The objective of this study was to investigate selenium toxicosis in larval northern pike (Esox lucius) originating from reproductively mature pike collected downstream of a uranium milling operation in northern Saskatchewan, Canada. Eggs were obtained from female pike collected from a reference site and three sites representing an exposure gradient (approximately 2, 10, and 15 km downstream of effluent discharge). Embryos were incubated following a two-way (crossover) analysis of variance experimental design that allowed discrimination between effects due to maternal transfer to eggs and effects due to site water exposure in the developing embryos. The major finding of this study was a significant increase in the frequencies of individual deformities (skeletal curvatures, craniofacial deformities, and fin deformities) and edema in fry originating from high and medium exposure site females (mean selenium concentrations of 48.23 and 31.28 microg/g egg dry weight and 38.27 and 16.58 microg/g muscle dry weight, respectively) compared to reference site females. Selenium concentrations resulting in a 20% increase in total deformities above background levels (EC20S) were 33.55 and 21.54 micro/g dry weight in eggs and muscle, respectively. Mathematical conversion of the egg- and muscle-derived relationships to whole body selenium levels resulted in similar EC20S of 15.56 and 17.72 microg/g dry weight, respectively. These relationships between tissue selenium levels and larval deformities suggest that northern pike are within the same range of sensitivity to selenium as the majority of warm water (e.g., centrarchids and cyprinids) and cold water (e.g., salmonids) fish species studied to date.

For the past decade, considerable research has been conducted at a series of small lakes receiving treated liquid effluent containing elevated selenium (Se) from the Key Lake uranium (U) milling operation in northern Saskatchewan, Canada. Several studies related to this site, including field collections of water, sediment, and biota (biofilm and/or periphyton, invertebrates, fish, and birds), semicontrolled mesocosm and in situ caging studies, and controlled laboratory experiments have recently been published. The aim of the present investigation was to compile the site-specific information obtained from this multidisciplinary research into an integrative perspective regarding the influence of Se speciation on biogeochemical cycling and food web transfer of Se in coldwater ecosystems. Within lakes, approximately 50% of sediment Se was in the form of elemental Se, although this ranged from 0% to 81% among samples. This spatial variation in elemental Se was positively correlated with finer particles (less sand) and percent total organic C content in sediments. Other Se species detected in sediments included selenosulfides, selenite, and inorganic metal selenides. In contrast, the major Se form in sediment-associated biofilm and/or periphyton was an organoselenium species modeled as selenomethionine (SeMet), illustrating the critical importance of this matrix in biotransformation of inorganic Se to organoselenium compounds and subsequent trophic transfer to benthic invertebrates at the base of the food web. Detritus displayed a Se speciation profile intermediate between sediment and biofilm, with both elemental Se and SeMet present. In benthic detritivore (chironomid) larvae and emergent adults, and in foraging and predatory fishes, SeMet was the dominant Se species. The proportion of total Se present as a SeMet-like species displayed a direct nonlinear relationship with increasing whole-body Se in invertebrates and fishes, plateauing at approximately 70% to 80% of total Se as a SeMet-like species. In fish collected from reference lakes, a selenocystine-like species was the major Se species detected. Similar Se speciation profiles were observed using 21-day mesocosm and in situ caging studies with native small-bodied fishes, illustrating the efficient bioaccumulation of Se and use of these semicontrolled approaches for future research. A simplified conceptual model illustrating changes in Se speciation through abiotic and biotic components of lakes was developed, which is likely applicable to a wide range of northern industrial sites receiving elevated Se loading into aquatic ecosystems.

Experiments were performed to compare 14 C uptake, dissolved O 2 and CO 2 change, and microelectrode techniques for measuring benthic primary productivity and community metabolism at a site on the South Saskatchewan River, Saskatchewan. The highest estimates of primary productivity were obtained with O 2 microelectrodes (two to four times higher than simultaneous estimates from bulk-water dissolved O 2 measurements), presumably because measurements are biased toward active communities under optimal conditions for photosynthesis. In daytime experiments lasting~1.3 and 2.4 h, estimates from 14 C uptake were higher than those measured simultaneously from dissolved O 2 and CO 2 change, suggesting that 14 C uptake measured gross primary production (GPP) in these short-term incubations. Differences in experimental water velocity ranging from 0.2 to >6.5 cm⋅s -1 had less of an effect than chlorophyll a concentration on metabolic rates in diel experiments with rocks taken from a site where velocities were from 5.6 to 7.8 cm⋅s -1 . There was a potential for phosphorus and possibly NH 4 limitation of metabolic activity during long-term incubations. Results highlight areas in which further research is needed when using chambers to determine periphyton metabolism.Résumé : Nos expériences visaient à comparer l'assimilation du 14 C, les changements dans l'O 2 dissous et le CO 2 et les techniques faisant appel à des microélectrodes pour mesurer la productivité primaire benthique et le métabolisme des communautés sur un site de la rivière Saskatchewan sud (Saskatchewan). Ce sont les microélectrodes à O 2 qui ont donné les estimations les plus élevées de la productivité primaire (deux à quatre fois plus élevées que les estimations simultanées des mesures de l'O 2 dissous dans l'eau libre), ce qui est probablement dû au fait que les mesures sont biaisées en faveur des communautés actives dans les conditions idéales de la photosynthèse. Dans des expériences en lumière du jour d'une durée dẽ 1,3 et 2,4 h, les estimations établies à partir de l'assimilation du 14 C étaient plus élevées que celles fournies par les mesures simultanées du changement de l'O 2 dissous et du CO 2 , ce qui permet de penser que l'assimilation du 14 C mesurait la production primaire brute dans ces incubations de courte durée. Les différences dans la vitesse de l'eau pendant les expériences, de l'ordre de 0,2 à >6,5 cm⋅s -1 , avaient moins d'effet que la concentration de chlorophylle a sur le métabolisme dans les expériences diurnes réalisées avec des roches prélevées sur un site où les vitesses étaient de l'ordre de 5,6 à 7,8 cm⋅s -1 . Les incubations de longue durée présentaient un potentiel de limitation du métabolisme du phosphore et peut-être du NH 4 . Les résultats font ressortir les domaines où il est nécessaire de poursuivre les recherches quand on utilise des enceintes pour mesurer le métabolisme du périphyton. [Traduit par la Rédaction]Can.