Zaihua Liu

Temperature-driven meltwater production and hydrochemical variations at a glaciated alpine karst aquifer: implication for the atmospheric CO2 sink under global warming

About two hydrological years of continuous data of discharge, temperature, electrical conductivity and pH have been recorded at the Glarey spring in the Tsanfleuron glaciated karst area in the Swiss Alps, to understand how glaciated karst aquifer systems respond hydrochemically to diurnal and seasonal recharge variations, and how calcite dissolution by glacial meltwater contributes to the atmospheric CO2 sink. A thermodynamic model was used to link the continuous data to monthly water quality data allowing the calculation of CO2 partial pressures and calcite saturation indexes. The results show diurnal and seasonal hydrochemical variations controlled chiefly by air temperature, the latter influencing karst aquifer recharge by ice and snowmelt. Karst process-related atmospheric CO2 sinks were more than four times higher in the melting season than those in the freezing season. This finding has implication for understanding the atmospheric CO2 sink in glaciated carbonate rock terrains: the carbon sink will increase with increasing runoff caused by global warming, i.e., carbonate weathering provides a negative feedback for anthropogenic CO2 release. However, this is a transient regulation effect that is most efficient when glacial meltwater production is highest, which in turn depends on the future climatic evolution.

δ13C, δ18O and deposition rate of tufa in Xiangshui River, SW China: implications for land-cover change caused by climate and human impact during the late Holocene

Abstract Measurements of δ13C and δ18O values of the riverine tufa samples dated by the accelerating mass spectrometry-14C method have been used for discussion of land-cover change in the catchment area of the Xiangshui River, SW China during the late Holocene. The results show that tufa was deposited in this short river only between c. 4280 and c. 110 years BP. Based on the characteristics of δ13C values of the complete tufa profile in the river, three stages of land-cover conditions in the headwater area could be identified. The earliest, Stage I, contained the most extensive vegetation cover with mainly C3 plants, as shown by the lightest δ13C value, whereas the latest, Stage III, had the least land cover, reflected by the heaviest δ13C value. By comparison of speleothem and historical records, it was found that the land cover in Stage I was controlled mainly by climate change, whereas the land-cover changes in the later two stages were most probably related to major human disturbance (land use), especially since the Qin Dynasty and Ming Dynasty, in the headwater area of the river.

Spatiotemporal Variations of Soil CO2 in Chenqi, Puding, SW China: The Effects of Weather and LUCC

Long-term monitoring of soil CO2 dynamic was applied under different weather conditions and land uses to investigate the influences of weather and LUCC on soil CO2 variations as well as its potential carbon sink. Observation results demonstrate that seasonal variations of soil CO2 are mainly controlled by temperature-water combined effect, rising to the peak in wet–hot season and declining to the valley during dry–cold time. In spatial scale, soil CO2 concentration is largely regulated by LUCC and follows the descending order of forest, shrubbery, dry land, and paddy land except for rice growing season, but with an ascending sequence for coefficient of variations (C.V.s), among which the highest C.V. and the abrupt changes of CO2 in paddy land are mainly due to the alternate cultivation, flooding irrigation, and draining mechanism. Furthermore, by means of modeling calculations, wet–hot weather conditions and land uses as forests are provided with higher dissolved inorganic carbon (DIC) equilibrium concentration than the other sites, reflecting stronger karst process as well as larger potential carbon sink.