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

Sedimentary pyrite sulfur isotope compositions preserve signatures of the surface microbial mat environment in sediments underlying low-oxygen cyanobacterial mats

The sedimentary pyrite sulfur isotope (delta S-34) record is an archive of ancient microbial sulfur cycling and environmental conditions. Interpretations of pyrite delta S-34 signatures in sediments deposited in microbial mat ecosystems are based on studies of modern microbial mat porewater sulfide delta S-34 geochemistry. Pyrite delta S-34 values often capture delta S-34 signatures of porewater sulfide at the location of pyrite formation. However, microbial mats are dynamic environments in which biogeochemical cycling shifts vertically on diurnal cycles. Therefore, there is a need to study how the location of pyrite formation impacts pyrite delta S-34 patterns in these dynamic systems. Here, we present diurnal porewater sulfide delta S-34 trends and delta S-34 values of pyrite and iron monosulfides from Middle Island Sinkhole, Lake Huron. The sediment-water interface of this sinkhole hosts a low-oxygen cyanobacterial mat ecosystem, which serves as a useful location to explore preservation of sedimentary pyrite delta S-34 signatures in early Earth environments. Porewater sulfide delta S-34 values vary by up to similar to 25 parts per thousand throughout the day due to light-driven changes in surface microbial community activity that propagate downwards, affecting porewater geochemistry as deep as 7.5 cm in the sediment. Progressive consumption of the sulfate reservoir drives delta S-34 variability, instead of variations in average cell-specific sulfate reduction rates and/or sulfide oxidation at different depths in the sediment. The delta S-34 values of pyrite are similar to porewater sulfide delta S-34 values near the mat surface. We suggest that oxidative sulfur cycling and other microbial activity promote pyrite formation in and immediately adjacent to the microbial mat and that iron geochemistry limits further pyrite formation with depth in the sediment. These results imply that primary delta S-34 signatures of pyrite deposited in organic-rich, iron-poor microbial mat environments capture information about microbial sulfur cycling and environmental conditions at the mat surface and are only minimally affected by deeper sedimentary processes during early diagenesis

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

Sedimentary pyrite sulfur isotope compositions preserve signatures of the surface microbial mat environment in sediments underlying low- oxygen cyanobacterial mats

The sedimentary pyrite sulfur isotope (δ34S) record is an archive of ancient microbial sulfur cycling and environmental conditions. Interpretations of pyrite δ34S signatures in sediments deposited in microbial mat ecosystems are based on studies of modern microbial mat porewater sulfide δ34S geochemistry. Pyrite δ34S values often capture δ34S signatures of porewater sulfide at the location of pyrite formation. However, microbial mats are dynamic environments in which biogeochemical cycling shifts vertically on diurnal cycles. Therefore, there is a need to study how the location of pyrite formation impacts pyrite δ34S patterns in these dynamic systems. Here, we present diurnal porewater sulfide δ34S trends and δ34S values of pyrite and iron monosulfides from Middle Island Sinkhole, Lake Huron. The sediment- water interface of this sinkhole hosts a low- oxygen cyanobacterial mat ecosystem, which serves as a useful location to explore preservation of sedimentary pyrite δ34S signatures in early Earth environments. Porewater sulfide δ34S values vary by up to ~25- ° throughout the day due to light- driven changes in surface microbial community activity that propagate downwards, affecting porewater geochemistry as deep as 7.5 cm in the sediment. Progressive consumption of the sulfate reservoir drives δ34S variability, instead of variations in average cell- specific sulfate reduction rates and/or sulfide oxidation at different depths in the sediment. The δ34S values of pyrite are similar to porewater sulfide δ34S values near the mat surface. We suggest that oxidative sulfur cycling and other microbial activity promote pyrite formation in and immediately adjacent to the microbial mat and that iron geochemistry limits further pyrite formation with depth in the sediment. These results imply that primary δ34S signatures of pyrite deposited in organic- rich, iron- poor microbial mat environments capture information about microbial sulfur cycling and environmental conditions at the mat surface and are only minimally affected by deeper sedimentary processes during early diagenesis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/171214/1/gbi12466_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/171214/2/gbi12466.pd

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

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

Abstract 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