Collaborative Research: Influence of the Riparian Zone on Nitrogen Cycling in Streams of Puerto Rico: Role of Nitrification and Denitrification

该项目将调查可能影响热带雨林溪流中氮行为的基本过程。人们对河流水和土壤水之间的水文相互作用以及这种相互作用对热带生态系统中氮循环的潜在影响知之甚少。在波多黎各山地雨林流域收集的初步数据表明，土壤水将大量溶解的氮以铵的形式带入河岸带。然而，在水流中发现的铵或硝酸盐非常少，这表明氮在进入大量水流之前就从溶液中除去了。确定从溶液中去除的氮是通过硝化或反硝化作用以气态形式从生态系统中输出，还是通过植物吸收在内部循环，这一点很重要。假设在这些热带河流中：1)可利用的河侧无机氮支持一个活跃的硝化-反硝化偶联；2)这对偶联对河内氮化学有主要影响。此外，假设通过流侧区的流动路径将对氮动力学产生可预测的影响。为了验证这些假设，将进行以下工作：1)在具有不同流侧水力特征的河流河段建立观测井样带，并测量这些地点的无机氮和有机氮初始浓度；2)测试氮富集对这些站点氮化学的影响；3)估计实验室土壤和沉积物系统中硝化和反硝化的潜力，然后用氮-15示踪技术量化氮损失的具体机制。这种野外测量、野外操作和实验室实验的结合将使我们能够研究典型热带河流生态系统中硝化、反硝化和植物吸收的相对重要性和空间特征。

This project will investigate fundamental processes that are likely to influence the behavior of nitrogen in tropical rain forest streams. Very little is known about hydrologic interactions between stream water and soil water or the potential influences such interactions could have on the nitrogen cycle in tropical ecosystems. Preliminary data collected in montane rain forest watersheds in Puerto Rico indicae that soil water carries large amounts of dissolved nitrogen as ammonium into the riparian zone. Very little ammonium or nitrate is found in stream water, however, suggesting that nitrogen is removed from solution before it enters bulk stream flow. It is important to determine whether the nitrogen removed from solution is exported from the ecosystem in a gaseous form by nitrification or denitrification or whether it is recycled internally by plant uptake. It is hypothesized that in these tropical streams: 1) available stream-side inorganic nitrogen supports an active nitrification- denitrification couple and that 2) this couple has a major influence on in-stream nitrogen chemistry. Furthermore, it is hypothesized that flow paths through the stream-side zone will have a predictable influence on nitrogen dynamics. To investigate these hypotheses work will be performed: 1) to established transect of observation wells on stream reaches with differing stream-side hydraulic characteristics and measure initial concentrations of inorganic and organic nitrogen at these sites; 2) test the effects of nitrogen enrichments on nitrogen chemistry at these sites; and 3) estimate the potential for nitrification and denitrification in laboratory soil and sediment systems, then quantify specific mechanisms of nitrogen loss with nitrogen-15 tracer techniques. This combination of field measurements, field manipulations, and laboratory experiments will enable us to examine the relative importance and spatial characteristics of nitrification, denitrification, and plant uptake in typical tropical stream ecosystems.