Modern sensors, arrays, and buoy platforms allow us to continuously and remotely monitor aquatic ecosystems. Using high-resolution time-series data from the Muskegon Lake Observatory, the Biddanda Lab at AWRI has chronicled the seasonally recurring bottom water hypoxia – low concentrations of dissolved oxygen (DO) – in Muskegon Lake since 2011 (www.gvsu.edu/buoy). Each summer, the observatory tracked the gradual development, intensification, and erosion of hypoxia (mild hypoxia at 2-4 mg/L DO in which most fish are impaired and severe hypoxia <2 mg/L DO in which most fish cannot survive for extended periods) below the ~6 m thermocline in the lake, occurring in synchrony with changes in temperature and phytoplankton biomass in the water column during July-October. During 2011-2013, ~9-24% of Muskegon Lake’s volume experienced hypoxia for ~29-85 days/year with the potential for benthic habitat degradation and sediment phosphorus release leading to further eutrophication and hypoxia. Time-series data suggested the following proximal causes of the observed seasonal bottom water DO dynamics: stratified summer water column, reduced wind-driven mixing, longer summer residence time, episodic intrusions of cold DO-rich and nutrient-poor nearshore Lake Michigan water, nutrient runoff from the watershed, and phytoplankton blooms. Lessons learned about how weather and hydrodynamics influence Muskegon Lake’s productivity and hypoxia could be applied to other coastal estuarine systems, like western Lake Erie, to help solve emerging problems of societal significance such as eutrophication, hypoxia, and harmful algal blooms.
The paper is now published online with open access in the Journal of Great Lakes Research (https://www.sciencedirect.com/science/article/pii/S0380133018300029) and a short commentary is available in the February 2017 issue of InterChange, the newsletter of GVSU's Regional Math and Science Center, under its Connections for the STEM Classroom section (http://www.gvsu.edu/rmsc/interchange/connections-for-the-stem-classroom-299.htm).
Image caption: Bopi Biddanda, Katie Knapp and Tony Weinke clowning around in winter survival suits after a successful late in the year buoy maintenance run on the lake. For additional information including project resources, data and interactive data analysis tools visit www.gvsu.edu/buoy/.