TY - GEN A1 - Friedland, Giulia A1 - Grüneberg, Björn A1 - Hupfer, Michael T1 - Geochemical signatures of lignite mining products in sediments downstream a fluvial-lacustrine system T2 - Science of The Total Environment KW - Freshwater sediment composition KW - Water chemistry Y1 - 2021 UR - www.sciencedirect.com/science/article/abs/pii/S0048969720374738?via%3Dihub U6 - https://doi.org/10.1016/j.scitotenv.2020.143942 SN - 0048-9697 VL - 760 ER - TY - GEN A1 - Friedland, Giulia A1 - Grüneberg, Björn A1 - Hupfer, Michael T1 - Iron from lignite mining enhances phosphorus uptake in lake sediments of River Spree (NE Germany) T2 - Deutsche Gesellschaft für Limnologie e.V., Ergebnisse der Jahrestagung in Leipzig 2021 KW - eutrophic lakes Y1 - 2022 UR - https://www.dgl-ev.de/publikationen/dgl-tagungsbaende/tagungsberichte.html SN - 978-3-9818302-6-2 SP - 136 PB - Eigenverlag der DGL CY - Essen ER - TY - GEN A1 - Kommana, Giulia A1 - Grüneberg, Björn A1 - Hupfer, Michael T1 - Iron from lignite mining increases phosphorus fixation in sediments, but does not affect trophic states of lakes along River Spree (Germany) T2 - Water, Air, & Soil Pollution KW - Eutrophication KW - Lusatian area Y1 - 2023 U6 - https://doi.org/10.1007/s11270-023-06441-2 SN - 1573-2932 VL - 234 IS - 7 ER - TY - GEN A1 - Ulrich, Christoph A1 - Hupfer, Michael A1 - Schwefel, Robert A1 - Bannehr, Lutz A1 - Lausch, Angela T1 - Mapping Specific Constituents of an Ochre-Coloured Watercourse Based on In Situ and Airborne Hyperspectral Remote Sensing Data T2 - Water KW - remote sensing KW - hyperspectral data Y1 - 2023 U6 - https://doi.org/10.3390/w15081532 VL - 15 IS - 8 PB - MDPI ER - TY - GEN A1 - LaBrie, Richard A1 - Hupfer, Michael A1 - Lau, Maximilian P. T1 - Anaerobic duration predicts biogeochemical consequences of oxygen depletion in lakes T2 - Limnology and Oceanography Letters KW - Aquatic Science KW - Oceanography Y1 - 2023 U6 - https://doi.org/10.1002/lol2.10324 SN - 2378-2242 VL - 8 IS - 4 SP - 666 EP - 674 ER - TY - GEN A1 - Gonsiorczyk, Thomas A1 - Hupfer, Michael A1 - Hilt, Sabine A1 - Gessner, Mark O. T1 - Rapid eutrophication of a clearwater lake : trends and potential causes inferred from phosphorus mass balance analyses T2 - Global change biology N2 - Many clearwater lakes increasingly show symptoms of eutrophication, but the underlying causes are largely unknown. We combined long‐term water chemistry data, multi‐year sediment trap measurements, sediment analyses and simple mass balance models to elucidate potential causes of eutrophication of a deep temperate clearwater lake, where total phosphorus (TP) concentrations quadrupled within a decade, accompanied by expanding hypolimnetic anoxia. Discrepancies between modeled and empirically determined P inputs suggest that the observed sharp rise in TP was driven by internal processes. The magnitude of seasonal variation in TP greatly increased at the same time, both in surface and deep water, partly decoupled from deep water oxygen conditions. A positive correlation between annual P loss from the upper water column and hypolimnetic P accumulation could hint at a short‐circuited P cycle involving lateral TP transport from shallow‐water zones and deposition and release from sediments in deep water. This hypothesis is also supported by P budgets for the upper 20 m during stable summer stratification, suggesting that sediments in shallow lake areas acted as a P net source until 2018. These changes are potentially related to shifts in submerged macrophytes from wintergreen charophyte meadows ( Nitellopsis obtusa ) to annual free‐floating hornwort ( Ceratophyllum demersum ) and to increased sulfide formation, promoting iron fixation in the sediments. Iron bound to sulfur is unavailable for binding P, resulting in a positive feedback between P release in shallow lake areas, primary productivity, macrophyte community structure and redox‐dependent sediment biogeochemistry. Overall, our results suggest that relationships more complex than the commonly invoked increase in internal P release under increasingly anoxic conditions can drive rapid lake eutrophication. Since the proportion of littoral areas is typically large even in deep stratified lakes, littoral processes may contribute more frequently to the rapid lake eutrophication trends observed around the world than is currently recognized. KW - Anoxia KW - Clearwater lakes KW - Eutrophication KW - Internal P loading KW - Macrophytes KW - Phosphorus KW - Sedimentation KW - Sediments Y1 - 2024 U6 - https://doi.org/10.1111/gcb.17575 SN - 1354-1013 SN - 1365-2486 VL - 30 IS - 11 SP - 1 EP - 15 PB - Wiley CY - Hoboken ER - TY - GEN A1 - van Kuppevelt, Harm A1 - Reitzel, Kasper A1 - Hupfer, Michael T1 - Vivianite as a phosphorus source in lake sediments : importance of increased sulphate reduction on phosphorus mobilisation T2 - Journal of soils and sediments N2 - Purpose Eutrophication of freshwater systems is primarily driven by excessive nutrient inputs, particularly phosphorus (P). While external nutrient control has been emphasized, the prediction and management of internal P loading from sedimentary sources remain complex. This study examines the role of vivianite (Fe(II)3(PO4)2·8H2O), a P-bearing mineral in anoxic sediments, in contributing to internal P release under sulfidic conditions. Materials and methods A mesocosm experiment was conducted using sediment cores from Lake Arendsee, Germany. The cores were exposed to elevated sulfate concentrations to induce sulfate reduction, simulating anoxic and sulfidic conditions. Both water column chemistry and sediment solid-phase analyses were performed. Phosphorus release from vivianite-rich sediments was monitored, along with changes in iron (Fe) mineral phases using sequential extraction and X-ray diffraction. Results and discussion Increased sulfate reduction rates significantly mobilized P from vivianite-rich sediments, leading to elevated soluble reactive P levels in the water column. A marked decrease in vivianite content and an increase in sulfide-bound Fe species were observed in the sediments. These findings demonstrate that vivianite in Fe-rich sediments serves as an important internal P source under sulfidic conditions, exacerbating P release. Conclusions This study highlights the role of sulfur cycling in internal P loading and suggests that increased sulfate inputs may enhance eutrophication by mobilizing P from buried vivianite. Effective management of eutrophication should consider both external inputs and internal P sources like vivianite. KW - Vivianite KW - Lake restoration KW - Phosphorus cycling KW - Internal loading KW - Sulphur cycling Y1 - 2025 U6 - https://doi.org/10.1007/s11368-025-03986-z SN - 1439-0108 SN - 1614-7480 VL - 25 IS - 4 SP - 1406 EP - 1421 PB - Springer Berlin Heidelberg CY - Berlin ; Heidelberg ER - TY - GEN A1 - Hilt, Sabine A1 - van de Weyer, Klaus A1 - Meis, Sebastian A1 - Päzolt, Jens A1 - Gessner, Mark O. A1 - Gonsiorczyk, Thomas A1 - Alirangues‐Nuñez, Marta Maria A1 - Hupfer, Michael T1 - Facilitation of lake eutrophication by altered feedback loops between submerged macrophyte vegetation and phosphorus retention T2 - Freshwater biology N2 - Charophytes (stoneworts) often dominate the submerged vegetation in nutrient‐poor hardwater lakes, where they support high benthic phosphorus (P) retention. As a consequence, epilimnion P concentrations remain low and water clarity high, resulting in a positive feedback. When perennial charophytes, retaining P all year round, are replaced by vascular macrophytes, P is retained only during summer but rapidly released during decomposition in the autumn and winter. Epilimnion P thus becomes available to phytoplankton in the following growing season, reducing lake water clarity and further shifting plant dominance from bottom‐dwelling charophytes to taller vascular species. We tested the hypothesis that changes in lake P concentrations may be partly related to changes in the structure of submerged macrophytes in a deep hardwater lake that experienced a dramatic increase in total P (TP) concentrations over a decade with no evidence of changes in external P loading. We repeatedly measured water transparency, macrophyte maximum colonisation depth (MCD) and abundance between 2008 and 2022 and determined macrophyte tissue P content in 2020 to test whether changes in submerged vegetation could explain gaps in the lake's P budget and shifts in P sink/source functions of littoral areas. In 2008, charophyte communities were dominated by wintergreen Nitellopsis obtusa . The subsequent decline of the species was negatively correlated with the spring TP concentration in the upper water layer (0–20 m) of the lake and positively correlated with Secchi depth and macrophyte MCD, which decreased from 13.5 to 9.5 m. In contrast, the cover of annual vascular macrophytes (mainly rootless hornwort, Ceratophyllum demersum ) increased and was positively correlated with P losses from the upper water layer in summer and negatively correlated with Secchi depth and MCD. Budget calculations showed that the littoral zone was a P source during the period when N. obtusa declined. Despite the relatively low contribution of P directly released from lost charophyte biomass, declines of N. obtusa partly explained the temporary P source function of the littoral zone and the increasing P concentrations in the upper water layer at the beginning of May. This was most probably due to the positive effects of charophytes on particle retention and the negative effects on sediment resuspension. Conversely, the growth of C. demersum can explain P losses from the upper water layer, turning the littoral zone into a temporal P sink during summer. However, most of this P is likely to return to the upper water layer during the decomposition of plant biomass after the growing season. In conclusion, our data indicate that replacement of charophytes by submerged vascular plants can facilitate rapid lake eutrophication due to changes in the feedback loop between submerged vegetation, benthic P retention, epilimnion P availability, water transparency, and MCD. KW - Charophytes KW - Macrophytes KW - Phosphorus budget Y1 - 2025 U6 - https://doi.org/10.1111/fwb.70051 SN - 0046-5070 SN - 1365-2427 VL - 70 IS - 5 SP - 1 EP - 11 PB - Wiley CY - Oxford ER - TY - GEN A1 - Schröder, Lucas A1 - Schmieder, Peter A1 - Hupfer, Michael T1 - Polyphosphate content in sediments of stratified lakes and activated sludge of wastewater treatment plants is controlled by iron-mediated phosphorus availability T2 - ACS ES&T water N2 - Biogenic polyphosphate storage contributes to the fixation of phosphorus at the surface of aquatic sediments and is the essential process for the proper functioning of wastewater treatment plants (WWTPs) with an enhanced biological phosphorus removal setup. We hypothesized that, in lake sediments and activated sludge of WWTPs, the close coupling of the iron and phosphorus cycles influences phosphorus availability for polyphosphate formation. We compiled a data set based on 31P nuclear magnetic resonance spectroscopy investigations for the determination of biogenic phosphorus compounds in activated sludge from 16 WWTPs and 34 sediments from stratified lakes and conducted (nonlinear) regressions of polyphosphate as a function of element contents and biogenic or total phosphorus pools. In lake sediments and activated sludge, biogenic phosphorus had a positive effect and iron had a negative one on the polyphosphate content. However, approximately three times more polyphosphate was formed per milligram of biogenic phosphorus in activated sludge than in lake sediments. The relative importance of the biogenic polyphosphate pool in the phosphorus cycle at the sediment–water interface increases in iron-poor lakes. Furthermore, in WWTPs, polyphosphate yields (polyphosphate: biogenic phosphorus) decrease for molar phosphorus-to-iron ratios <1.6, indicating a negative effect of extensive iron dosing on polyphosphate formation. KW - sediments KW - Biogenic phosphorus storage KW - Phosphorus cycle KW - P NMR spectroscopy KW - Activated sludge KW - Sediment−water interface Y1 - 2025 U6 - https://doi.org/10.1021/acsestwater.5c00426 SN - 2690-0637 VL - 5 IS - 7 SP - 4188 EP - 4196 PB - American Chemical Society (ACS) CY - Washington, D.C. ER - TY - GEN A1 - Schröder, Lucas A1 - Schmieder, Peter A1 - Hupfer, Michael T1 - Biogenic polyphosphate as relevant regulator of seasonal phosphate storage in surface sediments of stratified eutrophic lakes T2 - Biogeochemistry N2 - Polyphosphate is formed by polyphosphate-accumulating organisms occurring in various terrestrial, freshwater, and marine ecosystems as well as industrial environments. Although polyphosphate-accumulating organisms and polyphosphate have been well studied in enhanced biological phosphorus (P) removal from wastewater treatment plants, their role in the internal P cycle of natural lakes remains unclear. Several studies have shown that polyphosphate storage is widespread in lake sediments. In this study, 31 P nuclear magnetic resonance spectroscopy was used to analyse the seasonal dynamics of polyphosphate and its drivers at the sediment surface of three stratified German lakes with strong seasonality of hypolimnetic oxygen concentrations. Similar seasonal patterns of polyphosphate were observed in all three lakes. Polyphosphate content increased by a factor of three to five at the beginning of summer stratification, with the maximum content observed in May when oxygen was already very low. During this period, strong redox gradients prevailed within the topmost sediment layer, and highly soluble reactive P concentrations were present in the pore water due to the reductive release of P bound to iron(III)oxides and oxide-hydroxides. Polyphosphate acted as a temporary P storage and was released after a delay, which may mitigate sedimentary P release into the water body during the (early) summer stratification. The observed seasonal dynamics of polyphosphate at the sediment surface offer a novel insight into the link between the P and iron cycles in lakes. KW - Polyphosphate KW - Lake sediment KW - Phosphorus cycle KW - P NMR KW - Nuclear magnetic resonance Y1 - 2025 U6 - https://doi.org/10.1007/s10533-025-01230-x SN - 1573-515X VL - 168 IS - 2 SP - 1 EP - 16 PB - Springer International Publishing CY - Cham ER -