Abstract

Seagrasses are in decline worldwide, and restoration of these ecosystems are difficult to conduct. Fertilization, a popular restoration technique, can have variable results or pollute the surrounding ecosystem. The use of fertilizers with low dissolution rates may reduce nutrient pollution and improve restoration success, as the nutrient load is mostly intercepted by the seagrass rhizosphere rather than being leached out to the open water. Struvite, a slow release fertilizer sustainably harvested from wastewater treatment plants, was compared to Osmocote, a popular granular fertilizer, to assess their effects on seagrass fitness (measured via shoot counts) and the biogeochemistry of the sediment. Two experiments have compared the effectiveness of both fertilizers in a subtropical mesocosm experiment, with one current project applying the results in a seagrass scar restoration experiment off Crystal River, FL. The first study added a single 0.5 mg P per gram DW dose of Osmocote and struvite fertilizers to seagrass plots inside a subtropical 6 meter diameter mesocosm. Seagrass shoot counts were significantly higher in the struvite treatments than both the Osmocote and controls (p < 0.02). We also determined a significant difference between total phosphorus in the Osmocote treatment vs struvite and controls (p < 0.0005), suggesting a faster dissolution rate compared to struvite. This may pose problems if Osmocote is implemented in seagrass restoration efforts, especially in concentrated doses like those used in this experiment, leading to pollution and even seagrass stress (possibly observed in the roots). Results from a subsequent mesocosm experiment using lower doses of fertilizer, as well as preliminary data/drone imagery from the field experiment will also be presented.

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