Characterising mediterranean catchments: hydrological regime, riverine export, nitrogen balance and agricultural water footprint

Agriculture has been identified as one of the main cause of water consumption and degradation, due to the large use of fertilizers and pesticides. In a catchment, nitrogen (TN) export from terrestrial ecosystems to rivers is controlled by hydrological regimes and TN balance. Hence, before assessing the sustainability of agriculture and defining how the current use of water resources can affect their quantity and quality is important to characterise the hydrological regime, the anthropogenic TN input and the riverine export. In such a context, this research was designed to develop a simple approach for classify the stream regime, to quantify the soil system TN budget and the riverine export, and to assess the sustainability of agriculture through a full agricultural Water Footprint Assessment at a catchment scale in Mediterranean Region characterised by temporary streams. A set of 37 Hydrological Indicators (HIs) were examined in three Mediterranean catchments (Carapelle, Candelaro and Cervaro) and two HIs (flow permanence, MF and flow predictability, SD6) were identified as the best indicators for classify streams regime in Mediterranean watershed. The TN balance and the riverine export were quantified in the Celone watershed (South-East, Italy) through several survey campaigns, continuous measures of streamflow and discrete determinations of concentrations recorded from July 2010 to June 2011. Major N inputs derived from fertilizers and animal manure correspond to 68 and 12 kg N ha-1 yr-1, respectively. TN fluxes in stream during flood events accounted for about 60% of the annual loading. The riverine TN export (from diffuse sources) was estimated to be about 34.5 kg ha-1 yr-1. On a yearly basis, the difference between N inputs and outputs including riverine export (from diffuse sources) was estimated in about 8.1 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. Meanwhile, results for the study period (July 2010 – June 2011) show the total WF to be 79.9 million m3 y-1, subdivided into 30.3% green water, 0.5% blue water and 69.2% grey water, thus highlighting the importance of grey water in the estimate of agricultural water use. Moreover, the results show the grey WF estimates to be highly sensitive both to leaching and runoff fractions, and applied water standards, and affected by large uncertainty. The sustainability assessment of present water consumption, subdivided into the three WF components, indicates sustainable use of green water, fluctuating sustainability of blue water resources, depending on the season and the environmental flow requirement, and unsustainable grey water production and water pollution level for the Celone River. The methodologies and the results presented in this research constitutes a useful tool for ecologists and water resource managers in order to classify the ‘river type’, understand TN loss dynamics and execute more functional water management and land use planning. Hence, this research constitutes a helpful analysis for the Water Framework Directive implementation process in Mediterranean watershed with a temporary river system.

Le attività agricole sono tra le maggiori fonti di consumo e degrado dell'acqua, a causa dell'uso massiccio di fertilizzanti e pesticidi. In un bacino idrico, l'esportazione di azoto (TN) dagli ecosistemi terrestri ai fiumi è controllata dal regime idrologico e dall'equilibrio del TN. Pertanto, prima di valutare la sostenibilità dell'agricoltura e definire come l'uso corrente delle risorse idriche possa influenzarne la loro quantità e qualità è importante caratterizzare il regime idrologico, l'input antropico di TN e l'esportazione fluviale. In tale contesto, questa ricerca sviluppa tematiche inerenti alla classificazione del regime idrologico, alla quantificazione del bilancio del TN ed all'esportazione fluviale dello stesso. Inoltre, è effettuata una valutazione completa dell'impronta idrica agricola a livello di bacino idrografico, in una regione mediterranea caratterizzata da flussi temporanei, al fine di valutare la sostenibilità dell'agricoltura.