Ditch networks in drained peatland forests are maintained regularly to prevent water table rise and subsequent decrease in tree growth. The growing tree stand itself affects the level of water table through evapotranspiration, the magnitude of which is closely related to the living stand volume. In this study, regression analysis was applied to quantify the relationship between the late summer water table depth (DWT) and tree stand volume, mean monthly summertime precipitation (Ps), drainage network condition, and latitude. The analysis was based on several large data sets from southern to northern Finland, including concurrent measurements of stand volume and summer water table depth. The identified model demonstrated a nonlinear effect of stand volume on DWT, a linear effect of Ps on DWT, and an interactive effect of both stand volume and Ps. Latitude and ditch depth showed only marginal influence on DWT. A separate analysis indicated that an increase of 10 m3·ha–1 in stand volume corresponded with a drop of 1 cm in water table level during the growing season. In a subsample of the data, high bulk density peat showed deeper DWT than peat with low bulk density at the same stand volume.
Effects of ditch network maintenance on the chemistry of run-off water from peatland forests.Ditch run-off chemistry of 40 catchments was monitored before and for 2 -3 yrs after maintenance of the peatland ditch network and compared with data collected from 34 control catchments. Increases in mean pH, electrical conductivity, and the concentrations of suspended solids and base cations (sodium, potassium, calcium and magnesium) and a decrease in the concentration of dissolved organic carbon were observed. Because of high concentrations in a few areas immediately after the digging operations and during the rst post-treatment year in general, the mean concentrations of aluminium and iron also increased. No major changes occurred in the concentrations of total dissolved nitrogen (N) and total dissolved phosphorus. High phosphorus concentrations were observed at a few sites immediately after the digging operations. Concentrations of mineral N, especially NH 4 » -N, increased signi cantly, while the concentrations of organic N decreased. The largest relative changes in element transport during the 3 yr period following treatment were the increases in the loads of NH 4 » -N and suspended solids. From the point of view of water protection, the loading of suspended solids was considered the most harmful effect of ditch network maintenance.
In Finland nearly 6 million hectares of peatlands are drained for forestry purposes. Ditch network maintenance in the drained peatlands, i.e. cleaning old ditches or digging complementary ditches, deteriorates surface water quality by increasing the export of dissolved elements and suspended solids (SS). Effect of ditch network maintenance on the export of SS, dissolved organic carbon (DOC), and dissolved nitrogen (N), phosphorous (P), iron (Fe), aluminum (Al) and manganese (Mn) was studied in nine pairs of treated and control (no maintenance) catchments located in southern and central Finland. In this study we extended the paired catchment approach by combining data from several catchments and identifying the treatment effect on SS and element loads from the entire dataset. Following the method of Laurén et al. (2009) we identified how uncertainty in correlation between treatment and control catchments during pre-treatment period is reflected in the estimated treatment effect on SS and element loads. In the experiment, the export of SS increased significantly for the four year study period following the ditch network maintenance and Al export increased for one year. The export of N, P and Fe was not significantly changed and DOC and Mn export decreased after the ditch maintenance operation.
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