Effects of atmospheric nitrogen deposition on nutrient limitation and phytoplankton biomass in unproductive Swedish lakes

Abstract

We used chemical data (3,907 lakes) and phytoplankton biomass (chlorophyll a) data (225 lakes) from Swedish lake monitoring programs to assess the effects of atmospheric nitrogen (N) deposition on nutrient limitation and phytoplankton biomass in unproductive Swedish lakes. There was a clear north-south gradient of increasing lake concentrations of dissolved inorganic nitrogen, which was related to the pattern of atmospheric N input. On the basis of positive relationships between total phosphorus (P) concentrations and phytoplankton biomass we conclude that lakes in areas of enhanced N deposition are mainly P limited during summer. This relationship was not detected in lakes in pristine areas with low N deposition, which, together with experimental evidence from the literature, suggest possible N limitation. During summer, lakes in high N-deposition areas had clearly higher phytoplankton biomass relative to the total phosphorus concentrations compared to lakes in low N-deposition areas. Thus, in Swedish unproductive lakes, high atmospheric N input is reflected by increased lake concentrations of dissolved inorganic nitrogen and, possibly, by a shift from natural N limitation of phytoplankton to P limitation. Our results also reveal that increased N input has caused a eutrophication with higher phytoplankton biomass as the result.

Chemodiversity of dissolved organic matter in lakes driven by climate and hydrology

“…A high association with total nutrients suggests that nutrient import from the catchment promotes chemodiversity, enhancing in-lake production and transformation of DOM. Total phosphorus was not significantly correlated to chemodiversity, possibly a consequence of frequent N-limitation observed in hyper-oligotrophic northern lakes 30 . Nonetheless, nutrients are washed in from the catchment, along with terrestrial DOM, highlighting the importance of catchment properties such as land use in enhancing chemodiversity.…”

Land-use change, not climate, controls organic carbon burial in lakes

“…An alternative explanation for increasing C burial in Minnesota's boreal lakes is that atmospheric inputs of reactive nitrogen are increasing lake productivity [29,30]. Disruption of the global N cycle is now comparable to alteration of the carbon cycle [31], and there is increasing evidence for direct effects of atmospheric N deposition on lakes [32].…”

Atmospheric phosphorus deposition may cause lakes to revert from phosphorus limitation back to nitrogen limitation

“…Part of the excess N circulates through the atmosphere and is deposited with precipitation, reaching areas that would otherwise be free of direct human impact. Recent research has addressed the global impact of atmospherically deposited N as a nutrient [4][5][6] in lakes, showing that reactive N of human origin has caused an increase in the stoichiometric N/phosphorus (P) ratio, and hence a shift from N limitation to P limitation of phytoplankton growth. These findings challenge the classical paradigm of lake phytoplankton productivity being naturally limited by P availability, and support the notion put forward by Goldman 7 that P limitation of phytoplankton growth is a derived character induced by atmospheric N deposition.…”