Groundwater impacts on surface water quality and nutrient loads in lowland polder catchments: monitoring the greater Amsterdam area

Abstract

Abstract. The Amsterdam area, a highly manipulated delta area formed by polders and reclaimed lakes, struggles with high nutrient levels in its surface water system. The polders receive spatially and temporally variable amounts of water and nutrients via surface runoff, groundwater seepage, sewer leakage, and via water inlets from upstream polders. Diffuse anthropogenic sources, such as manure and fertiliser use and atmospheric deposition, add to the water quality problems in the polders. The major nutrient sources and pathways have not yet been clarified due to the complex hydrological system in lowland catchments with both urban and agricultural areas. In this study, the spatial variability of the groundwater seepage impact was identified by exploiting the dense groundwater and surface water monitoring networks in Amsterdam and its surrounding polders. A total of 25 variables (concentrations of total nitrogen (TN), total phosphorus (TP), NH 4 , NO 3 , HCO 3 , SO 4 , Ca, and Cl in surface water and groundwater, N and P agricultural inputs, seepage rate, elevation, land-use, and soil type) for 144 polders were analysed statistically and interpreted in relation to sources, transport mechanisms, and pathways. The results imply that groundwater is a large source of nutrients in the greater Amsterdam mixed urban-agricultural catchments. The groundwater nutrient concentrations exceeded the surface water environmental quality standards (EQSs) in 93 % of the polders for TP and in 91 % for TN. Groundwater outflow into the polders thus adds to nutrient levels in the surface water. High correlations (R 2 up to 0.88) between solutes in groundwater and surface water, together with the close similarities in their spatial patterns, confirmed the large impact of groundwater on surface water chemistry, especially in the polders that have high seepage rates. Our analysis indicates that the elevated nutrient and bicarbonate concentrations in the groundwater seepage originate from the decomposition of organic matter in subsurface sediments coupled to sulfate reduction and possibly methanogenesis. The large loads of nutrient-rich groundwater seepage into the deepest polders indirectly affect surface water quality in the surrounding area, because excess water from the deep polders is pumped out and used to supply water to the surrounding infiltrating polders in dry periods. The study shows the importance of the connection between groundwater and surface water nutrient chemistry in the greater Amsterdam area. We expect that taking account of groundwater-surface water interaction is also important in other subsiding and urbanising deltas around the world, where water is managed intensively in order to enable agricultural productivity and achieve water-sustainable cities.

Paleoclimate Signals and Groundwater Age Distributions From 39 Public Water Works in the Netherlands; Insights From Noble Gases and Carbon, Hydrogen and Oxygen Isotope Tracers

“…For our study, we did not consider using chlorofluorocarbons (CFCs, Busenberg & Plummer, 1992; Hinsby et al., 2007; Laier, 2014; Sebol et al., 2007) for characterizing the modern waters of age group Y, because the earlier work of Visser, Schaap, et al. (2009) showed signs of degradation for CFC‐11, CFC‐12 and even CFC‐13 in the Dutch settings which are dominated by anoxic and often methanogenic groundwater below 10–20 m depth (Griffioen et al., 2013; Visser, Schaap, et al., 2009; Yu et al., 2018; Zhang et al. 2009, 2012).…”

“…However, the set of tracers that we applied in the current study is ready for practical application in larger regional studies and especially the NGT appeared to be a crucial tracer for the time scales involved in the groundwater circulation in our study area. For our study, we did not consider using chlorofluorocarbons (CFCs, Busenberg & Plummer, 1992;Hinsby et al, 2007;Laier, 2014;Sebol et al, 2007) for characterizing the modern waters of age group Y, because the earlier work of Visser, Schaap, et al (2009) showed signs of degradation for CFC-11, CFC-12 and even CFC-13 in the Dutch settings which are dominated by anoxic and often methanogenic groundwater below 10-20 m depth (Griffioen et al, 2013;Visser, Schaap, et al, 2009;Yu et al, 2018;Zhang et al 2009Zhang et al , 2012. The use of sulfur-hexafluoride (SF 6 , Busenberg & Plummer, 2000) may however add further value as degassing did not typically affect the samples in the current study.…”

Salt of the Earth: Quantifying the Impact of Water Salinity on Global Agricultural Productivity

“…Various studies in the hydrological literature have begun to show that groundwater can be a major and potentially long-term contributor to contamination of surface water ((e.g. Yu et al 2018;Delsman et al, 2015;De Louw et al, 2010;Holman et al, 2008). The interactions between river water and groundwater are determined by the relative difference between groundwater level and river stage (Mukherjee et al, 2018).…”

Impacts of massive pumping on flood processes in polders—with a case study on Lannihu basin in the Dongting Lake District, China

“…Polders, low‐lying farmland surrounded by dikes and drained mainly by pumping stations, are widely distributed in the middle and lower Yangtze River Plain and the Pearl River Plain of China (Alfonso et al, 2010; Roth & Warner, 2007; Yu et al, 2018). While embankments usually provide flood protection, these low‐lying regions with abundant rainfall and interlaced ditch networks are still subject to severe flooding hazards due to the heavy rainwater that cannot be drained to outer rivers effectively (Hesselink et al, 2003; Lindenschmidt et al, 2008; Rahman et al, 2016; Stijnen et al, 2014).…”