Wetland Demonstration To Improve Great Lakes Tributary Water Quality

The Challenge

Nutrient pollution, extreme storms, and warmer temperatures have led to the emergence of Harmful Algal Blooms (HABs) as a major concern in the Western Lake Erie Basin. The basin covers more than seven million acres, encompassing most of northwest Ohio and portions of northeast Indiana and southeast Michigan, and is one of the United States’ most significant networks of inland rivers and streams. Over the last decade, HABs of unprecedented size and severity have caused ecosystem, economic, and human health impacts.

The HABs are primarily fueled by agricultural runoff from the Maumee watershed, which is approximately 80% agricultural land. Innovative solutions to watershed scale pollution have been recommended to reduce HABs traced to nonpoint source phosphorus runoff. Wetlands designed and constructed to optimize phosphorus removal, or P-optimal wetlands, are one potential nature-based solution to reduce nutrient runoff and control algal blooms.

The Solution

LimnoTech, with the USACE-Buffalo District and ERDC, and other partners, designed and constructed a 10-acre demonstration wetland to serve as a prototype or model for optimizing phosphorus retention and nonpoint source phosphorus load reduction from agricultural landscapes.

The first step of this effort was to evaluate the large-scale feasibility of wetlands as an agricultural control measure. The factors considered included major obstacles to wetlands as agricultural BMPs, critical design elements related to phosphorus removal effectiveness, long-term operation and maintenance, regulatory considerations, costs, and the advantages and disadvantages compared to other BMPs.

Next, candidate sites were identified for the demonstration wetland. This step consisted of a four-tiered selection process that included targeting subwatersheds, then individual land parcels, public engagement, and field-scale verification. The site selection process resulted in two final candidate locations, both owned by public entities in Ohio. The team conducted hydrologic investigations, water quality measurements, soil sampling, and site surveys at the two final candidate locations.

The parcel owned by the City of Defiance near the Defiance Municipal Reservoir was selected as a suitable location for the construction of the P-optimal demonstration wetland. Conceptual designs were developed by SmithGroup and LimnoTech and evaluated based on phosphorus removal, cost, and research opportunities. The wetland was designed to capture high tributary flows and associated phosphorus loads and filter them through a series of treatment cells. The wetland construction was completed in late 2021.

A primary goal of the wetland demonstration site is to identify wetland characteristics that promote phosphorus retention, identify potential limitations of the technology, and improve water quality in tributaries to the Maumee River. Field-scale research at the demonstration site is ongoing and includes weather monitoring and an evaluation of the hydraulics, biogeochemistry, and water quality parameters associated with optimal phosphorus removal in constructed wetlands. LimnoTech and Freeboard Technology have worked together to develop and deploy sensors, including water level sensors, multi-parameter water quality probes, and automated nutrient analyzers. All of the sensors report in real-time, and data are delivered to a custom dashboard to view the data.

LimnoTech has also supported public outreach and other information-sharing activities, including multiple wetland site tours and online webinars to promote P-optimal wetlands to various groups comprised of government officials, watershed managers, and decision makers, other scientists and engineers, the agricultural community, and the general public.