Landscape legacies in rivers: retrospective analyses of changes in ecosystem function across two centuries

物理过程中的自然变化改变了生态系统的结构和功能，其中最大的影响是由自然和人类干扰造成的，这些干扰改变了定义生态系统如何运行的控制机制。河流中的主要生态系统驱动力与作为自然流态一部分的丰水期和枯水期的时间、水量和持续时间有关。对改变的控制机制的生态反应可以是线性的，也可以是非线性的，后者包括一些不可预测的阈值反应，即群落突然转移到生态系统功能的另一种状态。对替代状态的研究可能会决定向不受欢迎的替代状态的某些转变是否既是可预测的，也是可逆的。不幸的是，由于资金的限制，大多数关于替代稳定状态的研究都是理论上的，而且时间非常有限。我们的项目绕过了这些问题，使用博物馆标本的稳定同位素分析来确定100-150年来自然水流状况的变化如何改变了中大型河流中的食物网复杂性。我们最初的项目将集中在密西西比河上游三个地貌不同的地区的主河道、副河道和死水中食物网复杂性的差异，以响应水流制度的变化。食物网将由多个喂食组的实时和博物馆鱼类样本构建。该项目还将有助于缓解人们对河流功能普遍缺乏的认识，因此将把重点放在生物多样性相对下降的程度远远超过北美受影响最严重的陆地生态系统的生态系统。这种关于生态系统驱动因素变化对河流生态系统功能影响的历史知识至关重要，因为我们需要预测未来干扰的影响，如果如预期的那样，全球气候变化和对更多所谓绿色能源的需求增加了建造更多大坝的社会经济压力。最初的项目采取概念验证研究的形式，因此在人员和机会方面受到限制，为我们的全面研究提出了更广泛的影响。然而，该项目将包括来自两所大学的本科生助理，他们将学习田间和实验室技术，并对复杂生态系统的生态学有更广泛的了解。

Natural variations in physical processes alter ecosystem structure and function, with the greatest impacts caused by natural and human disturbances that alter the control mechanisms defining how an ecosystem operates. The primary ecosystem driver in rivers relates to the timing, volume of water, and duration of high- and low-water periods as part of the natural flow regime. Ecological responses to altered control mechanisms can be linear or nonlinear, with the latter including somewhat unpredictable threshold responses where a community shifts abruptly to an alternative state of ecosystem function. Research on alternative states may determine whether some shifts to undesired alternative states are both predictable and reversible. Unfortunately, most studies of alternative stable states have been theoretical and very limited in time due to funding constraints. Our project circumvents these problems by using stable isotope analysis of museum specimens to determine how changes in the natural flow regime over a period of 100-150 years have altered food web complexity in medium to large rivers. Our initial project will focus on differences in food web complexity in the main channel, side channels, and backwaters of three geomorphically diverse areas of the Upper Mississippi River in response to altered flow regimes. Food webs will be constructed from real-time and museum samples of fish in multiple feeding groups. This project will also help alleviate the general dearth of knowledge about the functioning of rivers and will thus focus on ecosystems that have experienced relative declines in biodiversity far greater than those in the most affected terrestrial ecosystems of North America. This historical knowledge of effects of changing ecosystem drivers on functioning of river ecosystems is vital because we need to predict effects of future disturbances if, as expected, global climate changes and the need for more so-called green energy increases socioeconomic pressures to build more dams. The initial project takes the form of a proof-of-concept study and is thus limited in personnel and opportunities for the extensive broader impacts proposed for our full study. However, the project will include undergraduate assistants from two universities who will learn both field and lab techniques as well as gain a broader appreciation of the ecology of complex ecosystems.