Groundwater shapes sediment biogeochemistry and microbial diversity in a submerged Great Lake sinkhole

For a large part of earth’s history, cyanobacterial mats thrived in lowâ oxygen conditions, yet our understanding of their ecological functioning is limited. Extant cyanobacterial mats provide windows into the putative functioning of ancient ecosystems, and they continue to mediate biogeochemical transformations and nutrient transport across the sedimentâ water interface in modern ecosystems. The structure and function of benthic mats are shaped by biogeochemical processes in underlying sediments. A modern cyanobacterial mat system in a submerged sinkhole of Lake Huron (LH) provides a unique opportunity to explore such sedimentâ mat interactions. In the Middle Island Sinkhole (MIS), seeping groundwater establishes a lowâ oxygen, sulfidic environment in which a microbial mat dominated by Phormidium and Planktothrix that is capable of both anoxygenic and oxygenic photosynthesis, as well as chemosynthesis, thrives. We explored the coupled microbial community composition and biogeochemical functioning of organicâ rich, sulfidic sediments underlying the surface mat. Microbial communities were diverse and vertically stratified to 12 cm sediment depth. In contrast to previous studies, which used lowâ throughput or shotgun metagenomic approaches, our highâ throughput 16S rRNA gene sequencing approach revealed extensive diversity. This diversity was present within microbial groups, including putative sulfateâ reducing taxa of Deltaproteobacteria, some of which exhibited differential abundance patterns in the mats and with depth in the underlying sediments. The biological and geochemical conditions in the MIS were distinctly different from those in typical LH sediments of comparable depth. We found evidence for active cycling of sulfur, methane, and nutrients leading to high concentrations of sulfide, ammonium, and phosphorus in sediments underlying cyanobacterial mats. Indicators of nutrient availability were significantly related to MIS microbial community composition, while LH communities were also shaped by indicators of subsurface groundwater influence. These results show that interactions between the mats and sediments are crucial for sustaining this hot spot of biological diversity and biogeochemical cycling.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136330/1/gbi12215_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136330/2/gbi12215.pd

Monitoring Freshwater Salinization in an Urban Watershed

Salt pollution from road de-icers and building material weathering change the major ion composition and increase salinity of freshwaters. These alterations are pronounced in urban watersheds due to drainage of impervious surfaces. Wetlands in urban areas receive pulses of high salt concentrations and may retain dissolved salts, reaching toxic levels for aquatic biota and possibly altering biogeochemical processes. To characterize freshwater salinization in an urban wetland, we monitored water quality in a mitigation wetland complex and an adjacent first order stream at the Cleveland Metroparks Watershed Stewardship Center in Parma, Ohio. We analyzed surface water samples for major ion concentrations (n=359) and collected high temporal resolution (5 min) specific conductance data from July, 2018 to November, 2019. Specific conductance remained elevated above typical freshwater levels throughout most of the year. Observations of high specific conductance (&gt;2,000 µS/cm) corresponded with periods of snowmelt and during the summer and early fall low water periods, suggesting evaporative concentration of salt ions. Declines in specific conductance along hydrologic flow paths within the wetland complex sub-sites suggest that salts are removed by the system, either through soil or groundwater retention.</p

Mud in the city: Effects of freshwater salinization on inland urban wetland nitrogen and phosphorus availability and export

https://kent-islandora.s3.us-east-2.amazonaws.com/node/17530/87530-thumbnail.jpgAbstract Salinization and eutrophication are nearly ubiquitous in watersheds with human activity. Despite the known impacts of the freshwater salinization syndrome (FSS) to organisms, we demonstrate a pronounced knowledge gap on how FSS alters wetland biogeochemistry. Most experiments assessing FSS and biogeochemistry pertain to coastal saltwater intrusion. The few inland wetland studies mostly add salt as sodium chloride. Sodium chloride alone does not reflect the ionic composition of inland salinization, which derives from heterogeneous sources, producing spatially and temporally variable ionic mixtures. We develop mechanistic hypotheses for how elevated ionic strength and changing ionic composition alter urban wetland sediment biogeochemistry, with the prediction that FSS diminishes nutrient removal capacity via a suite of related direct and indirect processes. We propose that future efforts specifically investigate inland urban wetlands, a category of wetland heavily relied on for its biogeochemical processing ability that is likely to be among the most impacted by salinization.</p