Institute of Geosciences and Earth Resources (IGG), CNR, U.O.S. Pavia, via Ferrata 1, 27100 Pavia, Italy; Department of Earth and Environmental Sciences, University of Pavia, via Ferrata 1, 27100 Pavia, Italy.
Sci Total Environ. 2014 Jan 1;466-467:924-38. doi: 10.1016/j.scitotenv.2013.07.092. Epub 2013 Aug 25.
This study aims at evaluating sources and processes affecting NO₃(-) concentrations in the Oglio River. Five sampling campaigns considered the main watercourse, tributaries, point pollution sources, springs, and groundwater. Physico-chemical parameters, N forms, B, Sr(2+), stable isotopes (δ(2)HH₂O, δ(18)OH₂O, δ(15)NNO₃, δ(18)ONO₃, δ(11)B) and discharge were measured. Hydrological modelling was performed using mass balance and End Member Mixing Analysis equations. During the irrigation period, in the upstream reach, up to 90% of the natural river flow is diverted for irrigation and industrial purposes; excess water drained from agricultural fields is returned to river in the downstream reach. Results evidenced, in the middle reach, a large input of NO₃(-)-rich groundwater which could be quantified using hydrological modelling. Groundwater inputs are responsible for the sharp, tenfold increase in NO₃(-) in the river water, from 2.2-4.4 up to 33.5 mgL(-1), and are more evident in summer, when discharge is lower. Nevertheless, river water preserves its natural B isotopic composition, indicating that the two tracers do not have a common origin and are not co-migrant. In the lower plain, surface-groundwater interconnections and human disturbances in the water cycle favour the recycling of the compounds in the environment, and lead to a similarity in composition of the different water bodies (Oglio River, tributaries and groundwater). The long lasting agronomical practices have profoundly modified the surface-groundwater equilibrium and chemical characteristics, resulting in a highly buffered system. Infiltrating irrigation water leaches down NO₃(-) which is subsequently denitrified; when returned to the Oglio River, groundwater modifies the river water composition by dilution, in the case of NO₃(-), or by addition, for other constituents (e.g. Cl(-), B). The results of this study indicate that, in order to reduce the NO3(-) transport towards the Adriatic Sea, groundwater contamination should be addressed first, with expected long recovery times.
本研究旨在评估影响奥格利奥河硝酸盐浓度的来源和过程。五次采样调查了主要河道、支流、点污染源、泉水和地下水。测量了理化参数、氮形态、硼、锶（2+）、稳定同位素（δ（2）HH₂O、δ（18）OH₂O、δ（15）NNO₃、δ（18）ONO₃、δ（11）B）和流量。使用质量平衡和端元混合分析方程进行水文模拟。在灌溉期，在上游河段，高达 90%的天然河流流量被用于灌溉和工业用途；从农田排出的多余水被排回下游河段。结果表明，在中游河段，有大量富含硝酸盐的地下水输入，可以通过水文模拟来定量。地下水输入是导致河水硝酸盐浓度急剧增加十倍的原因，从 2.2-4.4 增加到 33.5 mgL（-1），在夏季更为明显，当时流量较低。然而，河水保持其天然硼同位素组成，表明这两种示踪剂没有共同的来源，也不是共同迁移的。在下游平原，地表水-地下水相互作用以及水循环中的人为干扰有利于化合物在环境中的再循环，导致不同水体（奥格利奥河、支流和地下水）的组成相似。长期的农业实践极大地改变了地表水-地下水的平衡和化学特性，导致系统高度缓冲。渗透灌溉水淋滤出硝酸盐，随后被反硝化；当返回奥格利奥河时，地下水通过稀释（对于硝酸盐）或添加（对于其他成分，如 Cl（-）、B）来改变河水的组成。本研究结果表明，为了减少硝酸盐向亚得里亚海的输送，首先应解决地下水污染问题，预计需要很长的恢复时间。
