Integrated Assessment of the impact of Aqueous Contaminant Stressors on Surface Water Ecosystems

Release of chemicals, either by accidental spillage (e.g. xenobiotics) or direct application/release (e.g. pesticides, micropollutants), is recognized as a significant threat to water resources worldwide. However, little is known about the impact of groundwater contamination on surface water ecosystems.

Traditional approaches for managing aquatic resources have often failed to account for the potential effects of anthropogenic disturbances on biota. To fulfil the requirements of the EU Water Framework Directive will be challenging, as it is difficult to successfully separate and evaluate all pressures stressing an ecosystem.

Here, methods for determining ecological status in streams are evaluated to see if they are capable of capturing the effects of stressors potentially affecting ecosystems. Specifically, they are tested on a case study where the effects of physical habitat degradation can be ruled out as a stressor on stream ecological conditions (Rasmussen et al., 2011).

This study follows earlier work conducted on a Danish case study involving a TCE groundwater plume discharging into a small stream, located in an area with protected drinking water interests (McKnight et al., 2010). In that study, an integrated modelling approach explicitly linked the contaminant point source in groundwater to both surface water and ecological impacts.

The purpose of this study is to: (1) compare two modelling approaches; (2) extend the model for additional xenobiotics, pesticides and micropollutants to generalise the findings in the case study; (3) compare two sampling-based indices, i.e. the SPE cies At Risk (Liess et al., 2008) and Danish Stream Fauna Index (Miljøstyrelsen, 1998).

Both indices are linked to the EU water quality class system and applied to the results of an extensive field campaign carried out in summer 2010. The campaign included an analysis of xenobiotics in surface water, inorganic chemistry, diffuse source (run-off) impacts and ecology along a gradient of contamination in the stream.

Modelling results indicate that naphthalene, glyphosate and 4-nonylphenol could adversely impact ecosystems at expected environmentally-relevant concentrations. In general, thresholds determined for all compounds in the study were within the source mass discharge ranges expected at sites where contaminants may leach into groundwater (ITR C, 2010).

Results of a sensitivity analysis revealed (low) oxygen content, as well as hydro-morphological changes to the stream channel (i.e. percent rifflerun- pool, channel type) to be dominant controls affecting the modelled stream ecosystem. In addition, the field study indicates that the Danish Stream Fauna Index, currently used in Denmark for evaluating ecological status in streams, is not capable of capturing the effects of nonnutrient stressors on benthic macroinvertebrates.