Using a predetermined gauge constant caused smaller errors than using daily, pre-dawn constants set in situ. The steady-state assumption was violated only in early and late hours of the day, and the inclusion of a term to account for the change in heat stored by the stem only marginally improved daily estimates of water use. The assumption of radially uniform temperature across the heated stem segment is violated at very high flows (e.g., >700 g·h–1), but can be corrected for by using wider heaters and adjusting the placement of thermocouples. For a mature, potted vine in the greenhouse, the maximum absolute error in cumulative daytime water use between a sap gauge and a precision load cell was about –10%, with the gauge almost exclusively underestimating water loss. A custom-built, 20-gauge system was run continuously in the field for 90 days. Vine-to-vine variability in water use was not accounted for by normalizing sap flow by leaf area, suggesting that it is critical to include in any field study the largest number of gauges that are technically feasible.

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Denise Neilsen, Gerry Neilsen, Sunghee Guak, and Tom Forge

). Fig. 1. Monthly average minimum (□), mean (○), and maximum (▵) daily temperature for 2007 (— –); 2008 (—); 2009 (– –); 1981–2010 averages (—) and total monthly precipitation for 2007 ( ); 2008 ( ); 2009 ( ); 1971–2000 average ( ). Climate change

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Gerry H. Neilsen, Denise Neilsen, Sung-hee Guak, and Tom Forge

three crop load treatments assigned to subplot units. There were six replicates of five tree plots (three measurement and two guard trees). The irrigation treatments included I1: 100% ET replaced daily via 2 × 4-L⋅h −1 emitters per tree. The irrigation

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Gregory Peck, Megan McGuire, Thomas Boudreau IV, and Amanda Stewart

Thompson-Witrick et al. (2014) using apples harvested in 2013 from the same trees (1 year before this study). There was no difference in total polyphenol concentration among crop load treatments at either harvest, but after fermentation, cider from the

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Todd C. Einhorn, Debra Laraway, and Janet Turner

generated by an IFPNet meteorological station ( Wy'East RC&D, 2009 ), located within 100 m from the experimental orchard. Accumulation of GDD from full bloom was calculated using the average daily minimum and maximum temperatures, and a low temperature