TY - JOUR A1 - Brothers, Soren M. A1 - Hilt, Sabine A1 - Meyer, Stephanie A1 - Köhler, Jan T1 - Plant community structure determines primary productivity in shallow, eutrophic lakes JF - Freshwater biology N2 - Regime shifts are commonly associated with the loss of submerged macrophytes in shallow lakes; yet, the effects of this on whole-lake primary productivity remain poorly understood. This study compares the annual gross primary production (GPP) of two shallow, eutrophic lakes with different plant community structures but similar nutrient concentrations. Daily GPP rates were substantially higher in the lake containing submerged macrophytes (58623gCm(-2)year(-1)) than in the lake featuring only phytoplankton and periphyton (40823gCm(-2)year(-1); P<0.0001). Comparing lake-centre diel oxygen curves to compartmental estimates of GPP confirmed that single-site oxygen curves may provide unreliable estimates of whole-lake GPP. The discrepancy between approaches was greatest in the macrophyte-dominated lake during the summer, with a high proportion of GPP occurring in the littoral zone. Our empirical results were used to construct a simple conceptual model relating GPP to nutrient availability for these alternative ecological regimes. This model predicted that lakes featuring submerged macrophytes may commonly support higher rates of GPP than phytoplankton-dominated lakes, but only within a moderate range of nutrient availability (total phosphorus ranging from 30 to 100gL(-1)) and with mean lake depths shallower than 3 or 4m. We conclude that shallow lakes with a submerged macrophyte-epiphyton complex may frequently support a higher annual primary production than comparable lakes that contain only phytoplankton and periphyton. We thus suggest that a regime shift involving the loss of submerged macrophytes may decrease the primary productivity of many lakes, with potential consequences for the entire food webs of these ecosystems. KW - macrophytes KW - oxygen curves KW - periphyton KW - regime shift KW - trophic status Y1 - 2013 U6 - https://doi.org/10.1111/fwb.12207 SN - 0046-5070 VL - 58 IS - 11 SP - 2264 EP - 2276 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Attermeyer, Katrin A1 - Premke, Katrin A1 - Hornick, Thomas A1 - Hilt, Sabine A1 - Grossart, Hans-Peter T1 - Ecosystem-level studies of terrestrial carbon reveal contrasting bacterial metabolism in different aquatic habitats JF - Ecology : a publication of the Ecological Society of America N2 - In aquatic systems, terrestrial dissolved organic matter (t-DOM) is known to stimulate bacterial activities in the water column, but simultaneous effects of autumnal leaf input on water column and sediment microbial dynamics in littoral zones of lakes remain largely unknown. The study's objective was to determine the effects of leaf litter on bacterial metabolism in the littoral water and sediment, and subsequently, the consequences for carbon cycling and food web dynamics. Therefore, in late fall, we simultaneously measured water and sediment bacterial metabolism in the littoral zone of a temperate shallow lake after adding terrestrial particulate organic matter (t-POM), namely, maize leaves. To better evaluate bacterial production (BP) and community respiration (CR) in sediments, we incubated sediment cores with maize leaves of different quality (nonleached and leached) under controlled laboratory conditions. Additionally, to quantify the incorporated leaf carbon into microbial biomass, we determined carbon isotopic ratios of fatty acids from sediment and leaf-associated microbes from a laboratory experiment using C-13-enriched beech leaves. The concentrations of dissolved organic carbon (DOC) increased significantly in the lake after the addition of maize leaves, accompanied by a significant increase in water BP. In contrast, sediment BP declined after an initial peak, showing no positive response to t-POM addition. Sediment BP and CR were also not stimulated by t-POM in the laboratory experiment, either in short-term or in long-term incubations, except for a short increase in CR after 18 hours. However, this increase might have reflected the metabolism of leaf-associated microorganisms. We conclude that the leached t-DOM is actively incorporated into microbial biomass in the water column but that the settling leached t-POM (t-POML) does not enter the food web via sediment bacteria. Consequently, t-POML is either buried in the sediment or introduced into the aquatic food web via microorganisms (bacteria and fungi) directly associated with t-POML and via benthic macroinvertebrates by shredding of t-POML. The latter pathway represents a benthic shortcut which efficiently transfers t-POML to higher trophic levels. KW - bacterial production KW - carbon turnover KW - community respiration KW - leaf litter KW - phospholipid-derived fatty acid KW - PLFA KW - Schulzensee KW - Germany KW - sediments KW - shallow lakes KW - stable isotopes KW - terrestrial subsidies Y1 - 2013 U6 - https://doi.org/10.1890/13-0420.1 SN - 0012-9658 SN - 1939-9170 VL - 94 IS - 12 SP - 2754 EP - 2766 PB - Wiley CY - Washington ER - TY - JOUR A1 - Brothers, Soren M. A1 - Hilt, Sabine A1 - Attermeyer, Katrin A1 - Grossart, Hans-Peter A1 - Kosten, Sarian A1 - Lischke, Betty A1 - Mehner, Thomas A1 - Meyer, Nils A1 - Scharnweber, Inga Kristin A1 - Köhler, Jan T1 - A regime shift from macrophyte to phytoplankton dominance enhances carbon burial in a shallow, eutrophic lake JF - Ecosphere : the magazine of the International Ecology University N2 - Ecological regime shifts and carbon cycling in aquatic systems have both been subject to increasing attention in recent years, yet the direct connection between these topics has remained poorly understood. A four-fold increase in sedimentation rates was observed within the past 50 years in a shallow eutrophic lake with no surface in-or outflows. This change coincided with an ecological regime shift involving the complete loss of submerged macrophytes, leading to a more turbid, phytoplankton-dominated state. To determine whether the increase in carbon (C) burial resulted from a comprehensive transformation of C cycling pathways in parallel to this regime shift, we compared the annual C balances (mass balance and ecosystem budget) of this turbid lake to a similar nearby lake with submerged macrophytes, a higher transparency, and similar nutrient concentrations. C balances indicated that roughly 80% of the C input was permanently buried in the turbid lake sediments, compared to 40% in the clearer macrophyte-dominated lake. This was due to a higher measured C burial efficiency in the turbid lake, which could be explained by lower benthic C mineralization rates. These lower mineralization rates were associated with a decrease in benthic oxygen availability coinciding with the loss of submerged macrophytes. In contrast to previous assumptions that a regime shift to phytoplankton dominance decreases lake heterotrophy by boosting whole-lake primary production, our results suggest that an equivalent net metabolic shift may also result from lower C mineralization rates in a shallow, turbid lake. The widespread occurrence of such shifts may thus fundamentally alter the role of shallow lakes in the global C cycle, away from channeling terrestrial C to the atmosphere and towards burying an increasing amount of C. KW - calcite precipitation KW - CO2 emissions KW - global carbon cycle KW - metabolism KW - regime shift KW - sedimentation KW - submerged macrophytes KW - temperate zone KW - trophic status Y1 - 2013 U6 - https://doi.org/10.1890/ES13-00247.1 SN - 2150-8925 VL - 4 IS - 11 PB - Wiley CY - Washington ER - TY - JOUR A1 - Eigemann, Falk A1 - Hilt, Sabine A1 - Salka, Ivette A1 - Grossart, Hans-Peter T1 - Bacterial community composition associated with freshwater algae species specificity vs. dependency on environmental conditions and source community JF - FEMS microbiology ecology N2 - We studied bacterial associations with the green alga Desmodesmus armatus and the diatom Stephanodiscus minutulus under changing environmental conditions and bacterial source communities, to evaluate whether bacteriaalgae associations are species-specific or more generalized and determined by external factors. Axenic and xenic algae were incubated in situ with and without allelopathically active macrophytes, and in the laboratory with sterile and nonsterile lake water and an allelochemical, tannic acid (TA). Bacterial community composition (BCC) of algae-associated bacteria was analyzed by denaturing gradient gel electrophoresis (DGGE), nonmetric multidimensional scaling, cluster analyses, and sequencing of DGGE bands. BCC of xenic algal cultures of both species were not significantly affected by changes in their environment or bacterial source community, except in the case of TA additions. Species-specific interactions therefore appear to overrule the effects of environmental conditions and source communities. The BCC of xenic and axenic D.armatus cultures subjected to in situ bacterial colonization, however, had lower similarities (ca.55%), indicating that bacterial precolonization is a strong factor for bacteriaalgae associations irrespective of environmental conditions and source community. Our findings emphasize the ecological importance of species-specific bacteriaalgae associations with important repercussions for other processes, such as the remineralization of nutrients, and organic matter dynamics. KW - allelopathy KW - bacteriaalgae associations KW - heterotrophic bacteria KW - species-specific Y1 - 2013 U6 - https://doi.org/10.1111/1574-6941.12022 SN - 0168-6496 VL - 83 IS - 3 SP - 650 EP - 663 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Sachse, Rene A1 - Petzoldt, Thomas A1 - Blumstock, Maria A1 - Moreira, Santiago A1 - Paetzig, Marlene A1 - Ruecker, Jacqueline A1 - Janse, Jan H. A1 - Mooij, Wolf M. A1 - Hilt, Sabine T1 - Extending one-dimensional models for deep lakes to simulate the impact of submerged macrophytes on water quality JF - Environmental modelling & software with environment data news N2 - Submerged macrophytes can stabilise clear water conditions in shallow lakes. However, many existing models for deep lakes neglect their impact. Here, we tested the hypothesis that submerged macrophytes can affect the water clarity in deep lakes. A one-dimensional, vertically resolved macrophyte model was developed based on PCLake and coupled to SALMO-1D and GOTM hydrophysics and validated against field data. Validation showed good coherence in dynamic growth patterns and colonisation depths. In our simulations the presence of submerged macrophytes resulted in up to 50% less phytoplankton biomass in the shallowest simulated lake (11 m) and still 15% less phytoplankton was predicted in 100 m deep oligotrophic lakes. Nutrient loading, lake depth, and lake shape had a strong influence on macrophyte effects. Nutrient competition was found to be the strongest biological interaction. Despite a number of limitations, the derived dynamic lake model suggests significant effects of submerged macrophytes on deep lake water quality. (C) 2014 Elsevier Ltd. All rights reserved. KW - Lake model KW - Macrophytes KW - Water quality Y1 - 2014 U6 - https://doi.org/10.1016/j.envsoft.2014.05.023 SN - 1364-8152 SN - 1873-6726 VL - 61 SP - 410 EP - 423 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Lischke, Betty A1 - Hilt, Sabine A1 - Janse, Jan H. A1 - Kuiper, Jan J. A1 - Mehner, Thomas A1 - Mooij, Wolf M. A1 - Gaedke, Ursula T1 - Enhanced input of terrestrial particulate organic matter reduces the resilience of the clear-water state of shallow lakes: A model study JF - Ecosystems N2 - The amount of terrestrial particulate organic matter (t-POM) entering lakes is predicted to increase as a result of climate change. This may especially alter the structure and functioning of ecosystems in small, shallow lakes which can rapidly shift from a clear-water, macrophyte-dominated into a turbid, phytoplankton-dominated state. We used the integrative ecosystem model PCLake to predict how rising t-POM inputs affect the resilience of the clear-water state. PCLake links a pelagic and benthic food chain with abiotic components by a number of direct and indirect effects. We focused on three pathways (zoobenthos, zooplankton, light availability) by which elevated t-POM inputs (with and without additional nutrients) may modify the critical nutrient loading thresholds at which a clear-water lake becomes turbid and vice versa. Our model results show that (1) increased zoobenthos biomass due to the enhanced food availability results in more benthivorous fish which reduce light availability due to bioturbation, (2) zooplankton biomass does not change, but suspended t-POM reduces the consumption of autochthonous particulate organic matter which increases the turbidity, and (3) the suspended t-POM reduces the light availability for submerged macrophytes. Therefore, light availability is the key process that is indirectly or directly changed by t-POM input. This strikingly resembles the deteriorating effect of terrestrial dissolved organic matter on the light climate of lakes. In all scenarios, the resilience of the clear-water state is reduced thus making the turbid state more likely at a given nutrient loading. Therefore, our study suggests that rising t-POM input can add to the effects of climate warming making reductions in nutrient loadings even more urgent. KW - climate change KW - PCLake KW - bistability KW - alternative stable states KW - critical nutrient loading KW - ecosystem modeling KW - allochthony KW - t-POM Y1 - 2014 U6 - https://doi.org/10.1007/s10021-014-9747-7 SN - 1432-9840 SN - 1435-0629 VL - 17 IS - 4 SP - 616 EP - 626 PB - Springer CY - New York ER - TY - JOUR A1 - Brothers, Soren M. A1 - Koehler, J. A1 - Attermeyer, Katrin A1 - Grossart, Hans-Peter A1 - Mehner, T. A1 - Meyer, N. A1 - Scharnweber, Inga Kristin A1 - Hilt, Sabine T1 - A feedback loop links brownification and anoxia in a temperate, shallow lake JF - Limnology and oceanography N2 - This study examines a natural, rapid, fivefold increase in dissolved organic carbon (DOC) concentrations in a temperate shallow lake, describing the processes by which increased DOC resulted in anoxic conditions and altered existing carbon cycling pathways. High precipitation for two consecutive years led to rising water levels and the flooding of adjacent degraded peatlands. Leaching from the flooded soils provided an initial increase in DOC concentrations (from a 2010 mean of 12 +/- 1 mg L-1 to a maximum concentration of 53 mg L-1 by June 2012). Increasing water levels, DOC, and phytoplankton concentrations reduced light reaching the sediment surface, eliminating most benthic primary production and promoting anoxia in the hypolimnion. From January to June 2012 there was a sudden increase in total phosphorus (from 57 mg L-1 to 216 mg L-1), DOC (from 24.6 mg L-1 to 53 mg L-1), and iron (from 0.12 mg L-1 to 1.07 mg L-1) concentrations, without any further large fluxes in water levels. We suggest that anoxic conditions at the sediment surface and flooded soils produced a dramatic release of these chemicals that exacerbated brownification and eutrophication, creating anoxic conditions that persisted roughly 6 months below a water depth of 1 m and extended periodically to the water surface. This brownification-anoxia feedback loop resulted in a near-complete loss of macroinvertebrate and fish populations, and increased surface carbon dioxide (CO2) emissions by an order of magnitude relative to previous years. Y1 - 2014 U6 - https://doi.org/10.4319/lo.2014.59.4.1388 SN - 0024-3590 SN - 1939-5590 VL - 59 IS - 4 SP - 1388 EP - 1398 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Hilt, Sabine A1 - Wanke, Thomas A1 - Scharnweber, Inga Kristin A1 - Brauns, Mario A1 - Syvaranta, Jari A1 - Brothers, Soren M. A1 - Gaedke, Ursula A1 - Köhler, Jan A1 - Lischke, Betty A1 - Mehner, Thomas T1 - Contrasting response of two shallow eutrophic cold temperate lakes to a partial winterkill of fish JF - Hydrobiologia : acta hydrobiologica, hydrographica, limnologica et protistologica N2 - Food-web effects of winterkill are difficult to predict as the enhanced mortality of planktivorous fish may be counterbalanced by an even higher mortality of piscivores. We hypothesised that a winterkill in a clear and a turbid shallow lake would equalise their fish community composition, but seasonal plankton successions would differ between lakes. After a partial winterkill, we observed a reduction of fish biomass by 16 and 43% in a clear-water and a turbid small temperate lake, respectively. Fish biomass and piscivore shares (5% of fish biomass) were similar in both lakes after this winterkill, but young-of-the-year (YOY) abundances were higher in the turbid lake. Top-down control by crustaceans was only partly responsible for low phytoplankton biomass at the end of May following the winterkill in both lakes. Summer phytoplankton biomass remained low in the clear-water lake despite high abundances of YOY fish (mainly roach). In contrast, the crustacean biomass of the turbid lake was reduced in summer by a high YOY abundance (sunbleak and roach), leading to a strong increase in phytoplankton biomass. The YOY abundance of fish in shallow eutrophic lakes may thus be more important for their summer phytoplankton development after winterkill than the relative abundance of piscivores. KW - Anoxia KW - Fish KW - Regime shifts KW - Roach KW - Shallow lakes KW - Submerged macrophytes Y1 - 2015 U6 - https://doi.org/10.1007/s10750-014-2143-7 SN - 0018-8158 SN - 1573-5117 VL - 749 IS - 1 SP - 31 EP - 42 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Attermeyer, Katrin A1 - Tittel, Joerg A1 - Allgaier, Martin A1 - Frindte, Katharina A1 - Wurzbacher, Christian A1 - Hilt, Sabine A1 - Kamjunke, Norbert A1 - Grossart, Hans-Peter T1 - Effects of Light and Autochthonous Carbon Additions on Microbial Turnover of Allochthonous Organic Carbon and Community Composition JF - Microbial ecology N2 - The fate of allochthonous dissolved organic carbon (DOC) in aquatic systems is primarily controlled by the turnover of heterotrophic bacteria. However, the roles that abiotic and biotic factors such as light and DOC release by aquatic primary producers play in the microbial decomposition of allochthonous DOC is not well understood. We therefore tested if light and autochthonous DOC additions would increase allochthonous DOC decomposition rates and change bacterial growth efficiencies and community composition (BCC). We established continuous growth cultures with different inocula of natural bacterial communities and alder leaf leachates (DOCleaf) with and without light exposure before amendment. Furthermore, we incubated DOCleaf together with autochthonous DOC from lysed phytoplankton cultures (DOCphyto). Our results revealed that pretreatments of DOCleaf with light resulted in a doubling of bacterial growth efficiency (BGE), whereas additions of DOCphyto or combined additions of DOCphyto and light had no effect on BGE. The change in BGE was not accompanied by shifts in the phylogenetic structure of the BCC, but BCC was influenced by the DOC source. Our results highlight that a doubling of BGE is not necessarily accompanied by a shift in BCC and that BCC is more strongly affected by resource properties. KW - Bacterial growth efficiency KW - Continuous cultures KW - Carbon decomposition KW - Leaf litter KW - Photolysis Y1 - 2015 U6 - https://doi.org/10.1007/s00248-014-0549-4 SN - 0095-3628 SN - 1432-184X VL - 69 IS - 2 SP - 361 EP - 371 PB - Springer CY - New York ER - TY - JOUR A1 - Périllon, Cécile A1 - Hilt, Sabine T1 - Groundwater influence differentially affects periphyton and macrophyte production in lakes JF - Hydrobiologia : acta hydrobiologica, hydrographica, limnologica et protistologica N2 - Groundwater influx can significantly contribute to nutrient and carbon budgets of lakes, and its influence is the strongest in littoral areas dominated by macrophytes and periphyton. We have reviewed the effects of groundwater-borne nitrogen and phosphorus and dissolved inorganic and organic carbon (DIC, DOC) on these benthic primary producers in lakes. We develop a hypothesis for groundwater effects including the less studied impacts of periphyton shading on macrophytes. Groundwater-borne nutrients and DIC promote both macrophytes and periphyton. Direct studies on groundwater-borne DOC effects are lacking, but coloured DOC contributes to light attenuation and thus can restrict the growth of benthic primary producers. We predict that above certain threshold levels of nutrient influx by groundwater, periphyton and macrophyte biomass should decline owing to shading by phytoplankton and periphyton, respectively. However, because of their higher light requirements, those thresholds should be lower for macrophytes. For macrophytes, a threshold level is also predicted for a shift from DIC limitation to light limitation. Differences in light requirements are expected to result in lower thresholds of DOC loading for declines of macrophytes than periphyton. KW - Dissolved inorganic carbon KW - Dissolved organic carbon KW - Light KW - Macrophytes KW - Nutrients KW - Periphyton Y1 - 2016 U6 - https://doi.org/10.1007/s10750-015-2485-9 SN - 0018-8158 SN - 1573-5117 VL - 778 SP - 91 EP - 103 PB - Springer CY - Dordrecht ER -