Sediment-Water Column Exchange of Nutrients in Coastal and Shelf-Sea Waters

在过去的50年里，由于人类的影响，进入北海等沿海海域的营养元素氮、磷和硅的浓度有所增加。沿海海域在控制地球生命所必需的这些元素的循环方面非常重要，特别是因为世界上近三分之一的海洋初级生产发生在这些区域。初级生产是浮游植物的生长-漂浮的微型植物也被称为藻类。藻类的生长是由这些营养元素推动的，它从大气中吸收二氧化碳，从而有助于调节这种温室气体在大气中的浓度。直到最近，人们还认为北海从河流和大气中获得了足够的营养，以维持在那里观察到的大型浮游植物水华。在春季结束时，浮游植物几乎耗尽了水柱中所有可用的营养物质，它们死亡并沉入海底。人们认为，主要来自河流和海洋的营养物质在冬季的再生足以在春季再次开始循环。然而，人们发现，来自河流和周围海洋的实际数量少于春季重新开始循环所需的数量。现在的假设是，在搅动沉积物的过程中（即通过海床表层的再悬浮）释放的沉积物源将水中的营养物质浓度提高到足以在春季刺激浮游植物大量繁殖的水平，而春季的光照水平也有利于藻类生长。沉积物再悬浮可由强风、海浪、潮汐以及捕鱼中使用的拖网渔具造成。在这项拟议的研究中，我们将调查沉积物再悬浮对营养物质的影响，并确定它是一个源（将营养物质从沉积物中放入水中）还是一个汇（将营养物质从水中取出进入沉积物）。为了进行这项研究，我们将参加对北海3个区域的研究巡航，在那里我们将在海床上放置设备以模拟沉积物的搅拌。我们将收集沉积物再悬浮和营养盐释放的数据，并测量没有再悬浮的营养盐背景转移。我们还将收集沉积物，在实验室中在更受控的条件下研究相同的过程。这些数据将与该系统的计算机模型一起使用，以测试模型，并有助于更好地预测再悬浮事件对水柱中营养物质的影响。拟议项目的结果将使我们更好地了解营养物和沉积物在沿海和陆架海中的相互作用及其对初级生产的影响。因此，这项工作将有助于量化再悬浮在控制区域和全球预算中营养物命运方面的作用。收集到的数据将为制作这些系统的数学描述的建模人员提供额外的工具和信息，以帮助有效管理沿海沃茨的质量。

Over the last 50 years concentrations of the nutrient elements nitrogen, phosphorus and silicon entering coastal seas such as the North Sea have increased due to Human influences. Coastal seas are very important in controlling the cycling of these elements essential to life on Earth, particularly as nearly a third of the world's ocean primary production takes place in these regions. Primary production is the growth of phytoplankton - floating microscopic plants also known as algae. Algal growth, which is fuelled by these nutrient elements, takes up carbon dioxide from the atmosphere, thus helping to regulate atmospheric concentrations of this greenhouse gas. Until recently, it was thought that the North Sea receives enough nutrients from rivers and the atmosphere to sustain the large phytoplankton blooms that are observed there. At the end of spring; the phytoplankton have used up nearly all the available nutrients in the water column and they die and sink to the sea bed. It was thought the regeneration of nutrient levels occurring over the proceeding winter period mainly from rivers and the oceans was sufficient to start the cycle again in the spring. However, it has been discovered that the actual amount coming in from rivers and surrounding seas is less than that needed to start the cycle again in the spring. It has now been hypothesised that a sediment source released during the stirring up of sediments (i.e. through resuspension of the surface layers of the sea bed) elevates the concentration of nutrients in the water to levels high enough to stimulate large phytoplankton blooms in the spring when light levels also favour algal growth. Sediment resuspension can be caused by strong winds, waves, tides and also by trawling gear used in fishing. In this proposed study, we will investigate the impact of sediment resuspension on nutrients and determine if it is either a source (puts nutrients from the sediment into the water) or a sink (takes nutrients out of the water into the sediment). To do this study we will take part in research cruises to 3 areas of the North Sea where we will place equipment on the sea bed to simulate the stirring of the sediments. We will collect data on sediment resuspension and nutrient release as well as make measurements of background transfer of nutrients without resuspension. We will also collect sediment to study the same processes in the laboratory under more controlled conditions. The data will be used with computer models of this system to test the models and help to provide better predictions of the impact of resuspension events on nutrients in the water column. The results of the proposed project will provide us with a better understanding of the role of nutrients and sediment interactions in coastal and shelf seas and the influence this has on primary production. Consequently, this work will contribute to quantifying the role of resuspension in controlling the fate of nutrients in regional and global budgets. The gathered data will give modellers who produce mathematical descriptions of these systems, additional tools and information to help effectively manage the quality of coastal waters.