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

本研究将探讨酸雨引起的溪流酸化如何影响地表水中氮的生物去除。随着人类活动不断增加氮污染物的浓度，了解环境对氮吸收的控制是必不可少的。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知之甚少。研究人员将研究弗吉尼亚州谢南多厄国家公园的9条河流，这些河流的长期pH值不同，以推断氮吸收过程是如何随着酸化而变化的。这组科学家使用应激反应的一个基本概念——资源分配从生长转向维持——来指导有机体和生态系统尺度上的调查。实验室实验旨在测量来自所有溪流的叶片生物膜的氮吸收、呼吸和酶活性的生物量特异性速率。同位素技术将用于就地测量河流的氮需求，并将这些速率与全河流的呼吸速率和微生物生物量相结合，以努力解释应激反应生理背景下的生态系统行为。最后，研究人员将利用同位素技术在四条沿着pH梯度的河流中测量在实验中增加的氮浓度水平下的氮需求，以预测未来河流的吸收潜力。

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.