Steven A. Ruberg

Lake Erie hypoxia prompts Canada‐U.S. study

Because of its size and geometry, the central basin of Lake Erie, one of North Americas Great Lakes, is subject to periods in the late summer when dissolved oxygen concentrations are low (hypoxia). An apparent increase in the occurrence of these eutrophic conditions and ‘dead zones’ in recent years has led to increased public concern. The International Field Years for Lake Erie (IFYLE) project of the Great Lakes Environmental Research Laboratory (GLERL, a U.S. National Oceanic and Atmospheric Administration (NOAA) laboratory), was established in 2005 in response to this increase. This project is investigating the causes and consequences of hypoxia in the lake. As part of the effort, scientists from the United States and Canada conducted an extensive field study in 2005 to gather more information on the duration and extent of the hypoxic zone and its effects on the biota in the lake. This article gives a brief history and description of the problem and presents initial results from the field study.

Groundwater Plume Mapping in a Submerged Sinkhole in Lake Huron

A multidisciplinary exploratory project team from the Institute for Exploration, the Great Lakes Environmental Research Laboratory, Grand Valley State University, and the University of Michigan located and explored a submerged sinkhole in Lake Huron during September 2003. A CTD system and an ultra-short baseline (USBL) acoustic navigational tracking system integrated with an open frame remotely operated vehicle (ROV) provided high-resolution depth, temperature, and conductivity maps of the sinkhole and plume. Samples were also peristaltically pumped to the surface from a depth of 92 meters within and outside of the sinkhole plume. A 1-2 m thick cloudy layer with a strong hydrogen sulfide odor characterized the water mass close to the plume. Relative to ambient lake water, water samples collected within this layer were characterized by slightly higher (4-7.5 oC) temperatures, very high levels of chloride and conductivity (10-fold) as well as extremely high concentrations of organic matter (up to 400 mg C/L), sulfate, and phosphorus. Our observations demonstrated the occurrence of unique biogeochemical conditions at this submerged sinkhole environment. I N T R O D U C T I O N he Laurentian Great Lakes were formed about 10,000-12,000 years before present (ybp), and presently contain approximately 19% of the Earth’s surface liquid freshwater (Beeton, 1984). The Lake Huron Basin is mostly covered with a layer of glacial till, sand, silt and clay. Underlying these sediments are aquifers formed within Paleozoic (Silurian-Devonian) bedrock. These bedrock aquifers were laid down when the shallow seas still spread widely over the continental areas approximately 350430 million ybp. The Silurian-Devonian aquifer consists of carbonate, shale, and sandstone matrix with some evaporite beds, and has fresh and saline water, which can contain varying amounts of sulfates, chlorides and iron. Dissolution of the Silurian-Devonian evaporites has produced the major karst features (Olcott, 1992) such as the sinkholes discovered during the 2001 acoustic survey expedition (Coleman, 2002) conducted by the Thunder Bay National Marine Sanctuary and the Institute for Exploration. The sinkhole vents, producing a visible cloudy layer above the lake bottom (Figure 1), were a serendipitous discovery made during a 2002 remotely operated vehicle (ROV) survey of the sinkholes. Recharge areas of freshwater replenishment for the Silurian-Devonian aquifers have been documented on land in the Lake Huron basin; these areas are typically sinkholes (Figure 2). In this report, we discuss the mapping of the Isolated Sinkhole located approximately 10 miles from shore at a depth of 93 m in the north central region of the Thunder Bay National Marine Sanctuary during September 2003.

Observations of the Middle Island Sinkhole in Lake Huron: A Unique Hydrologic and Glacial Creation of 400 Million Years

In the northern Great Lakes region, limestone sediments deposited some 400 million ybp during the Devonian era have experienced erosion, creating karst features such as caves and sinkholes. The groundwater chemical constituents of the shallow seas that produced these rock formations now contribute to the formation of a unique physical (sharp density gradients), chemical (dissolved oxygen-depleted, sulfate-rich) and biological (microbe-dominated) environment in a submerged sinkhole near Middle Island in freshwater Lake Huron. A variety of methods including aerial photography, physico-chemical mapping, time series measurements, remotely operated vehicle (ROV) survey, diver observations and bathymetric mapping were employed to obtain a preliminary understanding of sinkhole features and to observe physical interactions of the system’s groundwater with Lake Huron. High conductivity ground water of relatively constant temperature hugs the sinkhole floor creating a distinct sub-ecosystem within this Great Lakes ecosystem. Extensive photosynthetic purple cyanobacterial benthic mats that characterize the benthos of this shallow sinkhole were strictly limited to the zone of ground water influence. tions of chloride, and 100-fold higher concentrations of sulfate (Ruberg et al., 2005). A variety of non-photosynthetic benthic microbial mats were observed in this deepwater aphotic sinkhole system. Water samples collected from the sinkhole plume contained bacterial concentrations (~9x109 cells l-1) an order of magnitude higher than ambient lake concentrations (~1x109 cells l-1), and showed evidence for the occurrence of significant chemosynthesis in this lightless deep water environment (Biddanda et al., 2006). These rates of chemosynthesis occurring in the Lake Huron Isolated sinkhole were comparable to those measured in thermal vents in Yellowstone Lake (Cuhel et al., 2002). Understanding the nature of the groundwater emerging in Lake Huron’s sinkholes requires an introduction P A P E R

Great Lakes Sinkholes: A Microbiogeochemical Frontier

Recent underwater explorations have revealed unique hot spots of biogeochemical activity at several submerged groundwater vents in Lake Huron, the third largest of the Laurentian Great Lakes. Fueled by venting groundwater containing high sulfate and low dissolved oxygen, these underwater ecosystems are characterized by sharp physical and chemical gradients and spectacularly colorful benthic mats that overlie carbon-rich sediments. Here, typical lake inhabitants such as fish and phytoplankton are replaced by communities dominated by microorganisms: bacteria and archaea that perform unique ecosystem functions. Shallow, sunlit sinkholes are dominated by photosynthetic microorganisms and processes, while food webs in deep aphotic sinkholes are supported primarily by chemosynthesis.

Diverse manganese(II)-oxidizing bacteria are prevalent in drinking water systems

Manganese (Mn) oxides are highly reactive minerals that influence the speciation, mobility, bioavailability and toxicity of a wide variety of organic and inorganic compounds. Although Mn(II)-oxidizing bacteria are known to catalyze the formation of Mn oxides, little is known about the organisms responsible for Mn oxidation in situ, especially in engineered environments. Mn(II)-oxidizing bacteria are important in drinking water systems, including in biofiltration and water distribution systems. Here, we used cultivation dependent and independent approaches to investigate Mn(II)-oxidizing bacteria in drinking water sources, a treatment plant and associated distribution system. We isolated 29 strains of Mn(II)-oxidizing bacteria and found that highly similar 16S rRNA gene sequences were present in all culture-independent datasets and dominant in the studied drinking water treatment plant. These results highlight a potentially important role for Mn(II)-oxidizing bacteria in drinking water systems, where biogenic Mn oxides may affect water quality in terms of aesthetic appearance, speciation of metals and oxidation of organic and inorganic compounds. Deciphering the ecology of these organisms and the factors that regulate their Mn(II)-oxidizing activity could yield important insights into how microbial communities influence the quality of drinking water.

Societal Benefits of the Real-Time Coastal Observation Network (ReCON): Implications for Municipal Drinking Water Quality

Environmental conditions on Lake Erie in summer 2006 produced hypoxic waters (1.2 mg/l dissolved oxygen), with characteristic low pH (7.2), low temperature (18°C) and high manganese levels, negatively impacting water processing at the Cleveland Water Department. A ReCON system deployed in 2005 recorded the onset of similar conditions and is used to explain the episodic nature of the event. Internal waves initiated by winds can propagate around the central basin of Lake Erie for several days explaining the cyclical nature of the event. Future deployments of a ReCON buoy system in Lake Erie’s central basin will provide real-time observations of temperature and dissolved oxygen to water department managers. The buoy will function as an early warning system for the detection of low oxygen and the onset of internal waves responsible for delivering hypoxic waters to water intakes, thus ensuring the quality of drinking water for approximately 1.5 million residents of Cleveland, OH. 2007), is currently engaged in collaborative research to create ecosystem forecasting tools in the Great Lakes benefiting a wide range of regional constituents. The Great

A wireless real‐time coastal observation network

A new integrated coastal observation system is providing preliminary data from the North American Great Lakes. This system can be implemented in other coastal regions. To date, it has been successfully deployed on Lakes Michigan, Huron, and Erie to make seabed to sea-surface measurements of chemical, biological, and physical parameters, which are transmitted wirelessly through buoys and permanent stations. Called the Real-Time Coastal Observation Network (ReCON), the new system leverages existing networking technology to provide universal access to a wide variety of instrumentation through the use of an underwater Ethernet port server [Austin, 2002]. A team of NOAA engineers and scientists has completed the development and testing of this integrated coastal observation network. Utility of the Network An Ethernet-based coastal observation network design enables the creation of system components, such as sensor drivers, data transfer software, system control functions, database management, web display ,and archival functions, using standard web-design tools. The underwater, universal hub easily allows the attachment of sensors at any time during the deployment period. Portable buoys and permanent stations transferring data into network nodes distributed across broad coastal regions can be integrated at a central location using the Internet. This implementation of a coastal network providing real-time chemical, biological, and physical observations has already benefited ecosystem research ers, resource managers, forecasters, educational institutions, and public users. Further, regional observations downloaded at time intervals required to describe particular ecosystem features and events can be presented to managers and operational forecasters through ad hoc web displays or to students and researchers through searchable database management systems. Using this approach, an observation network can be deployed in any coastal region with Internet availability. Buoys need only be placed within antenna range of the shore station. Deployment range, dependent on the height of the shore antenna, can be as much as 32 kilometers allowing buoy placement anywhere within an approximate 1400 square kilometer area. Additional buoys or fixed stations can be used to extend range through the use of the relay capability inherent in wireless network devices. The observation network supplies enough throughput capacity to simultaneously support continuous measurements from both standard oceanographic and meteorological instrumentation (such as wind and temperature measurements, current velocity profilers, and chemical sensors) and more advanced surface and underwater applications such as streaming imagery. By leveraging existing internet technology for real-time data collection, NOAA’s observation infrastructure can be signifi cantly upgraded to provide forecasters, researchers, coastal resource managers, and the public with the data necessary to make informed decisions in response to ecosystem change [Ocean.US, 2002]. The transition of this research and development effort to an operational coastal implementation has the potential to improve forecasts and forecast verification, increase marine safety, and reduce public health risks while responding to established national goals [Ocean.US, 2006].

Novel Large Sulfur Bacteria in the Metagenomes of Groundwater-Fed Chemosynthetic Microbial Mats in the Lake Huron Basin

Little is known about large sulfur bacteria (LSB) that inhabit sulfidic groundwater seeps in large lakes. To examine how geochemically relevant microbial metabolisms are partitioned among community members, we conducted metagenomic analysis of a chemosynthetic microbial mat in the Isolated Sinkhole, which is in a deep, aphotic environment of Lake Huron. For comparison, we also analyzed a white mat in an artesian fountain that is fed by groundwater similar to Isolated Sinkhole, but that sits in shallow water and is exposed to sunlight. De novo assembly and binning of metagenomic data from these two communities yielded near complete genomes and revealed representatives of two families of LSB. The Isolated Sinkhole community was dominated by novel members of the Beggiatoaceae that are phylogenetically intermediate between known freshwater and marine groups. Several of these Beggiatoaceae had 16S rRNA genes that contained introns previously observed only in marine taxa. The Alpena fountain was dominated by populations closely related to Thiothrix lacustris and an SM1 euryarchaeon known to live symbiotically with Thiothrix spp. The SM1 genomic bin contained evidence of H2-based lithoautotrophy. Genomic bins of both the Thiothrix and Beggiatoaceae contained genes for sulfur oxidation via the rDsr pathway, H2 oxidation via Ni-Fe hydrogenases, and the use of O2 and nitrate as electron acceptors. Mats at both sites also contained Deltaproteobacteria with genes for dissimilatory sulfate reduction (sat, apr, and dsr) and hydrogen oxidation (Ni-Fe hydrogenases). Overall, the microbial mats at the two sites held low-diversity microbial communities, displayed evidence of coupled sulfur cycling, and did not differ largely in their metabolic potentials, despite the environmental differences. These results show that groundwater-fed communities in an artesian fountain and in submerged sinkholes of Lake Huron are a rich source of novel LSB, associated heterotrophic and sulfate-reducing bacteria, and archaea.