ASSESSING IMPACTS OF ANTHROPOGENIC CONTAMINANTS ON MICROBIAL COMMUNITIES AND ORGANIC MATTER COMPOSITION IN TWO WEST COAST ESTUARIES USING ORGANIC GEOCHEMICAL TECHNIQUES

Aquatic environments on the west coast of the United States have been subjected to increasing pollution pressure due to exponential population growth over the past century. Near-shore coastal and estuarine sediments are important repositories for organic contaminants, whose fate and effect relate directly to ecosystem health and function. The microbial community plays a critical role in the recycling of organic material, including organic contaminants. The objectives of this project are to examine spatial and temporal changes in the health and diversity of sedimentary microbial communities and changes in organic matter (OM) sources to estuaries, as inferred from chemotaxonomic indicators and stable isotopes, in response to environmental changes and contaminant loading.

We compare a core from South San Francisco Bay [1.2 m, 2-cm to 5-cm intervals, ≤ 50 y age range], a highly urbanized estuary that receives urban and agricultural runoff and wastewater discharge, and a core from Elkhorn Slough (CA) [0.76 m, 1-cm to 5-cm intervals, ~300 y age range], a more pristine estuary that receives mainly agricultural input. We measured downcore profiles of total organic carbon (TOC), nitrogen (N), δ¹³C and δ¹⁵N of bulk organic matter and several classes of current use, legacy, and emerging contaminants [e.g., carbamates, anilines, triazines, organophosphates, DDT/DDD/DDE, chloracetanilides, pyrethroids, PAHs]. We found notable differences between the two cores and in each core through time, attesting to the environmental and ecological changes that have taken place in recent decades to centuries [San Francisco Bay/Elkhorn Slough: TOC = 1 – 3/2 – 7%, N = 0.1 – 0.2/0.2 – 0.5%, δ¹³C = -24 – -27/-24 – -27‰, δ¹⁵N = 4 – 9/2 – 7].

In addition to these baseline data, we are beginning to assess the impact of anthropogenic contamination on microbial populations and other OM sources through the use of molecular tracers, (lipid biomarkers), e.g., organic compound classes such as aliphatic hydrocarbons, fatty acids and sterols. We are in the process of determining biomarker distributions in the two sediment cores, and relating these to the concentration profiles of organic contaminants to determine if changes in the microbial community composition can be linked to contamination and/or changes in OM sources.