BACKGROUND AND OBJECTIVES: The lakes in the state of Minnesota (MN) have undergone accelerated changes with the passing of time, where cattle ranching, agriculture, the increase of industrial jobs and urban area development have changed their condition from pristine to critical. To evaluate this problem, secondary data obtained from the public domain of three lakes from a county used for a long period for agriculture and cattle (Carver County) and three lakes from a county where the land has been used more for housing and industrial economy (Hennepin County). The aim of the study was to use the information to evaluate the trophic status, and compare the results of the lakes of rural areas versus lakes in urban areas in order to create a possible mitigation plan to improve the condition of the area.
METHODS: Trophic status was determined to evaluate the water quality of each lake. ANOVA analysis was employed to analyze the data set obtained from the public domain in the official webpage of the Minnesota Pollution Control Agency.
FINDINGS: Data results for total phosphorus, Secchi Disk and Chlorophyll-a, showed that all lakes are under eutrophic-hypereutrophic status with Trophic State Index (TSI) results between 59 to 80. Hennepin County had two of the three lakes evaluated in hypereutrophic states when compared with Carver County lakes. Carver County has only one lake out of the three evaluated under hypereutrophic conditions. Statistical analysis showed that p <α. The results demonstrated that lakes near areas used mainly for urban/industrial purposes are more contaminated than lakes near areas used for agriculture/livestock.
CONCLUSION: The restoration of wetlands that are near the lakes is proposed as a possible bioremediation method to improve water quality. Alternatively, an artificial wetland could be implemented in the lakes that do not have this natural system. Placing a Subsurface Flow System (SFS) artificial wetland in parallel trenches, which bypasses the lake and/or into the mouth of the river, would allow the sedimentation process to occur in these spaces. In addition, the use of Phosphor-Accumulator Organisms (PAO) and specialized aquatic plants, such as Hydrodictyon reticulatum, Elodea canadensis, Eichhornia crasspies, Eleocharis plantaginea, Pistia stratiotes and Hydrilla verticillate will trap contaminants and aid in their removal.
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