VARIATION IN STREAM WATER CHEMISTRY AND HYDROGRAPH SEPARATION IN A SMALL DRAINAGE-BASIN

In the present study, the change in chemical composition of stream wat er was investigated for a small Atlantic salmon stream (Catamaran Broo k) of the Miramichi River system in New Brunswick, Canada. Chemical co mposition of runoff and groundwater flow was established, as were rela tions between concentration of dissolved materials and discharge. Spec ific storm events were analysed to determine changes in chemistry and to carry out a hydrograph separation using specific chemical parameter s. The hydrograph separation was used to identify the relative contrib ution of groundwater flow to total streamflow. By selective sampling o f stream water during high flow (runoff) and low flow (groundwater) pe riods it was possible to observe the range in chemical composition of many parameters in Catamaran Brook. Most relationships between concent ration of chemical parameters and discharge were significant at P < 0. 0001, with sodium having the highest coefficient of determination (r(2 ) = 0.849). Concentration returned to pre-storm levels in approximatel y 10 days following an event. As observed in previous studies, the pea k groundwater flow plays an important role during the storm hydrograph and can account for as much as 91% of the total peak how for small ev ents. For higher flow events in Catamaran Brook, the groundwater flow contribution was markedly lower (55% of total streamflow). The composi te hydrograph separation revealed that conductivity, as a single param eter, provided the best results in representing the composite separati on.