MANAGEMENT OF URBAN AND RURAL WATERS TO REDUCE FLOODING AND NUTRIENTS

Management of stormwater and shallow groundwater to prevent flooding and improve water quality is becoming a higher priority for communities across the state of Iowa. This increased attention is a result of more frequent and stronger storms causing damage and because of concern about surface waters used for recreation. The City of Storm Lake, IA is taking a proactive role in the management of its stormwater and shallow groundwater resulting in the initiation of multiple long-term projects, such as the instillation of artificial wetland, pervious pavers, rain gardens, and woodchip bioreactors. In addition to reducing flooding, these projects also provide the benefit of removing nutrients such as nitrate as nitrogen, NO₃-N, from waters through microbial degradation and plant uptake. However, the rate of removal can be variable.

To establish baseline NO₃-N concentrations and to assess the initiatives already in place, collection of water samples from tile drains, a local stream and wetland, and from a woodchip bioreactor were started in the spring of 2017. The data from the water samples indicate NO₃-N concentrations of the tile drains, stream and wetland, and bioreactor inlet to be in excess of 10 ppm throughout the sample period. The results also indicate NO₃-N concentrations of the bioreactor outlet decreased up to 85 % from the concentrations of the bioreactor inlet and NO₃-N concentrations decreased along the wetland up to 70% from initial concentrations.

The decreases in NO₃-N from the surface water and groundwater due to the initiatives taken by the City of Storm Lake are encouraging. Monitoring of these projects will continue so as to determine what future projects are needed to better manage the stormwater and shallow groundwater of the city. Ongoing and future work will focus on determining the seasonal and long term variations in water chemistry to determine how ongoing efforts are reducing nutrient loads as part of Iowa’s Nutrient Reduction Strategy.