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Long-term retention and accumulation of heavy metals in surface water and sediment pose a great threat to the sustainable development of aquatic ecosystems and human health. In this research, macrozoobenthos, and surface water and sediment heavy metal (Mn, Cr, Cu, Ni, Pb, Zn, Cd, and As) samples were collected from 23 sites in the upper and middle reaches of the Heihe River in the summers of 2019–2020. The interrelationships between heavy metals and macrozoobenthos were analyzed by Pearson correlation analysis and redundancy analysis (RDA), and the contamination level and potential ecological risk of the heavy metals in surface water and sediments were assessed by comprehensive pollution index (WQI), single potential ecological risk index ( E r i ), and sediment quality guideline-quotient (SQG-Q), respectively. The results showed that the level of heavy metal pollution in the surface water of the Heihe River was extremely low, but the contents of Mn and Pb exceeded the third class of surface water environmental quality standards (GB 3838–2002). The spatial distribution of heavy metals in surface sediments were significantly different, and the average concentration of 8 heavy metals exceeded the background values of Gansu Province. Meanwhile, the pollution level of heavy metals in surface sediments was high pollution, and the ecological risk level was moderate risk. Combining E r i and SQG-Q evaluations showed that Cd, Ni, and Cr were the main ecological risk factors. In addition, the distribution coefficients of Cr and Cd were low, indicating that Cr and Cd were easily released from the surface sediments, causing secondary pollution. In terms of the source of the heavy metals, Cu, As, Zn, Cr, and Ni mainly came from industrial and agricultural wastewaters, Pb was from the mining industry and natural sources, and Mn and Cd mainly came from tailings and their landfill leachate. Basommatophora and Araneae can be used as potential indicator organisms for heavy metal pollution in surface water, and Basommatophora, Coleoptera, Hemiptera, and Araneae can be used as indicator species for heavy metal pollution in surface sediments. The study showed that macroinvertebrate community characteristics had a sensitive response to heavy metals in the surface waters and sediments of the Heihe River, which can be used to evaluate the pollution status of heavy metals in inland rivers. [ABSTRACT FROM AUTHOR]

[Display omitted] • The changes in nineteen secondary LU types and their ESVs were predicted under the BAU and EDP scenarios by 2030 and 2050. • The LU pattern under EDP scenario is more conducive to the increase of ESV, with the increment by 2050 is 13.6 times that under BAU scenario. • Under the EDP scenario, the growth of ESV mainly comes from the positive contributions of the expansion of Forest (55.4%), Water (48.6%), and Grassland (19.1%). • Under the EDP scenario, the negative contributions of the decreases in Farmland and Unused land to the increment of ESV are −16.2% and −10.8%, respectively. The effects of land use/cover change (LUCC) on the spatial distribution and change of ecosystem service value (ESV) are still ambiguous, and cannot effectively guide the formulation of land use (LU) management policies based on the concept of harmonious development. Therefore, based on LUCC data from 1980 to 2020, this study adopted the MCE-CA-Markov model to simulate and predict the LUCC under the Business As Usual (BAU) and Ecological Development Priority (EDP) scenarios in 2030 and 2050. The historical and future ESVs as well as the effects of LUCC on ESV change were calculated in Gansu province, Northwest China. The results showed that the LU and ESV of Gansu province changed greatly between 1980 and 2020, with an increase in Forest (568.62 km2), medium- and high-coverage grassland (1517.58 km2), and Construction land (2264.58 km2), and a decrease in Farmland (-730.17 km2) and Unused land (-2858.58 km2), resulting in an increase of 8.162 billion CNY in total ESV. From 2020 to 2050, the LUCC under the EDP scenario will be more conducive to the increase in ESV, with the increment (52.765 billion CNY) being much higher than that under the BAU scenario (3.885 billion CNY). The growth of ESV will mainly result from the expansion of Forest, Water, and Grassland, accounting for 55.4%, 48.6%, and 19.1% of the total ESV increment, respectively, while the decrease in ESV will be attributed to the changes in Farmland and Unused land, accounting for −16.2% and −10.8% of the total ESV increment, respectively. The results have a certain reference for the future LU structure optimization and ecological benefit growth in northwest China. [ABSTRACT FROM AUTHOR]

• Soil carbon storage in afforested lands and in abandoned lands was compared in arid and semi-arid area, China • Carbon storage to a 1.0 m soil depth under the abandoned lands (80.58 Mg ha-1) was significantly higher than under the afforested stands (71.82 Mg ha-1) • As the loss of arable lands to urbanization worsening food security, focus should be placed on the economic use of abandoned lands through consolidation As in the rest of the world, China assumed afforestation was an effective means of helping to mitigate the negative impacts of global warming, soil erosion and soil degradation, and returned large areas of farmland to woodland. At the same time, due to industrialization and urbanization, large tracts of arable land were abandoned, especially on the Loess Plateau. To explore which land use type has greater potential to absorb carbon dioxide from the atmosphere and thus provide suggestions for land use policy in this region, a comparison of soil organic carbon storage under abandoned and afforested lands was undertaken in the northwest part of the Loess Plateau (Huining County, Gansu province, China). The soil water content, pH, soil bulk density, soil organic carbon content and overall organic carbon storage of soils (0-1.0 m depth) were measured in each of 21 plots (10 m × 10 m) on the abandoned (apricot trees) lands, and 21 similar plots on the afforested lands. Soils under the two land use types showed no significant differences in gravimetric water content or pH up to 1.0 m in depth. The soil bulk density, organic carbon content and organic carbon storage under the abandoned lands (1.18 Mg m-3, 7.07 g kg-1, and 80.58 Mg ha-1, respectively) were all significantly higher than under the afforested lands (1.13 Mg m-3, 6.62 g kg-1, and 71.8 Mg ha-1, respectively). Although benefits such as strong soil carbon fixation and lower water consumption were greater in the abandoned lands, this does not imply that afforested lands should be converted into abandoned lands, as they can provide wind barriers, reduce soil erosion, and maintain high biodiversity. However, given the integration of urban and rural development policies, as well as worsening food security issues attributable to the loss of arable lands to urbanization, some focus should be placed on the use of abandoned lands through consolidation. [ABSTRACT FROM AUTHOR]