And Groundwater Dissolved Load of the Dommel River (Meuse Basin): Constraints by Boron and Strontium Isotopes and Gadolinium Anomaly

ARTICLE IN PRESS

Journal of Hydrology xxx (2009) xxx–xxx

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Journal of Hydrology

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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 farming, 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 anthropogenic 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 influencing 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 5mgL1 (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

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)2) 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.

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). The cover for B isotopes. Each bottle was carefully rinsed with the filtered sands are underlain by the Sterksel Formation consisting of Pleisto- water before being completely filled. The samples for major cations cene sand and gravel deposits from the Meuse River. In the Cam- and trace elements and for Sr-isotope analyses were acidified with pine High, the Sterksel Formation is the top unit. In the Kempen ultrapure HNO3 to pH < or = 2. All samples were kept cool before region the sandy soils of the Boxtel and Sterksel formations are analysis. vulnerable to leaching due to the acidifying conditions caused by The pH and electrical conductivity (EC, standardized to 20 °C) an absence of carbonates, a small amount of clay minerals (<1%), were systematically measured on site, after calibration with stan- and low contents of organic matter (Wilkens and Loch, 1997). dard buffers, with a handheld WTW multi 340i meter equipped Agriculture occupies 56% of the Dommel catchment and con- with a Sentrix 81 WTW pH-electrode and a Tetra Con 325 WTW sists mainly of intensive livestock farming. Crops are mainly maize Ec-electrode. and grassland with lesser amounts of arable farming and tree cul- The water samples were analyzed by ICP-AES (Ca, Na, K, Mg; tivation. About 20% is urbanized and the remaining part is occu- uncertainty less than 10%) ion chromatography (Cl, SO4,NO3; pied by a dense network of nature reserves (Pieterse et al., 2003). uncertainty less than 10%) and ICP-MS (B, Cd, Co, Cs, K, Li, Ni, The mean annual rainfall in the Dommel area is approximately REE, Rb, Sr, Sb, Tl, Zn; uncertainty 10–15%) and potentiometric 740 mm/yr, the reference evapotranspiration for grassland is 560 2 method according to N EN ISO 9963-1(HCO3 ; CO3 , uncertainty mm/yr and the average annual runoff is 190 mm/yr. Groundwater 5%). seepage is estimated to contribute up to 70% to the annual runoff Chemical separation of Sr was done with an ion-exchange col- for the Dommel catchment (Pieterse et al., 2003; Rozemeijer and umn (Sr-Spec), with total blank <0.5 ng for the entire chemical pro- Broers, 2007). cedure. After chemical separation, 1/5th of the sample was loaded The flow chart of the basin is supplied in Fig. 2, the long-term onto a tungsten filament and analyzed with a Finnigan MAT average discharge figures are from Waterboard de Dommel 262 multiple collector mass spectrometer. The 87Sr/86Sr ratios (www.Dommel.nl) and the Vlaamse Milieu Maatschappij (VMM, were normalized to a 86Sr/88Sr ratio of 0.1194. An average internal www.VMM.be). The four WWTPs have a treatment capacity of precision of ±10106 (2r) was obtained during this study. The 55,000 equivalent habitants. According to the Waterboard de Dom- reproducibility of 87Sr/86Sr ratio measurements was tested through mel, about 25% of the WWTP effluent water is household water, the duplicate analyses of the NBS 987 standard and the mean value rest being drainage and overflow water from urban areas. The con- was close to 0.710227 ± 17106 (2r; n = 70). tribution of the WWTPs to the Dommel discharge at Neerpelt (1.3 Boron isotopes were determined on a Finnigan MAT 261 solid- m3 s1) is over 30%. Inputs from the Lommel WWTP are about 1.6 source mass spectrometer after removing the major ions from the times higher than the discharge of the Eindergatloop stream. water sample using a cationic resin IR120, and boron separation Upstream from the confluence with the Keersop and Run streams, using Amberlite IRA-743 selective resin according to the procedure the Dommel also receives water from the Hageven nature reserve, of Mossadik, 1997. The boron sample was then loaded onto a single which is partly fed by seepage from the Bocholt–Herenthals canal Ta filament with mannitol and Cs, and the B isotopes determined (0.3 m3 s1), the latter containing water from the Meuse River. þ by measuring the Cs2BO2 ion. The values are plotted on the d scale In addition to urban wastewater, the basin receives contaminated waters from industrial and agricultural activities. The (expressed in ‰) relative to the NBS951 boric acidnh . standard, where anthropogenic impact of past and present zinc smelting activities the d value is defined as: d11B(‰)= 11B 10B sample can be considered firstly as diffuse source through past atmo- 11 10 3 11 10 B BÞstandardg1:10 . The B/ B value obtained for the spheric Zn and Cd emissions, now concentrated in the soil and NBS951 boric acid standard after oxygen correction was clearly higher than the natural background in the rivers, and sulfur 11 4.0431 ± 0.0023 (2rm, n = 31). The reproducibility of the d B dioxide (SO2) emissions. The zinc smelting can also be considered determination, based on replicate analysis, is ± 0.5‰ and internal as a point source, as the treated wastewater from the Umicore errors are often better than 0.3‰. smelter discharges into the Eindergatloop stream. These effluents The REE concentrations (Table 2) were directly measured by are the final products from the physico-chemical treatment of ICP-MS, without the generally used pre-concentration step to en- smelter wastewater through several pH adjustments (using hance REE concentrations (Hennebruder} et al., 2004). amongst others chalk hydrate) where the metals, fluorides and sul- fates are removed (OVAM, 2006). Recent improvements in the The study area treatment processes (OVAM, 2006) have led to a reduction of more than 90% for Cd and 60% for Zn in the Eindergatloop water in 2006– The Dommel catchment 2007, compared to the 2002–2005 period. Since the 1970s, agricultural activity changed from dairy farm- The Dommel catchment, 1.800 km2 large, is a riverine system in ing to intensive livestock farming, the manure of which leads to a northern Belgium (380 km2) and the southern part of the Nether- heavy load of nitrogen, phosphates, metals and sulfate, in addition lands. The Dommel discharges into the Meuse River downstream to the sulfate originating from industrial sulfur-dioxide emissions. of Eindhoven (Fig. 1). The main tributaries are the Eindergatloop, Wastewater of the urban areas is collected and treated in wastewa- Keersop and Run (Figs. 1 and 2). From Wouberg to Eindhoven, ter treatment plants in the upper Dommel, four of them (Peer, Ek- the Dommel streambed is approximately 2 m below the surface, sel, Overpelt and Lommel in Belgium) discharging their effluents in the flow velocities are 0.5–1.0 m s1 (Waterboard de Dommel, streams. These effluents are major pollution point sources and also 2007) and because of these high flow velocities the bottom sedi- an appreciable water input in the hydrological balance.

4 E. Petelet-Giraud et al. / Journal of Hydrology xxx (2009) xxx–xxx

Fig. 2. Flow chart with the relationships between sampling points, tributaries, Bocholt–Herenthals canal and point and diffuse sources. Long-term average discharges are taken from Waterboard de Dommel (www.Dommel.nl) and the Vlaamse Milieu Maatschappij (VMM, www.VMM.be).

Monitoring stations (K2FeO4) is used as an environmentally friendly oxidant. The high boron contents also suggest the use of borate. The sampling locations are schematically shown on Fig. 2. Sta- All major-element data (Table 1) are plotted in a Piper diagram tions 240013, 240013AV, 240013Run and 240013DBR were regu- (Fig. 3) representing the ion proportions. The cation diagram larly sampled from December 2004 to September 2006. Stations clearly distinguishes the Run and Keersop samples (surface and 241015, 241012, 240011, 240013Run, 240013AV and 240013 were groundwater) from the smelter effluents (mainly composed of also sampled for the ‘‘Snapshot” campaign. In addition to the Na + K). The Eindergatloop-Up, whose discharge mainly consists Waterboard de Dommel monitoring, additional monitoring sta- of the Lommel WWTP effluents, is also very concentrated in tions were selected around the confluence of the Dommel with Na + K. The Dommel-Up sample presents lower Ca and higher Na its tributary Run (Figs. 1 and 2) as the latter flows only through contents than the Run and Keersop, and is also partly fed by WWTP an agricultural area and is assumed to be representative of diffuse effluents. The Dommel River samples taken downstream of the source input in the upper Dommel catchment. Water was also ta- Eindergatloop plot between these two groups of samples, confirm- ken from an artificial pond (240013AV) isolated from the streams ing that it is a mixture between the Eindergatloop and the Dom- and fed only by groundwater and rainwater. mel-Up. In the anion diagram, the Run waters show the highest

SO4 proportion together with the lowest Cl + NO3 proportions. At Results and discussion the opposite, the smelter effluents have the lowest SO4 proportion together with the highest Cl + NO3 proportions. Thus, in the gen- Anthropogenic sources: diffuse and point sources eral diagram, the water from the Run and Keersop tributaries are of the CaSO4 type, mostly reflecting the diffuse atmospheric sulfur The monitoring during this study shows that the wastewater fallout from past and present smelting activities, agriculture, and from Umicore has high contents, among others, of B, Ca, K, Na, likely also from denitrification processes by pyrite oxidation (Roze-

Rb, SO4 and occasionally Sr. These elements are related to the meijer and Broers, 2007). The above-mentioned SO4 sources are chemicals used in efﬂuents treatment, e.g. Ca from chalk water superimposed on each other in these agricultural catchments. On (OVAM, 2006) in the WWTP, or produced as a secondary product, top of the large amount of SO4 in these tributaries, chlorine and ni- e.g. SO4 (OVAM, 2006). Although it is unknown which chemical trates are also good indicators of agricultural activities with maize, products are used by Umicore for removing the metals, the high al- the only crop to which an unlimited amount of manure and fertil- kali contents of the wastewater suggests that potassium ferrate izers can be applied.

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 laect hsatcei rs s eee-iad . ta.Ntrlvru nhooei ore ntesrae n rudae . .Hy- J. ... groundwater and surface- the in sources anthropogenic versus Natural al. et E., doi:10.1016/j.jhydrol.2009.02.029 Petelet-Giraud, (2009), as: drol. press in article this cite Please Table 1 Major elements (mg L1), 87 Sr/86 Sr and d11 B(‰) and associated Sr and B concentrations (lgL1) of the main stations in the Dommel Basin monitored for this study. Complementary data used in this paper are available upon request from the authors. 1 1 1 1 1 1 1 1 11 87 86 1 1 Name/date Na (mg L ) Mg (mg L ) K (mg L ) Ca (mg L ) HCO 3 (mg L ) Cl (mg L )NO3 (mg L )SO4 (mg L ) d B(‰) Sr/ Sr B ( lgL )Sr(lgL ) Dommel river Dommel-Up 17/07/07 23.7 5.6 11.3 26.9 48.2 39.8 20.8 50.1 2.9 0.71137 43 98 Dommel-DBR 09/09/05 96.4 6.6 69.2 44.9 – – – – 1.6 0.71029 136 161 30/09/05 76.6 6.3 52.0 40.7 22.1 143.4 14.3 134.5 2.1 0.71036 123 152 25/11/05 71.5 6.8 45.0 42.3 74.5 116.8 14.1 115.5 2.8 0.71042 68 125 20/12/05 75.7 7.2 35.5 41.3 102.1 108.1 16.4 101.8 2.0 0.71053 57 126 23/01/06 60.6 6.9 34.9 41.7 72.6 93.5 15.2 104.8 2.6 0.71055 52 130 27/02/06 54.7 7.3 32.6 42.0 70.4 89.1 17.4 97.8 5.2 0.71058 55 134 06/04/06 53.4 7.6 29.2 44.3 71.9 82.4 15.3 91.5 4.6 0.71061 35 110 01/06/06 – – – – 73.1 81.6 16.5 93.2 7.1 0.71049 45 125 17/07/07 47.9 6.4 31.9 38.3 77.6 84.3 12.9 86.3 3.3 0.71050 55 127 Dommel-Down 20/07/05 54.8 4.8 44.9 32.6 0.0 136.1 12.6 139.0 1.2 0.71031 94 144 xxx–xxx (2009) xxx Hydrology of Journal / al. et Petelet-Giraud E. 09/09/05 91.5 6.9 65.4 43.5 21.8 172.2 12.2 152.0 2.6 0.71038 130 159 30/09/05 75.5 6.9 50.5 40.5 30.9 135.6 13.9 135.7 2.6 0.71048 120 155 25/11/05 65.6 7.0 40.3 40.7 72.0 105.3 14.1 112.1 3.9 0.71057 62 123 20/12/05 61.6 7.6 29.7 40.5 84.3 93.0 16.0 99.7 3.5 0.71068 49 130 PRESS IN ARTICLE 23/01/06 56.6 7.3 32.5 41.8 68.0 87.1 15.0 106.0 3.3 0.71066 38 133 27/02/06 50.0 7.6 30.1 41.7 67.4 82.0 16.5 98.8 6.9 0.71069 51 134 08/03/06 63.8 93.6 17.8 98.7 – – – 145 06/04/06 50.0 7.7 28.6 44.6 65.6 80.3 15.4 95.1 4.7 0.71072 30 106 03/05/06 54.0 6.9 23.3 37.9 74.5 70.5 13.6 95.3 2.7 0.71067 – 137 01/06/06 67.9 80.5 16.7 96.9 8.1 0.71062 44 102 17/07/07 48.0 6.8 30.5 38.6 73.6 79.8 12.3 87.5 – – 51 128

Tributaries Eindergatloop-Up 30/01/06 190.7 8.3 146.3 62.9 175.6 287.0 34.6 254.4 – – 110 156 17/07/07 106.6 6.0 90.4 26.6 171.2 111.6 13.1 155.0 2.6 0.70972 68 64 Eindergatloop-Down 30/01/06 395.4 7.9 338.8 113.8 158.6 698.6 31.2 472.3 – – 188 201 17/07/07 265.8 6.0 182.8 43.2 152.7 362.7 14.2 265.5 1.0 0.70954 100 90 Keersop 30/01/06 25.1 9.1 9.6 44.0 59.2 38.2 12.0 84.2 – – 15 162 17/07/07 20.2 7.7 7.2 42.8 88.2 34.4 7.7 65.1 13.9 0.71034 29 158 Run 20/07/05 17.8 9.7 7.6 31.2 17.9 29.2 1.4 104.7 24.3 0.71161 27 168 09/09/05 18.8 9.5 8.2 32.8 33.5 28.3 3.4 97.6 22.4 0.71162 35 170 30/09/05 15.0 10.0 8.5 33.0 5.1 28.4 5.7 112.9 27.3 0.71184 23 184 25/11/05 17.5 8.5 10.2 33.0 29.4 30.6 8.1 92.0 25.9 0.71156 18 135 20/12/05 19.2 10.9 14.2 42.6 48.8 30.2 15.8 110.5 24.7 0.71149 16 157 23/01/06 19.2 11.0 12.3 42.7 41.2 31.3 13.9 112.4 25.4 0.71150 15 161 27/02/06 18.4 10.6 12.6 40.9 38.7 32.0 17.7 112.4 25.4 0.71154 20 161 08/03/06 – – – – 39.3 32.6 16.1 111.5 – – – 164 06/04/06 20.1 11.3 13.3 43.4 37.9 31.3 15.2 108.2 25.9 0.71150 13 143 03/05/06 17.7 9.8 10.3 37.8 36.5 29.0 9.2 106.3 26.1 0.71144 – 154 01/06/06 – – – – 43.1 30.2 16.0 104.5 23.9 0.71147 23 146

Groundwater(near Run) 20/07/05 17.0 8.9 8.7 29.0 46.0 26.0 B.D. 79.2 22.9 0.71149 25 147 09/09/05 16.8 9.2 8.6 32.6 48.9 27.4 B.D. 84.6 22.8 0.71154 28 160 (continued on next page) 5 ARTICLE IN PRESS

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In an NO3 vs. Cl diagram (Fig. 4), the groundwater from the Run ) 1

basin shows very low NO3 and Cl contents. This is in contrast with

gL the reconstructed historical nitrates concentration in recharging l 1 102 226 332 495 136 126 123 132 138 144 143 159 groundwater that indicates a maximum of over 250 mg L in 1159 1988 (Visser et al., 2007) that subsequently decreased as a result

of the EU Nitrates Directive (EU, 1991). The low amount of NO3 )Sr( 1

in groundwater can be due to reduction of the NO3 by denitriﬁca-

gL tion (Pieterse et al., 2003; Broers, 2004; Visser et al., 2007), and/or l 725 534

– this pond is fed by deep unpolluted groundwater. The Run tributary presents very low Cl content all along the hydrological cycle, 1 but has an NO3 content between 2 and 18 mg L . In this region Sr B (

86 with its sandy soils, during periods with high precipitation, the

Sr/ streams get their water mainly from shallow groundwater, origi- – – – 87 nating from recent rainfall that has leached the highly polluted soils (Reijnders et al., 1998; Fraters et al., 1998; Broers, 2002; Bro- ) ers and Van der Grift, 2004; Waterboard de Dommel, 2007). During ‰

B( dry periods, surface water is mainly fed by deep groundwater with 3.5 0.70906 231 1.2 0.70880 4912 11 23.624.5 0.71141 0.71143 8 18 24.7 0.71142 – 25.1 0.71147 18 24.3 0.71149 12 24.5 0.71153 15 24.0 0.71158 22 23.3 0.71154 26 – – – d long travel times and with unpolluted basic values for major and trace elements (Meinardi, 2003), and/or with denitriﬁed water.

) This leads to a seasonal pattern in surface-water pollution with 1 the highest nutrient values in winter and the lowest in summer.

The lack of relation between NO3 and Cl pleads in favor of N– (mg L 4 80.3 81.6 83.2 82.7 84.8 87.5 89.6 91.2 81.0 NO3 inputs from agriculture, as there is no other anthropogenic in- 2520.6 1262.5 2362.9 2158.2 put in the Run catchment. The Dommel upstream and the Einder- gatloop upstream, collecting treated wastewater, present

)SO 1 1 ﬂuctuating NO3 contents (10–62 mg L ) with higher Cl contents than the waters of the Run and Keersop that are only impacted

(mg L by agriculture. The smelter wastewater efﬂuents have very high 3 1 0.4 6.1 1.2 3.5 1.8 7.4 3.6 1.4 3.7 3.4 3.1 2.0 Cl contents (2500–4500 mg L ), clearly impacting the chemistry 13.5 of the Eindergatloop downstream. The Dommel River samples, collected downstream from the conﬂuence with the Eindergatloop )NO 1

(DBR) and also that of the Run, present a generally negative corre-

lation between NO3 and Cl, reflecting the impact of smelter efflu- 24.8 24.2 25.8 24.8 25.6 26.1 26.1 27.1 26.7 ents all along the Dommel. Fig. 4 also illustrates the boron versus 4240.7 2577.5 3494.7 4524.0 NO3 relation in Run catchment samples with very low boron content, i.e. agriculture does not release significant amounts of boron ) Cl (mg L 1 compared to urban wastewater via the WWTP effluents. The smelter releases a large amount of B (240–4000 lgL1) depending upon

(mg L the treatment processes. These binary relations (Fig. 4) point out 3 the major anthropogenic inputs into the basin, which are (1) agri- 0.0 30.6 50.9 36.6 45.2 45.6 46.2 79.0 45.5 48.0 52.8 48.4 49.4 culture, mainly with N–NO3, (2) WWTP efﬂuents, and (3) the smelter efﬂuents. ) HCO

1 Major and trace element contents in waters draining the upper Dommel system helped in pointing out the main pollution sources affecting the basin, i.e. point sources versus diffuse regional pollu- 34.4 32.9 33.1 34.6 35.3 35.0 31.9 – – – tion. Nevertheless, this approach is limited in terms of real discrim- ination of the anthropogenic sources, because chemical elements

) Ca (mg L can have various anthropogenic and/or natural origins, and their 1 concentrations can vary over the hydrological cycle. In order to fur- 9.1 8.8 8.6 9.0 9.2 9.0 8.5 ther investigate this problem, we used a coupled isotopic approach 748.3 167.7 2032.9 555.5 – – – 2357.2 432.0 with strontium and boron isotopes, together with the Gd anomaly.

) K (mg L Water origin and circulation 1

Strontium-isotope ratios (87Sr/86Sr) vary in nature because one of the strontium isotopes (87Sr) is formed by the radioactive decay 4.6 – 8.5 2.3 – – 8.1 8.4 4.6 8.8 9.0 9.1 9.0 of the naturally occurring element rubidium (87Rb). The 87Sr/86Sr ratios are used mainly as tracers of water–rock interaction (Bullen ) Mg (mg L 1

et al., 1997; Petelet-Giraud et al., 2003a). The primary sources of Sr ) in groundwater are atmospheric input, dissolution of Sr-bearing minerals and anthropogenic input. The Sr concentrations in rainwater are generally low and ﬂuctuate accordingly to the aerosol continued

( sources (Négrel and Roy, 1998; Négrel et al., 2007). The Sr content in precipitation decreases with increasing distance from the sea. The inland Sr content in rain is generally less than 5 lgL1 (Négrel B.D.: below detection limit. 17/07/07 2593.7 01/06/06 – 06/04/06 16.2 Smelter 20/07/05 2274.2 01/06/06 – 08/03/0603/05/06 – 15.5 27/02/06 15.7 30/01/06 1602.6 23/01/06 16.7 20/12/05 17.0 25/11/05 17.0 30/09/05 16.1 Table 1 Name/date Na (mg L and Roy, 1998; Chabaux et al., 2005; Négrel et al., 2007). Rainwater

Name/date La (ng L 1) Ce (ng L 1) Pr (ng L 1) Nd (ng L 1) Sm (ng L 1) Eu (ng L 1) Gd (ng L 1) Tb (ng L 1) Dy (ng L 1) Ho (ng L 1) Er (ng L 1) Tm (ng L 1) Yb (ng L 1) Lu (ng L 1) Dommel river Dommel upstream (Dup) 7/17/2007 39 76 12 57 14 3 62 2 16 3 11 2 13 2 Dommel before Run (DBR) 9/9/2005 38 71 10 43 11 3 20 2 14 3 14 2 21 4 9/30/2005 31 60 9 44 13 4 37 3 19 4 17 3 24 5 11/25/2005 53 106 14 71 20 5 33 4 22 5 17 3 23 4 12/20/2005 81 157 22 112 27 7 40 5 34 8 28 4 35 7 1/23/2006 100 201 27 131 31 8 44 5 35 8 26 4 31 6 2/27/2006 94 188 26 128 30 8 47 5 35 8 28 4 34 6 4/6/2006 123 244 35 155 36 9 47 6 40 10 30 5 37 7 6/1/2006 54 104 15 69 18 5 29 3 23 6 20 3 28 5 7/17/2007 52 100 15 65 17 5 37 3 23 5 19 3 25 5 Dommel downstream(after Run) 7/20/2005 40 72 10 44 11 3 25 2 14 3 12 2 16 3 .PtltGru ta./Junlo yrlg x 20)xxx–xxx (2009) xxx Hydrology of Journal / al. et Petelet-Giraud E. 9/9/2005 40 75 11 45 12 3 21 2 15 4 14 2 20 4 9/30/2005 43 83 12 54 15 4 37 3 22 5 18 3 25 5 11/25/2005 58 110 15 75 20 5 32 4 24 6 20 3 24 4 12/20/2005 118 227 33 156 38 10 51 7 45 10 37 6 42 8 RIL NPRESS IN ARTICLE 1/23/2006 82 167 23 114 26 8 42 5 35 8 26 4 33 6 2/27/2006 118 241 33 160 37 10 54 7 43 10 34 5 38 7 3/8/2006 193 392 52 249 57 15 73 10 64 14 45 7 48 9 4/6/2006 109 218 30 137 34 8 46 6 38 9 30 4 35 7 5/3/2006 35 66 9 47 12 4 22 3 18 4 17 3 23 4 6/1/2006 68 127 18 84 21 6 30 4 25 6 20 3 23 4 7/17/2007 18 34 6 27 10 3 24 2 14 4 14 3 21 4

Tributaries Eindergatloop upstream 1/30/2006 46 83 12 52 12 3 93 2 13 3 13 2 16 3 7/17/2007 33 70 11 47 12 4 77 2 16 5 15 2 20 4 Eindergatloop downstream 1/30/2006 168 254 35 150 27 8 83 5 30 7 23 4 24 4 7/17/2007 49 86 14 55 15 4 68 3 18 5 17 2 22 4 Keersop 1/30/2006 73 155 21 107 27 7 36 5 35 8 31 5 46 9 7/17/2007 73 142 20 92 25 8 36 5 36 9 33 6 46 9 Run 7/20/2005 96 165 22 102 24 7 31 4 28 6 18 2 19 3 9/9/2005 146 263 34 150 35 9 46 6 40 8 26 4 25 4 9/30/2005 75 133 18 85 20 6 29 4 26 5 19 3 21 4 11/25/2005 122 219 29 141 36 10 49 7 45 10 32 5 34 6 12/20/2005 346 655 89 433 105 28 135 18 120 26 83 12 85 14 1/23/2006 238 455 61 306 72 21 98 13 89 20 66 10 68 12 2/27/2006 476 937 124 582 139 35 173 23 143 32 97 13 93 16 3/8/2006 435 835 111 548 125 32 156 21 133 29 91 13 88 15 4/6/2006 259 487 69 305 75 20 95 13 82 20 59 9 59 10 5/3/2006 57 99 14 71 20 5 26 4 26 6 21 3 26 5 6/1/2006 166 303 41 201 52 14 67 9 62 14 43 7 47 8

Smelter 7/20/2005 44 62 7 42 B.D. B.D. 23 4 11 B.D. B.D. B.D. B.D. B.D. 1/30/2006 25 40 8 22 5 1 7 1 4 2 2 0.4 2 0.4 6/1/2006 29 33 7 20 23 9 33 B.D. 10 4 B.D. 2 6 3 7/17/2007 17 16 5 15 6 2 11 1 8 3 10 2 12 2 7 B.D.: below detection limit. ARTICLE IN PRESS

8 E. Petelet-Giraud et al. / Journal of Hydrology xxx (2009) xxx–xxx

Fig. 3. Piper diagram of the main stations of the Dommel Basin monitored during the 2005–2006 hydrological cycle. samples from the RIVM network in Vredepeel (Dommel region) Petelet-Giraud et al., 2007) and the Sr-isotopic signature can pro- gave [Sr] = 3 ppb and 87Sr/86Sr = 0.709185. With a local evapotrans- vide constraints on the mixing from these sources. All data from piration concentration factor F close to 2.5, the atmospheric input the Dommel are plotted in the classical diagram 87Sr/86Sr vs. 1/Sr for Sr represents less than 5% of the Dommel River Sr content and (Fig. 5). The different groups of samples can be described as up to 12% of the most Sr-depleted sample (Eindergatloop up- follows: stream). Thus, at the study site, the proportion of Sr originating from atmospheric input can be considered as negligible and the The Meuse data from Eijsden station are used to define the sig- 87Sr/86Sr ratio should, therefore, not be significantly modified by nature of the Bocholt–Herenthals canal, as this is directly fed by rain input. the Meuse River (Figs. 1 and 2). The mean Meuse signature Sr-isotope ratios coupled with Sr concentrations can be used for based on monthly monitoring (2005–2006) is about 0.7094 with investigating the mixing of different groundwater bodies, or for a mean Sr content of 175 lgL1; the highest 87Sr/86Sr ratios discerning connections between surface and groundwater (Petelet measured (>0.7099) were not taken into account as they seem et al., 1998, 2003b; Petelet-Giraud and Négrel, 2007; Land et al., to be linked to flood discharge (or just after a big flood) and 2000; Négrel et al., 2003, 2004). The 87Sr/86Sr ratio in water reflects are probably not representative of the summer signature of the different Sr sources (water–rock interaction and pollution, the canal that is required for our purpose.

Fig. 4. NO3 vs. Cl and B (a and b diagrams, respectively) for main stations of the Dommel Basin monitored during the 2005–2006 hydrological cycle.

E. Petelet-Giraud et al. / Journal of Hydrology xxx (2009) xxx–xxx 9

Fig. 5. 87Sr/86Sr vs. 1/Sr for main stations of the Dommel Basin monitored during the 2005–2006 hydrological cycle. a: Meuse data (TNO/BRGM, unpublished) are used as a proxy of the Bocholt–Herenthals canal. Calculated mixing curve between the mean Run and Meuse values is also shown. b: Focus on the ‘‘Snapshot” samples (17/07/2007) to highlight mixing at the basin scale. Calculated mixing curves between end-members are shown.

The Keersop tributary drains the same lithologies as the Run (Fig. 1), i.e. fine-grained sandy deposits with heterogeneous loam and peat layers and small amounts of micas and feldspars. However, the Sr-isotopic signature is completely different compared to the Run one, although both basins are supposed to have the same anthropogenic pressure (mainly agriculture). At the source of the Keersop, artificial infiltration of water from the Bocholt–Herenthals canal is carried out that comes from the Meuse. Because of this infiltration, the Keersop is impacted by the ‘‘Meuse signature” as shown in Fig. 5, where its supposed original isotopic signature (similar to that of the Run) is shifted down by a water input with a clearly lower 87Sr/86Sr ratio. This water input is fully compatible with Meuse water infiltration from the canal. According to Fig. 5, and considering a simple binary mixing between the mean Run and mean Meuse signatures, the Keersop integrates about 50% of a ‘‘Meuse like” water, fully compatible with a large amount of groundwater supply in the rivers during low-flow periods (Pieterse et al., 1998; Meinardi, 2003). Fig. 6. d11B vs. B content for main stations of the Dommel Basin monitored during The Dommel River, sampled in the upper part of the catchment the 2005–2006 hydrological cycle. Calculated mixing curves with between the end- (241015, Fig. 2) and before the confluence of the Eindergatloop members of the ‘‘Snapshot” campaign are shown. tributary, presents a Sr-isotopic signature similar to that of the Run reflecting a drainage of the same lithologies. It is worth noting that the Dommel-Up sample integrates the WWTP effluents flow (July–September 2006). The DBR is sampled just after the of the Peer–Eksel–Overpelt stations in addition to the agricul- Keersop confluence, which suggests that the initial Dommel sig- tural impact, whereas the Run is only impacted by agricultural nature (Dommel-Up + Eindergatloop) is completely hidden by practices. It thus seems that the treated wastewaters do not that of the Keersop. Together with a Keersop contribution, impact the Sr-isotopic signature, possibly because of a low Sr groundwater supply is highly probable during this hydrological content as reflected by the Dommel-Up sample that has a lower period (Pieterse et al., 1998) all along the Dommel River, drain- Sr content than the Run. ing the Hageven nature reserve containing ‘‘Meuse like” water The Eindergatloop stream, sampled in its upper part and after from the B–H canal. During the other hydrological periods, the the discharge of the Lommel WWTP effluent, presents a 87Sr/86Sr DBR signature varies inside a triangle in the 87Sr/86Sr vs. 1/Sr ratio in the same range as the B–H canal signature represented diagram (Fig. 5), reflecting the ternary mixing between (1) Dom- by the Meuse samples. A water contribution through infiltration mel-Up, (2) Eindergatloop-Down and (3) Keersop waters, i.e. the from the canal could explain the 87Sr/86Sr ratio, but the Sr con- natural mixing of water from upstream to downstream in the tent in the Eindergatloop-Up is significantly lower than the Dommel River. In this diagram, it is worth noting that the Dom- Meuse one, implying another component with a very low Sr con- mel-Down signature is very similar to that of the DBR sample, tent. This suggests that the Eindergatloop-Up signature reflects a reflecting a very low contribution by the Run river (<10%) that complex mixing where the natural signature is probably com- fully agrees with the discharge values measured in the rivers. pletely hidden by anthropogenic components; the Lommel WWTP effluent representing twice the natural discharge of the As strontium isotopes allow a clear identification of each tribu- river supports this suggestion. tary in the basin, it is also possible to calculate mixing proportions. The Eindergatloop-Down sample is enriched in Sr together with a For instance a ‘‘Snapshot” sampling campaign for obtaining an lower 87Sr/86Sr, reflecting the impact of the smelter wastewater. instantaneous view, was done at the basin scale. All samples were The Dommel before the Run confluence (DBR) has a Sr-isotopic taken July 17th, 2007, and mixing calculations were done during signature similar to that of the Keersop during the low summer this low-flow period. Fig. 5b focuses on the snapshot samples,

10 E. Petelet-Giraud et al. / Journal of Hydrology xxx (2009) xxx–xxx the straight lines corresponding to the calculated mixing curves the Meuse. No boron-isotope data are available for the Meuse, (Faure, 1986). The water contribution of the smelter effluent is but we interpret the higher boron content and lower d11B of the about 10% in the Eindergatloop just before its confluence in the Keersop as being caused by infiltrating B–H canal water at the Dommel River, in agreement with the mean annual water contri- source of the Keersop. This implies that the boron content at the butions to the Eindergatloop discharge. It is worth noting that as Keersop source (40–70 lgL1) must be higher than at the Keersop the Eindergatloop-Down sample lies not exactly on the mixing mouth (15–44 lgL1), which is indeed the case. The Eindergat- curve, a groundwater contribution from the H–B canal with a loop-Down sample should mainly represent the mixing between Meuse-like signature cannot be excluded. Downstream, the Dom- Eindergatloop-Up water and smelter effluents, as shown by Sr iso- mel (DBR) results reflect the ternary mixing of Dommel-Up topes. Considering the snapshot samples, the d11B of the mixing (30%) + Eindergatloop-Down (20%) + Keersop (50%) waters. (Eindergatloop-Down) is clearly higher than that of both mixing During this period, groundwater being the main component of sur- terms, implying another component (possibly via a groundwater face flow, it is nevertheless difficult to assess its exact contribution contribution) and/or an isotopic fractionation through secondary as the groundwater signature was only defined in the Run basin. processes. The Dommel before the Run confluence (DBR) repre- However, on 17 July 2007, the water infiltration from the B–H ca- sents a complex signature of at least three components (Dom- nal (Meuse water) constituted about 50% of the Keersop discharge mel-Up + Eindergatloop-Down + Keersop), as Fig. 6 shows that and thus can represent 25% of the total discharge of the Dommel at the DBR samples all plot between the mixing curves of these three the Dommel-Down station. components. Two DBR samples (September 2005) clearly plot out- side this domain; they have higher B contents and reflect a Dom- Constraints on anthropogenic pollution sources mel signature impacted by a higher smelter contribution. After the confluence with the Run, the Dommel boron-isotopic ratio Boron is a ubiquitous trace element, but it is also quite common slightly increases, reflecting the very small contribution of this in man-made components such as chemical fertilizers or deter- tributary to the total Dommel discharge. gents. Thus, boron concentrations in urban wastewaters can be The boron isotopes allow a clear identification of the tributaries, as high as 5 mg L1 (Lazarova et al., 2003) as boron is not removed but two main anthropogenic inputs (urban wastewater and the in traditional WWTPs. It also appears to be conservative in rivers smelter effluent) present similar d11B values probably because of and is not influenced by adsorption onto suspended matter and/ borate use in both cases. Thus there is a need for using another or by consumption by micro-organisms (Chetelat and Gaillardet, geochemical tracer that specifically distinguishes wastewater 2005). Isotopes of boron are even more sensitive than boron alone effluents from other anthropogenic input. The gadolinium anom- for tracing urban wastewater in surface water (Barth, 2000; Chet- aly, one of the rare earth elements (REE), is such a tracer (Bau elat and Gaillardet, 2005). Boron used as a bleaching agent in and Dulski, 1996). detergents in Europe is mostly derived from Californian and Turk- REE are ubiquitous in water where they originate from rocks or ish borate deposits with d11B between 5 and +3‰ (Barth, 1998). sediments with which the water interacts (Goldstein and Jacobsen, Boron isotopes thus are a good potential tracer of anthropogenic 1987; Négrel et al., 2000). In recent years, REE have been widely input into rivers, as river waters usually present positive values used in some human activities (catalysts, industry), resulting in (mean d11B 10‰; Rose et al., 2000; Lemarchand et al., 2002; Chet- REE emissions into the environment. A first anthropogenic impact elat and Gaillardet, 2005). on REE distribution in water was revealed in 1996 (Bau and Dulski, Atmospheric boron input is shown on Fig. 6 (d11B vs. B contents) 1996), consisting of a positive gadolinium anomaly (Gd*) defined together with all the Dommel watershed samples. If the boron iso- by comparison with Sm and Tb, its two neighboring REE. The most topic signature of seawater is well constrained and roughly homo- significant anomaly was found in a wastewater treatment plant geneous worldwide (d11B 39.5‰; Spivack and Edmond, 1987), effluent and reached a value of 1680, i.e. 7000 pmol kg1 of Gd in the rainfall signature is more variable even in coastal regions water, as compared to the natural background estimated at 4 where marine spray is dominant (Mather and Porteous, 2001). pmol kg1. Similar positive gadolinium anomalies have since been One monthly cumulative rain sample from the IRVM network in found in Europe (Moller et al., 2000, 2003; Elbaz-Poulichet et al., Vredepeel (May–June 2006) was analyzed and presents a d11Bof 2002; Rabiet et al., 2005) and elsewhere. Gadolinium is used in 21.3‰ and a [B] of 2.3 lgL1, whereas a sample from the Belgian medical magnetic-resonance imaging (MRI) as a contrast agent in coast has a clearly higher signature, close to that of seawater the form of Gd(DTPA)2 complex, which is excreted by the patient (d11B = 34.9‰, Kloppmann et al., 2008). The Run watershed sam- without being metabolized only a few hours after the examination ples (surface and groundwater) show low boron contents (<35 (Bau and Dulski, 1996; Kummerer and Helmers, 2000). Such and <27 lgL1 respectively, minimum-flow period) with a practi- anthropogenic Gd thus remains mainly in solution (Moller et al., cally constant d11B (23–27‰), which could represent the natural 2002), the excess of gadolinium in water originating from its use end-member of the Dommel Basin (atmospheric input + water– in medical imaging. Gd passes through wastewater treatment rock interaction). The Dommel-Up and the Eindergatloop-Up sam- plants almost unchanged because Gd organic complexes are nei- ples both have higher boron contents than the Run and negative ther adsorbed or co-precipitated, nor undergo ion exchange with d11B values (2.6 and 2.8‰) in close agreement with those of organic or inorganic particulate sewage matter ( Moller et al., WWTP effluents (Barth, 1998; Widory et al., 2005) that constitute 2003). An anthropogenic gadolinium anomaly thus seems to be a a large part of their discharge. The smelter releases a large load of very promising tool to study the mixing of water bodies, and to de- boron in its effluents (up to 5 mg L1), probably because of the use tect and quantify the influx of potentially contaminated surface of borate in the treatment processes. The Keersop has a boron con- water into aquifers, even if the long-term conservative character tent higher than that of the Run, with a lower d11B 14‰. In 2007, of gadolinium in the environment, in particular during its transport the boron contents were between 20 and 100% higher in the Keer- from surface water, through the soil, to groundwater, needs to be sop than in the Run, depending upon the hydrological cycle period. further investigated. At the source of the Keersop, B–H canal water (Meuse water) is Normalization of REE concentrations to shale (North American artificially infiltrated in the Keersop. The Meuse has a median [B] Shale Composite – NASC, Hannigan and Sholkovitz, 2001) provides 60 lgL1 during low-water periods and 30 lgL1 during high- a representation of REE abundance relative to the upper continen- water discharges. These high B contents during the low-discharge tal crust (Kulaksiz and Bau, 2007). When normalized to REE con- periods come from a larger contribution of WWTP effluents along centrations in shale, semi-logarithmic plots of normalized

E. Petelet-Giraud et al. / Journal of Hydrology xxx (2009) xxx–xxx 11

Fig. 7. Daily variation of the Gd anomaly on 23 March 2005, 01 June 2006, 22 September 2006 and 17 July 2007 in the Dommel from Neerpelt, Belgium, to Eindhoven, The Netherlands. The conﬂuence of the Dommel with the Eindergatloop is taken as reference position; sampling points are located downstream from this conﬂuence. The REE concentrations are normalized to North American Shale Composite (NASC, Taylor and McLennan, 1985; Hannigan and Sholkovitz, 2001).

concentration vs. element show smooth patterns. Large anomalies logical conditions (mean = 1.24 ± 0.05, n = 20) and the Keersop may occur for the redox-sensitive elements cerium (Ce) and euro- (mean = 1.21 ± 0.04, n = 4) can be considered as representing the pium (Eu), but natural Gd anomalies are only small. A Gd anomaly natural Gd* background in the Dommel Basin. If we consider a nat- (Gd*), i.e., the excess Gd in water, is calculated by interpolating the ural Gd* value to be 1.3, this is in good agreement with water with- NASC-normalized concentrations (suffix N) of its two neighboring out wastewater impact (Rabiet et al., 2005). Therefore, Gd REE (Sm and Tb) using the following equation: anomalies over 1.3 can be considered as reflecting wastewater- impacted waters. Gd¼Gd =ð0:33 Sm þ 0:67 Tb Þð1Þ N N N In June 2006, the REE patterns were similar to those of March Fig. 7 shows the REE patterns of the Dommel water from Dommel- 2005, and only in the stations before (240013DBR) and after Up (241015, 0 km) to Eindhoven (Dommel-Down, 240013, 19.6 km) (240013) the Run confluence no distinct positive Gd anomaly on 20 March 2005, 01 June 2006, 22 September 2006, and 17 July was found (Fig. 7). In September 2006 and July 2007, all the Dom- 2007. mel samples had a positive Gd anomaly, indicating that the contri- In March 2005, the Dommel-Up sample showed a small Gd bution from the Keersop and Run was too low to compensate the anomaly (Gd* = 1.47) just after the discharge of the Overpelt Gd anomaly (Dommel-Down Gd* = 2.13 and 2.24, respectively). WWTP. Stations in the Dommel downstream of the Eindergatloop Downstream of the Eindergatloop confluence, the REE patterns (240011, 2004-7 and 240012) have larger and much more distinct in all Dommel samples show a small but systematic HREE enrich- * Gd (1.76, 1.65 and 1.76 respectively) anomalies than the Dommel- ment [(Lu/Tb)N up to 4, calculated according to (Lu/Tb)N =(Lusample/ * Up sample. These higher Gd values must therefore originate from Tbsample)/(LuNASC/TbNASC)] in comparison with the REE patterns the Eindergatloop. The smelter discharging in this tributary has no measured in Dommel-Up [(Lu/Tb)N 1; Fig. 7]. This Dommel-Up Gd anomaly (Gd* 1), but samples taken in the Eindergatloop be- sample is clearly impacted by the Overpelt, Eksel and Peer WWTPs fore and after the smelter have distinct Gd anomalies (Fig. 8), (Fig. 2) and the Gd signature of these WWTPs is consistently found caused by the Lommel WTTP that discharges its effluent in the Ein- in water sampled in this part of the Dommel (Fig. 7).Directly after dergatloop. The Dommel-Down sample (after the Keersop and Run the inflow of the Eindergatloop, the Dommel flows under the H–B confluences) has a very small Gd anomaly (Gd* = 1.38). The Keer- canal with Meuse water (Fig. 2), which water (0.3 m s1) is used for sop and Run waters have no Gd anomalies (Run Gd* = 1.2; Fig. 8) infiltrating the neighboring Hageven nature reserve. The Hageven and the contribution of Keersop and Run water is enough to com- dewaters on the Dommel between the canal and the next station, pensate for the Gd anomaly in the Dommel water. These two trib- located 3.9 km downstream of the Eindergatloop. The NASC-nor- utaries flow only through agricultural areas with no WWTPs, and malized REE patterns of the Meuse (Fig. 8), present a negative Ce in addition all the houses are connected to the large Eindhoven anomaly and a distinct HREE enrichment [(Lu/Tb)N up to 5], char- WWTP of that discharges its effluent into the Dommel downstream acteristic of waters draining carbonate rock. No analyses from the of that city. Thus, the Gd* values of the Run representing all hydro- canal are available, but we assume that the canal has a similar REE

12 E. Petelet-Giraud et al. / Journal of Hydrology xxx (2009) xxx–xxx

Fig. 8. Variation of Gd anomaly in Belgian part of the Dommel, Eindergatloop, Run and Keersop, and comparison of the REE patterns in the Keersop at its source and the Meuse. The confluence of the Dommel with the Eindergatloop is taken as reference location; sample points are located upstream from this confluence. pattern as that of the Meuse. The slightly higher HREE enrichment Each of the tracers applied has its own properties and limita- of the Dommel water in the stations located downstream of the cations that are partially to totally overcome by the combination of nal is most likely caused by the infiltrating Meuse water. different geochemical tools. Such tool combinations are crucial Near the source of the Keersop, the water again has small neg- for a reliable assessment of the functioning of a watershed, in ative Ce anomalies and distinct HREE enrichment (Fig. 8). Here, terms of surface–groundwater relationships and of characterizing artificial infiltration of water from the H–B canal occurs. The con- and discriminating the anthropogenic pressure (diffuse and point sistent HREE over LREE enrichment in station 240011 [(Lu/La)N sources). This level of understanding then allows proposing appro- up to 7.8] 3 km downstream from the canal, suggests that this is priate recommendations for an integrated surface-water and also caused by infiltration water from this canal. groundwater management. The REE data, and especially the use of the Gd anomaly, have demonstrated the generalized impact of WWTP effluents on the streams of the Dommel Basin, characterized by low river dis- Conclusions charges in close connection with the groundwater. If a significant Gd anomaly suggests contamination by wastewater, its absence Water quality in the Dommel Basin is strongly influenced by the does not preclude any such contamination. Indeed, the presence discharge from point and diffuse pollution sources (industry, urban and contents of Gd* in WWTP effluents are not constant through- wastewater and agriculture). The objective of this study was to dis- out the year (Rabiet et al., 2005), as they especially depend on criminate the natural (including infiltration of Meuse water) versus the number of inhabitants that underwent a MRI, the day of the anthropogenic sources and also to decipher the various pollution week when the water samples were taken (residence time in a hu- sources (agriculture, industrial activities, wastewater treatment man body is six hours and during the weekend the MRI facilities plant effluents) using geochemical tools based on major and trace are generally closed) and on the water-residence time in the elements, Sr and B isotopes, and rare earth elements. Sampling was WWTP that differs according to the treatment processes. Thus, un- carried out monthly over one year in the Dommel River (up- to der these conditions and during high-flow periods, the proportion downstream), its main tributaries, and in groundwater; this was of WWTP effluents discharging into the rivers becomes too low and combined with a ‘‘Snapshot” sampling campaign to obtain an the Gd* content becomes negligible. instantaneous geochemical picture of the whole basin. This work The coupled use of different geochemical tracers (Sr and B iso- enabled to: (1) Identify and characterize the main pollution topes together with Gd*) in addition to the standard major ele- sources involved in the basin (point and diffuse sources); (2) Iden- ments, has allowed discriminating the various anthropogenic tify and quantify the main role of Meuse River water infiltration components influencing the Dommel Basin water quality, as well through the Bocholt–Herenthals canal, estimated to represent as better assessing the complex water circulation and exchanges 25% of the total Dommel discharge during the snapshot campaign between water compartments, including the preponderant role of on 17 July 2007; (3) Identify the influence of smelter effluents on Meuse water through the Bocholt–Herenthals canal. the Eindergatloop tributary and its remaining impact on the Dom-

E. Petelet-Giraud et al. / Journal of Hydrology xxx (2009) xxx–xxx 13 mel several kilometres after their confluence; (4) Highlight the wastewater recharge into a coastal aquifer by environmental isotopes (B, Li, O, generalized impact of urban wastewater on the rivers of the Dom- H). Environmental Science & Technology 42 (23), 8759–8765. Kulaksiz, S., Bau, M., 2007. Contrasting behaviour of anthropogenic gadolinium and mel Basin, except in the Run catchment where all domestic waste- natural rare earth elements in estuaries and the gadolinium input into the water is collected and treated farther downstream. North Sea. Earth and Planetary Science Letters 260 (1–2), 361–371. This general understanding of the functioning of the Dommel Ba- Kummerer, K., Helmers, E., 2000. Hospital effluents as a source of gadolinium in the aquatic environment. Environmental Science & Technology 34 (4), 573–577. sin became only possible because of the coupled use of different geo- Land, M., Ingri, J., Andersson, P.S., Öhlander, B., 2000. Ba/Sr, Ca/Sr and87Sr/86Sr ratios chemical tracers, i.e. Sr and B isotopes together with Gd anomalies, in in soil water and groundwater: implications for relative contributions to stream addition to classical major-element analyses. Such tracer combina- water discharge. Applied Geochemistry 15, 311–325. Lazarova, V., Nicolai, M., Sheilds, P., Emsellem, Y., 2003. Aquifer recharge; the tions result in a powerful tool for assessing basin functioning, from relevance of boron isotopes as an environmental tracer of recycled water. In: water circulation (relations between surface water and groundwa- Proceedings of the 4th International Symposium on Wastewater Reclamation ter) to industrial, urban and agricultural anthropogenic pressure, and Reuse, Mexico City, November 12–14 (CD-ROM). Lemarchand, D., Gaillardet, J., Lewin, E., Allègre, C.J., 2002. Boron isotope systematics leading thus to new arguments that can be used by water managers in large rivers: implications for the marine boron budget and paleo-pH for sustainable management at the scale of an entire river basin. reconstruction over the Cenozoic. Chemical Geology 190 (1–4), 123–140. Mather, J.D., Porteous, N.C., 2001. The geochemistry of boron and its isotopes in Acknowledgments groundwaters from marine and non-marine sandstone aquifers. Applied Geochemistry 16, 821–834. Meinardi, C.R., 2003. Basiswaarden voor spoorelementen in het zoete grondwater This work was supported by the European Union FP6 Integrated van Nederland RIVM rapport 714801028. Project AquaTerra (Project no. GOCE 505428) under the thematic Moller, P., Dulski, P., Bau, M., Knappe, A., Pekdeger, A., Sommer-von Jarmersted, C., 2000. Anthropogenic gadolinium as a conservative tracer in hydrology. Journal priority ‘‘Sustainable Development, Global Change and Ecosys- of Geochemical Exploration 69, 409–414. tems”. The views expressed are purely those of the writers and Moller, P., Paces, T., Dulski, P., Morteani, G., 2002. Anthropogenic Gd in surface may not under any circumstances be regarded as stating an official water, drainage system and the water supply of the City of Prague Czech Republic. Environmental Science & Technology 36 (11), 2387–2394. position of the European Commission. Moller, P., Morteani, G., Dulski, P., 2003. Anomalous gadolinium, cerium, and The authors thank Marco de Jonge and Bertil van Os for their yttrium contents in the Adige and Isarco river waters and in the water of their technical assistance during the sampling, and Erik van Vilsteren, tributaries (Provinces Trento and Bolzano/Bozen, NE Italy). Acta Hydrochimica et Hydrobiologica 31 (3), 225–239. Helen de Waard and Piet Peereboom for their analytical assistance. Mossadik, H., 1997. Les isotopes du bore, traceurs naturels dans les eaux: mise au The major- and trace element analyses were performed by TNO point de l’analyse en spectrométrie de masse à source solide et application à labs in Utrecht (NL), and the isotopic analyses (strontium and différents environnements. Thèse de Doctorat, Université d’Orléans, France, 224pp. boron) were done by BRGM (TIMS team leaded by C. Guerrot) in Négrel, Ph., Roy, S., 1998. Chemistry of rainwater in the Massif Central (France): a Orléans (FR). The constructive comments and suggestions from strontium and major element study. Applied Geochemistry 13 (8), 941–952. reviewers were very helpful in improving the manuscript. Négrel, Ph., Guerrot, C., Cocherie, A., Azaroual, M., Brach, M., Fouillac, Ch., 2000. Rare earth elements, neodymium and strontium isotopic systematics in mineral waters: evidence from the Massif Central France. Applied Geochemistry 15, References 1345–1367. Négrel, Ph., Petelet-Giraud, E., Barbier, J., Gautier, E., 2003. Surface water– Barth, S., 1998. Application of boron isotopes for tracing sources of anthropogenic groundwater interactions in an alluvial plain: chemical and isotopic contamination in groundwater. Water Research 32 (3), 685–690. systematics. Journal of Hydrology 277 (3–4), 248–267. Barth, S.R., 2000. Boron isotopic compositions of near-surface fluids: a tracer for Négrel, Ph., Petelet-Giraud, E., Widory, D., 2004. Strontium isotope geochemistry of identification of natural and anthropogenic contaminant sources. Water, Air, & alluvial groundwater: a tracer for groundwater resources characterisation. Soil Pollution 124 (1–2), 49–60. Hydrology and Earth System Sciences 8 (5), 959–972. Bau, M., Dulski, P., 1996. Anthropogenic origin of positive gadolinium anomalies in Négrel, Ph., Guerrot, C., Millot, R., 2007. Chemical and strontium isotope river waters. Earth and Planetary Science Letters 143 (1–4), 245–255. characterisation of rainwater in France. Isotopes in Environmental and Health Broers, H.P., 2002. Strategies for Regional Groundwater Quality Monitoring. Ph.D. Studies 43, 179–196. Thesis, Utrecht University, Utrecht, 231pp. OVAM, 2006. Actieplan Cadmium – February 2006. Broers, H.P., 2004. Nitrate reduction and pyrite oxidation in the Netherlands. In: AIH Petelet, E., Luck, J.M., Ben Othman, D., Négrel, Ph., Aquilina, L., 1998. Geochemistry Selected Papers on Hydrogeology. Balkema, pp. 141–149. and water dynamics of a medium-sized watershed: the Herault southern France Broers, H.P., van der Grift, B., 2004. Regional monitoring of temporal changes in 1. Organisation of the different water reservoirs as constrained by Sr isotopes groundwater quality. Journal of Hydrology 296 (1–4), 192–220. major and trace elements. Chemical Geology 150 (1–2), 63–83. Bullen, T., White, A., Blum, A., Harden, J., Schulz, M., 1997. Chemical weathering of a Petelet-Giraud, E., Négrel, Ph., Casanova, J., 2003a. Variability of Sr-87/Sr-86 in soil chronosequence on a granitoid alluvium: II. Mineralogic and isotopic water draining granite revealed after a double correction for atmospheric and constraints on the behavior of strontium. Geochimica et Cosmochimica Acta 61 anthropogenic inputs. Hydrological Sciences Journal–Journal des Sciences (2), 291–306. Hydrologiques 48 (5), 729–742. Chabaux, F., Riotte, J., Schmitt, A.D., Carignan, J., Herckes, P., Pierret, M.C., Wortham, Petelet-Giraud, E., Luck, J.M., Ben Othman, D., Négrel, Ph., 2003b. Dynamic scheme H., 2005. Variations of U and Sr isotope ratios in Alsace and Luxembourg rain of water circulation in karstic aquifers as constrained by Sr and Pb isotopes. waters: origin and hydrogeochemical implications. Comptes Rendus Application to the Herault watershed Southern France. Hydrogeology Journal 11 Geosciences 337 (16), 1447–1456. (5), 560–573. Chetelat, B., Gaillardet, J., 2005. Boron isotopes in the Seine River, France: a probe of Petelet-Giraud, E., Négrel, Ph., 2007. Geochemical flood deconvolution in a anthropogenic contamination. Environmental Science & Technology 39 (8), Mediterranean catchment (Herault, France) by Sr isotopes major and trace 2486–2493. elements. Journal of Hydrology 337 (1–2), 224–241. Elbaz-Poulichet, F., Seidel, J.L., Othoniel, C., 2002. Occurrence of an anthropogenic Petelet-Giraud, E., Négrel, Ph., Gourcy, L., Schmidt, C., Schirmer, M., 2007. gadolinium anomaly in river and coastal waters of Southern France. Water Geochemical and isotopic constraints on groundwater–surface water Research 36 (4), 1102–1105. interactions in a highly anthropized site The Wolfen/Bitterfeld megasite EU, 1991. Nitrates Directive No. 91/676/EEC. (Mulde subcatchment, Germany). Environmental Pollution 148 (3), Faure, G., 1986. Principles of Isotope Geology, second ed. John Wiley & sons, New 707–717. York. 588 pp. Pieterse, N.M., Schot, P.P., Verkroost, A.W.M., 1998. Simulatie van de Regionale Fraters, D., Boumans, L.J.M., van Drecht, G., de Haan, T., de Hoop, W.D., 1998. Hydrologie in het stroomgebied van de Dommel. In: Demonstration Project for Nitrogen monitoring in groundwater in the sandy regions of the Netherlands. the Development of Integrated Management Plans for Catchment Areas of Small Environmental Pollution 102, 479–485. Trans-Border Lowland Rivers: The River Dommel. Scientific Project Leader: Dr. Goldstein, S.J., Jacobsen, S.B., 1987. The Nd and Sr isotopic systematics of river- A.W.M. Verkroost (ISBN 90-73083-23-0). water dissolved material: implications for the sources of Nd and Sr in seawater. Pieterse, N.M., Bleuten, W., Jorgensen, S.E., 2003. Contribution of point sources and Chemical Geology (Isotope Geoscience Section) 66, 245–272. diffuse sources to nitrogen and phosphorus loads in lowland river tributaries. Hannigan, R.E., Sholkovitz, E.R., 2001. The development of middle rare earth Journal of Hydrology 271 (1–4), 213–225. element enrichments in freshwaters: weathering of phosphate minerals. Rabiet, M., Brissaud, F., Seidel, J.L., Pistre, S., Elbaz-Poulichet, F., 2005. Deciphering Chemical Geology 175, 495–508. the presence of wastewater in a medium-sized Mediterranean catchment using Hennebruder,} K. et al., 2004. Determination of gadolinium in river water by SPE a multitracer approach. Applied Geochemistry 20 (8), 1587–1596. preconcentration and ICPMS. Talanta, 309–316. Reijnders, H.F.R., van Drecht, G., Prins, H.F., Boumans, L.J.M., 1998. The quality of the Kloppmann, W., Van Houtte, E., Picot, G., Vandenbohede, A., Lebbe, L., Guerrot, C., groundwater in the Netherlands. Journal of Hydrology 207 (3–4), Millot, R., Gaus, I., Wintgens, T., 2008. Monitoring reverse osmosis treated 179–188.

14 E. Petelet-Giraud et al. / Journal of Hydrology xxx (2009) xxx–xxx

Rose, E.F., Chaussidon, M., France-Lanord, C., 2000. Fractionation of boron isotopes Spivack, A.J., Edmond, J.M., 1987. Boron isotope exchange between seawater and the during erosion processes: the example of Himalayan rivers. Geochimica et oceanic crust. Geochimica et Cosmochimica Acta 51, 1033–1043. Cosmochimica Acta 64 (3), 397–408. Visser, A., Broers, H.P., van der Grift, B., Bierkens, M.F.P., 2007. Demonstrating trend Rozemeijer, J.C., Broers, H.P., 2007. The groundwater contribution to surface water reversal of groundwater quality in relation to time of recharge determined by contamination in a region with intensive agricultural land use (Noord-Brabant, H-3/He-3. Environmental Pollution 148 (3), 797–807. The Netherlands). Environmental Pollution 148 (3), 695–706. Waterboard de Dommel, 2007. Monitor gegevens de Dommel 2002–2007. Schokker, J., 2003. Patterns and processes in a Pleistocene fluvio-aeolian . environment. Fysische Geografie. Utrecht, Utrecht University. 142pp. Widory, D., Petelet-Giraud, E., Négrel, Ph., Ladouche, B., 2005. Tracing nitrate Sholkovitz, E.R., Elderfield, H., Szymczak, R., Casey, K., 1999. Island weathering: river sources in groundwater by coupled nitrogen and boron isotopes: a synthesis sources of rare earth elements to the Western Pacific Ocean. Marine Chemistry essay. Environmental Science & Technology 39, 539–548. 68 (1–2), 39–57. Wilkens, B.J., Loch, J.P.G., 1997. Accumulation of cadmium and zinc from diffuse Smedley, P.L., 1991. The geochemistry of the rare earth elements in groundwater immission on acid sandy soils, as a function of soil composition. Water, Air & from the Carnmenellis area southwest England. Geochimica et Cosmochimica Soil Pollution 96 (1), 1–16. Acta 55, 2767–2779.

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