Four decades' dynamics of coastal blue carbon storage driven by land use/land cover transformation under natural and anthropogenic processes in the Yellow River Delta, China

Dynamics of land cover changes and carbon emissions driven by large dams in China

The recent surge in dam construction has sparked debates regarding their contribution to carbon neutrality and food security, focusing on trade-offs between production benefits and ecological drawbacks. However, how dams affect carbon emissions and land cover changes, including their spatial differentiations, remains unclear. We quantified spatiotemporal variations in carbon emissions and storage of 137 large dams in China from 1992 to 2020, resulting from land cover change in potentially affected areas. We observed a lesser increase in carbon emissions and a more pronounced increase in carbon storage driven by forest conservation and regeneration within dam-affected areas compared to unaffected areas. Additionally, we noticed an increased grain yield in nearby areas potentially due to increased water availability. Our findings highlight the importance of considering land cover change when assessing carbon neutrality or grain yield at regional and national scales. This study provides useful insights into optimizing dam locations to mitigate future carbon emissions effectively.

Dynamics of carbon storage driven by land use/land cover transformation in coal mining areas with a high groundwater table: A case study of Yanzhou Coal Mine, China

Intensive anthropogenic activities have led to drastic changes in land use/land cover (LULC) and impacted the carbon storage in high-groundwater coal basins. In this paper, we conduct a case study on the Yanzhou Coalfield in Shandong Province of China. We further classify waterbodies by using the Google Earth Engine (GEE) to better investigate the process of LULC transformation and the forces driving it in four periods from 1985 to 2020 (i.e., 1985-1995, 1995-2005, 2005-2015, and 2015-2020). We modeled the spatiotemporal dynamics of carbon storage by using InVEST based on the transformation in LULC and its drivers, including mining (M), reclamation (R), urbanization and village relocation (U), and ecological restoration (E). The results indicate that carbon storage had depleted by 19.69 % (321099.06 Mg) owing to intensive transformations in LULC. The area of cropland shrank with the expansion of built-up land and waterbodies, and 56.31 % of the study area underwent transitions in land use in the study period. U was the primary driver of carbon loss while E was the leading driver of carbon gain. While the direct impact of M on carbon loss accounted for only 5.23 % of the total, it affected urbanization and led to village relocation. R led to the recovery of cropland and the reclamation of water for aquaculture, which in turn improved the efficiency of land use. However, it contributed only 2.09 % to the total increase in carbon storage. Numerous complicated and intertwined processes (211) drove the changes in carbon storage in the study area. The work here provides valuable information for decision-makers as well as people involved in reclamation and ecological restoration to better understand the link between carbon storage and the forces influencing it. The results can be used to integrate the goals of carbon sequestration into measures for land management.

New insight into blue carbon stocks and natural-human drivers under reclamation history districts for sustainable coastal development: A case study from Liaohe River Delta, China

Blue carbon is a vital aspect of climate change mitigation, which necessitates the identification of stocks and drivers for implementing mitigation strategies. However, reclamation may be among the most invasive forms, and the question of its influence has not been addressed well in blue carbon research. Therefore, the effects of reclamation on carbon stocks and the interaction of crucial drivers from reclamation time areas (1930s, 1960s, 1990s) were evaluated in the Liaohe River Delta (LRD) and compared with natural reserves (core, buffer, experimental areas). Carbon stocks based on InVEST model were lower than preexisting conditions (1.930 × 10⁶ Mg-1.893 × 10⁶ Mg). One-way Analysis of Variance showed that average carbon stocks accumulated 55 years after reclamation and reached the lowest value (13.19 Mg·ha^-1) in 85 years. The interaction analysis of dominant drivers affecting carbon showed the difference between reclaimed areas and reserves regarding potential effect pathways. In the 1930s and 1960s reclamation time areas, crop yield and industrial output determined blue carbon by changing NO₃^--N and AP. In the 1990s reclamation time area, population density played an important role. In defining the impact of vegetation cover on carbon within the reserves, the distance to the coast and residence were significant factors. This study demonstrated that coastal management practices, such as the size of industry and population control and the balanced fertilization techniques in reclamation areas, maintaining adequate vegetation cover in reserve, played a crucial role in the improvement of blue carbon sinks.

Analysis of the implementation effects of ecological restoration projects based on carbon storage and eco-environmental quality: A case study of the Yellow River Delta, China

As an important means to address global climate change and land-use/land-cover (LULC) change, ecological restoration projects (ERPs) have a large effect on carbon storage functions and eco-environmental quality. However, the various ERPs carried out in the Yellow River Delta region have important implications for ecological security strategies in China. Therefore, based on land-use data and remote sensing image data, with the help of ArcGIS and Google Earth Engine (GEE) platforms, this study uses the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model, an improved remote sensing ecological index (RSEI) model and other methods to deeply examine the evolutionary trends of eco-environmental quality and carbon storage during the implementation of ERPs in the Yellow River Delta and selects key implementation areas for in-depth analysis to determine the implementation effects of ERPs. Our findings suggested that the RSEI and carbon storage levels in the study area had opposite evolutionary trends from 2001 to 2020. Among them, the RSEI showed a fluctuating upwards trend (0.4461 (2001) and 0.5185 (2020)), while the total carbon stock showed a fluctuating downwards trend (30.67 Tg (2001) and 26.40 Tg (2020)). However, from 2015 to 2020, the RSEI and carbon storage were at a relatively stable level, which indirectly indicated that the ERPs carried out during the period from 2015 to 2020 had achieved a good comprehensive implementation effect. In addition, the areas with better improvement effects from 2015 to 2020 were primarily located in the mouth of the Yellow River Delta (Areas C and D), and their RSEI and the total carbon stock showed a certain upwards trend. This research can promote the formulation of the management strategy of ERPs in the Yellow River Delta, which is of tremendous importance to the ecological environmental preservation and high-quality development of the Yellow River Basin.

Seawall-induced impacts on large river delta wetlands and blue carbon storage under sea level rise

Coastal wetlands have been enclosed by thousands of kilometers of seawalls in China to obtain extra land for rapid socio-economic development in the coastal region. Although understanding seawall-induced impacts on delta wetlands and their ecosystem can provide valuable decision-making information to support coastal management, quantifying and measuring long-term, cumulative ecological impacts of harden seawall under sea level rise (SLR) remains a vital research gap. In this study, by combining the land-use transformation trajectory analysis, ecosystem services assessment, and the SLAMM (Sea Level Affecting Marshes Model), we have explored the seawall-induced effects on temporal-spatial dynamics of tidal wetlands and the Coastal Blue Carbon storage (CBCs) in the Yellow River Delta (YRD) under the SLR by 2050 and 2100. Our study revealed that the delta wetland area would have increased by 2327.87 km² after seawall removal without regard for SLR while increasing by 3050 km² in 2100 in both seawall scenarios under SLR. The effects of driving processes trajectory on the changes in CBCs indicated two-sided seawall-induced impacts on the delta wetlands in the YRD, i.e., functioning as a physical coastal defense to prevent coastal erosion (before 2050) while intensifying coastal squeeze effects and quickening the loss in delta wetlands and the CBCs by hindering their inland migration under SLR. For example, the gap of CBCs between the seawall-impacting and seawall-removal scenarios would have reached at 9.94 × 10⁶ Mg by 2050 under the SLR, and the magnitude of the final decrease effect on CBCs induced by the seawall-impacting would be nearly 5 times higher than its gain after seawall-removal in the regressive succession, while the same magnitudes in the salinization process on both scenarios. Our study has provided valuable insights for shoreline management by mitigating seawall-induced impacts on the delta wetlands and their ecosystem services such as CBCs.

Impacts of rapid urbanization on spatial dynamics of land use-based carbon emission and surface temperature changes in the Semarang Metropolitan Region, Indonesia

This study explores the relationship between carbon emission patterns and the land surface temperature (LST) changes due to the rapid urbanization in the Semarang Metropolitan Region (SMR), an Indonesian area that has experienced rapid urban growth compared to other urban areas. This research used the stock-difference and gain-loss methods to calculate carbon stocks and emissions. Then, band 6 on Landsat 5 TM (2008) and band 10 on Landsat 8 OLI (2013 and 2018) were used to calculate the LST changes. These results showed that the peri-urban area had a more significant change. The correlation between carbon emissions and an increased SMR temperature correlates to 0.646. This shows that the carbon emissions pattern promotes temperature dynamics in the SMR. Furthermore, this study proved the release of carbon emissions in line with LST dynamics spatially. In this case, this study proved that rapid urbanization in the SMR promotes both carbon emission and LST. Those changes are also affected by vegetation canopy availability and other activities. As a result, the government must prioritize spatial planning in the SMR to mitigate environmental change risk. In addition, the government must develop novel strategies to deal with a wide range of fast and unpredictable potential changes in the urban area and its surroundings.

Exploring the Relationship between Ecosystem Services under Different Socio-Economic Driving Degrees

The large-scale transformation of natural ecosystems to socio-economic development land types under human activities was a primary reason for the decline of regional ecosystem services. It is a key issue for regional ecosystem planning and management to reveal the relationship between ecosystem services of different land use types under different socio-economic driving degrees. However, the current related research was not in-depth. Based on the land use data of Wuhan City in 1980, 1990, 2000, 2010, and 2020, this study classified land use into three categories according to the different degrees of human activities on natural ecosystem development: the land use of a natural ecosystem (LUNE), the land use of a productive ecosystem (LUPE), and the land use of a socio-economic system (LUSE). The InVEST model was used to simulate five ecosystem services (grain yield, water yield, carbon storage, habitat quality, and water purification), and the spatio-temporal distribution and functional transformation of the three land use types were analyzed. Results showed that with the intensified urban expansion in Wuhan, the LUSE types increased to 2.7 times that of the original. However, the natural land types basically maintained a stable area, coupling with the large-scale transformation between the LUPE and LUSE types. Land use change resulted in significant spatial changes of five ecosystem services, especially carbon storage and habitat quality. The correlation analysis indicated that the five kinds of ecosystem services mainly showed a synergistic relationship, meanwhile the LUSE type denoted the most significant correlation with ecosystem services among these three category types. This study indicated that besides the protection of natural ecosystems, the LUSE type would become the key land use type in the planning and management of improving regional ecological function.

Hidden challenges behind ecosystem services improvement claims

Substantial evidence indicates that China’s afforestation statistically contributed to the ecosystem services (ES) improvement. However, we found the potential challenges behind this improvement, especially in water-limited areas. We propose an attribution analysis method, which can assess the specific contribution of natural, human and cognition degree drivers to ES dynamics. The results found that the ratio of natural and human drivers in the area north of China’s 400 mm precipitation isopleth is 2:7. This means local vegetation capacity has already exceeded water limitation, implying a conflict between nature and humans. However, the natural contribution in the area between 400 and 800 mm precipitation isopleth is negative, whereas the human contribution is 91%. This means this area has fragile natural conditions and needs more flexible policies. The ratio of natural and human drivers in the region south of 800 mm precipitation isopleth is 6:3, suggesting the ecological policies here can be maintained.

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PDE is used to assess the contribution of natural and human drivers to ES changes

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Land use management dominantly contributed (55%) to China’s ES improvement

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Re-vegetation in the area north of 400 mm precipitation isohyet exceeded NPP threshold

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The area between 400 and 800 mm isoprecipitation line is the key area with ES decrease

Evidence of improvements in the water quality of coastal areas around China

Coastal areas are huge carbon stores and hotspots for marine carbon fixation. Changes in the water quality of coastal areas are closely linked to their carbon fixation function. In this study, monitoring data were analyzed to identify how the water quality in China's coastal areas changed from 2001 to 2020. The results showed that the water quality in the coastal areas had improved gradually since 2001. The proportion of water quality in Class II and above gradually increased from 41.4% in 2001 to 77.4% in 2020, meanwhile, the proportion of water quality less than Class II, decreased from 58.6% to 22.6%, respectively. Of the four sea areas, the water quality was best in the Yellow Sea, and was poor in the East China Sea. The water quality varied between the different coastal provinces and cities and was good in coastal areas of Hainan, Guangxi, Shandong, and other provinces and cities, but was poor in Shanghai, Zhejiang, and Tianjin. Terrestrial anthropogenic pollutants were the main influence on the water quality in the coastal areas. As a hotspot for fixing blue carbon, the continuous improvement of the water quality of coastal areas laid a foundation for the health of the blue carbon ecosystems.

How to Account for Changes in Carbon Storage from Coal Mining and Reclamation in Eastern China? Taking Yanzhou Coalfield as an Example to Simulate and Estimate

Carbon sequestration in terrestrial ecosystems plays an essential role in coping with global climate change and achieving regional carbon neutrality. In mining areas with high groundwater levels in eastern China, underground coal mining has caused severe damage to surface ecology. It is of practical significance to evaluate and predict the positive and negative effects of coal mining and land reclamation on carbon pools. This study set up three scenarios for the development of the Yanzhou coalfield (YZC) in 2030, including: (1) no mining activities (NMA); (2) no reclamation after mining (NRM); (3) mining and reclamation (MR). The probability integral model (PIM) was used to predict the subsidence caused by mining in YZC in 2030, and land use and land cover (LULC) of 2010 and 2020 were interpreted by remote sensing images. Based on the classification of land damage, the LULC of different scenarios in the future was simulated by integrating various social and natural factors. Under different scenarios, the InVEST model evaluated carbon storage and its temporal and spatial distribution characteristics. The results indicated that: (1) By 2030, YZC would have 4341.13 ha of land disturbed by coal mining activities. (2) Carbon storage in the NRM scenario would be 37,647.11 Mg lower than that in the NMA scenario, while carbon storage in the MR scenario would be 18,151.03 Mg higher than that in the NRM scenario. Significantly, the Nantun mine would reduce carbon sequestration loss by 72.29% due to reclamation measures. (3) Carbon storage has a significant positive spatial correlation, and coal mining would lead to the fragmentation of the carbon sink. The method of accounting for and predicting carbon storage proposed in this study can provide data support for mining and reclamation planning of coal mine enterprises and carbon-neutral planning of government departments.

Effects of Land Use/Land Cover Changes on Carbon Storage in North African Coastal Wetlands

Healthy wetlands are among the most effective sinks for carbon on the planet, and thus contribute to mitigate climate change. However, in North Africa, coastal wetlands are under high pressure especially from urban sprawl and tourism development, due to the rapid population growth and migration. This paper analyzed the effects of land use/land cover changes on carbon stocks, over 20 years, in six North African coastal wetlands, and estimated the economic value of the carbon sequestered during the considered period. The methodology used combined remote sensing and modeling. The results showed that among the six studied sites, only two (Moulouya and Moulay Bouselham) showed an increase in stored carbon and therefore are potential carbon sinks. In turn, the other four showed a more or less significant loss of carbon, which will likely be released into the atmosphere. The underlying processes that drive changes in carbon dynamics are mainly urban expansion and land use conversion, which often occurs at the expense of the natural habitats surrounding the wetlands. Understanding these processes can provide valuable decision-making information for land use planning, wetlands conservation and carbon reduction policies.

The Dynamics Characteristics of Soil Water Infiltration and Capillary Rise for Saline–Sodic Soil Mixed with Sediment

Yellow River sediment is the potential resource for saline–sodic soil reclamation. Experiments of one-dimensional soil columns were conducted to investigate the upward and downward soil water transportation characteristics for saline–sodic soil mixed with different sediment addition (0, 10, 20 kg/m2 in the top 20 cm layer). The saturated hydraulic conductivity, ratio of macroporosity, cumulative capillary adsorption and infiltration rate all increased with the increase in sediment addition. No significant differences were detected for both the initial capillary rise rate and the initial infiltration rate for the upward and downward water transportation treatments, respectively. The average adsorption and infiltration rates showed an increasing trend with the increased sediment addition. The initial and average infiltration rates were higher than the initial capillary rise rate and average adsorption rates. The Philip model seems the optimal choice for the dynamic simulation of both upward and downward soil water transportation. The results may provide useful information for soil salinization amelioration.

Dynamics of Tree outside Forest Land Cover Development and Ecosystem Carbon Storage Change in Eastern Coastal Zone, Bangladesh

Tree outside forest (TOF) has immense potential in economic and environmental development by increasing the amount of tree vegetation in and around rural settlements. It is an important source of carbon stocks and a critical option for climate change regulation, especially in land-scarce, densely populated developing countries such as Bangladesh. Spatio-temporal changes of TOF in the eastern coastal zone of Bangladesh were analyzed and mapped over 1988–2018, using Landsat land use land cover (LULC) maps and associated ecosystem carbon storage change by linking the InVEST carbon model. Landsat TM and OLI-TIRS data were classified through the Maximum Likelihood Classifier (MLC) algorithm using Semi-Automated Classification (SAC). In the InVEST model, aboveground, belowground, dead organic matter, and soil carbon densities of different LULC types were used. The findings revealed that the studied landscapes have differential features and changing trends in LULC where TOF, mangrove forest, built-up land, and salt-aquaculture land have increased due to the loss of agricultural land, mudflats, water bodies, and hill vegetation. Among different land biomes, TOF experienced the largest increase (1453.9 km2), and it also increased carbon storage by 9.01 Tg C. However, agricultural land and hill vegetation decreased rapidly by 1285.8 km2 and 365.7 km2 and reduced carbon storage by 3.09 Tg C and 4.89 Tg C, respectively. The total regional carbon storage increased by 1.27 Tg C during 1988–2018. In addition to anthropogenic drivers, land erosion and accretion were observed to significantly alter LULC and regional carbon storage, necessitating effective river channel and coastal embankment management to minimize food and environmental security tradeoff in the studied landscape.

Spatiotemporal Change and the Natural-Human Driving Processes of a Megacity's Coastal Blue Carbon Storage

Coastal blue carbon storage (CBCS) plays a key role in addressing global climate change and realizing regional carbon neutrality. Although blue carbon has been studied for some years, there is little understanding of the influence of a megacity’s complex natural and human-driven processes on CBCS. Taking the Shanghai coastal area as an example, this study investigated the spatiotemporal change in CBCS using the InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) model during 1990–2015, and analyzed the response of the CBCS to a megacity’s complex natural- and human-driven processes through a land use/land cover transition matrix and hierarchical clustering. The results were as follows: (1) Thirty-three driving processes were identified in the study area, including four natural processes (e.g., accretion, succession, erosion, etc.), two human processes (reclamation and restoration) and twenty-seven natural–human coupled processes; they were further combined into single and multiple processes with positive and negative influences on the CBCS into four types (Mono+, Mono−, Multiple+ and Multiple− driving processes). (2) Shanghai’s CBCS increased from 1659.44 × 10⁴ Mg to 1789.78 ×10⁴ Mg, though the amount of Shanghai’s coastal carbon sequestration showed a decreasing trend in three periods: 51.28 × 10⁴ Mg in 1990–2000, 42.90 × 10⁴ Mg in 2000–2009 and 36.15 × 10⁴ Mg in 2009–2015, respectively. (3) There were three kinds of spatiotemporal patterns in the CBCS of this study area: high adjacent to the territorial land, low adjacent to the offshore waters in 1990; high in the central part, low in the peripheral areas in 2009 and 2015; and a mixed pattern in 2000. These patterns resulted from the different driving processes present in the different years. This study could serve as a blueprint for restoring and maintaining the CBCS of a megacity, to help mitigate the conflicts between socioeconomic development and the conservation of the CBCS, especially in the Shanghai coastal area.

Effect of straw decomposition on organic carbon fractions and aggregate stability in salt marshes

Straw addition can increase the content of soil organic carbon (SOC), and affect the content of aggregates and organic carbon fractions. The changes in aggregates and organic carbon fractions in the natural salt marsh, 10-year and 15-year freshwater pumping areas in the Yellow River Estuary were studied by 120-day field in situ culture experiments with Phragmites australis straw addition. The results showed that straw addition mainly enhanced the soil aggregate stability in the 10-year freshwater pumping area, and the organic carbon content of small macro-aggregates increased significantly by 26.36% (P < 0.05). In particular, the content of coarse particulate organic carbon (cPOC) with small macro-aggregates in all areas increased significantly with the addition of straw (P < 0.05). For small macro-aggregates in the 10-year pumping area, the cPOC contents increased significantly by 21.73 g/kg (P < 0.05); and were significantly higher than the fine particulate organic carbon (fPOC) and mineral-associated organic carbon (mSOC) contents, as the fPOC contents in micro-aggregates increased by 85.92% (P < 0.05). Additionally, the cPOC contents of small macro-aggregates and fPOC contents of micro-aggregates increased by 34.59% and 43.24% in the 15-year pumping area. The contents of mSOC were the lowest in different aggregates across all areas. Thus, straw addition had a significant effect on the contents of cPOC and fPOC, while freshwater pumping in the YRE could affect the distribution of fPOC and mSOC with aggregates.

Spatial relationships between ecosystem services and socioecological drivers across a large-scale region: A case study in the Yellow River Basin

Understanding the relationships between ecosystem services (ES) and their underlying socioecological drivers is essential for forming the efficient management decisions of ecosystems. We use a large watershed area as a case-study to analyze trade-offs/synergies and bundles of ESs and identify the associated socioecological variables (SEVs). This study assessed the supply of 7 ES indicators, namely, three provisioning services (crop production, livestock production, and industrial production), three regulating services (water conservation, soil conservation, and carbon sequestration), and one cultural service (recreation), across 65 municipalities in the Yellow River Basin (YRB) in China. We analyzed the paired trade-offs/synergies using Spearman's coefficient and identified the ES bundles (ESBs) by applying principal component analysis and K-means clustering. Subsequently, we detected the SEVs that affect the ES supply using the geo-detector model and characterized the associations between ESBs and socioecological clusters according to the spatial overlap. The results demonstrated that the synergies between ESs substantially exceeded the trade-offs, among which the strongest synergies were between the crop production and the livestock production, and both responded strongly to the cropland and the population density. Trade-offs were identified between provisioning services and soil conservation. Municipalities were grouped into three ESBs in the YRB. The ESB, which was dominated by provisioning ESs, was associated with areas where cropland, precipitation and socioeconomic conditions were all important, and the regulation of ESB was linked to regions with distinct ecological characteristics. We also identified an ESB that was dominated by carbon sequestration, as determined by extensive grassland and bare land. The land use/land cover strongly affected the characteristics of the ESBs. The findings can be used by land managers to identify areas in which ESs are dominant, to determine the associations of these compositions of the ESs with SEVs, and to support the formulation of optimal ES management in large-scale basins.

The impact assessment of hydro-biological connectivity changes on the estuary wetland through the ecological restoration project in the Yellow River Delta, China

Yellow River Delta (YRD) is one of the youngest delta with complex hydrological and biological connectivity in the world, where offers habitats to the famous waterfowls in the Eastern Asia. Meanwhile, one specific ecological restoration project named as the "Wuwanmu" and followed by the "Shiwanmu" within the National Nature Reserve of the Yellow River Delta (NNRYRD) complicated the hydrological and biological connectivity. How to quantitatively evaluate the extent of coastal wetland affected by the project will be a difficult problem. Hence the authors presented three innovative models of the Marine Connectivity Change Index (MCCI), the Coupling Index of Hydro-biological Connectivity (CIHBC), and the Assessment Index of Suitability on Bird Habitats (AISBH). After the project, the habitat of Phragmites australis has been restored effectively with the increased area of 24.59%, while the habitat of Suaeda salsa as the native species lost largely with decreased area of 84.62%. And the tidal channel having been cut off by the project resulted in isolating the buildup restoration area from seawater, and reshaping completely the plant habitat environment. So the hydrological and biological connectivity has been changed largely with the 47.79% decreased MCCI area and the 16.3% decreased zero-valued CIHBC area. However the AISBH non-zero-valued area increased 10.7%, and with the hidden worry of the decreased Grallatores number. From the connectivity prospective, three models presented a significant methodology to evaluate the complex impact on the estuary wetland habitat caused by the restoration project. In the long run, the ecological impacts should be highlighted to the change of tidal channel and the corresponding tidal issues, and the continuous and big loss of native plant spices such as S. salsa. The further study needs to explore the longer-term assessment of the ecological restoration project and its multiple effect in the future.

Variation of soil organic carbon and physical properties in relation to land uses in the Yellow River Delta, China

Soil physical properties and soil organic carbon (SOC) are considered as important factors of soil quality. Arable land, grassland, and forest land coexist in the saline-alkali reclamation area of the Yellow River Delta (YRD), China. Such different land uses strongly influence the services of ecosystem to induce soil degradation and carbon loss. The objective of this study is to evaluate the variation of soil texture, aggregates stability, and soil carbon affected by land uses. For each land use unit, we collected soil samples from five replicated plots from "S" shape soil profiles to the depth of 50 cm (0-5, 5-10, 10-20, 20-30, and 30-50 cm). The results showed that the grassland had the lowest overall sand content of 39.98-59.34% in the top 50 cm soil profile. The content of soil aggregates > 0.25 mm (R_0.25), mean weight diameter and geometric mean diameter were significantly higher in grassland than those of the arable and forest land. R_0.25, aggregate stability in arable land in the top 30 cm were higher than that of forest land, but lower in the soil profile below 20 cm, likely due to different root distribution and agricultural practices. The carbon management index (CMI) was considered as the most effective indicator of soil quality. The overall SOC content and CMI in arable land were almost the lowest among three land use types. In combination with SOC, CMI and soil physical properties, we argued that alfalfa grassland had the advantage to promote soil quality compared with arable land and forest land. This result shed light on the variations of soil properties influenced by land uses and the importance to conduct proper land use for the long-term sustainability of the saline-alkali reclamation region.

Hydrological connectivity dynamics of tidal flat systems impacted by severe reclamation in the Yellow River Delta

River deltas contain complex self-organizing channel networks that continuously exchange fluxes of water, matter, energy, and information with their surroundings. The connectivity of these exchange processes plays a crucial role in controlling the evolution and dynamic stability of river deltas. However, connectivity patterns related to tidal channel networks have rarely been studied, especially in the Yellow River Delta (YRD), which is impacted by severe reclamation. Here, we evaluated the potential hydrological connectivity dynamics between the tidal channel network and its surroundings using an index of connectivity (IC) in the whole YRD and its three sub-regions: erosion zone, oil field zone and deposition zone. The results suggested that different areas had different spatial connectivity potential. The mean value of the IC related to the channel networks showed little difference for any zones. However, the total connectivity response area (CRA; set of connectivity response units) varied with the study scale. A decreasing trend was found on the delta scale and a relatively stable trend was found in the deposition zone. In terms of dynamic connectivity, the tidal flat system did not show a continuous trend over time. Our results indicated that the YRD is such a dynamic complex that a relatively stable connectivity pattern is unlikely to be achieved over time. Therefore, future ecological restoration based on hydrological connectivity needs to consider more related influencing factors and their temporal and spatial dynamics.

A Harmonious Satellite-Unmanned Aerial Vehicle-Ground Measurement Inversion Method for Monitoring Salinity in Coastal Saline Soil

Soil salinization adversely impacts crop growth and production, especially in coastal areas which experience serious soil salinization. Therefore, rapid and accurate monitoring of the salinity and distribution of coastal saline soil is crucial. Representative areas of the Yellow River Delta (YRD)—the Hekou District (the core test area with 140 sampling points) and the Kenli District (the verification area with 69 sampling points)—were investigated. Ground measurement data, unmanned aerial vehicle (UAV) multispectral imagery and Sentinel-2A multispectral imagery were used as the data sources and a satellite-UAV-ground integrated inversion of the coastal soil salinity was performed. Correlation analyses and multiple regression methods were used to construct an accurate model. Then, a UAV-based inversion model was applied to the satellite imagery with reflectance normalization. Finally, the spatial and temporal universality of the UAV-based inversion model was verified and the soil salinity inversion results were obtained. The results showed that the green, red, red-edge and near-infrared bands were significantly correlated with soil salinity and the spectral parameters significantly improved this correlation; hence, the model is more effective upon combining spectral parameters with sensitive bands, with modeling precision and verification precision of the best model being 0.743 and 0.809, respectively. The reflectance normalization yielded good results. These findings proved that applying the UAV-based model to reflectance normalized Sentinel-2A images produces results that are consistent with the actual situation. Moreover, the inversion results effectively reflect the distributions characteristic of the soil salinity in the core test area and the study area. This study integrated the advantages of satellite, UAV and ground methods and then proposed a method for the inversion of the salinity of coastal saline soils at different scales, which is of great value for real-time, rapid and accurate soil salinity monitoring applications.

Impacts of land reclamation on tidal marsh 'blue carbon' stocks

Tidal marsh ecosystems are among earth's most efficient natural organic carbon (C) sinks and provide myriad ecosystem services. However, approximately half have been 'reclaimed' - i.e. converted to other land uses - potentially turning them into sources of greenhouse gas emissions. In this study, we applied C stock measurements and paleoanalytical techniques to sediments from reclaimed and intact tidal marshes in southeast Australia. We aimed to assess the impacts of reclamation on: 1) the magnitude of existing sediment C stocks; 2) ongoing C sequestration and storage; and 3) C quality. Differences in sediment horizon depths (indicated by Itrax-XRF scanning) and ages (indicated by lead-210 and radiocarbon dating) suggest a physical loss of sediments following reclamation, as well as slowing of sediment accumulation rates. Sediments at one meter depth were between ~2000 and ~5300 years older in reclaimed cores compared to intact marsh cores. We estimate a 70% loss of sediment C in reclaimed sites (equal to 73 Mg C ha^-1), relative to stocks in intact tidal marshes during a comparable time period. Following reclamation, sediment C was characterized by coarse particulate organic matter with lower alkyl-o-alkyl ratios and higher amounts of aromatic C, suggesting a lower extent of decomposition and therefore lower likelihood of being incorporated into long-term C stocks compared to that of intact tidal marshes. We conclude that reclamation of tidal marshes can diminish C stocks that have accumulated over millennial time scales, and these losses may go undetected if additional analyses are not employed in conjunction with C stock estimates.