Goals and Objectives:

To provide the Iowa Department of Natural Resources with a diagnostic and feasibility study of North and South Twin Lakes, Calhoun County, Iowa for planning and implementing lake and watershed improvement efforts.

Progress:

All monitoring activities and physical, chemical, and biological analyses of water samples have been completed for the project. A draft of the final project report was submitted to Iowa DNR in April 2016. We hosted a local steering committee meeting in November 2015 to discuss project findings with the technical advisory team and local steering committee. Additionally, we hosted a public meeting in May 2016 to discuss project findings and restoration alternatives for North and South Twin Lakes with local stakeholders. The final project report will be submitted by May 31, 2016 and a final local steering committee meeting will be held in Autumn 2016 to discuss restoration alternatives with the technical advisory team and local steering committee.

Conclusions and Recommendations:

North and South Twin Lakes suffer from water quality problems associated with high nutrient and sediment loads originating in this predominantly agricultural watershed, although development around the lakes, especially North Twin Lake, can also contribute to these problems. Elevated phosphorus loads fuel phytoplankton (i.e., algae) growth, resulting in large amounts of phytoplankton that are dominated by potentially toxic Cyanobacteria (i.e., blue-green algae). Combined with phytoplankton in the water column, high amounts of inorganic suspended solids derived from the watershed, such as soil particles, reduce water transparency and lead to high sediment accumulation rates. Additionally, the lakes lack a diverse, healthy, and sustainable aquatic community. Poor water quality continues to plaque the sport fishery of each lake, despite extensive management efforts to improve them.

To improve water transparency and the overall health of North and South Twin Lakes, efficient management strategies to reduce the amounts of nutrients and sediment entering the lakes from the watershed need to be developed. Because direct rainfall and dryfall of total phosphorus (TP) to the lakes cannot be effectively controlled, it is only possible to achieve maximum TP loading reductions of 80% for North Twin Lake and 70% for South Twin Lake. If these maximum targets are realized, water transparency are anticipated to improve by 2.5× in North Twin Lake (1.2 ft to 2.9 ft) and by 4× in South Twin Lake (0.6 ft to 2.5 ft). A cost-effective, comprehensive restoration strategy for North Twin Lake could involve 1) diverse BMPs targeting direct TP runoff from the unconsolidated watershed (i.e., area surrounding the lake), 2) creating a series of cascading detention ponds or wetlands near Featherstone Memorial County Park, and 3) reducing nutrient loading from tile drainage by routing tile drainage through treatment structure or re-routing tile drainage away from the lake. For South Twin Lake, a restoration strategy could involve 1) moving the outfall of North Twin Lake and routing it through a diked wetlands complex, 2) diverse BMPs targeting direct TP runoff from the unconsolidated watershed, and 3) enhancing the existing wetland complex near 230th street.

Funding Organization: Iowa Department of Natural Resources (IDNR)

Duration: 10/01/2013 to 05/31/2016

Principal Investigator(s): John Downing