Antropogenic input of nitrogen and riverine export from a Mediterranean catchment. The Celone, a temporary river case study

In a catchmnent, nitrogen (N) export from terrestrial ecosystems to rivers is controlled by the hydrological processes and N balance. In the present paper, the soil system N budget and riverine export were quantified in a Mediterranean watershed, the Celone (South-East, Italy). The study area (72 km(2)) consists of agricultural land (70%) and deciduous forests with three small residential areas. Major N inputs derived from fertilizers and animal manure, corresponding for the whole watershed area to 68 and 12 kg N ha(-1) yr(-1), respectively. N input from point sources was 1% of total input and atmospheric depositions measured in a gauging station near the study area was quantified in similar to 6 kg N ha(-1) yr(-1). Crop N uptake was the main N output from agricultural land; it was estimated in similar to 37 kg N ha(-1) yr(-1) by using data on crop yields provided by local farmers. Total flux of N in surface water was quantified for a year at the outlet of the study area by using continuous measures of flow and discrete measures of N concentrations carried out with a different frequency during the normal and low flow and when floods occurred. The hydrological regime of the stream, which is a temporary river, plays an important role in N transport. Water quality was found to vary considerably through the year in terms of both nutrient concentrations and loads. Riverine N export was quantified in 41% of total N input, and it was mainly transported during flood events, similar to 60% of the annual load was delivered during floods occurred in 38 days. Organic nitrogen and nitrate were the main N forms in surface water, and the contribution per hectare was about 24 and 14kg N, respectively. On a yearly basis, the difference between N inputs and outputs including riverine export was estimated in about 4 kg N ha(-1) yr(-1) for the whole watershed area. This amount partly accumulates in soils in different N forms and the remaining part, mainly in form of nitrate, percolates through unsaturated soil towards groundwater. This study reports an important analysis of N pollution in a Mediterranean watershed with a temporary river system and limited data availability. Data acquisition and handling have proved to be an important challenge to overcome in N balance quantification. The results and the methodology of the present work can be useful for understanding nitrogen loss dynamics and for functional water management and land use planning. (C) 2017 Elsevier B.V. All rights reserved.