By Greg Knothe
By canoe, boat and airboat the threats assessment team (A.K.A. “The Bankfull Boyz”) are covering hundreds of river miles inventorying areas of habitat degradation on the Peace and Withlacoochee Rivers and major tributaries. Indicators of habitat degradation include:
- active streambank erosion
- streambank mass-wasting
- sediment deposition
- riparian zone degradation
- channel alteration
- potential areas of non-point source pollution
We are following a rapid assessment methodology developed by the United States Fish and Wildlife Service (USFWS) Panama City Ecological Services Office and David Rosgen’s Watershed Assessment of River Stability and Sediment Supply (WARSSS).
The whole project really boils down to sediment and river stability. So, why are we so fed up with sediment? The United States Environmental Protection Agency ranks sediment as the leading cause of water quality impairment in streams and rivers. Stream channel instability and accelerated erosion can have severe biotic impacts on food chains, habitat complexity, spawning and rearing habitats, instream cover and temperatures.
The threats assessment project is a 3-year State Wildlife Grant funded study which is administered through FWC’s Florida’s Wildlife Legacy Initiative (FWLI). The project is match funded by FWC’s Aquatic Habitat Enhancement and Restoration Subsection (AHRE). The FWLI’s State Wildlife Action Plan listed the Peace and Withlacoochee as high ranking watersheds for habitat enhancement since they exhibit high potential for urban development, a high number of threats and a high number of Species of Greatest Conservation Need. The project is a joint venture with principal investigators within FWRI’s Ecosystem Assessment and Restoration (Freshwater Plants Program) and the Division of Freshwater Fisheries Management, and collaborators including the USFWS and AHRE.
The Peace River (106 miles) flows south from its headwaters in Green Swamp to Charlotte Harbor, Florida’s second largest open water estuary. The Peace River Watershed has experienced high levels of habitat degradation due to urbanization, agriculture, phosphate mining and altered flow regimes. While water quality in Charlotte Harbor is generally considered “good,” the Southwest Florida Water Management District expressed concern regarding reduced streamflow in the Peace River and areas within the river where water quality ranked “fair” or “poor.” The threats assessment team has located, scored and inventoried an alarming 353 impairment sites on the Peace River and major tributaries, to date. The highest concentration of impairment sites is located in the river corridor between Zolfo Springs and Gardner. Most impairment sites appear to be a result of poor cattle grazing practices. In part, we theorize that the uprooting of countless trees by Hurricane Charley in 2004, in combination with cattle grazing, led to deterioration of the riparian zone and high channel instability.
The Withlacoochee River (141 miles) originates in the Green Swamp and flows northwest through a diverse range of habitats to Withlacoochee Bay before flowing into the Gulf of Mexico. High urban development, pollution and altered flow regimes pose several threats to water quality within the watershed. Although the Withlacoochee River Watershed has been significantly altered through the construction of the Lake Rousseau Dam in 1909 and the Cross-Florida Barge Canal in the 1930’s, we have identified very few impairment sites (24 sites to date). This is largely due to the river and tributaries having an intact and vigorous riparian plant community, and there is little agriculture within the river’s riparian habitat. Another reason we are finding few impairment sites in the Withlacoochee River is because it was dammed. As a result, water levels were stabilized, which decreases stream power and shear stress, which in turn can decreases streambank erosion. So, while finding few impairment sites sounds like a positive thing, it’s a double-edged sword. The Withlacoochee River does not function like a free-flowing river and like the major issue with all reservoirs, we alter the natural flow regime of the system. Consequently, it’s common for rivers to be over widened above the dam due to backwatering and increased sediment, while being deeper and narrower below the dam since they are sediment starved (commonly called “Hungry Water”).
The overall goal of the project is to develop a prioritized list of restoration projects for each watershed. Preliminary recommendations for proposed restoration actions include a passive approach of fencing out cattle from rivers and riparian habitat, and allowing degraded areas to naturally restore. In more highly disturbed areas, an active restoration approach would be required including re-grading high slope or mass wasting banks, creating a bankfull floodplain bench and re-vegetation of banks to prevent further erosion. In a worst-case scenario (i.e. highly degraded and incised stream with no connection to its floodplain), a new channel could be excavated at a higher elevation with bankfull benches and floodplain connectivity.