Qinghai Lake Basin Research Articles

Modeling the Spatial Distribution of Plateau Pika (Ochotona curzoniae) in the Qinghai Lake Basin, China.

Simple SummaryThe plateau pika (Ochotona curzoniae) is a keystone species on the Qinghai–Tibetan Plateau (QTP). We identified key factors affecting its distribution and predicted it in Qinghai Lake basin by the maximum entropy (Maxent) model at 1-km spatial resolution. Our results showed that the suitable area for plateau pika in Qinghai Lake basin is approximately 3982 km2, which occupies 15.8% of the land area in the whole watershed. The distance to road emerged as the most important predictor of distribution patterns of plateau pika, while the soil type was of ancillary importance. With the constraint of human factors, the presence probability of plateau pika in about 1661 km2 will increase. These findings indicate that human factors have significant importance for plateau pika’s distribution, and provide evidence to guide plateau pika control in this and other similar regions. The plateau pika (Ochotona curzoniae) is a keystone species in the alpine rangeland ecosystem of the Qinghai–Tibetan Plateau. Most previous studies of habitat selection by plateau pika have been conducted at a local microhabitat scale; however, little is known about the relationship between the distribution of plateau pika and macrohabitat factors at broad spatial scales. Using a presence-only ecological niche model (maximum entropy, Maxent), we predicted the distribution of plateau pika in the Qinghai Lake basin based on a set of environmental and anthropogenic variables at 1-km spatial resolution, and identified key macrohabitat factors that contribute to the predictive performance. Our results showed suitable area for plateau pika in the Qinghai Lake basin being approximately 3982 km2, which is 15.8% of the land area in the whole watershed. The distance to road emerged as the most important predictor of the distribution patterns of plateau pika, while the soil type was of ancillary importance. Mean air temperature of wettest quarter, distance to resident site and altitude also produced high gains in defining plateau pika’s distribution. A higher predictive accuracy was achieved by the model that combined environmental and anthropogenic variables. With the constraint of human factors, the presence probability of plateau pika in about 1661 km2 will increase. These findings demonstrate the impact of human activities on the distribution of plateau pika, and the importance of vegetation reservation for plateau pika control.

Using coprophilous fungi to reconstruct the history of pastoralism in the Qinghai Lake Basin, Northeastern Qinghai-Tibetan Plateau

The history of permanent human settlement in the high-altitude regions (>3000 m above sea level [masl]) of the Qinghai-Tibetan Plateau (QTP) is important in understanding human adaptation to this cold “Third Pole” region. The Qinghai Lake Basin was an important corridor used by prehistoric humans migrating to the inner QTP. Pastoralism is currently the most important means of sustaining permanent human settlement in the high-altitude regions of the QTP. However, the lack of reliable proxy measures reflecting prehistoric pastoral activities impedes our understanding of how pastoralism developed. The identification of coprophilous fungi in prehistoric cultural deposits may help refine the history of pastoralism. We collected 21 modern domesticated herbivore dung samples and 66 surface soil samples from the Qinghai Lake Basin for fungal spore analyses. We then evaluated how useful such analyses are for identifying grazing activities. Fifty-three samples were also collected from the JXG2 stratigraphic profile (∼10.0–0 ka; 3312 masl) for fungal spore analysis. Results indicate that low and stable values of the total concentration of coprophilous fungi were present from ∼10.0 to ∼5.5 ka. Concentrations gradually increased from ∼5.5 to ∼4.2 ka, significantly increased from ∼4.2 to ∼2.6 ka, and then increased dramatically after ∼2.6 ka. By combining these results with charcoal concentrations (>50 µm), lithic artifacts, bones and potsherds recovered from the JXG2 site, we infer that early pastoralism in Qinghai Lake Basin appeared between ∼6.0 to ∼5.5 ka and gradually intensified throughout the remainder of the Holocene as herding and farming gradually replaced hunting–gathering as the primary subsistence strategies. These results are supported by pollen records, archeological remains and historical records in the northeastern QTP.

Geochemical characteristics of Holocene aeolian deposits east of Qinghai Lake, China, and their paleoclimatic implications.

The paleoclimate evolution of the northeastern Tibetan Plateau (TP), especially in the Qinghai Lake Basin (QLB), has long been a subject of interest to scholars due to the particularity of the geographical location. However, because of the uncertainties of the chronologies and the interpretations of the proxies used, climate change in this region remains controversial during the Holocene. The Hudong dunefield is located to the east of Qinghai Lake and is the largest sand accumulation area in the QLB. In this study, deposits in the Holocene aeolian sand-paleosol sequences Chengou East (CGE) and Qinghaihu Country (QHH) in the Hudong dunefield were analyzed to determine their elemental geochemical characteristics and paleoclimatic implications. Combining the grain size, total organic carbon (TOC) and redness, we investigate the paleoclimate changes in this region and its response to the East Asian Summer Monsoon (EASM) during the Holocene. The high Na2O/Al2O3 ratios and low chemical index of alteration (CIA) values suggest that most of the sediments are unweathered to weakly weathered, although some mid-Holocene samples are moderately weathered. The multiproxy analysis indicates that the local climate was broadly coincident with that of the northeastern TP and most regions of northern China, implying that the paleoclimate of the QLB was closely related with the evolution of the EASM during the Holocene. Additionally, after the 9.2 ka BP cold event, the chemical weathering increased gradually. The higher CIA and TOC contents and lower redness and mean grain size from 8.7 to 4.0 ka BP are possibly associated with the mid-Holocene optimum period and indicate intensified chemical weathering, denser vegetation cover and weakened aeolian activity in the QLB in response to a warmer and more humid climate. After 4.0 ka BP, the lower degrees of chemical weathering indicate that the study area was dominated by a relatively cold and dry climate, and several alternating warm-wet and cold-dry intervals occurred from 3.1 to 0.6 ka BP.

Convergent and divergent responses of topsoil nitrogen and phosphorus content to nutrient addition in natural and restored alpine grasslands around the Qinghai Lake Basin

The availability and variation of soil nutrients are especially important for plant growth and soil carbon accumulation in the ongoing climate change. As a climate-sensitive region, the Qinghai Lake Basin (QLB) has experienced extensive land-use transitions. A three-year manipulative experiment was conducted in two grassland types around the QLB, including a natural alpine grassland (NG) and its adjacent restored grassland (RG), to examine the responses of soil nitrogen (N) and phosphorus (P) content to nutrient application with land-use. N addition continuously increased soil NO3−-N (SAN) content of NG in the whole experiment period, while displaying no detectable effect on SAN content of RG in the first experiment year. Nutrient addition presented no direct effects on soil total N (STN) content. However, N addition potentially promoted STN content indirectly by increasing SAN content, both in NG and RG. P addition significantly increased soil available P (SAP) content during the whole study period for both grasslands. Nevertheless, P addition significantly increased soil total P (STP) content of NG in the last two experiment years, while only elevating STP content of RG in the last experiment year. The results revealed that soil N and P content presented convergent and divergent responses to nutrient addition between NG and RG. STN and STP content were both positively related to growing season precipitation (GSP). SAN content was positively associated with growing season temperature in NG, and RG in N addition treatment. SAP content was consistently positively related to GSP in P addition treatment, but negatively related to GSP in the treatment without P addition, both in NG and RG. These findings highlight the importance of precipitation for soil nutrient accumulation, and imply that warming and increasing precipitation will be beneficial for the mineralization of soil N and P, respectively, in this semi-arid grassland ecosystem.

Remotely sensed estimation and mapping of soil moisture by eliminating the effect of vegetation cover

Soil moisture (SM), which plays a crucial role in studies of the climate, ecology, agriculture and the environment, can be estimated and mapped by remote sensing technology over a wide region. However, remotely sensed SM is constrained by its estimation accuracy, which mainly stems from the influence of vegetation cover on soil spectra information in mixed pixels. To overcome the low-accuracy defects of existing surface albedo method for estimating SM, in this paper, Qinghai Lake Basin, an important animal husbandry production area in Qinghai Province, China, was chosen as an empirical research area. Using the surface albedo computed from moderate resolution imaging spectroradiometer (MODIS) reflectance products and the actual measured SM data, an albedo/vegetation coverage trapezoid feature space was constructed. Bare soil albedo was extracted from the surface albedo mainly containing information of soil, vegetation, and both albedo models for estimating SM were constructed separately. The accuracy of the bare soil albedo model (root mean square error=4.20, mean absolute percent error=22.75%, and theil inequality coefficient=0.67) was higher than that of the existing surface albedo model (root mean square error=4.66, mean absolute percent error=25.46% and theil inequality coefficient=0.74). This result indicated that the bare soil albedo greatly improved the accuracy of SM estimation and mapping. As this method eliminated the effect of vegetation cover and restored the inherent soil spectra, it not only quantitatively estimates and maps SM at regional scales with high accuracy, but also provides a new way of improving the accuracy of soil organic matter estimation and mapping.

Geochemical and isotopic (U, Th) variations in lake waters in the Qinghai Lake Basin, Northeast Qinghai-Tibet Plateau, China: origin and paleoenvironmental implications

A uranium (U) geochemical study of lake water samples from Qinghai Lake, Northeast Qinghai-Tibet Plateau, China, was undertaken to assess the primary controls on lake water chemistry. The 234U/238U activity ratios of lake water exhibited limited spatial and vertical variations and were relatively high compared to the values measured in rivers worldwide ((234U/238U) = 1.171), lower than in the four river discharge inside the Lake Qinghai catchment. The U concentrations also varied minimally within three vertical sampling profiles and exhibited spatial patterns in surface waters that correlated with the distribution of total dissolved solid (TDS) values and salinity concentrations. These data suggest that the variability in U, TDS, and salinity are partially controlled by evaporation or a different secondary concentration pathway. Moreover, the U concentration and 234U/238U activity ratio indicates that the length of this procedure, which is controlled by the duration of water-rock interaction, is probably an important factor to consider when accounting for the variable salinities of lakes located in similar geographical areas. The 230ThXS content is primarily derived from the decay of dissolved 234U. The various 230Thxs concentrations observed in the water column are interpreted to reflect various scavenging residence times in Qinghai Lake, ranging from 0.7 to 4 years. The lower water mass age, such as at site 123, suggests a more rapid scavenging rate. Dissolved 232Th is placed into the lake via the incomplete dissolution of lithogenic substances, such as dust aerosol, or other lithogenic sources (e.g., lake bed sediment or suspended riverine sediment). Water column 232Th concentration data suggest that the Th concentrations of the lake water are controlled by three processes: (1) the dissolution of aerosol dust, (2) the dissolution of riverine and lake bed sediment, and (3) the scavenging of Th from the water.

MODIS remote sensing dataset for Qinghai Lake basin

MODIS remote sensing dataset for Qinghai Lake basin

Measurements and Modeling of the Water Budget in Semiarid High‐Altitude Qinghai Lake Basin, Northeast Qinghai‐Tibet Plateau

AbstractWater budget plays an important role in ecological functions and biogeochemical cycles on the Qinghai‐Tibet Plateau (QTP). However, the key factors that govern the water budget across spatiotemporal scales in natural conditions are poorly understood, especially in the alpine region. To advance our understanding of how and why the water budget varies at the ecosystem and catchment scales, this study measured and modeled the main water budget components in the Qinghai Lake Basin (QLB) and further investigated the key factors for evapotranspiration and streamflow. The results showed that most monthly precipitation from June to September was greater than the corresponding evapotranspiration from the high‐altitude Kobresia meadow (KMd.) and Potentilla fruticosa shrub (PFSh.) ecosystem, and vice versa for the low‐altitude Achnatherum splendens steppe (ASSt.) ecosystem. The mean annual proportions of evapotranspiration of precipitation for the KMd., PFSh., and ASSt. ecosystems were 0.83, 1.06, and 1.02, respectively, from 2014 to 2015. The study highlights that the high‐altitude KMd. ecosystem is the main contributing area for runoff generation in the QLB. From ASSt. to PFSh. and then to the KMd. ecosystem, the key factors for evapotranspiration switched from water conditions to temperature conditions with the increase in elevation. The future scenario of climate warming and precipitation increase may cause a rise in evapotranspiration and streamflow in the QLB. Moreover, the increasing precipitation may be consumed mainly by evapotranspiration in the high altitude with low slope and by transfer into streamflow in the area with high slope.

Assessing the impact of human activities on surface pollen assemblages in Qinghai Lake Basin, China

ABSTRACTThe aim of this study is to evaluate the local impact of human activities on surface pollen assemblages and identify pollen indicators associated with grazing and cultivation in the Qinghai‐Tibetan Plateau. We analyzed 80 surface and 10 dung pollen samples from five communities of vegetation in the Qinghai Lake Basin. Each vegetation zone was identifiable based on surface pollen assemblages. Principal component analysis of 33 pollen taxa and two supplementary variables of human influences was used to assess the impact of anthropogenic activities on surface pollen assemblages in the Qinghai Lake Basin. Surface pollen assemblages were moderately influenced by cultivation, as indicated by the content of the cultivation‐associated Hordeum‐type and Brassiaceae pollen. Severe grazing led to changes in pollen assemblages, including increases in Chenopodiaceae, Plantago, Potentilla‐type, Thymelaeaceae and Aster‐type pollen. Pollen assemblages are similar among dung samples and are dominated by Artemisia, Poaceae, Fabaceae and Asteraceae. Hordeum‐type pollen content is relatively higher in dung samples, indicating herbivores are important in the dispersion of Cerealia Poaceae pollen into pastures. Characterizing modern pollen assemblages will provide a more precise reference for reconstructing prehistoric human activities during the Holocene based on fossil pollen assemblages in the Qinghai Lake Basin.

A new find of macrofossils of Picea crassifolia Kom. in early–middle Holocene sediments of the Qinghai Lake basin and its paleoenvironmental significance

AbstractHere we report a new find of abundant woody debris and cones in stratum of two sections located to the east of the Qinghai Lake basin in China. Analysis of the anatomical structure of the wood and cones confirmed that they are Picea crassifolia Kom. The results of accelerator mass spectrometry 14C dating indicate that the buried Qinghai spruce grew during 9.7–4.2 ka, and the ages of the large trunks or branches are mainly concentrated within the interval 7.5–6.5 ka. This finding gives direct evidence at the species level about the presence of coniferous forest in the early–middle Holocene in Qinghai lake basin. In addition, the buried cones suggest that the early-middle Holocene environment was suitable for the propagation of Picea crassifolia Kom. The variations in the occurrence of Qinghai spruce forest in the Holocene probably reflect changes in humidity/moisture. The humid early-middle Holocene was suitable for the growth and reproduction of Qinghai spruce forest, while a shift toward an increasingly arid climate during the late Holocene resulted in the disappearance of Picea crassifolia Kom. from the Qinghai Lake basin, although human activities may also have contributed to the environmental change.

Late Quaternary OSL chronologies from the Qinghai Lake (NE Tibetan Plateau): Inter-comparison of quartz and K-feldspar ages to assess the pre-depositional bleaching

Abstract Signal resetting prior to deposition is an important factor for the accuracy of luminescence dating. In this study, resetting of the quartz optically stimulated luminescence (OSL) signal from samples collected from different depositional environments (alluvial, beach, and aeolian sediments) around the Qinghai Lake basin (northeastern Tibetan Plateau) was examined using its inter-comparison with post-IR infrared stimulated luminescence (IRSL) measured at 290 °C (pIRIR290) from K-feldspar. Dose recovery tests were carried out to test the success of the single aliquot regenerative-dose (SAR) protocol for quartz and feldspar. Additionally, stability tests (first IR temperature plateau and g-values) were performed for the pIRIR290. We observe that most of the K-feldspar pIRIR290 and quartz OSL ages are consistent with each other (within 10%), suggesting that the quartz OSL signal was well-bleached prior to the deposition. The ages of loess samples range between ∼13.1 and ∼1.5 ka, the alluvial sediments between ∼35 ka and ∼14 ka, and beach sediments between 60 and 50 ka, corresponding to early Marine Isotope Stage (MIS) 3. These quartz OSL chronologies suggest a lake highstand during very early MIS 3, a lowstand during late MIS 3 and MIS 2, and widespread loess accumulation through the Holocene in the Qinghai Lake basin.

OSL dating of a mega-dune in the eastern Lake Qinghai basin (northeastern Tibetan Plateau) and its implications for Holocene aeolian activities

Abstract Aeolian sediments are widely distributed in the Lake Qinghai basin of the northeastern Tibetan Plateau (TP), but the history of aeolian activities in the basin is indistinct, and the underlying impacting factors are still poorly understood. In this study, depositional history of a mega-dune from the eastern Lake Qinghai basin was determined by optically stimulated luminescence (OSL) dating. The results show that nearly 30 m thick of sands accumulated during the interval of 7-6 ka, followed by soil formation during the last ∼5 ka. Together with previously published OSL ages of aeolian sediments, the Holocene aeolian activity in the Lake Qinghai basin was reconstructed as following: (1) The temporary aeolian activity appears to be characterized with a pattern of strengthened intensity during the first half of Holocene but relatively lowered intensity with a gradual decreasing trend afterward; (2) The interval of 7-6 ka in the middle Holocene witnessed a transition from dune activation towards stabilization; (3) A very low sand accumulation rate during the period of 5-3 ka and the contemporaneous extensive palaeosol development imply the least aeolian activity at that period. We inferred that the Holocene aeolian activity in the Lake Qinghai basin was mainly controlled by sediment supply, which was in turn modulated by the lake-level change of Lake Qinghai. Large amounts of sand were available, when the lake level dropped and then beach sands could exposure for deflation.

Abnormal Rb/Sr ratio in lacustrine sediments of Qaidam Basin, NE Qinghai–Tibetan Plateau: A significant role of aeolian dust input

The Rb/Sr ratio is an important indicator of weathering intensity in both lacustrine and loess sediments because of the inertness of the Rb element and the activity of the Sr element during the weathering process. Generally, the environmental interpretation of Rb/Sr ratio proxy in lacustrine sediments is contrary to that in the loess-paleosol sequence: it shows a negative correlation between the Rb/Sr ratio and chemical weathering intensity in lacustrine sediments, but shows a positive pattern in the loess-paleosol sequence. However, in this study, we investigated the Rb/Sr ratio of a lacustrine core (ISL1A) from Qarhan Salt Lake (QSL) in eastern Qaidam Basin (QB), and found the Rb/Sr ratio indicated a positive correlation with regional precipitation. This pattern is similar to that of the loess-paleosol sequence rather than the lacustrine sediments. According to grain size statistics and the comparison of Rb/Sr ratio with other proxies (halite and calcite contents, grain size, and F values of grain size discriminant function), we preliminarily proposed that the abundant input of aeolian materials, transported by the strong northwest wind, cause these unexpected Rb/Sr ratio fluctuations in the ISL1A core. The comparison between background Rb and Sr elemental data of relevant regions and these of the core indicated the aeolian origin of Rb/Sr ratio in the lacustrine sediments, and the Rb and Sr elemental composition probably represents the geochemical characteristics of the dust source area. The Sr-Nd isotopic composition indicates that the erosive paleo-lake strata in western QB could be the origin of aeolian materials in lacustrine sediments in the QSL, as well as the loess deposits in Dulan County, Qinghai Lake Basin, and Xining Basin. The regional correlation between proxies of the ISL1A core and other aeolian records also supports the aeolian origin of detrital input in the core. Finally, we propose that the origin of the detrital input must be distinguished before the Rb/Sr ratio is applied as a weathering intensity proxy in lacustrine sediments, especially in arid basins.

Effects of simulated warming on soil respiration to XiaoPo lake

The main flux of carbon cycling in terrestrial and atmospheric ecosystems is soil respiration, and soil respiration is one of the main ways of soil carbon output. This is of great significance to explore the dynamic changes of soil respiration rate and its effect on temperature rise, and the correlation between environmental factors and soil respiration. In this study, we used the open soil carbon flux measurement system (LI-8100, LI-COR, NE) in the experimental area of the XiaoPo Lake wetland in the Qinghai Lake Basin, and the Kobresia (Rs) were measured, and the soil respiration was simulated by simulated temperature (OTC) and natural state. The results showed that the temperature of 5 cm soil was 1.37 °C higher than that of the control during the experiment, and the effect of warming was obvious. The respiration rate of soil under warming and natural conditions showed obvious diurnal variation and monthly variation. The effect of warming on soil respiration rate was promoted and the effect of precipitation on soil respiration rate was inhibited. Further studies have shown that the relationship between soil respiration and 5 cm soil temperature under the control and warming treatments can be described by the exponential equation, and the correlation analysis between the two plots shows a very significant exponential relationship (p < 0.001). The warming treatment not only increased the Q10 value of soil respiration rate, but also increased the sensitivity of soil respiration rate. The relationship between soil respiration and soil moisture can be explained by the quadratic linear equation (p < 0.05). It can be concluded that under the condition of sufficient rainfall, the soil temperature is the main influencing factor of soil respiration in this region.

Qinghai Lake Basin Critical Zone Observatory on the Qinghai‐Tibet Plateau

Core Ideas The QLBCZO is an observatory to study carbon–water processes on the Qinghai‐Tibet Plateau. Multiscale, multi‐interface, and multi‐process studies investigate the CZ in the alpine region. Models predict carbon sequestration and water resources in the Qinghai Lake Basin. The surface–subsurface architecture of the critical zone (CZ) regulates the hydrologic and geochemical processes that drive the CZ function. Due to the complex heterogeneity, highly coupled processes, and the dynamic controlling mechanisms across scales, CZ science faces grand challenges on interface coupling, process integration, and scaling. Carbon–water cycles are important physical‐geochemical processes in the CZ. However, the key factors that govern the carbon–water processes across spatiotemporal scales under natural conditions are poorly understood. Especially, such research in the CZ of the alpine region, e.g., the Qinghai‐Tibet Plateau (QTP), has not been reported yet is challenging to conduct. The Qinghai Lake Basin Critical Zone Observatory (QLBCZO) is being established to study alpine hydrology, carbon–water processes, and ecological functions on the northeastern QTP. Previous studies in the QLBCZO mainly focused on ecohydrologic processes and the water budget. Currently, the QLBCZO is designed to integrate state‐of the‐art observation techniques (such as including deep coring, ground‐penetrating radar, electrical resistance tomography, isotope technique, and remote sensing) and frontier modeling approaches to investigate: (i) the three‐dimensional architecture of the subsurface environment (vegetation–soil–rock–microbial community) as well as the carbon and water storage, (ii) multiscale carbon–water processes and carbon–water budget, (iii) interactions between freeze–thaw and carbon–water processes, and (iv) carbon sequestration and water resources. The establishment of the QLBCZO and its associated research would be crucial for advancing both theory and methodology for the CZ and Earth system science research on the QTP and alpine regions in general.

Validation of the MODIS LAI product in Qinghai Lake Basin combined with field measurements using Landsat 8 OLI data

The leaf area index (LAI) has been widely used in various scientific studies to characterize the dynamics and functions of vegetation using remote sensing. Validation of NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) LAI products is of high significance, due to its role as an important input parameter for climate and eco-hydrological models at global and regional scales. However, recent validation activities have mainly been located in North America, Europe, and Africa. Furthermore, the validations principally focused on forests and savanna. As one of the representative areas in which unique and sensitive alpine ecosystems are widely distributed, the Qinghai Lake Basin maintains the ecological security of the eastern Tibetan Plateau. Therefore, exploring the precision and applicability of MODIS LAI applied to the alpine ecosystem of Qinghai Lake Basin is a crucial prerequisite to using the LAI parameter for weather forecast and water resource management models. In this paper, the inversion accuracy of the Collection 5 MODIS LAI (MOD15A2) products was examined for three typical vegetation types, i.e., alpine meadow, steppe, and subalpine shrub, in the Qinghai Lake Basin. On the basis of the validation of the plots' representation of MODIS pixels, we measured LAI of 84 plots covering the entire basin during August 10 and 20, 2015, in order to establish the Normalized Difference Vegetation Index (NDVI)–LAI exponent regression model using Landsat 8 OLI remote sensing data. The Landsat 8 LAI map with 1-km spatial resolution, which is the same as that of the MODIS LAI product, was then obtained by aggregating Landsat 8 LAI data with 30-m resolution derived from the NDVI–LAI model. The aggregation progress was performed using a scaling-up method, referred to as average aggregation. The validation and applicability analysis of the MOD15A2 LAI product then were carried out through a pixel by pixel method. The results can be summarized as follows. (1) The MODIS LAI product in the study area agrees well with the Landsat 8 inverted results for alpine meadow and steppe. (2) Validation of the product varies with different vegetation types. Specifically, the MODIS LAI product is underestimated by approximately 10% for alpine meadow (R2=0.77), overestimated by approximately 9% for steppe (R2=0.59), underestimated by approximately 51% for subalpine shrub (R2=0.42), and underestimated by approximately 16% when the vegetation of the entire basin is not distinguished (R2=0.36). (3) The precision of the MODIS LAI product may be influenced by the uncertainty of the sampling strategy, surface heterogeneity, surface reflectance, and the NDVI–LAI statistical model. Of these, spatial heterogeneity has the major impact on the uncertainty of the MODIS LAI product. Consequently, MODIS LAI products should be combined with vegetation maps when applied for a particular vegetation type in the Qinghai Lake Basin. Simultaneously, correction is necessary for MODIS LAI products to improve the accuracy. The results of this study can provide an important basis for researching the selection and correction of MODIS LAI products used in the Qinghai Lake Basin.

Linkage of Climatic Factors and Human Activities with Water Level Fluctuations in Qinghai Lake in the Northeastern Tibetan Plateau, China

Changes in the water level of Qinghai Lake, the largest inland lake in China, directly affect the ecological security of Qinghai province and even the northwest of China. This study aimed to investigate the lake level and identify causes of changes in the lake level of Qinghai Lake. The results showed that the lake level was 3196.55 m in 1959 and gradually declined to 3192.86 m in 2004, with an average decreasing rate of 8.2 cm·year−1 over 45 years. However, the lake level increased continuously by 1.04 m from 2005 to 2010. During the period 1961–2010, the annual average temperature showed an increasing trend in the Qinghai Lake basin, at a rate of 0.32 °C/decade, and the annual precipitation showed obvious fluctuations with an average precipitation of 381.70 mm/year. Annual evaporation showed a decreasing trend (−30.80 mm/decade). The change in lake level was positively correlated to precipitation, surface runoff water and groundwater inflow into the lake and negatively correlated to evaporation from the lake surface. The total water consumption by human activities merely accounted for a very small part of precipitation, surface runoff inflow and groundwater inflow (1.97%) and of lake evaporation (1.87%) in Qinghai Lake basin. The annual water consumption of artificial afforestation and grass plantation accounting for 5.07% of total precipitation, surface runoff inflow and groundwater inflow and 5.43% of the lake evaporation. Therefore, the water level depended more on climatic factors than on anthropogenic factors.

Adaptive Surface Modeling of Soil Properties in Complex Landforms

Abstract: Spatial discontinuity often causes poor accuracy when a single model is used for the surface modeling of soil properties in complex geomorphic areas. Here we present a method for adaptive surface modeling of combined secondary variables to improve prediction accuracy during the interpolation of soil properties (ASM-SP). Using various secondary variables and multiple base interpolation models, ASM-SP was used to interpolate soil K+ in a typical complex geomorphic area (Qinghai Lake Basin, China). Five methods, including inverse distance weighting (IDW), ordinary kriging (OK), and OK combined with different secondary variables (e.g., OK-Landuse, OK-Geology, and OK-Soil), were used to validate the proposed method. The mean error (ME), mean absolute error (MAE), root mean square error (RMSE), mean relative error (MRE), and accuracy (AC) were used as evaluation indicators. Results showed that: (1) The OK interpolation result is spatially smooth and has a weak bull's-eye effect, and the IDW has a stronger ‘bull’s-eye’ effect, relatively. They both have obvious deficiencies in depicting spatial variability of soil K+. (2) The methods incorporating combinations of different secondary variables (e.g., ASM-SP, OK-Landuse, OK-Geology, and OK-Soil) were associated with lower estimation bias. Compared with IDW, OK, OK-Landuse, OK-Geology, and OK-Soil, the accuracy of ASM-SP increased by 13.63%, 10.85%, 9.98%, 8.32%, and 7.66%, respectively. Furthermore, ASM-SP was more stable, with lower MEs, MAEs, RMSEs, and MREs. (3) ASM-SP presents more details than others in the abrupt boundary, which can render the result consistent with the true secondary variables. In conclusion, ASM-SP can not only consider the nonlinear relationship between secondary variables and soil properties, but can also adaptively combine the advantages of multiple models, which contributes to making the spatial interpolation of soil K+ more reasonable.

Early human impacts on vegetation on the northeastern Qinghai-Tibetan Plateau during the middle to late Holocene

The ecosystems of the Qinghai-Tibetan Plateau are regarded as being primarily regulated by climate because of the harsh environment of the region and the resulting sparse human population. Recent studies have revealed that Neolithic farmers and nomads extensively settled in the northeastern Qinghai-Tibetan Plateau from 5.2 ka (ka = cal ka BP); however, it is unclear how and to what extent human activity has affected its vegetation. Here we combine the results of the pollen analysis of a sediment core from Genggahai Lake, a shallow lake in Gonghe Basin on the northeastern Qinghai-Tibetan Plateau, with archaeological evidence and use them to assess the extent and nature of human impacts on the regional vegetation during the middle and late Holocene. The pollen record indicates that Stellera, an indicator of the extent of grazing-induced grassland degradation, first appeared at 4.7 ka, expanded during 3.6–3.0 ka, and finally increased significantly after 1.6 ka. In support of this finding, archaeological data indicate that the agro-pastoral Majiayao people arrived at ∼5 ka and groups of Kayue people, who practiced pastoralism, intensively colonized the Gonghe Basin and nearby Qinghai Lake basin during 3.6–3.0 ka. After ∼1.6 ka, from the Tang Dynasty onwards, human settlement and grazing activity intensified on the northeastern Qinghai-Tibetan Plateau, and this is in accord with the observed high percentages of Stellera in the pollen record. Based on comparison with other records, we conclude that the sediments of Genggahai Lake provide a record of anthropogenic impacts on vegetation, and that human activity may have contributed to regional forest decline during the middle Holocene, and to grassland degradation in the late Holocene. Grassland degradation caused by human activity may be an indicator of the start of the Anthropocene and potentially may have contributed to global climate change via increased dust emission to the atmosphere.

Dynamic assessment of the value of vegetation carbon fixation and oxygen release services in Qinghai Lake basin

Studies on ecosystem service function have an important significance for analyzing and understanding global warming. With the introduction of geographic information system (GIS) and remote sensing (RS) technologies for the evaluation of ecosystem service function, the scope for analysis has been widening. Increasing number of researchers use these technologies to quantify the value of ecosystem service functions and reveal their spatial-temporal variability. By using the data for the interpretation of five RS images and net primary productivity (NPP) in Qinghai Lake basin, we assessed the value of vegetation carbon fixation and oxygen release services and revealed their dynamic variation in this basin. The result suggested that the average values of vegetation carbon fixation and oxygen release services in Qinghai Lake basin between 1987 and 2010 were spatially distributed in a ring shape around the Qinghai Lake and decreased from southeastern to the north and northwestern regions; the northwestern areas had the lowest value. The vegetation carbon fixation value between 1987 and 2010 was on an average 28.87×108yuan/a in Qinghai Lake basin, whereas the oxygen release value was 64.41×108yuan/a. Alpine meadow ecosystem showed the highest value of vegetation carbon fixation and oxygen release services function in Qinghai Lake basin, with average values of 18.28×108yuan/a and 40.79×108yuan/a, respectively, followed by those of temperate steppe and sparse vegetation. The vegetation carbon fixation and oxygen release values in Qinghai Lake basin gradually increased from 1987 to 2010, with the maximum value in 2010. By the end of 2010, the values increased by 7.19×108 yuan and 16.04×108 yuan, respectively. The values slightly decreased in barren land, lakeside marsh, river valley swamp, and sandy areas, but increased to different degrees in other ecosystems. Among them, the largest increase was noted in alpine meadow (4.38×108 yuan and 9.78×108 yuan, respectively), followed by those in temperate steppe with increased values of 1.12×108 yuan and 2.49×108 yuan, respectively.