Spring Freshet Research Articles

Trends in Canadian streamflow

This study presents trends computed for the past 30–50 years for 11 hydroclimatic variables obtained from the recently created Canadian Reference Hydrometrie Basin Network database. It was found that annual mean streamflow has generally decreased during the periods, with significant decreases detected in the southern part of the country. Monthly mean streamflow for most months also decreased, with the greatest decreases occurring in August and September. The exceptions are March and April, when significant increases in streamflow were observed. Significant increases were identified in lower percentiles of the daily streamflow frequency distribution over northern British Columbia and the Yukon Territory. In southern Canada, significant decreases were observed in all percentiles of the daily streamflow distribution. Breakup of river ice and the ensuing spring freshet occur significantly earlier, especially in British Columbia. There is also evidence to suggest earlier freeze‐up of rivers, particularly in eastern Canada. The trends observed in hydroclimatic variables are entirely consistent with those identified in climatic variables in other Canadian studies.

Sensitivity of bed load transport in Harris Creek: Seasonal and spatial variation over a cobble‐gravel bar

Bed load sediment was caught in pit traps at several locations on a bar in Harris Creek, a cobble‐gravel stream with a nivally dominated hydrograph, a structurally highly organized bed, and very low rates of bed material transport. Observations were made during two spring freshets. In order to obtain representative grain size distributions of the material in transport, the traps were left for periods of up to 24 hours, so that samples of up to 30 kg were recovered. We examine the sensitivity of bedload flux to flow variations via trap‐specific ratings for narrowly defined textural subranges. All the ratings are very sensitive, indicating that bed load flux remains in the regime of “partial transport.” The ratings also exhibited seasonal hysteresis and varied from trap to trap and from year to year. At one trap the ratings for large material are distinctly segmented, with no strong correlation for the highest flows. Significant transport for material >8 mm in size begins at ∼7 m3 s−1, considerably higher than for sand. At flows competent to move the local bed gravel the portion of the sand load between 0.25 and 0.50 mm goes into suspension (finer material being dominantly suspended at all flows). Most of the sand transported at <7 m3 s−1 is washed in from upstream while the local bed remains stable. Auxiliary tracer studies demonstrate that at no observed stage (up to mean annual flood level) was the local bed generally mobilized.

Sand dynamics at the mouth of a rock-bound, tide-dominated estuary

The lowermost Kennebec River is a relatively narrow, deep, bedrock-cut estuary situated along the highly indented, central coast of Maine. A large tidal prism and strong tidal currents control bedload sediment transport at the estuary mouth. Riverine sediment is introduced to the estuary during spring freshets when freshwater discharge may increase by an order of magnitude. During the same time, some of the existing estuarine sediment is exported to the nearshore. A barrier adjacent to the estuary is the product of an abundant riverine sand supply and numerous bedrock ridges, which anchor this sand deposit. A variety of sedimentologic, geomorphic, and hydraulic data collected over a 14-year period document a clockwise, sand-circulation cell that involves the exchange of bedload among the entrance channel to the estuary, adjacent beaches, nearshore, and offshore region. Tidal currents transport sand from the estuary through a subsidiary channel, bordered on both sides by bedrock islands, to an offshore subtidal bar. Northeast storm waves breaking along this outer bar move sand westward and landward toward the beach, leading to the development of large bar complexes. The welding of a bar complex to the western end of Hunnewell Beach occurs every 6–9 years and adds 2–300,000 m3 of sand to the shoreline. Sediment transport calculations along the outer bar are consistent with this volume of sand. The sediment gyre is completed as beach sands are moved eastward along the beach and dumped into the estuarine channel. This movement of sand is produced by wave action and tidal currents that enter the estuary peripherally during the flooding tide. During the ebb cycle, strong tidal currents flowing seaward through the subsidiary channel advect water from along the beach, which enhances sand transport into the estuary. Thirteen years of beach profile surveys demonstrate a good correspondence between bar welding events and short-term (1–4 years) accretionary shoreline changes. However, the volumetric changes of Hunnewell Beach cannot be accounted for by bar welding alone. The apparent movement of sand between Hunnewell Beach and other sand is further evidenced by the 135 year record of historical shoreline changes that reveal up to 200 m of shoreline excursions over a 26 year period. These data suggest that erosional–depositional trends along Hunnewell Beach are complex and the result of the exchange of sand among the adjacent beaches, nearshore zone, Fox and Wood Island tombolos, Kennebec River channel, and offshore region. The effects of major spring floods and strong bedrock influences produce patterns of sedimentation and a distribution of sand bodies at the mouth of Kennebec River that differ markedly from accepted estuarine models that are based on the relative importance of wave and tidal energy. This study demonstrates the need to consider structural controls when using these models.

Modeling the Effects of Supersaturated Dissolved Gas on Resident Aquatic Biota in the Main-Stem Snake and Columbia Rivers

Abstract Dissolved-gas levels in the Columbia and Snake rivers during the spring freshet often exceed 110% of saturation, the maximum level permitted by the U.S. Environmental Protection Agency. The highest levels of supersaturation result from high springtime river flows and turbine outages, conditions over which there is little control and that cause high volumes of water passing over the dams and through spillways instead of through turbines. During the spring freshets of 1994–1997, we surveyed nonsalmonid fishes and invertebrates for signs of gas bubble disease (GBD) and conducted holding experiments in three river reaches where gas saturation commonly exceeds 120%. We developed a dissolved-gas exposure index for nonsalmonid fishes sampled at specific times and locations; mean daily total dissolved-gas saturation (TDGS) was ranked and then summed over a 7-d period. We analyzed observations of 39,924 nonsalmonid fishes in an iterative process, which led to development of a mathematical equivalence mode...

Recovery plan for Kootenai River white sturgeon (Acipenser transmontanus)

Summary The white sturgeon (Acipenser transmontanus) of the Kootenai River was listed as endangered on September 6, 1994 by the United States Fish and Wildlife Service. This transboundary population, residing in Kootenay Lake and Kootenay River in Canada, and the Kootenai River in the US, has been in general decline since the mid-1960's. There has been very little recruitment to this population in the last 20 years. This population became isolated from other white sturgeon populations of the Columbia River basin during the last ice age of approximately 10,000 years ago. The population adapted to the pre-development conditions of the Kootenai system, with a high spring freshet and extensive side channel and low-lying delta marshlands. Modification of the Kootenai River by human activities, such as industrial developments, floodplain dyking, and dam construction has changed the hydrograph of the Kootenai River, altering sturgeon spawning, incubation and rearing habitats and reducing overall biological productivity. A Kootenai River white sturgeon draft recovery plan was prepared by the US Fish and Wildlife Service in cooperation with other agencies in the US and Canada. The plan was peer reviewed and there was a parallel public consultation process, where public commentary was invited from both sides of the international border. The short-term recovery objectives of the recovery plan are to prevent extinction and re-establish successful natural recruitment. The identified long-term objectives are the re-establishment of a self sustaining population and the restoration of productive habitat, in order to downlist to threatened status and subsequently delist this population when recovery is well established. Specific actions needed for recovery include spring flow augmentation during the reproduction period; a conservation aquaculture program to prevent near-term extinction; habitat restoration, and research and monitoring programs to evaluate recovery progress.

Phytoplankton pigment in the Gulf of St. Lawrence, Canada, as determined by the Coastal Zone Color Scanner—Part II: multivariate analysis

We report here on a statistical study of physical-biological interactions in the Gulf of St. Lawrence that uses for the first time ocean color images (phytoplankton pigments) and data on runoff and wind. Based on a Monte Carlo test for statistical significance, we extracted four orthogonal (independent) spatial patterns (Empirical Orthogonal Functions, EOF) in pigments that explain 64% of the total variance. We also computed four EOFs from the wind data that explain 90% of the total variance. Based on multiple correlations among these EOFs and runoff anomalies, we derived two modes of physical-biological variability. The first mode is the dual regulation of production by runoff in the Lower St. Lawrence Estuary (LSLE) and the western Gulf and by alongshore wind stress in the northeastern Gulf. The second mode incorporates mesoscale circulation features (eddies, meanders) that respond to low frequency fluctuations in runoff (in the lower estuary) or wind (Gaspé Current, northwestern Gulf, northern Esquiman Channel). The third mode reflects the impact of seasonal wind regimes on pigment levels in the LSLE, the Gaspé Current, and the southwestern Gulf. The fourth mode is dominated by one coccolithophore bloom event in August 1979. The analysis also gives some insight into sources of interannual variability in pigment levels and distributions. The spring bloom does not dominate the seasonal pigment cycle; only the third pigment EOF (5% of the variation) displays a spring peak stronger than the fall peak. The seasonal cycle of pigments is in part linked to that of runoff, driven mostly by year to year differences in the spring freshet. However, year to year differences in the summer wind and runoff regimes also play a role. This suggests that late summer and fall blooms and the physical factors that regulate them deserve more study.

Downstream variations of phytoplankton in the St.Lawrence River (Québec, Canada)

Longitudinal variations of phytoplankton biomass and composition were assessed in a 250 km-long section of the St.Lawrence River, which alternately runs through narrow (< 2 km) river cross sections and wide (up to 10 km) fluvial lakes. In the main river stem, concentrations of suspended matter and total phosphorus increased with distance downstream, whereas light penetration decreased. Seasonal changes in plankton composition and biomass were more important than those resulting from differences in water mass (tributary) of origin. Sampling at three cross river sections and in two fluvial lakes showed a progressive downstream decrease in phytoplankton biomass and changes in size structure and taxonomic composition. River plankton was primarily composed of small (< 10 µm equivalent spherical diameter), truly planktonic cells belonging to Cryptophyceae and diatoms, with Chlorophyceae in summer. Plankton sampled in summer among rooted macrophytes in fluvial lakes exhibited a higher biomass of resuspended periphytic algae than in the main river stem, which contributed slightly to downstream phytoplankton biomass. Successive river cross sections always shared about 50% of their taxa, indicating a rapid downstream transport of algae within the main water mass. However, the proportion of species common to all cross sections was highest during the spring freshet, and lowest during summer low discharge, likely resulting from the development of a distinct flora in fluvial lakes during summer. Conversely, about 30% of the identified taxa were exclusive to a cross section and were replaced by others occurring downstream. Overall, phytoplankton composition along the St.Lawrence River is primarily controlled by advective forces, which result in a homogeneous flora in the main river stem, with a local contribution of resuspended periphyton from fluvial lakes.

DOWNVALLEY GRADIENTS IN FLOW PATTERNS, SEDIMENT TRANSPORT AND CHANNEL MORPHOLOGY IN A SMALL MACROTIDAL ESTUARY: DIPPER HARBOUR CREEK, NEW BRUNSWICK, CANADA

Dipper Harbour Creek's lower reaches run through a narrow salt marsh on the Bay of Fundy, New Brunswick, Canada. This 2 km long section of the creek constitutes an extreme example of a tide-dominated estuary exhibiting strong downvalley morphology and sedimentology gradients. Dipper Harbour Creek drains a basin of roughly 8.8 km2, but except during the spring snowmelt freshet, tidal flow so overshadows freshwater flow within the salt marsh reach that the system essentially functions as a tidal creek. To identify and explain the main geomorphic processes controlling the creek system, records were collected in summer 1993 of tidal stage and velocity fluctuations, sand dune migration rates, bed material composition, channel cross-sectional geometry and channel sinuosity. Bed materials become progressively finer upvalley, with deposits of medium to coarse sands concentrated in the highly sinuous central reach of the creek during the summer. Current velocities within the creek are strongly flood-dominant, featuring a consistent low-stage peak in flood velocity, a secondary high-stage flood surge, and a weaker ebb peak occurring around bankfull stage. Under summer low freshwater discharge conditions, the predominant direction of bed sand transport is upvalley. The spring freshet, however, causes a major downvalley shift of sand deposits, suggesting a seasonal cycling of medium to coarse sands within Dipper Harbour Creek.

Seasonal Use of Estuaries by Winter Flounder in the Southern Gulf of St. Lawrence

The seasonal distribution of winter flounder Pleuronectes americanus in the southern Gulf of St. Lawrence was examined by analyzing data from research surveys conducted from 1986 to 1994 in the southern Gulf and from beach seining, trawling, and sampling of commercial fisheries in the Miramichi Estuary. During June–August, most winter flounder were found in coastal waters (<40 m deep) and within a temperature range of 3–16°C. Abundance in coastal waters declined sharply between September and late November–early December. Winter flounder were not captured in deep offshore waters during winter; rather, large numbers moved into the Miramichi Estuary during October and November and remained until spring. The brackish water under the ice of the Miramichi Estuary was warmer (–1 to 0°C) than the full salt water under the ice of the southern Gulf (below –1.5°C) and could provide a thermal refuge for winter flounder as well as protection from ice contact during winter storms. Adult winter flounder left the Miramichi Estuary by May, before the spring freshet, to move onto spawning and feeding areas.

DOWNVALLEY GRADIENTS IN FLOW PATTERNS, SEDIMENT TRANSPORT AND CHANNEL MORPHOLOGY IN A SMALL MACROTIDAL ESTUARY: DIPPER HARBOUR CREEK, NEW BRUNSWICK, CANADA

Dipper Harbour Creek's lower reaches run through a narrow salt marsh on the Bay of Fundy, New Brunswick, Canada. This 2 km long section of the creek constitutes an extreme example of a tide-dominated estuary exhibiting strong downvalley morphology and sedimentology gradients. Dipper Harbour Creek drains a basin of roughly 8.8 km2, but except during the spring snowmelt freshet, tidal flow so overshadows freshwater flow within the salt marsh reach that the system essentially functions as a tidal creek. To identify and explain the main geomorphic processes controlling the creek system, records were collected in summer 1993 of tidal stage and velocity fluctuations, sand dune migration rates, bed material composition, channel cross-sectional geometry and channel sinuosity. Bed materials become progressively finer upvalley, with deposits of medium to coarse sands concentrated in the highly sinuous central reach of the creek during the summer. Current velocities within the creek are strongly flood-dominant, featuring a consistent low-stage peak in flood velocity, a secondary high-stage flood surge, and a weaker ebb peak occurring around bankfull stage. Under summer low freshwater discharge conditions, the predominant direction of bed sand transport is upvalley. The spring freshet, however, causes a major downvalley shift of sand deposits, suggesting a seasonal cycling of medium to coarse sands within Dipper Harbour Creek.

Sources, distribution and transport of atrazine in the St. Lawrence River (Canada)

A Lagragangian sampling strategy was chosen in order to evaluate the main sources of atrazine to the St. Lawrence River, Canada. Lagrangian sampling was carried out during six sampling trips, one at every hydrological season except winter from the period of the summer low flow of 1990 to the spring freshet of 1992. Loadings of atrazine are subject to annual variations induced by different climatic and hydrological conditions. Loadings of atrazine are also dependent on season. Results emphasize the persistence of atrazine as it was found in significant amounts at the end of the growing season and in the following spring. Variations in loadings of atrazine along the river as well as the lateral distribution of atrazine concentrations in a downstream direction suggest inputs within the province of Quebec. The Great Lakes and the international corridor of the St. Lawrence River contribute 68% of the loading exported to the estuary, while Quebec tributaries account for 8% of the inputs. The inportance of the unmeasured sources within the river itself (24%) stresses the need for further research on internal processes and contaminant transfer in the aquatic environment.

Evidence for an earthquake-triggered basin collapse in Saguenay Fjord, Canada

On February 5, 1663, perhaps the largest earthquake ever witnessed in eastern North America struck the Saguenay Fjord basin with such force that landslides and submarine slides were triggered over a wide region. Over 3 km 3 of clayey Holocene sediments collapsed from the margins of the fjord, resulting in amalgamated debris flow and slide deposits that covered much of the basin floor. These deposits reached thicknesses of up to 100 m, and extended over an area of 100 km 2. The ambient seafloor was compressed under the impact and load of these debris masses, and/or liquefied under the cyclic stress of the seismic wave. A 0.2 km 3 landslide also occurred at this time, blocking the Saguenay River and possibly facilitating an extra large spring freshet (discharge). Biotracers (planktonic and benthic foraminifera, arcellaceans, pollen and wood), in conjuction with mass physical properties of sediment cores and high-resolution seismic and sidescan profiler data, have been used to identify local and distal sediment sources, including their original water depth of deposition, and their subsequent mode of mass gravitational transport. The landslide material was eroded by the river, and super-elevated sediment concentrations are considered responsible for a long-lasting (28 days) turbidity current that entered the Saguenay Fjord depositing a single 0.3 km 3 turbidite. The 2 to 10 m thick turbidite is considered to have been self-igniting having eroded into the surface of the collapsed basin debris. Paleo-hydraulic calculations suggest that this turbid flow averaged 0.45 m/s and reached a flow thickness of 30 m.

The Formation of High Nutrient–Low Salinity Water in the Gulf of Maine: a Nutrient Trap?

Waters with low salinity and high nitrate were identified in the south-western Gulf of Maine by Townsend and Christensen (1992). Their extreme characteristics were attributed to local remineralization processes, and the operation of a nutrient trap. This paper uses a newly compiled data set, and an algorithm relating nitrate to hydrographic properties to examine the occurrence and characteristics of this type of water. Observations of low salinity–high nitrate water are not uncommon, and represent approximately 20% of the database. Based on the occurrence of the most extreme waters of this type identified by the algorithm, it is concluded that two related mechanisms cause its formation. The mixing of low salinity Maine Surface Water with remnant Maine Intermediate Water in the fall starts this process. The interaction of newly formed Maine Intermediate Water with the spring freshet of Maine rivers completes it. These mechanisms can explain the formation of low salinity–high nitrate water, including ‘ nutrient trap ’ water, in general.

Temporal and spatial patterns of sedimentation in the subarctic fjord malangen, Northern Norway

Abstract Sedimentation processes in Malangen, a relatively wide and deep North-Norwegian fjord, are dependent on seasonal patterns in the biological production of auto- and heterotrophic plankton, different modes of advective transport and erosion of particulate materials, and freshwater discharge due to precipitation and snow-melting. Sedimentation rates of total particulates (TPM), chlorophyll a (Chl a), phaeopigments and particulate organic carbon (POC) and nitrogen were measured from March to October 1991 at five moored arrays covering the entire fjord area. On an average during the period studied, sedimentation pulses of TPM from the euphotic zone were in the range 2-7 g m·2 day-1. Secondary sedimentation due to resuspension and advection of bottom sediments was considerable at all trap moorings. Maximum contributions of inorganic matter were obtained at a mooring in the Miilselv Estuary, especially during the spring freshet peak in the second half of June. The highest pulses in Chl ·a sedimentation occurred in the first half of April (maximum values), the end of May and the beginning of July at all moorings, ranging between 0.2 and 1.4 mg m·2 day-1 at 30 m depth. A similar pattern is true for the settling of POC, however, high contributions of detrital carbon not coinciding with Chl · fluxes complicate the picture. Seasonal POC sedimentation ranged between 60 and 770 mg ·2 day-1 throughout the period studied, apart from two massive sedimentation pulses where resuspension caused exceptional rates of 1.3 and 1.8 g m·2 day-1, respectively, at the two outermost locations.

Impact of freshwater on a subarctic coastal ecosystem under seasonal sea ice (southeastern Hudson Bay, Canada). I. Interannual variability and predicted global warming influence on river plume dynamics and sea ice

Abstract Analysis of sea ice cover, runoff and air temperature observations in Hudson Bay shows marked interannual variability. This variability is thought to play a major role in determining overall productivity of the coastal ecosystem by changes to river plume extent, under-ice light conditions and nutrient levels during spring. Extensive field work off the Great Whale River in southeastern Hudson Bay has shown the importance of freshwater discharge, sea ice cover and meteorological forcing on the production of under-ice microalgae and the success of first feeding in fish larvae. Recent global climate model (GCM) results for a doubling of present atmospheric carbon dioxide indicate increases of both air temperature and precipitation in the Hudson Bay area. Predictions based on GCM results are used to estimate future changes to the sea ice and runoff regime. Sea ice breakup in the offshore is predicted to occur about one month earlier than presently. Estimates of the spring freshet in the Great Whale River indicate it will also advance by approximately one month. Onset of the spring freshet will occur about one month before Hudson Bay ice breakup, similar to present. A predicted reduction of about 35% in maximum sea ice thickness will lead to an increase in the ice-ocean interface irradiance and a decrease in melt water input to the Hudson Bay surface waters. These results are used in a discussion of potential effects of global climate change on northern coastal marine environments.

Seasonal patterns of atrazine loading for the St Lawrence River (Canada) and its tributaries

The annual variability in atrazine concentrations and loadings have been studied for the St Lawrence River (Canada) and four of its tributaries. Hydrological parameters appear to be the principal controls on the loadings of atrazine in the St Lawrence River system throughout the year, except during the post-application period. In terms of the annual variability of loadings, prior to the application period, the spring freshet coincided with a major pulse of atrazine. A post-application peak load of atrazine was detected in the main river as well as in its tributaries. During the fall, atrazine loadings increased again. The results show that atrazine inputs to the system can be detected long after application. Average loadings in 1990 and 1991 were 7.7 and 4.4 kg/d in the St Lawrences River, and 0.4 and 0.2 kg/d in the tributaries studied. The seasonal variation of atrazine concentrations in surface waters of the tributaries was consistent with the temporal distribution reported in the literature, viz. peak concentrations during the post-application period. There was also an increase in concentrations in the main river channel during the fall, reflecting the fact that the main river also receives inputs from the Great Lakes and not only from proximate agricultural sources. The annual variability in atrazine concentration and loading in the tributaries was directly related to the proximity of agricultural sources. Average concentrations in 1990 and 1991 were 10.4 and 3.4 ng/l in the St Lawrence River, and 31.1 and 27.9 ng/l in the tributaries. The persistence of atrazine is believed to be a key element controlling its dynamics in these aquatic systems. The results demonstrate the widespread dispersion of atrazine in this river basin, with similar responses and seasonal trends being exhibited throughout.

In-situ characteristics of particles settling within a deep-water estuary

A Floc Camera Assembly is used to obtain the in-situ size, shape, concentration and settling velocity of marine particles, providing insight into the in-situ excess-density, porosity and mass of flocs, their population characteristics, and aggregation and sedimentation rate. Data highlight the time-dependent character of marine snow, including near-instantaneous, daily and seasonal influences for a mid-latitude estuary, Halifax Inlet. Methods are developed for estimating the mean size of the constituent particles comprising flocs, for determining the number spectra of non-flocculated and flocculated particles, and for determining the mass concentration and mass flux spectra for suspended flocs. The most active aggregation level is just below the estuarine surface layer. The largest aggregation rates involve the finest (< 10 μm) suspended particles colliding by both differential settling and turbulent shear. During plankton blooms, large floes become attached to the mucoid stringers. The settling velocity of stringers is, in turn, controlled by these large floes attached to their base. Floc settling velocity varies with floc size, and as a seasonally-variable power function. A floc's excess density also varies with floc size, but the relationship changes daily. Floes account for between 36% and 100% of the total suspended mass within Halifax Inlet, and >90% of the mass below the surface layer. Floc concentrations may change by a factor of four in just a few minutes, affected by the flux of larger floes. When river input of suspended load is high, floc concentration is also high, but the portion of total particulate matter composed of floc is low. Mean floc size varies considerably between seasons and sometimes between estuarine location. Small floes form when primary production is low and river input is high. Large flocs form when river input is very low. Suspended stringers are highest during the spring freshet and associated plankton bloom.

Trends in the Abundance of Chinook Salmon (Oncorhynchus tshawytscha) of the Nechako River, British Columbia

Trends in abundance of chinook salmon (Oncorhynchus tshawytscha) of the Nechako River, a tributary of the Fraser River, were analyzed to quantify the ecological effects of water abstraction for electricity generation. In years when the majority of returning chinook adults used the upper Nechako River for spawning, the survival of offspring for the entire river was poorer than in years when spawning was concentrated in the lower reaches. Relative to the historical discharge, the upper Nechako River has experienced the greatest degree of water abstraction, and the lower survival of chinook broods originating from the upper river may be due to early emergence of fry caused by elevated fall and winter water temperatures or to higher rates of predation on juveniles and loss of rearing habitat caused by the elimination of the spring freshet. Poor recruitment resulting from broods spawning predominately in the upper river has caused the trend in the abundance of Nechako River chinook to diverge from the trend of chinook populations of similar life history from unregulated tributaries of the Fraser River. Additional reductions in flow may further affect the capacity of the upper Nechako River to produce chinook salmon.

Importance of Habitat Productivity Differences, Competition and Predation for the Migratory Behaviour of Arctic Charr

Landlocked Arctic charr (Salvelinus alpinus) inhabiting the oligotrophic Lake Visjon (NW Sweden) grew very slowly in the 10-20 cm size interval, which suggests a competitive bottleneck. Fish in the upper part of this interval showed a propensity to leave the lake. Migration took place during spring freshets and was directed upstream. The migrants had a significantly (p < 0.05) lower condition factor than residents, indicating that they were less successful in the competition for food, and that the current feeding situation of a fish affected its migratory behaviour. Migrants entered many of the tributaries of L. Visjon, but a majority of the migrants ended up in unproductive habitats and returned downstream shortly after the ascent

Runoff Generation in a High Boreal Wetland in Northern Canada

The stable isotope composition of water and major-ion concentrations were measured in a small catchment tributary to Manners Creek, situated in the zone of discontinuous permafrost near Fort Simpson, Northwest Territories. Hydrograph separation calculations based on δ18O and δ2 H values of snow, active-layer water, and streamflow reveal that snowmelt contributions were secondary to active-layer storage contributions throughout the spring freshet period of 1990. At the time of peak spring runoff an estimated 40 to 50 % of streamflow was contributed by snowmelt, while over the entire spring period only 25 to 30 % of streamflow was contributed by snowmelt. Overland and pipe flow are shown to be important mechanisms of rapid snowmelt runoff from permafrost slopes.