Reprint Series No. 17
Reprinted November 1992

THE EFFECT OF LANDFILL LEACHATE FROM PADILLA BAY ON THE ABUNDANCE OF EPIBENTHIC HARPACTICOID COPEPODS AND SEDIMENT TOXICITY MEASURED WITH THE AMPHIPOD BIOASSAY (RHEPOXINIUS ABRONIUS)

James R. Wiggins

1992

Bibliographic Citation
Wiggins, James R. 1992. The Effect of Landfill Leachate from Padilla Bay on the Abundance of Epibenthic Harpacticoid Copepods and Sediment Toxicity Measured with the Amphipod Bioassay (Rhepoxinius abronius). Master of Science Thesis, Western Washington University, Bellingham, Washington. 58pp. Padilla Bay National Estuarine research Reserve Reprint Series No. 17.

Abstract
Landfills are disposal sites for municipal and industrial waste. Landfill leachate, whether from seepage through the landfill as a result of rainfall or groundwater or as direct runoff from discarded liquid wastes, affects various marine communities in coastal waters. Combining chemical analyses, sediment bioassays for toxicity analyses, and in-situ community sampling allows for a thorough determination of the degree of impact leachate has on a nearshore marine system.

Landfill leachate enters a small embayment in the southwest corner of Padilla Bay. Acting for the EPA, the Washington Department of Ecology (WDOE) found no significant contamination of priority pollutants in this area in 1986.

After visiting this site in 1989, I became concerned about the WDOE results and decided to incorporate a sediment quality triad approach to complete a site assessment. Using the WDOE chemistry results for the first portion of the triad, I performed a sediment bioassay using the amphipod (Rhepoxinius abronius) and analyzed for the abundance of epibenthic harpacticoid copepods. The area exposed to the landfill leachate runoff showed no significant decline in harpacticoid copepod abundance compared to the control. The amphipod sediment bioassay for this location showed a significantly higher mortality than the control. The analysis of another area where leachate showed visible signs of oil contamination at depth had a significantly higher abundance of harpacticoids on the surface than the control and landfill leachate affected area and had the highest mortality in the amphipod bioassay (100% mortality using the top 2 cm of sediment). The top 2 mm of the sediment column for the oil contaminated site showed similar bioassay results as the control, indicating a natural sediment "cap" over toxic sediments.

Local harpacticoid copepod species, predominantly Harpacticus sp. and Tisbe sp. (a portion of the epibenthos) reside in the sediment surface layer. The sediment is oxidized, high in humic content, and well mixed. This study indicates that the sediment surface layer provides adequate conditions to support an epibenthic community by separating it from toxic benthic sediments.