Patterns of in-stream summer transport of total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) in a high gradient second order stream in southwestern British Columbia were described. Some biological, physical, and chemical processes were also identified and evaluated with respect to their role in regulating in-stream transport of TDN and TDP. Fifteen water sampling stations were established along an alternating series of open clearcut and densely forest covered drainage areas, each several hundred metres in length. These drainage sections represented young and midsuccessional ecosystems. The furthest upstream section (which was forest covered) and an adjacent downstream open clearcut section each had weirs which were used for comparisons of TDN and TDP export between the successionally different systems. Export of TDN was consistently lower from the clearcut section than from the upstream forested section. This indicated that there was consistent in-stream absorption of TDN within the clearcut section. Nitrate flux dominated the absorption of TDN. A pairing analysis of precutting nitrate export data from 1972 with post-treatment export data from 1979 indicated that the absorption of nitrate was due to increased solar radiation reaching the stream channel. It was proposed that the increased light inputs which provided an additional energy input to the stream ecosystem, increased nitrate spiralling rates. Without disruptive stormflow events the net effect was a retention of nitrate within the stream. Concentrations of TDP were often less than detectable limits so comparisons of P export could not be made. The TDN data suggested that if nutrient absorption in small watershed streams is widespread, nutrient retention on land may have been overestimated in past small watershed nutrient budget studies. A further analysis of downstream flux in element concentrations was conducted for all forms of TDN and TDP using three-dimensional images (distance downstream x time x element concentration) from data collected in summer 1979. Nitrate concentrations consistently declined in open sections but increased in densely forest covered sections. Trends in ammonium concentrations were difficult to detect. Orthophosphate levels were rarely greater than the detectable limit of 3 ug/1 in all sections. Dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) flux was highly variable with no apparent trend. Nutrient spiralling processes were proposed to explain the flux of each of these forms of TDN and TDP. An enrichment experiment conducted in a clearcut section of the study stream in mid-summer indicated that rates of disappearance of N0₃⁻-N, NH₄⁺-N, and HP0₄⁻²-P from solution were directly related to element concentrations in solution and that relationship could be expressed as fourth, first, and third degree polynomials respectively. Disappearance rates of the three ions were in the order NH₄⁺-N> HP0₄⁻²--P> N0₃⁻-N. Reasons for the differences in disappearance rates between elements and element forms were proposed. The first end-of-summer storm event produced a 20-fold increase in stream discharge at peak flow over summer base flow. This resulted in a 10-fold increase in N0₃⁻-N concentrations in all stream sections. The increased loading was attributed to flushing of N0₃⁻-N from land. Stream power was not destructive, however, and N0₃⁻-N removed from solution increased over that during summer base flow. The increased uptake rates were attributed to an increase in active nutrient processing areas of the stream substrate. DON and DOP concentrations and export increased during the storm but NH₄⁺-N and HPO₄⁻²-P concentrations did not change. Again, detailed explanations for this element behaviour were proposed. Results of an enrichment experiment designed to evaluate the role of periphyton in regulation of nutrient transport were insufficient to fully assess the quantitative role of periphyton. Hypotheses were proposed, however, to further evaluate the role of periphyton using alternative methods. Concluding hypotheses were presented to aid in the development of future research plans. / Forestry, Faculty of / Graduate

Juvenile coho, steelhead, and cutthroat trout commonly spend from one to three or more years in coastal streams before migrating to the sea. Much of this time is spent in streams during the winter, making a study of these fishes' winter habitat requirements, distribution, behavior, and the possible influences of stream habitat alteration on them a useful undertaking. Some physical characteristics of areas selected by juvenile coho and steelhead were observed by snorkeling in a small west coast of Vancouver Island stream between September 1972 and April 1973. Observations revealed that with lowering water temperatures from 9°C to 2°C coho and older steelhead tended to move into deeper water while most steelhead fry remained in shallow, marginal sections of the stream. As water temperatures dropped in the winter, juvenile fish fed less and moved closer to areas offering low water velocities and cover. Steelhead fry were most often found under rubble while coho and older steelhead were most often found within upturned roots and under logs. Results from fish traps located on the lower ends of two small tributary streams indicated that juvenile coho, steelhead and cutthroat trout moved upstream into these tributaries in the late fall. Overwinter survival of coho in one tributary was 3-6 times as great as the estimated survival of coho in the main stream. Together the two tributaries contributed between 15 and 25 per cent to the total coho smolt production of the larger system. A series of experiments comparing coho and cutthroat preference for alternative habitat types in sidepool areas as may occur before and after stream disturbance were carried out during the winter. Both coho and cutthroat demonstrated a strong preference for bay areas offering overhanging bank cover as opposed to bays without cover, and for bays offering clean rubble substrate as opposed to silted rubble substrate. The impacts of timber harvesting on overwintering fish as suggested by the results from the underwater observations, winter movements, and the sidepool experiments are discussed and management recommendations are made. / Forestry, Faculty of / Graduate