The development of new strategies for the operation of existing dams is essential for restoring ecosystems that have already been affected by the construction and current regulation of these dams. The assessment of environmental flows (EFs) is significant in guiding such strategic dam operations. However, most of the existing methods just focus on one species or guild without simultaneously considering the interactions with other aquatic organisms. This study proposes an innovative method to determine comprehensive environmental flows (CEFs) for multi‐guilds (fish, macroinvertebrates, and hygrophytes) based on the habitat simulation model. We focused on the riparian habitats in the middle reaches of the Yangtze River, coupled the biological preferences of multi‐guilds with suitable habitat factors, including velocity, depth, and substrate, and then analyzed the relationships of flow and weighted usable areas to determine the CEFs for multi‐guilds. The results showed that while the optimal CEFs could be satisfied only in Spring and Summer, the threshold CEF conditions could be met in the Jianli reach throughout the year after the impoundment of Three Gorges Dam (TGD). The results obtained by using the CEFs assessment could better satisfy the EFs for multi‐guilds than the ones developed for individual species. The CEFs could be also used to evaluate the impact of TGD on multi‐guilds’ habitats and optimize ecologically‐friendly operations in already designed dams. This study is helpful for maintaining ecosystem integrity in Yangtze River and provides a good example for use in other dams facing similar issues.

Secchi disk depth (Z_SD) is used to quantify water clarity as an important water-quality parameter, and one of the most used mechanistic models for Z_SD is the quasi-analytical algorithm (QAA), of which the latest version is QAA_v6. There are two models in QAA for clear and turbid waters (referred to as QAA_clear and QAA_turbid). QAA_v6 switches between the two models by setting a threshold value for the remote sensing reflectance (R_rs, sr⁻¹) at the selected reference band of 656 nm. However, some researchers found that this reference band or the threshold value does not apply to many turbid inland lakes. In Honghu Lake, the R_rs (656) (R_rs at 656 nm) in the whole lake is less than 0.0015 sr⁻¹; therefore, only QAA_turbid can be applied. Moreover, we found that QAA_clear resulted in overestimation while QAA_turbid resulted in significant underestimations. The waters of inland lakes usually continuously vary between clear and turbid water. We proposed a hypothesis that QAA_turbid and QAA_clear transition evenly, rather than being distinguished by one threshold value, and we developed a model that combined QAA_clear and QAA_turbid according to our assumption. This model simulated the process of continuous change in water clarity. The results showed that our model had a better performance with an RMSE that reduced from 0.5 to 0.28, an MAE that reduced from 0.43 to 0.21, and bias that reduced from −0.4 to −0.05 m compared with QAA_v6. We applied QAA_Honghu to Landsat TM, ETM+, and OLI data and obtained 205 Z_SD maps with high spatial resolution in Honghu Lake. The results were consistent with the existing in situ measurements. From 1987–2020, the Z_SD results of Honghu Lake showed an overall downward trend and a distinct seasonal pattern.

Gymnocypris przewalskii (i.e., Qinghai Lake naked carp) is a migratory fish species that lives in highland brackish water. It is important to understand the abiotic environment required by this fish to reproduce naturally so that its habitat can be protected and the wild population can be conserved. Here, artificial simulation and spawning ground substrate transformation experiments were conducted to examine the riverbed substrate requirements for G. przewalskii to naturally reproduce. Using various techniques (in vitro markers, videography, and Ethovision XT behavior tracking), this study systematically investigated the riverbed substrate preferences of G. przewalskii as well as the characteristics and effectiveness of natural reproduction induced by pebble riverbed substrate. The findings can be summarized as follows: (1) the habitat preferences of G. przewalskii differed significantly between various riverbed substrate, with pebble substrate being preferred during natural reproduction, and sand substrate being preferred pre- and post-spawning, and (2) the natural reproduction of G. przewalskii was heavily reliant on pebble riverbed substrate. Specifically, pebble substrate significantly improved spawn quantity and fertilization rate. These findings provide scientific evidence for the improvement and restoration of G. przewalskii spawning grounds, and insights regarding the artificial bionic reproduction of G. przewalskii.

Estimation of primary production in Qinghai Lake is crucial for the aquatic ecosystem management in the northeastern Qinghai–Tibet Plateau. This study used the Vertically Generalized Production Model (VGPM) with ocean color satellite data to estimate phytoplankton primary productivity (PP) in Qinghai Lake during the non-freezing period from 2002 to 2023. Field data from 2018 and 2023 were used to calibrate and verify the model. The results showed a seasonal trend in chlorophyll-a and PP, with the lowest values in May and peaks from June to September. Qinghai Lake was identified as oligotrophic, with annual mean chlorophyl-a of 0.24–0.40 µg/L and PP of 40–369 mg C/m²/day. The spatial distribution of PP was low in the center of the lake and high near the shores and estuaries. An interesting periodic increasing trend in PP every 2 to 4 years was observed from 2002 to 2023. This study established a remote sensing method for PP assessment in Qinghai Lake, revealing seasonal and interannual variations and providing a useful example for monitoring large saline mountain lakes.