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Ponds are often identified by their small size and shallow depths, but the lack of a universal evidence-based definition hampers science and weakens legal protection. Here, we compile existing pond definitions, compare ecosystem metrics (e.g., metabolism, nutrient concentrations, and gas fluxes) among ponds, wetlands, and lakes, and propose an evidence-based pond definition. Compiled definitions often mentioned surface area and depth, but were largely qualitative and variable. Government legislation rarely defined ponds, despite commonly using the term. Ponds, as defined in published studies, varied in origin and hydroperiod and were often distinct from lakes and wetlands in water chemistry. We also compared how ecosystem metrics related to three variables often seen in waterbody definitions: waterbody size, maximum depth, and emergent vegetation cover. Most ecosystem metrics (e.g., water chemistry, gas fluxes, and metabolism) exhibited nonlinear relationships with these variables, with average threshold changes at 3.7 ± 1.8 ha (median: 1.5 ha) in surface area, 5.8 ± 2.5 m (median: 5.2 m) in depth, and 13.4 ± 6.3% (median: 8.2%) emergent vegetation cover. We use this evidence and prior definitions to define ponds as waterbodies that are small (

Northern regions are expected to experience large environmental change over the next few decades. The response of biota will depend on changes in the local environment, regional processes that influence lake connectivity, and species interactions. In 2008, we surveyed 92 lakes and ponds across Wapusk National Park, located on the southwestern shore of Hudson Bay. At each site we assessed water chemistry and zooplankton community composition. In an effort to understand how the aquatic ecosystems will respond to future environmental change, we determined local characteristics (e.g., water chemistry), regional spatial factors (e.g., dispersal), and biotic interactions (e.g., species associations) influencing community composition. Important environmental variables included lake area, pH, ionic composition, total phosphorus, and chlorophyll a; however, spatial variables explained more variation than environmental variables, suggesting that dispersal is an important driver of zooplankton composition in this region. Additionally, species exhibited negative co-occurrence patterns, suggesting biotic interactions are important in structuring the zooplankton communities. As environmental conditions change and the distribution of habitat (i.e., coastal fen, interior peatland, and spruce forest) shifts, evidence that the park's zooplankton community is spatially structured coupled with our suspicion that zooplankton are likely to experience high dispersal levels in Wapusk leads us to suggest zooplankton may indeed be able to track changing environmental conditions within the park, although it remains unclear how species interactions will modify this expectation.

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 [...]

Wetlands in the Prairie Pothole Region of the North American Northern Great Plains perform multiple ecosystem services and are biodiversity hotspots. However, climatological changes can result in sudden shifts in these important ecosystems. For example, marked increases in precipitation in the last few decades have resulted in a widespread shift in wetlands across the Prairie Pothole Region to a new ecohydrological state. We used multiproxy analyses (diatom community composition and invertebrate stable isotopes) of 210Pb‐dated sediment cores from two adjacent, but morphologically and hydrologically different, prairie‐pothole wetlands to assess the effects of hydroclimatic variability on these wetland ecosystems. Our results provide evidence that the recent ecohydrological shift in the region's wetlands is unprecedented over the past ca. 178 yr. Oxygen stable isotopes in chironomid head capsules provide a record of paleohydrology changes. The most recent sediments (i.e., those deposited after the state shift) from both wetlands revealed novel changes in diatom communities that differed greatly from earlier community compositions. In addition, a depleted signal in deuterium and 13C carbon stable isotopes observed in chironomid head capsules and Daphnia ephippia, respectively, after 1993 is likely related to an increase in methane production in these wetlands. Our study highlights the importance of considering basin morphometry including whether a wetland has an overflow point, and multiple biological indicators to study climate‐change influences on freshwater ecosystems. Research using these techniques can lead to an improved understanding of recent ecosystem shifts, an understanding that will be essential for future climate‐change adaptation and mitigation in this ecologically important region. [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 [...]

Recent studies using remote sensing analysis of lake-rich thermokarst landscapes have documented evidence of declining lake surface area in response to recent warming. However, images alone cannot identify whether these declines are due to increasing frequency of lake drainage events associated with accelerated thermokarst activity or to increasing evaporation in response to longer ice-free season duration. Here, we explore the potential of combining aerial photograph time series with paleolimnological analyses to track changes in hydrological conditions of a thermokarst lake in the Old Crow Flats (OCF), Canada, and to identify their causes. Images show that the water level in lake OCF 48 declined markedly sometime between 1972 and 2001. In a sediment core from OCF 48, complacent stratigraphic profiles of several physical, geochemical, and biological parameters from ∼1874-1967 indicate hydro-limnological conditions were relatively stable. From ∼1967-1989, declines in organic matter content, organic carbon isotope values, and pigment concentrations are interpreted to reflect an increase in supply of minerogenic sediment, and subsequent decline in aquatic productivity, caused by increased thermo-erosion of shoreline soils. Lake expansion was likely caused by increased summer rainfall, as recorded by increased cellulose-inferred lake-water oxygen isotope compositions. Stratigraphic trends defining the lake expansion phase terminated at ∼1989, which likely marks the year when the lake drained. Above-average precipitation during the previous year probably raised the lake level and promoted further thermo-erosion of the shoreline soils that caused the lake to drain. These are meteorological conditions that have led to other recent lake-drainage events in the OCF. Thus, the decline in lake level, evident in the aerial photograph from 2001, is unlikely to have been caused by evaporation, but rather is a remnant of a drainage event that took place more than a decade earlier. After drainage, the lake began to refill, and most paleolimnological parameters approach levels that are similar to those during the stable phase. These findings indicate that combined use of aerial images and paleolimnological methods offers much promise for identifying the hydrological consequences of recent climatic variations on thermokarst lakes. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]