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The seasonal pattern of dissolved oxygen, and hypolimnetic deoxygenation, in two tropical Australian reservoirs

机译：澳大利亚两个热带水库的溶解氧和低氧脱氧的季节性模式

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The dissolved oxygen concentrations in Darwin River Reservoir (DRR) and Manton River Reservoir (MRR), both located in the wet/dry tropics of Australia, were investigated over an 8-year period. Average oxygen concentrations were lower in MRR than in DRR, indicating the dominance of consumptive processes not compensated by photosynthetic production of oxygen, despite MRR’s higher chlorophyll a concentration. With the onset of thermal stratification, dissolved oxygen in the hypolimnion of each reservoir was depleted at average rates of 3.4–7.1 mg L−1 month−1. These are higher than rates reported for temperate water-bodies (0.10–3.0 mg L−1 month−1). This was ascribed primarily to the effect of temperature on microbial metabolism, while the influence of the reservoirs’ high epilimnion to hypolimnion volumetric ratios (approximately 10:1) and reservoir trophic state were considered secondary. Due to the temperature dependence of hypolimnetic oxygen depletion, the trophic classification of lakes based on hypolimnetic deoxygenation and anoxia is not globally applicable, but is applicable to water-bodies of similar hypolimnetic temperatures, especially when morphometric influences are also taken into account. Both reservoirs experienced long periods of anoxia (average: 9 months in MRR, 5 months in DRR). In DRR, the extent of hypolimnetic anoxia was related to hypolimnion volume. Hypolimnetic anoxia in the reservoirs, when quantified by the anoxic factor (AF; number of days that a sediment area, equal to the whole-lake surface area, is overlain by anoxic waters), was high compared with similar water-bodies in North America, providing quantitative evidence that anoxia in more prevalent in tropical reservoirs. Ammonia, iron and manganese accumulated in the hypolimnion of both DRR and MRR, with concentrations decreasing exponentially from the sediments to the oxycline. Sediment phosphorus release was detected in MRR, but not detected in DRR, despite the reservoir’s long periods of hypolimnetic anoxia. The high water temperatures and lengthy periods of hypolimnetic anoxia of the reservoirs provided a favourable environment for anoxygenic phototrophic bacteria.
机译：在澳大利亚湿/干热带地区的达尔文河水库（DRR）和曼顿河水库（MRR）中的溶解氧浓度进行了为期8年的调查。 MRR中的平均氧气浓度低于DRR，这表明尽管MRR的叶绿素a浓度较高，但消费过程的优势并未被光合作用的氧气补偿。随着热分层的开始，每个储层低渗层中的溶解氧以3.4–7.1 mg L-1 month-1的平均速率消耗。这些高于温带水体的报告率（0.10–3.0 mg L-1 month-1）。这主要归因于温度对微生物代谢的影响，而储层的高上扬与下层的容积比（约10：1）和储层营养状态的影响被认为是次要的。由于低通量氧气消耗的温度依赖性，基于低通量脱氧和缺氧的湖泊的营养分类在全球范围内不适用，但适用于低通量温度相似的水体，尤其是在考虑形态学影响的情况下。两个储层都经历了长时间的缺氧（平均：MRR为9个月，DRR为5个月）。在DRR中，低通气性缺氧的程度与低通气量有关。与北美地区类似的水体相比，用无氧因子（AF；相当于全湖表面积的沉积物被无氧水覆盖的天数）量化时，储层的降膜性缺氧率很高。 ，提供定量证据表明缺氧症在热带水库中更为普遍。氨，铁和锰在DRR和MRR的次生水合物中积累，浓度从沉积物到奥克西林呈指数下降。尽管储层长期处于低铁性缺氧状态，但在MRR中检测到了沉积物磷释放，但在DRR中未检测到。较高的水温和储层的低铁性缺氧时间长，为产氧光养细菌提供了良好的环境。

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