Mechanisms controlling summertime oxygen depletion in western Long Island Sound
Mechanisms controlling summertime oxygen depletion in western Long Island Sound
复制标题
控制长岛海峡西部夏季氧气消耗的机制
DOI：
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发表时间：
1991
期刊：
影响因子：
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通讯作者：
F. Craig Eller
中科院分区：
文献类型：
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作者：
Barbara L. Welsh;F. Craig Eller
利用物理剖面数据(盐度、温度、氧气和下流照度)以及光瓶和暗瓶的原位培养来描述长岛海峡西部夏季低氧的垂直结构和控制机制。耗氧期与热控层结时期相对应。表层和底层之间的体积密度差只有1.2到2.7西格玛-t单位；但它们显然足以抵抗风和潮汐的去层化。因此，氧气消耗是整个夏天的一个累积过程。在层结期间，净产氧量(用轻型BOD瓶测量)被限制在1.8-4.5m的狭窄表面区，在这一区下方是高净吸氧量的中间带，其下是亚潜伏带，其吸氧量很低。总摄氧率(深色瓶装)在表层最大，并随着深度的增加而减小。身体条件与代谢结构之间存在密切的耦合关系。在平静的天气中，氧气的产生和清除的垂直格局最强。中间带的位置与催产层的位置一致。带的厚度和跃层的陡度由物理层结和生物生产和呼吸的深度和强度决定。上层水柱的物理混合削弱了生物结构，秋季解层使中间带消失。我们假设，水柱内的生物吸收通过两种机制影响氧气的消耗。(1)在底层水域，单位体积的摄取率很低，但由于所涉及的水量很大，总体摄取量是氧气消耗的一个重要因素。(2)呼吸吸收也很重要的中间带位于氧气更新的表层和底部的耗氧区之间，在那里它构成了一个活性过滤器，加强了倒跃层作为垂直氧气扩散的屏障。水体中氧的直接去除相对于沉积物需氧量的大小以及这种生物过滤机制的潜在影响是理解富营养化动力学和管理长岛海湾的重要考虑因素。如果动力模型(1)低估了水柱吸收的作用，(2)只包含物理分层的两个区域特征，则倾向于(A)高估沉积物对夏季氧气缺乏的贡献，以及(B)高估底层水的垂直扩散和再通风的速率。
Physical profile data (salinity, temperature, oxygen, and downwelling irradiance) and in situ incubations of light and dark bottles were used to characterize vertical structure and elucidate mechanisms controlling summertime hypoxia in western Long Island Sound. The period of oxygen depletion corresponded with the period of thermally-controlled stratification. Bulk density differences between surface and bottom waters were only 1.2 to 2.7 sigma-t units; but they were apparently sufficient to resist destratification by winds and tides. Thus oxygen depletion was a cumulative process through the summer. During the stratification period, net oxygen production (measured using light BOD bottles) was confined to a narrow surface zone of 1.8–4.5 m. Below this zone was an intermediate zone of high net oxygen uptake, beneath which was a subpycnoclinic zone where oxygen uptake was very low. Rates of total oxygen uptake (dark bottles) were greatest in the surface layer and diminished with depth. There was close coupling between physical conditions and metabolic structure. Vertical patterns of oxygen production and removal were strongest in calm weather. The location of the intermediate zone corresponded with that of the oxycline. The thickness of the zone and the steepness of the oxycline were determined by the depth and intensity of both physical stratification and biological production and respiration. The biological structure was weakened by physical mixing in the upper water column, and the intermediate zone disappeared with fall destratification. We hypothesize that biological uptake within the water column influences oxygen depletion through two mechanisms. (1) In bottom waters, uptake rates per unit volume are low, but bulk uptake is a significant factor in oxygen depletion because of the large volume of water involved. (2) The intermediate zone, where respiratory uptake is also significant, is strategically located between the surface zone of oxygen renewal and the bottom zone of depletion, where it constitutes an active filter which reinforces the pycnocline as a barrier to vertical oxygen dispersion. The magnitude of direct oxygen removal in the water column relative to removal by sediment oxygen demand and the potential effects of this biological filtering mechanism are important considerations for understanding eutrophication dynamics and managing Long Island Sound. Dynamic models which (1) underestimate the role of water column uptake and (2) incorporate only the two-zone characteristics of physical stratification will tend to (a) overestimate the contribution of sediments to summertime oxygen deficits and (b) overestimate rates of vertical dispersion and reventilation of bottom waters.