Water is essential for every life living on the planet. However, we are facing a more serious situation such as water pollution since the industrial revolution. Fortunately, many efforts have been done to alleviate/restore water quality in freshwaters. Numerous sensors have been developed to monitor the dynamic change of water quality for ecological, early warning, and protection reasons. In the present review, we briefly introduced the pollution status of two major pollutants, i.e., pesticides and heavy metals, in freshwaters worldwide. Then, we collected data on the sensors applied to detect the two categories of pollutants in freshwaters. Special focuses were given on the sensitivity of sensors indicated by the limit of detection (LOD), sensor types, and applied waterbodies. Our results showed that most of the sensors can be applied for stream and river water. The average LOD was72.53±12.69 ng/ml (n=180) for all pesticides, which is significantly higher than that for heavy metals (65.36±47.51 ng/ml,n=117). However, the LODs of a considerable part of pesticides and heavy metal sensors were higher than the criterion maximum concentration for aquatic life or the maximum contaminant limit concentration for drinking water. For pesticide sensors, the average LODs did not differ among insecticides (63.83±17.42 ng/ml,n=87), herbicides (98.06±23.39 ng/ml,n=71), and fungicides (24.60±14.41 ng/ml,n=22). The LODs that differed among sensor types with biosensors had the highest sensitivity, while electrochemical optical and biooptical sensors showed the lowest sensitivity. The sensitivity of heavy metal sensors varied among heavy metals and sensor types. Most of the sensors were targeted on lead, cadmium, mercury, and copper using electrochemical methods. These results imply that future development of pesticides and heavy metal sensors should (1) enhance the sensitivity to meet the requirements for the protection of aquatic ecosystems and human health and (2) cover more diverse pesticides and heavy metals especially those toxic pollutants that are widely used and frequently been detected in freshwaters (e.g., glyphosate, fungicides, zinc, chromium, and arsenic).

Macroinvertebrates are sensitive to environmental disturbances, however, the effects of human activities on macroinvertebrate community structures and functional traits in glacier-fed streams are concerning. To elucidate the effects of horse, cattle and sheep grazing, hot spring scenic development, and historic iron ore mine development on macroinvertebrate communities, we conducted a study in three glacier-fed streams of the Tianshan Mountains in northwest China in April 2021. Our results showed that the species richness and density significantly decreased due to grazing (p < 0.05). There were more taxa with resilience traits such as “small size at maturity” in the grazing stream. The EPT richness and density affected by hot spring scenic development significantly decreased compared to the undisturbed point (p < 0.05). There was a significant increase in taxa with resistance traits such as “bi-or-multivoltine” in the hot spring stream. The stream affected by historic mine development is currently in the self-recovery stage following the closure of the mine ten years ago. Additionally, the species richness, EPT richness, and density at the mining site were significantly higher than the source site (p < 0.05), reflecting that the habitat fragmentation caused by previous mining activities prevented the upward dispersal of macroinvertebrates. The taxa in the mining stream were also characterized by higher resistance traits such as “abundant occurrence in drift”. These results were attributed to the impacts of human disturbance on habitat stability, habitat heterogeneity, water quality, and material cycling of stream ecosystems, indicating human disturbance on the efficiency of resource utilization and functional diversification. In addition, our results showed that functional indicators of macroinvertebrate communities are helpful for monitoring and evaluating habitat conditions.

Subtropical rivers support a highly diverse array of benthic macroinvertebrates. In this study, by combining historical data and new data, we identified specific changes in the Guanlan River, in South China, from 1981 to 2011, and evaluated the effectiveness of an ecological restoration project under highly polluted conditions. From 1981 to 2011, the water quality in the Guanlan River underwent three major stages. With the deterioration of water quality, there was an overall decrease in the species number of macroinvertebrates in the Guanlan River, an increase in macroinvertebrate density, and a reduction of the biodiversity, and a reduction of functional feeding groups. In 2011, after five years of comprehensive remediation, the Guanlan River was somewhat improved. Macroinvertebrate biodiversity in the middle reach of the Guanlan River, where a key ecological restoration engineering project was implemented, did not differ significantly from other sites. This finding indicates that the effectiveness of ecological restoration measures in highly polluted rivers, particularly at the reach-scale, is very limited and even ineffective.

Habitat loss is a key factor affecting Siberian crane stopovers. The accurate calculation of water supply and effective water resource management schemes plays an important role in stopover habitat restoration for the Siberian crane. In this paper, the ecological water demand was calculated and corrected by developing a three-dimensional model. The results indicated that the calculated minimum and optimum ecological water demand values for the Siberian crane were 2.47 × 10⁸ m³~3.66 × 10⁸ m³ and 4.96 × 10⁸ m³~10.36 × 10⁸ m³, respectively, in the study area. After correction with the three-dimensional model, the minimum and optimum ecological water demand values were 3.75 × 10⁸ m³ and 5.21 × 10⁸ m³, respectively. A water resource management scheme was established to restore Siberian crane habitat. Continuous, area-specific and simulated flood water supply options based on water diversions were used to supply water. The autumn is the best season for area-specific and simulating flood water supply. These results can serve as a reference for protecting other waterbirds and restoring wetlands in semi-arid areas.