[Source and Optical Dynamics of Chromophoric Dissolved Organic Matter in the Watershed of Lake Qinghai].

Lake Qinghai is the largest lake in China and is of great significance to maintain the ecological security of the Qinghai-Tibet Plateau. Few studies have been carried out to investigate the optical composition and source of chromophoric dissolved organic matter (CDOM) in large lakes on the Qinghai-Tibet Plateau. It is of great significance to study the source and optical dynamics of CDOM in Lake Qinghai watershed for water quality protection and filling in the gaps in the knowledge of CDOM variability in a remote area. Two sampling campaigns in the Lake Qinghai watershed were carried out, and excitation-emission matrices coupled with parallel factor analysis (EEMs-PARAFAC) were used to unravel the optical composition and the sources of CDOM. Our results indicated that the mean dissolved organic carbon (DOC) concentration, a250:a365, and the spectral slope of CDOM absorption S275-295 in the lake were significantly higher than that in the inflow river (P<0.0001, t-test), whereas the mean absorption coefficient of CDOM a350, humification index (HIX), fluorescence peak integration ratio IC:IT, and specific ultraviolet absorbance at 254 nm SUVA254 of CDOM were shown to be lower in the lake than in the inflow river (P<0.0001), indicating that compared with the lake itself, CDOM in the inflow was humic-rich and highly aromatic. Four fluorescent components were obtained using PARAFAC, including a terrestrial human-like component C1, a microbial human-like component C2, a tyrosine-like C3, and a tryptophan-like C4. The mean DOC concentration, S275-295, and a250:a365in the headwater streams of the Lake Qinghai watershed were lower than those in the downstream estuary, indicating that the CDOM abundance increased, and the molecular weight decreased, from the headwaters to the downstream river mouths. The mean of SUVA254, C1, and the first axis of principal component analysis were positively related to terrestrial input (i.e., the PC1 values were significantly higher in rivers than in lakes (P<0.001)), indicating that the aromaticity of CDOM in rivers was higher than that in lakes. Particularly, the contribution of terrestrial humic-like C1 was higher in the Quanji River, Shaliu River, and Khargai River compared with that in other tributaries due to an intensified cultivated land use at the downstream estuary of these rivers.

[Variations of Stable Oxygen and Deuterium Isotopes in River and Lake Waters During Flooding Season Along the Middle and Lower Reaches of the Yangtze River Regions].

Stable isotope tracers have been widely applied to water sources and evolution, transforming relations, and pollution sources of various water bodies. This study analyzed the spatial variations of δ2H and δ18O in river and lake waters during flooding season, and revealed the factors underlying their variations along the middle and lower reaches of the Yangtze River based on a field sampling campaign in July 2018. Our results showed that δ2H and δ18O in the Yangtze River water were enriched from the Three Gorges reservoir region to the lower reaches of the Yangtze River, which was closely linked to isotopic variations in precipitation. There was no significant difference in δ2H and δ18O values in the mainstream river waters between the Three Gorges Reservoir Region and Yichang-Chenglingji. However, d-excess values in river water displayed a small variation range. In contrast, δ2H and δ18O values in the lake group from Dongting to Jianghan and Huayang to Poyang Lake were lower than in the lake group from Taihu to the Yangtze Delta. Negative d-excess values were observed in lake water from Taihu to the Yangtze Delta, suggesting the combined influence of enriched isotopic compositions in precipitation and strong evaporative enrichment. Of the lakes, the highest isotopic values were found in Dianshan Lake and Datong Lake, whereas the lowest isotopic values were recorded in Dongting Lake and Poyang Lake because of their direct connection with the Yangtze River. The water regimes of Dongting Lake and Poyang Lake were influenced by the Yangtze River, especially when a high water level of the Yangtze River occurred, and thus altered the isotopic compositions of Dongting Lake and Poyang Lake water. Hence, these findings will provide scientific data revealing the precipitation-river-lake interactions and investigating the rational utilization and management of water resources in the middle and lower reaches of the Yangtze River regions.

Revealing the spatio-temporal variability of evapotranspiration and its components based on an improved Shuttleworth-Wallace model in the Yellow River Basin.

Identifying the spatio-temporal variations of evapotranspiration (ET) from its components (soil evaporation and plant transpiration) can greatly improve our understanding of water-cycle and biogeochemical processes. However, partitioning evapotranspiration into evaporation (E) and transpiration (T) at regional scale with high accuracy still remains a challenge. This study has aimed to reveal the spatio-temporal variations of evapotranspiration and its components by using an improved Shuttleworth-Wallace (SWH) model to partition ET in the Yellow River Basin during 1981-2010. The environmental factors affecting the spatial and temporal variations of evapotranspiration and its components were also assessed. Results showed that the mean annual ET, T and E in the Yellow River Basin were 372.18 mm, 179.64 mm, and 192.54 mm, respectively, over the last 30 years. The spatial pattern of mean annual ET and T displayed a decreasing trend from southeast to northwest in the Yellow River Basin, and the temporal variation showed a significant increasing trend with rates of 1.72 mm yr-1 and 1.54 mm yr-1, respectively. It meant that T accounted for the variations of ET, while E showed no significant changes in recent decades. Moreover, the normalized differential vegetation index (NDVI) and temperature were identified as the main factors controlling the variations of ET and T in the Yellow River Basin. Among them, the area with NDVI as the dominant factor for ET and T could reach 63.82% and 78.47% of the whole basin respectively. However, the variations of E were affected by complex factors, and evaporation in the western alpine region was mainly controlled by temperature. Our findings are expected to not only have implications for developing sustainable policies of water management and ecological restoration in this region, but also provide valuable insight in methodology of ET partitioning in regional or global scale.