Influences of Extreme Weather Conditions on the Carbon Cycles of Bamboo and Tea Ecosystems

Tea plantations have expanded rapidly during the past several decades in China, the top tea-producing country, as a result of economic development; however, few studies have investigated the influence of tea plantations on the carbon cycle, especially from the perspective of climate change and increases in extreme weather events. Therefore, we employed combined observational and modeling methods to evaluate the water and carbon cycles at representative bamboo and tea plots in eastern China. Green tea growth and the corresponding water and carbon cycles were reproduced using the Community Land Model after applying fertilizer. Old-growth bamboo was reasonably simulated as broadleaf evergreen forest in this model. The mean observed soil respiration ranged from 1.79 to 2.57 and 1.34 to 1.50 µmol m−2 s−1 at the bamboo and tea sites, respectively, from April 2016 to October 2017. The observed soil respiration decreased by 23% and 55% due to extreme dryness in August 2016 at the bamboo and tea plots, respectively, and the model reproduced these decreases well. The modeling results indicated that tea acted as a stronger carbon sink during spring and a stronger carbon source during autumn and winter compared with old-growth bamboo. The carbon cycle was affected more by extremely dry weather than by extremely wet weather in both the bamboo and tea plots. Extremely dry periods markedly reduced the carbon sink at both plots, although this trend was more pronounced at the tea plot

Spatial variations of hydrochemistry and stable isotopes in mountainous river water from the Central Asian headwaters of the Tajikistan Pamirs

Water resources in Central Asia from the mountainous headwater catchments is changing due to the shrinkage of glaciers in the Tian Shan and Pamir mountain systems. In order to predict future changes in water quality, it is crucial to understand what factors are governing the spatial variations of water chemistry and hydrological processes in mountainous headwater catchments. In this study, water chemistry including major ions and stable isotopes in the headwaters of major Tajikistan rivers was studied. Results showed that Tajikistan river water had an alkaline pH value (mean: 8.2) and total dissolved solids (mean: 368.5mg/L) were higher than the global average value. Ca2+, Na+, HCO3-, and SO42- in the rivers were the most abundant cations and anions, controlled by the rock weathering process and evaporation-crystallization processes. The hydrochemical facies of river water was dominated by Ca-HCO3 (71.7%) and exhibited spatial heterogeneity, which was related to the lithologic compositions and water source across Tajikistan. A significant negative correlation of river water delta O-18 with elevation was observed with a vertical lapse rate of 0.17%/100 m. The more negative delta O-18 values in rivers from eastern Tajikistan were scattered in the lower left corner of the delta O-18-delta H-2 plot, implying that the rivers were primarily supplied by snow/glacier meltwater because of the substantial number of glaciers and high elevation mountain in eastern regions. The drinking and irrigation suitability from ionic compositions revealed that the water quality of Tajikistan rivers was naturally good, though some sites posed a safety concern. These findings can provide new insights into sustainable management of water quality in the climatically and lithologically distinct segments of headwater regions in the Tajikistan Pamirs

Disturbances of Temperature-Depth Profiles by Surface Warming and Groundwater Flow Convection in Kumamoto Plain, Japan

Subsurface temperatures depend on climate and groundwater flow. A lack of observations of subsurface temperature collected over decades limits interpretation of the combined influences of surface warming and groundwater flow on subsurface thermal regimes. Subsurface temperature-depth profile data acquired for Kumamoto Plain, Japan, between 1987 and 2012 were collected and analyzed to elucidate regional groundwater and heat flows. The observed and simulated temperature-depth profiles showed the following: subsurface water flows from northeast to southwest in the study area; the combined influence of surface warming and water flow perturbation produces different temporal changes in thermal profiles in recharge, intermediate, and discharge areas; and aquifer thermal properties contribute more than hydraulic parameters to the perturbation of temperature-depth profiles. Spatial and temporal evolution features of subsurface thermal regimes may be utilized to investigate the influence of surface warming events on subsurface water and heat flows at the basin scale

Comparing and Modifying Eight Empirical Models of Snowmelt Using Data from Harp Experimental Station in Central Ontario

Aims: To modify two empirical models of snowpack and snowmelt, and compare eight such models. Study Design: Test and modify the models by using five years of snow measurements from Harp Lake. Place and Duration of Study: Dorset Environmental Science Centre, Ontario Ministry of Environment, and Department of Geography, Nipissing University, between January 2009 and August 2012. Methodology: The old daily-run WINTER model was the first model. It was modified to create a second model. The enhanced-temperature-index (ETI) model was slightly modified to be the third model. Modified WINTER and ETI were combined into the fourth model. Hydrology model BROOK90 and SWAT were used as the fifth and sixth model, also daily-run. Operating the WINTER and ETI in hourly steps created the seventh and eighth model. The calculated snow water equivalent (SWE) by each model was evaluated against the observed data to give a coefficient of efficiency (CE). Accuracy and performance of the models were compared based on CE values. Results: Modified WINTER model improved original WINTER by 20.7% (CE increased 20.7%). The performance of ETI model was 27.6% higher than the original WINTER. The new combination model produced additional improvement by 40.7 % over the original WINTER, or by 16.5% over the modified WINTER or 10.3% over the ETI. Running the model with hourly time steps rather than daily steps increased model’s accuracy: hourly WINTER raised CE by 15.4% and hourly ETI raised CE by 7.9%. Two watershed hydrology models BROOK90 and SWAT performed even better than the above six simpler snow models. Conclusion: It is suggested that the daily combination model be considered if only daily data is available, or hourly WINTER and ETI models be used if hourly runs are desired while new calibration are required when applying them to any new locations. If data requirements by BROOK90 or SWAT are met, these hydrology models would be tried

The Coupling of Glacier Melt Module in SWAT+ Model Based on Multi-Source Remote Sensing Data: A Case Study in the Upper Yarkant River Basin

Glaciers have proven to be a particularly sensitive indicator of climate change, and the impacts of glacier melting on downstream water supplies are becoming increasingly important as the world’s population expands and global warming continues. Data scarcity in mountainous catchments, on the other hand, has been a substantial impediment to hydrological simulation. Therefore, an enhanced glacier hydrological model combined with multi-source remote sensing data was introduced in this study and was performed in the Upper Yarkant River (UYR) Basin. A simple yet efficient degree-day glacier melt algorithm considering solar radiation effects has been introduced for the Soil and Water Assessment Tool Plus model (SWAT+), sensitivity analysis and auto calibration/validation processes were integrated into this enhanced model as well. The results indicate that (i) including glacio-hydrological processes and multi-source remote sensing data considerably improved the simulation precision, with a Nash–Sutcliffe efficiency coefficient (NSE) promotion of 1.9 times and correlated coefficient (R2) of 1.6 times greater than the original model; (ii) it is an efficient and feasible way to simulate glacio-hydrological processes with SWAT+Glacier and calibrate it using observed discharge data in data-scarce and glacier-melt-dominated catchments; and (iii) glacier runoff is intensively distributed throughout the summer season, accounting for about 78.5% of the annual glacier runoff, and glacier meltwater provides approximately 52.5% (4.4 × 109 m3) of total runoff in the study area. This research can serve the runoff simulation in glacierized regions and help in understanding the interactions between streamflow components and climate change on basin scale

Influences of Extreme Weather Conditions on the Carbon Cycles of Bamboo and Tea Ecosystems

Tea plantations have expanded rapidly during the past several decades in China, the top tea-producing country, as a result of economic development; however, few studies have investigated the influence of tea plantations on the carbon cycle, especially from the perspective of climate change and increases in extreme weather events. Therefore, we employed combined observational and modeling methods to evaluate the water and carbon cycles at representative bamboo and tea plots in eastern China. Green tea growth and the corresponding water and carbon cycles were reproduced using the Community Land Model after applying fertilizer. Old-growth bamboo was reasonably simulated as broadleaf evergreen forest in this model. The mean observed soil respiration ranged from 1.79 to 2.57 and 1.34 to 1.50 µmol m−2 s−1 at the bamboo and tea sites, respectively, from April 2016 to October 2017. The observed soil respiration decreased by 23% and 55% due to extreme dryness in August 2016 at the bamboo and tea plots, respectively, and the model reproduced these decreases well. The modeling results indicated that tea acted as a stronger carbon sink during spring and a stronger carbon source during autumn and winter compared with old-growth bamboo. The carbon cycle was affected more by extremely dry weather than by extremely wet weather in both the bamboo and tea plots. Extremely dry periods markedly reduced the carbon sink at both plots, although this trend was more pronounced at the tea plot

Decoding the hundred-year water level changes of the largest Saline Lake in China: A joint lake-basin modeling study based on a revised SWAT+

Study region: Qinghai Lake Basin (QLB), the largest saline lake in China and its collecting basin Study focus: Climate change has caused clear shrinkage or dramatic water level fluctuation of lakes in arid and semi-arid regions, while the underlain mechanisms remain unclear. The joint lake-basin investigations (spatial) and long-term studies (temporal) are urgently needed. This study developed SWAT+ to jointly simulate the water cycle of QLB and investigated how the hydrological regime of QLB changed at the hundred-year scale. New hydrological insights for the region: The modeling framework consisted of the revised SWAT+ , reanalysis data, and reconstructed water level based on lake gravity core performed quite well (NSE > 0.9 for lake water level) in simulating the hydrological processes of QLB at the hundred-year scale (1910 – 2018). Temporally, decadal variations of hydrological components in QLB decreased in sequence of precipitation (46.33 mm), lateral flow (26.85 mm), evapotranspiration (16.03 mm), snowmelt (10.44 mm), groundwater flow (5.66 mm), and overland flow (1.18 mm). Spatially, precipitation, water yield, lateral flow, and groundwater flow in upstream regions of QLB, where the precipitation amount was small, were most sensitive to climate change. The long-term water level decrease of Qinghai Lake during 1928 – 2003 was mainly driven by variations of river runoff and lake surface evaporation; the clear water level increase since 2004 was dominated by river runoff changes

Stable isotope signatures of river and lake water from Poyang Lake, China: Implications for river-lake interactions

Interactions between the Yangtze River and Poyang Lake are undergoing rapid changes due to intensive human activities and ongoing climate change. This study investigates the spatiotemporal variations of isotopic compositions (delta H-2 and delta O-18) in river and lake water to explore the river-lake interactions in combination with water level and discharge in Poyang Lake watershed. The results showed that river and lake water isotopes (delta H-2 and delta O-18) exhibited highly temporal heterogeneity across seasons but their spatial differences were not remarkable, which is closely related with water sources from local precipitation and groundwater, and lake hydrology. The homogeneous patterns of lake water delta H-2 and delta O-18 indicated that Poyang Lake is a well-mixed lake in spatial scales. By contrast, the river (10.7 parts per thousand) and lake (10.8 parts per thousand) water d-excess and lc-excess (0.6 parts per thousand) were close to precipitation d-excess and lc-excess suggesting that precipitation is the main source for the lake and river. The slope and intercept of the river water line were slightly lower than those of the local meteoric water line and lake water line, which could be attributed to a greater evaporative enrichment in river water impacted by water flow regulation in the watershed. Interactions between Poyang Lake and Yangtze River vary seasonally, as evidently shown by the variations of water discharge and isotope compositions in river and lake water. The delta H-2 and delta O-18 of the Yangtze River water become more positive in the downstream zone than those in the upstream zone, indicating that the water from Poyang Lake has a great impact on downstream river water. This result can also be demonstrated by the efflux rate from the Poyang Lake to the Yangtze River, ranging from 17.9 parts per thousand to 67.9 parts per thousand across seasons except for the outlier rate in October resulted from the backflow of water from Yangtze River to the Poyang Lake. The complex lake-river interactions between Poyang Lake and Yangtze River mainly resulted from the regulation of Three Gorges Dam and water discharge from Poyang Lake watershed. These findings of the complex lake-river interactions will help to improve understanding of the hydrological processes and transport of pollutants and solutes around the confluence zone of the Yangtze River and Poyang Lake