Nearly 10,000 different types of seaweed algae thrive in the world’s oceans and seas (Abbott and Dawson, 1978; Fritsch, 1965). Algae in the genus Sargassum of the sargassum family (Sargassaceae) include more than 150 species distributed throughout the tropical and temperate oceans around the world, thriving in warmer oceans and seas (Abbott and Dawson, 1978; Fritsch, 1965). Two planktonic species (S. fluitans and S. natans) drift en masse onto the shores of the Texas Gulf Coast, and are known collectively as brown algae, gulfweed, seaweed, sea holly, or sargassum. Sargassum that “washes” to shore can accumulate into massive, troublesome mounds, which substantially affects local coastal economies that rely on the beaches associated with the local tourism industry (Gaskill, 2015; Texas General Land Office, 2007). Sargassum was added to the Global Invasive Species Database in 2011 (Invasive Species Specialist Group, 2011) and has been identified along the shorelines of North America, Central America, the Caribbean Islands, the western Atlantic, Southwest Asia, and Southeast Asia (Guiry and Guiry, 2013).
Free-floating species of sargassum reproduce asexually by fragmentation (Awasthi, 2005; Rogers, 2011). Both require warmer oceans and sea temperatures to thrive, as well as chemical properties in their aquatic environment to survive (Abbott and Dawson, 1978; Fritsch, 1965; Round, 1981). Sargassum decreases in size after landing on the shore, and within a 5-d period, the seaweed decreases about three times in volume, becomes brittle, and changes from a light yellow to dark brown color (Round, 1981).
Nutrients absorbed from the sea, in combination with the energy from the sun, make seaweed rich in major nutrients and trace nutrients, and these nutrients can be used as soil amendments and fertilizers (Verkleij, 1992). Williams and Feagin (2010) studied the application of sargassum on native coastal plants beach sunflower (Helianthus debilis), fiddle-leaf morning glory (Ipomoea stolonifora), bitter panicgrass (Panicum amarum), seashore dropseed (Sporobolus virginicus), and seaside oats (Uniola paniculata) as a natural solution to enhance native dune plant growth. The study found sargassum acted as a natural fertilizer for bitter panicgrass (Williams and Feagin, 2010). Another study (Verkleij, 1992) found adding a seaweed-based soil amendment supplemented nutrient-poor sandy soils (Verkleij, 1992). In addition, some biological agriculture and horticulture practices have applied diluted seaweed extracts to enhance growth, deter insects and diseases, and improve quality of harvests (Verkleij, 1992).
Beaches along the Texas coastline are maintained by various organizations including federal and state agencies, cities, counties, and private owners (Gaskill, 2015; Texas General Land Office, 2007; Williams and Feagin, 2007). Variations of management procedures and methods are used by these organizations; however, basic beach maintenance objectives include maintaining safe and sanitary conditions, allowing for the use of recreational activities (e.g., sunbathing, camping, wildlife observation, and beach combing), monitoring trash removal, protecting wildlife habitats, and limiting the amount of sargassum on the coastline (Williams and Feagin, 2007).
The sargassum on beaches is handled using a variety of methods; if small amounts of biomass float onto the shore, large rakers are used to remove it. For large amounts, front-end loaders are allowed access to the shoreline to scrape tons of sargassum and sand, where it is then either placed at the edge of the foredune and allowed to revegetate or placed in temporary holding centers (Williams and Feagin, 2010). This method is used to create “maintenance dunes” seaward of the natural dunes (Gaskill, 2015).
Raking is only implemented during the 4–6 months of the year when the mats of sargassum rest on the shore. A large concern of some property owners and cities is that the peak times of sargassum deposits overlap with peak tourist seasons. Tourists often expect pristine beaches free from any debris and view seaweed mats as poor beach maintenance (Gaskill, 2015). In local economies that are highly dependent on tourism dollars, maintaining or increasing tourist numbers is essential (Gaskill, 2015; Texas General Land Office, 2007).
Although sargassum are used to create stabilized maintenance dunes, many coastal areas are running out of beach space because of rising sea levels, erosion, and the increasing size of these dunes (Williams et al., 2015). Even though wider dunes allow more protection from strong storms and increased native vegetation, the public demands and expects fast and easy access to the beach, and view these wider dunes or “long walks” as impeding beach enjoyment (Williams et al., 2015).
Composting is a biomechanical process during which microorganisms such as bacteria and fungi convert organic matter (OM) and “waste” materials into a soil-like product called compost (Rynk, 1992). The addition of compost to soil provides various benefits including increasing soil fertility, improving soil structure, increasing water holding capacity, and decreasing runoff (Dougherty, 1999; Rynk, 1992). Composting is increasingly used as a waste management method, a technique for pollution diversion, and to produce a valuable commodity for agricultural, horticultural, and related users (Walker et al., 2006).
Compost created from saline feedstocks (e.g., oceanic algae) must be carefully controlled and monitored for proper electrical conductivity (EC) amounts (Vendrame and Klock-Moore, 2013). Previous studies have used irrigation to wash away the soluble salt content before or during the compost process. Eyras et al. (1998) showed that time also plays a role: compost containing high-salinity feedstock aged for 20 months contained dramatically lower amounts of salt than compost aged for 9 months. Feedstocks of high salinity also can be combined with low salinity feedstocks to dilute the final product. Finally, actively turning the piles (rather than leaving them static) was shown to increase the rate of compost creation while decreasing the level of salinity (Eyras et al., 1998).
Seaweed extracts that contained different plant phytohormones and growth regulators increased crop yields when they were applied exogenously (Panda and Nayak, 2012). Some biological agriculture and horticulture practices have used diluted seaweed extracts or “seaweed fertilizers” to “promote growth, prevent pests and disease, and improve the quality of the products” (Verkleij, 1992). Therefore, producing compost that uses seaweed as a feedstock has the potential to create a nutrient-rich soil amendment product (Klock-Moore, 2000; Panda and Nayak, 2012).
The purpose of this study was to evaluate the potential to manage the invasive species sargassum using composting and to test the quality of the resulting compost.
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