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TOC as a regional sediment condition indicator: Parsing effects of grain size and organic content
Citation:
NELSON, W. G., M. R. FRAZIER, AND H. LEE, II. TOC as a regional sediment condition indicator: Parsing effects of grain size and organic content. Presented at Coastal and Estuarine Research Federation conference, Daytona Beach, FL, November 06 - 10, 2011.
Impact/Purpose:
TOC content of sediments is often used as an indicator of benthic condition. Percent TOC is generally positively correlated with sediment percent fines.
Description:
TOC content of sediments is often used as an indicator of benthic condition. Percent TOC is generally positively correlated with sediment percent fines. While sediment grain size may have impacts on benthic organisms independent of organic content, it is often not explicitly considered in calibrating a TOC indicator. The EPA National Coastal Assessment data (n=1172 sites) from the U.S. West Coast shows a significant positive relationship of TOC to percent fines at regional scale. Using the NCA values of 2 and 5 % sediment TOC to represent fair and poor sediment condition, 97 and 11 sites were scored as fair and poor. The 95% CL from the regional regression relationship was used to calculate the residual expectation of TOC after accounting for grain size. This correction reduced the count to an estimate of 15 fair and 8 poor sites, suggesting that the uncorrected TOC index will substantially overestimate potentially impacted sites. The regional correction will be compared to TOC – percent fines relationships from 8 west coast estuaries to determine whether it is appropriate at within-estuary scale. A variety of approaches will be used to determine if the adjusted TOC indicator captures biotic responses.