ARTICLE IN PRESS Journal of Hydrology xxx (2009) xxx–xxx Contents lists available at ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol Natural versus anthropogenic sources in the surface- and groundwater dissolved load of the Dommel river (Meuse basin): Constraints by boron and strontium isotopes and gadolinium anomaly Emmanuelle Petelet-Giraud a,*, Gerard Klaver b, Philippe Negrel a a BRGM, 3 Avenue C. Guillemin, BP6009, 45060 Orléans Cedex 2, France b DELTARES, Budapestlaan 4, Postbus 80015, 3508 TA Utrecht, The Netherlands article info summary Available online xxxx The river Dommel, a tributary of the Meuse River, drains an area of intensive agriculture (livestock farm- ing, maize and grassland over 50% of the basin), and a dense population of about 600,000 people repre- Keywords: senting 20% of the total area. The combined human activities in the Dommel catchment lead to a large Sr isotopes amount of dissolved elements and compounds released in surface- and groundwaters. The aim of this B isotopes study was to discriminate the natural (including infiltration of Meuse water) versus anthropogenic Gd anomaly sources of the dissolved load, and to identify the various pollution sources such as agriculture, industrial Dommel basin activity, and wastewater treatment plants, using geochemical tools including major- and trace elements, Sr and B isotopes, and rare earth elements (REE). For that purpose, a same-day geochemical ‘‘Snapshot” picture of the entire basin was combined with monthly monitoring in strategic points. The major- and trace elements analyses allowed discriminating the main pollution sources affecting the basin, i.e. point versus diffuse sources. Strontium isotopes helped to identify each tributary and to calculate mixing proportions. Combining these calculations with the Sr- isotopic data obtained from the ‘‘Snapshot” sampling campaign during a low-flow period, shows that Meuse water infiltration represents 25% of the total Dommel discharge. Boron isotopes used for assessing the amount of water affected by anthropogenic input cannot discriminate between the two main anthro- pogenic inputs, i.e. urban wastewater and the zinc-smelter effluent, as they have similar d11B values. Finally, the REE, and especially the use of Gd anomalies (Gd*), demonstrated the generalized impact of urban wastewater on the streams of the Dommel Basin. The coupled use of different geochemical tracers (Sr and B isotopes together with Gd*) in addition to the standard major-element analyses, led to discriminating the various anthropogenic components influenc- ing the Dommel Basin water quality. With these tools it also became possible to assess the complex water circulation and exchanges between water compartments, including the major role of Meuse water through the Bocholt–Herenthals canal. Ó 2009 Elsevier B.V. All rights reserved. Introduction The Dommel is a small river that has its source in north-eastern Belgium and runs through the southern part of the Netherlands Application of multiple geochemical tracers makes it possible to where it joins the river Meuse close to ‘s-Hertogenbosch (Fig. 1). differentiate between point and diffuse pollution sources influenc- The upstream water quality in the Dommel is strongly influenced ing river-water quality. An ideal tracer for distinguishing between by discharge from point- and diffuse sources. In all tributaries the different sources should be conservative and thus neither react flowing through densely populated areas, the water quality is af- with solids and other waterborne elements, nor be biodegradable. fected by industrial and urban waste-water inflow. In the upstream Its content in the (waste) water of point- and diffuse sources part of the Dommel, the wastewater treatment plants (WWTP) of should differ markedly from that in natural water to allow detec- Peer, Eksel, Overpelt and Lommel in Belgium discharge into the tion of low discharge water contents (Rabiet et al., 2005; Kulaksiz river. A suitable tracer, successfully used in previous wastewater and Bau, 2007). studies, is boron and its isotopes. Boron is used in detergents and boron concentrations in urban wastewater can be as high as 5mgLÀ1 (Lazarova et al., 2003); as it is not removed in traditional * Corresponding author. Tel.: +33 2 38 64 37 75; fax: +33 2 38 64 34 46. WWTPs it also appears to be conservative in rivers (Chetelat and E-mail address: [email protected] (E. Petelet-Giraud). Gaillardet, 2005). Boron isotopes are even more sensitive than 0022-1694/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jhydrol.2009.02.029 Please cite this article in press as: Petelet-Giraud, E., et al. Natural versus anthropogenic sources in the surface- and groundwater ... J. Hy- drol. (2009), doi:10.1016/j.jhydrol.2009.02.029 ARTICLE IN PRESS 2 E. Petelet-Giraud et al. / Journal of Hydrology xxx (2009) xxx–xxx Fig. 1. Dommel catchment and simplified geological map. The letters A and B represent respectively the Feldbiss and the Peel Faults. boron concentrations for tracing urban wastewater in surface some of these geochemical tracers will be used in combination water (Barth, 2000; Chetelat and Gaillardet, 2005). However, this with strontium isotopes as tracers for the discharge water of holds only when no other substances with the same isotopic signa- the zinc smelter. ture are discharged into the river and if the background value of In addition, since the 1970s agricultural activity has changed the surface water differs sufficiently from that of the urban waste- from dairy farming to intensive livestock farming; the manure of water (Barth, 2000). the latter is spread on land and leads to a large load of nitrogen, Another suitable tracer for wastewater is anthropogenic gado- phosphate and metals. Thus, the anthropogenic pollution in the linium (Gd). In water, the rare earth element (REE) signature is lar- Dommel and its tributaries not only derives from the point sources gely inherited from the rocks or sediments with which this water outlined above, but also from the diffuse input from historical interacts. In urban areas, their natural distribution is modified in industrial and recent agricultural activities. This diffuse input of relationship with anthropogenic influences and the REE signature anthropogenic substances in the surface water of the Dommel is can be used for tracing the provenance of water in rivers (Smedley, not constant, but varies depending upon the groundwater com- 1991; Sholkovitz et al., 1999; Elbaz-Poulichet et al., 2002). These partment discharging to the surface water (Rozemeijer and Broers, changes consist mainly in a pronounced positive gadolinium 2007). anomaly. Gd is used in the form of gadopentetic acid (Gd(DTPA)2À) The geochemical and isotopic variations caused by both point as a contrast agent in magnetic-resonance imaging (MRI). This sources and variably diffuse input into the Dommel were regularly complex, which remains stable in water, displays excess concen- monitored from December 2004 to September 2006. The purpose trations above natural levels in Europe (Bau and Dulski, 1996; of this paper is to identify the abovementioned sources. In addition Kummerer and Helmers, 2000; Elbaz-Poulichet et al., 2002; Rabiet to the fixed long-term monitoring stations, a ‘‘snapshot” sampling et al., 2005; Kulaksiz and Bau, 2007). Effluents from wastewater (samples taken the same day all over the catchment) was done to plants will contain positive Gd anomalies and Gd is therefore a follow the geochemical tracers through the upper Dommel from potentially good tracer for WWTPs in urban areas where almost their point sources towards the downstream monitoring station. all households are connected to a WWTP. In this manner an ‘‘instantaneous view” of the behavior of the ap- Upstream in the Dommel, the most important industrial dis- plied tracers was obtained and could be used as input for interpret- charge is the Umicore zinc smelter in Overpelt (Belgium). Re- ing the monitoring results. The main goal of this study was to trace leased zinc and cadmium cannot be used as effective tracers as the transfer of the identified pollutants from their respective they adsorb onto particles in the river. The discharge water of sources through the hydrological compartments, together with a the smelter also contains exceptionally high concentrations of, better characterization of the functioning of the Dommel Basin, among others, Cl, Cs, Tl, Rb, K, Mo, Li and also B. As the behavior especially for the relations between surface water and of Cl, Cs, Tl, Rb K, Mo and Li in surface water is conservative, groundwater. Please cite this article in press as: Petelet-Giraud, E., et al. Natural versus anthropogenic sources in the surface- and groundwater ... J. Hy- drol. (2009), doi:10.1016/j.jhydrol.2009.02.029 ARTICLE IN PRESS E. Petelet-Giraud et al. / Journal of Hydrology xxx (2009) xxx–xxx 3 Sampling and analytical methods ment consists mainly of sand. Groundwater levels are usually within 1–3 m below surface. Water is pumped from the middle of the river at a depth of 10 Geologically, the upper Dommel catchment is divided into two cm below surface with a peristaltic pump (Eikelkamp 12.25.01). It parts. The south-western part is the Campine High and the rest of is then filtered through a 0.45 lm polyethersulfon filter in a the catchment lies in the Roer Valley Graben, which is bounded 142 mm diameter filtration unit (Eikelkamp, 12.31.01). For each by the Feldbiss and Peel faults (Schokker, 2003, Fig. 1). The Roer sample, four bottles are filled: a brown PE bottle for anions, a Valley Graben is covered by the Boxtel Formation, a sandy deposit 500 ml HDPE bottle for major cations and trace elements, a with small amounts of micas and feldspars, and by heterogeneous 100 ml HDPE bottle for Sr isotopes and a 1000 ml HDPE bottle loam and peat layers; maximum thickness 35 m).