Effects of increasing complexity in biogeochemistry and hydrology on variability of total phosphorus concentration in models of a low flow subtropical wetland

In south Florida, treatment wetlands known as stormwater treatment areas (STAs) are used to reduce total phosphorus (P) concentrations of agricultural and urban stormwater runoff before discharging into the Ever-glades Protection Area. The remobilization of P from immobile forms stored in soils and litter has the potential to negatively affect STA treatment efficiency. Phosphorus biogeochemical dynamics in one of the best performing Everglades STA flow-ways, STA-2 FW1, were modeled mechanistically and empirically using diverse streams of data (flow, total P in water, soil, floc, vegetation). We evaluated the effect of P wetland uptake and hydrologic transport on STA-2 FW1's simulated outflow P concentrations by juxtaposing varying complexities of biogeo-chemistry (1-2 vs 13 wetland P pools) and hydrology (uniform vs. nonuniform flow) models. The uniform flow model considers a constant velocity with each time step while velocity in the nonuniform flow model is a sto-chastic ensemble mimicking spatial flow variability. When coupled with uniform or nonuniform flow, the variability of water column P concentration in the most complex model was significantly different from the two simple biogeochemistry models, although it was lower compared to data in all models. Regardless of the biogeochemistry model, uniform versus nonuniform transport did not affect simulated outflow P concentration. Significant interaction effects between the choices of biogeochemistry and hydrology models were observed. The most complex model included specific compartments for vegetation, floc and soil and reproduced data trends of more P accumulated in upstream areas that decreases with increasing distance away from inflow. Modeling biotic mechanisms and tracking P in vegetation and sediments, confirms the importance of including biogeo-chemistry in understanding and predicting outflow P concentrations in STA-2 FW1. This modeling tool could be used to guide future STA data collection needs and inform Everglades STA performance optimization efforts.

Automated summary

This study modeled the phosphorus biogeochemical dynamics in one of the best performing Everglades treatment wetlands and found that the complexity of the hydrological system significantly affected the simulated water column P concentration. The modeling tool developed in this study can guide future data collection and optimization efforts for treatment wetlands in the Everglades.