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Evaporation from global oceans is an important moisture source for glaciers and headwaters of major Asian rivers in the Tibetan Plateau (TP). Although the accelerated global hydrological cycle, the altered sea–land thermal contrast and the amplified warming rate over the TP during the past several decades are known to have profound effects on the regional water balance, the spatial distribution of oceanic moisture contributions to the vast TP remains unclear. This hinders the accurate quantification of regional water budgets and the reasonable interpretation of water isotope records from observations and paleo archives. Based on historical data and moisture tracking, this study systematically quantifies the absolute and relative contributions of oceanic moisture to long-term precipitation in the TP. Results show that the seasonal absolute and relative oceanic contributions are generally out of phase, revealing the previously underestimated oceanic moisture contributions brought by the westerlies in winter and the overestimated moisture contributions from the Indian Ocean in summer. Quantitatively, the relative contribution of moisture from the Indian Ocean is only ∼30 % in the south TP and further decreases to below 10 % in the northernmost TP. The absolute oceanic contribution exhibits a spatial pattern consistent with the dipole pattern of long-term precipitation trends across the Brahmaputra Canyon region and the central-northern TP. In comparison, relative oceanic contributions show strong seasonal patterns associated with the seasonality of precipitation isotopes across the TP.

Precipitation changes in the Three Gorges Reservoir Region (TGRR) play a critical role in the operation and regulation of the Three Gorges Dam (TGD) and the protection of residents and properties. The potential impacts of the TGD on local and regional circulation patterns, especially the precipitation patterns, have received considerable attention since its construction. However, how the moisture transport affects precipitation changes in the TGRR spatially and temporally remains obscure. In this study, we investigate the long-term moisture sources of precipitation and their contributions to precipitation changes over the TGRR using an atmospheric moisture tracking model. Results suggest that although there is seasonal variation, the moisture contributing to the TGRR precipitation primarily originates from the areas southwest of the TGRR dominated by the Indian summer monsoon. In particular, the sources with the highest annual moisture contribution are the southwestern part of the Yangtze River basin and the southeastern tip of the Tibetan Plateau (TP). On average, 41 %, 56 %, and 3 % of the TGRR precipitation originates from ocean, land, and local recycling, respectively. In addition, the decreased precipitation over the TGRR during 1979–2015 is mainly attributed to the significantly decreased moisture contribution from the source regions southwest of the TGRR (especially around the southeastern tip of the TP). Compared to dry years, the higher precipitation in the TGRR during wet years is contributed by the extra moisture from the southwestern source regions that is delivered by the intensified southwesterly monsoon winds.

Evaporation from global oceans is an important moisture source of glaciers and headwaters of major Asia rivers in the Tibetan Plateau (TP). Although recent accelerated global hydrological cycle, altered sea-land thermal contrast, and amplified warming rate over the TP are known to have profound effects on the regional water balance, the contribution of oceanic evaporation, in particular its spatial variability over the vast TP, remains unclear. The lack of such knowledge hinders an accurate quantification of regional water budgets and the reasonable interpretation of water isotope records from observations and paleo archives. Based on historical data and moisture tracking, this study systematically quantifies the absolute and relative contributions of oceanic moisture to the long-term TP precipitation. Results show that seasonal absolute and relative oceanic contributions are generally out of phase, revealing previously overlooked oceanic moisture contributions to the TP in winter as dominated by the westerlies and overestimated moisture contribution from the Indian Ocean in summer. Especially, the relative contribution of moisture from Indian Ocean is only ~30 % in the southern TP and further decreases to below 10 % in the northern TP. Absolute oceanic contributions explain the dipole pattern of long-term precipitation trends across the southern slope of the Himalayas and the central-northern TP. In comparison, the seasonality of relative oceanic contribution is associated with that of precipitation isotopes across the TP.

Precipitation change in the Three Gorges Reservoir Region (TGRR) plays a critical role in the operation and regulation of the Three Gorges Dam (TGD) as well as the protection of residents and properties. The potential impacts of the TGD on local and regional circulation patterns, especially the precipitation patterns, have received considerable attention since its construction. However, how the moisture transport affects the precipitation change in the TGRR spatially and temporally remains obscure. In this study, we investigate the long-term moisture sources of precipitation as well as their contributions to the precipitation change over the TGRR using an atmospheric moisture tracking model. Results suggest that although with seasonal variation, the moisture contributing to the TGRR precipitation primarily originate from the areas southwest of the TGRR dominated by the Indian summer monsoon. In particular, the sources with the highest annual moisture contribution are the southwestern part of the Yangtze River Basin and the southeastern tip of the Tibetan Plateau (TP). On average, 41 %, 56 %, and 3 % of the TGRR precipitation originate from ocean, land, and local recycling, respectively. In addition, the decreased precipitation over the TGRR during 1979–2015 is mainly attributed to the significantly decreased moisture contribution from the source regions southwest of the TGRR (especially around the southeastern tip of the TP). Compared to dry years, the higher precipitation in the TGRR during wet years is contributed by the extra moisture from the southwestern source regions delivered by the intensified southwesterly monsoon winds.

Ponds play a critical role in biogeochemical carbon cycling and have been identified as hot spots of methane (CH4) emission. Yet, most existing studies focused on ponds in the boreal zone and current estimates of the relevance of ponds in global CH4 budgets as well as knowledge of the environmental factors regulating their emissions are poorly constrained. Both nutrient concentration and temperature can potentially alter CH4 dynamics in shallow ponds, but there are still few investigations into the response of CH4 emission to nutrient enrichment and rising temperatures. Here we studied the magnitude and regulation of two CH4 pathways (diffusion and ebullition) from a shallow and eutrophic pond located in the subtropical zone in Central China. Ebullitive fluxes were on average 96.4 mg CH4 m−2 d−1 and contributed 88.6 % to the total (diffusive + ebullition) CH4 emissions. Daily CH4 fluxes were related to daily mean water temperature, with ebullition having a stronger temperature dependence than diffusion (Q10 of 5.52 vs. 2.05). Relationships between temperature and CH4 emission were affected by seasonal variation of the concentration of total phosphorus. The temperature dependence of both ebullitive and diffusive fluxes increased with increasing phosphorous concentration. Our study highlights that increasing eutrophication by anthropogenic impacts and climate warming will increase CH4 emissions from ponds, thus representing a positive feedback mechanism to global warming.

Biogenic methane (CH4) emissions from inland waters contribute substantially to global warming. In aquatic systems, CH4 dissolved in freshwater lakes and reservoirs is highly heterogeneous both in space and time. To better understand the biological and physical processes that affect sources and sinks of CH4 in lakes and reservoirs, dissolved CH4 needs to be measured with a highest temporal resolution. To achieve this goal, we developed the Fast-Response Automated Gas Equilibrator (FaRAGE) for real-time in situ measurement of dissolved CH4 concentration at the water surface and in the water column. FaRAGE can achieve an exceptionally short response time (t95 % = 12 s when including the response time of the gas analyzer) while retaining an equilibration ratio of 63 % and a measurement accuracy of 0.5 %. An equilibration ratio as high as 91.8 % can be reached at the cost of a slightly increased response time (16 s). The FaRAGE is capable of continuously measuring dissolved CH4 concentrations in the nM-to-mM (10−9–10−3 mol L−1) range with a detection limit of sub-nM (10−10 mol L−1), when coupled with a cavity ring-down greenhouse gas analyzer (Picarro GasScouter). It enables the possibility of mapping dissolved CH4 concentration in a quasi three-dimensional manner in lakes. The FaRAGE is simple to operate, inexpensive, and suitable for continuous monitoring with a strong tolerance to suspended particles. The easy adaptability to other gas analyzers such as Ultra-portable Los Gatos and stable isotopic gas analyzer (Picarro G2132-i) also provides the potential for many further applications, e.g. measuring dissolved 13δC-CH4 and CO2.