Responses of a Major Land Margin Ecosystem to Changes in Terrestrial Nutrient Inputs: Internal Nutrient Cycling, Production and Export

研究营养循环过程及其与自养生产的关系在自然生态系统分析中具有重要意义。尽管陆地-海洋界面的水生生态系统是生物圈中生产力最高的生态系统之一是不言而喻的，但令人惊讶的是，人们对陆地的养分输入、这些养分的去向和循环以及相关的有机生产知之甚少。最近的分析表明，河口一般可能是异养的(初级生产总值低于群落呼吸)，这意味着它们是海洋的营养源，而不是陆地输入的汇。在拟议的研究计划中，一个由生态学家、地球化学家、模型师和海洋学家组成的具有凝聚力的跨学科团队已经被聚集起来，以解决两个假设：1)切萨皮克湾作为沿海平原河口的例子，支持一个N限制的自养(GPP超过R)群落，由于内部循环和转化过程，该群落将DON输出到近海；春季陆地输入的氮通过浮游植物同化和生物量沉积以及随后的底栖生物更新和夏季垂直运输与夏季生产力最大值相耦合。在这个为期5年的项目中，将通过定期测量主要盐度梯度沿线各站的水文变量和关键的碳和营养过程，并有时强调春季和夏季，来检验这些假设。河口，在这种情况下，特别是切萨皮克湾，是重要的生态互动区，调解大陆和海洋的交换过程。它们提供了广泛的可开发资源，就像河口系统本身一样脆弱。这样的研究将使沿海生态系统的管理更有见地。

The study of nutrient cycling processes and their relation to autotrophic production is of fundamental importance in the analysis of natural ecosystems. While it is axiomatic that aquatic ecosystems at the land-sea interface are among the most productive in the biosphere, surprisingly little is known about nutrient inputs from land, fate and cycling of these nutrients, and associated organic production. Recent analyses have suggested that estuaries may be generally heterotrophic (gross primary production is less than community respiration), implying that they are nutrient sources to the sea rather than sinks of terrestrial inputs. For the proposed research program, a cohesive interdisciplinary team of ecologists, geochemists, modelers and oceanographers has been assembled to address two hypotheses: 1) Chesapeake Bay, as an example of a coastal plain estuary, supports a N-limited autotrophic (GPP exceeds R) community which exports DON offshore as a consequence of internal cycling and transformation processes; and 2) spring inputs of N from land are coupled to the summer productivity maximum by phytoplankton assimilation and biomass deposition in spring with subsequent benthic regeneration and vertical transport during summer. These hypotheses will be tested in this 5-year project by making regular measurements of hydrographic variables and key carbon and nutrient processes at stations along the main salinity gradient and at times emphasizing spring and summer periods. Estuaries, in this cases especially the Chesapeake Bay, are important zones of ecological interaction mediating the exchange processes of continents and oceans. They provide a broad array of exploitable resources as fragile as the estuarine system itself. Research such as this will allow the more informed management of coastal ecosystems.