Projects

Restoration of salinity patterns in upper apalachicola bay through reconnection of severed historica

End Date: 6/1/2015

Objectives

The primary ecological goals of this project are to (1) re-establish historical salinity patterns in the upper reaches of East Bay, Apalachicola Bay, FL and (2) improve habitat conditions in the nursery area of upper East Bay for a variety of bay species, including the gulf sturgeon (a federally threatened species). Secondary ecological goals include to (3) reconnect the natural drainage pathways within the watershed, and (4) restore historical wetland structure and function which in turn will improve habitat conditions for a variety of wetland flora and fauna utilizing the upstream marshes and wetlands, including four federally endangered and threatened species.

Methodology

The proposed project incorporates a combination of hydrologic modifications (e.g., low water crossings, ditch blocks, culvert modifications) to restore the wetland systems and hydrologic connectivity in the watershed. As currently proposed, the overall project encompasses the placement of 19 low-water crossings, 44 culvert modifications (either replacement, removal or addition), 6 flashboard risers, 44 ditch blocks and 0.8 mile of road removal. Some revision of these proposed numbers may occur after detailed site surveys and inspections. Low-water crossings are relatively short sections of road that have the roadbed lowered in elevation to match natural grade, allowing a more-or-less uninterrupted flow of surface water. They are placed in areas where the road disconnects an historical drainage pathway. Ditch blocks and flashboard risers are placed at appropriate locations in the ditches associated with these low-water crossings to redirect or hold back the flow of water. Retaining water in the ditches rehydrates the adjacent wetlands, increases water storage and assists in restoring the historical hydroperiod in the wetlands and downstream in the estuary. Road removals allow for the unhindered movement of water through the area. These physical modifications are located in severed or restricted flow pathways and reconnect the historical drainage systems. This in turn results in more natural freshwater flows (with respect to magnitude, timing, and duration) and provides for a more stable salinity structure in the marshes and nursery areas of upper East Bay.

Rationale

Tates Hell Swamp extends over approximately 205,000 acres in Franklin and Liberty counties in the Florida panhandle with the western portion providing significant drainage into East Bay, the primary nursery area for Apalachicola Bay (Livingston 1983, 1984). Historically, this area, which was primarily wetlands, acted as a storage and filter for fresh water entering the estuary, especially during critical low-water periods of the year. The swamp was originally dominated by a diversity of wetland types, including wet savanna, cypress strand, and hardwood wamps. During the 1960s and 1970s, the hydrology of Tates Hell was severely altered by an extensive network of access roads (nearly 800 miles) and associated ditches constructed for the purpose of establishing pine plantations. This ditching and subsequent draining has significantly lowered the water table, resulting in extensive loss of wetland habitat and alteration of wetland community structure. These alterations have adversely impacted water quality and habitat in East Bay by reducing storage and interrupting freshwater delivery patterns. The road-ditch system, in conjunction with silvicultural operations in the area, have resulted in intense pulses of turbid, low pH runoff reaching the estuary following substantial rainfall events. Salinity levels drop dramatically after storm activity only to rebound to high levels in a relatively short time. Prior to watershed alterations, water storage in the wetlands provided for slow, more continuous delivery of freshwater seasonally and a lower, more stable salinity regime in the upper estuary.
Meeting the goals set forth for this project will likely provide a number of significant benefits to the natural system and economy of the Apalachicola Bay area. It is estimated approximately 2,300 acres of forested floodplain, 1,650 acres of salt marsh, 32 acres of submerged aquatic vegetation and 2,225 acres of open water in upper East Bay will be positively affected by the hydrologic improvements proposed in this project. With improved salinity conditions in estuarine habitats, survival rates may rise in a variety of dominant bay species that have seen declines associated with degraded environmental quality, such species include bay anchovies, sand sea trout, and white shrimp. An added benefit to restoring a more stable salinity regime in this region of the bay may be an increase in available habitat of federally threatened gulf sturgeon (Acipenser oxyrinchus desotoi). Apalachicola and East Bays are designated Critical Habitat for the gulf sturgeon (USFWS 2003) and provide essential feeding and migration areas 
for the relatively small Apalachicola population. Wetland reconnectivity and re-establishment of a lower, more stable salinity regime in the upper bay will provide some protection from possible effects of sea level rise. Salt intrusion into the upper marshes and wetlands as a result of rising sea level may be offset by modifying the timing and duration of freshwater inflows into the system. This in turn may provide some degree of coastal resiliency and enhance nursery function in this important habitat. 

Results

Restoration of salinity patterns upper Apalachicola Bay through reconnection of severed historic watershed drainage pathways