Systems off-balance? Exploring the cumulative impacts of enriched coastal waters, altered nutrient ratios and a warming climate on coastal phytoplankt

由于富营养化，沿海生态系统正面临前所未有的压力，这可能导致有害的水华和缺氧。减少河流养分输入和保护沿海生态系统服务的立法措施优先考虑减少磷转移、N：P比率和营养限制特征。当一种无机养分降至其可利用的浓度以下时，生产力受到该养分从有机物或光合作用生物直接利用溶解的有机养分的速度的限制。为了评估增加N：P对磷限制的影响程度，将在田间采集样品中测定溶解的无机N、P、Si和溶解的有机磷。还将分析碱性磷酸酶活动率，以确定浮游植物和细菌对DOP的利用。将这些与营养物质补充培养相结合，将有助于我们了解北海营养物质限制的作用。将结果与相关的盐度梯度联系起来，将利用一年一度的Cefas Endeavour夏季北海调查巡航，对夏季磷酸盐限制的状况和影响进行详细评估。全年还将与CEFA、环境局和苏格兰海洋组织一起进行更短的采样旅行，以评估两个不同地点--斯通海文和泰晤士河--营养限制的季节性。还将使用监督小组的数据和我们之前测试过的公开数据集，编制英国海域河流营养物质浓度和近海营养物质循环的综合数据集。这将确定i)过去50年来我们的河流和海洋中N：P的变化程度，以及ii)这在多大程度上影响了硝酸盐和磷酸盐限制之间的平衡。学生还将使用现有的基于卫星和海洋的浮游植物丰度和类型数据来探索使用这些数据来表明浮游植物对N：P输入或现有数据中P限制的响应变化的可能性。与气候有关的变化(温度、环流和混合、春季水华动态等)也将被考虑到这一分析中，并可通过生物地球化学建模工作进一步探索。该项目还将涉及使用由Cefas和其他机构开发的浮游生物指数，以评估与MSFD下的评估相关的中上层生物多样性的变化，并了解食物网的潜在变化。这将对气候变化时期营养管理对海洋群落的影响进行更全面的评估，并探讨气候和水质的累积影响和相互作用。这将提供关于不同养分管理措施对国家/国际状况评估、不断变化的基线和重要生态系统商品和服务的潜在影响的信息。

Coastal ecosystems are under unprecedented stress through eutrophication which can lead to harmful blooms and hypoxia. Legislative measures to reduce riverine nutrient inputs and preserve coastal ecosystem services have prioritised reductions in phosphorus shifting the N:P ratio and nutrient limitation characteristics. When an inorganic nutrient drops below its useable concentration, productivity is limited by the rate at which that nutrient can be recycled from organic matter or photosynthetic organisms can directly utilise dissolved organic nutrients. To assess the degree to which increasing N:P is affecting phosphate limitation, dissolved inorganic N, P, Si and dissolved organic phosphorus will be determined in samples collected in the field. Alkaline phosphatase activity rates will also be analysed to determine utilisation of DOP by phytoplankton and bacteria. Combining these with nutrient add-back incubations will help us understand the role of nutrient limitation across the North Sea. Linking the results to associated salinity gradients will allow a detailed assessment of the status and impacts of phosphate limitation in the summer period, making use of the annual Cefas Endeavour summer North Sea survey cruise. Additional shorter sampling trips will be done throughout the year with Cefas, the Environment Agency and Marine Scotland to assess the seasonality of nutrient limitation at 2 contrasting locations - Stonehaven and the Thames. A comprehensive dataset of riverine nutrient concentrations and offshore nutrient cycles in UK seas will also be compiled using data from the supervisory team and publicly available datasets we have tested previously. This will establish i) the degree to which N:P has changed over the past >5 decades in our rivers and seas and ii) how much this has affected the balance between nitrate and phosphate limitation. The student will also use existing satellite and ocean-based data for phytoplankton abundance and type to explore the possibility of using such data to indicate changes in phytoplankton response to N:P input or P limitation in existing data. Climate-related changes (temperature, circulation and mixing, Spring bloom dynamics etc) will also be considered in this analysis and could be further explored by biogeochemical modelling work. The project will also involve the use of the Plankton Index, developed by Cefas and others, to assess changes in pelagic biodiversity of relevance to assessments under the MSFD and understanding potential shifts in food webs. This will provide a more holistic assessment of the impact of nutrient management on marine communities in a period of changing climate, and explore the cumulative impacts and interactions of climate and water quality. This will provide information about the potential impact of different nutrient management measures on national/international status assessments, shifting baselines and vital ecosystems goods and services.