@misc{KommanaGruenebergHupfer, author = {Kommana, Giulia and Gr{\"u}neberg, Bj{\"o}rn and Hupfer, Michael}, title = {Iron from lignite mining increases phosphorus fixation in sediments, but does not affect trophic states of lakes along River Spree (Germany)}, series = {Water, Air, \& Soil Pollution}, volume = {234}, journal = {Water, Air, \& Soil Pollution}, number = {7}, issn = {1573-2932}, doi = {10.1007/s11270-023-06441-2}, pages = {26}, language = {en} } @misc{UlrichHupferSchwefeletal., author = {Ulrich, Christoph and Hupfer, Michael and Schwefel, Robert and Bannehr, Lutz and Lausch, Angela}, title = {Mapping Specific Constituents of an Ochre-Coloured Watercourse Based on In Situ and Airborne Hyperspectral Remote Sensing Data}, series = {Water}, volume = {15}, journal = {Water}, number = {8}, publisher = {MDPI}, doi = {10.3390/w15081532}, pages = {12}, language = {en} } @misc{LaBrieHupferLau, author = {LaBrie, Richard and Hupfer, Michael and Lau, Maximilian P.}, title = {Anaerobic duration predicts biogeochemical consequences of oxygen depletion in lakes}, series = {Limnology and Oceanography Letters}, volume = {8}, journal = {Limnology and Oceanography Letters}, number = {4}, issn = {2378-2242}, doi = {10.1002/lol2.10324}, pages = {666 -- 674}, language = {en} } @misc{GonsiorczykHupferHiltetal., author = {Gonsiorczyk, Thomas and Hupfer, Michael and Hilt, Sabine and Gessner, Mark O.}, title = {Rapid eutrophication of a clearwater lake : trends and potential causes inferred from phosphorus mass balance analyses}, series = {Global change biology}, volume = {30}, journal = {Global change biology}, number = {11}, publisher = {Wiley}, address = {Hoboken}, issn = {1354-1013}, doi = {10.1111/gcb.17575}, pages = {1 -- 15}, abstract = {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.}, language = {en} } @misc{vanKuppeveltReitzelHupfer, author = {van Kuppevelt, Harm and Reitzel, Kasper and Hupfer, Michael}, title = {Vivianite as a phosphorus source in lake sediments : importance of increased sulphate reduction on phosphorus mobilisation}, series = {Journal of soils and sediments}, volume = {25}, journal = {Journal of soils and sediments}, number = {4}, publisher = {Springer Berlin Heidelberg}, address = {Berlin ; Heidelberg}, issn = {1439-0108}, doi = {10.1007/s11368-025-03986-z}, pages = {1406 -- 1421}, abstract = {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.}, language = {en} } @misc{HiltvandeWeyerMeisetal., author = {Hilt, Sabine and van de Weyer, Klaus and Meis, Sebastian and P{\"a}zolt, Jens and Gessner, Mark O. and Gonsiorczyk, Thomas and Alirangues-Nu{\~n}ez, Marta Maria and Hupfer, Michael}, title = {Facilitation of lake eutrophication by altered feedback loops between submerged macrophyte vegetation and phosphorus retention}, series = {Freshwater biology}, volume = {70}, journal = {Freshwater biology}, number = {5}, publisher = {Wiley}, address = {Oxford}, issn = {0046-5070}, doi = {10.1111/fwb.70051}, pages = {1 -- 11}, abstract = {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.}, language = {en} } @misc{SchroederSchmiederHupfer, author = {Schr{\"o}der, Lucas and Schmieder, Peter and Hupfer, Michael}, title = {Polyphosphate content in sediments of stratified lakes and activated sludge of wastewater treatment plants is controlled by iron-mediated phosphorus availability}, series = {ACS ES\&T water}, volume = {5}, journal = {ACS ES\&T water}, number = {7}, publisher = {American Chemical Society (ACS)}, address = {Washington, D.C.}, issn = {2690-0637}, doi = {10.1021/acsestwater.5c00426}, pages = {4188 -- 4196}, abstract = {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.}, language = {en} } @misc{SchroederSchmiederHupfer, author = {Schr{\"o}der, Lucas and Schmieder, Peter and Hupfer, Michael}, title = {Biogenic polyphosphate as relevant regulator of seasonal phosphate storage in surface sediments of stratified eutrophic lakes}, series = {Biogeochemistry}, volume = {168}, journal = {Biogeochemistry}, number = {2}, publisher = {Springer International Publishing}, address = {Cham}, issn = {1573-515X}, doi = {10.1007/s10533-025-01230-x}, pages = {1 -- 16}, abstract = {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.}, language = {en} }