Stable isotope constraints on hydrostratigraphy and aquifer connectivity in the Table Mountain Group

The Table Mountain Group is a folded, faulted, quartzite-dominated sedimentary sequence, metamorphosed to lower greenschist facies, that forms steep mountains dominating the topography of the Western Cape and causing orographic rainfall in an otherwise semi-arid region. These quartzites are highly fractured to depths of kilometres and act as a complex aquifer system that supplies groundwater directly and indirectly, through baseflow, essential for sustaining the natural environment and human activity in the region. Hydrogen and oxygen isotope data for rain, rivers and groundwater (boreholes and springs) in the region give typical altitude effects of -1.8‰ δD/100 m and -0.33‰ δ18O/100 m, and a very strong continental effect of -30‰ δD/100 km and -4.7‰ δ18O/100 km. This allows for application of stable isotopes as natural hydrological tracers. Groundwater at several locations had stable isotope compositions different from ambient rainfall, but similar to rainfall at high altitudes in adjacent mountains, indicating recharge at high altitude. The groundwater flow is through the Skurweberg Aquifer, here defined as all three formations of the Nardouw Subgroup. Observations on the Peninsula Aquifer suggest a very well mixed aquifer, due to extensive fracturing. Potential exists to delineate groundwater protection zones, detect overabstraction and understand aquifer connectivity better by applying stable isotope hydrology to the Table Mountain Group.

Nitrate and Aquifer Protection

Nitrate is the most common chemical contaminant in groundwater, affecting both human health and ecosystems. This chapter discusses how nitrate in groundwater has affected the health of the Chesapeake Bay and how it takes decades for changes in farming practices to reverse these trends. The chapter also examines the human health impacts of nitrate in groundwater within poor communities in California’s Central Valley. The chapter concludes with a discussion of source water protection by illustrating the comprehensive program for mapping groundwater protection zones in Denmark.

Berechnung von Mehraufwand und Minderertrag infolge des Trinkwasserschutzes im Wald

Calculation of additional expense and reduced revenue as a result of drinking water protection in the forest A good portion of the drinking water in Switzerland originates from groundwater wells in the forest. Within the framework of the Water Protection Ordinance these forest areas are designated as groundwater protection zones (core zone, S1; inner protection zone, S2; further protection zone, S3) to protect the drinking water supply against contamination. The designation of a forest area as a protection zone is connected to prescriptions and recommendations influencing forest management and causing additional costs for forest enterprises. On behalf of the Federal Office for Environment, an Excel tool has been developed. With this tool, the additional expense and reduced revenue can be calculated quickly and easily. To reflect the requirements in the tool, courses of action were defined, as they occur in forest management (e.g. no chemical wood treatment in the S2 and S3 zone, utilization of non-polluting fuels and lubricants). Subsequently, these courses were converted into mathematical formulae quantifying the additional costs. Three harvesting methods common in forest management were thereby distinguished, a motor-manual harvesting method, a fully mechanized harvesting method and a harvesting method for steep slopes. The results calculated with the drinking water protection tool can form an essential basis for the discussion on compensation payment for water services from forest management and provide a better communication between forest managers and water suppliers. However, the results of the tool are to be regarded rather as guidelines and should not be taken as absolutely.