Respiratory quotients predict increases in reducing products in the hypolimnion of a stratified lake

1995 ◽  
Vol 52 (6) ◽  
pp. 1183-1189 ◽  
Author(s):  
Thomas E. Murray ◽  
Peter H. Rich
Keyword(s):  
Steady State ◽  
Respiratory Quotient ◽  
Inorganic Carbon ◽  
Anaerobic Metabolism ◽  
Dissolved Inorganic Carbon ◽  
Limited Extent ◽  
Stratified Lake ◽  
Benthic Respiration ◽  
Rate Of Increase ◽  
Reduced Products

The benthic respiration of Crystal Lake, Connecticut, was modeled with two respiratory quotients, the volumetric respiratory quotient (VRQ) and the fundamental respiratory quotient (FRQ). The VRQ is defined as the quotient of the increase in dissolved inorganic carbon (DIC) and the decrease in dissolved oxygen (DO) resulting from respiration at a given depth. Those changes are relative to concentrations determined early in spring. The FRQ is the slope of the regression of DIC against DO at all depths not chronically anoxic. Respiratory quotients describe the predominance of anaerobic over aerobic metabolism and should, therefore, predict the accumulation of the products of anaerobic metabolism (i.e., Fe2+, H2S). VRQs successfully predicted the increase in reduced products in the hypolimnion of Crystal Lake. FRQs successfully predicted the rate of increase of reduced products early in stratification. FRQ was unsuccessful in predicting the continued accumulation of reducing products later in the summer, which may reflect a steady state between the production of DIC and reduced products and the diffusion of oxygen across the thermocline, or may reflect methodological constraints imposed by the calculation of FRQ. Both models were successful to a limited extent in predicting the accumulation of the products of anaerobic metabolism.

scholarly journals On the Isotopic Composition of Dissolved Inorganic Carbon in Rivers and Shallow Groundwater: A Diagrammatic Approach to Process Identification and A More Realistic Model of the Open System

Radiocarbon ◽  
1997 ◽  
Vol 39 (3) ◽  
pp. 251-268 ◽  
Author(s):  
C. B. Taylor
Keyword(s):  
Steady State ◽  
New Zealand ◽  
Isotopic Composition ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Dynamic Balance ◽  
Shallow Groundwater ◽  
Realistic Model ◽  
Essential Information ◽  
Aquifer Systems

Rivers and shallow groundwater are deep groundwater precursors. Their dissolved inorganic carbon content (DIC) and its isotopic composition are end members in the evolution of these properties in confined situations, and are therefore essential information when applying carbon isotopes as tracers of groundwater processes and determining aquifer residence times using 14C.During studies of regional aquifer systems in New Zealand, a simple model has been developed to explain the isotopic compositions of DIC encountered in rivers and shallow groundwater. The model format incorporates a diagrammatic approach, providing a framework for tracing the subsequent evolution of DIC in both precipitation- and river-recharged aquifers under closed conditions.DIC concentration of rivers continuously adjusts toward chemical and isotopic equilibrium between direct addition of CO2 to the water (via plant respiration and decay of dead organic material) and exchange of CO2 across the river-air interface. In the shallow groundwater situation, the gaseous reservoir is soil CO2, generally at significantly higher partial pressure. In both cases, calcite dissolution or other processes may be an additional source of DIC directly added to the bicarbonate and dissolved CO2 components; while these may add or remove DIC, steady-state isotopic concentrations are considered to be determined only by the dynamic balance between directly added CO2 and gas exchange. This model allows the calculation of steady states, using selectable parameters in river or groundwater situations. These appear as straight lines in 13C or 14C vs. 1/DIC, or total 14C vs. DIC plots, into which the experimental data can be inserted for interpretation. In the case of 14C, the steady-state balance is very often complicated by the presence of an old component in the directly added DIC; the understanding achieved via the 13C patterns is helpful in recognizing this.Data from four contrasting aquifer systems in New Zealand. The success of the approach has depended crucially on DIC concentrations measured very accurately on the isotope samples, rather than separate chemical analyses.

A Survey of the 14C Content of Dissolved Inorganic Carbon in Chinese Lakes

Radiocarbon ◽  
2017 ◽  
Vol 60 (2) ◽  
pp. 705-716 ◽  
Author(s):  
Taibei Liu ◽  
Weijian Zhou ◽  
Peng Cheng ◽  
G S Burr
Keyword(s):  
Steady State ◽  
Simple Model ◽  
Residence Time ◽  
Surface Waters ◽  
Lake Water ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Water Cycle ◽  
Average Residence Time ◽  
Exchange Character

AbstractWe present radiocarbon (14C) measurements of dissolved inorganic carbon (DIC) from surface waters of 11 lakes, widely distributed in China. Surface lake water DIC F14C values show distinct differences, and we relate these to the physical exchange character (“open” or “closed”) of each lake. Open lakes studied here generally have lower DIC F14C values than closed lakes. We present a simple model of a lake water cycle to calculate an average residence time for each lake. Comparisons between lake DIC F14C and average residence time shows that the DIC F14C increases with the average residence time and reflects a steady-state.

scholarly journals The water column distribution of carbonate system variables at the ESTOC site from 1995 to 2004

2010 ◽  
Vol 7 (10) ◽  
pp. 3067-3081 ◽  
Author(s):  
M. González-Dávila ◽  
J. M. Santana-Casiano ◽  
M. J. Rueda ◽  
O. Llinás
Keyword(s):  
Carbon Dioxide ◽  
Time Series ◽  
Mixed Layer ◽  
Atmospheric Carbon Dioxide ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Total Alkalinity ◽  
Anthropogenic Co2 ◽  
Rate Of Increase ◽  
Atmospheric Carbon

Abstract. The accelerated rate of increase in atmospheric carbon dioxide and the substantial fraction of anthropogenic CO2 emissions absorbed by the oceans are affecting the anthropocenic signatures of seawater. Long-term time series are a powerful tool for investigating any change in ocean bio-geochemistry and its effects on the carbon cycle. We have evaluated the ESTOC (European Station for Time series in the Ocean at the Canary islands) observations of measured pH (total scale at 25 °C) and total alkalinity plus computed total dissolved inorganic carbon concentration (CT) from 1995 to 2004 for surface and deep waters, by following all changes in response to increasing atmospheric carbon dioxide. The observed values for the surface partial pressure of CO2 from 1995 to 2008 were also taken into consideration. The data were treated to better understand the fundamental processes controlling vertical distributions in the Eastern North Atlantic Ocean and the accumulation of anthropogenic CO2, CANT. CT at constant salinity, NCT, increased at a rate of 0.85 μmol kg−1 yr−1 in the mixed layer, linked to an fCO2 increase of 1.7±0.7 μatm yr−1 in both the atmosphere and the ocean. Consequently, the mixed layer at ESTOC site has also become more acidic, −0.0017±0.0003 units yr−1, whereas the carbonate ion concentrations and CaCO3 saturation states have also decreased over time. NCT increases at a rate of 0.53, 0.49 and 0.40 μmol kg−1 yr−1 at 300, 600, and 1000 m, respectively. The general processes controlling the vertical variations of alkalinity and the inorganic carbon distribution were computed by considering the pre-formed values, the production/decomposition of organic matter and the formation/dissolution of carbonates. At 3000 m, 30% of the inorganic carbon production is related to the dissolution of calcium carbonate, increasing to 35% at 3685 m. The total column inventory of anthropogenic CO2 for the decade was 66±3 mol m−2. A model fitting indicated that the column inventory of CANT increased from 61.7 mol m−2 in the year 1994 to 70.2 mol m−2 in 2004. The ESTOC site is presented as a reference site to follow CANT changes in the Northeast Atlantic Sub-tropical gyre.

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