Nitrogen Deposition

Nitrogen deposition (2006–2008)

During recent decades, atmospheric N deposition to lakes has greatly increased as a result of human activities. This study is attempting to determine if N deposition affects lake food webs by changing the elemental composition of phytoplankton. Specifically, we hypothesize that increasing inputs of N to lakes cause the phytoplankton to become strongly limited by phosphorus (P). When P-limited, phytoplankton produce biomass that has a very low P content and thus potentially become nutritionally unsuitable for growth of zooplankton. In summer 2006 and 2007 we tested for P limitation of phytoplankton and zooplankton growth in lakes receiving different levels of N deposition in central Colorado and in southern Norway. In summer 2008 we will perform a larger scale field study that deliberately manipulates N inputs to experimental mesocosms deployed in a lake that receives low N deposition under normal conditions. This study will provide potentially important information about an indirect but potentially significant impact of human activity on seemingly pristine ecosystems and the food webs they support.



NSF Ecology Program