SGER:RUI:Collaborative: Impacts of a Catastrophic Flood on Nutrient Sources and Organic Processing in Large River Ecosystems

9320303索普，密西西比河及其一些支流目前正在经历灾难性的洪水，极大地改变了它们的典型水文模式。在正常汛期以外发生的极端洪水的生态影响应该对这一重要的热带生态系统产生重大影响，例如改变有机质和养分的正常输入、储存和运输模式。此外，通常无法获得的有机物质来源可能会在此时被引入河流。营养供应和时机的这些变化应该会对密西西比河生态系统的营养动态造成重大干扰。我们假设，目前发生在密西西比河生态系统中的灾难性洪水将通过改变河流食物链中不同有机质来源的作用，导致正常营养过程的转变。这一假设将通过评估四条河流(两条洪水泛滥的平原河流和两条未洪水泛滥的平原河流)的食物网中的稳定同位素比率来验证。在一年的三个日期期间，我们将收集每条河流21个样本单位的5个重复，每个样本代表有机加工者的营养来源。然后，我们将确定样品单位中13C和15N的组成和C/N比。为了确定密西西比河生态系统随时间的变化是否反映了洪水的影响，还是仅仅代表了正常的季节性变化，我们将从四条河流获取样本：密苏里河和密西西比河上游，目前正在经历本世纪最严重的洪水，以及俄亥俄河和瓦巴什河，这是洪水平原河流，尚未被洪水淹没。这项研究的信息将有助于建立一个数据库，用于作出涉及洪泛区在河流生态系统中的作用的管理决策。

9320303 Thorp The Mississippi River and some of its tributaries are currently experiencing catastrophic floods which have significantly modified their typical hydrological patterns. The ecological impacts of an extreme flood occurring outside of the normal flood period should have substantial effects on this important lotic ecosystem, such as altering normal patterns of input, storage, and transport of organic matter and nutrients. In addition, sources of organic matter which are not normally available may be introduced onto the river at this time. These changes in nutrient supply and timing should act as a major disturbance to the trophic dynamics of the Mississippi River ecosystem. We hypothesize that the catastrophic flood presently occurring in the Mississippi River ecosystem will produce a shift in normal trophic processes by altering the role of different sources of organic matter in the riverine food web. This hypothesis will be tested by evaluating the stable-isotope ratios in the food webs of four rivers (two flooded and two unflooded, flood plain rivers). During three dates over a year period, we will collect 5 replicates of 21 sample units per river, each representing a nutrient source of organic processor. We will then determine the composition of 13C and 15N and C/N ratio in the sample units. To ascertain whether changes in the Mississippi River Ecosystem over time reflect the effects of the flood or merely represent normal seasonal variations, we will obtain samples from four rivers: the Missouri and upper Mississippi Rivers, which are currently experiencing the worst floods of the century, and the Ohio and Wabash Rivers, which are flood plain rivers that have not been inundated by flood waters. Information from this study will contribute to a data base useful for making management decisions involving the role of flood plains in river ecosystems.