Spatio-temporal variation and risk assessment of hydrochemical indices in a large diversion project of the Yellow River, northern China, from 2008 to 2017

Significant influence of water diversion and anthropogenic input on riverine sulfate based on sulfur and oxygen isotopes

The transportation of dissolved sulfate (SO42-) to the ocean via river systems plays a critical role in the global sulfur cycle. However, the increasing anthropogenic input has made it challenging to quantify the various pristine contributions accurately. The riverine sulfur and oxygen isotopes of sulfates (δ34SSO4 and δ18OSO4) and the advantages of the Markov-Chain Monte Carlo model were used to distinguish the anthropogenic input in Fenhe River, a tributary of the Yellow River. The SO42- concentrations and δ34SSO4 and δ18OSO4 values of the mainstream river were normally distributed with minor seasonal variations (P > 0.05). However, the upstream riverine SO42- concentrations were significantly altered by the water diversion from the Yellow River. The midstream and downstream sections exhibited a continuous increase in the riverine SO42- concentration and δ34SSO4 and δ18OSO4 values during both seasons. The coal mining drainage significantly impacted the tributaries near coal mining activities, and chemical fertilizers and sewage contributed more sulfate in the midstream and downstream sections. The yearly sulfate flux of the Fenhe River accounted for 4.2% of that of Yellow River, among which over 60% was from anthropogenic sources. The average δ34SSO4 and δ18OSO4 values had elevated to 11.0‰ and 6.0‰, respectively, due to the extensive input of anthropogenic sulfate. Our findings confirm the utility of δ34SSO4 and δ18OSO4 for tracing anthropogenic input and underscore its impacts on river systems and the global sulfur cycle.

Evaluating the impacts of inter-basin water transfer projects on ecosystem services in the Fenhe River Basin using the SWAT model

Inter-basin water transfer (IBWT) projects have been widely constructed to alleviate the pressure on water resources in water shortage basins. However, the ecological effects of IBWT projects have often been ignored. Based on the Soil and Water Assessment Tool (SWAT) model and a constructed total ecosystem services (TES) index, the impacts of IBWT projects on recipient basin ecosystem services were analyzed in this study. The results showed that the TES index was relatively stable from 2010 to 2020, but in the wet season it was 1.36 times that of the other months with high water yield and nutrient loads. Spatially, areas with high index values were mainly distributed in the sub-basins around the reservoirs. The IBWT projects had positive impacts on ecosystem services, and the TES index with IBWT projects was 5.98% higher than that without projects. Water yield and total nitrogen were the two most affected indexes, with increased of 5.65% and 5.41%, respectively, under the impacts of IBWT projects. Seasonally, the change rates of the TES index were less than 3% while the change rates of water yield and nitrogen load peaked at 8.23% and 53.42%, respectively, in March, owing to the large amount of water released from the reservoirs. Areas affected by the three evaluated IBWT projects accounted for 61%, 18%, and 11% of the watershed, respectively. Under the impact of each project, the TES index generally increased, whereas the impact decreased as the distance from the inflow location increased. Intense changes in ecosystem services occurred in sub-basin 23, the sub-basin closest to an IBWT project, with water yield, water flow, and local climate regulation increasing the largest.

Microeukaryotic Community Shifting Along a Lentic-Lotic Continuum

As an important regulator of ecosystem functions in river systems, microeukaryotes play an important role in energy and material conversion, yet little is known about the shift along a lentic-lotic continuum. In this study, the 18S rRNA genes sequencing was used to identify the microeukaryotic communities at 82 sites along a lentic-lotic continuum with the aim of understanding the impact of upstream inlet river on microeukaryotic communities in Baiyang Lake (BYD) and its downstream. Our results showed that the upstream inlet river affected the diversity and community composition of microeukaryotes in BYD and downstream rivers, and environmental variables greatly affected the composition of microeukaryotic community. The community composition in BYD had lower variabilities. Co-occurrence network analysis revealed that the network was non-random and clearly parsed into three modules, and different modules were relatively more abundant to a particular area. As keystone taxa, some nodes of the upstream microeukaryotic network played an important role in structuring network and maintaining the stability of the ecosystem. In BYD and downstream, the microeukaryotic network was highly fragmented, and the loss of keystone taxa would have an adverse impact on the integrity and function of the microeukaryotic community. Microeukaryotes had strong tendencies to co-occur, which may contribute to the stability and resilience of microeukaryotic communities. Overall, these findings extend the current understanding of the diversity and community composition of microeukaryotic along a lentic-lotic continuum.