Findings

Winter is now approaching in the Great Lakes.

The high winds and cold temperatures have ended our field work for the year. Our data collection efforts have given way to sample processing and data analysis until we can resume field data collection this coming spring. We obtained sensor measurements and collected samples at nearshore El Cajon and the Middle Island SinkhThe scientists report that some deep sinkholes act as catch basins for dead and decaying plant and animal matter and collect a gelatinous, black sludge often topped by a bacterial film.ole system and the offshore Isolated Sinkhole system during the summer and fall. Sensor observations and diver observations have given us insight into the physical, biological, and chemical characteristics of the sinkholes. Sample processing continues to reveal the way life in these extreme systems behaves, as well as to provide hopeful insights into the potential value of these organisms for use in pharmaceutical applications. We have also begun to publish some of our results in scientific journals.

Tom Johengen’s Lab collected nutrient samples from all three sinkhole locations during three different surveys. The goal was to sample the groundwater end member as well as comparative control (lake water) samples at each of the sinkhole sites. Samples will be analyzed for a variety of nutrients, including nitrogen, phosphorous, and silicon as well as other ions (such as chloride, sulfate, bromide, and fluoride).  Chemical analyses will help to define the signatures (i.e., source and strength) of the groundwater input and will be examined in terms of its potential influence on observed levels of photosynthesis and chemosynthesis present within the sinkhole basins.

Steve Nold’s Lab is providing an understanding of microbial ecology by characterizing the fine-scale vertical organization of multi The sinkhole ecosystems are in a class not only with Antarctic lakes, but also with deep-sea, hydrothermal vents and cold seeps.-celled animal communities inhabiting the sinkholes and determining the source of organic carbon in sinkhole sediments. We collected and thin-sectioned sediment cores from Middle Island Sinkhole and extracted and separated phospholipids from the cell membranes of sinkhole inhabitants. These samples are currently at the Soil Science Department at the University of Wisconsin–Madison awaiting analysis. They will be separated by gas chromatography, and individual lipid components will be analyzed by isotope ratio mass spectrometry for 13C content. These data will provide a comprehensive view of microbial community composition, including metazoan and bacterial inhabitants. By illuminating patterns of 13C incorporation into individual membrane lipids, these data will also link metazoans to their food source (presumably the cyanobacterial phototrophs in this ecosystem).

 

Mark Baskaran’s Lab collected a suite of water samples in around the three vents. Radioisotopes and stable isotopes of oxygen and hydrogen were analyzed in these water samples. We found the radium isotopes give the groundwater a unique isotopic signature with 100 more times radium in the sinkhole groundwater than in the surrounding lake water. We will be able to quantify the amount of submarine groundwater discharge into the lake using this unique signature. The analysis of stable isotopic oxygen indicated that the sinkhole water is highly depleted in oxygen isotopic composition. The hydrogen isotopic composition also indicates similar depletion. When the analysis is completed on additional radium isotopes we anticipate obtaining the velocity of the movement of sinkhole water into the lake, using isotopic activity ratios. We also anticipate obtaining the vertical and horizontal diffusion rates of sinkhole water, using the concentration gradient of radium isotopes.

 

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