Deep sewage discharge leads to inestimable damage to the ambient water (lakes, oceans and reservoirs), which has caused widespread social concern. In the current paper, a three‐dimensional (3D) buoyancy plume model for deep sewage discharge was developed. It simulates sediment‐laden flow with the effects of temperature and salinity differences. Taking the turbulent diffusion coefficient of salinity (αsal) as the calibration parameter, a comparison between the RNG k‐ε and the standard k‐ε models was performed. The proposed model was verified well and agreement with experiment, which proved that the RNG model with the αsal value of 0.4 was the optimal calibration. Then the model was applied to quantify the behavior of the buoyant plume in the ambient fluid (salt water) with respect to different contours of turbulent kinetic energy (k), temperature, salinity and sediment. The dimensionless centerline trajectory positions and boundary positions of them were determined. The results indicated that the discharge of low‐salinity sediment‐bearing water influenced the deep ambient water spatially, both near the free surface and in the vertical plane. Different diffusion and spreading shapes (butterfly, Ginkgo biloba, bean) can be observed on the surface. Accurately evaluating the impact of deep discharge on ambient water has great significance for maintaining healthy and sustainable environments in offshore areas, deep lakes and reservoirs.

Global climate change has greatly increased the drought duration, frequency, and severity of intermittent river ephemeral stream (IRES), affecting the microbial-mediated biogeochemical process. While there is limited information about the responses of community structure and ecosystem functions of benthic biofilms in IRES, especially under the increased drought duration. Here, we focused on the increased drought duration and summarized their effects on the structure and functions of benthic biofilms in IRES. First, the increased dehydration duration led to distinct effects on the α-diversity or β-diversity of benthic microbial communities. The interaction network should be considered in future research as they are essential to maintain biofilm structure and play key roles in the resistance and resilience in biofilm community recovery under hydrological stress. In addition, inconsistent response patterns of the fundamental functions, such as gross primary production, ecosystem respiration, and functional enzymes activity of biofilms were discussed. Besides, the emissions of greenhouse gases (GHGs) of biofilms in IRES deserve more attention due to that their emission flux of biofilms could be significantly altered after prolong dehydration duration with a huge pulse when rewetting. More important, it is ecosystem multifunctionality rather than a single function that needs to be fully considered when studying the microbial functions and the biogeochemical process mediated by biofilms in IRES under increased dehydration duration. Also, more research is needed at larger spatial and longer temporal scales to evaluate the effects from a more macro perspective for better understanding the ecological impacts of increased dehydration duration in IRES ecosystems.