Characteristics of nitrogen and phosphorus loads in peat mining wastewater.

Runoff water quality from a peat mine was studied during 1995 and 1996 in Central Finland. Water samples from three drained sub-catchments and groundwater were analysed for all the standard physio-chemical parametres including different forms of nitrogen and phosphorus. The annual leaching of phosphorus, nitrogen and suspended solids was estimated to be 16-38 kgkm(-2), 1,073-1,500 kgkm(-2), and 2-8 tkm(-2), respectively. The variation in nutrient concentrations could be best explained by the relative volumes of new water (5-day sum of rainfall), ditchwater temperature and conductivity. Heavy rainfall caused new water to infiltrate washing nitrate out of the unsaturated peat layer resulting in high concentrations in ground- and ditchwater. Ditchwater phosphorus concentrations always decreased with increased runoff and peaked, as did COD and colour, after dry spells when old groundwater dominated runoff. A large part of the suspended solids load occurred during snowmelt, whereas dissolved solids and nitrogen loads peaked during summer flows.