Groundwater - The Disregarded Component in Lake Water and Nutrient Budgets

Abstract:

Lake eutrophication is a large and still growing problem in many parts of the world, commonly due to anthropogenic sources of nutrients such as fertilizer, manure or sewage. Improved quantification of nutrient inputs is required to address this problem. Lacustrine groundwater discharge (LGD) transports nutrients from catchments to lakes. Unfortunately, LGD has often been disregarded in lake nutrient studies due to many different reasons, although first reports of LGD are more than 40 years old. Most measurement techniques are based on separate determinations of seepage volume and nutrient concentration of exfiltrating groundwater; i.e., by multiplying both values. We review the international literature, give a brief overview of measurement techniques, and present typical volumes, concentrations and loads reported in literature. Furthermore, we describe the fate of nitrogen and phosphorus on their subsurface pathway from the catchment through the reactive aquifer-lake interface into the lake, and compare LGD related processes with those of two other groundwater-surface water interfaces: the hyporheic zone in streams and the interface between aquifer and marine systems where SGD (submarine groundwater discharge) occurs.