Water and nutrient fluxes at the sediment-water ecotone of lakes: How important is exchange with groundwater?

English Abstract:

The stability and viability of the groundwater-surface-water ecotone depends largely on fluxes of water and nutrients across the sediment-water interface. Larger rates of groundwater discharge create a more stable environment at and near the interface. However, ecosystem viability suffers if groundwater delivers contaminants or excessive nutrient loads. A comprehensive literature survey was conducted to compile reported rates of water and nutrient exchange in lake settings. Exchange of lake water and groundwater is highly variable in space and time in nearly all lakes. Nutrient fluxes are further complicated by chemical processes that affect nitrogen differently from phosphorus (P) and depend on the redox state of the aquifer. Reported rates of flow from groundwater to lake water range from near 0 to 7.45 m/day. The median of 102 reported studies is 0.007 m/day. Reported flows from lake water to groundwater are far fewer and range from near 0 to 2.63 m/day with a median value of 0.006 m/day. Median discharge of phosphorus and nitrogen to lakes was 34.7 and 1310 mg/m²/year, respectively. Uncontaminated groundwater approaching a sediment-water interface of a lake commonly contained less than 50 μg/L phosphate P. Reported phosphate-P values for nutrient-enriched groundwater ranged from 100 to 4900 μg/L. Nitrite, nitrate, and ammonium concentrations of groundwater approaching lakes were commonly less than 0.01, 10, and 0.2 mg/L, respectively, with nitrate having the greatest variance. Groundwater anthropogenically enriched with nitrogen had nitrite, nitrate, and ammonium concentrations approximately 2, 1, and 1 orders of magnitude larger, respectively. This comprehensive summary indicates that groundwater is an important influence for both the ecotone at the sediment-water interface and often the entire lake ecosystem.