Terrestrial or Aquatic Habitat? How to Determine Whether Soil or Sediment Criteria Should Be Applied in Wetlands

摘要

Background/Objectives. Ecological risk assessments involve comparing a calculated dose to appropriate criterion for a particular exposure scenario. This criterion is selected for its relevance to the species of concern and the exposure pathway. We propose basing the selection of a relevant criterion on the nature of the receptors in the ecological community. During a recent ecological risk assessment, the receptors of interest were macroinvertebrates present on the wetlands “floor.” To select the appropriate criterion – sediment or soil – it was first necessary to answer the following question: Are the invertebrate receptors terrestrial or aquatic? A macroinvertebrate survey provided the data to answer this question and guided the selection of the appropriate criteria. Approach/Activities. While there are insects whose larval stages are aquatic and whose adult stages are aerial and, in a sense, terrestrial, most macroinvertebrate species are obligated to either an aquatic or a terrestrial environment. The premise of the invertebrate survey was that the composition of the invertebrate species in a sample reflects the history of conditions that a particular location has experienced in the recent past. That is, the presence of terrestrial taxa and the absence of aquatic taxa in a sample indicate a habitat where drier, more upland conditions are most common; a sample containing mostly aquatic taxa indicates an aquatic regime. In November 2010, an invertebrate survey was performed in a wetland in the Pacific Northwest (site) to evaluate whether chemical concentrations in wetlands soil samples should be compared to soil or sediment criteria. Sample locations were selected from areas that – at the time of the survey – appeared to have been constantly inundated, occasionally inundated, and not inundated during the survey. The wetlands soil samples were collected to obtain representative species assemblages for aquatic and terrestrial communities within the wetland. Results/Lessons Learned. The site is dominated by trees and shrubs at higher elevations, and samples collected from these areas contained only terrestrial invertebrates. At lower elevation, certain features of the site – drainage ditch and depressions – were more apparently aquatic in nature and this was reflected in the samples collected from these locations, which contained almost exclusively aquatic invertebrates. By total area, the majority of the site is represented by habitat that contains a terrestrial invertebrate community. This approach, the use of biological community as an indicator of habitat type, can be a valuable technique in conducting ecological risk assessments for wetlands.