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SFS Annual Meeting

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Anthropogenic nutrient load accelerates eutrophication of surface waters. We studied long–term trends in summer chlorophyll-a (Chl-a) and nutrient concentrations in 18 regularly monitored Finnish rivers (1985–2016). We divided the rivers into three groups based on the percentage of organic soil types in the catchment: <13% (Low Peat Rivers), 13–25% (Medium Peat Rivers) and >25% (High Peat Rivers). Catchments with highly erosion-sensitive clay soils form a fourth group. The Mann-Kendall non-parametric test was used for trend detection and the Boosted Regression Tree analysis to study the influence and interaction of explanatory variables with Chl-a. We found decreasing trends for Chl-a in High Peat and Clay Rivers and an increasing trend in Low Peat Rivers. Increasing trends were found for total organic carbon, water temperature and turbidity, while both increasing and decreasing trends appeared for total phosphorus (TP) and total nitrogen (TN) depending on the river group. TP, TN, water temperature and turbidity explained best the variations in Chl-a. TP showed more >50% relative influence on Chl-a in the combination of all river’s data. Higher water temperatures led to Chl-a increases suggesting that warming will challenge management of rivers suffering eutrophication.

José Enrique Cano Bernal (Primary Presenter/Author), Finnish Environment Institute (SYKE),;