Water Quality Dynamics in Long Bay, SC

The nearshore region of Long Bay has been the site of a growing number of hypoxic events (dissolved oxygen [DO] <2 mg/L) primarily during summer months. Although anecdotal evidence exists for earlier hypoxic events, researchers and resource managers documented low DO immediately adjacent to the shoreline in the summer of 2004.  From July 15 to July 22, 2004, surveys from a number of piers in 7 m water depth indicated a stratified water column and bottom water DO concentrations < 2 mg/L (Sanger et al., in review).  Exceptionally high catches of flounder, a bottom fish, were reported off the Grand Strand’s recreational fishing piers during this time, while catch rates of most other species declined abruptly. Fishermen reported that the flounder were lethargic and often caught in the surf zone. This hypoxic event prompted the creation of a workgroup of researchers and resource managers (Long Bay Working Group, LBWG) to study available data pertaining to this event. An examination of meteorological data revealed that hypoxia occurred during a period of upwelling-favorable winds that coincided with “anomalous” water-cooling and a stratified water column, suggesting the importance of physical forcing.

A multi-disciplinary approach has been established to gain additional insight into future hypoxicconditions by: (1) continuing nearshore water quality monitoring (salinity, temperature, DO) and expanding this monitoring to include 222Rn (a tracer of groundwater inputs) and chlorophyll, CDOM, and turbidity; (2) examining the biological response (productivity) during times of enhanced nutrient input and low DO levels; and (3) analyzing prior and newly collected data to better understand the interconnection between offshore and onshore driving forces.