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  • 1
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    Lakes as sentinels of climate change (2009)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 54 (6). pp. 2283-2297.
    Details
    Publication Date: 2017-10-24
    Description: While there is a general sense that lakes can act as sentinels of climate change, their efficacy has not been thoroughly analyzed. We identified the key response variables within a lake that act as indicators of the effects of climate change on both the lake and the catchment. These variables reflect a wide range of physical, chemical, and biological responses to climate. However, the efficacy of the different indicators is affected by regional response to climate change, characteristics of the catchment, and lake mixing regimes. Thus, particular indicators or combinations of indicators are more effective for different lake types and geographic regions. The extraction of climate signals can be further complicated by the influence of other environmental changes, such as eutrophication or acidification, and the equivalent reverse phenomena, in addition to other land-use influences. In many cases, however, confounding factors can be addressed through analytical tools such as detrending or filtering. Lakes are effective sentinels for climate change because they are sensitive to climate, respond rapidly to change, and integrate information about changes in the catchment.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lo.2009.54.6_part_2.2283
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Photosynthetic picoplankton dynamics in Lake Tahoe: temporal and spatial niche partitioning among prokaryotic and eukaryotic cells (2009)
    Oxford Univ. Press
    In:  Journal of Plankton Research, 31 (11). pp. 1307-1320.
    Details
    Publication Date: 2020-07-20
    Description: Dynamics of prokaryotic and eukaryotic picophytoplankton were investigated over a 2-year time period using flow cytometry and combined with an in situ experiment in Lake Tahoe, USA to better characterize to which extent environmental factors control these communities. Pronounced seasonal patterns and clear temporal and spatial partitioning were observed between picocyanobacteria and picoeukaryotes. Picocyanobacteria dominated in the nutrient deficient upper water column during the stratified season, while picoeukaryotes reached maximum abundance during isothermal conditions and maintained high numbers in deep-water layers during the stratified season. Picocyanobacteria were more sensitive to high solar and UV radiation compared with picoeukaryotes, which were not affected by high solar radiation and nutrient enrichment stimulated their growth. The opposing response of these two populations is consistent with their vertical distribution: picocyanobacteria dominate below the 30% isolume and above the nitrocline depth, whereas picoeukaryotes increase in the vicinity of the nitrocline and thus increased nutrient concentration. This spatial separation of picophytoplankton groups along environmental gradients in Lake Tahoe is consistent with other deep-oligotrophic lakes and the marine environment, suggesting that these marine and freshwater organisms have similar ecophysiological requirements. These results highlight that the smallest photosynthetic communities show taxon-specific responses to mixing and resource availability, which affect the structure and dynamics of picophytoplankton.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1093/plankt/fbp074
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Patterns of spatial and temporal variability of UV transparency in Lake Tahoe, California-Nevada (2009)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Biogeosciences, 114 . G00D03.
    Details
    Publication Date: 2018-02-06
    Description: Lake Tahoe is an ultra-oligotrophic subalpine lake that is renowned for its clarity. The region experiences little cloud cover and is one of the most UV transparent lakes in the world. As such, it is an ideal environment to study the role of UV radiation in aquatic ecosystems. Long-term trends in Secchi depths showed that water transparency to visible light has decreased in recent decades, but limited data are available on the UV transparency of the lake. Here we examine how ultraviolet radiation varies relative to longer-wavelength photosynthetically active radiation (PAR, 400-700 nm, visible wavelengths) horizontally along inshore-offshore transects in the lake and vertically within the water column as well as temporally throughout 2007. UV transparency was more variable than PAR transparency horizontally across the lake and throughout the year. Seasonal patterns of Secchi transparency differed from both UV and PAR, indicating that different substances may be responsible for controlling transparency to UV, PAR, and Secchi. In surface waters, UVA (380 nm) often attenuated more slowly than PAR, a pattern visible in only exceptionally transparent waters with very low dissolved organic carbon. On many sampling dates, UV transparency decreased progressively with depth suggesting surface photobleaching, reductions in particulate matter, increasing chlorophyll a, or some combination of these increased during summer months. Combining these patterns of UV transparency with data on visible light provides a more comprehensive understanding of ecosystem structure, function, and effects of environmental change in highly transparent alpine and subalpine lakes such as Tahoe.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2008JG000816
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Lake warming favours small-sized planktonic diatom species (2009)
    Royal Society of London
    In:  Proceedings of the Royal Society B - Biological Sciences, 276 (1656). pp. 427-435.
    Details
    Publication Date: 2020-06-08
    Description: Diatoms contribute to a substantial portion of primary production in the oceans and many lakes. Owing to their relatively heavy cell walls and high nutrient requirements, planktonic diatoms are expected to decrease with climate warming because of reduced nutrient redistribution and increasing sinking velocities. Using a historical dataset, this study shows that diatoms were able to maintain their biovolume with increasing stratification in Lake Tahoe over the last decades; however, the diatom community structure changed. Increased stratification and reduced nitrogen to phosphorus ratios selected for small-celled diatoms, particularly within the Cyclotella genus. An empirical model showed that a shift in phytoplankton species composition and cell size was consistent within different depth strata, indicating that altered nutrient concentrations were not responsible for the change. The increase in small-celled species was sufficient to decrease the average diatom size and thus sinking velocity, which strongly influences energy transfer through the food web and carbon cycling. Our results show that within the diverse group of diatoms, small-sized species with a high surface area to volume ratio were able to adapt to a decrease in mixing intensity, supporting the hypotheses that abiotic drivers affect the size structure of planktonic communities and that warmer climate favours small-sized diatom cells.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1098/rspb.2008.1200
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Disrupted seasonal clockwork in the population dynamics of a freshwater copepod by climate warming (2009)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 54 (6). pp. 2493-2505.
    Details
    Publication Date: 2014-01-30
    Description: Life history responses are expected to accompany climate warming, yet little is known how long-term effects of climate and environmental change affect the seasonal dynamics of planktonic organisms. We used an historical data set from Lake Washington (U.S.A.) to quantify population responses of a calanoid copepod (Leptodiaptomus ashlandi) to long-term changes in temperature and resource availability and explore potential mechanisms for the responses. Increasing water temperatures (annual mean increase of 1.5 degrees C in the upper 10-m water volume) and longer stratification periods (about 4 weeks) were observed between 1962 and 2005, coincident with a pronounced decline in Leptodiaptomus densities. However, production was maintained because of an increase in the production to biomass ratio and a life cycle shift in Leptodiaptomus from an annual to a 6-month cycle. Cross-wavelet analyses demonstrated that the annual thermal forcing of copepod recruitment observed during the first two decades of the study weakened substantially, leading to more stochastic population dynamics during the past two decades. This shift from one to two generations per year was most likely produced by a longer and warmer growing period combined with changing fluctuations in resource (phytoplankton) availability. Climate change can lead to higher-frequency voltinism in ectothermic organisms and to temporal reorganization of their population dynamics.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lo.2009.54.6_part_2.2493
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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