Seasonal patterns of river connectivity and saltwater intrusion in tidal freshwater forested wetlands
2012
Anderson, Christopher J. | Lockaby, B Graeme
Hydrology can be difficult to interpret in tidal freshwater forested wetlands because of several influencing factors including river discharge, tidal stage, local precipitation, evapotranspiration, groundwater and prevailing winds. River discharge and tidal stage are considered the primary factors affecting these wetlands and both vary on a seasonal basis and have potential implications for wetland saltwater intrusion. We examined the hydrologic patterns of tidal freshwater swamps along the lower reach (20âkm) of the Apalachicola River system in northwest Florida, USA. Water level recorders were installed in five wetlands along this reach and recorded ground and surface water levels at 15âmin intervals from December 2006 to April 2009 (nonâcontinuously). Seasonal trends related to flooding frequency and duration were compared to long term (2000–2008) records of creek and river salinities measured in the tidal freshwater forested zone. Tidal freshwater swamps tended to maintain a narrow water level range (often ±20âcm of the ground surface) except during high river flows (>680âcms or 24â000âcfs) when levels increased 1 to 2âm above ground and dampened tidal effects. All tidal forested wetlands had the highest mean water levels and most days tidally pulsed during the Jul–Oct season which coincided with peak river/creek salinities and low riverâflows associated with drought conditions. We explored the implications for the timing of salt water intrusion in these swamps and potential changes related to sea level rise and water management in the Apalachicola River drainage basin.
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