Periphyton responses to nitrogen decline and warming in eutrophic shallow lake mesocosms

Periphyton is a key primary producer in shallow lakes, sensitive to global warming and changes in nutrient balances. Reduced nitrogen availability due to accelerated denitrification at higher temperatures or in response to reduced N loadings aimed to reduce the eutrophication may affect periphyton biomass and composition, to compensate for the low N availability (e.g. promoting N2-fixing). We analysed periphyton responses to N decline in 12 eutrophic shallow lake mesocosms during one year of low N compared to high N, under three temperature scenarios: ambient, A2 IPCC scenario and A2 increased by 50%. We used two submerged macrophytes (Potamogeton crispus and Elodea canadensis) and artificial imitations of these as substrates for periphyton growth. Nitrogen decline increased periphyton biomass and induced compositional changes irrespective of season, plant type, and temperature. Periphyton biomass was negatively associated to phytoplankton and positively to plant complexity. Warmer scenarios negatively affected periphyton exclusively at high N loadings. Low N conditions were associated with lower periphyton taxonomic richness, lower N2-fixing cyanobacteria biovolume and increased biovolume of large-sized chlorophytes and non-N2-fixing cyanobacteria. Our results suggest that low N conditions promoted periphyton due to a more efficient use of nutrients and improved light conditions resulting from lower phytoplankton biomass and contrasting effects of temperature. © 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG.This study was supported by the Sino-Danish Centre – Aarhus University, the University of the Chinese Academy of Sciences and the University of the Republic, Uruguay. E.J. was also supported by the TÜBITAK, BIDEB 2232 program (118C250). C.A. was supported by the Doctoral INPhINIT–INCOMING program, fellowship code (LCF/BQ/DI20/11780004), from “la Caixa” Foundation (ID 100010434). We thank Beibei Hao for her valuable assistance with the experimental design and Ann Lene Vigh and Kathrine Tabermann Uhrenholt for the field and lab assistance

Understanding biological responses to degraded hydromorphology and multiple stresses. Deliverable 3.2 of REFORM (REstoring rivers FOR effective catchment Management), a Collaborative project (large-scale integrating project) funded by the European Commission within the 7th Framework Programme under Grant Agreement 282656

The aim of this deliverable is to conceptually model and empirically test the response of biota to the effects of both hydromorphological pressures acting in concert with one another or with other types of pressures. Best use is made of existing large national monitoring datasets (Denmark, UK, Finland, France, Germany, Austria & WISER datasets), case studies and modeling to provide evidence of multiple stressors interacting to alter river biota (Biological Quality Elements: BQE)

Guidance on how to identify impacts of hydromorphological degradation on riparian ecosystems. Deliverable 3.4 of REFORM (REstoring rivers FOR effective catchment Management), a collaborative project (large-scale integrating project) funded by the European Commission within the 7th Framework Grant Agreement 282656

The aim of this deliverable is to address the impact of hydromorphological degradation on floodplain and riparian ecosystems, with specific focus on vegetation, fish and invertebrate responses and to provide guidance on how to identify those impacts