NO3EXCESS - Nitrogen Origin, EXport and Cycling in coastal irrigatEd SettingS

Abstract:

The issue of a continuous and increasing nitrogen (N) input represents one of the main threats affecting ecosystems, having significant and non-skippable impacts on surface and groundwater quality, greenhouse gas emissions, ecosystems and finally on human health. In this view, the Nitrogen Origin, EXport and Cycling in coastal irrigatEd SettingS project (hereafter NO3EXCESS) represents a multidisciplinary plan aimed at quantifying N loads in lowland agricultural settings by considering their origin, pathways, transformations, and impacts, with the final objective to identify and adopt the most effective countermeasures to reduce them.
The study area is the Po di Volano-Sacca di Goro watershed (PV), the terminal portion of the Po River Basin and a recently reclaimed deltaic territory. This basin suffers from high nutrient loads due to anthropogenic activities, together with water resources overexploitation, saltwater encroachment along the rivers and nutrient release from peaty lenses. For all the above-mentioned reasons the Po di Volano basin represents an optimal benchmark to validate the NO3EXCESS concept, since it could be considered as a representative example of the future for irrigated lowlands.
To reach its goal, NO3EXCESS workflow will be unfold by four main activities:

• field measurements will allow to identify the main biogeochemical processes governing N cycle and to build a detailed hydrological conceptual model;
• laboratory experiments will deepen the understanding of the processes acting in the field sites and allow their quantification to close the water and N budgets;
• numerical modelling will contribute to the validation of the conceptual model via an iterative approach that will employ 2D reactive transport models and 3D groundwater flow models. This approach will provide a point-by-point estimate of the water and N species export towards the lagoon, clarifying and quantifying the contribution of groundwater to N cycle;
• finally, the review of the available information will allow to evaluate the environmental and economic feasibility of diverse remediation strategies to control eutrophication and reduce greenhouse gas emissions in lowland coastal irrigated settings, with a particular focus on the conservative management of aquatic vegetation in the canal network as a tool for NO3- mitigation.

The adoption of a holistic approach to the N mass balance at the watershed scale will be possible thanks to the involvement of a multidisciplinary consortium having distinct and complementary expertise in water ecology, biogeochemistry, hydrogeology, hydrogeochemistry, soil science, stratigraphy, and numerical modelling.

Risultati attesi: 

The main aim of NO₃EXCESS is to quantify nitrogen (N) loads in lowland agricultural settings, considering their origin, pathways, transformations and impacts. This will help to identify and implement the most effective countermeasures, especially in productive agricultural areas located in fragile environments such as the deltas. The use of N fertilizers and irrigation practices generate imbalances in both the hydrological cycle and the nitrogen cycle, leading to disturbances in the ecological status and the water-related ecosystem services. NO₃ EXCESS outcomes will shed light on: i) the identification and quantification of all biogeochemical processes governing N processing and fate both in surface water (SW) and groundwater (GW), ii) the quantification of N species export to the terminal receptors, i.e. the coastal lagoons, iii) the identification of the most suitable remediation strategies (RS) to control eutrophication, by reducing N input to the coastal area (i.e. conservative management practices of aquatic vegetation), and to mitigate climate change by reducing greenhouse gas (GHG) emissions.

Understanding how agricultural practices affect GW-SW interactions and impair the quality of water conveyed to coastal zones is challenging. Therefore, quantifying the contribution of GW to the generation of N loads and the subsequent transfer of contamination to SW in coastal irrigated settings is crucial, particularly in European river basins where water quality requirements are defined by two specific directives, i.e. the Water Framework Directive and the Groundwater Directive.

Specifically, it is expected to obtain the following:

• understand the role of seasonality in biogeochemical N processes acting in lowlands agricultural irrigated settings;
• identify hot spots and hot moments of GHG emissions;
• demonstrate the importance of including anthropogenic stressors, such as irrigation, drainage, fertilization and land cover, in the calculation of water and nitrogen budgets;
• promote the use of a deterministic approach (like numerical simulations) to address water and N budgets calculations in a physically-based manner;
• make “visible” the contribution of the GW in the generation of N loads and the consequent transfer of contamination to SW in coastal irrigated settings;
• promote policy to foster effective RS to decrease N loads towards the coastal zones;
• rise awareness about SW and GW pollution prevention.