Nonlinear Feedbacks in Coupled Element Cycles During Eutrophication of Shallow Coastal Ecosystems

然而，目前关于氮污染的概念模型不适用于浅水海洋生态系统(深度10米)，这些生态系统通常由底栖初级生产者，如海草、大型藻类和底栖微藻等主导。在这些生态系统中，元素循环耦合发生了重大的非线性变化，因为它们从周围流域的人为变化中承受着越来越多的外部N负荷。大量的生物地球化学反馈会加速富营养化，并加剧其某些后果，包括增加有害藻华的发生率。来自康奈尔大学、弗吉尼亚大学和伍兹霍尔生态系统中心的研究人员组成的联盟将利用一项全生态系统“实验”，在未来3-5年内，随着N污染地下水的涌入河口，马萨诸塞州科德角79公顷沿海系统的外部N负荷将增加约一倍。这一“实验”反映了从低到中等，最终到高营养负荷的转变，跨越了生态系统区域内富营养化阶段的连续体。还将继续研究严重富营养化的生态系统(波士顿港)在将废水转移到近海(2000年N负荷减少10倍)后的浅部恢复情况。过程和通量测量将侧重于N、C、P、O、S、Fe、Mn和Si循环之间的非线性反馈和相互作用，以及这些循环与富营养化不同阶段生物结构的关系。在过程和整个系统尺度上的建模将整合研究，并使管理层能够了解结果。这项研究具有重大而广泛的影响，因为氮污染(及其导致的富营养化)是对沿海海洋生态系统生态完整性和功能的最大威胁之一，美国三分之二的沿海河流和海湾因氮污染而中度或严重退化。

0420575HowarthCurrent conceptual models of N pollution are inadequate for shallow marine ecosystems (depths 10 m) that are typically dominated by benthic primary producers such as seagrasses, macroalgae and benthic microalgae. Major nonlinear changes in the coupling of element cycles occur in these ecosystems as they receive increasing external N loads from anthropogenic changes in surrounding watersheds. Numerous biogeochemical feedbacks can accelerate eutrophication and aggravate some of its consequences including increased incidences of harmful algal blooms. A consortium of researchers from Cornell University, University of Virginia and The Ecosystems Center in Woods Hole, Ma will take advantage of a whole-ecosystem "experiment" in which external N loading to a 79-hectare coastal system on Cape Cod, MA, will approximately double over the next 3-5 years, as a plume of N-polluted groundwater reaches the estuary. This "experiment" reflects the transition from low to moderate, and ultimately to high, nutrient loading, and spans the continuum of eutrophication stages within the ecosystem zones. A study of the recovery of the shallow portions of a severely eutrophied ecosystem (Boston Harbor) following diversion of wastewater offshore (N-loading decreased 10-fold in 2000) will also be continued. Process and flux measurements will focus on non-linear feedbacks and interactions among the cycles of N, C, P, O, S, Fe, Mn, and Si, along with the relationship of these cycles to biotic structure during different stages of eutrophication. Modeling at both the process and whole-system scales will integrate the research, and make the results accessible to the management community. This research has a significant broader impact since N pollution (and the resulting eutrophication) is one of the greatest threats to the ecological integrity and functioning of coastal marine ecosystems, with two-thirds of coastal rivers and bays in the U.S. moderately or severely degraded from N pollution.