Moncie Wright, University of Maryland, Baltimore County

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Abstract:

Sediment cores were collected in St. Martin River and Blackwater National Wildlife Refuge (BNWR) to determine sediment accumulation rates and textural properties. One core was collected and analyzed from St. Martin (SM14), and two were collected and analyzed from the open-water area of BNWR (Lake Blackwater; cores BW3 and BW4). SM14 and BW4 have similar textural properties, consisting mostly of fine-grained mineral sediments. Also, the grain-size profile for BW4 shows upward fining, which is characteristic of channel-fill deposits, suggesting that BW4 was located in a relict river channel. In contrast, the other BNWR core (BW3) is mostly composed of organic material (i.e., peat), which is probably composed of eroded marsh material. The mass accumulation rate for BW3 is 0.5 g/cm2/y, which, if extrapolated to the entire Lake Blackwater area, would account for ~50% of the estimated export of sediment from the adjacent marshes by previous studies. The BNWR results demonstrate the high spatial variability present in Lake Blackwater sediments and the need for further research. In St. Martin River, the sediment accumulation rate at SM14 is ~3 mm/y, which is similar to the average rate of sea-level rise in the Chesapeake Bay region, indicating that this area is keeping up with sea-level rise. However, rapid population growth and high nutrient loading in recent years are likely to have impacts on shorter-term (<100 y) sedimentation processes.