Increased relative abundance of colonial scaled chrysophytes since pre-industrial times in minimally disturbed lakes from the Experimental Lakes Area, Ontario

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 [...]