Climate change impact on the leaching of a heavy metal contamination in a small lowland catchment

The objective of this study was to assess the potential effects of climate change on the transport of pre-existing spatially-extensive trace metal contamination to a small lowland catchment in the south of the Netherlands. The area surrounding the Keersop has been contaminated with heavy metals by the atmospheric emissions of four zinc ore smelters. This heavy metal contamination, e.g. with Cd and Zn, has accumulated in the topsoil and leaches towards surface water system, especially during high groundwater levels and high discharge rates. Simulated projections of future climate predict increased precipitation in winter, less precipitation in summer, and higher air temperatures throughout the year. These climate change scenarios projected lower groundwater levels and lower discharge rates. As a result of lower groundwater levels, transport of Cd and Zn towards surface water is also projected to decrease in the future climate. These results indicate a positive effect of climate change on a limited aspect of surface water quality

Omzetting van nitraat in de ondergrond; kunnen we daarop vertrouwen? : discussie naar aanleiding van waarnemingen op proefboerderij De Marke en nabijgelegen drinkwaterwinning 't Klooster

Melkveehouderijbedrijven op de droge zandgronden belasten het grondwater met nitraat. Hierdoor voldoet het grondwater in veel melkveehouderijgebieden niet aan de nitraatnorm van 50 mg/l. Project De Marke is erop gericht om een bedrijfssysteem te ontwikkelen waarin productie wordt gecombineerd met milieudoelen. Een belangrijk aspect is het halen van de nitraatnorm van 50 mg/l in het bovenste grondwater. De nitraatconcentratie in het bovenste grondwater is sinds de start van De Marke gedaald van meer dan 300 mg/l naar rond de 50 mg/l. Metingen van TNO-NITG in de ondergrond tot een diepte van 20 meter onder het maaiveld geven aan dat nitraat deels op 6 meter diepte wordt omgezet en op 17 meter diepte geheel verdwijnt. Het verdwijnen van nitraat is een gevolg van een reductieproces. Nitraatreductie kan op gang komen door reactie van organische stof of pyriet onder zuurstofarme omstandigheden. TNO-NITG heeft sedimentmonsters genomen van de ondergrond onder De Marke. Hieruit bleek dat nitraat waarschijnlijk verdwijnt door een zeer kleine hoeveelheid organische stof. Omdat de reactiviteit ten aanzien van nitraat chemisch kan worden bepaald, is het mogelijk om de nitraatreductiecapaciteit van bodemprofielen in kaart te brengen. Als deze capaciteit benut wordt, zal dat moeten gebeuren binnen de randvoorwaarden van bodembehee

The spatial distribution of groundwater age for different geohydrological situations in the Netherlands: Implications for groundwater quality monitoring at the regional scale

The spatial distribution of groundwater age is a key factor determining the distribution of dissolved contaminants in the subsurface when contamination loadings have increased in time. The effects of surficial drainage and aquifer heterogeneity on the spatial distribution of groundwater age in unconsolidated aquifers in flat areas were investigated, and consequences were presented for the monitoring of contaminants from diffuse sources. First, the effects were assessed using model simulations. Second, the groundwater age distribution was evaluated in the two regional monitoring networks of Noord-Brabant and Drenthe using tritium measurements. Theoretically, a simple spatial distribution of groundwater age is present in homogeneous aquifers with natural groundwater recharge, characterized by a horizontal pattern of residence time isochrones and a gradual increase of groundwater age with depth. The model simulations show that the isochrone pattern becomes distorted in areas with a surficial drainage network, resulting in relatively old groundwater at shallow depth and larger spatial variation in groundwater age at a specific depth. This drainage effect on the spatial distribution of groundwater age is relatively large compared with effects of regional scale aquifer heterogeneity or spatially varying groundwater recharge. The effects of surficial drainage on the spatial distribution of groundwater age were confirmed by tritium measurements made in the regional monitoring networks of two provinces in the Netherlands. At about 24 m depth, the proportion of post-1950 groundwater in drained areas was significantly less and the spatial variation of groundwater age was larger than in recharge areas that lack a drainage network. The age of the groundwater appeared to be related to the drainage network density and the water table regime. A preliminary survey showed that contamination patterns in the two networks agree well with the proportion of post-1950 groundwater. © 2004 Elsevier B.V. All rights reserved

Regional monitoring of temporal changes in groundwater quality

Changes in agricultural practices are expected to affect groundwater quality by changing the loads of nutrients and salts in recharging groundwater, but regional monitoring networks installed to register the changes often fail to detect them and interpretation of trend analysis results is difficult. This study aims to improve the detection and understanding of groundwater quality changes with time, combining time series information, concentration-depth profiles, age dating and concentration-depth prognoses based on the historical inputs of solutes. For trend detection, a combination of trend analysis on time series at specific depths and time-averaged concentration-depth profiles was used. To reveal trends that have become obscured by chemical reactions, additional conditionally conservative indicators were introduced that are insensitive to those reactions under specific conditions. Detected trends were matched with prognoses of conservative and reactive transport to aid the understanding of trends. Data of the regional networks in 2 area-types with intensive livestock farming in the Dutch province of Noord-Brabant were used to illustrate the approach. The downward movement of the agricultural pollution front was demonstrated for the 2 area-types. However, many targeted contaminants have become retarded or delayed and quality changes were hard to detect for many reactive solutes, including nitrate. Pollution fronts of these targeted chemical components are still limited to the first 15 m of the subsoil. At deeper level, about 20-25 m, the effects of agricultural pollution and acidification were indicated by chemical indicators that have not been considered by others: oxidation capacity, the sum of cations and chloride. Increasing trends of the conditionally conservative indicators 'oxidation capacity' and 'sum of cations' were found at a depth of 18-25 m below surface. Increasing trends for potassium were found at shallower depth (7-13 m), which is explained by retardation of potassium due to cation-exchange with calcium and magnesium. The modelled cation-exchange explained the shape of the concentration-depth profile and the increasing trends at shallow depth in the aquifer. © 2004 Elsevier B.V. All rights reserved

Tools voor trendanalyse in grondwater

De Europese regelgeving op het gebied van grondwater (Grondwater Richtlijn) is gericht op het aantonen van trendomkeringen. Binnen het werkpakket TREND2 uit het Aquaterra-project (zie bijlage A en bijlage B) zijn technieken ontwikkeld voor trendanalyse. Deze technieken zijn toegepast op verschillende studiegebieden in Europa. Binnen dit werkpakket en eerdere studies zijn twee geschikte technieken voor trendanalyse gevonden: de Mann-Kendall-Trendtool (Broers et al., 2004; Visser et al., 2006) en de Back-Scaling-Trendtool (Visser et al., 2007). Deze trendtools zijn binnen het project Delft Cluster KRW Tools geschikt gemaakt voor operationeel gebruik en in dit document beschreven