Ecological restoration is not sufficient for reconciling the trade-off between soil retention and water yield: A contrasting study from catchment governance perspective

Vegetation cover dynamics and its constraint effect on ecosystem services on the Qinghai-Tibet Plateau under ecological restoration projects

Ecological restoration projects (ERPs) are implemented worldwide to restore degraded ecosystems and promote ecosystem sustainability. In recent years, a series of ERPs have been implemented to enhance vegetation cover in the unique alpine ecosystems of the Qinghai-Tibet Plateau (QTP). However, the current assessment of the ecological benefits of ERPs is relatively single, and the scale and extent of future ecological restoration project implementation cannot be determined. We quantified trends in normalized vegetation index (NDVI) since the implementation of ERPs. Changes in four major ecosystem services were assessed before and after ERPs implementation, including wind erosion protection, soil retention, water yield, and net primary productivity (NPP). The relationship between NDVI and ecosystem services was further explored using a constraint line approach to identify NDVI as a threshold reference for ERPs implementation. The results showed that: (1) since the implementation of ERPs, 21.80% of the regional NDVI of the QTP has increased significantly. (2) After the implementation of ERPs, the average total ecosystem services index (TES) increased from 0.269 in 2000 to 0.285 in 2020. The average soil retention and water yield increased but the NPP and sandstorm prevention decreased slightly. (3) NDVI had no significant constraint effect on soil retention and NPP, but there was a significant constraint effect on wind erosion prevention and water yield. (4) The constraint line of NDVI on TES was S-shaped. After the implementation of ERPs, the TES gradually reached a threshold value when NDVI was 0.65-0.75. Our findings identify significant contributions of ERPs and thresholds for the constraining effects of vegetation cover on ecosystem services, which can inform sustainable ERPs for governments.

Exploring interactions in water-related ecosystem services nexus in Loess Plateau

Scientific understanding of the driving relationship between water-related ecosystem services (WESs) and influencing factors, as well as the trade-off and synergy relationship between WESs and WESs, is the premise of reasonably bringing them into management decisions. However, the existing research often separates the above-mentioned two relationships and conducts independent research, which leads to the conflict of research conclusions and cannot be well adopted by managers. Therefore, based on the panel data of Loess Plateau in 2000-2019, this paper uses the simultaneous equation model to combine the two kinds of relationships existing between WESs and influencing factors, establish a feedback loop, and reveal the interactions mechanism of WESs nexus. The results show that: (1) The fragmentation of land use leads to the uneven spatial-temporal distribution of WESs. (2) Vegetation factors and land factors are the main driving factors that affect WESs, and the impact of climate factors on WESs is decreasing year by year. (3) The increase of water yield ecosystem services will lead to the obvious increase in soil export ecosystem services, and there is a synergistic relationship between soil export ecosystem services and nitrogen export ecosystem services. The conclusion can provide an important reference for implementing the strategy of ecological protection and high-quality development.

Distribution of ecological restoration projects associated with land use and land cover change in China and their ecological impacts

China is prone to broad land degradation and thus has been implementing ecological restoration projects (ERPs) since the reform and opening up. The extent of ERPs, as well as the varied planting efforts including tree gain projects (TGPs), grass gain projects (GGPs), and shrub gain projects (SGPs), have remained largely unknown. In addition, the mixed success of ERPs on preventing soil erosion and improving biodiversity is not well known. Based on a land use and land cover (LULC) product and a trajectory-based change detection approach, we successfully generated the first national map of ERPs associated with land use and land cover change (LUCC) and its three associated subcategories. Then, we applied the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model to evaluate the dynamics of sediment retention and habitat quality. In addition, we explored the heterogeneous patterns for the ecological impacts of ERPs. Our results suggested that during the past 40 years, a total ERP area of 9.54 × 10⁶ hm² was observed nationwide, mainly in the northwestern provinces of China. Of the three ERP subcategories, TGPs accounted for the largest area (48.55%), followed by GGPs (47.50%) and SGPs (3.96%). The national average sediment retention experienced a significant increase, whereas the national average habitat quality experienced a significant decline. ERP-driven increases in habitat quality were offset partly by the LUCCs induced by economic development policies in some regions, especially in northeast China. The simultaneous effect of construction land expansion and ERP implementation on sediment retention made the synchronization between ERP implementation and sediment retention improvement insignificant. We also suggested the optimal direction for ERP implementation.

Multi-scale assessment of water security under climate change in North China in the past two decades

Climate change is projected to affect the hydrological cycles in China, while the effects are expected to vary spatiotemporally. Understanding the variations in water security conditions and their sensitivity to climatic variables is crucial for assessing regional ecosystem responses to climate change. In the present study, we estimated the water yield capacity, an important indicator of water security in North China (NC), at a spatial resolution of 1 km during the last two decades based on the Budyko framework and quantified the sensitivity of water yield change to climate change among different vegetation types. The results showed that the performances of the Budyko framework were reliable both at the pixel scale and across large watersheds. The annual water yield in North China was estimated to be 7.61 ± 2.67 ∗ 10¹⁰ m³/yr, with an average mean water yield (MWY) of 49.51 ± 17.49 mm/yr. The spatial pattern of mean water yield change (MWYC) exhibited high heterogeneity; 46% of the study region was dominated by an increasing trend, while 9.84% was statistically significant (P < 0.05). Compared with temperature, the water yield capacity was more sensitive to precipitation variation. A consistent trend of variation was found in cropland between water yield and precipitation, while negative sensitivity coefficients were found in natural vegetation types. The variation in sensitivity coefficients (Swyp) in natural vegetation showed that in regions with a decrease in precipitation, the variation in water yield capacity also decreased, while in regions with an increase in precipitation from 0 to 8 mm/yr, the water yield capacity first decreased and then increased with precipitation. Our findings suggest that grass and shrubs would be more beneficial to regional water security in North China's revegetation, while afforestation would provide protection for the regional environment from extreme rainfall events.

Quantitative Assessment for the Spatiotemporal Changes of Ecosystem Services, Tradeoff–Synergy Relationships and Drivers in the Semi-Arid Regions of China

Ecosystem services in arid inland regions are significantly affected by climate change and land use/land cover change associated with agricultural activity. However, the dynamics and relationships of ecosystem services affected by natural and anthropogenic drivers in inland regions are still less understood. In this study, the spatiotemporal patterns of ecosystem services in the Hexi Region were quantified based on multiple high-resolution datasets, the InVEST model and the Revised Wind Erosion Equation (RWEQ) model. In addition, the trade-offs and synergistic relationships among multiple ecosystem services were also explored by Pearson correlation analysis and bivariate spatial autocorrelation, and redundancy analysis (RDA) was also employed to determine the environmental drivers of these services and interactions. The results showed that most ecosystem services had a similar spatial distribution pattern with an increasing trend from northwest to southeast. Over the past 40 years, ecosystem services in the Hexi Region have improved significantly, with the water retention and soil retention increasing by 87.17 × 108 m3 and 287.84 × 108 t, respectively, and the sand fixation decreasing by 369.17 × 104 t. Among these ecosystem services, strong synergistic relationships were detected, while the trade-offs were found to be weak, and showed significant spatial heterogeneity in the Hexi Region. The spatial synergies and trade-offs in the Qilian Mountains were 1.02 and 1.37 times higher than those in the Hexi Corridor, respectively. Human activities were found to exacerbate the trade-offs between ecosystem services by increasing water consumption in the Hexi Corridor, with the exception of carbon storage. In particular, there were significant tradeoffs between food production and water retention, and between soil retention and habitat quality in the oases of the Hexi Corridor, which is affected by rapid population growth and cropland expansion. Additionally, precipitation, temperature and vegetation cover in the Qilian Mountains have increased significantly over the past four decades, and these increases significantly contributed to the enhancements in water retention, carbon storage, habitat quality, soil retention and food production. Nevertheless, the amount of sand fixation significantly decreased, and this was probably associated with the reduction in wind speed over the past four decades. Our results highlighted the importance of climate wetting and water resource management in the enhancement of ecosystem services and the mitigation of food production trade-offs for arid inland regions.

Off-office audit of natural resource assets and water pollution: a quasi-natural experiment in China

Purpose

The purpose of this paper is to analyze the impact of the off-office audit of natural resource assets on the prevention and control of water pollution against a background of big data using a differences-in-differences model.

Design/methodology/approach

This study constructs a differences-in-differences model to evaluate the policy effects of off-office audit based on panel data from 11 cities in Anhui Province, China, from 2011 to 2017, and analyzes the dynamic effect of the audit and intermediary effect of industrial structure.

Findings

The implementation of the audit system can effectively reduce water pollution. Dynamic effect analysis showed that the audit policy can not only improve the quality of water resources but can also have a cumulative effect over time. That is, the prevention and control effect on water pollution is getting stronger and stronger. The results of the robustness test verified the effectiveness of water pollution prevention and control. However, the results of the influence mechanism analysis showed that the mediating effect of the industrial structure was not obvious in the short term.

Practical implications

These findings shed light on the effect of the off-office audit of natural resource assets on the prevention and control of water pollution, and provide a theoretical basis for the formulation of relevant environmental policies. Furthermore, these findings show that the implementation of the audit system can effectively reduce water pollution, which has practical significance for the sustainable development of China's economy against the background of big data.

Originality/value

This study quantitatively analyzes the policy effect of off-office auditing from the perspective of water resources based on a big data background, which differs from the existing research that mainly focuses on basic theoretical analysis.

Construction of Ecological Network Based on Multi-Scale Conversion and Nesting

Ecological protection and the restoration of full-array ecosystems is an important part of ecological civilization construction, which is a powerful measure to implement the concept of green development and help bridge the gap between the respective inevitable requirements of the current ecological environment and economic development. To solve this problem, a multi-scale index system was constructed to identify ecological sources comprehensively. The minimum-cost path method, the circuit theory, and the cyclic window search method were adopted to quantitatively identify the important ecological sources and corridors in scale nesting and pinch points and barrier points that affect multi-level connectivity. Furthermore, the specific optimization layout strategy of the ecological network structure of the Hefei metropolitan area was proposed. According to the results, if ecological sources and corridors at two scales are overlaid, the coincident area of ecological sources at two scales is 1719.95 km2. As important ecological sources, Chaohu Lake Basin, Niuwangzhai, and Wuding Mountain, which are important areas to maintain the ecological network, need to be protected. Ten overlapping ecological corridors, which are mainly distributed in Changfeng County, are easily damaged long term. As a result, ecological nodes should be set up as temporary habitats for species transfer. In addition, based on the circuit theory and the cyclic window search method, calculating areas of pinch points at two scales yields 1637.75 km2 and 434.22 km2, respectively, and for areas of barrier points yields 2182.75 km2 and 126.97 km2, respectively. The ecological pinch points at two overlapping scales among them are important areas for future protection. Due to the small and fragmented spatial distribution in the urban area, pinch points with an average size of 0.58 km2 are easy to be restored and will greatly improve the connectivity of the ecological network after restoration. Furthermore, through the quantitative identification of ecological network elements of two scales, the paper puts forward an optimization strategy for an ecological network in the Hefei metropolitan area from three aspects of “point-line-polygon.” The research results can reference decision-making concerning the delineation of urban growth boundary, regional ecological security pattern, land space renovation, and ecosystem restoration.

Exploring soil erosion trajectories and their divergent responses to driving factors: a model-based contrasting study in highly eroded mountain areas

Soil erosion threatens environmental sustainability worldwide. Exploring the trajectories of soil erosion and associated drivers is of great significance for combating land degradation. This study selected the highly eroded Loess Plateau (LP) and Karst Plateau (KP) as contrasting regions to monitor soil erosion dynamics. Monitoring was performed by applying the Revised Universal Soil Loss Equation based on a GIS platform and multi-source input data to investigate associated drivers. The results established that soil erosion in both regions was substantially reduced by ecological restoration projects and significant land use/cover conversions. Landscape and geomorphological variables were found to be the dominant factors controlling soil erosion in the LP and KP, as they influenced land use patches and geomorphological patterns, respectively. The correlations between fragmentation metric indices and soil erosion indicated that the appropriately intensive fragmentation in the LP could mitigate or prevent soil erosion by disturbing its formation and transportation and ultimately positively influenced soil erosion control. Geomorphological patterns were also determinative factors, particularly for the KP, where almost all geomorphological variables were significantly correlated with the erosion modulus. Owing to the peculiar landform and landscape conditions in karst areas and loess hilly-gully areas, geomorphological and landscape variables should be considered when determining the main factors affecting soil erosion processes and integrated into the forecasting model to improve the accuracy of the simulation. The findings of this study are expected to (i) improve the efficacy of soil erosion control and (ii) promote the sustainable planning and management of land and soil resources.