Flow regulation by large dams has transformed the freshwater and floodplain ecosystems of the Middle Amur River basin in Northeast Asia, and negatively impacted the biodiversity and fisheries. This study aimed to develop environmental flow recommendations for the Zeya and Bureya rivers based on past flow rate records. The recommended floodplain inundation by environmental flow releases from the Zeya reservoir are currently impracticable due to technical reasons. Therefore, the importance of preserving the free-flowing tributaries of the Zeya River increases. Future technical improvements for implementing environmental flow releases at the Zeya dam would improve dam management regulation during large floods. The recommendations developed for environmental flow releases from reservoirs on the Bureya River should help to preserve the important Ramsar wetlands which provide habitats for endangered bird species while avoiding flooding of settlements. The results emphasize the importance of considering environmental flow during the early stages of dam planning and the need to enhance the role of environmental flow in water management planning.

Hydropower development causes a multitude of negative effects on freshwater ecosystems, and to prevent and minimize possible damage, environmental impact assessments must be conducted and optimal management scenarios designed. This paper examines the impacts of both existing and proposed hydropower development on the transboundary Amur River basin shared by Russia, China, and Mongolia, including the effectiveness of different tools and measures to minimize damage. It demonstrates that the application of various assessment and conservation tools at the proper time and in the proper sequence is the key factor in mitigating and minimizing the environmental impacts of dams. The tools considered include basin-wide assessments of hydropower impacts, the creation of protected areas on rivers threatened by dam construction, and environmental flows. The results of this work show how the initial avoidance and mitigation of hydropower impacts at early planning stages are more productive than the application of any measures during and after dam construction, that the assessment of hydropower impacts must be performed at a basin level rather than be limited to a project implementation site, and that the full spectrum of possible development scenarios should be considered. In addition, this project demonstrates that stakeholder analysis and robust public engagement are as crucial for the success of environmental assessments as scientific research is for the protection of river basins.

The large Zeya hydropower dam is located on the Zeya River, the largest left-bank tributary of the Amur-Heilong River in Russia. The dam had been constructed by 1980 and its operation has significantly transformed the flow regime of the Zeya River. The flow regulation has reduced the magnitude of periodic flooding of the floodplain areas located downstream from the Zeya dam and disrupted habitats of flora and fauna. An estimation of the transformation of the freshwater ecosystems is required to develop measures necessary either to maintain or restore disrupted ecosystems. Application of remote sensing methods allows measuring characteristics of the ecosystem's components. Two sections of a floodplain below the Zeya dam were considered for analysis in order to detect changes in objects at each site during the comparison of remote data from 1969/1971 and 2016.

This study focuses on developing scientifically grounded approaches to transboundary flow allocation in the Ural River Basin, considering ecosystem needs and international approaches to aquatic ecosystem conservation. Amid increasing competition for water resources and climate change, there is a growing necessity to shift from allocating fixed water volumes toward more flexible, ecosystem-oriented solutions. Based on an analysis of international practices, the provisions of the existing agreement on the joint use and protection of water bodies in the Ural River Basin, and an assessment of the current state of its aquatic ecosystems, the study highlights the need to revise established water allocation mechanisms. Methods. The research is based on analyzing international approaches to transboundary flow allocation, statistical processing of reconstructed hydrological observation series, and a comprehensive assessment of aquatic ecosystems using abiotic and biotic indicators. It also applies methods of critical hydrological conditions and ecohydrological normalization for calculating environmental flow. Results. The study proposes an approach to justify environmental flow as a key element in the system of transboundary water resource allocation. Based on an assessment of ecosystem conditions in the Ural River Basin, the objectives for implementing environmental flow have been formulated, including reserving a portion of the flow to maintain and restore ecosystems, adapt to climate change, and preserve biodiversity. Estimated environmental flow volumes near the Russia–Kazakhstan border have been identified, which may serve as a basis for planning joint decisions on water resource allocation that take ecosystem needs into account. The results can be applied by intergovernmental commissions and expert groups in refining transboundary water allocation mechanisms.

Relevance. The transboundary Irtysh River basin is characterized by intensive economic development, transformation of the natural water regime, and increasing water demand. This creates a need for scientifically grounded recommendations on water resources allocation among the riparian countries. At the same time, there are no agreed water allocation mechanisms in the basin that take ecosystem requirements into account. In global water resources management practice, such requirements are taken into account through the concept of environmental flow. This study presents an assessment and justification of environmental flow parameters for the Irtysh River to enable taking them into account in developing recommendations on the water allocation. Methods. The study is based on the analysis of water use and the state of the Irtysh transboundary basin ecosystems, analysis of the long-term hydrological observations, including the data of the reconstructed naturalized flow series. The method of critical hydrological conditions was used to substantiate the environmental flow parameters; floodplain inundation was adopted as the key indicator. Calculations were performed for the Irtysh-Tatarka gauging station located near the Russia-Kazakhstan boundary considering the specific features of flow formation in the study reach. Results. The functions and indicative parameters of environmental flow were identified. The preliminary environmental flow value is about 80 % of the annual naturalized runoff volume. The importance of maintaining environmental flow during the spring–summer period was highlighted. Maintaining May runoff volumes above 4 km³ is considered a hydrological condition necessary for floodplain inundation. These results may provide a basis for incorporating ecosystem requirements into water allocation mechanisms in the transboundary Irtysh River basin.