Melt runoff (MR) contributes significantly to the total runoff in many river basins. Knowledge of the meltwater contribution (MCR, defined as the ratio of MR to the total runoff) to the total runoff benefits water resource management and flood control. A process-based land surface model, Noah-MP, was used to investigate the spatiotemporal characteristics of MR and MCR in the Upper Changjiang River (as known as Yangtze River) Basin (UCRB) located in southwestern China. The model was first calibrated and validated using snow cover fraction (SCF), runoff, and evapotranspiration (ET) data. The calibrated model was then used to perform two numerical experiments from 1981 to 2010: control experiment that considers MR and an alternative experiment that MR is removed. The difference between two experiments was used to quantify MR and MCR. The results show that in the entire UCRB, MCR was approximately 2.0% during the study period; however, MCR exhibited notable spatiotemporal variability. Four sub-regions over the Qinghai-Tibet Plateau (QTP) showed significant annual MCR ranging from 3.9% to 6.0%, while two sub-regions in the low plain regions showed negligible annual MCR. The spatial distribution of MCR was generally consistent with the distribution of glaciers and elevation distribution. Mann-Kendall (M-K) tests of the long-term annual MCR indicated that the four sub-regions in QTP exhibited increasing trends ranging from 0.01%/year to 0.21%/year during the study period but only one displayed statistically significant trend. No trends were found for the peak time (PT) of MR and MCR, in contrast, advancing trend were observed for the center time (CT) of MR, ranging from 0.01 months/year to 0.02 months/year. These trends are related to the changes of air temperature and precipitation in the study area.

El Niño is now a focal point for global climate change research, but its influence on the Western Pacific is still uncertain. Taiwan Strait is an important pathway, which connects the South China Sea and the East China Sea, and is strongly influenced by the monsoon. Generally, in winter, the strong winter monsoon brings the cold and nutrient-rich Changjiang Diluted Water¡]CDW¡^southward. While during the El Niño event, because of the weakened south wind in northern Taiwan, more cold CDW moves southward, and hence the decreased seawater temperature in spring and fall. The trend is opposite in summer. There is a high salinity signal in the seas outside of Hsin-Chu, suggesting sea water coming from the Kuroshio, which has circumvented the northeast tip of Taiwan. Meanwhile, there is a front which separates this Kuroshio water and CDW. During the El Niño, the front moves eastward, especially in summer. The salinity east of the front decreases gradually from spring to winter water, the center of upwelling located at the eastern side of the front in spring, and at or near the front from summer to winter. Furthermore, The N/P ratio of the northern Taiwan Strait water became higher after the Three Gorges Dam (TGD) became operational. The nitrous oxide (N2O) is a long-lived greenhouse gas. Unfortunately, in Taiwan, there are few data about N2O emission from rivers, lakes and coastal areas. This research also studies the N2O distribution in natural waters around Taiwan. The average surface water concentration and sea to air flux in the Taiwan Strait¡]7.81¡Ó1.28nM¡F0.28¡Ó0.38£gmol/m2/hr¡^is higher than in the South China Sea¡]SCS¡F7.55¡Ó2.45 nM¡F0.21¡Ó0.27£gmol/m2/hr¡^and the West Philippine Sea¡]WPS¡F5.3¡Ó0.62nM¡F-0.20¡Ó0.25£gmol/m2/hr¡^, which displays a rare sink signal in the world oceans. There is an N2O maximum observed around 1000m in the WPS, and another shollower one around 700m in the SCS, presumably because of the intenive upwelling and vertical mixing in the SCS basin. There are some rather high N2O concentrations (N2O>30nM) in the SCS, observed near the continental slope. We assume that these are released from sediments on the continental slope. Although the sea-to-air flux of N2O is much lower than the flux of CO2, N2O emission in the SCS contributes more than two times the greenhouse effect than CO2 does. Besides, The N2O concentration during El Niño is lower than usual, probably due to a smaller amount of the CDW. Finally, the average N2O concentrations of river and submarine groundwater discharge in Taiwan are about 32.3¡Ó43.3nM and 9.72¡Ó13.2 nM, respectively.

Ce travail a pour but d'améliorer la connaissance des transferts de métaux entre les phases dissoute et particulaire en milieux estuariens afin d'évaluer et de mieux comprendre les variations de la répartition des métaux et de leur spéciation en fonction des conditions physico-chimiques des systèmes étudiés. Les estuaires sont caractérisés par des gradients importants de nombreux paramètres physico-chimiques tels que la salinité, le pH, la teneur en ligands organiques, la turbidité etc... Cinq estuaires ont été sélectionnés en raison de leurs caractéristiques hydrologiques, morphologiques physico-chimiques et biologiques différentes. Deux de ces estuaires sont microtidaux et débouchent sur la Méditerranée (le Rhône et l'Ebre), le troisième est un exemple type d'estuaire macrotidal pollué (l'Escaut) et les deux derniers ont des débits liquides et solides qui les situent parmi les dix plus grands fleuves du monde (le Changjiang et la Lena). Nous avons sélectionné cinq métaux (Cs, Cd, Zn, Mn et Co) dont le devenir est tributaire de la plupart des processus recensés en estuaire. Ces métaux ont par ailleurs des isotopes émetteurs gamma ayant des périodes de demi vie assez grandes, ce qui nous a permis d'utiliser une méthode de mesure des coefficients de distribution qui caractérisent les seules fractions labiles. L'application du modèle de complexation de surface pour l'interprétation des mesures de coefficients de distribution des cinq métaux dans les différents estuaires pour différentes conditions de débit et de saison a permis d'identifier les processus qui jouent un rôle dans la spéciation de ces métaux dans de tels milieux. Ces résultats peuvent s'appliquer à la compréhension des mécanismes de transfert entre phases dissoute et particulaire dans le cas d'autres métaux et d'autres systèmes aquatiques. Un intérêt particulier a été porté au rôle des colloïdes et des ligands organiques dissous dans la spéciation des métaux dans les milieux estuariens étudiés. D'une part nous avons montré que les composés organiques dissous qui s'adsorbent à la surface des particules en suspension modifient leurs propriétés de surface et contrôlent leur réactivité de surface vis-à-vis des métaux. D'autre part les colloïdes et ligands organiques dissous contribuent à la complexation des métaux dans la phase dissoute. Une méthode simple basée sur l'ajout d'un ligand ayant un fort pouvoir complexant, 1'EDTA (éthylène-diamine-tétra-acétate) a permis d'évaluer le pouvoir complexant des colloïdes et des ligands organiques dissous pour Zn et Cd dans l'estuaire du Rhône. Cependant la nature et la concentration de ces composés dissous restent inconnues.