@article{PerillonPoeschkeLewandowskietal.2017,
  author    = {P{\´e}rillon, C{\´e}cile and P{\"o}schke, Franziska and Lewandowski, J{\"o}rg and Hupfer, Michael and Hilt, Sabine},
  title     = {Stimulation of epiphyton growth by lacustrine groundwater discharge to an oligo-mesotrophic hard-water lake},
  series = {Freshwater Science},
  volume    = {36},
  journal   = {Freshwater Science},
  publisher = {Univ. of Chicago Press},
  address   = {Chicago},
  issn      = {2161-9549},
  doi       = {10.1086/692832},
  pages     = {555 -- 570},
  year      = {2017},
  abstract  = {Periphyton is a major contributor to aquatic primary production and often competes with phytoplankton and submerged macrophytes for resources. In nutrient-limited environments, mobilization of sediment nutrients by groundwater can significantly affect periphyton (including epiphyton) development in shallow littoral zones and may affect other lake primary producers. We hypothesized that epiphyton growth in the littoral zone of temperate oligomesotrophic hard-water lakes could be stimulated by nutrient (especially P) supply via lacustrine groundwater discharge (LGD). We compared the dry mass, chlorophyll a (chl a), and nutrient content of epiphyton grown on artificial substrates at different sites in a groundwater-fed lake and in experimental chambers with and without LGD. During the spring-summer periods, epiphyton accumulated more biomass, especially algae, in littoral LGD sites and in experimental chambers with LGD compared to controls without LGD. Epiphyton chl a accumulation reached up to 46 mg chl a/m(2) after 4 wk when exposed to LGD, compared to a maximum of 23 mg chl a/m(2) at control (C) sites. In the field survey, differences in epiphyton biomass between LGD and C sites were most pronounced at the end of summer, when epilimnetic P concentrations were lowest and epiphyton C:P ratios indicated P limitation. Groundwater-borne P may have facilitated epiphyton growth on macrophytes and periphyton growth on littoral sediments. Epiphyton stored up to 35 mg P/m(2) in 4 wk (which corresponds to 13\% of the total P content of the littoral waters), preventing its use by phytoplankton, and possibly contributing to the stabilization of a clear-water state. However, promotion of epiphyton growth by LGD may have contributed to an observed decline in macrophyte abundance caused by epiphyton shading and a decreased resilience of small charophytes to drag forces in shallow littoral areas of the studied lake in recent decades.},
  language  = {en}
}
@phdthesis{Perillon2017,
  author    = {P{\´e}rillon, C{\´e}cile},
  title     = {The effect of groundwater on benthic primary producers and their interaction},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-406883},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVII, 180},
  year      = {2017},
  abstract  = {In littoral zones of lakes, multiple processes determine lake ecology and water quality. Lacustrine groundwater discharge (LGD), most frequently taking place in littoral zones, can transport or mobilize nutrients from the sediments and thus contribute significantly to lake eutrophication. Furthermore, lake littoral zones are the habitat of benthic primary producers, namely submerged macrophytes and periphyton, which play a key role in lake food webs and influence lake water quality. Groundwater-mediated nutrient-influx can potentially affect the asymmetric competition between submerged macrophytes and periphyton for light and nutrients. While rooted macrophytes have superior access to sediment nutrients, periphyton can negatively affect macrophytes by shading. LGD may thus facilitate periphyton production at the expense of macrophyte production, although studies on this hypothesized effect are missing. The research presented in this thesis is aimed at determining how LGD influences periphyton, macrophytes, and the interactions between these benthic producers. Laboratory experiments were combined with field experiments and measurements in an oligo-mesotrophic hard water lake. In the first study, a general concept was developed based on a literature review of the existing knowledge regarding the potential effects of LGD on nutrients and inorganic and organic carbon loads to lakes, and the effect of these loads on periphyton and macrophytes. The second study includes a field survey and experiment examining the effects of LGD on periphyton in an oligotrophic, stratified hard water lake (Lake Stechlin). This study shows that LGD, by mobilizing phosphorus from the sediments, significantly promotes epiphyton growth, especially at the end of the summer season when epilimnetic phosphorus concentrations are low. The third study focuses on the potential effects of LGD on submerged macrophytes in Lake Stechlin. This study revealed that LGD may have contributed to an observed change in macrophyte community composition and abundance in the shallow littoral areas of the lake. Finally, a laboratory experiment was conducted which mimicked the conditions of a seepage lake. Groundwater circulation was shown to mobilize nutrients from the sediments, which significantly promoted periphyton growth. Macrophyte growth was negatively affected at high periphyton biomasses, confirming the initial hypothesis. More generally, this thesis shows that groundwater flowing into nutrient-limited lakes may import or mobilize nutrients. These nutrients first promote periphyton, and subsequently provoke radical changes in macrophyte populations before finally having a possible influence on the lake's trophic state. Hence, the eutrophying effect of groundwater is delayed and, at moderate nutrient loading rates, partly dampened by benthic primary producers. The present research emphasizes the importance and complexity of littoral processes, and the need to further investigate and monitor the benthic environment. As present and future global changes can significantly affect LGD, the understanding of these complex interactions is required for the sustainable management of lake water quality.},
  language  = {en}
}
@article{DarwallBremerichDeWeveretal.2018,
  author    = {Darwall, William and Bremerich, Vanessa and De Wever, Aaike and Dell, Anthony I. and Freyhof, Joerg and Gessner, Mark O. and Grossart, Hans-Peter and Harrison, Ian and Irvine, Ken and J{\"a}hnig, Sonja C. and Jeschke, Jonathan M. and Lee, Jessica J. and Lu, Cai and Lewandowska, Aleksandra M. and Monaghan, Michael T. and Nejstgaard, Jens C. and Patricio, Harmony and Schmidt-Kloiber, Astrid and Stuart, Simon N. and Thieme, Michele and Tockner, Klement and Turak, Eren and Weyl, Olaf},
  title     = {The alliance for freshwater life},
  series = {Aquatic Conservation: Marine and Freshwater Ecosystems},
  volume    = {28},
  journal   = {Aquatic Conservation: Marine and Freshwater Ecosystems},
  number    = {4},
  publisher = {Wiley},
  address   = {Hoboken},
  issn      = {1052-7613},
  doi       = {10.1002/aqc.2958},
  pages     = {1015 -- 1022},
  year      = {2018},
  abstract  = {1. Global pressures on freshwater ecosystems are high and rising. Viewed primarily as a resource for humans, current practices of water use have led to catastrophic declines in freshwater species and the degradation of freshwater ecosystems, including their genetic and functional diversity. Approximately three-quarters of the world's inland wetlands have been lost, one-third of the 28 000 freshwater species assessed for the International Union for Conservation of Nature (IUCN) Red List are threatened with extinction, and freshwater vertebrate populations are undergoing declines that are more rapid than those of terrestrial and marine species. This global loss continues unchecked, despite the importance of freshwater ecosystems as a source of clean water, food, livelihoods, recreation, and inspiration. 2. The causes of these declines include hydrological alterations, habitat degradation and loss, overexploitation, invasive species, pollution, and the multiple impacts of climate change. Although there are policy initiatives that aim to protect freshwater life, these are rarely implemented with sufficient conviction and enforcement. Policies that focus on the development and management of fresh waters as a resource for people almost universally neglect the biodiversity that they contain. 3. Here we introduce the Alliance for Freshwater Life, a global initiative, uniting specialists in research, data synthesis, conservation, education and outreach, and policymaking. This expert network aims to provide the critical mass required for the effective representation of freshwater biodiversity at policy meetings, to develop solutions balancing the needs of development and conservation, and to better convey the important role freshwater ecosystems play in human well-being. Through this united effort we hope to reverse this tide of loss and decline in freshwater biodiversity. We introduce several short- and medium-term actions as examples for making positive change, and invite individuals, organizations, authorities, and governments to join the Alliance for Freshwater Life.},
  language  = {en}
}
@article{BrothersHiltMeyeretal.2013,
  author    = {Brothers, Soren M. and Hilt, Sabine and Meyer, Stephanie and K{\"o}hler, Jan},
  title     = {Plant community structure determines primary productivity in shallow, eutrophic lakes},
  series = {Freshwater biology},
  volume    = {58},
  journal   = {Freshwater biology},
  number    = {11},
  publisher = {Wiley-Blackwell},
  address   = {Hoboken},
  issn      = {0046-5070},
  doi       = {10.1111/fwb.12207},
  pages     = {2264 -- 2276},
  year      = {2013},
  abstract  = {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.},
  language  = {en}
}