Variability in epilimnion depth estimations in lakes
Variability in epilimnion depth estimations in lakes
复制标题
湖泊水表深度估计的变异性
DOI：
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发表时间：
2020
影响因子：
6.3
通讯作者：
E. Jennings
中科院分区：
文献类型：
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作者：
H. Wilson;Ana I. Ayala;I. D. Jones;A. Rolston;D. Pierson;E. de Eyto;H. Grossart;M. Perga;R. Woolway;E. Jennings
抽象的。表层水层是湖泊的表层，其特征通常是混合良好，并且由于密度的急剧变化而与水层层分离。水层的概念（更广泛地说，分层湖泊的三层结构）是湖泊学的基础，计算水层的深度对于理解许多物理和生态湖泊过程至关重要。然而，尽管该术语无处不在，但并没有客观或通用的方法来定义“eplimnion”，并且文献中盛行多种方法。鉴于具有高时空分辨率的湖泊水温和密度剖面数据的可用性不断增加，使用此类数据的自动计算尤其常见，并且它们在与不断发展的长期全球测量和建模数据集一起使用方面具有巨大的潜力。然而，多地点和多年的研究，包括与未来气候影响相关的研究，需要强大的自动化算法来估计水层深度。在这项研究中，我们使用 17 年的组合数据集以及来自两个欧洲湖泊的 4700 多个每日温度剖面，对常用的表层深度估计方法进行了全面比较。总体而言，我们发现两个湖泊的所有研究方法和阈值的估计表层深度存在很大程度的变异性。这些差异在高频数据上表现出来，导致了对表层深度的根本不同的理解。此外，表层深度的估计对阈值的微小变化、复杂的热水柱结构和垂直数据分辨率高度敏感。这些结果对任意方法选择的习惯以及这可能导致对估计水表中发生的生态过程、多湖泊比较或长期时间序列分析感兴趣的研究造成潜在问题提出了质疑。我们还发现了方法之间重要的系统差异，这证明了方法如何以及为何出现分歧。这些结果可能为未来的研究提供依据，以根据其特定目的并认识到个别方法的局限性来选择适当的表皮层定义。虽然没有规定选择特定方法的理由，但将表层深度定义为最浅深度（其密度比表面密度大 0.1kgm−3）的方法作为通用方法可能特别有用。
Abstract. The epilimnion is the surface layer of a lake typically characterised as well mixed and is decoupled from the metalimnion due to a steep change in density. The concept of the epilimnion (and, more widely, the three-layered structure of a stratified lake) is fundamental in limnology, and calculating the depth of the epilimnion is essential to understanding many physical and ecological lake processes. Despite the ubiquity of the term, however, there is no objective or generic approach for defining the epilimnion, and a diverse number of approaches prevail in the literature. Given the increasing availability of water temperature and density profile data from lakes with a high spatio-temporal resolution, automated calculations, using such data, are particularly common, and they have vast potential for use with evolving long-term globally measured and modelled datasets. However, multi-site and multi-year studies, including those related to future climate impacts, require robust and automated algorithms for epilimnion depth estimation. In this study, we undertook a comprehensive comparison of commonly used epilimnion depth estimation methods, using a combined 17-year dataset, with over 4700 daily temperature profiles from two European lakes. Overall, we found a very large degree of variability in the estimated epilimnion depth across all methods and thresholds investigated and for both lakes. These differences, manifesting over high-frequency data, led to fundamentally different understandings of the epilimnion depth. In addition, estimations of the epilimnion depth were highly sensitive to small changes in the threshold value, complex thermal water column structures, and vertical data resolution. These results call into question the custom of arbitrary method selection and the potential problems this may cause for studies interested in estimating the ecological processes occurring within the epilimnion, multi-lake comparisons, or long-term time series analysis. We also identified important systematic differences between methods, which demonstrated how and why methods diverged. These results may provide rationale for future studies to select an appropriate epilimnion definition in light of their particular purpose and with awareness of the limitations of individual methods. While there is no prescribed rationale for selecting a particular method, the method which defined the epilimnion depth as the shallowest depth, where the density was 0.1 kg m−3 more than the surface density, may be particularly useful as a generic method.