Improved water quality monitoring indicators may increase carbon storage in the oceans

Evolution of hydrochemical characteristics and the influence of environmental background in the Hailar River basin, China

Understanding the evolution of hydrochemical characteristics in river systems is essential for environmental assessment and water resource management. This study explores the spatiotemporal distribution and the determinants of hydrochemical characteristics in the Hailar River basin, China, over an extensive period. Our results revealed that CODMn and CODCr were the primary concerns for long-term river management, with exceedance rates of 42.92% and 50.62%, respectively. These exceedances were predominantly driven by interactions between riparian soils and surface water, rather than anthropogenic pollution, as suggested by the strong correlations between dissolved organic carbon and soil water-extractable organic carbon, and the limited human footprint in this region. Piper trilinear and Gibbs diagram analysis further revealed that long-term rack weathering shaped the basin's hydrochemical characteristics, resulting in distinct HCO3--Ca2+ and HCO3--Ca2+-Na+ signatures. In addition, APCS-MLR analysis identified that elevated of CODMn and CODCr levels were mainly attributed to the interactions with adjacent soils, which are extensively covered by forests and grasslands. In contrast, leaching and migration processes contributed significantly on total dissolved solids and total phosphorus. The study also found that environmental self-purification processes played a key role in regulating Fe concentrations. This investigation provides a nuanced understanding of the environmental background's influence on hydrochemistry and dissolved organic matter (DOM) in the Hailar River basin, which offers valuable insights and methodologies for the rational assessment of water quality and aquatic ecosystem health in similar riverine systems.

The interaction between warming and enrichment accelerates food-web simplification in freshwater systems

Nutrient enrichment and climate warming threaten freshwater systems. Metabolic theory and the paradox of enrichment predict that both stressors independently can lead to simpler food-webs having fewer nodes, shorter food-chains and lower connectance, but cancel each other's effects when simultaneously present. Yet, these theoretical predictions remain untested in complex natural systems. We inferred the food-web structure of 256 lakes and 373 streams from standardized fish community samplings in France. Contrary to theoretical predictions, we found that warming shortens fish food-chain length and that this effect was magnified in enriched streams and lakes. Additionally, lakes experiencing enrichment exhibit lower connectance in their fish food-webs. Our study suggests that warming and enrichment interact to magnify food-web simplification in nature, raising further concerns about the fate of freshwater systems as climate change effects will dramatically increase in the coming decades.

ResNet14Attention network for identifying the titration end-point of potassium dichromate

With the rapid development of industry, the increasing discharge of sewage causes the detection of water quality to be of increasing importance. Potassium dichromate titration is one of the most important testing methods in water quality detection; the ability to accurately identify the titration end-point of potassium dichromate is currently a research challenge. To identify titration end-point quickly and accurately, this study proposes a ResNet14Attention network, which utilizes residual modules that focus on original image information and an attention mechanism that focuses highly on classification targets. The proposed ResNet14Attention network is compared with 12 convolutional neural networks such as ResNet series networks, VGG, and GoogLeNet. The results of comparison experiments reveal that only the proposed ResNet14Attention network has the highest training and testing accuracy of 100% among all convolutional neural networks in the comparison experiment; the proposed ResNet14Attention network has the highest training speed compared to all the networks that over 90% accuracy.

A hybrid remote sensing approach for estimating chemical oxygen demand concentration in optically complex waters: A case study in inland lake waters in eastern China

Chemical oxygen demand concentration (C_COD) is widely used to indicate the degree of organic pollution of lakes, reservoirs and rivers. Mastering the spatiotemporal distribution of C_COD is imperative for understanding the variation mechanism and controlling of organic pollution in water. In this study, a hybrid approach suitable for Sentinel 3A/Ocean and Land Colour Instrument (OLCI) data was developed to estimate C_COD in inland optically complex waters embedding the interaction between C_COD and the absorption coefficients of optically active constituents (OACs). Based on in-situ sampling in different waters, the independent validations of the proposed model performed satisfactorily in Lake Taihu (MAPE = 23.52 %, RMSE = 0.95 mg/L, and R² = 0.81), Lake Qiandaohu (MAPE = 21.63 %, RMSE = 0.50 mg/L and R² = 0.69), and Yangtze River (MAPE = 29.34 %, RMSE = 0.83 mg/L, and R² = 0.64). In addition, the approach not only showed significant superiority compared with previous algorithms, but also was suitable for other common satellite sensors equipped same or similar bands. The hybrid approach was applied to OLCI images to retrieve C_COD of Lake Taihu from 2016 to 2020 and reveals substantial interannual and seasonal variations. The above results indicate that the proposed approach is effective and stable for studying spatiotemporal dynamic of C_COD in optically complex waters, and that satellite-derived products can provide reliable information for lake water quality management.

Effective and Low-Cost Adsorption Procedure for Removing Chemical Oxygen Demand from Wastewater Using Chemically Activated Carbon Derived from Rice Husk

Wastewater treatment by adsorption onto activated carbon is effective because it has a variety of benefits. In this work, activated carbon prepared from rice husk by chemical activation using zinc chloride was utilized to reduce chemical oxygen demand from wastewater. The as-prepared activated carbon was characterized by scanning electron microscope, Fourier transform infrared spectroscopy and nitrogen adsorption/desorption analysis. The optimum conditions for maximum removal were achieved by studying the impact of various factors such as solution pH, sorbent dose, shaking time and temperature in batch mode. The results displayed that the optimum sorption conditions were achieved at pH of 3.0, sorbent dose of 0.1 g L−1, shaking time of 100 min and at room temperature (25 °C). Based on the effect of temperature, the adsorption process is exothermic in nature. The results also implied that the isothermal data might be exceedingly elucidated by the Langmuir model. The maximum removal of chemical oxygen demand by the activated carbon was 45.9 mg g−1. The kinetic studies showed that the adsorption process follows a pseudo-first order model. The findings suggested that activated carbon from rice husk may be used as inexpensive substitutes for commercial activated carbon in the treatment of wastewater for the removal of chemical oxygen demand.

Effects of Industrial Structure Adjustment on Pollutants Discharged to the Aquatic Environment in Northwest China

Northwest China is located along China’s Belt and Road Initiative routes and represents the frontier and core region for China’s construction and development of the Silk Road Economic Belt. In recent years, the conflict between economic development and environmental pollution has become increasingly intense in this region, with the latter mainly caused by disorderly industrialization brought about by rapid urbanization processes. Inappropriate industrial structure is the primary reason for environmental degradation in Northwest China, which has limited precipitation and available water. Due to its fragile aquatic environment and unsustainable use of water resources, the pollution and degradation of the aquatic environment has become a bottleneck that severely restricts the sustainable development of China’s northwest region. In the present study, five provinces or autonomous regions in Northwest China were selected as the study objects. Based on the vector autoregressive (VAR) model, quantitative research methods, such as impulse response function and variance decomposition analysis, were applied to quantify the dynamics between industrial structure adjustment and changes in industrial pollutant discharges to the aquatic environment, so that the impact of industrial structure adjustment on pollutants discharged to the aquatic environment could be quantified and characterized. Therefore, the present study has both theoretical and practical significance. The conclusions are as follows: (1) In general, industrial structure in most provinces in Northwest China imposes a positive effect over the discharge of pollutants to the aquatic environment. Adjusting industrial structure and reducing the proportion of secondary industry present can to some extent promote reductions in the discharge of pollutants to the aquatic environment. However, such beneficial effects may vary among different provinces. (2) Specifically, for Gansu, province industrial structure adjustment could help reduce the discharge of pollutants to the aquatic environment effectively during the early stages, but this positive effect gradually weakens and disappears during the later stages. In Qinghai province, industrial structure adjustment could not help reduce the discharge of pollutants to the aquatic environment effectively during the early stages, but a positive effect gradually increases and continues to function later. The performance in Shaanxi and Xinjiang provinces was quite similar, with industrial structure adjustment helping to effectively reduce the discharge of pollutants to the aquatic environment over a long period of time. This positive effect can play a more sustained and stable role. For Ningxia province, industrial structure adjustment can not only help significantly reduce the discharge of pollutants to the aquatic environment but also displays a significant positive effect. (3) Given the specific conditions and characteristics of the region under study, relevant policies for industrial structure adjustment should be formulated and implemented.