Drivers of nitrogen and phosphorus dynamics in a groundwater-fed urban catchment revealed by high-frequency monitoring

Abstract. Eutrophication of water bodies has been a problem causing severe degradation quality in cities. To gain mechanistic understanding the temporal dynamics nitrogen (N) and phosphorus (P) groundwater-fed low-lying urban polder, we applied high-frequency monitoring Geuzenveld, polder city Amsterdam. The equipment was installed at pumping station where leaves polder. From March 2016 to June 2017, total (TP), ammonium (NH4), turbidity, electrical conductivity (EC), temperature were measured intervals less than 20 min. This paper discusses results three timescales: annual scale, rain event single scale. Mixing upwelling groundwater (main source N P) runoff from precipitation on pavements roofs dominant hydrological process governing pattern EC, while P fluxes also regulated by primary production iron transformations. In our groundwater-seepage controlled catchment, NH4 appeared be form with surface concentrations range 2–6 mg L−1, which stems an organic-rich subsurface. governed mixing autumn winter reduced down 0.1 L−1 during algal growing season spring. depletion dissolved spring suggests uptake producers, consistent high chlorophyll a, O2, suspended solids this period. Total turbidity (range 0.5–2.5 200–1800 FNU, respectively, FNU represents Formazin Nephelometric Unit) due release anoxic sediment column, Fe2+ rapidly oxidized precipitated as oxides contributed turbidity. other seasons, is retained sorption oxides. Nitrogen exported receiving waters throughout whole year, mostly but organic mainly winter, primarily associated Fe(OH)3 colloids P. Based new suggested management strategies that may effectively control reduce eutrophication polders downstream waters.