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The increasing rate of glacier retreat and turbid glacial runoff can have a strong influence on freshwater ecosystems. Seton and Anderson lakes (British Columbia, Canada) are sockeye salmon (Oncorhynchus nerka) nursery systems. Since the 1940s, the Bridge River Diversion (BRD) introduced glacially turbid water into Seton Lake. To assess the impact of the BRD on the production of Seton Lake, we combined data from limnological surveys with the analysis of subfossil cladocerans and diatoms from sediment cores, using Anderson Lake as a reference. The modern data indicate that the euphotic zone is 14 m shallower and the cladoceran density and biomass are significantly lower in Seton Lake in comparison with Anderson Lake. The paleo- data indicate that following the BRD, the sedimentary fluxes of cladoceran and diatom declined 2- to 10-fold in Seton Lake and remained low thereafter. Together, our data support declines in primary and secondary producers following the BRD, likely due to changes in light penetration and (or) other indirect influence, and provides insights into the impact of turbid meltwater on the biological production of downstream lakes. L'acceleration de la fonte des glaciers et de l'ecoulement des eaux glaciaires turbides peuvent exercer une forte influence sur les ecosystemes d'eau douce. Les lacs Seton et Anderson (Colombie-Britannique, Canada) sont des frayeres a saumons rouges (Oncorhynchus nerka). Depuis les annees 1940, l'amorcement de la derivation partielle de la riviere Bridge (DRB) a introduit de l'eau de fonte glaciaire turbide dans le lac Seton. Afin d'evaluer l'impact de la DRB sur la production du lac Seton, nous avons combine des donnees de releves limnologiques avec l'analyse de subfossiles de cladoceres et de diatomees issus de carottes de sediments, et utilise le lac Anderson comme reference. Les donnees limnologique indiquent que la zone eutrophe est moins profonde de 14 m et que la densite et la biomasse de cladoceres sont significativement plus faibles dans le lac Seton que dans le lac Anderson. Les paleo-donnees indiquent que, suite a la construction du DRB, les flux de cladoceres et de diatomees dans les sediments etaient de 2 a 10 fois moindres dans le lac Seton et qu'ils sont demeures faibles par la suite. Collectivement, ces donnees concordent avec des declins de producteurs primaires et secondaires a la suite de la construction du BRD, probablement causes par des changements de la penetration de lumiere ou par d'autres facteurs indirectes, et elles fournissent de nouveaux renseignements sur l'incidence des eaux de fonte galcieres turbides sur la production biologique de lacs situes en aval., Introduction The increased rate of glacier retreat is a direct, visible, and perhaps one of the most widely known outcomes of the rise in global air temperatures (IPCC 2014). The [...]

Babine Lake, British Columbia, is Canada's largest sockeye salmon (Oncorhynchus nerka) nursery lake, sustaining numerous ecosystem services (e.g., fisheries, recreation, cultural and spiritual benefits). The lake and its watershed have experienced significant anthropogenic and natural disturbances since the early 1900's, including extensive logging, pine beetle infestations, mining, fisheries enhancements, and climate change. To help understand the cumulative impacts of local and regional factors on the trophic ecology of this large freshwater ecosystem, we used the paleolimnological approach to reconstruct changes over the past ∼ 200 years of primary production (subfossil pigments, diatom microfossils), secondary production (cladoceran zooplankton microfossils) and geochemistry (carbon and nitrogen isotopes, elemental analyses, % organic matter). Between ca. 1950 and the 2000's changes in the sedimentary proxies are consistent with an enhanced influx of nutrients and dissolved organic carbon likely due to the cumulative landscape disturbances and an increase in precipitation. These changes include shifts in diatom composition ca. 1950 to higher abundances and taxa indicative of decreased light penetration and nutrient enrichment. Increases in δ15N (∼ +1‰) and cladoceran concentrations, concurrent with increasing sockeye salmon escapement post ca. 1975, is indicative of a higher pelagic fish production that occurs concurrently with both fisheries enhancements and sustained higher precipitation. The largest and most abrupt change in algal pigments occurred post ca. 2000, characterized by increases in motile and buoyant algae (i.e., chrysophytes, cryptophytes, colonial cyanobacteria), a time of increasing regional air temperatures, reduced spring and autumn winds, and resultant changes in patterns of lake mixing. [ABSTRACT FROM AUTHOR]

We integrated limnological, paleolimnological, and fisheries analyses in Tuya Lake, British Columbia, Canada, to explore the effects and interactions of climate warming and sockeye salmon introductions on northern lake ecology. We tracked millennially unprecedented, climate-correlated changes in inferred lake production, stratification, and trophic structure since the mid-1800s, most likely resulting from declining ice cover and enhanced stratification. Post-1970s algal (diatom) species turnover, coeval across several remote northern Cordilleran lakes, marked an apparent increase in warming and the induction of inferred nitrogen deficiencies in Tuya Lake. Lower post-stocking phosphorus (P) and nitrogen (N) concentrations and a strong P-modeled salmon biomass correlation ([r.sup.2] = 0.87) indicated salmon production reduced epilimnetic nutrient availability. Post-stocking chlorophyll reductions, late-summer algal dominance by heterocystous cyanobacteria and low-N-tolerant diatoms, and a strong chlorophyll-modeled salmon biomass correlation ([r.sup.2] = 0.87) indicated that salmon influenced lake productivity, most likely by enhancing climate-induced N-deficiencies. Predicted smolt-biomass nutrient exports were minimal, with post-introduction nutrient reductions likely related to planktivory and enhanced sedimentation losses. Our study highlights how climate warming changes northern lake ecosystem structure and functioning, influencing responses to subsequent stresses. Nous integrons des analyses limnologiques, paleolimnologiques et halieutiques dans le lac Tuya, Colombie-Britannique, Canada, afin d'explorer les effets et les interactions du rechauffement climatique et des empoissonnements de saumons rouges sur l'ecologie d'un lac boreal. Nous avons recherche les changements sans precedent a l'echelle du millenaire relies au climat dans les donnees deduites de production, de stratification et de structure trophique depuis le milieu des annees 1800, resultant le plus vraisemblablement du declin de la couverture de glace et de l'augmentation de la stratification. Apres les annees 1970, le remplacement des especes d'algues (diatomees), phenomene simultane dans plusieurs lacs eloignes de la cordillere, marque une augmentation apparente du rechauffement et l'apparition de carences presumees en azote dans le lac Tuya. Des concentrations reduites de phosphore (P) et d'azote (N) apres l'empoissonnement et une forte correlation ([r.sup.2] = 0,87) modelisee entre P et la biomasse des saumons indiquent que la production des saumons reduit la disponibilite des nutriments dans l'epilimnion. Les reductions de la chlorophylle apres l'empoissonnement, la dominance des cyanobacteries heterocystes chez les algues en fin d'ete, la presence de diatomees tolerantes aux faibles concentrations de N et une forte correlation ([r.sup.2] = 0,87) entre la chlorophylle et la biomasse modelisee des saumons montrent que les saumons affectent la productivite du lac, le plus vraisemblablement en accentuant les carences en N provoquees par le climat. Les exportations predites de nutriments en forme de biomasse de saumoneaux sont minimales, car les reductions de nutriments apres l'empoissonnement sont vraisemblablement liees a la planctonophagie et aux pertes accrues vers les sediments. Notre etude met en lumiere comment les changements dus au rechauffement climatique dans la structure et le fonctionnement d'un lac boreal influencent les reactions aux stress subsequents. [Traduit par la Redaction], Introduction Climate is a principal driver of global aquatic ecosystems. Climate variability modulates the physiologies, phenologies, and distributions of species, community compositions and interactions, and ultimately shapes the structure and [...]

Cultus Lake Sockeye Salmon (Oncorhynchus nerka) were first assessed as endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 2002 in an emergency assessment and confirmed as such in 2003. Owing largely to socioeconomic considerations Cultus Lake Sockeye Salmon were not listed under Schedule 1 of the Species at Risk Act (SARA) at this time. In 2017, as part of a COSEWIC assessment of 24 Fraser Sockeye Designatable Units (DUs), Cultus Lake Sockeye was again assessed as endangered. This Recovery Potential Assessment (RPA) provides an overview of Cultus Lake Sockeye biology, habitat requirements, threats, and limiting factors in Elements 1-11, and identifies recovery targets, population projections, mitigation assessments and recommendations on allowable harm in Elements 12-22. Threats to persistence with the highest population risks include degradation of critical freshwater habitats from anthropogenic forcings, and direct population losses due to harvests in the mixedstock fishery. Lake eutrophication, in particular, and its interactions with climate change, are newly-understood since the last assessment, and are quantified, and highly-influential mechanisms of population depression. Feasible options for mitigation of the various pathways and nutrient loadings to Cultus Lake have been developed both in the literature and this RPA, and are viewed as essential to population recovery, requiring targeted, interdisciplinary and inter-jurisdictional actions. Recognizing the distinction between recovery and survival of a population or species, an abundance target of 7,000 spawners (four-year average) is proposed for recovery of the Cultus Lake Sockeye Salmon DU, and a generational average of 2,500 spawners is proposed as a survival target. Model results suggest that without hatchery supplementation the population will be unable to sustain itself under the current threats and limiting factors, and is predicted to continue to decline over the next three generations (12 years). With ongoing supplementation, extinction is averted, but the population is unlikely to reach survival or recovery targets within this timeframe, without active threat mitigation. Addressing fisheries-related mortality and mitigating freshwater habitat threats (i.e. lake eutrophication), in particular, are anticipated to improve population trends and are highly recommended. [ABSTRACT FROM AUTHOR]

Migratory animals, such as Pacific salmon, can significantly shape communities in recipient habitats both by altering the flux of resources, and changing community composition and subsequent trophic interactions. Here we mainly used paleoecological records from natural sockeye salmon nursery lakes to quantify the response of plankton communities to the influx of salmon-derived nutrients and consumers (juvenile salmon). Our long-term data show that increases in the density of spawning salmon often elevated influx of nutrients, and, in turn, zooplankton production over the past few centuries. In contrast, significant correlations were not detected in two lakes with extremely low or high average spawner densities (i.e. 1.5 and 34.7 × 103 spawners km−2 year−1 respectively). With increasing spawner densities across lakes, analysis of the size structure of subfossils in sediments revealed a strong decrease in body size of a main juvenile salmon prey item ( Eubosmina longispina; r2= 0.36, p < 0.001, n = 67), consistent with an overriding effect of predation in lakes with high salmon densities. These long-term data not only highlight the key role of salmon-derived nutrients in stimulating plankton communities, but also suggest that the relative effect of nutrient and consumer subsidies varies along gradients of lake production, despite a single ultimate causal mechanism (migrating fish). [ABSTRACT FROM AUTHOR]

1. Pacific salmon are a textbook example of migratory animals that transfer nutrients between ecosystems, but little is known about how salmon-derived nutrients (SDN) affect the biodiversity of recipient freshwater ecosystems. We examined paleolimnological records from six Alaskan lakes to define how changes in SDN from sockeye salmon ( Oncorhynchus nerka) influenced sedimentary diatom community structure and beta-diversity among lakes and through time. 2. Using an isotopic mixing model, we showed that SDN loading could account for >80% of the lake total nitrogen budgets and strongly regulated diatom community composition. Spatial dissimilarity in diatom communities was positively related to differences in SDN among lakes ( r = 0.69, P < 0.01, n = 10). Likewise, temporal dissimilarity in diatom communities was positively related to differences in SDN in a sediment core with substantial variation in salmon spawner dynamics between 1700 and 1950 AD ( r = 0.34, P < 0.01, n = 19). Finally, beta-diversity metrics quantifying temporal turnover within each lake's sediment record were also positively related to the variance in SDN loading among lakes ( r = 0.88, P < 0.05, n = 5). Mean SDN was only negatively correlated to temporal diatom beta-diversity. 3. Spatially subsidised systems often receive temporally variable resource inputs, and thus, it is not surprising that, unlike previous studies, we found that resource variability was the key driver of community composition and beta-diversity. In habitats that receive strongly fluctuating external nutrient loads, environment heterogeneity may overweigh stochastic community processes. In addition, freshwater diatoms are characterised by great dispersal capabilities and short life cycles and therefore may be a more sensitive indicator for evaluating the role of resource variability than previously used model organisms. These results suggest that productivity-diversity relationship vary with the nature of nutrient loading and the life history of the community studied. 4. Overall, our study highlights that the transport of nutrients by sockeye salmon across ecosystem boundaries is a significant driver of algal community and biodiversity in nursery lakes, mainly through changing the magnitude of nutrient variation. As such, freshwater species diversity in regions like the U.S. Pacific Northwest may become impoverished where there have been long-term declines in salmon populations and decreases in nutrient variability among lakes. [ABSTRACT FROM AUTHOR]