A large fraction of aquatic metabolism is attributable to picoplankton ($$2 and $$20 and $<$20... more A large fraction of aquatic metabolism is attributable to picoplankton ($$2 and $$20 and $<$200 $\mu$m) protozoa were abundant (average carbon 40.5 and 16.2 $\mu$g C liter$\sp{-1}$). Community composition of both nano- and micro- protozoan was skewed towards the small end of the size spectrum by the prevalence of small chrysomonads and spirotrichs (average size 3.3 and 20.6 $\mu$m, respectively). Heterotrophic protozoan biomass (heterotrophic nanoflagellates and ciliates) was more than 70% of crustacean zooplankton biomass, while phototrophic protozoa (phototrophic nano- and micro-flagellates) constituted nearly 50% of phytoplankton biomass. Also, phototrophic protozoan carbon production contributed nearly 25% of total phytoplankton production, whereas daily heterotrophic protozoan production was large enough to consume 135% (assuming 30% assimilation) of bacterial production. Nano- and micro- protozoa also appear to be significant prey items for macrozooplankton in Lake Michigan. Clearance rates (3.5 and 2.5 ml $\mu$g dry wt. liter$\sp{-1}$ $\rm d\sp{-1}$, respectively) were high, with little evidence for grazing among protozoa. These findings show that protozoan production is important in Lake Michigan (11 $\mu$g C liter$\sp{-1}$) and a substantial fraction of this production is being consumed by macrozooplankton (66%). Given this, picoplankton carbon in Lake Michigan may be more directly transferred to higher trophic levels via a picoplankton-flagellate-zooplankton link, compared with the less efficient picoplankton-flagellate-ciliate-zooplankton link proposed for oligotrohic marine systems.Ph.D.Natural ResourcesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/103272/1/9034396.pdfDescription of 9034396.pdf : Restricted to UM users only
Biofilms generally account for the majority of P assimilation in streams. However, relatively few... more Biofilms generally account for the majority of P assimilation in streams. However, relatively few direct measurements have been made that link nutrient loadings to biofilm assimilation. We measured P uptake rates for natural benthic biofilms sampled from 8 streams situated along a productivity gradient in the mid-Atlantic region, where point-source nutrient loadings were applied with an in situ enrichment system (ISES). ISES consisted of vials spiked with increasing concentrations of P with and without N. Short-term radiotracer (H333PO4) experiments were conducted to measure P uptake by biofilms growing on the surface of the vials collected from the streams. The relationship between P uptake and P loading in each stream was explained using simple linear regression. In all streams, P uptake rates declined with increased experimental P loading and as a function of stream productivity. Biofilms had significantly higher uptake rates overall in low- vs high-productivity streams (1.29 and 0.84 log10[nmol P μg−1 chlorophyll d−1], respectively) (F1,30 = 6.21, p = 0.018). These results indicated that assemblages in low-productivity streams were physiologically adapted to use new P additions, whereas biofilms in productive streams showed signs of P saturation such that these assemblages had reduced demand for new P loadings. N loading synergistically affected biofilm P uptake ability in high-productivity streams, where N appeared to have been a secondarily limiting nutrient. Our work emphasizes that P uptake was heterogeneous across landscapes. P-saturation was common in high-productivity streams (embedded in agriculturally dominated watersheds) and was mediated by N-enrichment and nutrient stoichiometry.
Lake chemistry is influenced by land use in the surrounding watershed, particularly in complex ur... more Lake chemistry is influenced by land use in the surrounding watershed, particularly in complex urban landscapes, which are commonly subjected to an increase in material loadings. Because land use is rarely uniform, individual ecosystems embedded within the landscape may reflect varying water quality conditions. The Lake Merced system is composed of three lake basins with watersheds (surface area = 13
... in Antarctic and subantarctic freshwaters SARAH A. SPAULDING, BART VAN DE VUVER,DOMINIC A. HO... more ... in Antarctic and subantarctic freshwaters SARAH A. SPAULDING, BART VAN DE VUVER,DOMINIC A. HODGSON, DIANE M. MCKNIGHT, ELIE VERLEYEN, AND LEE STANISH ... South Orkney.. // Schirmacher'Qasis Islands' _,Q~:r.;:~ lies Crozet - II~ Kerguelen Heard Island-...
A large fraction of aquatic metabolism is attributable to picoplankton ($$2 and $$20 and $<$20... more A large fraction of aquatic metabolism is attributable to picoplankton ($$2 and $$20 and $<$200 $\mu$m) protozoa were abundant (average carbon 40.5 and 16.2 $\mu$g C liter$\sp{-1}$). Community composition of both nano- and micro- protozoan was skewed towards the small end of the size spectrum by the prevalence of small chrysomonads and spirotrichs (average size 3.3 and 20.6 $\mu$m, respectively). Heterotrophic protozoan biomass (heterotrophic nanoflagellates and ciliates) was more than 70% of crustacean zooplankton biomass, while phototrophic protozoa (phototrophic nano- and micro-flagellates) constituted nearly 50% of phytoplankton biomass. Also, phototrophic protozoan carbon production contributed nearly 25% of total phytoplankton production, whereas daily heterotrophic protozoan production was large enough to consume 135% (assuming 30% assimilation) of bacterial production. Nano- and micro- protozoa also appear to be significant prey items for macrozooplankton in Lake Michigan. Clearance rates (3.5 and 2.5 ml $\mu$g dry wt. liter$\sp{-1}$ $\rm d\sp{-1}$, respectively) were high, with little evidence for grazing among protozoa. These findings show that protozoan production is important in Lake Michigan (11 $\mu$g C liter$\sp{-1}$) and a substantial fraction of this production is being consumed by macrozooplankton (66%). Given this, picoplankton carbon in Lake Michigan may be more directly transferred to higher trophic levels via a picoplankton-flagellate-zooplankton link, compared with the less efficient picoplankton-flagellate-ciliate-zooplankton link proposed for oligotrohic marine systems.Ph.D.Natural ResourcesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/103272/1/9034396.pdfDescription of 9034396.pdf : Restricted to UM users only
Biofilms generally account for the majority of P assimilation in streams. However, relatively few... more Biofilms generally account for the majority of P assimilation in streams. However, relatively few direct measurements have been made that link nutrient loadings to biofilm assimilation. We measured P uptake rates for natural benthic biofilms sampled from 8 streams situated along a productivity gradient in the mid-Atlantic region, where point-source nutrient loadings were applied with an in situ enrichment system (ISES). ISES consisted of vials spiked with increasing concentrations of P with and without N. Short-term radiotracer (H333PO4) experiments were conducted to measure P uptake by biofilms growing on the surface of the vials collected from the streams. The relationship between P uptake and P loading in each stream was explained using simple linear regression. In all streams, P uptake rates declined with increased experimental P loading and as a function of stream productivity. Biofilms had significantly higher uptake rates overall in low- vs high-productivity streams (1.29 and 0.84 log10[nmol P μg−1 chlorophyll d−1], respectively) (F1,30 = 6.21, p = 0.018). These results indicated that assemblages in low-productivity streams were physiologically adapted to use new P additions, whereas biofilms in productive streams showed signs of P saturation such that these assemblages had reduced demand for new P loadings. N loading synergistically affected biofilm P uptake ability in high-productivity streams, where N appeared to have been a secondarily limiting nutrient. Our work emphasizes that P uptake was heterogeneous across landscapes. P-saturation was common in high-productivity streams (embedded in agriculturally dominated watersheds) and was mediated by N-enrichment and nutrient stoichiometry.
Lake chemistry is influenced by land use in the surrounding watershed, particularly in complex ur... more Lake chemistry is influenced by land use in the surrounding watershed, particularly in complex urban landscapes, which are commonly subjected to an increase in material loadings. Because land use is rarely uniform, individual ecosystems embedded within the landscape may reflect varying water quality conditions. The Lake Merced system is composed of three lake basins with watersheds (surface area = 13
... in Antarctic and subantarctic freshwaters SARAH A. SPAULDING, BART VAN DE VUVER,DOMINIC A. HO... more ... in Antarctic and subantarctic freshwaters SARAH A. SPAULDING, BART VAN DE VUVER,DOMINIC A. HODGSON, DIANE M. MCKNIGHT, ELIE VERLEYEN, AND LEE STANISH ... South Orkney.. // Schirmacher'Qasis Islands' _,Q~:r.;:~ lies Crozet - II~ Kerguelen Heard Island-...
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