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Mass flux calculations show strong allochthonous support of freshwater zooplankton production is unlikely.

Brett MT, Arhonditsis GB, Chandra S, Kainz MJ - PLoS ONE (2012)

Bottom Line: Lakes with high loading of t-DOC also have high hydraulic flushing rates.Because t-DOC is processed, i.e., mineralized or lost to the sediments, in lakes at ≈ 0.1% d(-1), in systems with the highest t-DOC inputs (i.e., 1000 mg m(-2) d(-1)) a median of 98% of the t-DOC flux is advected and therefore is not available to support zooplankton production.Further, advection is the primary fate of t-DOC in lakes with hydraulic retention times <3 years.

View Article: PubMed Central - PubMed

Affiliation: Department of Civil and Environment Engineering, University of Washington, Seattle, Washington, United States of America. mtbrett@uw.edu

ABSTRACT
Many studies have concluded terrestrial carbon inputs contribute 20-70% of the carbon supporting zooplankton and fish production in lakes. Conversely, it is also known that terrestrial carbon inputs are of very low nutritional quality and phytoplankton are strongly preferentially utilized by zooplankton. Because of its low quality, substantial terrestrial support of zooplankton production in lakes is only conceivable when terrigenous organic matter inputs are much larger than algal production. We conducted a quantitative analysis of terrestrial carbon mass influx and algal primary production estimates for oligo/mesotrophic lakes (i.e., TP ≤ 20 µg L(-1)). In keeping with the principle of mass conservation, only the flux of terrestrial carbon retained within lakes can be utilized by zooplankton. Our field data compilation showed the median (inter-quartile range) terrestrial particulate organic carbon (t-POC), available dissolved organic carbon (t-DOC) inputs, and in-lake bacterial and algal production were 11 (8-17), 34 (11-78), 74 (37-165), and 253 (115-546) mg C m(-2) d(-1), respectively. Despite the widespread view that terrestrial inputs dominate the carbon flux of many lakes, our analysis indicates algal production is a factor 4-7 greater than the available flux of allochthonous basal resources in low productivity lakes. Lakes with high loading of t-DOC also have high hydraulic flushing rates. Because t-DOC is processed, i.e., mineralized or lost to the sediments, in lakes at ≈ 0.1% d(-1), in systems with the highest t-DOC inputs (i.e., 1000 mg m(-2) d(-1)) a median of 98% of the t-DOC flux is advected and therefore is not available to support zooplankton production. Further, advection is the primary fate of t-DOC in lakes with hydraulic retention times <3 years. When taking into account the availability and quality of terrestrial and autochthonous fluxes, this analysis indicates ≈ 95-99% of aquatic herbivore production is supported by in-lake primary production.

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The influence of t-DOC loading and retention on absolute and available t-DOC fluxes.The absolute t-DOC loading values are from Fig. 2B. The available t-DOC flux was calculated as the absolute flux multiplied by the corresponding in-lake t-DOC retention from Fig. 2C, i.e., (areal t-DOC loading)*(σ/(σ + ρ)).
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pone-0039508-g003: The influence of t-DOC loading and retention on absolute and available t-DOC fluxes.The absolute t-DOC loading values are from Fig. 2B. The available t-DOC flux was calculated as the absolute flux multiplied by the corresponding in-lake t-DOC retention from Fig. 2C, i.e., (areal t-DOC loading)*(σ/(σ + ρ)).

Mentions: Our conclusion that much of the t-DOC input to short HRT lakes is advected downstream is extremely important for the zooplankton allochthony hypothesis [1]–[5], because it is only the flux of t-DOC retained within lakes that may have been used to support food web processes. If the total t-DOC flux is corrected for retention, the mass flux of t-DOC that is removed in-lake is obtained (Fig. 3). This results in a factor ≈10 lower estimate of t-DOC availability, i.e., 303 (80–1420) versus 34 (11–78) mg C m−2 d−1 (Fig. 3), because the lakes with the highest t-DOC loading rates also have very low removal (Fig. 2D). In fact, after accounting for removal, the available flux in the 32% of cases with absolute t-DOC loading greater than 1000 mg C m−2 d−1 declined from a median of 2661 (1552–7249) mg C m−2 d−1 to only 55 (23–137) mg C m−2 d−1, indicating 98% of t-DOC is advected from the lakes with the highest areal t-DOC loading rates. Terrestrially derived DOC that is removed in-lake may be photochemically degraded, flocculated and subsequently sedimented, or metabolized by bacteria to produce greenhouse gases (CO2 or CH4), or new cells [30]. However, the growth efficiency of bacteria utilizing t-DOC is very low [29] and both t-DOC derived flocs and bacteria are likely very low nutritional quality resources for zooplankton [6], [18], [19]. These mass flux calculations also indicate the total flux of available terrestrial inputs will be approximately a factor 4–7 smaller than rates of algal primary production in typical oligo/mesotrophic lakes; i.e., 48 (26–89) mg C m−2 d−1 vs 253 (115–546) mg C m−2 d−1, respectively. Conversely, del Giorgio and Peters [37] challenged the traditional phytoplankton photosynthesis paradigm in limnology and concluded that in the oligotrophic and mesotrophic systems they sampled, phytoplankton production was often only a minor fraction of whole lake carbon metabolism. These different conclusions were mainly because del Giorgio and Peters [37] assumed all of their lakes had input t-DOC concentrations of 24 mg C L−1 based on watershed carbon yields [44], whereas our meta-analysis of temperate and boreal streams indicated concentrations of 11.1±7.4 mg C L−1. del Giorgio and Peters’ high assumed input t-DOC concentration increased their reported available t-DOC flux, and the t-DOC degradation rate derived from their data, by a factor of 3.5±0.7. If the results of their study are recalculated with 11.1 mg L−1 as the input t-DOC concentration, t-DOC metabolism as a percent of phytoplankton production for their lakes declines from 139% (95–275%) to 37% (29–93%).


Mass flux calculations show strong allochthonous support of freshwater zooplankton production is unlikely.

Brett MT, Arhonditsis GB, Chandra S, Kainz MJ - PLoS ONE (2012)

The influence of t-DOC loading and retention on absolute and available t-DOC fluxes.The absolute t-DOC loading values are from Fig. 2B. The available t-DOC flux was calculated as the absolute flux multiplied by the corresponding in-lake t-DOC retention from Fig. 2C, i.e., (areal t-DOC loading)*(σ/(σ + ρ)).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3383696&req=5

pone-0039508-g003: The influence of t-DOC loading and retention on absolute and available t-DOC fluxes.The absolute t-DOC loading values are from Fig. 2B. The available t-DOC flux was calculated as the absolute flux multiplied by the corresponding in-lake t-DOC retention from Fig. 2C, i.e., (areal t-DOC loading)*(σ/(σ + ρ)).
Mentions: Our conclusion that much of the t-DOC input to short HRT lakes is advected downstream is extremely important for the zooplankton allochthony hypothesis [1]–[5], because it is only the flux of t-DOC retained within lakes that may have been used to support food web processes. If the total t-DOC flux is corrected for retention, the mass flux of t-DOC that is removed in-lake is obtained (Fig. 3). This results in a factor ≈10 lower estimate of t-DOC availability, i.e., 303 (80–1420) versus 34 (11–78) mg C m−2 d−1 (Fig. 3), because the lakes with the highest t-DOC loading rates also have very low removal (Fig. 2D). In fact, after accounting for removal, the available flux in the 32% of cases with absolute t-DOC loading greater than 1000 mg C m−2 d−1 declined from a median of 2661 (1552–7249) mg C m−2 d−1 to only 55 (23–137) mg C m−2 d−1, indicating 98% of t-DOC is advected from the lakes with the highest areal t-DOC loading rates. Terrestrially derived DOC that is removed in-lake may be photochemically degraded, flocculated and subsequently sedimented, or metabolized by bacteria to produce greenhouse gases (CO2 or CH4), or new cells [30]. However, the growth efficiency of bacteria utilizing t-DOC is very low [29] and both t-DOC derived flocs and bacteria are likely very low nutritional quality resources for zooplankton [6], [18], [19]. These mass flux calculations also indicate the total flux of available terrestrial inputs will be approximately a factor 4–7 smaller than rates of algal primary production in typical oligo/mesotrophic lakes; i.e., 48 (26–89) mg C m−2 d−1 vs 253 (115–546) mg C m−2 d−1, respectively. Conversely, del Giorgio and Peters [37] challenged the traditional phytoplankton photosynthesis paradigm in limnology and concluded that in the oligotrophic and mesotrophic systems they sampled, phytoplankton production was often only a minor fraction of whole lake carbon metabolism. These different conclusions were mainly because del Giorgio and Peters [37] assumed all of their lakes had input t-DOC concentrations of 24 mg C L−1 based on watershed carbon yields [44], whereas our meta-analysis of temperate and boreal streams indicated concentrations of 11.1±7.4 mg C L−1. del Giorgio and Peters’ high assumed input t-DOC concentration increased their reported available t-DOC flux, and the t-DOC degradation rate derived from their data, by a factor of 3.5±0.7. If the results of their study are recalculated with 11.1 mg L−1 as the input t-DOC concentration, t-DOC metabolism as a percent of phytoplankton production for their lakes declines from 139% (95–275%) to 37% (29–93%).

Bottom Line: Lakes with high loading of t-DOC also have high hydraulic flushing rates.Because t-DOC is processed, i.e., mineralized or lost to the sediments, in lakes at ≈ 0.1% d(-1), in systems with the highest t-DOC inputs (i.e., 1000 mg m(-2) d(-1)) a median of 98% of the t-DOC flux is advected and therefore is not available to support zooplankton production.Further, advection is the primary fate of t-DOC in lakes with hydraulic retention times <3 years.

View Article: PubMed Central - PubMed

Affiliation: Department of Civil and Environment Engineering, University of Washington, Seattle, Washington, United States of America. mtbrett@uw.edu

ABSTRACT
Many studies have concluded terrestrial carbon inputs contribute 20-70% of the carbon supporting zooplankton and fish production in lakes. Conversely, it is also known that terrestrial carbon inputs are of very low nutritional quality and phytoplankton are strongly preferentially utilized by zooplankton. Because of its low quality, substantial terrestrial support of zooplankton production in lakes is only conceivable when terrigenous organic matter inputs are much larger than algal production. We conducted a quantitative analysis of terrestrial carbon mass influx and algal primary production estimates for oligo/mesotrophic lakes (i.e., TP ≤ 20 µg L(-1)). In keeping with the principle of mass conservation, only the flux of terrestrial carbon retained within lakes can be utilized by zooplankton. Our field data compilation showed the median (inter-quartile range) terrestrial particulate organic carbon (t-POC), available dissolved organic carbon (t-DOC) inputs, and in-lake bacterial and algal production were 11 (8-17), 34 (11-78), 74 (37-165), and 253 (115-546) mg C m(-2) d(-1), respectively. Despite the widespread view that terrestrial inputs dominate the carbon flux of many lakes, our analysis indicates algal production is a factor 4-7 greater than the available flux of allochthonous basal resources in low productivity lakes. Lakes with high loading of t-DOC also have high hydraulic flushing rates. Because t-DOC is processed, i.e., mineralized or lost to the sediments, in lakes at ≈ 0.1% d(-1), in systems with the highest t-DOC inputs (i.e., 1000 mg m(-2) d(-1)) a median of 98% of the t-DOC flux is advected and therefore is not available to support zooplankton production. Further, advection is the primary fate of t-DOC in lakes with hydraulic retention times <3 years. When taking into account the availability and quality of terrestrial and autochthonous fluxes, this analysis indicates ≈ 95-99% of aquatic herbivore production is supported by in-lake primary production.

Show MeSH
Related in: MedlinePlus