Biogeochemical impacts of clearfelling and reforestation on blanket peatland streams I. phosphorus |
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| Authors: | T Cummins Edward P Farrell |
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| Institution: | Forest Ecosystem Research Group, Department of Environmental Resource Management, University College Dublin, Dublin 4, Ireland |
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| Abstract: | Forest drains and streams on blanket peatland in western Ireland were sampled weekly, 1996–2000, using continuous, depth-proportional passive sampling, and analysed for molybdate-reactive phosphorus (MRP) by the acid–antimony-molybdate method. The study area was largely clearfelled and partly reforested with wind-rowing, drainage, planting, and aerially applied rock phosphate equivalent to 70 kg P/ha. Further felled areas were not wind-rowed, drained or fertilised for reforestation. Catchment areas were of the following orders: 1 ha (two forest drains); 10–20 ha (two semi-permanent drains, one permanent stream); 1–3 km2 (three permanent streams). Streamwater from three undisturbed closed-canopy-forest catchments had pre-felling median concentrations of MRP (all values are μg MRP l?1) of 9 (catchment approximately 1 km2), 13 (1 ha) and 93 (1 ha). Clearfelling was associated with large increases (maxima 305, 4164 and 3530 μg MRP l?1) in MRP concentrations in each case. Following protracted mechanical operations in four other catchments of ca. 1 km2, 20, 10 and 10 ha, with apparently existing elevated MRP concentrations (medians 41, 328, 102, 214 μg MRP l?1) fertilising gave major rises (maxima 218, 2723, 806, 2323 μg MRP l?1). The three smaller catchments showed subsequent exponential-type declines, while the 1 km2 catchment had sustained high values (median 74 μg MRP l?1) over the remaining study period. The higher values in this one larger stream were seasonally cyclical, with a late summer maximum. Annual median MRP values above 70 μg l?1 represent a seriously polluted state for these streams, which qualify as waterways under relevant statutes, but it is not clear what implications these results have for downstream river-water quality in larger channels. |
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| Keywords: | Biogeochemistry P Blanket peatland Stream Forest drains Fertiliser Leaching of P |
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