Hydrochemical properties of small Spodosol-dominated catchments with contrasting disturbance from windthrow in a temperate rainforest, southeast Alaska

We examined the influence of windthrow on the hydrochemistry of small Spodosol-dominated catchments on a 200 hectare forested island located in the panhandle of southeast Alaska. Four watersheds (0.3 to 0.8 ha) with contrasting disturbance histories were selected and sampled using an event based sampling scheme. Baseflow conditions and six rainstorms were sampled over a 14-month period, representing a range of antecedent and rainfall intensity conditions. During rainstorms, stream flow was measured and water samples were collected on average every 4 hours from each catchment. Stream flow peaked 4 to 12 hours earlier on less-disturbed catchments than on the more-disturbed catchments. During rainstorm events, stream water temperatures were more equilibrated to ambient air temperatures in the less-disturbed catchments than in the more-disturbed catchments. Water discharged from more-disturbed catchments had greater concentrations of Si and lower DOC than water from less-disturbed catchments. Hydrograph separation of rainstorm events suggests more of the water flowed through or originated from deeper mineral soil horizons in the more disturbed catchments. We conclude that catastrophic windthrow disturbance can smooth hydrograph response to rainstorm events, and increase the chemical interaction of rainwater with mineral soil horizons, by increasing rainwater infiltration and storage in deeper mineral soil.