Marco Napoli3, Anna Dalla Marta3
1
CREA – Research Centre for Agricultural Policies and Bioeconomy, via Po 14, 00198 Rome, Italy 2
FAO – Food and Agriculture Organization of the United Nations, Viale delle Terme di Caracalla, 00153 Rome, Italy 3 UNIFI – Dipartimento di Scienze delle Produzioni Agroalimentari e dell'Ambiente, Piazzale delle Cascine 18, 50144 Florence
*giuseppe.pulighe@crea.gov.it Abstract
In the upcoming years bioenergy production in the European Union (EU) is expected to grow significantly in order to meet the targets of the new Renewable Energy Directive (RED II). To this end, marginal, contaminated and underutilized lands in Mediterranean regions have the potential to contribute to meeting EU goals through the production of sustainable feedstock. However, far too little attention has been paid to investigate the environmental effects of growing dedicated energy crops in these environments. The SWAT model (Soil and Water Assessment Tool) was used to simulate the effectiveness of agronomic practices on bioenergy feedstock production on potential streamflow, soil erosion and nutrient losses at the watershed level in the Sulcis area (Sardinia, Italy). Results of hypothetical bioenergy scenario, under different agronomic practices and input strategies, were compared with the current land use as a reference scenario. The first results of this investigation show that the SWAT model is a reliable predictor of hydrological flow and water quality indicators of bioenergy-induced modifications in marginal lands for the Mediterranean agricultural systems. Dedicated bioenergy crops are able to reduce sediment transport in rivers and nutrient losses from the soil if compared with traditional row crops. Keywords
Bioenergy crops, streamflow, nutrient losses, SWAT, Sulcis Parole chiave
Colture bioenergetiche, deflusso, perdite di nutrienti, SWAT, Sulcis Introduction
Large quantities of cellulosic biomass are necessary over the upcoming years to meet the targets of the European Union (EU) Renewable Energy Directive (RED II). The newly revised policy will set measures leading to achieving at least 27% renewables in the final energy consumption (electricity, heating and cooling, and transportation sectors) by 2030.
In this framework, the expansion of bioenergy crops on marginal, contaminated and underutilized areas in the Mediterranean basin could be a valuable pathway to achieve EU goals while avoiding competition with food and feed production (Pulighe et al., 2016).
One of the greatest challenges is to identify and evaluate potential impacts of these crops on water quality and availability in order to implement best management practices for environmental sustainability. In fact, unregulated bioenergy expansion could have considerable implications on rivers and water resources due to largest input of chemical nutrients, pesticides, and sediments mobilized by agronomic practices and new cultivation management.
In this work, the semi-distributed process-based hydrologic SWAT model (Soil and Water Assessment Tool) was used to simulate the impact of planting bioenergy crops in the Sulcis area (Sardinia, Italy). The main objectives are to: (1) implement the SWAT model for a baseline scenario that
represents the actual land use with conventional crops representative of Mediterranean area and identifying a set of best setting parameters; (2) simulate the production of high yielding perennial energy crops in the irrigated and rainfed area in order to evaluate the effects of land use changes on discharge, sediments and nutrient flows by monitoring the water balance.
Materials and Methods
The SWAT model is a public domain well-established hydrologic tool developed by the United States Department of Agriculture (USDA) through its Agricultural Research Service (USDA-ARS) and Texas A&M AgriLife Research. The model is being successfully used for assessing soil erosion, water quality and non-point source pollution in a variety of applications (Chen et al., 2017; Trybula et al., 2015). The model delineated the watershed into different sub-basins and further units on single Hydrologic Response Units (HRUs) that can be defined as homogeneous aggregation of soil, land use and slope for computing water cycle dynamics.
In this work, we used the ArcSWAT2012 version to manage all data in a GIS environment. Specifically, the input data used to implement the model are:
• Digital Elevation Model (10x10 m resolution); • Hydrologic network;
• Land use map (21 classes – durum wheat 60 km2, irrigated area 78 km2);
• Soils map showing soil types (31 map units); • Meteorological data (4 stations);
• Stream flow data (1 gauging station – 12 years); • Water quality data (2 stations – 8 years).
Firstly, all input data was set-up to delineate the watershed, sub-basins and new drainage network. Secondly, the model was run to assess the hydrologic effects of the actual land use, considering 3-year warm-up period (1980-1982) and long-term effects for the following years (1983-2013). Finally, the model was set and run incorporating and simulating the presence in the land use the perennial energy crops, in order to evaluate their growth and response compared with traditional crops.
Results
Climatic data show a typical bimodal pattern of Mediterranean environments for rainfall distribution and temperature (mean rainfall 668 mm; mean temperature 17.3 °C) (Fig. 1). The model results in a watershed area of 254,8 km2, 736 HRUs, 101 sub-basins, potential evapotranspiration of 1584 mm. The simulated stream discharge resembled with the observed discharge reasonably well for the observed period (years 1990-1992) (Fig. 2).
Fig. 1 - Climatic data of the study area. Fig. 1 - Dati climatici dell’area di studio.
Fig. 2 - Stream discharge of the study area. Fig. 2 - Deflusso superficiale dell’area di studio.
The results of the simulation for a future cultivation of perennial energy crops in the arable land shows a significant decrease with regard to sediment deposition and nitrogen losses in the basin (Tab. 1). Less marked surface runoff in the energy crops scenario could be attributed the presence of perennial crops (e.g. vineyards) and partly to the model that requires further calibration.
Tab. 1 - Scenarios of feedstock production. Tab. 1 - Scenari per la produzione di biomasse..
Scenario Sediment
loading
N losses Surface
runoff
Baseline scen. 2.4 Mg/ha 33.1 kg/ha 63.6 mm/yr Energy crops scen. 1.4 Mg/ha 16.3 kg/ha 62.4 mm/yr
Discussion and conclusions
The work shows that the semi-distributed SWAT model is a reliable instrument to estimate hydrological flow, sediment and nutrient cycle in the study area. Preliminary results suggest positive impacts of hypothetical scenarios of bioenergy feedstock production with perennial crops on water quality and other selected environmental impacts. Future work will be carried out to validate and calibrate the model using SWAT-CUP (Calibration Uncertainty Program), especially for setting streamflow and surface runoff. Data gathered from field trials and bibliography will help to identify the best setting parameters for testing new energy crops in the model (e.g. giant reed, cardoon, switchgrass). New scenarios of bioenergy feedstock production will be modeled and simulated for in-depth analysis of the impacts of different landscape scenarios comprising detailed management operations such as tillage, fertilizer, pesticide application, irrigation, and harvesting. Acknowledgments: The FORBIO project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 691846. This poster reflects only the author’s view and the INEA is not responsible for any use that may be made of the information it contains.
References
Chen, Y., Ale, S., Rajan, N., Munster, C., 2017. Assessing the hydrologic and water quality impacts of biofuel- induced changes in land use and management. GCB Bioenergy 9, 1461–1475.
Pulighe, G., Bonati, G., Fabiani, S., Barsali, T., Lupia, F., Vanino, S., Nino, P., Arca, P., Roggero, P., 2016. Assessment of the Agronomic Feasibility of Bioenergy Crop Cultivation on Marginal and Polluted Land: A GIS- Based Suitability Study from the Sulcis Area, Italy. Energies 9, 895.
Trybula, E.M., Cibin, R., Burks, J.L., Chaubey, I., Brouder, S.M., Volenec, J.J., 2015. Perennial rhizomatous grasses as bioenergy feedstock in SWAT: Parameter development and model improvement. GCB Bioenergy 7, 1185–1202.