Spatial heterogeneity and biological productivity in a large river ecosystem

我的研究计划的长期目标是在圣劳伦斯河（SLR）的物理和化学因素和较低的食物网过程之间的相互作用模型。确定支持食物网的碳的主要来源是理解水生生态系统结构和功能的基本步骤。一些研究认为陆地碳和异养在河流食物网中起主导作用，而另一些研究则强调原位光合来源的重要性。在任何一种情况下，河流中的运输物质都会被光或细菌活动转化，这会影响其生物利用度和流向下游消费者。本研究旨在了解物质（例如营养物质，浮游植物）和生物在栖息地（连通性）之间的转移如何控制食物供应和生物多样性，这对于确定支持大型河流生态系统食物网和生产力的碳源至关重要。圣皮埃尔湖（LSP）是SLR最大的河流湖泊（~400平方公里），以其高生产力而闻名。然而，有一个很大的差距，在知识的命运离开LSP到河流河口，连接到河口过渡区（ETZ）的物质。ETZ是光合作用的光限制区，标志着淡水与盐水相遇的地方。它被认为是其非常高的生产力，并作为一个大型苗圃区的几种鱼类。我推测，在ETZ的生产力很大程度上是依赖于从河流河口，这反过来又收到了高溶解有机物和营养物质从LSP输送的材料。我最近确定，LSP可以通过在春季破冰期间漂流的大量冰藻来显著提高下游生产力。这一发现为理解大型河流的水产生产力开辟了一个全新的视角。该NSERC SLR生态系统计划整合了：1）ETZ作为大型河流的关键栖息地，通过碳和沉积物的交换充当通往海洋的门户; 2）北温带河流的冬季生物活动，其中河冰生物群可能对年度初级生产力和碳转移有很大贡献沿着食物网。

The long-term objective of my research program is to model interactions between physical and chemical factors and lower food web processes in the St. Lawrence River (SLR). Identifying the primary sources of carbon supporting food webs is a fundamental step towards understanding the structure and function of aquatic ecosystems. Some studies have argued for a dominant role of terrestrial carbon and heterotrophy in river food webs while others have stressed the greater importance of in situ photosynthetic sources. In either case, the transported matter in the river is transformed by light or bacterial activity which affects its bioavailability and flow to downstream consumers. This study aims at understanding how the transfer of matter (e.g. nutrients, phytoplankton) and organisms between habitats (connectivity) is controlling food availability and biodiversity, important for determining carbon sources supporting food webs and productivity in large river ecosystems. Lac St. Pierre (LSP) is the largest fluvial lake (~400 km2) of the SLR and is well recognized for its high productivity. However, there is a large gap in knowledge about the fate of matter leaving LSP into the fluvial estuary, which connects to the estuarine transition zone (ETZ). The ETZ is light-limiting for photosynthesis and marks where freshwater meets saltwater. It is recognized for its very high productivity, and as a large nursery area for several fish species. I hypothesize that much of the productivity in the ETZ is dependent on transported material from the fluvial estuary, which in turn receives high dissolved organic matter and nutrients from LSP. I recently established that LSP can contribute significantly to downstream productivity through large populations of ice-algae drifting during the ice-break period in spring. This finding opens a totally new perspective for understanding aquatic productivity in large rivers. This NSERC program on the SLR ecosystem integrates: 1) ETZ as a key habitat of large rivers, acting as a gateway to the sea through the exchanges of carbon and sediments; and 2) winter biological activities in north-temperate rivers, in which river ice biota may substantially contribute to annual primary productivity and carbon transfer along the food web.