Zooplankton Assemblages in Crater Lake, Oregon, USA

Larson, Gary L.; McIntire, C. David; Truitt, Robert E.; Buktenica, Mark W.; Karnaugh-Thomas, Elena

doi:10.1080/07438149609354073

Cited by 14 publications

(13 citation statements)

References 38 publications

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“…Research on underwater UVR and its potential for biological impact has increased in response to concerns about depletion of stratospheric ozone and climate change (Schindler & Curtis, 1997;Pienitz & Vincent, 2000). Several reports on the distribution of organisms in Crater Lake suggest a possible inhibitory role for UVR (McIntire et al, 1994;McIntire et al, 1996;Larson et al, 1996b), especially above 40 m. UVR measurements in Crater Lake resumed in 1996 when a submersible wavelength-scanning radiometer (300-800 nm) was added to the monitoring program and used to acquire incident and underwater solar spectra at a range of depths. Visiting scientists made additional optical measurements in UV and visible wavelengths starting in 1999.…”

Section: Introductionmentioning

confidence: 96%

Ultraviolet radiation and bio-optics in Crater Lake, Oregon

et al. 2007

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Crater Lake, Oregon, is a mid-latitude caldera lake famous for its depth (594 m) and blue color. Recent underwater spectral measurements of solar radiation (300-800 nm) support earlier observations of unusual transparency and extend these to UV-B wavelengths. New data suggest that penetration of solar UVR into Crater Lake has a significant ecological impact. Evidence includes a correlation between water column chlorophyll-a and stratospheric ozone since 1984, the scarcity of organisms in the upper water column, and apparent UV screening pigments in phytoplankton that vary with depth. The lowest UV-B diffuse attenuation coefficients (K d,320 ) were similar to those reported for the clearest natural waters elsewhere, and were lower than estimates for pure water published in 1981. Optical proxies for UVR attenuation were correlated with chlorophyll-a concentration (0-30 m) during typical dry summer months from 1984 to 2002. Using all proxies and measurements of UV transparency, decadal and longer cycles were apparent but no long-term trend since the first optical measurement in 1896.

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Section: Introductionmentioning

confidence: 96%

Ultraviolet radiation and bio-optics in Crater Lake, Oregon

et al. 2007

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“…7). Some zooplankton species in Crater Lake exhibit diel vertical migrations with displacements between 20 and 40 m (Larson et al 1993(Larson et al , 1996b. This behavior is not easily accounted for in the model but may explain the apparent discrepancy in vertical structure between simulated and observed zooplankton.…”

Section: Resultsmentioning

confidence: 86%

Section: Limnological Datamentioning

confidence: 99%

“…Zooplankton were diluted with pre-filtered lake water, preserved with 4% formaldehyde/4% sucrose, concentrated by gravity settling (24 h), and counted by means of inverted microscopy (Larson et al, 1996b). Zooplankton weight conversion factors were estimated for each taxon from dried animals and used to convert organism densities to dry weight biomass (Larson et al, 1993). Here we converted from dry weight to biomass in units of carbon and nitrogen assuming that carbon constituted 48\% and nitrogen 10% of dry weight respectively (Andersen & Hessen 1991;Brett et al, 2000).…”

Section: Limnological Datamentioning

confidence: 99%

“…The populations of microorganisms show distinct vertical maxima during stratified conditions (McIntire et al, 1996;Larson et al, 1996b;Urbach et al, 2001). In July and August, diatoms and dinoflagellates reach their maximum biomass in the upper 20 m of the water column, isolated from below by a pronounced thermocline.…”

Section: Introductionmentioning

confidence: 99%

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Seasonal nutrient and plankton dynamics in a physical-biological model of Crater Lake

et al. 2007

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A coupled 1D physical-biological model of Crater Lake is presented. The model simulates the seasonal evolution of two functional phytoplankton groups, total chlorophyll, and zooplankton in good quantitative agreement with observations from a 10-year monitoring study. During the stratified period in summer and early fall the model displays a marked vertical structure: the phytoplankton biomass of the functional group 1, which represents diatoms and dinoflagellates, has its highest concentration in the upper 40 m; the phytoplankton biomass of group 2, which represents chlorophyta, chrysophyta, cryptomonads and cyanobacteria, has its highest concentrations between 50 and 80 m, and phytoplankton chlorophyll has its maximum at 120 m depth. A similar vertical structure is a reoccurring feature in the available data. In the model the key process allowing a vertical separation between biomass and chlorophyll is photoacclimation. Vertical light attenuation (i.e., water clarity) and the physiological ability of phytoplankton to increase their cellular chlorophyll-to-biomass ratio are ultimately determining the location of the chlorophyll maximum. The location of the particle maxima on the other hand is determined by the balance between growth and losses and occurs where growth and losses equal.The vertical particle flux simulated by our model agrees well with flux measurements from a sediment trap. This motivated us to revisit a previously published study by Dymond et al. (1996). Dymond et al. used a box model to estimate the vertical particle flux and found a discrepancy by a factor 2.5-10 between their model-derived flux and measured fluxes from a sediment trap. Their box model neglected the exchange flux of dissolved and suspended organic matter, which, as our model

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