Aquatic Habitat, Function, & Ecosystem Services
Water scarcity is causing once perennial streams to become intermittent, cease flowing, or dry completely for extended periods. For historically intermittent streams and wetlands, periods, where water is present, have shortened. We use a variety of ways to understand how drying affects aquatic places. Long term data are critical. We rely on diverse data sources from the internet for rainfall, streamflow, and groundwater levels.
We also operate our own weather stations to provide local data. These data are analyzed to understand changes in the frequency, duration, and intensity of floods and droughts. Our own studies focus on details of aquatic habitat quality and responses of aquatic life. They include surveyed and instrumented streams and wetlands to determine how water scarcity affects important animal groups including invertebrates, fishes, amphibians, reptiles, and birds. We also measure important processes including water quality, organic matter processing, evapotranspiration, and the cycling of important elements to get a sense of aquatic health.
Freshwater mussels are key inhabitants of many streams and rivers. They live in and on the sediment where they spend their lives filtering water to obtain nutrition. Filtering purifies the water and mussel beds provide a nutrient-rich habitat for other aquatic life. Mussel communities of the Flint River Basin (FRB) in southwestern Georgia are among the richest in the southeastern United States. Historically, 29 species of mussels, seven of which were endemic, existed in the Flint River.
In southwestern Georgia, period droughts combined with warming temperatures and increasing water withdrawals have resulted in extremely low flows in the lower FRB and its tributaries. We have documented declines in mussel abundance in streams subject to record low flow conditions. Our studies, along with historical studies, point to a long term decline for many mussel species in the Apalachicola, Chattahoochee, and Flint Basin attributable to a history of multiple disturbances. Once mussel populations are lost over large areas, remaining isolated populations, like those we’ve studied in the lower FRB, may have little chance of contributing to recovery through the larger basin.
For more information see:
DuBose T. P., C. L. Atkinson, C. C. Vaughn, S. W. Golladay. 2019. Drought-induced, punctuated loss of freshwater mussels alters ecosystem function across temporal scales. Frontiers in Ecology and Evolution 7:1-13 DOI: https://doi.org/10.3389/fevo.2019.00274
Gagnon, P. M., S. W. Golladay, W. K. Michener, and M. C. Freeman. 2004. Drought responses of freshwater mussels (Unionidae) in coastal plain tributaries of the Flint River Basin, Georgia. Journal of Freshwater Ecology 19:667-679.
Golladay, S. W., P. Gagnon, M. Kearns, J. M. Battle, and D. W. Hicks. 2004. Response of freshwater mussel assemblages (Bivalvia: Unionidae) to a record drought in the Gulf Coastal Plain of southwestern Georgia. Journal of the North American Benthological Society 23:494-506. DOI: https://doi.org/10.1899/0887-3593(2004)023<0494:ROFMAB>2.0.CO;2
Aquatic insects and crustaceans
Aquatic insects and crustaceans (like crayfish), spend most of their lives living in or on submerged surfaces in aquatic habitats. As consumers, their feeding promotes the recycling of plant and animal matter, and they serve as intermediate stages in aquatic food webs. Our ongoing research is examining how these aquatic organisms are responding to stream drying. Streams we have studied include perennial, near-perennial (ceased flowing but maintained a wetted channel during drought), intermittent-dry (seasonally dry), and intermittent-frequent (frequently dry). Distinct assemblages were documented across this gradient. Reaches that dried had a lower richness of aquatic insects, especially Ephemeroptera, Plecoptera, and Trichoptera taxa, partly due to inadequate time for life cycle completion and lack of adaptations to avoid drying. Intermittent reaches also included abundant and unique crustacean taxa such as Amphipoda and Isopoda. Projected trends towards increased temperature, water demand and drought occurrence in the region will shift communities towards drought-tolerant taxa as greater portions of stream networks become intermittent. The effect of these changes on aquatic food webs remains unknown.
For more information see:
Smith, C.R., P.V. McCormick, A.P. Covich, and S.W. Golladay. 2017. Comparison of macroinvertebrate assemblages across a gradient of flow permanence in an agricultural watershed. River Research and Applications 33: 1428-1438. DOI: https://doi.org/10.1002/rra.3211
The southeastern US is noted for having the most diverse freshwater fish fauna in North America (662 species listed in river basins, Virginia to Texas). About 1/3 of these species are of conservation concern due to water extraction, pollution, habitat alteration, and introduction of invasive species. Much of the native diversity is non-game species, often little known or studied. In southwestern Georgia, increasing temperatures and water withdrawal are increasing the frequency and extent of stream drying.
Our study of fishes indicated that only a subset of species could tolerate stream drying. Thus, as stream intermittency becomes more extensive in extent and frequency, extirpation of species may occur. Fish species most tolerant of drying has specific life-history traits, often involved with reproductive and development timing that allowed survival. Our ongoing work is examining how fish food webs are responding to water scarcity and stream drying.
For more information see:
Davis J.L., M.C. Freeman, and S.W. Golladay. 2019. Identifying life-history traits that promote occurrence for four minnows (Leuscicidae) species in intermittent Gulf Coastal Plain streams. Southeastern Naturalist 19: 103-127.
Geographically Isolated Wetlands
Geographically isolated wetlands (GIWs) are called ‘isolated’ because they do not have visible surface channels to streams, rivers, or lakes. Lack of connection has caused them to be overlooked in considerations of water management and environmental health. They are an important part of the longleaf pine landscape. Relatively small in area compared to the surrounding woodland, their value is relatively much greater than the area they occupy.
Wetlands are known for extremely high biodiversity, high rates of carbon intake and storage, and can help improve water quality. However, many wetlands are degraded due to lack of water during drought and increased water demand from climate change. Land management can also have a major impact on how wetlands work.
We use isolated wetlands at Ichauway as reference sites to understand basic ecological processes. We also study how forest and agricultural land management affects GIWs regionally.
GIWs and Forest Restoration
A common restoration practice in longleaf pine landscapes is the removal of hardwoods like water oak. Just such a treatment was done a decade ago around a wetland on Ichauway, where about a third of all the trees were removed in a wetland catchment (the area of land that contributes water to the wetland).
Using water table data from years before and after this hardwood removal, we found this land management strategy greatly extended the period of standing water in the wetland. This effect was greatest during drought years. This study shows that managing the surrounding forest can help conserving wetland biota that depends upon long wet periods to reproduce and grow.
GIWs and Agricultural Runoff
Recent scientific evidence suggests that GIWs are important sources of water storage and can protect water quality at regional scales. Understanding and demonstrating the contributions of isolated wetlands is critically important because they are a source of regulatory uncertainty. We have assembled a team that is uniquely qualified to understand the contribution of isolated wetlands in a working agricultural area.
Our studies are designed to describe and measure fundamental wetland processes leading to water storage, improved water quality, and lead to management practices improving environmental health. Our project is also unique in that we intend to partner with agricultural producers at all stages of this work. We will document this engagement process through the development of educational materials that describe the process of discovery as the research team and landowners learn about isolated wetlands. We hope this material will serve as a roadmap for other research teams and landowners working to better manage land and water. This project is in cooperation with Auburn University and funded through the USDA.