An examination of organic/carbonate-bound metals in bottom sediments of Bayou Trepagnier, Louisiana

To assess potential impact of metals on the biosphere in bottom sediments, forms were determined for selected metals in a southeastern Louisiana bayou, Bayou (B.) Trepagnier, which has been impacted by industrial activity at its head by a manufacturing complex (MC). Ten pairs of cores along the length of the bayou allowed variation with distance to be studied. Sequential extractions provided data on five chemical partitioning phases for subsamples from each of the cores.

Results show that, beyond the mineral residue phase (phase 6 of the extractions) the organic/carbonate phase (phase 4 of the extractions) generally contains the highest concentrations of metals. This paper focuses on phase 4. In addition, metals in phase 4 show significant downstream gradients, though concentrations towards the mouth do not generally appear to differ significantly from those at a control site outside of the bayou. Data were also examined for interrelationships, and high correlation coefficients were the impetus for moving to a multivariate statistical method, polytopic vector analysis (PVA). Six end-members (EMs) were produced. EMs 2, 5, and 6 have high relative proportions of anthropogenic metals and are observed in highest proportions upstream, near the MC. These EMs may reflect industrial input from the MC. EM 3 contains significant calcium, magnesium, and manganese, with minor amounts of lead and barium, and is related to input from nearby Lake Ponchartrain since it increases in weight downstream. EMs 1 and 4 are composed of components commonly found in detrital minerals (e.g., iron, aluminum, magnesium, manganese, and silicon) and are probably not the product of anthropogenic influence. For anthropogenically-weighted end-members (EMs 2, 5, and 6) there appears to be little difference between weights at the mouth of the bayou and weights at the control site outside the bayou.