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Georgia Water Resources Institute
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ItemIndicators of Long Term Hydrologic Change in the Flint River(Georgia Institute of Technology, 2013-04) Golladay, Stephen W. ; Hicks, David W.The occurrence of three substantial climatic and hydrologic droughts since 1998 has raised concerns about water supply and stream flow throughout Georgia. This concern is acute in the Flint River Basin where low flows of unusual duration and magnitude were observed. The Flint River is essentially unregulated, originating just south of Atlanta and joining the Chattahoochee River to form Lake Seminole in southwestern Georgia. In addition to being an important water supply, the Flint River is noted for its biological and habitat diversity. For our analyses we used long term daily flow records from four stations (USGS: 02344478 – Griffin, 02347500 – Carsonville, 0234750 – Montezuma, 02353000 – Newton) to examine potential changes in hydrologic characteristics. We compared the period of 1940-1974 to 1975-2010, with the later period representing extensive development and population growth in the upper basin, and expansion of irrigated agriculture in the lower basin. Trends in rainfall were compared over the same intervals. No long term changes in annual rainfall were observed. Cycles of above and below average rainfall were observed as were periodic multi-year droughts. Annual water yields (annual CFS/watershed area at the station) ranged from 1.0 to 1.6 CFS/mi2 at all stations during most years. A declining tendency was observed at each station during the 1975-2010 interval, but was only significant at the Montezuma Station (p = 0.04). Winter yields showed similar declines only being significantly lower at the Griffin Station (p = 0.05). Summer yields were lower at all sites and significant declines were observed at Griffin, Carsonville, and Newton (p < 0.05). Calculation of 32 hydrologic indicators showed that the frequencies of low June-September median monthly flows, 1-day, 3-day, 7-day, and 30-day low flows were more common in the 1975-2010 interval at all stations. Our results indicate that human water use is causing increased severity and duration of low flows during the spring and summer seasons throughout the Flint River. These tendencies are pronounced during seasonal and extended droughts. Increased demand is the result of population expansion in the upper basin and irrigation expansion in the lower basin. Current rates of water use are likely unsustainable and pose a significant threat to stream health and the unique biological diversity characteristic of the Flint River.
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ItemColeoptera Indicator Species in Wet vs. Dry Climate Regimes in Three Southwestern Georgia Wetland Types(Georgia Institute of Technology, 2011-04) Smith, Nathalie D. ; Golladay, Stephen W.Yearly variation in water availability has a profound effect on the presence and abundance of aquatic Coleoptera (beetles), particularly those dependent upon intermittent or seasonally inundated aquatic habitats. Thirty-four depressional wetlands, previously characterized as marshes, savannas or forested swamps, were sampled during above average and below average rainfall periods (1997-1998 and 2006-2007 respectively). Using Indicator Species Analysis, Coleoptera species were associated with wetland type and hydrologic regime linked to rainfall trends. Relying on species indicator values (p<0.05), marshes contained significantly higher numbers of indicator species compared to other wetland types during both wet and dry periods. Several indicator taxa were consistent within wetland type during the same hydrologic period, but these similarities were not consistent when compared across hydrologic regimes. Species diversity was higher during years with below normal rainfall. These findings indicate that marshes provide more suitable habitat and provide refugia that allow for survival and recovery beetle populations during unusually dry and wet periods. Faced with intermittent aquatic habitat and climate variation, Coleoptera taxa vary in life history characteristics and dispersal abilities which allow long term persistence within the larger landscape.
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ItemIdentifying Groundwater/Stream Interaction in the Lower Flint River Basin Using Multiple Stream Parameters and Remote Sensing Data Sets(Georgia Institute of Technology, 2011-04) Rugel, Kathleen ; Golladay, Stephen W. ; Jackson, C. RhettMany streams in the lower Flint River Basin are hydraulically connected to the underlying Upper Floridan Aquifer which supplies millions of gallons of water per day to irrigated agriculture throughout the Coastal Plain province of Georgia. Extensive pumping of surface and groundwater within the lower Flint River Basin has resulted in significant streamflow declines, threatening aquatic species which are listed as endangered and threatened in this region. Our research focuses on detecting fracture and dissolution paths between Ichawaynochaway Creek and the underlying Upper Floridan Aquifer. We collected and analyzed stream samples for NO3 -, Ca+, δ18O, and δD, as well as specific conductivity, temperature and pH, at 1 km intervals along a 53 km reach of the Ichawaynochaway Creek in southwestern Georgia, USA. We hypothesized that stream reaches within close proximity to fractures and joints would reflect the chemical signature of inputs from the underlying aquifer. We compared stream chemistry with proximity to various surface features visible on remote sensing data sets in order to identify geomorphological characteristics which might be associated with and predictive of stream-aquifer exchange.
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ItemA Comparison of Gulf Coastal Plain Isolated Wetlands: Water Quality and Larval Mosquito Populations in Agricultural and Reference Sites(Georgia Institute of Technology, 2011-04) Golladay, Stephen W. ; Vedas, Ellen ; Blackmore, Mark ; Smith, Nathalie D.Geographically isolated wetlands, i.e. those surrounded completely by upland landforms and vegetation, are a common feature on the southeastern Coastal Plain. As a group they lack surface connection to perennial streams, rivers, or lakes and thus are not regulated under federal or state statutes. Lack of regulation has resulted in widespread isolated wetland loss or degradation, often without an appreciation for their contributions to the surrounding landscape. We sampled water quality and larval mosquito abundance in 10 reference and 10 agricultural wetlands in rural southwestern Georgia from spring through fall 2009. Generally, agricultural wetlands had higher pH, suspended solids, NO3-N, and PO4-P concentrations compared to reference sites. During weekly surveys we collected 23 species of larval mosquitoes from reference sites. Of these, 12 species were not observed in agricultural wetlands including Aedes albopictus, Culex peccator, Cx. pilosus, Cx. quinquefasciatus, Cx. salinarius, Cx. tarsalis, Ochlerotatus atlanticus, Oc. canadensis, Oc. infirmatus, Oc. mitchellae Oc. thibaulti, and Oc. triceriatus. We collected 13 species of larvae from agricultural wetlands including 4 unique species (Cx. coronator, Psorophora columbiae, Ps. discolor and Ps. horrida). Species found in both types included Ae. vexans, Anopheles crucians, An. punctipennis, An. quadrimaculatus, Culiseta melanura, Cx. erraticus, Cx. restuans, Cx. territans, Oc. sticticus, Ps. howardii, and Uranotaenia sapphirina. Ae. vexans and Culex spp. were the most abundant larvae collected. Agricultural and reference wetlands support diverse larval mosquito populations including potential arbovirus vectors, however there has been little systematic sampling in rural areas of the Gulf Coastal Plain.