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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 [...]

Evaluation of large lake response to centennial changes in land use and climate can be complicated by high spatial and hydrological complexity within their catchments, particularly in regions of low relief. Furthermore, large lakes can exhibit abrupt changes in structure and function that obscure causes of eutrophication.We provide the first quantification of historical trends in lake production, cyanobacterial abundance, sediment geochemistry and diatom composition since c. 1800 in Lake Manitoba, the 29th largest lake in the world, and compared them to Lake Winnipeg, a morphologically similar, adjacent basin with a 10‐fold larger catchment and an abrupt increase in production around 1990.Before 1900, Lake Manitoba was mesotrophic, with low sedimentary concentrations of carbon, phosphorus, nitrogen, cyanobacteria and algal pigments, as well as assemblages of low‐light‐adapted benthic diatoms. Analysis of pigment time‐series with hierarchical generalised additive models revealed that Lake Manitoba eutrophied during 1900–1930 as a consequence of the development of intensive agriculture within its local catchment, but thereafter exhibited stable cyanobacterial densities with limited expansion of N2‐fixing cyanobacteria despite persistent eutrophication.Lake Manitoba did not undergo an abrupt change as seen in Lake Winnipeg.These findings suggest that catchment size had little influence on water quality degradation and that nutrient influx from proximal agricultural sources was sufficient to initially degrade these large prairie lakes. The abrupt change in Lake Winnipeg around 1990 required additional intensification of local land use that did not occur in the Lake Manitoba catchment. [ABSTRACT FROM AUTHOR]

A top-bottom paleolimnological analysis of 30 undisturbed lakes in the Experimental Lakes Area (ELA) in northwest Ontario showed marked increases in the relative abundance of colonial scaled chrysophyte taxa in most lakes since pre-industrial times. The increase in abundance of colonial taxa was primarily driven by Synura sphagnicola in small, high-nutrient, and warm lakes. The colonial taxa Synura petersenii and Synura echinulata also increased in the deeper study lakes. Detailed analysis of sediment cores from six lakes revealed that these changes occurred in the early to mid-1900s. Based on the modern distribution of scaled chrysophytes relative to lake physicochemical data, we propose multiple processes that may be contributing to these changes, such as changes in lake thermal properties and historical changes in the flux of important particles and solutes to lakes. Additional mechanisms that may contribute to the observed changes are discussed, including trophic interactions and changes in limnetic pC[O.sub.2]. Because the ELA is relatively undisturbed, our findings provide important information on the drivers responsible for increases in colonial chrysophyte abundance, which have been documented in studies of lakes in central Ontario and northeast United States. Une analyse paleolimnologique de la surface au fond de 30 lacs non perturbes dans la region des lacs experimental (RLE) du nord-ouest de l'Ontario revele des augmentations marquees de l'abondance relative de taxons coloniaux de chrysophytes a ecailles dans la plupart des lacs depuis l'epoque preindustrielle. L'augmentation de l'abondance de taxons coloniaux est principalement causee par Synura sphagnicola dans les petits lacs chauds a forte teneur en nutriments. L'abondance des taxons coloniaux Synura petersenii et Synura echinulata augmente egalement dans les lacs plus profonds etudies. L'analyse detaillee de carottes de sediments de six lacs revele que ces changements se sont produits du debut au milieu du 2[0.sup.e] siecle. A la lumiere de la repartition actuelle de chrysophytes a ecailles au vu de donnees physicochimiques sur les lacs, nous proposons differents processus qui pourraient participer a ces changements, comme des variations des proprietes thermiques des lacs et des changements historiques des flux de particules et de solutes importants vers les lacs. D'autres mecanismes qui pourraient intervenir dans les changements observes sont abordes, dont des interactions trophiques et des variations du pC[O.sub.2] limnetique. Comme la RLE est relativement non perturbee, nos constatations fournissent d'importants renseignements sur les facteurs a l'origine des augmentations de l'abondance de chrysophytes coloniaux qui ont ete documentees dans des etudes de lacs dans le centre de l'Ontario et le nord-est des Etats-Unis. [Traduit par la Redaction], Introduction Canada's boreal region represents an important component of the freshwater biome, containing an estimated 800 000 [km.sup.2] of surface fresh water (Cheskey et al. 2011). These freshwater systems have [...]

Lakes in the semiarid Southern Interior Plateau of British Columbia, Canada are vulnerable to future climate-driven changes in water quantity and quality. However, few long-term monitoring records exist to assess the effects of varying hydroclimate conditions on lake function. We present a high-resolution multiproxy paleolimnological record containing subfossil diatoms, μXRF via ITRAX, and chlorophyll-a that spans the past 1800 years from Roche Lake in south-central British Columbia. Generalized additive models indicate that the diatom assemblages were associated with changes in lake level and the accompanying effects of atmospheric forcing on lake thermal structure, and that these forcing mechanisms had a weak relationship with primary production. We infer two pronounced arid periods between ca. AD 600-950 and ca. AD 1730-1950 that correspond to evidence of reduced lake mixing and enhanced anoxia, but variable patterns in primary production. Synthesis of regional proxy records suggests that inferences of moist but possibly warm conditions during the Medieval Climate Anomaly may have occurred because of a complex interaction between prolonged La Niña-like conditions and higher radiative forcing. Overall, lakes in this region are sensitive to changes in hydroclimate generated by interactions between external forcing and Pacific Ocean-atmosphere processes, and the resulting changes in aridity may have potentially negative consequences on salmonid habitat. [ABSTRACT FROM AUTHOR]