Abstract: Report on the biophysical catchment-scale modelling of the River Louros demonstration site
The Louros is a medium-sized river (catchment size ≈900 km2) situated near the west coast of mainland Greece in a mountainous setting. The catchment is largely rural and relatively sparsely populated, dominated by mountainous shrubland, but with considerable areas of arable land in the lowland plain. The area is wet by Mediterranean standards, with an average annual precipitation up to 1300 mm in the higher areas. The Louros has been previously been highlighted as vulnerable to eutrophication although records of observed data are very ambiguous.
This study sought to calibrate the hydrological and hydrochemical models PERSiST, INCA-N with PERSiST and INCA-P with PERSiST, to simulate future hydrology, nitrogen and phosphorus under a number of different climate and land use scenarios. The models were calibrated for the period of 2001-2012. Thereafter, stream-flow, nitrogen and phosphorus concentrations were simulated for the baseline period of 1981-2010, and for the scenario period of 2031-2060, using three alternative climate models and four different land use scenarios.
Shortage of data proved to be the most serious obstacle for carrying out the model-based assessment, as data for calibration was collected from six different sources which, ultimately, poorly compatible. The models were eventually calibrated against observations from two different sites with only 11 observations from each. While this is far from sufficient for calibration of complex models such as those used, it was still possible to draw some conclusions from the climate and land use scenario simulations.
The modelled changes in discharge were significant for all three climate scenarios, with a reduction in average flow of 20-30 %. In contrast, neither climate, nor land use change had any substantial effect on nutrient concentrations (nitrate and phosphorus). As for the land use change scenarios, the inferred impacts on fertiliser loads were limited, and as the observed time series suggest very limited leaching of nutrients from arable land, the effects from land use scenarios on stream nutrient concentrations were negligible. For climate, the forecasted reduction in runoff is accompanied by a similar reduction of nutrient leaching from the soils. Thus, the modelled net effect from climate change on stream nutrient concentrations was small. However, the total loads of nutrients transported by the river to the Ambracian gulf were substantially reduced. The reason for the simulated reduction of nutrient leaching from the soils was that longer water residence time in the soil and less runoff meant that more of the nutrients were available for plant uptake. It should be acknowledged that this is a highly uncertain result, as negative effects on plant growth from drought cannot be ruled out. Given this possibility, nutrient concentrations could instead increase substantially in the future.
Finally, different mitigation measures to improve the water quality of River Louros were considered, all involving reduction of the fertiliser loads. The total reduction of fertilisers was up to 75 % of the baseline load for nitrogen and 67 % of the baseline load for phosphorus. The simulated effect of the mitigation measures was negligible for nitrate concentrations, whereas phosphorus concentrations were reduced by 27-32 %. However, the water quality fulfilled the criteria of “good ecological status” for both nitrate, ammonium, total phosphorus and SRP for all simulated scenarios, including the baseline.
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