Is phosphorus retention in autochthonous lake sediments controlled by oxygen or phosphorus?

Abstract

Eutrophication of various lakes on the Swiss Plateau was targeted in the 1980s by reducing external nutrient loading and installing aeration/oxygenation systems. For five eutrophic lakes, three of which have been artificially oxygenated and aerated for almost 20 yr, phosphorus (P) balances were established using input, water-column inventory, export via the outlet, and sediment core data. To separate the effects of aeration/oxygenation from the effects of P-input reduction, two measures of P retention were determined-the ratio of net sedimentation to input and the ratio of net sedimentation to gross sedimentation. A comparison among the five lakes shows that, presently, P retention does not differ significantly between lakes with aeration/oxygenation and lakes with an anoxic hypolimnion, whereas retention at times of maximum P concentrations in the 1970s and 1980s was significantly lower compared with retention in today's moderately eutrophic lakes. This is in agreement with the finding that net sedimentation in all lakes remained relatively constant between 280 and 950 kg km Ϫ2, independent of their P concentration. It is shown that constant net sedimentation is likely to prevail as long as P concentrations remain above a critical value of around 40 mg m Ϫ3 . Constant net sedimentation indicates that permanent deposition of P is limited by the sediment's binding capacity. Oxic conditions in the hypolimnion do not necessarily increase this capacity because redox-dependent P species may still be released within the anoxic bulk sediment and diffuse back into the water column. To characterize the P retention capacity of anoxic sediments, we suggest that the P burial rate be determined from dated sediment cores rather than from input/output balances.In natural, nonoxygenated lakes, trophic state and oxygen concentration of lake water and sediments are closely linked. First, high levels of primary production result in high dissolved oxygen (DO) consumption in the hypolimnion and a low penetration depth of oxygen into the sediment. Second, the DO concentration of the water overlaying the sediment affects the release of phosphorus (P) from the sediment: As Einsele (1936) proposed andMortimer (1941) demonstrated in his classical field and laboratory studies, P is retained effectively in the sediment if the overlaying water is oxic but is released as soon as this water turns anoxic. Numerous field studies (e.g., Ashley 1983; Prepas and Burke 1997) have shown the reduction of hypolimnetic P concentrations after the onset of artificial oxygenation.This interaction of P and DO has called for a combined approach when targeting eutrophication in Swiss lakes. On the Swiss Plateau (Fig.

Hypolimnetic oxygen consumption by sediment‐based reduced substances in former eutrophic lakes

“…The only efficient long-term measure to reduce summer anoxia and reestablish lake ecosystems is the reduction of anthropogenic nutrient loads or external organic loadings. A similar conclusion was found by Liboriussen et al (2009) regarding oxygenation to prevent anoxia and concurrent hypolimnetic NH z 4 accumulation, by Moosmann et al (2006) and Gä chter and Wehrli (1998) regarding oxygenation and artificial mixing to reduce lakeinternal P loading, by Annadotter et al (1999) regarding sediment dredging to reduce lake-internal P loading, and by Mü ller and Stadelmann (2004) regarding oxygenation and artificial mixing to improve conditions for egg survival of bottom-spawning fish. Nevertheless, the previously mentioned lake management measures can provide temporary relief from negative effects of anoxia.…”

“…Low hypolimnetic DO can in turn have a serious effect on biological processes, either via direct toxicity on fish and bottom organisms (Kalff 2002) or indirectly via toxic by-products of anaerobic mineralization (Wang and Chapman 1999). Moreover, it has been shown that hypolimnetic anoxia can enhance the sediment release of soluble reactive phosphorus (P; Larsen et al 1981;Hupfer and Lewandowski 2008), although the DO concentration at the sediment-water interface is not the only controlling factor (Moosmann et al 2006).…”

“…Low hypolimnetic DO can in turn have a serious effect on biological processes, either via direct toxicity on fish and bottom organisms (Kalff 2002) or indirectly via toxic by-products of anaerobic mineralization (Wang and Chapman 1999). Moreover, it has been shown that hypolimnetic anoxia can enhance the sediment release of soluble reactive phosphorus (P; Larsen et al 1981;Hupfer and Lewandowski 2008), although the DO concentration at the sediment-water interface is not the only controlling factor (Moosmann et al 2006).As a result, reaching or maintaining a sufficient hypolimnetic DO level is often a focus of lake management. Commonly used approaches focus on (1) the reduction of external P loading (Gä chter and Wehrli 1998), (2) increased DO supply to the hypolimnion through oxygenation or aeration (Singleton and Little 2006) or through artificial mixing in winter (Mü ller and Stadelmann 2004), or (3) the removal of accumulated deposits of organic matter through sediment dredging (Annadotter et al 1999).…”

Application of chemical fractionation and X-ray powder diffraction to study phosphorus speciation in sediments from Lake Hongfeng, China

“…These findings suggest that the content of OP in sediments is lower than that of IP, which primarily consists of Ca-P (apatitic phosphorus) in sediments from calcareous regions [19]. This is probably due to the typical carbonate-rock dissolution environment of the lake, where there is abundant calcium because deposition of phosphorus is limited by the binding capacity of the sediment [31]. Phosphorus in water is integrated into particles by biological absorption (primary production), chemical transfer (adsorption and sedimentation) and other processes, and the particles sink continually.…”

Evidence for vivianite formation and its contribution to long-term phosphorus retention in a recent lake sediment: a novel analytical approach

“…Organic P originates from settled organic material which is refractory or not yet mineralised by microorganisms. Inorganic phases include P sorbed onto the surface of iron(oxy)hydroxides, aluminium hydroxides, clays and calcite (Moosmann et al, 2006). P associated with Fe(III) minerals have been found in anoxic marine and estuarine sediments, indicating a resistance towards reductive dissolution of these compounds, at least under nonsulfidic conditions (Hyacinthe and Van Cappellen, 2004;Lehtoranta et al, 2009).…”