SOLUTIONS AND EFFECTIVENESS OF WATER PROTECTION STRUCTURES IN FOREST DRAINAGE SYSTEM MAINTENANCE: EXAMPLES FROM LATVIA

Abstract

Drainage system maintenance (DNM) is essential for the main function of the drainage system – to drain excess water ensuring the growth of high quality forest stands. However, it can contribute to erosion and increase the discharge of suspended solids and nutrients from drainage network catchments. To avoid deterioration of water quality, water protection structures should be constructed while carrying out DNM. This paper presents preliminary effectiveness assessment of a custom sedimentation pond sized according to catchment area and the first peak flow control (PFC) structure built in production forests in Latvia. We compared changes of various chemical and physical parameters in periods before and after construction of water protection structures as well as evaluated the effectiveness of the structures during DNM. Slight increase of pH, N-NH₄⁺, N-NO₃^- as well as slight decrease of P-PO₄^3- and DOC was observed after DNM in affected sites. Sedimentation pond and PFC structure proved their effectiveness in reducing concentrations of suspended solids (by 62% and by 65% respectively). Retention of nutrients in the structures was not significant, furthermore, mean nutrient concentrations during sampling period in all study sites were generally low. As nutrient accumulation by the living vegetation (that is not yet developed) is an important facet of the nutrient retention, sampling and assessment of effectiveness of the constructed water protection structures is still ongoing. In addition, study is being continued to further assess DNM impact on water quality.