Effects of Atmospheric Nitrogen Deposition on Phosphorus Limitation of Freshwater Zooplankton

氮是重要的植物营养元素，它可以通过大气输送，并通过降雨沉积到陆地和水生生境中。 近几十年来，由于人类活动，氮沉降大大增加，这主要是由于化肥施用量的扩大和化石燃料燃烧过程中硝酸盐（NO3）的形成。 这项研究将试图确定是否N沉降影响湖泊食物网的化学成分的微观植物（浮游植物），形成湖泊食物网的基础。 具体来说，这些研究人员假设，增加氮输入湖泊导致浮游植物成为另一个关键元素，磷（P）的强烈限制。 当磷有限时，浮游植物产生的生物量具有非常低的磷含量，因此可能变得营养上不适合下一个摄食水平，浮游动物的生长。 （浮游动物反过来又为鱼类提供了重要的食物基础，包括那些参与娱乐和商业渔业的鱼类。为了验证这一点，这些研究人员将在科罗拉多中部和挪威南部的湖泊中测量接受不同水平氮沉积的浮游动物生长的磷限制。 这些研究人员还将进行更大规模的实地研究，故意操纵N输入到部署在正常条件下接收低N沉积的湖泊中的实验性围隔生态系统。 这项研究将有助于基本了解湖泊食物网如何运作，同时也提供了有关人类活动对看似原始的生态系统及其所支持的食物网的间接但潜在重要影响的潜在重要信息。

The important plant nutrient, nitrogen (N), can be transported in the atmosphere and deposited into terrestrial and aquatic habitats in rainfall. During recent decades, N deposition has greatly increased as a result of human activities, largely due to expansion of fertilizer application and of formation of nitrates (NO3) during fossil fuel burning. This study will try to determine if N deposition affects lake food webs by changing the chemical composition of the microscopic plants (phytoplankton) that form the base of lake food webs. Specifically, these investigators hypothesize that increasing inputs of N to lakes cause the phytoplankton to become strongly limited by another key element, phosphorus (P). When P-limited, phytoplankton produce biomass that has a very low P content and thus potentially become nutritionally unsuitable for growth of the next feeding level, the zooplankton. (Zooplankton, in turn, provide an important food base for fish, including those that are involved in recreational and commercial fisheries.) To test this, these researchers will measure P limitation of zooplankton growth in lakes receiving different levels of N deposition in central Colorado and in southern Norway. These investigators will also 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 help in basic understanding of how lake food webs work while also providing potentially important information about an indirect but potentially important impact of human activity on seemingly pristine ecosystems and the food webs they support.