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

目前的N污染概念模型不适用于浅海生态系统（深度10米），这些生态系统通常由底栖初级生产者（如海草、大藻类和底栖微藻类）主导。在这些生态系统中，由于周围流域的人为变化，它们受到越来越多的外部氮负荷，因此元素循环耦合发生了主要的非线性变化。许多生物地球化学反馈可以加速富营养化，并加剧其一些后果，包括增加有害藻华的发生率。一个由康奈尔大学、弗吉尼亚大学和马萨诸塞州伍兹霍尔生态系统中心的研究人员组成的联盟将利用整个生态系统的“实验”，在未来3-5年里，随着氮污染的地下水到达河口，马萨诸塞州科德角79公顷的沿海系统的外部氮负荷将大约翻一番。这个“实验”反映了从低到中等，最终到高的营养负荷的转变，并跨越了生态区内富营养化阶段的连续体。一项关于严重富营养化生态系统（波士顿港）浅层部分在将废水转移到近海后（2000年氮负荷减少了10倍）恢复情况的研究也将继续进行。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。过程和整个系统尺度的建模将整合研究，并使管理社区能够访问结果。由于氮污染（以及由此产生的富营养化）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，因此本研究具有重要的广泛影响，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.