Collections > Electronic Theses and Dissertations > Historic transitions in primary producer communities in eastern North Carolina lakes
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Historic primary productivity and ecosystem stressors were reconstructed from sediment cores collected from eastern North Carolina lakes. Paleolimnological proxies such as sedimentary photosynthetic pigments, loss on ignition, stable isotopes, lignin oxidation products, and total organic carbon, nitrogen and phosphorus were measured to determine depositional changes in the sediment record. Sediment samples were dated by measuring excess 210Pb using the constant rate of supply model and 14C AMS. Lake Mattamuskeet is the largest lake in North Carolina (surface area=160 km2). Currently, Highway 94 divides the lake into two basins each containing a different primary producer community. The east side is macrophyte dominated and contains less turbid water while the west side is phytoplankton dominated with turbid water. Sediment cores taken from each basin showed that prior to the roadway both sides were phytoplankton dominated. After the building of the roadway, paleolimnological proxies suggest that physical, chemical and biological processes in the lake were altered. Shallow water levels, nutrient deposition differences and hydrological alterations caused the initiation and continuation of the two stable states. In addition, a long core collected from Lake Mattamuskeet showed that primary productivity generally increased from A.D. 1650 until human settlement around 1850. The changes in lignin concentrations and type suggest that the lake's catchment changed in response to cool and wet conditions of the Little Ice Age (1650-1850). Pungo Lake is a small, shallow dystrophic lake in eastern North Carolina. Paleolimnological proxies from a short sediment core show that the lake was highly productive and algal dominated prior to A.D. 1600. Following the onset of the moist and cool conditions of the Little Ice Age increasing organic carbon and nutrient loading caused an increase in certain algal groups that include cryptophytes, diatoms and cyanobacteria. Following this increase, it is inferred that allochthonous carbon levels reached a critical point where primary productivity became light limited, which is the current state of the ecosystem. General conclusions from this research center on the need to understand algal community responses to increasing organic matter inputs and light attenuation resulting from climatic, environmental and anthropogenic impacts.