Estimating ecological flows for fish overwintering in plain rivers using a method based on water temperature and critical water depth

Abstract

Ecological flow is the foundation for conservation of riverine fish habitat and ecosystem. Habitat models have been widely used to estimate ecological flow owing to their integration of hydrological regime and species hydraulic preference. Previous studies based on habitat methods focused more on the spawning season but paid less attention to the winter period, which is also essential to fish life stage. This study developed a novel approach to estimate the ecological flow for fish overwintering, particularly in plain rivers. The water depth for target fish safely overwintering was firstly determined based on the minimum tolerable water temperature of the species. A water balance model was built to estimate the ecological flow for securing the determined water depth. The developed approach was applied in the middle reaches of Huaihe River, where the flow is highly regulated by dams and sluices. Parabramis pekinensis was selected as the target fish, and the minimum water depth for it to overwinter in the river was about 20 m. The calculated ecological flow was 3.0 m3·s−1 in December, 2.2 m3·s−1 in January, and 2.1 m3·s−1 in February, respectively. The approach contributed a great supplement to fish spawning habitat model, and their combination could determine ecological flow regimes for the entire life cycle of the target fish.

Incorporating fish habitat requirements of the complete life cycle into ecological flow regime estimation of rivers

“…The ecological flow in plain rivers during overwintering period is difficult to be estimated by the habitat methods. Therefore, the water balance model (Wang et al, ) was adopted in this study. For comparison, the ecological flow regime by Tennant method was calculated and presented in Figure as well.…”

“…In this study, the semi‐implicit Eulerian–Lagrangian finite‐element model was used for simulating hydrodynamic conditions in the study area (Wang et al, ). Through this model, the depth‐averaged flow velocity and the water‐surface elevation were computed by solving the shallow‐water equations, with hydrostatic and Boussinesq approximations (Zhang & Baptista, ).…”

Meander reshaping – the formation process of a wintering riverbed depression of fish

“…Juveniles were seen to be more prone to the formation of aggregations than fish of older age groups. During the wintering season, the basic habitat requirements of other species of fish also shift to the most important aspects: sufficient depth and low flow rates (Mochek et al, 2019;Wang et al, 2019). In the study of riverbed depressions, it was shown (Mochek et al, 2015) that aggregations of fish in these water areas are also found during open-water periods.…”

“…In the lower reaches of the Irtysh River, there are wintering riverbed depressions with significant depths (> 35 m), which form on the meanders of the watercourse (Borisenko et al, 2013;Mochek et al, 2019). For fish, wintering is one of the critically important stages of their life cycle (Thayer et al, 2017;Wang et al, 2019;Studd et al, 2021;Sutton et al, 2021); in winter, juvenile fish have increased mortality compared to fish of older age groups (Deslauriers et al, 2018;Fernandes & McMeans, 2019;Takegaki & Takeshita, 2020). During this season, many species of fish (including sturgeons) prefer "temporal bottleneck" -wintering riverbed depressions (Thayer et al, 2017;Andrews et al, 2020).…”

Characteristics and Adaptability Assessment of Commonly Used Ecological Flow Methods in Water Storage and Hydropower Projects, the Case of Chinese River Basins

“…Overall, the e-flow methods are relatively mature, and the classification of flow grading for different purposes is relatively precise in developed countries. Moreover, they focus on the minimum flow of rivers, as well as the need to gradually expand from the minimum flow to the level of current needs to maintain the institutional functions of river ecosystems, with particular attention paid to the flow required for spawning migration of in-channel organisms [19,20].…”