TY - JOUR A1 - Weitere, Markus A1 - Altenburger, Rolf A1 - Anlanger, Christine A1 - Baborowski, Martina A1 - Bärlund, Ilona A1 - Beckers, Liza-Marie A1 - Borchardt, Dietrich A1 - Brack, Werner A1 - Brase, Lisa A1 - Busch, Wibke A1 - Chatzinotas, Antonis A1 - Deutschmann, Björn A1 - Eligehausen, Jens A1 - Frank, Karin A1 - Graeber, Daniel A1 - Griebler, Christian A1 - Hagemann, Jeske A1 - Herzsprung, Peter A1 - Hollert, Henner A1 - Inostroza, Pedro A. A1 - Jäger, Christoph G. A1 - Kallies, René A1 - Kamjunke, Norbert A1 - Karrasch, Bernhard A1 - Kaschuba, Sigrid A1 - Kaus, Andrew A1 - Klauer, Bernd A1 - Knöller, Kay A1 - Koschorreck, Matthias A1 - Krauss, Martin A1 - Kunz, Julia V. A1 - Kurz, Marie J. A1 - Liess, Matthias A1 - Mages, Margarete A1 - Müller, Christin A1 - Muschket, Matthias A1 - Musolff, Andreas A1 - Norf, Helge A1 - Pöhlein, Florian A1 - Reiber, Lena A1 - Risse-Buhl, Ute A1 - Schramm, Karl-Werner A1 - Schmitt-Jansen, Mechthild A1 - Schmitz, Markus A1 - Strachauer, Ulrike A1 - von Tümpling, Wolf A1 - Weber, Nina A1 - Wild, Romy A1 - Wolf, Christine A1 - Brauns, Mario T1 - Disentangling multiple chemical and non-chemical stressors in a lotic ecosystem using a longitudinal approach JF - Science of the Total Environment N2 - Meeting ecological and water quality standards in lotic ecosystems is often failed due to multiple stressors. However, disentangling stressor effects and identifying relevant stressor-effect-relationships in complex environmental settings remain major challenges. By combining state-of-the-art methods from ecotoxicology and aquatic ecosystem analysis, we aimed here to disentangle the effects of multiple chemical and non-chemical stressors along a longitudinal land use gradient in a third-order river in Germany. We distinguished and evaluated four dominant stressor categories along this gradient: (1) Hydromorphological alterations: Flow diversity and substrate diversity correlated with the EU-Water Framework Directive based indicators for the quality element macroinvertebrates, which deteriorated at the transition from near-natural reference sites to urban sites. (2) Elevated nutrient levels and eutrophication: Low to moderate nutrient concentrations together with complete canopy cover at the reference sites correlated with low densities of benthic algae (biofilms). We found no more systematic relation of algal density with nutrient concentrations at the downstream sites, suggesting that limiting concentrations are exceeded already at moderate nutrient concentrations and reduced shading by riparian vegetation. (3) Elevated organic matter levels: Wastewater treatment plants (WWTP) and stormwater drainage systems were the primary sources of bioavailable dissolved organic carbon. Consequently, planktonic bacterial production and especially extracellular enzyme activity increased downstream of those effluents showing local peaks. (4) Micropollutants and toxicity-related stress: WWTPs were the predominant source of toxic stress, resulting in a rapid increase of the toxicity for invertebrates and algae with only one order of magnitude below the acute toxic levels. This toxicity correlates negatively with the contribution of invertebrate species being sensitive towards pesticides (SPEARpesticides index), probably contributing to the loss of biodiversity recorded in response to WWTP effluents. Our longitudinal approach highlights the potential of coordinated community efforts in supplementing established monitoring methods to tackle the complex phenomenon of multiple stress. KW - Multiple stress KW - Running waters KW - Indicators KW - Ecological functions KW - Effect based analyses Y1 - 2021 UR - https://doi.org/10.1016/j.scitotenv.2020.144324 VL - 769 SP - 144324 ER - TY - JOUR A1 - Jäger, Christoph G. A1 - Hagemann, J. A1 - Borchardt, D. T1 - Can nutrient pathways and biotic interactions control eutrophication in riverine ecosystems? Evidence from a model driven mesocosm experiment JF - Water Research N2 - Ecological theory predicts that the relative importance of benthic to planktonic primary production usually changes along the rivers' continuum from a predomination of benthic algae in lower stream orders to a predomination of planktonic algae at higher orders. Underlying mechanisms driving the interaction between algae in these habitats, its controlling factors and consequences for riverine ecosystems are, however, only partly understood. We present a mechanistic analysis of the governing ecological processes using a simplified, numerical model and examine how abiotic factors and biotic interactions influence benthic and planktonic algae by changing resource competition. We compare the outcome of the model with the results of a factorial mesocosm experiment mimicking the parameter spaces of the model. The results show a remarkable similarity with regard to the temporal development of benthic and pelagic algal biomass and shifting dominance patterns. In particular we analyse the effects of the pathways of nutrient supply (upwelling from the hyporheic zone, direct supply to the surface water, or via both pathways) and grazing in a gradient of river depths. Our results show that detachment of benthic algae, sinking of planktonic algae and the pathway of nutrient supply are key processes determining the respective algal biomass distributions particularly in shallow and intermediate deep systems. Increasing nutrient supply increases algal biomasses, but does not change the general pattern of the interactions. Decreasing light supply decreases the dominance of planktonic algae, but increases dissolved nutrients. At intermediate to high grazing rates algal biomass can be controlled by grazers, but however, at high grazing rates, dissolved nutrients accumulate in the surface water. Our results indicate that nutrient pathways, resource competition and internal control by grazing need to be considered explicitly for the understanding and explanation of eutrophication phenomena in riverine ecosystems. As a consequence, ecologically effective eutrophication management of running water systems has to go beyond the control of nutrient emissions or the achievement of limiting threshold values in the receiving waters, but requires the consideration of the nutrient pathways (surface water versus groundwater) and the shifting biological controls from lower to higher order stream ecosystems. KW - Light KW - Sinking KW - Detachment KW - Depth KW - Resource competition KW - Ecological management Y1 - 2017 UR - https://doi.org/10.1016/j.watres.2017.02.062 VL - 115 SP - 162 EP - 171 ER -