ECOLOGICAL STOICHIOMETRY IN WATERSHEDS: FROM LAND TO WATER IN THE QINGHAI LAKE BASIN

We examined the influences of grassland status (as indexed by normalized difference vegetation index, NDVI) on carbon (C), nitrogen (N), and phosphorus (P) concentrations and stoichiometry, nutrient limitation, as well as microbial community structure in soil, stream, and/or lake ecosystems in the Qinghai Lake watershed, where grassland is the dominant landcover and more than half of the grassland is degraded. Chapter 2 showed that grassland degradation decreased C and N concentrations as well as C:N, C:P, and N:P ratios in soil. Moreover, grassland degradation decreased C, N, and P concentrations and influenced C:N and N:P ratios in soil microbial biomass. Soil microorganisms exhibited strong homeostatic behavior while variations of microbial biomass C:N and N:P ratios suggest changes in microbial activities and community structure. The soil became relatively more P rich and thus N limitation is anticipated to be more apparent with grassland degradation. Chapter 3 provided a picture of potentially differential influences of grassland degradation on DOC, TN, and TP in streamwater. The imbalances of C:N:P stoichiometry between streamwater and biofilms and the non-isometric relationships between biofilm C and P suggest that stream biofilms might be limited by P and sensitive to P variation. Chapter 4 indicated that grassland degradation has the potential to differentially influence the nutrients delivered to streams with substantial increases in P but decreases in N and N:P, alleviating P limitation of stream periphyton and, ultimately, stimulating P-limited phytoplankton growth in the lake. Chapter 5 revealed that grassland degradation shifted bacterial diversity and communities in soil, likely by changing soil moisture, soil organic carbon, total nitrogen, and total phosphorus. Chapter 6 showed that the variation of bacterial communities in stream biofilms was closely associated with rate of change in NDVI, pH, conductivity, as well as C, N, P contents and C:N ratio in biofilms per se. Alpha diversity was positively correlated with C, N, and P in biofilms. Abundant subcommunities of microbes were more strongly associated with environmental variables. Overall, my dissertation revealed strong impacts of grassland degradation on several aspects of nutrient dynamics and limitation as well as on microbial communities in terrestrial and aquatic ecosystems in the Qinghai Lake watershed

Linkages between Atmospheric Circulation, Weather, Climate, Land Cover and Social Dynamics of the Tibetan Plateau

The Tibetan Plateau (TP) is an important landmass that plays a significant role in both regional and global climates. In recent decades, the TP has undergone significant changes due to climate and human activities. Since the 1980s anthropogenic activities, such as the stocking of livestock, land cover change, permafrost degradation, urbanization, highway construction, deforestation and desertification, and unsustainable land management practices, have greatly increased over the TP. As a result, grasslands have undergone rapid degradation and have altered the land surface which in turn has altered the exchange of heat and moisture properties between land and the atmosphere. But gaps still exist in our knowledge of land-atmosphere interactions in the TP and their impacts on weather and climate around the TP, making it difficult to understand the complete energy and water cycles over the region. Moreover, human, and ecological systems are interlinked, and the drivers of change include biophysical, economic, political, social, and cultural elements that operate at different temporal and spatial scales. Current studies do not holistically reflect the complex social-ecological dynamics of the Tibetan Plateau. To increase our understanding of this coupled human-natural system, there is a need for an integrated approach to rendering visible the deep interconnections between the biophysical and social systems of the TP. There is a need for an integrative framework to study the impacts of sedentary and individualized production systems on the health and livelihoods of local communities in the context of land degradation and climate change. To do so, there is a need to understand better the spatial variability and landscape patterns in grassland degradation across the TP. Therefore, the main goal of this dissertation is to contribute to our understanding of the changes over the land surface and how these changes impact the plateau\u27s weather, climate, and social dynamics. This dissertation is structured as three interrelated manuscripts, which each explore specific research questions relating to this larger goal. These manuscripts constitute the three primary papers of this dissertation. The first paper documents the significant association of surface energy flux with vegetation cover, as measured by satellite based AVHRR GIMMS3g normalized difference vegetation index (NDVI) data, during the early growing season of May in the western region of the Tibetan Plateau. In addition, a 1°K increase in the temperature at the 500 hPa level was observed. Based on the identified positive effects of vegetation on the temperature associated with decreased NDVI in the western region of the Tibetan Plateau, I propose a positive energy process for land-atmosphere associations. In the second paper, an increase in Landsat-derived NDVI, i.e., a greening, is identified within the TP, especially during 1990 to 2018 and 2000 to 2018 time periods. Larger median growing season NDVI change values were observed for the Southeast Tibet shrublands and meadows and Tibetan Plateau Alpine Shrublands and Meadows grassland regions, in comparison to the other three regions studied. Land degradation is prominent in the lower and intermediate hillslope positions in comparison to the higher relative topographic positions, and change is more pronounced in the eastern Southeast Tibet shrublands and meadows and Tibetan Plateau Alpine Shrublands and Meadows grasslands. Geomorphons were found to be an effective spatial unit for analysis of hillslope change patterns. Through the extensive literature review presented in third paper, this dissertation recommends using critical physical geography (CPG) to study environmental and social issues in the TP. The conceptual model proposed provides a framework for analysis of the dominant controls, feedback, and interactions between natural, human, socioeconomic, and governance activities, allowing researchers to untangle climate change, land degradation, and vulnerability in the Tibetan Plateau. CPG will further help improve our understanding of the exposure of local people to climate and socio-economic and political change and help policy makers devise appropriate strategies to combat future grassland degradation and to improve the lives and strengthen livelihoods of the inhabitants of the TP

Changes and driving forces analysis of alpine wetlands in the first meander of the Yellow River based on long-term time series remote sensing data

IntroductionAs a vital component of the ecosystem of the Qinghai-Tibet Plateau, alpine wetlands coexist with their vulnerability, sensitivity, and abundant biodiversity, propelling the material cycle and energy flux of the entire plateau ecosystem. In recent decades, climate change and human activities have significantly altered the regional landscape. Monitoring and assessing changes in the alpine wetlands on the Qinghai-Tibet Plateau requires the efficient and accurate collection of long-term information.MethodsHere, we interpreted the remote sensing data of the first meander of the Yellow River of alpine wetlands from 1990 to 2020 based on Google Earth Engine (GEE) platform, using geographic information system (GIS) and landscape pattern index to analyze the spatial and temporal evolution of wetland landscape patterns, and the primary drivers of changes in wetland area were explored by GeoDetector.ResultsOur result showed that most wetland areas were found in regions with gradients less than 12° and elevations between 3315 and 3600 m. From 1990 to 2010, the area of alpine wetland in the study area decreased by 25.43%. During the period between 2010 and 2020 to the 1990s, the wetland area decreased by 322.9 km2. Conversion to and from grassland was the primary form of wetland transfer out and in, respectively. The overall migration of the wetland centroid in the study area was to the southwest between 1990 and 2010 and to the north between 2010 and 2020. The geometry of the wetland landscape was relatively simple, the landscape was relatively intact, and patches retained a high level of agglomeration and connectivity. However, their level of agglomeration and connectivity was disrupted. A quantitative analysis of the factor detector in GeoDetector revealed that the DEM, slope, and evaporation were the most important driving factors influencing the change of wetland area, with socioeconomic development also influencing changes in the wetland area to a lesser extent.DiscussionUsing interaction detectors, it was discovered that the interaction of various driving factors could better explain the long-term variations in wetland areas, with a greater degree of explanation than that of each driving factor alone

Grassland degradation on the Qinghai-Tibetan Plateau: reevaluation of causative factors

In light of Harris (2010) finding insufficient evidence to assert a causal linkage between any of the seven previously proposed causative factors and grassland degradation on the Qinghai-Tibetan Plateau (QTP), more recent empirical studies on QTP grassland degradation were explored to ascertain whether, in fact, these factors are casually linked to grassland degradation. The mischaracterization of the underlying causes of grassland degradation among policymakers has and continues to be an obstacle to sustainable regional grassland management practices. Accumulating evidence suggests that privatization and sedentarization, small mammals, climate change, harsh environments, fragile soils, and overgrazing contribute to grassland degradation. However, neither obsolete livestock husbandry methods nor the recent conversion of rangelands to agriculture had a meaningful influence. Estimates of the total area of degraded grasslands and the establishment of grassland degradation criteria have not been properly addressed in the literature. Both omissions constitute the basis for investigating the causes of grassland degradation across the QTP and the adoption of measures to manage these grasslands sustainably

Rural household energy consumption of farmers and herders in the Qinghai-Tibet Plateau

Rural energy consumption not only significantly affects the national economy but also affects the living conditions of rural residents. A comprehensive survey of households in the agropastoral area of Qinghai Province was conducted from 2017-2018 to identify its energy consumption characteristics. In this paper, a typical household energy flow model was established. The results show that 1) the proportion of noncommercial energy in the agropastoral area of Qinghai Province is 52.89%, and it is affected by the ‘returning farmland to forest’ (RFF) policy and the ‘returning grazing land to grassland project’ (RGLGP). Furthermore, the household energy consumption structure has shifted from traditional biomass to coal and a combination of other energy sources. 2) Households of different cultural backgrounds have different energy consumption patterns. 3) High-income households consume more energy and have more frequent energy flows compared with low-income households. The results of this survey will help policymakers and scholars to formulate strategies for energy conservation and more effectively assess energy policies

Deserts and Desertification

A desert is an ecosystem in an arid zone in which sand dunes cover the land and sandstorms often occur. Although desert vegetation is sparse, it plays an important role in ecosystem structure and function. Desertification is one of the most severe environmental problems today. Land desertification can be controlled through many measures, such as eco-villages, eco-agriculture, biodiversity conservation, and the combination of engineering and biology. This edited volume provides new insights into the pattern of desert ecosystems and the progress of desertification control. It is a useful resource for researchers in ecology, forestry, and land desertification control