Biomass, community composition and N:P recycling ratios of zooplankton in northern high‐latitude lakes with contrasting levels of N deposition and dissolved organic carbon

Global changes are causing decreases in inorganic nitrogen (N) concentrations, increases coloured dissolved organic carbon (DOC) and N to total phosphorus ratios (DIN:TP) northern lakes. The effects of these on phytoplankton zooplankton biomass the N:P recycling ratio remain unresolved. In 33 Swedish headwater lakes across subarctic-to-boreal gradients with different levels deposition (low north [Västerbotten, boreal; Abisko, subarctic] vs. high south [Värmland, Jämtland, subarctic]), we measured water chemistry, (chlorophyll-a [Chl-a], Chl-a:TP), seston mineral quality (C:P, N:P), as well biomass, community composition, C:N:P stoichiometry. We estimated nutrient imbalances using ecological stoichiometry models. There was a large-scale gradient from low lake DIN DIN:TP south, lower coinciding higher DOC within each region. Lower associated (lower Chl-a:TP). richer C:P N:P) biomass. Zooplankton composition differed dominance N-requiring calanoid copepods P-requiring cladocerans south. Also, greater differences were found between subarctic regions (with DOC) than boreal DOC), suggesting that declines reduce composition. combination DIN, DOC, led reduced ratios, possibly by reducing and/or enhancing copepod community. Our findings suggest declining increasing browning high-latitude will but concurrently enhance probably also their efficiency P relative N.