Carbon and nitrogen cycling on the Qinghai–Tibetan Plateau

Under a persistent warming climate and increasing human activities, permafrost in the Source Area of the Yellow River (SAYR) has been degrading regionally, resulting in many eco-environmental problems. This paper reviews the changes in air temperature and precipitation over the past 60 years and presents the distribution and degradation of alpine permafrost in the SAYR. The review is focused on the permafrost degradation–induced changes in hydrology, wetlands, thermokarst lakes, ponds, and vegetation. Mean annual air temperatures have been rising at an average rate of 0.4°C/10a over the past 60 years, while precipitation has increased only slightly (16 mm/10a). Borehole temperature monitoring at the depth of 15 m shows the permafrost warming rates of 0.01–0.21°C/10a in the Headwater Aera of the Yellow River. As a result of permafrost thaw, the amount of surface waters has declined while groundwater storage has increased. Due to permafrost degradation, the supra-permafrost water table lowers gradually, resulting in a reduction in areal extents of wetlands and lakes in the SAYR. We further renamed the concept of the burial depth of the ecologically-safe supra-permafrost water table, the minimum depth of the groundwater table for sustaining the normal growth of alpine grassland vegetation, for the SAYR to describe the relationship between the lowering permafrost table and succeeding alpine vegetation. Furthermore, we recommended more studies focusing on snow cover and carbon stock and emissions related to permafrost degradation under a warming climate. We also advised to timely establish the long-term monitoring networks for the rapidly changing mountain cryosphere, alpine ecology, alpine hydrology, eco-hydrology, cryo-hydrogeology, and carbon fluxes. Moreover, process-based models should be developed and improved to better simulate and predict the responses of alpine ecosystem changes to the interacting cryospheric and other environmental variables and their ecological and ecohydrological impacts in the SAYR and downstream Yellow River basins. This study can help better manage the ecological and hydrological environments in the Upper Yellow River that are sensitive to changes in the alpine climate and cryosphere.

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Impacts of Permafrost Degradation on Hydrology and Vegetation in the Source Area of the Yellow River on Northeastern Qinghai-Tibet Plateau, Southwest China

Time-frequency optimization of RSEI: A case study of Yangtze River Basin

Land use and hydrological factors control concentrations and diffusive fluxes of riverine dissolved carbon dioxide and methane in low-order streams.

Dissolved oxygen variation in the North China Plain river network region over 2011-2020 and the influencing factors.

Headwater stream ecosystem: an important source of greenhouse gases to the atmosphere

Twenty wetland-related data products (including remote sensing datasets, compilation datasets and model simulation datasets) were collected to evaluate the characteristics (area and distribution) of the wetlands in the Qinghai–Tibet Plateau (QTP) during four stages (1980s, 1990s, 2000s, and 2010s). We conducted a statistical analysis of the wetland areas from different datasets and compared the pixel consistency regarding wetland spatial distribution. The results showed that high uncertainty exists in the wetland area and low consistency exists in the distribution among the different datasets. The wetland area in the QTP ranged from 1.5 × 104 to 121.16 × 104 km2. In the remote sensing datasets, the wetland area in the QTP ranged from 3.25 × 104 to 11.28 × 104 km2, the calculated area was between 1.50 × 104 and 72.21 × 104 km2 in the compilation datasets, and the area simulated from model datasets was between 3.81 × 104 and 121.16 × 104 km2. For the total wetland area in the QTP, the uncertainty in the measured datasets was lower than that in the model simulation datasets. However, for the distribution of wetlands, the measured datasets were more inconsistent than the model datasets. In the measured datasets, as the pixel consistency increased, the corresponding probability throughout the area decreased. The probability of achieving 75% consistency was less than 2%, and was 0.61%, 0.35%, 1%, and 1.43% in the four stages, respectively. In the model products, the probability of achieving 75% consistency was 40.39%. Our study will enrich the global wetland database and contribute to the establishment of a plateau wetland information system, which will be significant for the protection and management of wetlands.

High uncertainties detected in the wetlands distribution of the Qinghai–Tibet Plateau based on multisource data

Soil erosion by water affects soil organic carbon (SOC) migration and distribution, which are important processes for defining ecosystem carbon sources and sinks. Little has been done to quantify soil carbon erosion in the three major basins in China, the Yangtze River, Yellow River and Pearl River Basins, which contain the most eroded areas. This research attempts to quantify the lateral movement of SOC based on spatial and temporal patterns of water erosion rates derived from an empirical Unit Stream Power Erosion Deposition Model (USPED) model. The water erosion rates simulated by the USPED model agreed reasonably with observations (R2 = 0.43, P < 0.01). We showed that regional water erosion ranged within 23.3–50 Mg ha–1 year–1 during 1992–2013, inducing the lateral redistribution of SOC caused by erosion in the range of 0.027–0.049 Mg C ha–1 year–1, and that caused by deposition of 0.0079–0.015 Mg C ha–1 year–1, in the three basins. The total eroded SOC was 0.006, 0.002 and 0.001 Pg year–1 in the Yangtze River, Yellow River and Pearl River Basins respectively. The net eroded SOC in the three basins was ~0.0075 Pg C year–1. Overall, the annual average redistributed SOC rate caused by erosion was greater than that caused by deposition, and the SOC loss in the Yangtze River Basin was greatest among the three basins. Our study suggests that considering both processes of erosion and deposition – as well as effects of topography, rainfall, land use types and their interactions – on these processes are important to understand SOC redistribution caused by water erosion.

Estimating soil organic carbon redistribution in three major river basins of China based on erosion processes

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Papers

Headwater stream ecosystem: an important source of greenhouse gases to the atmosphere

High uncertainties detected in the wetlands distribution of the Qinghai–Tibet Plateau based on multisource data

Estimating soil organic carbon redistribution in three major river basins of China based on erosion processes