Oxygen Controls the Phosphorus Release from Lake Sediments – a Long‐Lasting Paradigm in Limnology

Abstract

The pioneer works of EINSELE, MORTIMER, and OHLE on the linking between phosphorus (P) and iron (Fe) cycles seven decades ago created the theoretical basis for a long-standing paradigm among limnologists i.e., 'oxygen controls the P release from sediments'. While many empirical studies as well as strong correlations between oxygen depletion and P release seem to support this paradigm, various field observations, laboratory experiments, and repeated failures of hypolimnetic oxygenation measures cast doubt on its universal validity. The temporal existence of a thin oxidized sediment surface-layer could affect only fluctuations of the temporary P pool at the sediment surface but not the long-term P retention. On longer time scales P release is the imbalance between P sedimentation and P binding capacity of anoxic sediment layers. The P retention of lake sediments strongly depends on sediment characteristics and land use of the catchment. The presence of redox-insensitive P-binding systems such as Al(OH) 3 and unreducible Fe(III) minerals can enhance the P retention and completely prevent P release even in case of anoxic conditions. Alternative release mechanisms such as a dissolution of calcium-bound P and decomposition of organic P under both, aerobic and anaerobic conditions, are often more important than the redox driven Fe-coupled P cycle. Additionally, bacteria affect P cycling not only by altering the redox conditions but also by releasing P during mineralization of organic matter and by accumulation and release of bacterial P. Since microbial processes consume oxygen and liberate P it is difficult to distinguish whether oxygen depletion is the result or the cause of P release. Nowadays, the old paradigm is discarded and a paradigm shift takes place. Sedimentary P exchange ought to be considered as a complex process which is mainly determined by the amount and species of settled P as well as their subsequent diagenetic transformation in the sediment. The classical paradigm is only valid in special cases since reality is much more complex than suggested by that paradigm. Everything should be made simple as possible, but not simpler!ALBERT EINSTEIN

A Novel Modeling Approach to Quantify the Influence of Nitrogen Inputs on the Oxygen Dynamics of the North Sea

“…On the one hand, this may relate to changes in the inputs by the different sources relative to each other (e.g., different ratios between P loads of individual rivers compared to N loads). On the other hand, selected processes (e.g., nitrification) cannot be considered in case of P labeling, while other processes such as P release from the sediment under anoxic conditions would play an additional role when considering P (e.g., Hupfer and Lewandowski, 2008). However, this process is not included in ECOHAM as it is designed primarily to represent the O 2 cycle in relation to N and C. As N constitutes the limiting nutrient among these two with respect to organic matter production, we focused our analysis on N. In order to assess the overall impact of nutrients (i.e., N and P) from individual sources on the North Sea O 2 dynamics, an analogous analysis for P would be required.…”

Estimating internal P loading in a deep water reservoir of northern China using three different methods

“…In shallow lakes, internal P loading was widely regarded as a great source of nutrient (Welch and Cooke 1995;Nürnberg and LaZerte 2004;Steinman et al 2009). However, internal nutrient released from sediment is often related to anoxia (Hupfer and Lewandowski 2008). There has been a number of reports confirmed that phosphorus release from bottom sediments was dominant by anoxic conditions (Andersen and Ring 1999, James and Barko 1991, Steinman et al 2009, Welch and Cooke 1995.…”

The Importance of Eolian Input on Lake-Sediment Geochemical Composition in the Dry Proglacial Landscape of Western Greenland

“…The most likely interpretation is that PC-3 represents the redox conditions in the bottom waters, where less oxygen in the bottom waters would favor the incorporation of S as sulfides in the sediment (Holmer and Storkholm, 2001;Leng et al, 2012). For P, the opposite behavior would be expected, with oxic conditions favoring incorporation of P bound to iron hydroxides and oxyhydroxides, and anoxic or hypoxic conditions resulting in dissolution of iron hydroxides and a release of P to the water column (Davison, 1993;Hupfer and Lewandowski, 2008). This interpretation would also fit with the down-core variation in PC-3 scores where positive scores are mainly associated with unit Ia, but also to some extent with unit IIIb (Fig.…”