How does pulsed stratification alter coastal primary and secondary production? A case study in Liverpool Bay

利物浦湾是一个充满活力的沿海海域，从默西河、迪河和里伯河三条河流接收淡水，从大西洋接收咸水。它是商业渔业的重要区域，也是鱼类产卵的迁徙路线。但是，利物浦湾是一个脆弱的环境，150年来一直暴露在人为输入的影响下。根据最近的指令(欧洲委员会)，环境局(EA)和CEFAS监测营养输入，试图评估它们在推动沿海海域富营养化和有害藻华方面的影响。总体而言，沿海海域占全球初级生产力总量的25%，可能是一个重要的、对气候敏感的碳汇。为了了解利物浦湾与潮汐强迫和淡水输入有关的物理动力学，利物浦的普罗德曼海洋实验室正在指挥利物浦湾海岸观测站：每月，在该海湾对34个站的网格进行采样，并确定物理参数(例如温度、盐度、光照)。我们知道，淡水输入和潮汐推动混合水柱和稳定水柱之间的振荡，这强烈影响营养物质和光照的分布，这是浮游植物生长的关键要求。我们现在假设，在潮汐诱导的水柱稳定性增强期间，浮游植物的生长和碳的固定存在短暂的局部增加。然而，这一假设仍未得到检验。该项目将在利物浦湾的实际环境中直接评估营养和光照分布的变化对初级生产的影响，从而在大学、EA和CEFA之间创造横向的知识转移。它还将提供对该地区的基本了解，这是评估气候变化影响所必需的。具体地说，学生将研究水柱结构如何影响初级生产，并最终评估固定碳的命运。我们考虑了两种潜在的碳损失途径。碳可能进入“微生物循环”，被细菌循环，然后通过平流以溶解的有机碳的形式流失。或者，碳可以积累在颗粒物中，被中游动物捕食，通过沉积或流向其他远洋生物，从而为具有重要商业意义的较高营养水平提供食物来源。该研究由3个假设驱动的主题组成，每个主题最终都会导致同行评议的出版物。首先，学生将参加季节性海岸观测站巡航，以评估食物网结构(即浮游植物、细菌、微型和中游浮游动物的相对分布)与物理水柱结构之间的空间耦合。在第二个主题中，学生将把营养物浓度和浮游植物组成的高频观测与两个固定系泊地点(智能浮标，CEFAS)产生的实时物理数据结合起来，以评估和潜在地发展预测能力，以预测刺激利物浦湾浮游植物水华，特别是有害水华所需的水柱特性。第三个主题将评估在稳定(小潮)和混合(大潮)潮汐周期中，浮游植物、浮游动物和细菌对25小时潮汐周期中水柱稳定性变化的短暂、快速反应。在整个三个主题中，将特别强调碳转移和损失的途径。将鼓励学生通过将观测数据插入一维模型来生成第四个组成部分，该模型可用于进一步探索本地、区域和国际沿海环境中的物理-生物耦合。这项研究具有学术和社会经济两个方面；它将提高我们对利物浦湾物理和生物过程之间耦合程度的理解，这将有利于沿海海洋的总体研究。

Liverpool Bay is a dynamic coastal sea that receives freshwater from 3 rivers, the Mersey, Dee and Ribble, and saltwater from the Atlantic Ocean. It is an important region for commercial fisheries and is a migratory route for spawning fish. But, Liverpool Bay is a fragile environment that has been exposed to anthropogenic inputs for >150 years. Under recent directives (European Commission), the Environment Agency (EA) and CEFAS monitor nutrient inputs, in an attempt to assess their impact in driving eutrophication and harmful algal blooms in coastal seas. In general, coastal seas are responsible for 25% of the global total primary productivity and are potentially an important and climate-sensitive sink for carbon. To understand the physical dynamics in Liverpool Bay related to tidal forcing and freshwater inputs, Proudman Oceanographic Laboratories, (Liverpool), are directing the Liverpool Bay Coastal Observatory: monthly, a 34-station grid is sampled in the bay and physical parameters, (e.g. temperature, salinity, light) are determined. We know that freshwater inputs and the tides drive oscillations between a mixed and stable water column, which strongly influences the distribution of nutrients and light, key requirements for phytoplankton growth. We now hypothesise that during periods of tidal-induced enhancement in water column stability, there is a short-lived and local increase in phytoplankton growth and fixation of carbon. However, this hypothesis remains untested. This studentship will directly assess the impact of alteration in nutrient and light distributions on primary production in a physical context within Liverpool Bay, thus creating lateral knowledge transfer between the University, the EA, and CEFAS. It will also provide a fundamental understanding of the region, needed to estimate impacts of climate change. Specifically, the student will examine how water column structure influences primary production, and ultimately assess the fate of carbon fixed. We consider two potential pathways for carbon loss. Carbon may enter the 'microbial loop' and be recycled by bacteria and lost as dissolved organic carbon via advection. Alternatively, carbon may accumulate in particulate matter and be grazed by mesozooplankton and lost via sedimentation, or to other pelagic organisms, thus providing a food source for commercially important higher trophic levels. The studentship consists of 3 hypothesis-driven themes, each ultimately leading to peer-reviewed publications. First, the student will participate in seasonal Coastal Observatory cruises to assess spatial coupling between food web structure (i.e. the relative distribution of phytoplankton, bacteria, and micro and mesozooplankton) and physical water column structure. In the second theme, the student will couple high-frequency observations of nutrient concentrations and phytoplankton composition, with real-time physical data generated from 2 fixed mooring sites (Smart Buoys, CEFAS) to assess and potentially develop capabilities to predict the water column properties necessary to stimulate phytoplankton blooms, especially harmful blooms, in Liverpool Bay. The third theme will assess the short-lived, rapid response of phytoplankton, zooplankton, and bacteria to changes in water column stability over a 25-h tidal cycle during stable (neap) and mixed (spring) tidal cycles. Throughout the three themes, there will be specific emphasis on the pathway of carbon transfer and loss. The student will be encouraged to generate a fourth component by inserting observational data into a 1-D model which can be used to further explore physical-biological coupling in the local, regional and international coastal environment. This research has academic and socioeconomic aspects; it will improve our understanding of the degree of coupling between physical and biological processes in Liverpool Bay, which will benefit coastal seas studies in general.