Nitrogen inputs to a river course in a heavily impacted watershed: A combined hydrochemical and isotopic evaluation (Oglio River Basin, N Italy)

作者：Delconte C A^*; Sacchi E; Racchetti E; Bartoli M; Mas Pla J; Re V

来源：Science of the Total Environment, 2014, 466: 924-938.

DOI：10.1016/j.scitotenv.2013.07.092

• NO3- contamination
• Surface-groundwater interaction
• Stable isotopes
• Hydrological modelling
• Po plain

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, Sr2+, stable isotopes (delta H-2(H2O), delta(OH2O)-O-18, delta N-15(NO3), delta O-18(NO3), delta B-11) and discharge were measured. Hydrological modelling was performed using mass balance and End Member Mixing Analysis equations. %26lt;br%26gt;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 mg L-1, and are more evident in summer, when discharge is lower. Nevertheless, river water preserves its natural B isotopic compositionf indicating that the two tracers do not have a common origin and are not co-migrant., %26lt;br%26gt;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 NO which is subsequently denitrified; when returned to the Oglio River, groundwater modifies the river water composition by dilution, in the case of NW, or by addition, for other constituents (e.g. cl(-), B). %26lt;br%26gt;The results of this study indicate that, in order to reduce the NO transport towards the Adriatic Sea, groundwater contamination should be addressed first, with expected long recovery times.

• 出版日期2014-1-1