Dissertation Research: The Role of Anthropogenic Acidification in Stream Nitrogen Cycling: Understanding Stress Effects on Ecosystem Function

本研究将探讨酸雨造成的溪流酸化如何影响地表沃茨的生物脱氮。了解氮吸收的环境控制是必不可少的，因为人类活动不断增加流浓度的氮污染物。虽然已知溪流酸化对鱼类和无脊椎动物群落有负面影响，但对酸对氮循环的影响了解甚少。研究人员将研究弗吉尼亚州谢南多厄国家公园的九条溪流，这些溪流的慢性pH值不同，以推断氮吸收过程如何随时间的酸化而变化。研究人员使用压力反应的基本概念--资源分配从增长转向维持--来指导生物和生态系统尺度的研究。实验室实验的目的是测量生物量特定的氮吸收率，呼吸，和酶活性的叶生物膜从所有流。同位素技术将被用来测量原位流的氮需求，这些速率将结合呼吸和微生物生物量的全流速率，努力解释生态系统的行为在生理环境的压力响应。最后，研究人员将使用同位素技术在四个流沿着pH梯度测量氮的需求下，实验增加的氮浓度水平，以预测未来的流吸收潜力。

This research will investigate how stream acidification caused by acid rain influences the biological removal of nitrogen from surface waters. Understanding environmental controls on nitrogen uptake is essential as human activities continue to increase stream concentrations of nitrogen pollutants. While stream acidification is known to have negative effects on fish and invertebrate communities, there is little understanding of acid effects on nitrogen cycling. The investigators will study nine streams in Shenandoah National Park, VA, that differ in chronic pH to infer how nitrogen uptake processes change with acidification over time.The researchers use a basic concept of stress response - a shift in resource allocation away from growth and towards maintenance - to guide investigations at both organismal and ecosystem scales. Laboratory experiments are designed to measure biomass-specific rates of nitrogen uptake, respiration, and enzyme activity by leaf biofilms from all streams. Isotopic techniques will be used to measure the nitrogen demand of streams in situ, and these rates will be combined with whole-stream rates of respiration and microbial biomass in an effort to interpret ecosystem behavior in the physiological context of stress response. Finally, the investigators will use isotopic techniques in four streams along the pH gradient to measure nitrogen demand under experimentally-increased levels of nitrogen concentration to predict future stream uptake potential.