The internal loading of Big Lake in Polk County.

In shallow lakes there is intense interaction at the water sediment interface. Therefore, understanding sediment water interactions is crucial to understanding the nutrient dynamics of shallow lakes such as Big Lake (Scheffer, 1998). The sediments demand for oxygen is high as it is broken down by microbial communities. At the sediment surface, a difference of a few millimeters in oxygen penetration is the critical factor regulating exchange of nutrients and inorganic elements such as iron between the sediment and water. Under aerobic conditions, the exchange is largely from the water to the sediment. Under anaerobic conditions, however, phosphorus can move from depths up to 10 cm deep and be released into the water column (Wetzel, 2001). An analysis of the hypolimnetic nutrients of Big Lake has implications for best management actions in 2016 to 2018.

The Church Pine, Round, and Big Lake P&R District is sponsoring a project to assess the internal load in Big Lake. The final deliverables include all data collected, updated nutrient budget, and updated implementation strategy. Specific Phase 1 project tasks include: 1) In-Lake water quality monitoring; 2) Quantify lake nutrient budget; 3) Implementation strategy.