NUTRIENT, BACTERIA, AND SEDIMENT FLUXES IN A NATURAL WETLAND: AN ECOSYSTEM SERVICE OR DISSERVICE?

Abstract

Some wetlands have been shown to provide ecosystem services including flood water retention, water quality improvement, and habitat for wildlife and aquatic organisms. Wetlands are commonly created and/or restored to provide these services. Some wetlands though, may be exporters of carbon and other pollutants and thus could provide a disservice to the environment and eventually public health. The goal of this project was to determine if a natural wetland receiving drainage from an urbanizing catchment was a source or sink of nutrients, bacteria, and sediment. Inflow and outflow samples from the wetland were collected monthly for one year and analyzed for total dissolved nitrogen, phosphate, Escherichia coli and total suspended solids concentrations. Physiochemical properties of the samples including pH, dissolved oxygen, turbidity, specific conductance, flow, and temperature were also measured in the field. The pollutant treatment efficiency of the wetland was evaluated by comparing differences in inflow and outflow concentrations and loadings. Overall, the wetland reduced masses of total dissolved N (TDN) (51.6% reduction) and phosphate P (PO4-P) (62.9% reduction). The median outflow concentration of E. coli was 50% lower relative to inflow. Flow-weighted turbidity of wetland outflow wetland was 13.2% greater relative to the median inflow. Similarly, median total suspended solids mass increased 14.9% from inflow to outflow. Results from this research show that the wetland was a sink for N, P and E. coli reductions. However, the wetland was a source of sediment (and turbidity), likely because of erosion within the wetland. Efforts to slow urban runoff and stabilize the wetland are suggested to prolong (and perhaps enhance) the ecosystem services it is providing. Such practices may simultaneously inhibit some of the disservices (sources of pollution) caused by the wetland.