Project: Phosphor von der Quelle bis ins Meer - Integriertes Phosphor- und Wasserressourcenmanagement für nachhaltigen Gewässerschutz - PhosWaM abbreviates "Phosphorus from source to sea - Integrated phosphorus and water resources management for sustainable water protection". Phosphorus (P) is one of the essential nutrients for aquatic and terrestrial plants. While many aquatic ecosystems have a surplus of P, land used for agriculture is often phosphorus-deficient due to the extraction of biomass. As a result, farmers use phosphate as fertilizer on their land to promote plant growth. Additionally, industrial and sewage treatment plants release P-compounds into the environment. A large percentage of these compounds reaches the sea via rivers and estuaries. In aquatic environments, an over-abundance of nutrients (e.g. phosphorus) leads to the excessive growth of phytoplankton and other aquatic plants (eutrophication). This leads to turbid water, toxic algal blooms, oxygen deficiency and a loss of biodiversity. The goal in the joint project PhosWaM is to identify emission sources and to evolve effective measures to reduce the P-levels in aquatic environments. In this context, coupled marine physical biogeochemical simulations of the Baltic Sea were performed. First, input pathways of P into the Warnow River and measures to reduced riverine P loads were assessed in PhosWaM. Second, scenario simulations of P inputs from the Warnow River into the Baltic Sea were performed. Finally, the contribution of the Warnow River to the P budget of the Bay of Mecklenburg was evaluated by marine biogeochemical model simulations. The results of these model simulations are published here. The project PhosWaM (FKZ 033W042) is one of 15 joint research projects within the BMBF funding measure "Regional Water Resources Management for Sustainable Protection of Waters in Germany" (ReWaM). ReWaM is part of the BMBF funding priority "Sustainable Water Management" (Nachhaltiges Wassermanagement, NaWaM) in framework program "Research for Sustainable Development" (Forschung für Nachhaltige Entwicklung, FONA). Summary: A marine physical biogeochemical model simulation was performed with the model MOM-ERGOM for the years 1995 to 2014 covering the Baltic Sea. Previously, MOM-ERGOM had been initialized for several decades without tagging until 1984 and, then, from 1985 to 1994 with tagging (see below). The model output has been validated with measurement data of the "IOW Baltic Monitoring and long-term data program" (https://www.io-warnemuende.de/iowdb.html; IOW: Leibniz Institute for Baltic Sea Research Warnemünde) and from the HELCOM database (http://ocean.ices.dk/helcom/Helcom.aspx; HELCOM: Helsinki Commission). The model simulation was forced by coastDat2 COSMO-CLM data (doi:10.1594/WDCC/coastDat-2_COSMO-CLM). Riverine phosphorus input of the Warnow River was calculated with the Soil & Water Assessment Tool (SWAT; Bauwe et al., 2019, doi:10.1016/j.ecohyd.2019.03.003). Phosphorus from the Warnow River has been tagged in the model simulation according to a method by Menésguen et al. (2006, doi:10.4319/lo.2006.51.1_part_2.0591). Therefore, all phosphorus-containing model variables exist twice in the output: once as regular variables and once as tagged variable. The default phosphorus input by the Warnow River based on real phosphorus release patterns and real atmospheric conditions was used ("base scenario"; PhosWaM SWAT case "ist"). The turnover of phosphorus compounds in the Unterwarnow was calculated based on the "Unterwarnow turnover estimation v04" (see final project report of PhosWaM for details). The simulation was performed at the North-German Supercomputing Alliance (HLRN). The model output data were processed and evaluated on servers provided by the project 'PROSO - Prozesse von Spurenstoffen in der Ostsee' (FKZ 03F0779A).
