Collaborative Research: Effects of Flow Regime Shifts, Anticendent Hydrology, Nitrogen Pulses and Resource Quantity and Quality on Food Chain Length in Rivers

河流的水流模式会影响植物和动物的丰度以及支持渔业的食物网。冲刷河床的严重洪水可能会取代或杀死植物和动物，然而，人们对洪水（或干旱）或这些年份的时间如何影响食物网的复杂性和多样性知之甚少。一些研究表明，河流流量比植物产量对食物网中能量流动的影响更大，但人们对植物食物的质量如何影响食物链和生物多样性知之甚少。这项研究将提供基本信息，说明多年来洪水和干旱的时间如何影响水质（河流的硝酸盐输入）、初级生产以及食物网中较高位置动物（如鱼类）的生产。研究人员将在水文学和生态学方面进行综合研究，以改善干旱陆地河流的管理。这项工作将涉及从幼儿园到研究生阶段的基础知识和教育。该项目将产生许多更广泛的影响，包括培养几名本科生、研究生和一名博士后。研究人员将与一个非营利组织合作，将项目发现整合到一个由大自然保护协会赞助的关于河流干涸的现有公民科学项目中，并为K-5年级的学生制定一个环境教育项目。最后，研究团队将建立一个创新的开源、分布式的统计方法在生态学中的应用研究生研讨会。研究人员将研究跨越降雨时间梯度的河流，以检查变化的水文制度在改变干旱陆地河流中氮供应、能量供应和食物网结构中的作用。本研究将：1)量化食物质量、能量供应和能量效率对营养结构的影响；2)量化洪水之间的时间间隔对植物生产和营养结构的影响；3)通过直接死亡、食物网底部植物的转移和食物网结构来量化水流状态变化对营养结构的影响。拟议的研究活动包括水文制度的表征，跨水文气候梯度的食物网分析，以及氮供应的操纵。极端事件统计和光谱分析将表征亚利桑那州12个研究地点的洪水间隔和水流状态变化的特性，这些地点跨越降雨时间和水文变化（季风与冬季降水优势）的梯度。衍生的水文指标将与生态系统代谢、氮供应、次级消费者能量效率、资源化学计量和本地能源比例等指标结合使用，作为食物链长度和营养结构的预测变量，以了解将能量学和水文与食物链长度联系起来的机制。这项比较研究包括同一生物地理省内的12条河流，这些河流以藻类为主的食物来源和相似的生态系统规模为特征（1 -3级河流）。此外，研究人员将在6条河流中进行氮富集实验，以解开水流对氮循环的间接影响与对植物和动物的直接影响。

The pattern of water flow in a river can affect the abundance of plants and animals and the food web that supports fisheries. Severe floods that scour the riverbed can potentially displace or kill plants and animals, however, little is known about how floods (or droughts) or the timing of these across years affects the complexity and diversity of food webs. Some work suggests that river flow is a stronger determinant than the quantity of plant production on the flow of energy through the food web, but little is known about how the quality of plant food affects food chains and biodiversity. The study will provide fundamental information on how the timing of floods and droughts across years influences water quality (nitrate inputs to rivers), primary production, and the production of animals higher in the food web, such as fish. The researchers will produce a synthesis of research in hydrology and ecology to improve the management of arid land rivers. This work will reach across fundamental knowledge to education, from kindergarten to graduate levels. The project will have numerous broader impacts including training of several undergraduates, graduate students, and a postdoc. Researchers will work with a non-profit group to integrate project findings into an existing citizen science program on river drying sponsored by The Nature Conservancy, and develop an environmental education program for grades K-5. Finally, the research team will establish an innovative open source, distributed graduate seminar on application of statistical methods in ecology.Researchers will study streams spanning a gradient in the timing of rainfall to examine the role of changing hydrologic regimes in altering nitrogen supply, energy supply and food web structure in arid land streams. This proposal will: 1) Quantify the effect of food quality, energy supply and energetic efficiencies on trophic structure, 2) Quantify the effects of time between floods on stimulation of plant production and trophic structure, and 3) Quantify the effect of changes in flow regime on trophic structure via direct mortality, shifts in plants at the base of the food web, and the structure of the food web. Proposed research activities include characterization of the hydrologic regime, analysis of food webs across a hydroclimate gradient, and manipulation of nitrogen supply. Extreme event statistics and spectral analyses will characterize properties of flood intervals and flow regime shifts across 12 study sites spanning a gradient in timing of rainfall and hydrologic variation (monsoon vs. winter precipitation dominance) in Arizona. Derived hydrologic metrics will be used in combination with measures of ecosystem metabolism, N supply, secondary consumer energetic efficiencies, resource stoichiometry, and the proportion of autochthonous energy sources as predictor variables of food chain length and trophic structure to understand the mechanisms linking energetics and hydrology to food chain length. This comparative study includes 12 streams within the same biogeographic province that feature an algal-dominated food source and similar ecosystem size (1st-3rd order streams). Additionally researchers will conduct a nitrogen enrichment experiment in 6 streams to disentangle the indirect effects of water flow on nitrogen cycling versus the direct effects on plants and animals.