摘要:

Coulter counter and microscope counts were used to estimate filtration and ingestion rates experimentally for total zooplankton caught by a 233-μm mesh net from two depths during the spring bloom in Bedford Basin. Initially, most phytoplankton were <20 μm with larger, chain-forming diatoms becoming more important as the bloom developed. Peak concentrations were >14 μg chlorophyll∙L−1and >1 mg C∙L−1and particle volume was >10 mm3∙L−1. Maximum primary production was >30 mg C∙m−3∙h−1. Dominant phytoplankton includedChaetoceros septentrionaleearly in the bloom, followed bySkeletonema costatumandThalassiosira,Rhizosolenia, andChaetocerosspp. Barnacle nauplii andAcartia hudsonicawere the most common zooplankton near surface andPseudocalanussp. in deeper water. Ingestion was usually greatest at or near peaks in the Coulter counter particle spectrum. Filtration rate was proportional to grazer size and amount ingested and also to ambient particle concentration for near-surface but not deeper zooplankton. Higher ingestion was measured with the Coulter counter but microscopic counts gave higher filtration rates. Smaller surface-layer zooplankton apparently destroyed cells or chains that were not completely ingested. Microscopic estimates of particle volume ingested were 9–60% of that measured with the Coulter counter, suggesting utilization of detritus. Despite discrepancies in what the methods apparently measured, neither suggested a saturating functional response at ambient concentration, but with further concentration, both methods showed reduced filtration activity. Neither method revealed evidence for size-selective feeding, even when particles were compared on the basis of their maximum dimensions, but optical counts showed that single cells or chains of cylindrical shape were preferred to needle-like or spiney cells. Selection for biomass peaks could not be demonstrated using cell volume calculated from microscopic measurement. The 233-μm zooplankton utilized about 10–30% of daily primary production during

ISSN:0706-652X    

DOI:10.1139/f84-027

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Nonparametric correlation and principal component analysis were used to examine relations between digestive enzyme activity in zooplankton and qualitative and quantitative measures of particulate organic matter and between enzymes and composition of the zooplankton community. Barnacle nauplii in near-surface (5 m) water during the first part of the bloom caused heterogeneity, which confounded relationships between enzyme activity and potential substrate concentration. Lack of coherence among enzymes in the 5 m zooplankton was also observed. The less variable deepwater community showed intercorrelation among the enzymes measured. At 30 m, enzyme concentrations inPseudocalanuswere correlated with concentration of particles less than 20 μm, which were dominant in the first part of the bloom. Two time-related events significantly affected zooplankton enzyme levels: one was clearly related to the period of dominance of barnacle larvae and the other with an increase in the C:N ratio from around 5 to greater than 7 in midbloom coinciding with a shift in phytoplankton from smaller forms of apparently higher protein content to large colonial diatoms. The results generally support the hypothesis that the amount and chemical composition of food supply can affect zooplankton digestive enzymes, but they also demonstrate the problems of interpretation if community structure is not well defined and spatial and temporal distribution of organisms not carefully circumscribed.

ISSN:0706-652X    

DOI:10.1139/f84-028

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Forest fertilization (435 kg urea∙ha−1) on the Mohun drainage, northern Vancouver Island, during late fall 1979 resulted in a combined increase in urea, ammonia, and nitrate concentrations to 8000 μg N∙L−1above control levels in streams not protected with 50-m-wide leave (i.e. unfertilized) strips and 350 μg N∙L−1in those having leave strips. By spring 1980, dissolved nitrogen loads to Mohun Lake increased by a minimum of 55% in the largest basin and 1924% in the smallest basin. This corresponded to fertilizer losses of 2.1% of the total applied from drainages that had leave strips and up to 5.2% from those where the treatment included direct application to stream channels. Nitrogen transport was dominated by reduced nitrogen species and lasted up to 144 d. Relatively small changes in nitrate transport were attributed to low temperatures, which reduced rates of nitrification. Duringthe3-yr prior to forest fertilization, nitrogen and phosphorus were added to the lake at an N:P ratio of 4.5 (wt/wt) and a load of 1.4–2.2 mg P∙m−2∙wk−1. Spring overturn phosphorus concentrations were 4–5 μg∙L−1throughout the study and, except during the spring following forest fertilization, N:P ratios (NO3-N:TP) at spring overturn were 3–6 (wt/wt). Despite the low ratios, nitrogen-fixing phytoplankton were not dominant in Mohun Lake. After forest fertilization, average epilimnetic chlorophyll concentrations were 1.8 times higher than in 1979, the last year of lake fertilization. The increase is attributed to the much higher spring overturn N:P ratio that occurred after forest fertilization and to phosphorus recycling processes within the extensive littoral zone

ISSN:0706-652X    

DOI:10.1139/f84-029

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

The siltation of an experimental gravel bed, with three grades of sands moving in suspension and as bedload, was examined in a flume. For low suspended sediment concentrations (<300 mg∙L−1) the mean deposition rate was 1.34% of the initial gravel volume filled per hour. Deposition rates for sands 0.15–1.4 mm in diameter with suspended sediment concentrations of 38–9110 mg∙L−1and Froude numbers in the range 0.008–1.21 were constant with respect to Froude number. For all concentrations the deposition rate was strongly linearly correlated with the suspended sediment concentration. The downstream decrease in siltation rate from a point source was a negative exponential function of distance from that source. Turbulent resuspension of sediment prevented deposition in a surface layer of gravel of thickness approximately equal to the mean grain size of the gravel. Mean flow data, especially where derived from velocity profile data measured in the outer boundary layer, have limited value for siltation investigations concerned with processes occurring very close to the bed. Practically, results indicate that open-work gravels will rapidly become silted in flows with low concentrations of suspended solids. Consequently, mechanical cleansing of spawning beds has limited value where sediment pollution is likely to be a recurrent problem. A simple equation describing the downstream extent of silting from a point pollution source is presented that requires verification in natural stre

ISSN:0706-652X    

DOI:10.1139/f84-030

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Sporophytes ofCymathere triplicataappeared only in spring and density declined thereafter; overwinter mortality was 100%. Standing crop estimates were highest during May–July. Plants were heaviest and generally had the longest and widest laminae in July and August. Thickness of laminae increased through December, the greatest increase being in the basal part of the lamina. Sori were initiated in August and approximately 90% of plants were fertile by September. Epibiota were most abundant during August–October. Moisture content decreased 2–3% from spring through winter. A plot subjected to almost total harvest in August had approximately 50% recovery of standing crop after 1 yr and full recovery after 2 yr, compared with a control area. A comparable recovery rate was seen for a similar September harvest. Sustained yields for a region of coastline should be maintained if no more than 50% of the standing crop is removed by intensive harvesting within plots, and if harvesting is not allowed prior to spore production. Best quality laminae in terms of length, thickness, weight per area, and moisture content occurred in August and September.

ISSN:0706-652X    

DOI:10.1139/f84-031

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Pacific lamprey (Lampetra tridentata) were first observed in Babine Lake, the largest natural lake wholly contained in British Columbia, in 1963 and are currently found along approximately 15% of the length of the lake near the outlet. The number of spawning adults in 1982 was estimated to be 7281. Since Babine Lake is a major nursery area for sockeye salmon (Oncorhynchus nerka), the colonization of this lake by a parasitic lamprey is of concern, particularly if the species can become nonanadromous. The colonization may be beneficial if a commercial fishery can be sustained and if the species does not begin to feed in freshwater. The reason for the recent colonization is unknown but it coincides with increased human manipulation of fishes and habitat, including the removal of a major rock slide, 65 km downstream of the lake.

ISSN:0706-652X    

DOI:10.1139/f84-032

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

In the anoxic hypolimnion of Lake 227, Experimental Lakes Area, northwestern Ontario, ΣH2S exhibits a mid-depth maximum, while Fe2+increases with depth. At the mid-depth ΣH2S maximum and below, saturation with respect to amorphous FeS is reached, and the concentration of ΣH2S is limited by the high Fe2+concentrations, in accord with the FeS solubility product. Values for pKspfor FeS determined from the ΣH2S maximum and below averaged 3.16 in 1979 and agree well with other in situ and laboratory measurements. In the top 10 cm of sediment, pore water ΣH2S and Fe2+are in equilibrium with amorphous FeS. Analyses of cores confirms the existence of an iron sulfide phase. Fe2+, which is produced in the pore water from the decomposition of organic matter, increases to concentrations at which siderite may form, although the presence of siderite has not been verified. Comparison of calculated pore water fluxes of Fe2+with the observed increase of Fe2+in the anoxic hypolimnion reveals that about 90% of the observed flux originates at the sediment–water interface, while the remainder is derived from pore water flux.

ISSN:0706-652X    

DOI:10.1139/f84-033

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

A warm core ring and adjacent waters off the Scotian Shelf in June 1982 contained substantial numbers of larval and juvenile white hake,Urophycis tenuis, as far as 140 km seaward of the continental shelf break. The warm core ring, designated 81-G, had entrained shelf water on several occasions before the shipboard observations were made. We suggest that the ring contributed to the offshore advection of these fish, which probably were spawned on the continental shelf or upper slope. Warm core rings can disrupt the usual larval drift pattern of shelf–slope fishes and thereby affect recruitment. Larvae and juveniles of several species of tropical–subtropical fishes found in ring 81-G have been reported previously as rare specimens in ichthyoplankton surveys on the Scotian Shelf. Our observations support the hypothesis that warm core rings can be a mechanism for transport of these expatriated fishes onto the shelf.

ISSN:0706-652X    

DOI:10.1139/f84-034

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

A developmental series (4.2–28.7 mm standard length, SL) of larvae and pelagic juveniles of the saffron cod,Eleginus gracilis, from the Bering and Chukchi seas is described and illustrated for the first time. Larvae ofE.gracilishatch at about 3.5 mm SL, and yolk is absorbed by about 6.5 mm SL. Notochord flexion commences at about 11 mm SL and is completed by about 17 mm; transformation to the pelagic juvenile stage occurs at about 24–27 mm SL.Eleginus gracilislarvae are characterized by gut pigment and by the presence of two distinctive postanal bars of pigment. They may be distinguished from other cooccurring gadid iarvae in the Gulf of Alaska (walleye pollock,Theragra chalcogramma; Pacific cod,Gadus macrocephalus; Pacific tomcod,Microgadus proximus) as well as those in the Bering and Chukchi seas south of 70°N (T.chalcogramma,G.macrocephalus, and Arctic cod,Boreogadus saida) based on pigment patterns and meristic characters. Comments are included on the status of knowledge of larvae of three other gadids (in addition toE.gracilisandB.saida) present in North American arctic waters: ogac (Gadus ogac), toothed cod (Arctogadus borisovi) and polar cod (A.glacialis).

ISSN:0706-652X    

DOI:10.1139/f84-035

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

During the spring of 1982, lake trout (Salvelinus namaycush) sac fry were incubated at a spawning bed in a pH 5.7 lake with a history of lake trout recruitment failure. Four short episodes of substantial pH depression occurred at the spawning site. Observed sac fry mortalities (18%) occurred primarily during the longest depression (5 d at pH 4.5–5.0), which coincided with maximum surface runoff and peaks in concentrations (~50 μg/L) of inorganic (monomeric) Al. Although most mortalities were coincident with low pH and elevated inorganic Al concentrations, the high survival (82%) demonstrated that under natural conditions most sac fry could tolerate pH <5.0 and inorganic Al concentrations of 40–50 μg/L for at least 5 d. Substantially higher concentrations of inorganic Al (~80 μg/L) were observed in the interstitial waters of the spawning rubble than in ambient waters, which indicated that fry within a spawning substrate may be subjected to more toxic conditions than test fry in incubators above the substrate surface.

ISSN:0706-652X    

DOI:10.1139/f84-036

出版商:NRC Research Press    

年代:1984

数据来源: NRC