Collaborative Research: pH Dynamics and Interactive Effects of Multiple Processes in a River-Dominated Eutrophic Coastal Ocean

海洋酸化（OA）是指由于吸收大气中的二氧化碳（CO2）而导致海洋pH值降低（或酸度增加）。为了了解开放海洋如何受到OA的影响，已经做了大量的研究，但沿海系统却很少受到关注。在墨西哥湾北部（nGOM）陆架区域，底部水域的pH值比工业化前海洋表层的pH值低0.45个单位，而整个海洋的pH值总体下降了0.1个单位。即使pH值的微小变化也会极大地影响海洋中的碳酸盐化学，因此这些看似微小的变化会对海洋的生物和化学产生更大的影响。研究人员计划研究nGOM的沿海OA，这是一个受密西西比河大量营养物质影响的地区。这些主要来自肥料的人为氮的输入导致呼吸速率增加，从而降低水柱中的氧浓度，达到夏季缺氧的程度。本研究将告诉我们，受富营养化和缺氧影响的沿海水域的OA将如何影响该地区的化学和生物学。研究人员致力于墨西哥湾和东海岸地区的推广项目，与K-12学生和教师进行互动，对本科生/研究生进行培训，并开展各种推广工作（OA家庭研讨会，为公众和联邦、州和地方代表举办讲座）。此外，还将建立一个项目网站，向更广泛的受众传播研究结果。海洋对大气二氧化碳（CO2）的吸收增加导致海水pH值和碳酸盐矿物饱和状态下降0.1个单位，这一过程被称为海洋酸化（OA），它威胁到海洋生物的健康，改变海洋生态系统和生物地球化学过程。相当多的注意力集中在了解OA对公海的影响上，但对沿海地区的关注较少。最近的研究表明，墨西哥湾北部大陆架底部水域的pH值可能比工业化前的值低0.45个单位。这是因为二氧化碳输入（包括大气输入和原位呼吸）增加造成的酸化降低了海水的缓冲能力。这种相互作用将随着时间的推移而增加，预计到本世纪末，nGOM夏季底水pH值将降低0.85个单位，并将碳酸盐矿物推向欠饱和状态。来自特拉华大学和路易斯安那大学海洋联盟的研究人员将开展一个结合现场、实验室和建模的项目，以解决以下问题。(1)受大而富营养的密西西比河影响的沿海水域酸化的物理、化学和生物控制是什么？(2)沿海水体酸化、富营养化和缺氧之间的联系是什么？(3)底层水体低pH、高CO2浓度对秋冬季和暴风期混合水体CO2放出有何影响？(4)人为强迫下河流输入变化对沿海水体酸化有何影响？本研究的结果旨在进一步了解全球墨西哥湾和河流主导的陆架生态系统中受富营养化和缺氧影响的沿海水域海洋酸化过程。

Ocean acidification (OA) refers to the lowering of ocean pH (or increasing acidity) due to uptake of atmospheric carbon dioxide (CO2). A great deal of research has been done to understand how the open ocean is influenced by OA, but coastal systems have received little attention. In the northern Gulf of Mexico (nGOM) shelf region, pH in bottom waters can measure up to 0.45 units less than the pH of the pre-industrial surface ocean, in comparison to the 0.1 overall pH decrease across the entire ocean. Carbonate chemistry in the ocean is greatly influenced by even small changes in pH, so these seemingly minor changes lead to much greater impacts on the biology and chemistry of the ocean. The researchers plan to study coastal OA in the nGOM, a region subject to high inputs of nutrients from the Mississippi River. These inputs of anthropogenic nitrogen mostly derived from fertilizers leads to increased respiration rates which decreases oxygen concentrations in the water column to the point of hypoxia in the summer. This study will inform us how OA in coastal waters subject to eutrophication and hypoxia will impact the chemistry and biology of the region. The researchers are dedicated to outreach programs in the Gulf and east coast regions, interacting with K-12 students and teachers, undergraduate/graduate student training, and various outreach efforts (family workshops on OA, lectures for the public and federal, state, and local representatives). Also, a project website will be created to disseminate the research results to a wider audience. Increased uptakes of atmospheric carbon dioxide (CO2) by the ocean has led to a 0.1 unit decrease in seawater pH and carbonate mineral saturation state, a process known as Ocean Acidification (OA), which threatens the heath of marine organisms, alters marine ecosystems, and biogeochemical processes. Considerable attention has been focused on understanding the impact of OA on the open ocean but less attention has been given to coastal regions. Recent studies indicate that pH in bottom waters of the northern Gulf of Mexico (nGOM) shelf can be as much as 0.45 units lower relative to pre-industrial values. This occurs because the acidification resulting from increased CO2 inputs (both atmospheric inputs and in-situ respiration) decreases the buffering capacity of seawater. This interactive effect will increase with time, decreasing summertime nGOM bottom-water pH by an estimated 0.85 units and driving carbonate minerals to undersaturation by the end of this century. Researchers from the University of Delaware and the Louisiana Universities Marine Consortium will carry out a combined field, laboratory, and modeling program to address the following questions. (1) What are the physical, chemical, and biological controls on acidification in coastal waters impacted by the large, nutrient-laden Mississippi River?; (2) What is the link between coastal-water acidification, eutrophication, and hypoxia; (3) How do low pH and high CO2 concentrations in bottom waters affect CO2 out-gassing during fall and winter and storm periods when the water column is mixed?; and (4) What are the influences of changing river inputs under anthropogenic forcing on coastal water acidification?Results from this research aim to further our understanding of the processes influencing ocean acidification in coastal waters subject to eutrophication and hypoxia both in the GOM and river-dominated shelf ecosystems globally.