Hypoxia and Climate in Green Bay, Lake Michigan
Abstract
Phosphorus inputs to Green Bay, Lake Michigan are estimated to be 800 MT per year, approximately one-third of the total phosphorus loading the Lake Michigan basin as a whole. The bay, however, contains less than 1.5% of lake’s total volume, and hypereutrophic conditions have persisted for nearly a century. The bay serves as a very efficient nutrient trap sequestering up to 70% of the phosphorus load in organic rich sediments accumulating at up to a cm per year. Organic carbon content of surface sediments range from 5 to 10%. Organic matter decomposition rates are rapid and these sediments are anaerobic below a few millimeters. Consequently, dissolved oxygen concentrations, particularly during late summer under stratified conditions, are frequently below the water quality standard of 5 mg/L, and occasional episodes of hypoxia (< 2 mg/L) are not uncommon. Here we report the first preliminary set of recent observations obtained in 2009 and 2010 of the distribution of dissolved oxygen in the bay, and sediment oxygen demand. Because the bay is shallow, hypoxia appears highly dependent upon not only oxygen consumption by the sediments, but also upon the dynamic interaction between thermal stratification, wind mixing, and the intrusion of Lake Michigan bottom water. All three of these phenomena are dependent upon the wind climatology of the bay, which appears to have shifted since the 1980’s. This shift has the potential to worsen the spatial and temporal extent of hypoxia by reducing mixing, decreasing resuspension, and increasing the retention of labile organic matter in the lower bay.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H41E1119K
- Keywords:
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- 0414 BIOGEOSCIENCES / Biogeochemical cycles;
- processes;
- and modeling;
- 0439 BIOGEOSCIENCES / Ecosystems;
- structure and dynamics