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.

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In 1995-2001, the efficiency of riparian buffer zone areas to reduce the concentrations of suspended solids in discharge from peatlands drained for forestry purposes was studied at 7 locations in south-central Finland. The two largest buffer zones reduced the concentrations of suspended solids by > 70%. The efficiency of the three medium-sized buffer zones to reduce through-flow sediment concentrations was 50-60%, but no reduction occurred at the smallest two buffer areas. Thus, the capacity of buffer zones to reduce sediment concentrations was strongly related to their size. However, significant correlations were also found between reduction capacity and inflow water sediment concentrations, although the correlations at the two smallest buffer zones were low. The use of buffer zones in reducing sediment load from peatlands drained for forestry purposes is recommended, but relatively large areas for efficient removal capacity are needed.

Estimates of increased nutrient export caused by forest clear-cuttings are mostly based on long-term paired catchment studies, where the treatment effect is calculated using pre-treatment dataset regression and post-treatment records of nutrient loads. In these studies uncertainty in the regression between the pre-treatment loads from the control and from the treatment catchments is typically neglected, even though it affects determination of the magnitude and duration of the treatment effect. This uncertainty is described in terms of variance in regression coefficients and residuals. The aim was to study how uncertainty in a pre-treatment dataset is propagated to estimates of the treatment effects using two sets of paired catchment data in eastern Finland, where the total phosphorus loads following forest clear-cutting and site preparation were investigated. The results showed that neglecting the uncertainty in the pre-treatment data did not change the conclusions when the treatment effect was strong enough. However, when the treatment effect was small, neglecting the uncertainty in the pre-treatment dataset easily leads to over-interpretation of the results. The uncertainty in a pre-treatment dataset should be taken into account in the paired catchment studies in order to avoid bias in the estimation of management effects on the loads.

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