Response of net primary production to land use and climate changes in the middle-reaches of the Heihe River Basin

Historical trends and drivers of the laterally transported terrestrial dissolved organic carbon to river systems

Dissolved organic carbon (DOC) represents a critical component of terrestrial carbon (C) cycling and is a key contributor to the carbon flux between land and aquatic systems. Historically, the quantification of environmental factors influencing DOC leaching has been underexplored, with a predominant focus on land use changes as the main driver. In this study, the process-based terrestrial ecosystem model JULES-DOCM was utilized to simulate the spatiotemporal patterns of DOC leaching into the global river network from 1860 to 2010. This study reveals a 17 % increment in DOC leaching to rivers, reaching 292 Tg C yr-1 by 2010, with atmospheric CO2 fertilization identified as the primary controlling factor, significantly enhancing DOC production and leaching following increased vegetation productivity and soil carbon stocks. To specifically quantify the contribution of CO2 fertilization, a factorial simulation approach was employed that isolated the effects of CO2 from other potential drivers of change. The research highlights distinct regional responses. While globally CO2 fertilization is the dominant factor, in boreal regions, climate change markedly influences DOC dynamics, at times exceeding the impact of CO2. Temperate and sub-tropical areas exhibit similar trends in DOC leaching, largely controlled by CO2 fertilization, while climate change showed an indirect effect through modifications in runoff patterns. In contrast, the tropics show a relatively low increase in DOC leaching, which can be related to alterations in soil moisture and temperature. Additionally, the study re-evaluates the role of land use change in DOC leaching, finding its effect to be considerably smaller than previously assumed. These insights emphasize the dominant roles of CO2 fertilization and climate change in modulating DOC leaching, thereby refining our understanding of terrestrial carbon dynamics and their broader implications on the global C budget.

Unraveling the enigma of NPP variation in Chinese vegetation ecosystems: The interplay of climate change and land use change

Global carbon emissions have exacerbated the greenhouse effect, exerting a profound impact on ecosystems worldwide. Gaining an understanding of the fluctuations in vegetation net primary productivity (NPP) is pivotal in the assessment of environmental quality, estimation of carbon source/sink potential, and facilitation of ecological restoration. Employing MODIS and meteorological data, we conducted a comprehensive analysis of NPP evolution in Chinese vegetation ecosystems (VESs), employing Theil-Sen median trend analysis and the Mann-Kendall test. Furthermore, utilizing scenario-based analysis, we quantitatively determined the respective contributions of climate change and land use change to NPP variations across various scales. The overall NPP exhibited a discernible upward trend from 2000 to 2020, with a growth rate of 5.83 gC·m-2·year-1. Forestland ecosystem (FES) displayed the highest rate of increase (9.40 gC·m-2·year-1), followed by cropland ecosystem (CES) (4.00 gC·m-2·year-1) and grassland ecosystem (GES) (3.40 gC·m-2·year-1). Geographically, NPP exhibited a spatial pattern characterized by elevated values in the southeast and diminished values in the northwest. In addition, climate change had elevated 76.39 % of CES NPP, 90.62 % of FES NPP, and 71.78 % of GES NPP. At the national level, climate change accounted for 83.14 % of the NPP changes, while land use change contributed 14.14 %. Notably, climate change emerged as the primary driving force behind NPP variations across all VEGs, with land use change exerting the most pronounced influence on CES. At the grid scale (2 km × 2 km), land use change played a substantial role in all VEGs, contributing 60.01 % in CES, 54.20 % in FES, and 55.61 % in GES of the NPP variations.

Impacts of climate change on winter wheat net primary production: the regulatory role of crop management

BACKGROUND

The Huang-Huai-Hai Plain (3HP) is the main agricultural area in China. Although climate change (CC) and crop management (CM) are considered factors affecting the winter wheat net primary production (NPP) in this region, their effects remain unclear. In the present study, we evaluated the relative contributions of CC and CM to winter wheat aboveground NPP (ANPP) in the 3HP and the relationships between climatic factors and ANPP using the first-order difference method from 2000 to 2020.

RESULTS

CM had a greater influence on the ANPP of winter wheat than did CC. However, the relative contribution of CM to ANPP gradually decreased in humid and dry sub-humid regions with the development of winter wheat. Furthermore, in areas characterized by low temperatures and limited precipitation, CC became the dominant factor contributing to ANPP, indicating that varieties resilient to drought and cold should be selected in these regions. Minimum and average temperatures were the dominant factors driving spatiotemporal variations in ANPP during the early stage of winter wheat growth, whereas maximum temperature constrained growth throughout the winter wheat growth cycle. When winter wheat entered the vigorous growth stage, precipitation and solar radiation replaced temperature as the driving factors influencing winter wheat growth.

CONCLUSION

The results of the present study provide guidance for optimizing winter wheat crop management in the 3HP. © 2023 Society of Chemical Industry.

Cropland abandonment alleviates soil carbon emissions in the North China Plain

Land use change could profoundly influence the terrestrial ecosystem carbon (C) cycle. However, the effects of agricultural expansion and cropland abandonment on soil microbial respiration remain controversial, and the underlying mechanisms of the land use change effect are lacking. In this study, we conducted a comprehensive survey in four land use types (grassland, cropland, orchard, and old-field grassland) of North China Plain with eight replicates to explore the responses of soil microbial respiration to agricultural expansion and cropland abandonment. We collected surface soil (0-10 cm in depth) in each land use type to measure soil physicochemical property and microbial analysis. Our results showed that soil microbial respiration was significantly increased by 15.10 mg CO₂ kg^-1 day^-1 and 20.06 mg CO₂ kg^-1 day^-1 due to the conversion of grassland to cropland and orchard, respectively. It confirmed that agricultural expansion might exacerbate soil C emissions. On the contrary, the returning of cropland and orchard to old-field grassland significantly decreased soil microbial respiration by 16.51 mg CO₂ kg^-1 day^-1 and 21.47 mg CO₂ kg^-1 day^-1, respectively. Effects of land use change on soil microbial respiration were predominately determined by soil organic and inorganic nitrogen contents, implying that nitrogen fertilizer plays an essential role in soil C loss. These findings highlight that cropland abandonment can effectively mitigate soil CO₂ emissions, which should be implemented in agricultural lands with low grain production and high C emissions. Our results improve mechanistic understanding on the response of soil C emission to land use changes.

Response of Land Use and Net Primary Productivity to Coal Mining: A Case Study of Huainan City and Its Mining Areas

The terrestrial ecosystem carbon cycle is essential to the global carbon cycle. Mining activities have seriously damaged the terrestrial ecosystem and destroyed the carbon sequestration ability of vegetation, which is of great significance to studying the effect of coal mining on land structure change and carbon sink function in cities and mining areas. However, the existing research lacks the targeted analysis of the carbon sink level of the mining area combined with the mining data. Based on the coal-mining information, land-use data, and MODIS NPP data, this study analyzed the spatio-temporal change characteristics of land use and NPP in Huainan City and its mining areas from 2001 to 2020. The results showed that: (1) 22.5% of the land types in the mining area have changed, much higher than 3.2% in Huainan; 40.08 km2 of the cropland in the mining area has been transformed into waterbodies, seriously affecting regional food security. (2) NPP fluctuates with rainfall, has a weak correlation with temperature, and is restricted by coal-mining factors. The average NPP of most coal mines is significantly lower than that of non-mining areas. The NPP of Huainan City showed an overall growth trend of 2.20 g/(m2 × a), which was much higher than the average value of 0.43 g/(m2 × a) in the mining area. Especially in the Guqiao mine, the difference in NPPslope before and after mining was as high as 16.92 g/(m2 × a). (3) The probability integral method was used to estimate that 195.16 km2 of land in Huainan would be damaged by mining in 2020. The distribution of damage degree was negatively correlated with NPPslope, which meant the more serious the damage was, the less NPPslope was. This study revealed the characteristics of land-use change and NPP spatio-temporal response in resource-based cities and mining-disturbed areas. It quantitatively estimated the impact of mining activities on regional carbon sink function. It can provide theory and data support for mining areas to carry out ecological protection and restoration, improve the environmental service function of resource-based cities, and formulate sustainable development strategies.

Spatiotemporal changes in net primary productivity before and after the development of unused land in the hilly areas of Hebei, China

Net primary productivity (NPP) plays an important role in the carbon cycle of an ecosystem. To explore the impact of unused land development on NPP, this study adopted an improved Carnegie Ames Stanford Approach (CASA) model to analyze the changes in NPP before and after the development of unused land in Tang County, Hebei Province, in 2000, 2007, and 2018. The results showed that, due to the changes in land use types from unused land, forestland, arable land with high NPP values to urban and rural residential land, traffic land with low NPP values, and the changes in precipitation and temperature, the NPP in the study area showed an overall trend of decreasing first and then rising from 2000 to 2018. Before the development of unused land in 2000, the total NPP was 38.45×10¹⁰ g C. After the development in 2007 and 2018, the total NPP was 36.44×10¹⁰ g C and 41.05×10¹⁰ g C, respectively. The NPP of each land type in 2018 was arable land (1046.18 g C m^-2) > forestland (464.42 g C m^-2) > unused land (356.34 g C m^-2) > grassland (343.77 g C m^-2) > waters (182.56 g C m^-2) > urban and rural settlements (120.86 g C m^-2) > traffic land (120.70 g C m^-2). The distribution of NPP was generally high in the north and low in the south before and after development. NPP was mainly concentrated in the interval of 300 g C m^-2 yr^-1–400 g C m^-2 yr^-1, and the range of NPP change was mostly within 100 g C m^-2. The influence of elevation, temperature and precipitation on the spatial distribution of NPP was significant. Elevation and precipitation were positively correlated with NPP, while temperature was negatively correlated with NPP. The increase in NPP mainly originated from the conversion of unused land to forestland and arable land. The loss of NPP was mainly due to the conversion from forestland with high vegetation productivity to a land use type with low vegetation productivity, such as the conversion from forestland to urban and rural residential land. The results can provide references for making reasonable land planning decisions and ecological environment construction.

Comparative Study on Farmland Circulation between Plains and Mountainous Areas in an Arid Region: A Case Study of Zhangye City in Northwest China

Farmland circulation is essential for agricultural scale management. Due to rapid urbanization and industrialization, a large number of rural laborers have migrated to cities, resulting in accelerated farmland circulation. Revealing the farmland circulation in different geographical environments is conducive to efficient farmland management but remain largely unknown. To this end, based on the questionnaire survey data and statistical data of Zhangye City, we compared the features of farmland circulation between plains and mountainous areas, and used the binary logistic regression model and other methods to analyze the main factors affecting differentiated farmland circulation at the plot level. The main circulation modes and proportions in the plains were leasing (54.4%), exchange (22.4%), and subcontracting (16.2%), while the single leasing mode in mountainous areas accounted for 89.5%. The scale management units of more than 33.33 ha accounted for 6.48% and 30.72% in plains and mountainous areas, respectively. The proportion of circulation periods exceeding 5 years were 28.13% and 2.23% in plains and mountainous areas, respectively. The factor of “degree of farmland fragmentation” positively affected (p < 0.01) the farmland circulation in plains areas but negatively affected (p < 0.01) that in mountainous areas. The “farmland circulation price” promoted (p < 0.01) farmland circulation in both plains and mountainous areas. Whereas the “actual water diversion” (p < 0.01) and “river source water” (p < 0.05) only had varying degrees of negative impacts on farmland circulation in plains areas. Decision makers should practice management measures such as regulating farmland circulation behavior, formulating reasonable farmland circulation pricing models, and integrating farmland to promote the circulation and efficient use of farmland.

Modelling climate change impacts on regional net primary productivity in Turkey

This study projects and models the terrestrial net primary productivity (NPP) considering the representative concentration pathways (RCPs) scenarios of Turkey using remote-sensing-based biogeochemical modelling techniques. Changes in annual NPP between 2000-2010 and 2070-2080 were projected with the biogeochemical ecosystem model NASA-Carnegie Ames Stanford Approach (CASA). A multi-temporal data set, including 16-day MODIS composites with a spatial resolution of 250 m, was used within the CASA model. The 5th Assessment Report (AR5) of the IPCC presented several scenarios for RCPs named RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5 that laid the foundation for the future climate projections. The futuristic NPP modelling was based on the assumptions of maintaining CO₂ level in the range of 421 to 936 ppm and a rise in temperature from 1.1 to 2.6 °C. The NPP in Turkey averaged 1232 g C m² year^-1 as per the model results. Considering 2000-2010 as the baseline period, the NPP was modelled within the range of 9.6 and 316 g C m² year^-1. Modelled average NPP was 1332.4 g C m² year^-1 per year between 2061 and 2080. The forest productivity was also estimated to be increased up to 113 g C m^-2 year^-1 under the climate change scenarios. However, there were minor differences in the projected average NPP under the baseline period covering years from 2000 to 2080 from those under RCPs. It appeared that variation in temperature and precipitation as a result of climate change affected the terrestrial NPP. The regional environmental and socio-economic consequences of climate change on diverse landscapes such as Turkey were properly modelled and analysed to understand the spatial variation of climate change impacts on vegetation. Changes in NPP imply that forests in Turkey could be carbon sinks in the future as their current potential that would profile Turkey's climate mitigation. This is one of the pioneering studies to estimate the future changes of regional NPP in Turkey by integrating various spatial inputs and a biogeochemical model.

Assessment of Human-Related Driving Forces for Reduced Carbon Uptake Using Neighborhood Analysis and Geographically Weighted Regression: A Case Study in the Grassland of Inner Mongolia, China

The ever-rising concentration of atmospheric carbon is viewed as the primary cause for global warming. To discontinue this trend, it is of urgent importance to either cut down human carbon emissions or remove more carbon from the atmosphere. Grassland ecosystems occupy the largest part of the global land area but maintain a relatively low carbon sequestration flux. While numerous studies have confirmed the impacts on grassland vegetation growth from climate changes and human activities, little work has been done to understand the driving forces for a reduced carbon uptake (RCU)—a loss in vegetation carbon sequestration because of inappropriate grassland management. This work focused on assessing RCU in the grassland of Inner Mongolia and understanding the influential patterns of the selected variables (including grazing intensity, road network, population, and vegetation productivity) related to RCU. Neighborhood analysis was proposed to locate optimized grassland management practices from historical data and to map RCU. Ordinary least squares (OLS) and geographically weighted regression (GWR) models were applied to explore the driving forces for RCU. The results indicated that the human-related factors, including stock grazing intensity, population density, and road network were likely to present a spatially varied impact on RCU, which accounted for more than 1/4 of the total carbon sequestration.

Tradeoffs between agricultural production and ecosystem services: A case study in Zhangye, Northwest China

Humans have increasingly intervened in the nature to advance socioeconomic development at the expense of ecosystem services. Tradeoffs between ecosystem services and socioeconomic development are inevitable and should be considered in sustainable ecosystem management. This is no exception in Zhangye where intensive agricultural activities have significantly affected its ecological conditions. Thus, this study evaluated the tradeoffs between agricultural production and key ecosystem services along with their spatial distributions at the watershed level in Zhangye based on multisource observation data. The key ecosystem services, including net primary productivity (NPP), water yield, and soil conservation, were evaluated for the years 2000, 2010, and 2015 using remote sensing data and the InVEST model. The Morishima elasticity of substitution (MES) between these ecosystem services and agricultural production were then estimated by applying a quadratic directional output distance function, and mapped to determine the tradeoffs. The results showed that the average NPP and annual water yield respectively increased by 22% and 24%, while annual soil conservation decreased by 22% during 2000-2015. The average MES values for agricultural production with NPP, water yield, and soil conservation were 0.14, -0.69, and -0.56, respectively. This indicated the existence of a synergetic relationship between agricultural production and NPP as well as tradeoff relationships between agricultural production and water yield/soil conservation. Differences in the spatial patterns of the relationships between agricultural production and these ecosystem services were observed. Significant tradeoff relationships were observed for agricultural production with water yield and soil conservation in the upper reach of Zhangye. It indicated that increasing agricultural production would be at the cost of decreased water yield and soil conservation, especially in the upper reach area. The quantification and spatial pattern determinations of tradeoffs between ecosystem services and agricultural production is useful for the development of regional ecological conservation policy and sustainable ecosystem management.