Treatment of Log Yard Runoff Impacted by Aged Logs in a Free Water Surface Constructed Wetland

摘要

Hurricanes pose a great risk to forestry, and lead to high financial losses due to destroyed wood. For example, the hurricane 'Gudrun' devastated a large part of the forests of southern Sweden in January 2005. Windthrown logs are commonly removed from forest, temporarily stored on log yards, and often sprinkled with water to avoid decay. However, the subsequent runoff may cause environmental pollution. The aim of this original article is to assess the treatment of log yard runoff, which was impacted by logs of different age, in an inexpensive free water surface constructed wetland. Considering that there is often insufficient space for treatment wetlands, a small wetland was retrofitted into an existing ditch next to the log yard. Among other parameters, total organic carbon, total phosphorus, and total nitrogen were measured. Results show insufficient treatment of log yard runoff. Storage of aged windthrown logs led to a higher content of total phosphorus in the runoff. It was likely that the hydraulic loading rate in this wetland case study was too high, and that the concentration of oxygen in the runoff was too low for the biochemical processes in the wetland to reduce the concentrations of total phosphorus, total organic carbon, and suspended solids. It follows that a similar wetland treatment system to be designed in the future should either be made larger or supplemented by alternative further treatment solutions such as increased oxygenation or the introduction of aggregates promoting the adsorption of phosphorus.