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education: resources
for k-12 teachers and students BLACKWATER RIVER BASINS IN GEORGIA The Ogeechee, Suwanee, Ochlocknee, Satilla, and St. Mary's river basins drain sandy soils that lack the ability to retain dissolved organic matter leached from terrestrial vegetation. Hence their water is tea-colored, and they are called blackwater rivers. Even though there are high concentrations of dissolved organic matter in the river, the suspended sediment levels are low. Extremely low concentrations of dissolved oxygen occur in blackwater rivers during the warmer months of the year. These blackwater rivers have very little change in elevation per unit river length and extensive floodplains. Historically they had large amounts of woody debris and snags creating an intricate patchwork of rivers and riparian zones. Woody debris and snags are vital to the secondary production of aquatic insects, particularly because they provide the stable habitat for insects since the stream bottom consists primarily of constantly shifting sand. Snagging operations at the turn of the century changed the rivers. For example, wood removal operations were more intense in the Satilla River than the Ogeechee River; hence today there is less woody debris in the main channel of the Satilla.
Flooding plays an important role in the exchange between the surrounding watershed and the main channel of the river. Highest concentrations of total organic carbon occur during these flooding periods and the lowest concentrations are measured during low flow periods. Cypress and black gum forests fill the flood plain swamps that border the length of the Satilla River. This exchange between the mainstem and the floodplain occurs because of the lack of impoundments and the low gradient of these rivers. In the 48 contiguous states, there are only 42 free-flowing rivers that are greater than 200km in length. The Ogeechee, Satilla, St. Mary's, and Suwanee Rivers are four of these unimpounded rivers. The Ogeechee, Satilla, and St. Mary's Rivers are Atlantic Coast drainages. The Suwannee and Ochlockonee Rivers drain to the Gulf of Mexico. The St. Mary's and Suwanee Rivers drain portions of the Okefenokee Swamp. The St. Mary's River forms the boundary between Georgia and Florida. The pH of the Ogeechee River is near 7.0 since there is a large input of carbonate-rich water from Magnolia Springs. The Satilla River has a much lower pH (around 5.0) and lies entirely within the Coastal Plain. Development and industrial or residential pollution is very low, and there is relatively little agricultural runoff into the river. Stream Flow Table 1. Stream flow data from USGS. Stream flow is measured in units of cubic feet per second (cfs) flowing past a point.
Figures 3-5 denote the presence of urbanization, agriculture, and forests within the watersheds of three of the five blackwater rivers in Georgia. The black star on each map denotes the approximate location of the USGS gauging station referenced in Table 1. Figure 3. Land use and land cover in the Satilla River watershed. Source: Georgia Rivers LMER.
Figure 4. Land use and land cover in the St. Mary's River watershed. Source: Georgia Rivers LMER.
Figure 5. Land cover and land use in the Ogeechee River watershed. Source: Georgia Rivers LMER. Land cover and land use patterns Table 2. 1998 land cover statistics.
Additional information and sources Georgia Natural Heritage Program Benke, A.C. 1990. A perspective on America's vanishing streams. Journal of the North American Benthological Society 9(1): 77-88. Meyer, J.L. 1992. Seasonal Patterns of Water Quality in Blackwater Rivers of the Coastal Plain, Southeastern United States. Pages 250-276 in C.D. Becker and D.A. Neitzel, editors. Water quality in North American river systems. Columbus: Battelle Press. Meyer, J.L. 1990. A blackwater perspective on riverine ecosystems. Bioscience 40: 643-651. Environmental, Educational, and Community Action Organizations Upper Suwanee River Watershed Initiative Ogeechee River Valley Association, Inc. |
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