Changes in the ratio of benthic to planktonic diatoms to eutrophication status of Muskegon Lake through time: Implications for a valuable indicator on water quality

摘要

Ratio of benthic to planktonic diatoms has been used to indicate lake changes related to light availability reaching the bottom of the lake, such as changes in water clarity with eutrophication and changes in water depth. To explore using of the ratio to track long-term changes of eutrophication status of Muskegon Lake, we analyzed relationships between the ratio and land use change information, inferred TP based on diatoms from different habitats a good history of spatially and temporally isolated changes in the watershed and geochemistry indices of a long sediment core retrieved from the lake. We found the ratio related well with diatom-inferred TP (DI-TP) and geochemistry proxies at different temporal and spatial scales. From European settlement to around 1920, the ratios are relatively stable and indicates a relatively high natural nutrient status of the lake. When manufacturing and population boomed in the Muskegon River Watershed, the ratios greatly decreased with the increase of DI-TP and measured geochemistry proxies. Our results showed the decrease of the ratio was most possibly due to the increase of urban land use throughout watershed during this period. Both the ratio and the water clarity sharply increased in around 1973, which was probably caused by the great decrease of the nutrients input from the watershed. Low nutrient concentrations resulted in the collapse of eutrophic planktonic diatom community. Dreissenid mussel invasion might not have a great influence on the ratios because either quagga or zebra mussel did not increase to sufficiently high abundances in the 1990s in Muskegon Lake. On the other hand, the substrate of Muskegon Lake is not suitable for dreissenid mussel colonization. Performance of the ratio on indicating trophic status of the complex case of Muskegon Lake suggested the ratio would be a promising indicator for evaluating eutrophication status in lakes.