A comparison of system (02 and C02) and C-14 measurements of metabolism in estuarine mesocosms

Abstract

Metabolism in estuarine mesocosms was measured by total system oxygen and carbon dioxide and by C-14 bottle incubations to determine the effects of nutrient enrichment (6 levels) over a 9 mo period. These data provided an unprecedented opportunity for calculating metabolic ratios and determining the impact of other system processes. System metabolism ratios based on daily data varied from 0 to 5.0. System metabolism ratios of P.Q. and R Q. based on integrated data were highly correlated (r = 0.95 to 0.96) and similar to traditional ratios obtained in phytoplankton studies. A system photosynthetic quotient of 1.2 and a system respiratory quotient of 1.1 were calculated from the integrated data. These ratios were only slightly affected by carbon dioxide diffusion and 3 benthic processes: denitrification, sulfur metabolism and calcium carbonate dissolution. There was no trend for system metabolism ratios up the nutrient gradient. The C-14 estimations of productivity appeared nitrogen limited in the lower nutrient treatments and provided lower estimates than the 2 system measures of production

Magnitude and regulation of bacterioplankton respiratory quotient across freshwater environmental gradients

“…In line with the often assumed bacterial use of relatively reduced phytoplanktonic compounds , marine studies on plankton RQs have generally reported values slightly below, or around, 1 (Hopkinson, 1985;Oviatt et al, 1986;Berdalet et al, 1995;Robinson et al, 2002) (P del Giorgio, unpublished). Although high RQ might be physiologically explained by biogeochemical pathways of DOC degradation, it is not obvious how the community-level RQ could rise to values as high as 2 in response to cell biochemistry.…”

“…Alkalinity was calculated from in situ pH, dissolved inorganic carbon (measured using the IO Analytical TIC/TOC Analyzer) and temperature. The equilibration constants, in combination with alkalinity and incubation pCO 2 , was used to calculate the pH at each incubation time point, assuming constant alkalinity and that no other process other than CO 2 production caused changes in pH (Oviatt et al, 1986). As the respiratory CO 2 affects pH though a feedback loop involving changed ionization fractions, the incubation pH was not algebraically calculated, but solved iteratively using the 'Solver' module in Excel 2007.…”

“…There have been a handful of studies of marine RQ (Oviatt et al, 1986;Robinson et al, 2002), but to our knowledge, only one study targeting the RQ of natural freshwater bacterioplankton (Cimbleris and Kalff, 1998). Because of the lack of data on either the magnitude or the patterns of variability in ambient bacterial RQs, studies to date have applied fixed RQs in the range of 0.7-1.2 based on more or less arbitrary assumptions.…”

Nutrient cycling in the water column of a subtropical seagrass meadow

“…Consumption of dissolved oxygen in dark incubations during the daytime were added to the value for light incubations to obtain estimates of gross primary production. Water column gross primary production and respiration rates based on O2 were converted to units of carbon using photosynthesis and respiration quotients of 1.2 and 1.0, respectively (Oviatt et al 1986). …”

The influence of incubation periods on photosynthesis–irradiance curves

“…Laws (1991) suggested a PQ of 1.1F0.1 for growth on ammonia and a PQ of 1.4F0.1 for growth on nitrate. However, apparent PQ's substantially higher than expected from considerations of the N source assimilated by phytoplankton have been frequently measured, for instance, Oviatt et al (1986) estimated PQ values as high as 5.0 and Iriarte et al (1996) obtained a mean PQ of 2.2. In this study, a somewhat more standard PQ value of 1.2 was used according to Vollenweider (1974), Geider andOsborne (1989) and Laws (1991).…”