SEDIMENT PROPERTIES AND WATER COLUMN PROFILES OF THE WILMINGTON RIVER ESTUARY (SAVANNAH, GA)

The Wilmington River Estuary in Savannah, GA has water column and sediment properties typical of a well-mixed estuary. During a September 2006 study surface salinities ranged from 20.7 PSU at the furthest upstream sampling station to 31.4 PSU in Wassaw Sound, but salinities as low as 8 PSU have been observed at upstream sites in prior sampling events. The salinity gradient from surface to bottom waters was minimal and averaged 0.2 PSU. These nearly uniform water column profiles of salinity were expected since the Georgia coast has a large tidal range (2-3 m) and the Wilmington River is a small localized river with a limited drainage area. Turbidity is high and secchi depths during the study ranged from 0.5 to 2 m.

Grain size analyses of the upper 3 cm of box core samples taken along the axis of the estuary revealed finer sediments in the upper reaches of the estuary and coarser sediments in the lower estuary. Organic matter and calcium carbonate were not removed from the samples prior to analysis. Water depths at the sites ranged from 4.7 to 10.2 m. The site farthest upstream was comprised of 50% silt and clay, had a mode of 5 phi (< 63 µm), and a mean grain size of 4 phi (fine sand). This is in contrast to the site farthest downstream in Wassaw Sound which was comprised of 32% pebbles, had a mode of -1 phi (> 2 mm), and mean grain size of 0.7 phi (coarse sand). Shell material was abundant in the outer estuary samples and contributed to the coarse fractions. Most estuarine samples were poorly sorted (mean dispersion = 1.30) and negatively skewed (mean = -0.17).