Modelling and managing critical zone relationships between soil, water and ecosystem processes across the Loess Plateau

Lead Research Organisation: Lancaster University
Department Name: Lancaster Environment Centre

Abstract

The Loess Plateau of China covers an area 2.5x the size of the UK (some 640,000 square km) in the upper and middle reaches of China's Yellow River and is renowned for having the most severe soil erosion in the world; deforestation, over-grazing and poor agricultural practice have resulted in degenerated ecosystems, desertification and unproductive agriculture in the region. To control severe soil erosion on the Loess Plateau, the Chinese government imposed a series of policies for fragile ecosystems, such as the 1999 state-funded "Grain-for-Green" project, which has resulted in significant land use changes. Related programmes have produced beneficial effects on soil erosion and water cycles. However, the impact of these changes in soil and water processes on related ecosystem services is unknown and demands further study. The proposed research will focus on three spatial scales: slope, watershed, and region. It uses a combination of A) experiments to collect environmental, biological and agronomic data; B) remote sensing data and C) modelling approaches.

A) Data collection: Four experimental stations located in four main topographical regions of the Plateau are chosen as case studies: 1) Ansai Comprehensive Experimental Station of Soil and Water Conservation; 2) Changwu Agro-ecology Experiment Station; 3) Guyuan Ecological Station; 4) Shenmu Erosion and Environment Station. At each station, treatments of different vegetative covers, slopes, and the practices of soil and water conservation at the plot scale were set up in the 1980s and data collections include: soil water, canopy size, runoff, soil losses and meteorological records. Most of the Chinese members of this project have been involved in prior studies at the stations.
At the slope scale, additional environmental, biological and agronomic data will be monitored in a sub-set of the plots. At watershed scale, four watersheds where the stations are located will be monitored. The spatial distribution of the following variables will be measured: precipitation, soil properties, vegetative types, canopy size, runoff and soil loss.

B) Remote sensing data collection: At the regional scale, remote sensing combined with ground-truthing data will be used to investigate the spatial variability of vegetation type, land cover, productivity, the components of water balance, soil losses, soil type, etc.

C) Modelling approaches: a cascade approach will be used to build an improved model framework applied to different spatial scales. Mechanistic soil-water-plant models will be applied to the slope scale. Their outputs will then be used as inputs for models at watershed level. Spatial empirical/statistical models will be used at the regional level. Observed and collected data from A) and B) will be used to further develop, calibrate and validate our models.
Model simulations at the slope level will be used to reveal the dynamic mechanisms in soil and water in different regions and analyse the effects of vegetation type, soil type, slope degree, climatic factors and management practice. Watershed models will estimate soil and water carrying capacity for different vegetation types, predict the effect of land use/cover changes on soil losses, water cycle and ecosystem services and evaluate management scenarios in the practices of soil and water conservation, vegetative changes, and ecosystem services. The soil and water carrying capacity for different vegetation types and the optimal ecosystem services will be addressed at the regional scale. Outreach workshops and demonstrations will disseminate knowledge to farmers and policy makers.

The proposed research will elucidate the coupled relationships between soil and water processes and agro-ecosystem services at various scales, and evaluate the effects of vegetation cover and changes in land use on water cycle, soil erosion, and ecosystem services across the Loess Plateau.

Planned Impact

The primary impact will be the coupled benefits of environmental sustainability and the promotion of economic development and social welfare in the Loess region. This will be achieved through better understanding the relationships between the soil and water processes and agro-ecosystem services, including grain production, net primary production, carbon sequestration, water retention and soil erosion control. This research will provide guidance on practices and managements for sustainable ecosystem services in the fragile region, which will secure food production and save water resources in the arid Loess Plateau. Farmers in the area will receive guidance, enabling them to make informed decisions to adopt optimal agricultural and water management practises, thus increasing income by maintaining or increasing agricultural production. Likewise, environmental agencies and other organisations will have the tools to enable more accurate estimation of water balance, enabling stable management of ecosystems services.

To achieve the benefits, a series of workshops will be run during the project period to transfer our understanding to local people, mainly targeted at low income farmers. Workshops with main stakeholders including local government and environmental agency in year 3 and 4 will be held to introduce our research findings and recommendations.
 
Description We have worked with Chinese partners on examining the nitrate profiles in deep (up to 200m) extracted from the Loess Plateau. This was published in Science of the Total Environment in 2018. A further publication (Jia et al., 2019) shows the soil water carrying capacity of different plants in the Loess Plateau. We show that further re-vegetation needs careful reconsideration under the prevailing climatic, soil and topographic conditions, and provide a re-vegetation threshold to guide future re-vegetation activities and to ensure a sustainable eco-hydrological environment in the Loess Plateau.

We have been able to come up with an estimate of how long it takes for nitrate originating from fertilisers to move through the thick soils of the Loess Plateau, and hence get an idea of how long it takes before groundwater quality is degraded if fertiliser application rate is high. To do this we developed a model of the entire region of the Loess Plateau (about the size of France) that simulates the movement of fluids from the ground surface to the water table (which in this case is up to 200m deep). This was published in Turkeltaub et al.(2018). The modelling would not have been possible without access to immense data sources from our Chinese colleagues. We have also modelled local profiles of nitrate transport in order to compare directly with measured data from our colleagues in China. So far the results look good and we have prepared a manuscript for journal submission.

We have extended our regional modelling by comparing a downscaled approach from a global model to our upscaled approach. The comparison highlights the limitations of the global approach when dynamic soil water processes are neglected. We presented early results at Fall AGU 2017 and submitted a manuscript to Hydrological Processes. This is currently under review.

A capital award allowed us to carry out geophysical surveys at four of the five CZO project sites. All investigations were successful given the interest in geophysics by our Chinese partners that was triggered by our work. At the two karst sites in SW China we carried out a extensive geophysical field campaign lasting several months. The results have helped explain some of the complex behaviour of earlier hydrological field data and have helped develop a conceptual model for the catchment. This was published in Chen et al.(2018). We published two manuscripts detailing the geophysics (in the special issue of Environmental Earth Sciences on Karst). We also presented results at Fall AGU 2017.

Geophysical surveys at the Red Soil CZO have revealed the sensitivity of measurements of electrical conductivity to water uptake by crops.

Geophysical campaigns in the Loess Plateau have revealed the potential to use electrical conductivity for mapping the impact of crop water uptake in the region, which has undergone an extensive re-plantation project to minimise erosion. We presented the initial findings at Fall AGU 2018 and are currently writing this up for journal submission.
Exploitation Route Our colleagues in China working on the Loess Plateau have requested copies of our regional model and we are in the process of training them in its use. We are also hoping that the new MIDST China CZO project (of which we are a partner) will be able to utilise such modelling.

At one of the CZO sites (SPECTRA) our geophysical campaign has led to a new understanding of the variation in soil thickness, which should have implications on model development at the site.

The success of our geophysical surveys triggered purchase of geophysical equipment by Chinese teams at four of the CZO sites. This is clear evidence of impact of the work.

A postdoc on the project (Qinbo Cheng) returned to China with new skills in geophysics. He now has a position at Hohai University and plans to develop field geophysical programs further in China. We are working closely with colleagues at Hohai University (Nanjing), who are the Chinese lead on on CZO, to help develop knowledge of geophysical methods there. In fact we are currently discussing the opportunity to develop a student training course at Hohai.
Sectors Agriculture, Food and Drink,Environment

 
Title Loess Plateau regional hydraulic dataset for model 
Description Dataset compiled for regional model published in Turkeltaub et al.(2018) "Recharge and Nitrate Transport Through the Deep Vadose Zone of the Loess Plateau: A Regional-Scale Model Investigation" doi:10.1029/2017WR022190 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
Impact Dataset is associated with a model study - no measurable use by others to date 
 
Description BGS global modelling links 
Organisation British Geological Survey
Country United Kingdom 
Sector Academic/University 
PI Contribution We established a link with Matt Ascott and Daren Gooddy at BGS in order to share modelling expertise
Collaborator Contribution The link with BGS has allowed us to carry out global scale modelling of nitrate transport and downscale to address the Loess Plateau study in this project.
Impact Nature Comms paper: https://www.nature.com/articles/s41467-017-01321-w Fall AGU 2017 poster: H23I-1782: Global Patterns of Legacy Nitrate Storage in the Vadose Zone
Start Year 2016