Nitrogen is Falling into Remote Lakes
People on this planet are producing ten times more nitrogen now than they did a century ago, and some of it ends up in far-flung lakes where it alters aquatic ecology.
Remote lakes throughout North America and Europe are gaining nitrogen (N) that encourages heftier growth of algae.
The nitrogen arises from human activities, such as burning fossil fuels, that release nitrogen into the air. The nutrient gets carried by wind beyond inhabited areas and falls onto wilderness landscapes.
To find out about the extent of the nitrogen influx, this study examined nitrogen and phytoplankton levels of lakes in natural settings. None of the lakes receive nitrogen directly from sewage, agriculture or other human activities in the watershed. Nearly 8400 lakes in Europe, Canada and the United States were assessed, scattered from Spain to Finland and Alaska to Florida.
The same pattern was found for lakes in both North America and Europe. The concentration of dissolved inorganic nitrogen in the water corresponds to the amount of nitrogen being deposited from the atmosphere over the region each year.
Large areas of the two continents have lakes with raised nitrogen levels. Lakes in Slovakia and Czech Republic of central Europe have gained the most nitrogen, while the lowest amounts have fallen in Sweden and the northern US Rocky Mountains. Among all the lakes, concentrations of dissolved inorganic nitrogen varied 30-fold, while nitrogen inputs ranged by a factor of ten.
The lakes chosen for this study were all naturally low in nutrients, enough to limit the growth of aquatic organisms. The lakes acquiring the most nitrogen also had a three times higher ratio of phytoplankton biomass. This demonstrates how the addition of nitrogen from the atmosphere is moving the lakes to more eutrophic ecosystems. For some lakes, nitrogen no longer restricts phytoplankton productivity and instead phosphorus (P) is now the limiting nutrient.
Ann-Kristin Bergström and Mats Jansson. 2006. Atmospheric nitrogen deposition has caused nitrogen enrichment and eutrophication of lakes in the northern hemisphere. Global Change Biology. 12(4): 635-643.