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。沿海海洋对控制这些对地球上的生命至关重要的元素的循环非常重要，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。主要的生产是浮游植物的生长-漂浮的微型植物，也被称为藻类。在这些营养元素的推动下，藻类的生长吸收了大气中的二氧化碳，从而有助于调节大气中这种温室气体的浓度。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物质，足以维持在那里观察到的大型浮游植物的大量繁殖。在春天结束时，浮游植物几乎耗尽了水柱中所有可用的营养物质，它们死亡并沉入海床。人们认为，主要来自河流和海洋的营养水平在之前的冬季期间重新出现，足以在春季重新开始这种循环。然而，人们发现，来自河流和周围海域的实际排放量低于春季重新启动循环所需的水量。现在的假设是，在沉积物搅动过程中释放的沉淀物来源(即通过海床表层的再悬浮)将水中营养物质的浓度提高到足以在春季刺激大型浮游植物繁殖的水平，而此时的光照水平也有利于藻类的生长。沉积物再悬浮可由强风、海浪和潮汐引起，也可由用于捕鱼的拖网渔具引起。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，并确定它是源(将营养物质从沉积物中放入水中)还是汇(将营养物质从水中带到沉积物中)。为了做这项研究，我们将参加北海三个区域的研究巡航，在那里我们将在海床上放置设备来模拟沉积物的搅拌。我们将收集沉积物再悬浮和养分释放的数据，并对无再悬浮的营养物质的本底转移进行测量。我们还将收集沉积物，在更受控制的条件下在实验室研究相同的过程。这些数据将与该系统的计算机模型一起使用，以测试模型，并帮助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质和沉积物在沿海和陆架海相互作用的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质命运方面的作用。收集到的数据将为为这些系统提供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水域的质量。

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.