Corrigendum: Water Supply 21 (6), 2748–2759: Impacts of irrigation and nitrate fertilization scenarios on groundwater resources quantity and quality of Almyros Basin, Greece

The groundwater fluxes (Figure 3) have been simulated for the period of 1991 to 2018 for the scenarios of deficit irrigation (S1, S3) and deficit and rainfed conditions (S2, S4) and evaluated as described in the study of Lyra et al. (2021a).

The nitrates fluxes have been simulated with the MT3DMS model for the period of 1991 to 2018. The simulation was performed for all the four (4) scenarios (S1, S2, S3, S4) and evaluated as described in the study of Lyra et al. (2021a). The simulation results show that the nitrate contamination in the aquifer is mostly affected by the irrigation practices and irrigation return flow, due to the semi-arid climate and the low recharge, especially, in the northern and southern parts of the aquifer. The nitrate concentrations of scenario S4 are spatially lower than the results for the scenario S3. Although in the scenario S4, a large extent of the aquifer is covered by rainfed cultivations and the nitrate fertilization is reduced, the results show less reduction of the nitrate concentrations in spotted central areas, possibly due to the higher leaching rates of cultivars and the clayish material of the aquifer in that area (see Figure 3-Geological view in Lyra et al. (2021b)).

The chloride fluxes have been simulated using the SEAWAT model for the period of 1991 to 2018 and the simulation was performed for all the four (4) scenarios (S1, S1, S3, S4) and evaluated as described in the study of (Lyra et al. 2021a). The maximum chlorides concentration reduction in all scenarios reach a value of 18,000 mg/L in the north coastline area that is salinized in the baseline scenario S0 (Lyra et al. 2021b). The scenarios S1 and S3 show a spatial average reduction of 47 mg/L, and the scenarios S2 and S4 a spatial average of 57 mg/L, the latter has a larger extent of positive impact on the aquifer's water quality (Figure 5(d)).

The average monthly (Figure 6(a)) and the annual water budget (Figure 6(b)) of Almyros Basin aquifer for the deficit irrigation scenarios (S1, S3), and the deficit irrigation and rainfed cultivation scenarios (S2, S4), have been calculated and compared to the current historical groundwater regime of the Almyros aquifer for the simulation years 1991–2018 as described in the study of Lyra et al. (2021a). The practices of deficit irrigation (S1,S3) and deficit irrigation and rainfed conditions (S2,S4) show positive water balance at the end of the rainy period, and reduced deficit balance during the irrigation period. The annual water deficit of the baseline scenario S0 is 12.02 hm³ (Lyra et al. 2021b) is minimized in the deficit irrigation case to 7.9 hm³ (scenarios S1 and S3), and in the deficit irrigation and rainfed cultivation case (scenarios S2 and S4) to 0.3 hm³. The annual water deficit alleviation follows the water economy achieved with the irrigation practices. Both practices have a significant positive impact on the water balance.

All the scenarios (S1, S2, S3, S4) have a positive impact on the water balance, and the water deficit is reduced significantly by 4 hm³ in scenarios S1 and S3, and 11.7 hm³ in scenarios S2 and S4. The scenario practices show positive impacts on nitrate contamination, especially in scenarios S2 and S4. The nitrate concentrations are reduced in large extent and in all cases, but in the central area of the aquifer the irrigated and fertilized high leaching crops and the geological background contribute to lower reduction rate of nitrates. This is also validated in the simulation of doubled total groundwater recharge where the presence of high leaching crops (e.g. maize, cotton) are cultivated next to rainfed crops. The seawater intrusion is spatially more alleviated when the aquifer is enriched with additional recharge, yet the crop pattern and the hydrogeological background control the flow regime of chlorides and cause a reduced rate of aquifer remediation as compared to the less invasive to the flow regime irrigation practices of the present corrigendum. In conclusion, the hydro-geological background and the crop pattern play a critical role in the flow regime of the Almyros aquifer system when irrigation and agronomic practices are implemented and define the course of nitrate contamination and seawater intrusion. Future agricultural practices that aim at the sustainability of the coastal water resources of the Almyros aquifer system should be planned to take under consideration the crop pattern and the hydrogeological characteristics of the aquifer system.