ENVIRONMENTAL CHANGE OF NATURAL LAKES IN THE SE USA THROUGHOUT THE HOLOCENE WITH A FOCUS ON EUTROPHICATION

The southeastern United States contains over 8,000 lakes and paleolake beds constituting its own lake district. Most of these lakes systems are polymictic and shallow and have been heavily impacted by recent human disturbances. Nutrients (P, N) are considered the primary driver of trophic state change (e.g. primary productivity), but factors such as water depth, water residence time, dissolved color, temperature, salinity and contaminants have also been identified as potential drivers. Future projections suggest that agricultural, industrial and climate impacts on SE USA lakes will increase, creating the need to identify secondary drivers of environmental change. Here, Holocene sediment records from multiple shallow, subtropical lakes in the southeastern USA are reported and drivers of environmental change during periods of recent human impact and during times prior to substantial human disturbance (mid-late Holocene) are identified. Paleolimnological proxies of allochthonous inputs (organic mater, nutrients, and metals) and autochthonous responses (primary producer communities using photosynthetic pigments and cyanotoxins) were measured in sediment cores from Lakes Mattamuskeet and Pungo (North Carolina), Apopka and Griffin (Florida), Long Pond (Georgia) and Ditch Pond (Alabama). Sediment records from all six lakes display evidence of eutrophic conditions that predate intense human disturbance, and these episodes of eutrophy are linked to shifts in climate, hydrology, and land-water connectivity. Whereas nutrient inputs have been identified as the primary driver of eutrophication in shallow lakes, these findings suggest that other environmental drivers strongly influence lake environmental state. Most management and restoration plans for impacted shallow lakes focus on nutrient reduction, but such schemes might prove more effective if additional drivers were considered.