Manipal Centre for Natural Sciences, Manipal University, Manipal, 576104, India.
Environ Sci Pollut Res Int. 2014 Apr;21(7):5098-120. doi: 10.1007/s11356-013-2462-7. Epub 2013 Dec 28.
The study presents a 3-year time series data on dissolved trace elements and rare earth elements (REEs) in a monsoon-dominated river basin, the Nethravati River in tropical Southwestern India. The river basin lies on the metamorphic transition boundary which separates the Peninsular Gneiss and Southern Granulitic province belonging to Archean and Tertiary-Quaternary period (Western Dharwar Craton). The basin lithology is mainly composed of granite gneiss, charnockite and metasediment. This study highlights the importance of time series data for better estimation of metal fluxes and to understand the geochemical behaviour of metals in a river basin. The dissolved trace elements show seasonality in the river water metal concentrations forming two distinct groups of metals. First group is composed of heavy metals and minor elements that show higher concentrations during dry season and lesser concentrations during the monsoon season. Second group is composed of metals belonging to lanthanides and actinides with higher concentration in the monsoon and lower concentrations during the dry season. Although the metal concentration of both the groups appears to be controlled by the discharge, there are important biogeochemical processes affecting their concentration. This includes redox reactions (for Fe, Mn, As, Mo, Ba and Ce) and pH-mediated adsorption/desorption reactions (for Ni, Co, Cr, Cu and REEs). The abundance of Fe and Mn oxyhydroxides as a result of redox processes could be driving the geochemical redistribution of metals in the river water. There is a Ce anomaly (Ce/Ce*) at different time periods, both negative and positive, in case of dissolved phase, whereas there is positive anomaly in the particulate and bed sediments. The Ce anomaly correlates with the variations in the dissolved oxygen indicating the redistribution of Ce between particulate and dissolved phase under acidic to neutral pH and lower concentrations of dissolved organic carbon. Unlike other tropical and major world rivers, the effect of organic complexation on metal variability is negligible in the Nethravati River water.
本研究提供了印度西南部热带季风气候流域内痕量元素和稀土元素（REEs）的 3 年时间序列数据。该河流域位于变质转换边界上，分隔了属于太古代和第三纪-第四纪（西达瓦尔克拉通）的半岛片麻岩和南粒玄岩省。流域的岩石学主要由花岗岩片麻岩、紫苏花岗岩和变质沉积岩组成。本研究强调了时间序列数据对于更好地估算金属通量以及了解河流流域内金属地球化学行为的重要性。痕量元素在河水中的金属浓度表现出季节性，形成了两组截然不同的金属。第一组由重金属和微量元素组成，它们在旱季的浓度较高，而在季风季的浓度较低。第二组由属于镧系元素和锕系元素的金属组成，在季风季的浓度较高，而在旱季的浓度较低。尽管两组金属的浓度似乎都受到流量的控制，但仍有重要的生物地球化学过程影响其浓度。这包括氧化还原反应（对 Fe、Mn、As、Mo、Ba 和 Ce）和 pH 介导的吸附/解吸反应（对 Ni、Co、Cr、Cu 和 REEs）。氧化还原过程中产生的 Fe 和 Mn 氢氧化物的丰度可能是导致河水中金属地球化学再分配的原因。在溶解相中，Ce 存在不同时间的异常（Ce/Ce*），既有负异常也有正异常，而在颗粒相和底泥中则存在正异常。Ce 异常与溶解氧的变化相关，表明在酸性到中性 pH 和较低的溶解有机碳浓度下，Ce 在颗粒相与溶解相之间的再分配。与其他热带和主要世界河流不同，有机络合对金属变异性的影响在奈特拉瓦蒂河水中可以忽略不计。
