Biomass and nutrient storage of aquatic plants along phosphorus gradients in everglades stormwater treatment areas

Abstract

The Everglades Stormwater Treatment Areas (STAs) are large freshwater wetlands constructed to reduce phosphorus (P) in stormwater runoff discharged to the Everglades Protection Area. The STAs consist of compartmentalized flow-ways (FWs) containing one or more treatment cells, which are managed to promote either emergent aquatic vegetation (EAV) or a mixed marsh of EAV and submerged aquatic vegetation (SAV). This study evaluated biomass, nutrient content, and nutrient storage of common EAV (Typha spp.) and SAV (Chara spp.) species within well performing STA FWs (i.e., P discharges below 20 μg/L). Samples for both vegetation types were collected at inflow, midflow, and outflow locations. Typha samples were partitioned into aboveground and belowground components. All samples were analyzed for biomass, P, nitrogen (N), and carbon. Content (g kg−1) of P and N in Typha were significantly higher in belowground components compared to aboveground for all sites, while storage (g m−2) of P and N was highest at inflow sites compared to midflow and outflow sites. In Chara, P and N content were significantly higher at some midflow sites relative to outflow sites. The ratio of N:P (based on mass storage) typically increased from inflow to outflow, though ratios at most Typha sites indicated N limitation while P limitation was observed primarily at Chara dominated outflow sites. Typha nutrient storage measured in the present study was comparable to storages within floc and recently accreted soil layers measured during concurrent studies, indicating that Typha represents a significant pool of P within the STAs. Evaluations conducted here represent recent in situ biomass and nutrient storages for the most common STA vegetation, which have not been documented thoroughly since early in STA operation, and support ongoing STA biogeochemical modeling efforts.