Interactions between organisms and their environment are dynamic in nearshore environments. Determining gaps in our current knowledge relating to coastal Great Lakes ecosystems and the ecological processes that take place within allows us to target areas in need of additional research. This, in turn, promotes better management of available resources and supports a proactive approach to arising issues that may stress the ecosystem. The USGS-GLSC is examining ecological processes at work in western Lake Erie, Saginaw Bay, and rivermouth ecosystems (such as where the Maumee River empties into Lake Erie) to fill in knowledge gaps and improve ecosystem characterization, monitoring, and prediction efforts, as needed. For example, harmful algal blooms (HABs) are a growing problem in western Lake Erie and researchers are focused on uncovering essential pieces of information that will allow for better bloom forecasting and prevention. Through the USGS-GLSC’s coastal Gap Analysis Program, researchers are working to identify critical coastal habitat and species in need of specific and immediate management efforts. Many of these species in need are fish that utilize coastal habitats for feeding, spawning, or providing protection for juveniles. Known migratory corridors and preferred habitats are being examined so that restoration efforts can be improved and important fish species can be protected.
Methylmercury contamination is a high risk health threat to wildlife and people in many environments. Wetlands form a unique aquatic environment where the biochemical process that transforms elemental mercury to methylmercury is greatly intensified. Wetlands often either accumulate methylmercury or transport it into nearby areas. Therefore, determining whether a wetland is a source or a sink for methylmercury is vital in controlling methylmercury contamination.
- Determine background levels of mercury/methylmercury in a wetland complex in the USFWS Ottawa National Wildlife Refuge
- Determine if wetlands are acting as a source or sink of methylmercury
- Discuss results with refuge to evaluate future actions
Background & Justification
Mercury is a globally present pollutant that can have serious implications on the health of higher trophic level organisms and humans. There are many different forms of mercury found in the environment, but the methylated form (MeHg) is the most toxic and readily bioaccumulates. Wetlands have been well documented to be significant MeHg production sites. More specifically, the methylation process is facilitated by a frequent wet-dry cycle and sulfate-reducing and iron-reducing bacteria in sediments. The amount of methylmercury production is determined by a number of factors including presence / absence of bacteria, type of and physiochemical conditions of sediment, amount of Hg (II), and other environmental factors (e.g., dissolved organic matter, dissolved oxygen, nitrate / nitrite). In addition, methylmercury can potentially be degraded in wetlands through microbial activity and abiotic processes (e.g., photodegradation).
The production, storage, transport, and degradation of methylmercury in the Great Lakes is not well understood. To address this deficiency, Dr. David Krabbenhoft and others at USGS have GLRI funded research projects exploring methylmercury production in the open lakes. This work is not focused on coastal wetlands even though wetlands have the capability to act as either a source or a sink for methylmercury. Discussions with Dr. Krabbenhoft led to this project focused on the assessment of methylmercury in the wetlands at the USFWS Ottawa National Wildlife refuge. The refuge maintains both diked (i.e., managed) wetland pools and coastal wetlands in Crane Creek, a tributary to Lake Erie. Active water-level management and seasonal hydrologic changes in the pools often support a regular wet-dry cycle. Higher elevations within Crane Creek are also exposed frequently by both seiche activity and fluctuating annual lake levels. Therefore, the wetlands at the refuge appear to be a prime environment for production of methylmercury. Studying the production, magnitude, and transport of methylmercury within the Crane Creek wetland complex and nearby sites will help determine if the wetlands are supplying Lake Erie with methylmercury.
Historically, there has been a perception that each beach is a uniquely functioning system and that point sources of contamination were the drivers influencing microbiological contamination at each beach. Recent research, however, has highlighted the larger scale processes that interact to affect nearshore water quality along lengthy stretches of coastline; processes that influence the overall lake dynamics and interact with drivers at individual beaches. While there are still local influences, widespread fluctuations in bacterial communities can often be described by regional processes. An understanding is needed of the large-scale and small-scale processes that, combined, describe the water quality at a given beach. The integration of these empirical models with dynamic numerical models and bacterial community analyses is providing new insight for how coastal waters can be managed.
- Assess predictability of indicator bacteria at specific beaches by associating hydrometeorological predictors and dynamic process models.
- Integrate an understanding of bacterial communities with coastal processes to develop estimations of scale of influence and impact of bacteria sources on beach water quality.
Background & Justification
Depending on the size and relative influence of point source inputs, predictors of contamination may be related to rivers and streams at point source dominated locations or to shoreline processes. In regional modeling, beaches that are point source or non-point source dominated can both be included in predictive models. The use of regional models is helping to characterize E. coli fluctuations across a much broader region, which will help beach managers characterize and eliminate sewage sources, increase modeling effectiveness, and understand how to protect public health better. Current and future efforts will be devoted to expanding this concept with hydrodynamic modeling, additional extensive shorelines, and further examining beach groupings for simultaneous fluctuations.
In attempts to marry beach predictive models with dynamic physical processes, larger coastlines may provide significant insight. By integrating these two approaches, the application and concept of predictive modeling can be explored to improve both inputs and results. These efforts attempt to discriminate the components of variation for E. coli in swimming waters and to separate fluctuations in region-wide background bacterial communities with nearshore flux and beach-specific influences so as to distinguish driving sources at subject beaches. This research will help beach managers to understand the beach-specific influences at individual beaches, which will help improve E. coli predictions, allow for modifications to sampling strategies, and improve understanding of bacteria sources. All of this will aid in developing strategies for beach restoration.
This research will make advances toward lake-wide monitoring systems for recreational water quality. With the expansion of water quality predictions and the characterization of natural and human-derived bacterial populations, better assessments of public health risk can be made. Next research steps will include the continued expansion and refinement of predictive models with independent variables that incorporate dynamic biological and physical processes. Modeling will also incorporate new dependent variables that are better indicators of recent human sewage contamination and associated pathogens and disease-causing organisms.