Application of SWAT to assess peatland forestry impacts on water quality

Abstract

Peatland drainage can affect the natural state of hydrological conditions and nutrient loading but is rarely included in catchment-scale models. To understand the gap, we aimed to use the soil and water assessment tool (SWAT) to observe drained peatlands and their properties to predict nutrients and suspended solids (SS) in the peatland-dominated Simojoki catchment. We integrated drainage networks in SWAT to (i) identify drainage parameters; (ii) determine annual loads and mean concentrations of SS, organic phosphorus (Org-P), total phosphorus (TP), organic nitrogen (Org-N), and total nitrogen (TN); (iii) understand spatial variation of nutrients and SS; and (iv) investigate uncertainty ranges for the estimates. The calibrated model showed a 9.6 per cent bias between the simulated flow and the observations with low-to-medium loading variations for the water quality parameters. For Org-N and TN, the highest loading per year was at the downstream outlet, whereas for SS, Org-P, and TP, it was higher at the upstream outlet of the catchment. This approach of representing the drained peatland in SWAT indicated maximum spatial distributed load in the peat soil in the clear-cut area and can be beneficial in future hydrological modelling efforts in identifying the status of nutrients or SS.