Groundwater impacts on surface water quality and nutrient loads in
lowland polder catchments: monitoring the greater Amsterdam area
Liang Yu1,2, Joachim Rozemeijer3, Boris M. van Breukelen4, Maarten Ouboter2, Corné van der Vlugt2, and Hans Peter Broers51Life and Earth Sciences, Vrije University Amsterdam, Amsterdam, 1181HV, The Netherlands 2Waternet Water Authority, Amsterdam, 1096 AC, The Netherlands 3Deltares, Utrecht, 3508 TC, The Netherlands 4Delft University of Technology, Delft, 2628 CN, The Netherlands 5TNO Geological Survey of The Netherlands, Utrecht, 3584 CB, The Netherlands
Received: 20 Feb 2017 – Accepted for review: 13 Mar 2017 – Discussion started: 17 Mar 2017
Abstract. 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. Twenty-three variables (concentrations of Total-N, Total-P, NH4, NO3, HCO3, SO4, Ca, and Cl in surface water and groundwater, seepage rate, elevation, land-use, and soil type) for 144 polders were analysed. The results imply that groundwater is a large source of nutrients in these mixed urban/agricultural catchments. It is confirmed by high correlations (R2 up to 0.88) between solutes in groundwater and surface water, together with the close similarities in their spatial patterns. The groundwater nutrient concentrations exceeded the surface water Environmental Quality Standards (EQSs) in 93 % of the polders for TP and in 91 % for TN. 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.
Yu, L., Rozemeijer, J., van Breukelen, B. M., Ouboter, M., van der Vlugt, C., and Broers, H. P.: Groundwater impacts on surface water quality and nutrient loads in
lowland polder catchments: monitoring the greater Amsterdam area, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-99, in review, 2017.