REU: Stability of a Stream Ecosystem to Disturbance by Flooding and Drying

研究人员将研究在更大的沙漠景观中，河流生态系统在多大程度上是能量和氮的来源或汇。能量流可以概括为初级生产与呼吸的比值（P/R），氮循环可以概括为固氮与反硝化的比值（F/D）。对一个系统是源还是汇的判断将由嵌套的层次产生，范围从藻类组合到整个排水系统。结果将在一定程度上测试蒸汽生态分层方法的效用。山洪和干旱所产生的扰动效应，每一个不同的水文极端特征，将在层次结构的背景下进行研究。子系统的稳定性将在面对每种干扰和两者的组合时进行评估。对表层和潜流区有机碳和无机氮之间相互作用的详细研究将用于探索子系统相互作用如何影响每个子系统的稳定性。假设垂直交换增强了两个子系统的弹性。最后，将使用一个模拟模型来模拟扰动制度对整个排水系统的影响。结果将显示数年的扰动制度如何影响溪流与相邻生态系统的联系：下游水库、地下水含水层或平行河岸群落。研究人员完全有资格运行提案研究项目，有足够的设施，并有良好的发表记录。

The investigators will study the extent to which a stream ecosystem is a source or sink for energy and nitrogen in the larger desert landscape. Energy flow will be summarized as the ratio of primary production to respiration (P/R) and nitrogen cycling as the ratio of dinitrogen fixation to denitrification (F/D). Judgments of whether a system is a source or sink will be generated for nested hierarchys, ranging from the algal assemblage to the entire drainage. Results will test in part the utility of hierarchical approaches to steam ecology. Disturbance effects generated by flash flooding and drying, each characteristic of a different hydrologic extreme, will be studied in the context of the hierarchy. Stability of subsystems will be evaluated in the face of each disturbance and combinations of the two. Detailed study of interactions between surface and hyporheic zones involving organic carbon and inorganic nitrogen will be used to explore how subsystem interaction influences the stability of each. The hypothesis is that vertical exchange enhances resilience of both subsystems. Finally, a simulation model will be used To simulate the effect of disturbance regimes on the whole drainage system. Results will show how disturbance regimes of several years length influence the linkage of streams with adjacent ecosystems: downstream reservoirs, groundwater aquifers, or parallel riparian communities. The investigators are well qualified to run the proposal research program, have adequate facilities and have an excellent publication record.