Automated Determination of Total Dissolved Nitrogen: A Critical Technique for Identifying Nutrient Sources, Cycling Rates and Fate in Freshwaters

人类活动引起的无机氮(N；如铵和硝酸盐)的升高威胁到水生生态系统的健康以及饮用水供应的安全和质量。这也从根本上改变了地表水中溶解的碳和氮(C：N)的比例，从而导致连锁效应，如增加光合作用和呼吸速率，提高营养循环速率，并使地表水转向滋扰和产生毒素的藻类和蓝藻。绝大多数生物可利用的氮往往是有机氮，在偏远和北部的淡水中，这接近100%的有机氮，但由于方法的不同和旧仪器的问题，这些有机氮太少被测量，而且由于方法的不同和旧仪器的问题，实验室之间的测量往往相差很大。即使在偏远和北部的淡水中，这种溶解的有机氮在生态系统如何运作以及碳是长期储存在沉积物中还是作为二氧化碳流失到大气中都发挥着关键作用。为高质量的总溶解氮分析，需要资金购买一台分析仪器Jena Multi N/C 3100。该仪器包括一个高温和高回收系统，可以提供非常可靠的分析。我们的学生将立即使用该仪器，这样他们就可以在不影响质量的情况下按时完成他们的研究项目。

Elevated inorganic nitrogen (N; such as ammonium and nitrate) by human activities threatens aquatic ecosystem health and the security and quality of drinking water supplies. This also radically changes the dissolved carbon:nitrogen (C:N) ratio in surface waters leading to cascading effects such as increased photosynthesis and respiration rates, increases nutrient cycling rates, and shifting surface waters towards nuisance and toxin-producing algae and cyanobacteria. The vast majority of biologically available N is often organic N and this approaches 100% organic N in remote and northern freshwaters, yet this organic N is too infrequently measured and too often measurements vary widely from lab-to-lab due to differences in methods and problems with older instruments. Even in remote and northern freshwaters, this dissolved organic N plays a critical role in how ecosystems function and whether C is stored in sediments for the long-term or lost to the atmosphere as carbon dioxide. Funds are requested to purchase an Analytik Jena Multi N/C 3100 for high quality analysis of total dissolved N. This instrument includes a high-temperature and high-recovery system that can provide very reliable analyses. This instrument will immediately be used by our students so they may complete their research project on time and without compromising quality.