Interstitial water composition in Barataria Bay (Louisiana) sediment

Abstract

Two subareas in Barataria Bay, Louisiana, were studied. One, John the Fool Bayou, is influenced mainly by freshwater; the other Airplane Lake, is influenced mainly by sea water. Sediments in the former were rich in organic matter, but those in the latter contained low organic matter. It was found that the temperature at which samples were stored exerted significant influence on the subsequent results obtained. For example, preliminary study showed that surface sediments stored at 4 °C or on ice resulted in higher release of NH 4 + and SiO 2 to interstitial water than samples stored immediately on dry ice. It is believed that this was caused by decomposition of organic constituents. Surface sediments frozen immediately on dry ice resulted in higher release of free α-amino acids, total N, total P and PO 4 −3 P, indicating lysis of living tissues and/or cells of organisms. To prevent the labile biochemical constituents from decomposing, the procedure of immediately freezing the samples in the field with dry ice was adopted for all subsequent studies. A one-year study of interstitial waters from surface sediments frozen immediately in the field showed that dissolved SiO 2, NH 4 + and PO 4 −3 were higher from August through November than during other months. The yearly averages of these nutrients were many times higher than in the corresponding water columns in both areas. Free interstitial α-amino acids were higher in the relatively low organic Airplane Lake sediments than in those of the highly organic John the Fool Bayou.