SOURCE IDENTIFICATION AND IMPACT OF MULTIPLE STRESSORS ON SURFACE WATER QUALITY AT THE

CATCHMENT-SCALE

Post doc Ursula .S. McKnight1

PhD studerende Jes J. Rasmussen2

Professor Poul L. Bjerg1

PhD studerende Nanna .I. Thomsen1

PhD studerende Maria Loinaz1 Cand. scient. Mikael Emil Olsson1

Professor Brian Kronvang2

Lektor Philip J. Binning1

1 DTU Miljø, Danmarks Tekniske Universitet

2 Danmarks Miljøundersøgelser, Århus Universitet

RESUME

Der er gennemført en større undersøgelser af forskellige stressfaktorers påvirkning af den kemiske og økologiske vandkvalitet i et grundvandsopland ved Hove på Sjælland. Der er udvalgt vandløbslokaliteter i området, som er undersøgt for en lang række fysiske, kemiske og økologiske parametre og forhold. Lokaliteterne er prøvetaget i foråret 2010 og i august 2010. De 13 lokaliteter repræsenterer så vidt muligt 1. ordens vandløb, som fortrinsvis formodes at være påvirket af en af følgende stressfaktorer: forurenede grunde, landbrugsdrift og diffus urban påvirkning. Der er også en markant vandindvinding og et enkelt spildevandsrensningsanlæg i området. Vandvindingen sker primært omkring 3. og 4. ordens vandløb, så der er set bort fra denne stressfaktor i undersøgelsen. De foreløbige resultater viser, at der er et tydeligt aftryk fra pesticider på vandløbene i Hove oplande. Der er fundet pesticider, som direkte kan relateres til marksprøjtning i foråret 2010. Der er ved alle målinger også fundet gamle pesticider, der kan relateres til påvirkning fra grundvand (punktkilder eller diffuse kilder). Resultaterne fra undersøgelsen er ved at blive evalueret, og de foreløbige konklusioner vil blive præsenteret på ATV’s Vingsted møde 2011.

INTRODUCTION

Micropollutants and nutrients from a range of sources are well-known stressors that may cause a decline in groundwater and surface water quality and biodiversity of freshwater eco-systems (McKnight et al., 2010; Bacey and Spurlock, 2007). Effectively reducing cumulative impacts on groundwater-dependent aquatic ecosystems clearly requires an understanding of the different pressures that can be present in a particular catchment.

Ecosystem stressors include physical habitat degradation (e.g. channelization), diffuse sources (pesticide and nutrient applications on agricultural fields), sewage effluents (micro-pollutants, organic matter, nutrients) including urban discharges from scattered settlements, contaminated sites (pesticides, chlorinated solvents, gasoline compounds and other pollut-ants) and water abstraction.

The purpose of this study was twofold: to (1) identify the main stressors at catchment scale, and if possible discriminate sources from each other; (2) evaluate the chemical impact and stream ecosystem status represented by benthic macroinvertebrates.

MATERIAL AND METHODS The study was conducted on first-order stream reaches within the Hove study catchment near Copenhagen, Denmark (Figure 1). For the purpose of this study, sewage effluents and water abstraction could be disregarded since only one sewage treatment plant was present and the water abstraction areas were located on third and fourth-order stream segments, re-spectively.

Ecological indicators investigated were benthic macroinvertebrates. Stressor parameters in-vestigated from early spring until late summer include presence of pesticides from storm events (diffuse run-off), assessment of physical stream properties (habitat survey), general water chemistry, as well as presence of xenobiotics originating from both diffuse and point sources. The water sampling was conducted by grab sampling and storm flow samplers (Fig-ure 2).

Figure 1 Left: Hove catchment on Sealand. Right: A sub area (within the green line) where the investi-gation was conducted. The investigations were made primarily on 1. order streams green. The study

area is characterised by a significant groundwater abstraction by local water works and well fields managed by Copenhagen Energy.

A total of 13 sampling locations were broken into three categories of sites: 6 contaminated sites, 4 urban discharges and 3 diffuse agricultural sites. Additionally, 6 undisturbed first-or-der streams were included as reference conditions. GIS tools are applied for source identific-ation and multivariate statistics approach is applied to rank-order the impact of each ex-amined stressor on benthic macroinvertebrates.

Figure 2 Photos from field sampling and characterisation of physical, chemical and ecological parame-ters and properties of streams in the Hove Catchment.

RESULTS

The results for diffuse run-off after a storm event (sampling occurred 4 times between mid-may and mid-august) revealed that the sampling campaign successfully captured the early spring application of metamitron, a pesticide sprayed typically only during early spring (Fig-ure 3, May 16).

Figure 3 Sum of pesticides at two sampling dates in 2010. The May, 16 sampling represents sampling by stormwater samplers (Figure 2) immediately after a rain event. The sampling in August, 10 repres-ents grab samples at low flow in streams, where base flow is expected to dominate. Metamitron is only

found in the spring sampling.

2-methyl-4-chlorophenoxyacetic acid (MCPA), trichloroacetic acid, 2,6-dichlorbenzamide (BAM) and 4,6-Dinitro-o-cresol (DNOC) were found to dominate the pesticide results for all four sampling campaigns (Figure 3. These pesticides are not related to immediate spraying, but originate from groundwater inflow to the streams. In at least two cases, the presence of xenobiotics/pesticides in the stream could be linked to the contaminated sites.

FINAL REMARKS

The assessment of the large amount of data collected during this comprehensive field cam-paign is on-going. Preliminary conclusions on the stressors impact on the stream water qual-ity will be presented at the ATV Vingsted meeting 2011.

ACKNOWLEDGEMENT We wish to acknowledge the help from Capital Region of Denmark, Environmental Centre, Roskilde, the municipalities and site owners in the Hove Catchment. Technicians from the Technical University of Denmark and National Research Institution, Århus University contrib-uted to a significant part of the field and laboratory work. The project was conducted as part of the Risk point, which is supported by the Technical University of Denmark and Danish Council for Strategic Research.

REFERENCES

McKnight, U.S., Funder, S.G., Rasmussen, J.J., Finkel, M., Binning, P.J., Bjerg, P.L. (2010): An integrated model for assessing the risk of TCE groundwater contamination to human re-ceptors and surface water ecosystems. Ecological Engineering, 36, 1126-1137.

Bacey, J., Spurlock, F. (2007): Biological Assessment of Urban and Agricultural Streams in the California Central Valley. Environ Monit Assess, 130, 483–493.