Innovative approaches for characterizing groundwater contaminant plumes impacting aquatic ecosystems in peri-urban streams

The large number of micropollutants (pharmaceuticals, chlorinated solvents) and their transformation products makes it challenging to quantify their occurrence and ecological risk. Conventionally, chemical impacts to ecosystems and source types are assessed individually, and groundwater contamination is often neglected.

This may lead to critical underestimations of the combined impact caused by interactions occurring between stressors not typically evaluated together, e.g. organic groundwater pollutants and metals, and prevent the linkage of chemical and ecological impacts in peri-urban catchments. Contaminated sites represent a major environmental problem for Denmark, potentially polluting soil, groundwater and surface water.

Determination of flow paths and groundwater fluxes are essential for evaluating the transport and fate of contaminant plumes discharging to streams. Here, the application of novel approaches is presented for evaluating the governing parameters, including an appreciation of the scale of variability, in order to resolve ecological status under conditions of multiple stress and develop the scientific basis for assessing the risk potential of contaminated sites to impact streams.

The overall aims of the field investigations were to (i) test the applicability of different methods for mapping groundwater contamination impacting streams, (ii) perform a risk assessment using the contaminant mass discharge approach, and (iii) assess the stream’s chemical and ecological status. We identified sources and levels of chemical stressors along a 16-km groundwater-fed stream corridor (Grindsted, Denmark).

Potential pollution sources included two contaminated sites, aquaculture, wastewater/industrial discharges, and diffuse sources from agriculture/urban areas. The results indicate a substantial impact on Grindsted stream from multiple sources of many origins. Impaired ecological conditions, represented by a lower abundance of meiobenthic individuals, could be linked to zones where the groundwater plume discharges to the stream.

This study highlights the importance of stream-aquifer interfaces for ecosystem functioning, and that multiple stressor systems need to be tackled from a multidisciplinary perspective.