Dr. Johan Liebens

According to the EPA's 2000 National Water Quality Inventory (USEPA 2000), sediment pollution is the second leading cause of impairment to U.S. streams. In areas where sediment pollution and eroding stream banks coincide, professionals are apt to cite bank erosion as a suspected source of contamination. Bank erosion can lead to a number of problems, not only by contributing sediment, but by altering channel dimensions as bank area is lost. Thus, funds allotted to federal, state and county agencies for soil conservation and stream stabilization are often used to implement techniques aimed at curbing lateral erosion. Realistically, it is impossible to secure funding for complete restoration of all eroding channels. What is needed is a predictive field-based method for determining sites that will incur the most rapid erosion and approximately how much sediment will be contributed to the channel. With such a powerful tool for prioritizing restoration sites, more funding could be funneled to high risk sites, resulting in more comprehensive restoration projects.

In the last 10 years, several studies have been conducted correlating observed rates of bank erosion with field-measured erosion potential factors (Harmel et al. 1999; Rosgen 2001; Jennings and Harman 2001; Van Eps et al. 2004; Sass and Keane 2012). Such studies, when carried out in a single hydrophysiograhic region and on hydrologically and morphologically similar streams, can provide professionals a means for rapidly estimating the sediment contribution of eroding banks in that region. Our study is developing regional bank erosion curves for the Northeast Gulf Coastal Plain thereby providing local management experts a valuable tool for the speedy prioritization of enhancement and restoration projects and follow-up monitoring of restoration efforts. Our study applies an established method (Rosgen 2001; USEPA 2012) but seeks to improve on some of the weaknesses inherent to the method.

Escambia Bay is a large shallow estuary in northwest Florida, US. It receives most of its waters from the Escambia River which originates to the north in Alabama. Starting in the 1950’s several industrial facilities were constructed on the bay and river. Prior to the 1970’s there were unregulated releases from these facilities and from domestic sewage facilities that lead to a catastrophic environmental collapse of the system in the early 1970s. The present study assesses the current profiles of PCBs and PCDD/Fs in sediment of Escambia Bay and River and examines the concentrations, spatial patterns, and potential origin of these pollutants relative to environmental and human health concerns. Fifty-seven composite samples were collected with a ponar grab sampler. PCBs and PCDD/Fs were extracted with USEPA Method 3550. USEPA Method 1668A was employed to detect the concentrations of the 209 PCB congeners and USEPA 1613B was used to detect PCDD/Fs. Sediment PCBs have a mean concentration of 15.6 ug/kg and a range from 1.0 to 93.3 ug/kg. Twelve (21%) out of the 57 samples exceed the FDEP TEL of 21.6 ug/kg and no sample exceeds the FDEP PEL of 189 ug/kg. In spite of these relatively low concentrations, bioaccumulation of PCBs in seafood from the bay has resulted in advisories for seafood consumption. The 17 PCDD/F congeners that are considered to have significant toxicity have a mean of 1.9 ug/kg and a range of 0.022-11.0 ug/kg. The mean total TEQ of PCDD/Fs and dioxin-like PCBs combined is 2.6 ng/kg. PCDD/Fs contribute about 92% and PCBs about 8% of the total TEQ. About 33% of the samples exceed the NOAA TEL for total TEQ but not the AET and an additional 23% of the samples exceed the AET. This implies that about 56% of samples exhibit total TEQ toxicities that could impact sediments adversely. The current PCB profile most closely resembles Aroclor 1254 produced prior to 1972. This is consistent with the composition of a spill on the Escambia River in 1969 and suggests that the PCBs have persisted in the sediments for at least 40 years with only moderate degradation of the original profile. An overall decline of 3% in the chlorination of the PCBs is associated with a shift to the lesser-chlorinated congeners, however, the total TEQ did not decline. The PCDD/F congener profile is similar to what has been observed in local bayous in that octachlorodibenzop-dioxin (OCDD) is the dominant congener in the sediment but does not unequivocally point to a specific source.