Properties of phosphorus retention in sediments under different hydrological regimes: A laboratory-scale simulation study

Excessive nutrient loading and changing hydrological regimes can significantly impact the ecological function of wetland ecosystems. Three wetland sediment samples collected from West Lake, Xiazhuhu Wetland and Baoyang River in the Taihu Lake Watershed, China, were compared to understand the P retention properties responding to hydrological regimes by using static column and steady-flow flume laboratory-scale experiments. Sediment in Xiazhuhu Wetland currently function as a P sink with equilibrium P concentration (EPC0) values of 0.010 mg L−1, while sediments from West Lake and Baoyang River, have EPC0 values of 0.050 mg L−1 and 0.023 mg L−1, respectively, and serve as an internal P source. The P retention by sediments ranged from 17.20 to 22.61 mg m−2 d−1 under 35-d static conditions, while sediment beds continuously fed by the simulated inflow water containing 2 mg L−1 P ranged from 59.20 to 171.93 mg m−2 d−1. The P removal capacities by sediments were higher during the rainy season than the dry season when wetlands were subjected to excessive P input. Since the majority of external P stored in sediment is in the form of Al-P (e.g., for Xiazhuhu wetland), the application of alum to water column could potentially increase the P retention capacity of sediment.