Springs and their groundwater systems in South Limburg (NL) with special reference to the Central Plateau

Hendrix, Wilhelmus Petrus Alphonsus Marie; Lehmkuhl, Frank (Thesis advisor); Rüde, Thomas R. (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022

Abstract

This dissertation deals with the temporal and spatial variation of the qualitative and quantitative aspects of the springs and their groundwater systems in South Limburg, the most southern part of the Netherlands. The focus is on evaluations of physicochemical and hydrological measurements of natural springs and phreatic groundwater, performed in the period 1984-2018. The field measurements are mainly carried out on the Central Plateau, an excellent hydrogeological system for sampling to determine the physicochemical properties of the phreatic groundwater and spring water, as well as for measurements related to the hydrological properties of springs, such as discharge dynamics. Due to its hydrogeological character, the Central Plateau can be considered as an inverse catchment as well as a natural lysimeter. In addition, the ecological aspects of spring areas are also considered. The thesis starts with a description of the geological, climatological, hydrogeological and physicochemical conditions of the hydrogeological systems in South Limburg in general and the Central Plateau in particular. At the regional level of South Limburg the aquifers of the different hydrogeological systems are described in the horizontal and also the vertical plane, as well as the physicochemical character of their groundwater and spring water. The hydrogeological system of the Central Plateau has two important aquifers, the deeper Cretaceous limestone aquifer, which is used for drinking water production, and the phreatic aquifer, which is formed by Oligocene, Miocene and Pleistocene sands and gravels and feeding the numerous natural springs. The long- and short-term developments of the major physicochemical components of the phreatic groundwater and the spring water and also their long- and short-distance distribution are presented. In this context, a multivariate spatial-statistical analysis is performed using the Fuzzy c-means clustering method. A gradient of increasing concentrations of several compounds in the phreatic groundwater and spring water of South Limburg going from south to north is found. This gradient can be explained by higher precipitation amounts in the south and differences in the intensity of the land use and also in the travel time of the groundwater to the springs. In particular, high nitrate concentrations indicate eutrophication of water. In general, the nitrate concentration of the phreatic groundwater and spring water in South Limburg shows an increasing trend until the beginning of this millennium. For the period 1904-1920, the median nitrate concentration of 17 mg/L was calculated, for the period 1984-1985 this was 36 mg/L, for the period 1987-1991 40 mg/L and for the period 2000-2004 the median value was 68 mg/L. At the end of the first decade of this century (2008-2009), the median nitrate concentration decreased to 46 mg/L. The long-term and short-term variability of most physicochemical components of the phreatic groundwater and spring water during the period 1984-2010 is relatively low to medium and with no discernible trend for many parameters, although exceptions are present in spring water located in different areas.Special attention is paid to the relatively high nitrate concentration of spring water and phreatic groundwater of the Central Plateau and its temporal and spatial variability. The median values of the nitrate concentration of the groundwater and spring water of the Central Plateau (1984-2018; median values: 11-219 mg/L) show a long-term upward trend in the period 1984-2007 and a downward trend after 2007. The short-term variability of the nitrate concentration can range from low to a very high, for both monthly and weekly series of measurement. Several micro-components such as metals and organic substances, e.g. pesticides, are also considered for the Central Plateau.The land use was mapped, analyzed and assessed, primarily to determine the influence of the agricultural land use on the aquatic ecological characteristics of the phreatic groundwater and spring water. Nitrate, chloride, sulfate, sodium and potassium take in a central position in determining the relationship between land use and the physicochemical character of the phreatic groundwater and spring water of the Central Plateau. The influence of land use is evaluated for the Central Plateau by using the measured physicochemical data and land use areas or plots of different sizes, taken into account the hydrogeological structure and also the flow paths as well as and the travel time of the groundwater to the springs. However, in this way a clear relationship between land use and the physicochemical character of the spring water and the phreatic groundwater cannot be demonstrated at the level of the hydrogeological system of the Central Plateau. The impact of the agricultural land use on the groundwater and spring water composition is distributed over the total area, while the impact of landfills, industrial activities and old mining activities has mainly a local character. The water quality assessment of the phreatic groundwater and spring water is carried out for both South Limburg as for the Central Plateau using the current water quality standards. In this assessment, the high nitrate concentration plays a major role. However other components, such as pesticides, also have a negative impact on the quality of the spring water and the phreatic groundwater. An assessment of the water quality based on the standards for all important physicochemical components, finally leads to the conclusion for the Central Plateau that there is not a single sampling point in this area that meets the limit values for drinking water. The deterioration of the water quality minimises the use of spring water and groundwater as drinking water. In addition, it has a negative impact on the development of valuable biocoenoses of spring areas. The Central Plateau is a closed hydrogeological system. The phreatic groundwater is only fed by precipitation in its infiltration area. The upper aquifer of the Central Plateau has the character of a multiple layer leaky aquifer. The springs of the Central Plateau have an average annual total discharge of 72 % of the average annual recharge to the groundwater. This makes the Central Plateau system not only very suitable for field research, but also for hydrological modelling and balance calculations of components of the phreatic groundwater and spring water. Thus, for the Central Plateau, the nitrogen balance calculation can be determined using detailed data on agricultural land use, discharge measurements of springs and spring brooks and the measured nitrate concentration of the spring water. The results of these calculations show a nitrogen load in the groundwater caused by leaching. This reaches the springs after a residence time of a few weeks to many decades. The calculated nitrate concentration from the nitrogen balance deficit compared to the measured nitrate concentration made it possible to predict an increase in the nitrate concentration in the spring water in the following years. The measured median nitrate concentration of the phreatic groundwater and spring water of the Central Plateau increased from 78 mg/L in 1985 to 120 mg/L in 1999.Finally, some recommendations are made for further research on the springs and their groundwater systems in South Limburg. These recommendations concern, among others things, the continuation of field measurements. This is useful to establish long time series of physicochemical properties or attributes of phreatic groundwater and spring water. Further research on spring tufa is of importance for a sustainable development of the ecologically valuable spring biocoenoses. For a better understanding of the groundwater flow to springs, more detailed information about the infiltration areas of individual springs or spring complexes is needed. The ‘inverse catchment’ approach used in this study can also be used for other areas e.g. the Vijlen Plateau, the Ubachsberg Plateau and the Crapoel Plateau. Adding ‘emerging substances’ to measurement or monitoring programmes for groundwater and spring water quality is recommended. Finally, further research is recommended on the impact of pollution or eutrophication of water on the ecologically valuable biocoenoses of springs and spring brooks.

Institutions

• Division of Earth Sciences and Geography [530000]
• Chair of Physical Geography and Geoecology [551610]