1990. increased juvenile salmonid growth by wholeriver fertilization. Can. ). Fish. Aquat. Sci. 47: 862-872.Nutrient concentrations, periphyton standing crop and size of steelhead trout (8ncsrhynehus mykiss) and coho salmon (8. kisuteh) fry increased after the fertilization of a nutrient-deficient stream with inorganic phosphorus (P) and nitrogen (N). Wh~le-river fertilimation of the Keogh River, British Columbia, during 4983-86 to increase summer average nutrient csncentrations f r~r n <1 p, g POL-' and 25 pg lal-L-' to 1661 5 pg P-h-' and 30-100 pg N -L -' resulted in five-to 10-fold increases in periphyton standing crops on artificial substrata and 1.4-to 2.0fold Increases in late-September salmsnid fry weights. Diatoms and chlorsphytes dominated the algal periphyton on artificial substrata at fertilized sites. Cyanophytes were unimportant despite low N:P ratios in some cases. juvenile salmonids fed primarily on benthic insects. These results suggest that autochthonous primary production can be an important energy source in forested, middle-order streams, and indicate that the manipulation of autochthonous primary production can be a useful management tool to increase salmonid growth in nutrientpoor coastal streams.Les teneurs en 4l6ments nutritifs, la population exploitable du periphyton et la taille des truites arc-en-eiel (Owcorhywchus mykiss) et des alevins de saurnon coho (0. kisutch) ont augment6 apres fertilisation en pkosphore (P) et azote (N) inorganique d'un cours d'eau pauvre en elements nutritifs. La fertilisation de toute la riviPre Keogh en Colombie-Britannique entre 1983 et 1986, en vue d'accroitre les teneurs estivales moyennes en 6lernents nutritifs de < I pg P-L-' et 25 pg N-L-' a 10-15 p g P.L-' et 30-1 00 pg N-L-' a entraine des augmentations de 5a 10-fsis de la population exploitable du periphyton sur les substrats artificiels et de 1,4-A 2,O-fois dans les poids des aievins de salmonides a %a fin de septembre. Aux sites fertilises, Jes diatom6s et les chlorophyc4es 6taient les plus abondants du p6ripkyton d'algues sur les substrats artificiels. Les cyanophycees 6taient plus nornbreuses malgr6 les rapports N :P faibles dans certains cas. tes satrnonides juveniles se nourrissaient essentiel lernent d'insectes benthiques. Ces r6sultats semblent montrer que la production primaire akitochtogle peut constituer une source 6nergetique importante des cours d'eau moyens, en milieu boise, et indiquent que la manipulation de la production primaire autschtone peut &re un outil de gestion utile en vue d'augmenter la croissance des salmsnides dans des csurs d'eau cdtiers pauvres en Glernents nutritifs.

Periphyton accumulation rates and alkaline phosphatase activity were examined in reaches of the Keogh River, British Columbia, following additions of grain and inorganic fertilizer as separate treatments during spring–summer 1981. Two different levels of N and P addition were used: one to attain ambient N and P concentrations of 200 and 15 μg∙L−1, respectively, and the other to attain 400 and 20 μg∙L−1, respectively. Grain (rolled barley) was added monthly at 280 g∙m−2. N and P additions increased chlorophyll a accrual rates by more than an order of magnitude. Diatoms dominated the periphyton community until midsummer. In July and most of August, the relative importance of chlorophytes increased and biomass levels declined markedly in spite of continued nutrient additions. Grain additions resulted in no detectable change in periphyton accrual, but alkaline phosphatase activity increased by 35% over control levels. These results suggest that additions of labile organic matter to nutrient-deficient coastal streams can increase autotrophic P deficiency. Based on responses of juvenile salmonids, additions of inorganic nutrients to increase autotrophic production can maximize trophic enhancement in nutrient-deficient streams.

Spawning habitat used by white sturgeon Acipenser transmontanus in the lower Fraser River, British Columbia, is described based on field sampling in 1998 and 1999. Fraser River flow is unregulated and, within our study area, its channel morphology is largely unaltered by land use activities. The study area consisted of (1) the wandering reach (river km 98–143), which had side channels, wooded islands, and gravel bars; and (2) the confined reach (river km 145–181), which was naturally restricted by mountains, producing a single‐thread and simple channel. Six spawning sites were identified in the study area, five in side channels of the wandering reach and one in the main channel of the confined reach. Within the wandering reach, eggs and larvae were collected only from side channels despite sampling efforts in main‐channel areas. Multiple lines of evidence, including radio‐tracking of prespawning adults and visual observations, substantiated the use of side channels by white sturgeon for spawning. A total of 3 unfertilized and 80 fertilized eggs were captured at water velocities averaging 1.8 m/s, whereas 101 larvae were found in velocities averaging 1.0 m/s. Water depths averaged 2.9 m at capture locations for all life stages and were shallow compared with depths of egg and larval captures reported from most regulated rivers. Turbidity, which averaged 42 nephelometric turbidity units during the spawning period, was notably higher than in regulated rivers. We hypothesize that reduced light attenuation due to turbidity may substantially influence habitat suitability for spawning within the range of available water depths and velocities. Our observations of white sturgeon spawning activity outside of main‐channel habitats are unique, and we have demonstrated that spawning may occur over a wider range of habitat conditions than previously reported. Our observations of white sturgeon spawning in an unregulated river in which fluvial processes and channel morphology are relatively unaltered, albeit increasingly threatened by river engineering, are also unique.

Responses of stream periphytic algae and benthic insects to increases in dissolved inorganic phosphorus (P) were assessed in a streamside mesocosm. Controls and treatments were colonized continuously in summer by biota from the stream. P was maintained in the treatments at 10 μg∙L−1, [Formula: see text] times the concentration in the controls. In the treatments the biomass of chlorophyll a reached 3.5 times that of the controls, accompanied by an increase in Cyanophyta relative to diatoms. No difference was detectable in the numbers of insects drifting from controls and treatments. Numbers of individuals emerging (> 40 species) from the treatments over 7 wk were 2.2 times those from the controls. In both controls and treatments, 77% or more of emerging insects were Chironomidae. After week 7 the density of benthic insects in the treatments, determined without size selection, was 1.75 times that of the controls; size distributions in treatments and controls were similar. Addition of P, therefore, increased the food of insects and resulted in a doubling of their survival to emergence.

Abstract:Additions of inorganic N and P to replicated stream mesocosms were used to test the hypothesis that production of the benthic food web in the flow-controlled Nechako River, B.C., was N and P limited. N, P, and N + P additions were contrasted with controls to determine the responses of periphyton and macroinvertebrates over a 33-day period in late spring. Periphyton accrual under N + P addition was greater than two times that of the controls, and N alone produced a moderate increase. Periphyton showed relatively little response to P addition compared with controls. Macroinvertebrates, especially orthocladiine midges and mayflies, increased in density under N or N + P additions, in contrast with P additions and controls. Increased emergence rates of adult aquatic insects from the mesocosms were consistent with increases observed in benthic invertebrates. The results showed nutrient limitation of benthic productivity and that algal and benthic invertebrate responses were closely coupled. N was most limiting, but with additions of inorganic N as low as 10 µg⋅L -1 , P became limiting. The benthic invertebrates that increased most in abundance corresponded to the predominant prey in chinook salmon (Oncorhynchus tshawytscha) fry diets at the time of the experiment.Résumé : Nous avons ajouté du N et du P inorganiques dans une série de mésocosmes lotiques pour valider l'hypothèse selon laquelle la production de la chaîne alimentaire benthique dans la rivière Nechako, un cours d'eau de Colombie-Britannique à débit contrôlé, était limitée en N et en P. Les effets des ajouts de N, de P et de N + P ont été comparés à des valeurs témoins afin de déterminer les réponses du périphyton et des macroinvertébrés sur une période de 33 jours de la fin du printemps. L'accroissement du périphyton pour un ajout de N + P était plus du double que pour les témoins, et l'ajout de N seul a entraîné une augmentation modérée. Par contre, l'effet d'un ajout de P a eu relativement peu d'effet sur le périphyton. La densité des macroinvertébrés, particulièrement les chironomidés orthocladiinés et les éphéméroptères, a augmenté en cas d'ajout de N ou de N + P, mais pas en cas d'ajout de P ni dans les milieux témoins. Les taux accrus d'émergence observés chez les insectes aquatiques adultes des mésocosmes étaient conformes aux augmentations observées chez les invertébrés benthiques. Les résultats ont montré que la production benthique était limitée par les éléments nutritifs et que les réactions des algues et des invertébrés benthiques étaient étroitement liées. C'est l'azote qui était l'élément le plus limitant; pour des ajouts de N inorganique de seulement 10 µg⋅L -1 , P est devenu limitant. Les invertébrés benthiques dont l'abondance a le plus augmenté correspondaient aux principales proies des alevins du saumon quinnat (Oncorhynchus tshawytscha) au moment de l'expérience. [Traduit par la Rédaction]