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Korosi JB, Adano RC, Do PHP, Hall RI, Jeyarajah J, Stewart EM, Wiklund JA, Thienpont JR. 2024. Ecosystem impacts of an invasive charophyte (Nitellopsis obtusa) interpreted in a multiple stressor context using paleolimnology. Lake Reserv Manage. 40:132–144. Proliferation of Nitellopsis obtusa (starry stonewort), an aquatic invasive macroalga, is an emerging water quality concern in North America, but disentangling its effects is complicated by multiple stressors and a lack of long-term data. In this study, we investigated the potential impacts of N. obtusa on benthic oxygen depletion and the lower food web of Lake Scugog (southern Ontario, Canada) in a multiple-stressor context through a paleolimnological assessment of ecosystem changes up to the invasion and proliferation of N. obtusa. Results reveal that myxoxanthophyll, a pigment produced by colonial cyanobacteria, was no longer detected in the sediments after the early 1990s despite being prevalent throughout the earlier history of Lake Scugog. This indicates that recently documented blooms of Microcystis, which have been hypothesized to be unprecedented and facilitated by N. obtusa, are not a new phenomenon but instead may represent a resurgence in cyanobacteria production following a period of water quality improvement. Sediment cores also documented increased relative abundance of Chironomidae taxa associated with low benthic oxygen availability after about 1920, while changes in subfossil diatom assemblage provided evidence of increased frequency and/or duration of thermal stratification indicative of climate warming effects. This suggests that N. obtusa may be acting synergistically with existing stressors on Lake Scugog to exacerbate challenges with benthic hypoxia. [ABSTRACT FROM AUTHOR]

We present an alternative analysis of the observational record of historical ice-jam floods in the lower Peace River presented in Beltaos (2018) and illustrate the need to examine the history [...]

Climate variations exert rapid and strong control on the hydrology of shallow lake-rich subarctic landscapes, but knowledge of the associated effects on limnological conditions remains limited. Based on analysis of water isotope compositions and water chemistry at 56 lakes across Old Crow Flats (Yukon), a large thermokarst landscape, we assess if differences in source water inputs (snowmelt versus rainfall) affect limnological conditions during the ice-free season of 2007 and explore influences of catchment features. Results demonstrate that lakes with snowmelt-dominated source waters, situated in catchments that support tall shrub and woodland vegetation, possess significantly higher (p < 0.05) nutrient (N, P, Si[O.sub.2]) and dissolved organic carbon concentrations than lakes with rainfall-dominated source waters. Conversely, rainfall-dominated lakes, located in catchments dominated by dwarf shrubs and sparse vegetation, have significantly higher concentrations of major ions ([Mg.sup.2+], [Na.sup.+], S[O.sub.4.sup.2-]) and pH. These limnological differences persisted throughout the ice-free season. We suggest that interaction of snowmelt with organic-rich detritus raises nutrient concentrations in snowmelt-dominated lakes and that evaporative- concentration, shoreline erosion and possibly rainfall runoff are processes that raise the ionic content of lakes with rainfall- dominated source waters. Knowledge of these relations improves the ability to anticipate limnological responses to ongoing and future climate and hydrological change in Arctic and subarctic regions. Si les variations climatiques exercent un controle rapide et intense sur l'hydrologie des paysages subarctiques riches en lacs peu profonds, les connaissances concernant les effets associes sur les conditions limnologiques demeurent limitees. A la lumiere de l'analyse de la composition isotopique et de la chimie de l'eau de 56 lacs dans la plaine Old Crow (Yukon), un vaste paysage de thermokarst, nous tentons de determiner si des differences quant aux sources d'apport en eau (fonte de neige ou pluie) avaient une incidence sur les conditions limnologiques durant la periode sans glace de 2007 et nous examinons l'influence des caracteristiques du bassin versant. Les resultats demontrent que les lacs alimentes principalement par de l'eau de fonte de neige, situes dans des bassins versants qui supportent des arbrisseaux et une vegetation forestiere, presentent des concentrations de nutriments (N, P, Si[O.sub.2]) et de carbone organique dissous significativement plus grandes (p < 0,05) que les lacs principalement alimentes par de l'eau de pluie. A l'inverse, les lacs principalement alimentes par de l'eau de pluie, situes dans des bassins versants ou domine une vegetation buissonnante peu dense, ont des concentrations d'ions majeurs ([Mg.sup.2+], [Na.sup.+], S[O.sub.4.sup.2-]) et des pH significativement plus eleves. Ces differences limnologiques persistent durant toute la periode sans glace. Nous postulons que l'interaction de l'eau de fonte de neige avec des detritus riches en matiere organique accroit les concentrations de nutriments dans les lacs principalement alimentes par l'eau de fonte, alors que la concentration par evaporation, l'erosion des berges et possiblement le ruissellement de l'eau de pluie sont des processus qui accroissent les concentrations ioniques dans les lacs principalement alimentes par de l'eau de pluie. La connaissance de ces liens ameliore la capacite de prevoir les reactions limnologiques aux changements climatiques et hydrologiques actuels et futurs dans les regions arctiques et subarctiques. [Traduit ar la Redaction], Introduction Shallow lakes, a dominant feature in northern regions, are undergoing pronounced hydrological changes consistent with a rapidly warming Arctic (Smith et al. 2005; White et al. 2007; Marsh et [...]