Modelling the effects of NBS adoption in mitigating soil losses of a land reclamation area in the Massaciuccoli lake catchment (Central Italy)

Many types of Nature-Based Solutions (NBSs) have been applied worldwide to mitigate impacts of hydro-meteorological hazards produced by anthropic activities such as grazing and agriculture. Among them, vegetated buffer strips (VBSs) and winter cover crops (WCCs) are suitable solutions for reducing runoff and soil erosion rates from cultivated fields. However, their mitigating effects depends largely on local conditions such as morphology and soil nature.

This study investigated these aspects by modelling the NBS effects on soil and water dynamics in two test sites located within the Massaciuccoli agricultural plain (Vecchiano, Pisa, Central Italy) and characterised by different soil types (peaty and silty soils). The SWAT+ model has been chosen to simulate hydraulic and hydrological phenomena using high-resolution data such as digital terrain models (DTMs) from close-range photogrammetry, detailed land cover mapping, actual crop rotations, and detailed calendars of agronomic operations. We considered two types of NBSs: i) 3 m wide VBSs planted along both sides of field ditches, covering about 10% of the agricultural land, and ii) WCCs sowed after harvesting summer cash crops. Both NBSs exert their action on 30% of the experimental area. The mitigating effect was tested by comparing simulation results from NBS and control (conventional agriculture) scenarios under ongoing climatic conditions and future climate changes.

Results indicated that VBSs and WCCs showed different capabilities to reduce runoff and sediment losses, and the adoption of both can enhance the mitigation effect significantly. NBSs resulted effective also in completely flat areas since slight topographic irregularities can cause local preferential flows resulting in high runoff rate and sediment losses. Furthermore, it is demonstrated how the soil variability in texture and organic matter content can affect the amount of runoff and sediment loss on a local scale. Consequently, the mitigating effects of NBS can be closely driven by the soil nature and heterogeneity. This influence is even more significant under extreme climatic conditions such as higher temperatures and more aggressive rainfall events. In these cases, NBSs can play an essential role in mitigating runoff and soil erosion phenomena on fine-textured mineral soils. In contrast, they lose much of their effectiveness on peat soils.