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.

Phosphorus in groundwater discharge – A potential source for lake eutrophication

“…Temporal and especially spatial heterogeneities in LGD and nutrient concentrations have to be carefully considered, to minimize uncertainties in the nutrient budget. This has recently been confirmed for N by Kidmose et al (2014). In contrast to N, P has long been assumed to be immobile in the aquifer and thus generally low groundwater P concentrations are expected .…”

Groundwater-Surface Water Interactions in “La Charca de Suárez” Wetlands, Spain

“…The explanation could be due to the shallow depth of the wells and the lagoons and therefore, the regional discharge of the aquifer to the coast did not impact the water level measurements neither the groundwater-surface water interactions. The low-permeability sediments deposited on the lagoon-aquifer interface could have greatly influenced seepage rates [40], as well as the presence of organic sediments observed in other locations [54,55]. These could be the causes of the low percentage of the net groundwater exchange obtained in the water balance.…”

Residence Time Controls on the Fate of Nitrogen in Flow‐Through Lakebed Sediments

“…• Controlled experimental increases in labile carbon concentration and residence time increased nitrate removal and denitrification • Seasonal changes in carbon and residence time variables will change nitrate processing in the sediment-water interface in these lakes • A large less mobile porosity domain functions to produce nitrous oxide in bulk-oxic pore waters Zarnetske et al, 2011aZarnetske et al, , 2012, surface-groundwater exchanges in lakes also create the potential for N processing (Chen et al, 1972;Cherkauer et al, 1992;Kidmose et al, 2015;Lewandowski et al, 2015;Rysgaard et al, 1993;Schmadel et al, 2018;Smith et al, 2015;van Luijn et al, 1996). Consequently, SWIs can be described as permanent ecosystem control points (Bernhardt et al, 2017), as they are disproportionately important relative to the water column for N cycling in freshwater systems due to long timescales of reactive solute exchange with microbially active sediment volumes (Abbott et al, 2016;McClain et al, 2003;Zarnetske et al, 2012).…”

“…The most common form of N R is as nitrate (NO 3 − ), and many processes governing NO 3 − concentrations in freshwater systems take place within sediment‐water interfaces (SWIs; Abbott et al, ; Boulton et al, ; McClain et al, ). Though the role of the SWI in N processing is often studied in the context of river corridors (Harvey et al, ; Zarnetske et al, , ), surface‐groundwater exchanges in lakes also create the potential for N processing (Chen et al, ; Cherkauer et al, ; Kidmose et al, ; Lewandowski et al, ; Rysgaard et al, ; Schmadel et al, ; Smith et al, ; van Luijn et al, ). Consequently, SWIs can be described as permanent ecosystem control points (Bernhardt et al, ), as they are disproportionately important relative to the water column for N cycling in freshwater systems due to long timescales of reactive solute exchange with microbially active sediment volumes (Abbott et al, ; McClain et al, ; Zarnetske et al, ).…”