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Sökning: WFRF:(Stockwell Jason D.)

  • Resultat 1-10 av 15
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1.
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2.
  • Maasri, Alain, et al. (författare)
  • A global agenda for advancing freshwater biodiversity research
  • 2022
  • Ingår i: Ecology Letters. - 1461-023X .- 1461-0248. ; 25:2, s. 255-263
  • Tidskriftsartikel (refereegranskat)abstract
    • Global freshwater biodiversity is declining dramatically, and meeting the challenges of this crisis requires bold goals and the mobilisation of substantial resources. While the reasons are varied, investments in both research and conservation of freshwater biodiversity lag far behind those in the terrestrial and marine realms. Inspired by a global consultation, we identify 15 pressing priority needs, grouped into five research areas, in an effort to support informed stewardship of freshwater biodiversity. The proposed agenda aims to advance freshwater biodiversity research globally as a critical step in improving coordinated actions towards its sustainable management and conservation. 
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3.
  • Block, Benjamin D., et al. (författare)
  • The unique methodological challenges of winter limnology
  • 2019
  • Ingår i: Limnology and Oceanography. - : Wiley-Blackwell. - 1541-5856 .- 1541-5856. ; 17:1, s. 42-57
  • Forskningsöversikt (refereegranskat)abstract
    • Winter is an important season for many limnological processes, which can range from biogeochemical transformations to ecological interactions. Interest in the structure and function of lake ecosystems under ice is on the rise. Although limnologists working at polar latitudes have a long history of winter work, the required knowledge to successfully sample under winter conditions is not widely available and relatively few limnologists receive formal training. In particular, the deployment and operation of equipment in below 0 degrees C temperatures pose considerable logistical and methodological challenges, as do the safety risks of sampling during the ice-covered period. Here, we consolidate information on winter lake sampling and describe effective methods to measure physical, chemical, and biological variables in and under ice. We describe variation in snow and ice conditions and discuss implications for sampling logistics and safety. We outline commonly encountered methodological challenges and make recommendations for best practices to maximize safety and efficiency when sampling through ice or deploying instruments in ice-covered lakes. Application of such practices over a broad range of ice-covered lakes will contribute to a better understanding of the factors that regulate lakes during winter and how winter conditions affect the subsequent ice-free period.
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4.
  • Hampton, Stephanie E., et al. (författare)
  • Ecology under lake ice
  • 2017
  • Ingår i: Ecology Letters. - 1461-023X .- 1461-0248. ; 20:1, s. 98-111
  • Forskningsöversikt (refereegranskat)abstract
    • Winter conditions are rapidly changing in temperate ecosystems, particularly for those that experience periods of snow and ice cover. Relatively little is known of winter ecology in these systems, due to a historical research focus on summer ‘growing seasons’. We executed the first global quantitative synthesis on under-ice lake ecology, including 36 abiotic and biotic variables from 42 research groups and 101 lakes, examining seasonal differences and connections as well as how seasonal differences vary with geophysical factors. Plankton were more abundant under ice than expected; mean winter values were 43.2% of summer values for chlorophyll a, 15.8% of summer phytoplankton biovolume and 25.3% of summer zooplankton density. Dissolved nitrogen concentrations were typically higher during winter, and these differences were exaggerated in smaller lakes. Lake size also influenced winter-summer patterns for dissolved organic carbon (DOC), with higher winter DOC in smaller lakes. At coarse levels of taxonomic aggregation, phytoplankton and zooplankton community composition showed few systematic differences between seasons, although literature suggests that seasonal differences are frequently lake-specific, species-specific, or occur at the level of functional group. Within the subset of lakes that had longer time series, winter influenced the subsequent summer for some nutrient variables and zooplankton biomass.
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5.
  • Hrycik, Allison R., et al. (författare)
  • Earlier winter/spring runoff and snowmelt during warmer winters lead to lower summer chlorophyll-a in north temperate lakes
  • 2021
  • Ingår i: Global Change Biology. - 1354-1013 .- 1365-2486. ; 27:19, s. 4615-4629
  • Tidskriftsartikel (refereegranskat)abstract
    • Winter conditions, such as ice cover and snow accumulation, are changing rapidly at northern latitudes and can have important implications for lake processes. For example, snowmelt in the watershed—a defining feature of lake hydrology because it delivers a large portion of annual nutrient inputs—is becoming earlier. Consequently, earlier and a shorter duration of snowmelt are expected to affect annual phytoplankton biomass. To test this hypothesis, we developed an index of runoff timing based on the date when 50% of cumulative runoff between January 1 and May 31 had occurred. The runoff index was computed using stream discharge for inflows, outflows, or for flows from nearby streams for 41 lakes in Europe and North America. The runoff index was then compared with summer chlorophyll-a (Chl-a) concentration (a proxy for phytoplankton biomass) across 5–53 years for each lake. Earlier runoff generally corresponded to lower summer Chl-a. Furthermore, years with earlier runoff also had lower winter/spring runoff magnitude, more protracted runoff, and earlier ice-out. We examined several lake characteristics that may regulate the strength of the relationship between runoff timing and summer Chl-a concentrations; however, our tested covariates had little effect on the relationship. Date of ice-out was not clearly related to summer Chl-a concentrations. Our results indicate that ongoing changes in winter conditions may have important consequences for summer phytoplankton biomass and production.
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6.
  • Isles, Peter D. F., et al. (författare)
  • Climate-driven changes in energy and mass inputs systematically alter nutrient concentration and stoichiometry in deep and shallow regions of Lake Champlain
  • 2017
  • Ingår i: Biogeochemistry. - : SPRINGER. - 0168-2563 .- 1573-515X. ; 133:2, s. 201-217
  • Tidskriftsartikel (refereegranskat)abstract
    • Concentrations of nitrogen (N) and phosphorus (P) in lakes may be differentially impacted by climate-driven changes in nutrient loading and by direct impacts of temperature and wind speed on internal nutrient cycling. Such changes may result in systematic shifts in lake N:P under future climate warming. We used 21 years of monitoring data to compare long-term and intra-annual trends in total N (TN), total P (TP) and TN:TP at 15 sites in Lake Champlain to concurrent measurements of watershed nutrient inputs and meteorological drivers. TN:TP declined sharply lake-wide, particularly in the past decade, yet the drivers of this trend varied based on site depth. In deep sites, declines were driven by changes in watershed loading of dissolved P and N and (in some cases) by decreases in hypolimnetic dissolved oxygen. In shallow sites, declines in TN:TP were primarily driven by long-term increases in temperature and decreases in wind speed, and exhibited systematic seasonal variability in TN:TP due to the timing of sediment P loading, N removal processes, and external nutrient inputs. We developed a conceptual model to explain the observed trends, and suggest that while climate drivers have affected nutrient dynamics in shallow and deep sites differently, both deep and shallow sites are likely to experience further declines in N:P and increases in cyanobacteria dominance if recent climate trends continue.
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7.
  • Doubek, Jonathan P., et al. (författare)
  • The extent and variability of storm-induced temperature changes in lakes measured with long-term and high-frequency data
  • 2021
  • Ingår i: Limnology and Oceanography. - : WILEY. - 0024-3590 .- 1939-5590. ; 66:5, s. 1979-1992
  • Tidskriftsartikel (refereegranskat)abstract
    • The intensity and frequency of storms are projected to increase in many regions of the world because of climate change. Storms can alter environmental conditions in many ecosystems. In lakes and reservoirs, storms can reduce epilimnetic temperatures from wind-induced mixing with colder hypolimnetic waters, direct precipitation to the lake's surface, and watershed runoff. We analyzed 18 long-term and high-frequency lake datasets from 11 countries to assess the magnitude of wind- vs. rainstorm-induced changes in epilimnetic temperature. We found small day-to-day epilimnetic temperature decreases in response to strong wind and heavy rain during stratified conditions. Day-to-day epilimnetic temperature decreased, on average, by 0.28 degrees C during the strongest windstorms (storm mean daily wind speed among lakes: 6.7 +/- 2.7 m s(-1), 1 SD) and by 0.15 degrees C after the heaviest rainstorms (storm mean daily rainfall: 21.3 +/- 9.0 mm). The largest decreases in epilimnetic temperature were observed >= 2 d after sustained strong wind or heavy rain (top 5(th) percentile of wind and rain events for each lake) in shallow and medium-depth lakes. The smallest decreases occurred in deep lakes. Epilimnetic temperature change from windstorms, but not rainstorms, was negatively correlated with maximum lake depth. However, even the largest storm-induced mean epilimnetic temperature decreases were typically <2 degrees C. Day-to-day temperature change, in the absence of storms, often exceeded storm-induced temperature changes. Because storm-induced temperature changes to lake surface waters were minimal, changes in other limnological variables (e.g., nutrient concentrations or light) from storms may have larger impacts on biological communities than temperature changes.
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8.
  • Euclide, Peter T., et al. (författare)
  • Partial diel vertical migration in an omnivorous macroinvertebrate, Mysis diluviana
  • 2017
  • Ingår i: Hydrobiologia. - 0018-8158 .- 1573-5117. ; 787:1, s. 387-396
  • Tidskriftsartikel (refereegranskat)abstract
    • Partial migration, whereby only a portion of a population migrates, has just recently received attention in aquatic systems. Partial diel vertical migration (DVM) has received even less attention but could significantly influence our understanding of trophic interactions and nutrient movement in open water systems. Recent work in the Baltic Sea shows differences in isotope composition between benthic and pelagic Mysis salemaai sampled at night, suggesting that partial DVM may be fixed at the individual level. Historic observations of North American M. diluviana suggest partial DVMin this species, but this behavior has largely been ignored in the literature. We used length, occurrence of gravid females, and body delta C-13, delta N-15, delta S-34, and C:N ratio as markers to test for differences among adult M. diluviana collected from benthic and pelagic habitats at night in Lake Champlain, USA. We found differences in body length and occurrence of gravid females between pelagic- and benthic-caught M. diluviana and differences in C: N between pelagic-and benthic-caught non-gravid individuals, consistent with life stage and body condition hypotheses for partial migration. Partial DVM of M. diluviana could have significant impacts on population assessments which could bias food web models used in basic research and management.
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9.
  • Meyer, Michael F., et al. (författare)
  • Virtual Growing Pains : Initial Lessons Learned from Organizing Virtual Workshops, Summits, Conferences, and Networking Events during a Global Pandemic
  • 2021
  • Ingår i: Limnology and Oceanography Bulletin. - 1539-607X .- 1539-6088. ; 30:1, s. 1-11
  • Tidskriftsartikel (refereegranskat)abstract
    • For many, 2020 was a year of abrupt professional and personal change. For the aquatic sciences community, many were adapting to virtual formats for conducting and sharing science, while simultaneously learning to live in a socially distanced world. Understandably, the aquatic sciences community postponed or canceled most in-person scientific meetings. Still, many scientific communities either transitioned annual meetings to a virtual format or inaugurated new virtual meetings. Fortunately, increased use of video conferencing platforms, networking and communication applications, and a general comfort with conducting science virtually helped bring the in-person meeting experience to scientists worldwide. Yet, the transition to conducting science virtually revealed new barriers to participation whereas others were lowered. The combined lessons learned from organizing a meeting constitute a necessary knowledge base that will prove useful, as virtual conferences are likely to continue in some form. To concentrate and synthesize these experiences, we showcase how six scientific societies and communities planned, organized, and conducted virtual meetings in 2020. With this consolidated information in hand, we look forward to a future, where scientific meetings embrace a virtual component, so to as help make science more inclusive and global.
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10.
  • O'Malley, Brian P., et al. (författare)
  • An underwater video system to assess abundance and behavior of epibenthic Mysis
  • 2018
  • Ingår i: Limnology and Oceanography. - 1541-5856 .- 1541-5856. ; 16:12, s. 868-880
  • Tidskriftsartikel (refereegranskat)abstract
    • The application of remote video technologies can provide alternative views of in situ behavior and distribution of aquatic organisms that might be missed with traditional net‐based techniques. We describe a remote benthic video camera system designed to quantify epibenthic density of the macroinvertebrate Mysis diluviana. We deployed the camera multiple times during the day and night at a 60‐m depth site in Lake Champlain and quantified Mysis density from the footage using basic methods and readily available software. Density estimates from the video were on average 43 times higher than concurrent estimates from benthic sled tows, suggesting sleds may be inefficient at sampling mysids. Deployment caused initial scattering of individuals, resulting in low densities immediately after deployment that slowly increased. On some occasions, Mysis densities on video fluctuated greatly over several hours, consistent with organisms that have a patchy distribution on the lake bottom. The camera system provided novel insights on behavior and distribution of Mysis on benthic habitats, demonstrating potential for use as a tool to study partial diel vertical migration and predator–prey interactions.
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