Search

Globally, hydrological connectivity between rivers and their floodplains has been reduced by river flow management and land transformation. The Saskatchewan River Delta is North America's largest inland delta and a hub for fish and fur production. To determine the influence of connectivity on limnology within this northern floodplain, water chemistry and stable isotopes (δ][sup.18]O and δ²H) were analyzed during the winter of 2014 in 26 shallow lakes along a hydrological gradient. A total of five lake connectivity categories were determined by optical remote sensing imagary of surface water coverage area from years of varying flood intensities. Accuracy of categories was verified by degree of [sup.18]O and ²H enrichment within lakes. Both isotopes showed marked successional enrichment between connectivity categories, with more isolated lakes exhibiting greater enrichment. Water chemistry in lakes with greater connectivity to the main channel were characterized by higher pH, dissolved oxygen, nitrates, and sulfates and lower total nitrogen, total phosphorus, and ammonium compared with more isolated lakes. These findings illustrate how connectivity influences water chemistry in northern floodplain lakes and how it might determine the suitability of these lakes as winter refuge for fishes. Additionally, our study provides supporting evidence for the effective use of optical remote sensing imagery, an inexpensive and accessible source of data for researchers, when determining connectivity characteristics of large northern floodplain systems. Additionally, this study provides further evidence that the inundation of floodplain lakes by river water during peak discharge has an impact on the conditions within the lakes long into the winter ice-cover season. Understanding the year-round influence of river-floodplain connection is imperative for assessing potential impacts of climate change and future water regulation on such ecosystems. A l'echelle planetaire, la gestion des debits des rivieres et la transformation du territoire ont entraine une diminution de la connectivite hydrologique entre les rivieres et les plaines inondables. Le delta de la riviere Saskatchewan est le plus grand delta interieur d'Amerique du Nord et une plaque tournante pour la production de poissons et de fourrures. Afin de determiner l'influence de la connectivite sur la limnologie dans cette plaine inondable septentrionale, la chimie de l'eau et ses isotopes stables (δ[sup.18]O et δ²H) ont ete analyses durant l'hiver 2014 dans 26 lacs peu profonds le long d'un gradient hydrologique. Cinq categories de connectivite des lacs ont ete etablies au total sur la base d'images optiques de teledetection des aires recouvertes par les eaux de surface pour des annees caracterisees par differentes intensites des crues. L'exactitude des categories a ete verifiee a la lumiere du degre d'enrichissement en [sup.18]O et ²H dans les lacs. Les deux isotopes presentaient un enrichissement progressif marque entre les categories de connectivite, les lacs plus isoles montrant un enrichissement plus important. La chimie de l'eau dans les lacs de plus grande connectivite au chenal principal etait caracterisee par un pH et des concentrations d'oxygene dissous, de nitrates et de sulfates plus eleves et des concentrations d'azote total, de phosphore total et d'ammonium plus faibles comparativement aux lacs plus isoles. Ces resultats illustrent l'influence de la connectivite sur la chimie de l'eau dans les lacs de plaines inondables septentrionales et comment elle pourrait determiner l'adequation de ces lacs comme refuges hivernaux pour les poissons. En outre, notre etude fournit des donnees temoignant de l'utilite de l'imagerie optique de teledetection, une source de donnees accessible et peu couteuse, pour la determination des caracteristiques de connectivite des grands systemes de plaines inondables nordiques. L'etude fournit aussi de nouvelles donnees appuyant la these voulant que l'inondation des lacs de plaines inondables par l'eau de riviere en periode de debits de pointe ait une incidence persistante sur les conditions dans les lacs durant la periode hivernale de couverture de glace. La comprehension de l'influence tout au long de l'annee de la connexion riviereplaine inondable est necessaire a l'evaluation des impacts potentiels des changements climatiques et de la regularisation future de l'eau sur de tels ecosystemes. [Traduit par la Redaction], Introduction Floodplains are among the most productive and threatened ecosystems on earth. As a result of anthropogenic river flow management and land transformation, 90% of floodplains within North America have [...]

Skin ulcers in Atlantic salmon Salmo salar in the Canadian east coast salmon aquaculture industry lead to high mortality rates. This condition is clinically similar to winter ulcer disease in Norway with the exception that it occurs at temperatures above 10°C. Moritella viscosa is thought to be the causative agent for winter ulcer disease in Norway, and it is occasionally also isolated from skin ulcer cases in Atlantic Canada. This bacterium is known to produce cytotoxins. The objective of this study was to determine if extracellular products (ECP) from an Atlantic Canadian strain of M. viscosa could induce a tissue response similar to what is observed with M. viscosa infections in Atlantic salmon in eastern Canada. We injected fish subcutaneously with ECP and monitored the development of skin lesions. We sampled fish with early skin lesions and ulcers to describe the pathology associated with the condition. Samples were taken for histopathology, bacterial culture, and quantitative PCR (qPCR). All experimental fish expressed early skin lesions, with 5 fish (8.3%) developing deep skin ulcers after 12 d post-exposure. Our results suggest the ECP of M. viscosa from the east coast of Canada induces a similar tissue response to what is described in ulcer disease in Atlantic salmon. These extracelluar products may partially explain the pathology associated with M. viscosa.