title: The Role of Groundwater for Lake-Water Quality and Quantification of N Seepage.
abstract: The heterogeneous nature of both groundwater discharge to a lake (inflow) and nitrate concentrations in groundwater can lead to significant errors in calculations of nutrient loading. Therefore, an integrated approach, combining groundwater flow and transport modelling with observed nitrate and ammonium groundwater concentrations, was used to estimate nitrate loading from a catchment via groundwater to an oligotrophic flow-through lake (Lake Hampen, Denmark). The transport model was calibrated against three vertical nitrate profiles from multi-level wells and 17 shallow wells bordering a crop field near the lake. Nitrate concentrations in groundwater discharging to the lake from the crop field were on average 70 times higher than in groundwater from forested areas. The crop field was responsible for 96% of the total nitrate loading (16.2 t NO3 /year) to the lake even though the field only covered 4.5% of the catchment area. Consequently, a small change in land use in the catchment will have a large effect on the lake nutrient balance and possible lake restoration. The study is the first known attempt to estimate the decrease of nitrate loading via groundwater to a seepage lake when an identified catchment source (a crop field) is removed.
authors.affiliation: Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen, Denmark.
authors.forename: Jacob
authors.initials: J
authors.lastname: Kidmose
authors.affiliation: Department of Geography and Geology, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Engesgaard
authors.affiliation: Institute of Biology, University of Southern Denmark, Campusvej 55, 5230 Odense, Denmark.
authors.forename: Daniela A Oliveira
authors.initials: DA
authors.lastname: Ommen
authors.affiliation: Department of Hydrology, Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350 Copenhagen, Denmark.
authors.forename: Bertel
authors.initials: B
authors.lastname: Nilsson
authors.affiliation: Institute of Biology, University of Southern Denmark, Campusvej 55, 5230 Odense, Denmark.
authors.forename: Mogens R
authors.initials: MR
authors.lastname: Flindt
authors.affiliation: Institute of Biology, University of Southern Denmark, Campusvej 55, 5230 Odense, Denmark.
authors.forename: Frede Ø
authors.initials: FØ
authors.lastname: Andersen
mesh_terms: D000383:Agriculture; D064751:Ammonium Compounds / Q000032:analysis; D003718:Denmark; D065928:Forests; D060587:Groundwater / Q000032:analysis*; D060106:Lakes / Q000032:analysis*; D008962:Models, Theoretical; D009566:Nitrates / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D060753:Water Quality
chemical_list: D064751:Ammonium Compounds; D009566:Nitrates; D014874:Water Pollutants, Chemical