Phosphorus Retention in Treatment Wetlands? A Field Experiment Approach: Part 1, Hydrology
2025
Mohamed Z. Moustafa | Wasantha A. M. Lal
Stormwater Treatment Areas (STAs) are large wetlands constructed to reduce phosphorus (P) from agricultural and urban runoff into the Everglades Protection area. Wetland vegetation in these STAs reduce P in surface water, affects flow resistance, and causes delays of water deliveries. Vegetation resistance is commonly determined by the flow regime and vegetation porosity. Field experiments were conducted to seek alternative ways to estimate vegetation resistance in STAs. We generated small sinusoidal discharge perturbations superimposed on near-steady state flow conditions and measured in situ water levels inside the wetland. The elapsed time for the generated waves to reach various locations and wave amplitude attenuations inside the wetland were used to calculate porosity/transmissivity (K), a single parameter representing vegetation resistance. The vegetation index combined with calculated K distribution indicated that transmissivity is a straightforward way to represent vegetation resistance. High K values indicate sparse vegetation density or open water (low vegetation index), resulting in low vegetation resistance. Low K values indicate high vegetation density (high vegetation index), resulting in high vegetation resistance independent of vegetation and flow type. This manuscript describes a field experiment and discusses the relationship between K and the vegetation index (representing vegetation density). Part II will present the consequences of water movement on P retention in these systems.
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