Understanding Groundwater-Surface Water Interactions (GSI) for Assessing Ecological Risk and Establishing Stressor Causality Linkages

Abstract

Over half of the United States freshwater streams are impaired, many with a plethora of chemical contaminants. Since contaminants vary broadly in the toxicity and ecological risk, it is important to understand which site contaminants pose the biggest threat to the ecosystem. The in situ Toxicity Identification Evaluation (iTIE) technology was developed several years ago and continues to be refined and improved. Its purpose is to discern which chemical classes of common contaminants are causing the most toxicity at the site. This then allows site managers to target their restoration and remediation activities to remove the problem chemicals, such as ammonia, metals, non-polar organics, or pesticides. This study further advanced the iTIE technology by: 1) characterizing the propensity of surface waters to infiltrate down into sediments during porewater iTIE testing; 2) determining whether sediment-water interface impervious discs reduce the downward penetration of surface waters, 3) improving the filtering of solids from porewaters during in situ samplings; and 4) determine if the acetyl-cholinesterase (AChE) the assay can be used in the iTIE test on Hyalella azteca and Daphnia magna only exposed for 24 hrs – as an indicator of the presence of organophosphate insecticides. Results showed the surface waters will migrate downward and mix with the porewater during sampling. Sediments with less porosity slow the infiltration of the surface water. Rubber discs mounted to the iTIE the chamber will also reduce the down water flow. Small mesh (~250 micron) wrapped around the porewater sampler also reduces the transport of solids into the iTIE chamber. The AChE assay was successfully conducted on both test organisms, demonstrating it can be used in iTIE testing to separate out exposures and toxicity from organophosphate insecticides. The above findings advance the development of the iTIE and therefore our ability to more effectively restore and remediate chemically contaminated freshwater and marine sites.