Physical and Biological Controls on Short-Term Variations in Dissolved Oxygen in Shallow Waters of a Large Temperate Estuary

IF 2.3 3区 环境科学与生态学 Q3 ENVIRONMENTAL SCIENCES
Jeremy M. Testa, Wei Liu, Walter R. Boynton, Denise Breitburg, Carl Friedrichs, Ming Li, David Parrish, T. Mark Trice, Damian C. Brady
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引用次数: 0

Abstract

Hypoxia in coastal waters is a pressing ecological problem caused by continued eutrophication and climatic change that has widespread consequences for metazoan life and biogeochemical cycles. Numerous studies have investigated the controls on seasonal hypoxia formation and persistence in many of the world’s large estuaries and coastal hypoxic zones, but far fewer studies have examined the controls on short-term oxygen variability that leads to diel-cycling hypoxia in shallow-water environments. We utilized a unique, comprehensive (181 stations) record of dissolved oxygen concentrations collected at shallow water sites (primarily < 2 m) at high frequency (15 min) throughout the estuarine complex of the Chesapeake Bay and its tributaries to quantify how internal and external variables co-varied with dissolved oxygen. We used a combination of time-series analysis, harmonic analysis, and machine learning (e.g., classification and regression trees (CART)) approaches to identify spatial patterns in major controls on oxygen variability and the duration of moderate hypoxia. We found that key controls on oxygen variability varied substantially over space. For example, photosynthetically active radiation (PAR) was a strong predictor of oxygen dynamics in the majority of mesohaline waters. In more fetch-exposed stations, wind strongly controlled hypoxic duration, but in eutrophic, inshore locations, chlorophyll a, or turbidity were often better predictors. Specifically, diel oxygen variability was muted in upstream regions characterized by high turbidity. The duration of low oxygen conditions, which we defined conservatively as less than 4.8 mg O2 L−1 (156 µM), was strongly controlled by temperature, and simple projections of regional warming and CART-derived oxygen thresholds suggest that the Bay could experience a 10% increase in this type of hypoxia duration by mid-to-late twenty-first century. The ratio of tidal to biological variability in oxygen was found to increase under conditions of higher turbidity, stronger wind, and lower salinity, but biological variability was typically a factor of two higher than tidal variability. Although chlorophyll-a generated high oxygen concentrations at some locations, those stations with exceptionally high chlorophyll a (> 30 µg L−1) were the most vulnerable to hypoxia. Because conventional water quality modeling frameworks are designed to capture hypoxia on relatively long time scales, these new insights can help inform updated oxygen models to support the management of shallow-water estuaries in the face of managed nutrient reductions and climate change.

Abstract Image

大型温带河口浅水区溶解氧短期变化的物理和生物控制因素
沿岸水域缺氧是由于持续富营养化和气候变化引起的一个紧迫的生态问题,对元 生物的生活和生物地球化学循环有着广泛的影响。在世界许多大型河口和沿岸缺氧区,对季节性缺氧形成和持续的控制进行了大量研究, 但对浅水环境中导致昼夜循环性缺氧的短期氧气变化的控制研究则少得多。我们利用在切萨皮克湾及其支流河口综合体浅水区(主要是 2 米处)高频率(15 分钟)收集的独特、全面(181 个站点)的溶解氧浓度记录,来量化内部和外部变量如何与溶解氧共同变化。我们结合使用了时间序列分析、谐波分析和机器学习(如分类和回归树 (CART))方法,以确定氧气变化的主要控制因素的空间模式以及中度缺氧的持续时间。我们发现,氧气变异性的主要控制因素在空间上存在很大差异。例如,光合有效辐射(PAR)对大多数中盐水域的氧气动态具有很强的预测作用。在风力较大的站点,风力对缺氧持续时间的控制作用很强,但在富营养化的近岸地点,叶绿素 a 或浊度往往是更好的预测因子。具体而言,在上游高浊度地区,昼夜氧气变化不明显。低氧条件的持续时间(我们保守地将其定义为低于 4.8 mg O2 L-1 (156 µM))受温度的强烈控制,对区域变暖和 CART 导出的氧阈值的简单预测表明,到 21 世纪中后期,海湾的此类缺氧持续时间可能会增加 10%。研究发现,在浊度较高、风力较大和盐度较低的条件下,氧气的潮汐变化与生物变化之比会增大,但生物变化通常比潮汐变化高出两倍。虽然叶绿素 a 在某些地点会产生高浓度的氧气,但叶绿素 a 特别高(30 µg L-1)的站点最容易缺氧。由于传统的水质建模框架是为捕捉相对较长时间尺度上的缺氧而设计的,因此这些新见解有助于为更新的氧气模型提供信息,从而在有管理地减少营养物和气候变化的情况下支持浅水河口的管理。
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来源期刊
Estuaries and Coasts
Estuaries and Coasts 环境科学-海洋与淡水生物学
CiteScore
5.60
自引率
11.10%
发文量
107
审稿时长
12-24 weeks
期刊介绍: Estuaries and Coasts is the journal of the Coastal and Estuarine Research Federation (CERF). Begun in 1977 as Chesapeake Science, the journal has gradually expanded its scope and circulation. Today, the journal publishes scholarly manuscripts on estuarine and near coastal ecosystems at the interface between the land and the sea where there are tidal fluctuations or sea water is diluted by fresh water. The interface is broadly defined to include estuaries and nearshore coastal waters including lagoons, wetlands, tidal fresh water, shores and beaches, but not the continental shelf. The journal covers research on physical, chemical, geological or biological processes, as well as applications to management of estuaries and coasts. The journal publishes original research findings, reviews and perspectives, techniques, comments, and management applications. Estuaries and Coasts will consider properly carried out studies that present inconclusive findings or document a failed replication of previously published work. Submissions that are primarily descriptive, strongly place-based, or only report on development of models or new methods without detailing their applications fall outside the scope of the journal.
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