Dissolved Inorganic Geogenic Phosphorus Load to a Groundwater-Fed Lake: Implications of Terrestrial Phosphorus Cycling by Groundwater

Abstract

The general perception has long been that lake eutrophication is driven by anthropogenic sources of phosphorus (P) and that P is immobile in the subsurface and in aquifers. Combined investigation of the current water and P budgets of a 70 ha lake (Nørresø, Fyn, Denmark) in a clayey till-dominated landscape and of the lake’s Holocene trophic history demonstrates a potential significance of geogenic (natural) groundwater-borne P. Nørresø receives water from nine streams, a groundwater-fed spring located on a small island, and precipitation. The lake loses water by evaporation and via a single outlet. Monthly measurements of stream, spring, and outlet discharge, and of tracers in the form of temperature, δ18O and δ2H of water, and water chemistry were conducted. The tracers indicated that the lake receives groundwater from an underlying regional confined glaciofluvial sand aquifer via the spring and one of the streams. In addition, the lake receives a direct groundwater input (estimated as the water balance residual) via the lake bed, as supported by the artesian conditions of underlying strata observed in piezometers installed along the lake shore and in wells tapping the regional confined aquifer. The groundwater in the regional confined aquifer was anoxic, ferrous, and contained 4–5 µmol/L dissolved inorganic orthophosphate (DIP). Altogether, the data indicated that groundwater contributes from 64% of the water-borne external DIP loading to the lake, and up to 90% if the DIP concentration of the spring, as representative for the average DIP of the regional confined aquifer, is assigned to the estimated groundwater input. In support, paleolimnological data retrieved from sediment cores indicated that Nørresø was never P-poor, even before the introduction of agriculture at 6000 years before present. Accordingly, groundwater-borne geogenic phosphorus can have an important influence on the trophic state of recipient surface water ecosystems, and groundwater-borne P can be a potentially important component of the terrestrial P cycle.

Groundwater–Surface Water Interactions: Recent Advances and Interdisciplinary Challenges

“…Moreover, 15 out of 20 research papers in this Special Issue have a purely hydrological focus, while only five consider hydrological and biogeochemical interactions. In fact, only two contributions (both by Nisbeth et al [13,14]) focus on mass transport between groundwater and surface water by determining groundwater-borne phosphorus loads to a lake. This could be due to the challenging complexity of groundwater-surface water exchange processes alone, because the investigation of related mass fluxes adds to further complexity.…”

“…They sampled precipitation, lake water, river water, and groundwater for chloride concentrations and water-stable isotopes to delineate discharge and recharge areas for the dry (cold) and the wet season in the complex hydrogeological environment of Lake Hulun. Nisbeth et al [13,14] found that geogenic P might be a much more important P source in some instances than is generally assumed. Their study contributes to the still-overlooked problem of LGD-induced lake eutrophication [24,[28][29][30].…”

“…The majority of the contributions [3,5,[8][9][10][11][15][16][17][19][20][21][22][23] focus on the interactions between rivers or streams and groundwater. Three studies [6,13,14] investigate the interactions between lakes and groundwater, while two studies [4,18] deal with the exchange between groundwater and oceanic water. Two additional contributions [7,12] show the relevance of groundwater exchange processes in wetlands.…”

Water Scarcity Footprint Analysis of Container-Grown Plants in a Model Research Nursery as Affected by Irrigation and Fertilization Treatments

“…The combination and interrelated environmental elements such as increasing population, climate change, land use change, and pollution have resulted in the scarcity of high quality water for human use and ecosystem sustainability [3,4]. Increasing urban demand for water is not only due to increasing urban population, but also to aging and inadequate infrastructure that can be addressed to some extent They stated that the primary pollutant in their study was phosphate, which is supported by other studies [9].…”

Role of Groundwater-Borne Geogenic Phosphorus for the Internal P Release in Shallow Lakes

“…Nine small streams discharge into the lake (Figure 1b), numbered 1 to 9 in order of decreasing annual P loading to the lake. This numbering was based on the relative size of the annual dissolved inorganic P (DIP)-flux quantified by Nisbeth et al [48]. Stream 1 and the spring on Lucieø both represent anoxic groundwater discharging from a regional confined aquifer, with geogenic P and ferrous iron concentrations of~150 µg P/L and 1700 µg Fe/L, respectively [49].…”