Water Resources Research Act Program

Details for Project ID 2017ID215B

Estimating the bulk exchange of water and solutes between fringing wetlands and lakes to estimate the role of wetlands in water quality

Institute: Idaho
Year Established: 2017 Start Date: 2017-03-01 End Date: 2018-02-28
Total Federal Funds: $14,807 Total Non-Federal Funds: $29,668

Principal Investigators: Frank Wilhelm

Project Summary: ‘Coastal’ wetlands – those interfacing between open water and land - provide recognized ecosystem services including habitat, shoreline protection, and water quality improvement via removal of sediment and nutrients. Although wetlands are generally thought of as nutrient sinks, their high internal biological activity results in an environment that can be the source of nutrients. In addition, the source/sink nutrient dynamics of wetlands has been assessed with respect to the solutes of interest in the inflow versus the outflow. However, little attention has been given to the outflow as a source of nutrients, and its role in, and contribution to water quality of lakes is poorly quantified. For example, it is well-known that wetlands have reduced (anoxic) sediments because of high chemical and microbial activity which releases soluble phosphate. Thus in lakes in which the water budget is dominated by snowmelt runoff, and summer inflows drop to near or baseline flows, fringing wetlands may be significant sources of nutrients via wave action which stimulates bulk water exchange with the open water. These contributions of wetlands outside of the Great Lakes and coastal areas in estuaries and the ocean have not been examined. I plan to use an unmanned aircraft system (UAS) and waterborne dye to examine and quantify the exchange of water, and indirectly solutes, between a fringing lake wetland and the open water zone in a small North Idaho Lake to estimate the role of contributions of phosphorus from the wetland to the annual nutrient budget of the lake, especially during summer, when inflow is at baseflow conditions, and the wetland may be contributing significant mass of phosphorus to the lake. A short-lived (5-7 days) biologically inert dye will be added to the wetland and repeatedly monitored over 12 h with a UAS equipped with a senor capable of sensing the dye and taking georeferenced pictures. This will allow interpretation and analysis of the dye in a geographic information system (GIS) to determine intensity and rate of movement over time. To obtain water samples for the direct analysis of dye concentration via fluorometry to verify aerial images, a multi-station transect perpendicular to the lake/wetland complex will be sampled concurrently. Results will yield the mass of water and thus soluble phosphorus entrained from the wetland to the lake. Given the widespread distribution of fringing wetlands around lakes, results from this study should be widely applicable to estimate the contribution of wetlands to the nutrient mass balance in lakes. If such contributions are significant, it could help explain the occurrence of harmful algal blooms in late summer in some lake systems. Potential management implications could extend to lake level management, especially if nutrients have been identified as contributing to impaired water quality for a water body in which lake level is regulated via anthropogenic structures.