Variation in stream water chemistry and hydrograph separation in a small drainage basin

In the present study, the change in chemical composition of stream water was investigated for a small Atlantic salmon stream (Catamaran Brook) of the Miramichi River system in New Brunswick, Canada. Chemical composition of runoff and groundwater flow was established, as were relations between concentration of dissolved materials and discharge. Specific storm events were analysed to determine changes in chemistry and to carry out a hydrograph separation using specific chemical parameters. The hydrograph separation was used to identify the relative contribution of groundwater flow to total streamflow. By selective sampling of stream water during high flow (runoff) and low flow (groundwater) periods it was possible to observe the range in chemical composition of many parameters in Catamaran Brook. Most relationships between concentration 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 approximately 10 days following an event. As observed in previous studies, the peak 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 events. For higher flow events in Catamaran Brook, the groundwater flow contribution was markedly lower (55% of total streamflow). The composite hydrograph separation revealed that conductivity, as a single parameter, provided the best results in representing the composite separation.