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Physical conditions driving the spatial and temporal variability in aquatic metabolism of a subtropical coastal lake

机译：推动亚热带沿海湖泊水生代谢时空变化的物理条件

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We investigated the importance of meteorological and lake physical conditions for temporal, horizontal and vertical differences in the concentration of dissolved oxygen (DO) and water temperature, and the derived daily estimates of gross primary production (GPP), ecosystem respiration (R) and net ecosystem production (NEP). Our study was conducted in a subtropical and polymictic lake in Southern Brazil, during a spring-summer transition. Metabolic rates were determined from two sites using the open water oxygen technique. At the central deep site, oxygen sondes were deployed at three depths to assess patterns in vertical variability. During 10 days, an additional DO and temperature sonde was placed near the shoreline allowing us to compare metabolic differences in the surface layers between the central pelagic and littoral site, While GPP was similar, R was significantly higher at the shallower littoral site, causing NEP to be lower, although NEP was still positive. The littoral site had less diel changes in DO and higher daily variability in all metabolic rates. Variability in GPP and R at the littoral site was related to temperature, wind speed and rainfall suggesting that short-term variability in metabolic rates in shallow areas are sensitive to resuspension of sediments caused by a less stable water column. A clear vertical gradient was furthermore found for the metabolic rates at the central deep part of the lake, related to the light extinction, with highest GPP around 0.3 m and decreasing with depth, while respiration showed the inverse pattern. Below subsurface, respiration prevailed at 5.0 m depth and was uncoupled to primary production. Under conditions with high light and temperature, and low wind speeds, the mixing depth became shallower, in turn increasing the water column stability at the deep pelagic site, which resulted in higher mean light available and higher GPP in the water column. Our results confirm that deployment of sensors in different sites and depths allows for spatially, as well as temporally more representative estimates of lake metabolism. (C) 2016 Elsevier GmbH. All rights reserved.
机译：我们调查了气象和湖泊物理条件对于溶解氧浓度（DO）和水温的时间，水平和垂直差异的重要性，以及得出的每日一次总产值（GPP），生态系统呼吸（R）和净值的估算值生态系统生产（NEP）。我们的研究是在春季至夏季过渡期间，在巴西南部的亚热带多变湖泊中进行的。使用开放水氧技术从两个位置确定代谢率。在中央深部，在三个深度部署了氧气探空仪，以评估垂直变化的模式。在10天之内，在海岸线附近放置了另外的溶解氧和温度探空仪，使我们能够比较中上层和沿海地区之间表层的代谢差异。尽管GPP相似，但在沿海较浅地区的R值明显较高，从而导致NEP降低，尽管NEP仍为正面。沿岸部位DO的diel变化较小，而所有代谢率的日变化较大。沿海地区GPP和R的变化与温度，风速和降雨有关，这表明浅水区新陈代谢速率的短期变化对不稳定的水柱引起的沉积物再悬浮很敏感。此外，在湖中央深部的代谢速率与光的消灭有关，还发现了一个清晰的垂直梯度，代谢速率最高，约为0.3 m，并且随着深度的增加而降低，而呼吸呈相反的模式。在地下以下，呼吸主要发生在5.0 m深度，并且与初级生产无关。在高光照，高温度，低风速的条件下，混合深度变浅，从而增加了深层中上层水域的水柱稳定性，这导致了更高的平均可用光和更高的GPP。我们的结果证实，在不同位置和深度部署传感器可以在空间上以及时间上对湖泊新陈代谢进行更具代表性的估算。 （C）2016 Elsevier GmbH。版权所有。

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