Climate variability induced shifts in nitrogen loading from terrestrial to aquatic ecosystems

Nitrogen is a critical nutrient linked to degradation of freshwater and marine ecosystems. The nitrogen inputs to terrestrial ecosys- tems and subsequent loadings to aquatic ecosystems have been doubled and changed the nitrogen cycle as population and hu- man activities increased over the past century. One of the consequences of human alter- nation of the nitrogen cycle is the eutrophication of marine and freshwater ecosystems. We tested if climate variability can change nitrogen loading from terrestrial to aquatic ecosystems. We used stream nitrogen concen- trations from 2,125 sites and climate data from 301 stations from 30 eco-regions across British Columbia, Canada, to test our ob- jective and to compare it with anthropogenic loading of nitrogen in the same regions. We show that elevated air temperature and associated precipitation resulted in increase in nitrogen loading from terrestrial to aquatic ecosystems. Furthermore, inorganic ni- trogen (IN) loading increased more rapidly than organic nitrogen (ON) with increasing air temperature. Each oC increment annu- al air temperature caused a 24% increase in nitrogen loading to aquatic ecosystems and a 22% increase in ratio of IN: ON concen- trations in stream water. We also show that the coastal mountains ecosystems seem to be more vulnerable to temperature induced nitrogen loss than the interior ecosystems. We suggest that cli- mate warming and elevated loading of nitrogen from terrestrial to aquatic ecosystems will have major implications for the quality of water in freshwater and coastal marine ecosystems.