Stream Ecology (NR 280) Topic 12 β Stream Metabolism Metabolism, Carbon, and Energy Dynamics Methods to Measure Stream Metabolism Large-scale processes affecting Organic Matter RECALL: Basis of using O2 or CO2 for measuring metabolism Energy Photosynthesis π₯πΆπ2 + π₯π»2 π π₯πΆπ»2 π + π₯π2 Respiration Energy Energy and carbon processing are linked Energy Photosynthesis π₯πͺπ2 + π₯π»2 π π₯πͺπ»2 π + π₯π2 Respiration Energy Energy is embodied in the carbohydrate βfuelβ that is food for the comsumer Review and Extension: What do we mean by βmetabolismβ? β’ Energy acquisition β anabolic processes β Greek: ana=upward , ballein=to throw β’ Energy use β catabolic processes β Greek: kata=downward , ballein=to throw What are the primary anabolic and catabolic processes in streams? β’ What is the primary anabolic process? β Photosynthesis β’ What are the primary catabolic processes? β Respiration (aerobic) β Fermentation (anaerobic) Metabolic Frameworks for Streams β’ Organic matter and energy budgets β’ Methods to measure stream metabolism β Litter bag experiments β Bottle/Chamber oxygen measurements β Isotopic methods β Whole-stream metabolism β’ The P/R ratio An important historical connection Energy vs Carbon Budgets β’ Organic matter is held together by various forms of C bonds β’ Energy is released when these bonds are broken (e.g., burning wood) β’ Energy release can be used a βcommon currencyβ to compare C fluxes in ecosystems β’ Allows comparison to other important energy fluxes, most notably sunlight input Carbon budget for beaverimpacted stream Naiman et al. (1986) Energy (vs C) Budgets in Streams Computed by wet dichromate digestion and calorimetric relationships of O2 consumption during Cr3+ production from the reaction of org-C with dichromate. Fisher and Likens (1973) Energy (OM) budget for Bear Brook, NH Fisher and Likens (1973) With this framework, how could we go about measuring metabolism? Energy Photosynthesis π₯πΆπ2 + π₯π»2 π π₯πΆπ»2 π + π₯π2 Respiration Energy Possible approaches to estimate metabolism β’ Gross disappearance of CH2O β Works well in some cases, e.g. litter bags β Not easy to measure accurately in whole streams β’ Net consumption/production of CO2 β Often used in terrestrial studies where measuring CO2 in air is easy β Less often used in aquatic studies where measuring CO2 in water is more laborious β Isotope studies; radioactive and stable β’ Net consumption/production of O2 β Easy and accurate to measure with DO probes β Can be directly related to C production/consumption The Litter Bag Study Gross Disappearance of OM Litter π₯πΆπ2 + π₯π»2 π π₯πΆπ»2 π + π₯π2 Respiration Energy Over time the mass lost from the litter (CH2O) is followed. Litter bag studies Litter bags deployed (R. Gomez, MIRAGE) Mark Harmon, HJ Andrews LTER http://research.eeescience.utoledo.edu/lees Effect of lignin:nitrogen on decomposition rate (k) Isotopic Tracer Methods Incorporation of 14C or 13C into biomass Energy Photosynthesis π₯13πΆπ2 + π₯π»2 π π₯13πΆπ»2 π + π₯π2 Either 14C (radioactive) or 13C (stable) can be used. Mass Spectrometry http://INSTAAR.colorado.edu http://SERC.carleton.edu http://watercenter.unl.edu Change in DO Methods Production of O2 implies fixation of C Energy Photosynthesis π₯πΆπ2 + π₯π»2 π π₯πΆπ»2 π + π₯π2 Respiration Energy Sensitive probes are now available that can measure DO continuously at low levels and save the data in loggers. Conversions between O2, CO2, and energy Note: The stoichiometry is not 1:1 because not everything is glucose. Many compounds (e.g. fats) have a different (higher) C:O ratio and so it takes more O2 to liberate all of C. πππΆ βπΆπ2 ππ πΆ = βπ2 β π π β πππ2 Note: Dissolved oxygen (DO) is usually measured in ppm or mg O2/L and so carbon dioxide ends up in mg C/L. Ξ = change in either CO2 or O2 RQ = respiratory quotient Moles of CO2 released per mole O2 consumed Suggested value = 0.85 Note: photosynthetic quotient would be 1.2 MW = molecular weight of C or O2 YSI ROX data sonde Fluorescent quenching to measure DO Thermo Scientific RDO Pro Sensor Background on measuring metabolism by the change in DO methods πππ = πΊππ β πΆπ or πππ = πΊππ + (βπΆπ ) Note that in this formulation CR is a positive number subtracted from GPP. Some people prefer CR to be a negative number (indicating consumption) as in the second equation. Either formula is correct; you just have to meticulously keep the signs straight. βLightβ bottle = NPP βDarkβ bottle = CR only Light bottle + Dark bottle = GPP Be careful of sign!! Whole-Stream Metabolism Fin Daytime FR Night time FR [DO] Stream Reach [DO] Stream Reach Psyn β[π·π]π·ππ¦ = βπ‘ ππ π¦π R R (πΉπ ) + ππ π¦π β π π β[π·π]π·ππ¦ = β βπ‘ ππ π¦π = Fout Fin (πΉπ ) + π π β[π·π]π·ππ¦ β[π·π]πππβπ‘ β βπ‘ βπ‘ β[π·π]πππβπ‘ = βπ‘ π = (πΉπ ) β π (πΉπ ) β π π β[π·π]πππβπ‘ βπ‘ NOTE: Sum of Fi ~ 0 ΞDO Ξ± ΞCO2 ΞDOnight < 0 Fout NEP in three stream types Mulholland et al. (2001) Daily GPP and CR Walker Branch, TN Metabolism as a function of key environmental variables Mulholland et al. (2001) The P/R Concept Cummins (1974) Longitudinal patterns in stream metabolism Regional patterns in P/R Webster and Meyers (1997) Carbon and energy sources to stream ecosystems The River Continuum Concept β’ Detritus is continually carried downstream and processed along the way. β’ CPOM becomes FPOM and FPOM becomes finer and more recalcitrant β’ Different food and habitat types create opportunities for different species. β’ Community structure changes in predictable ways associated with the organic matter present. β’ The system P/R ratios shift in a predictable pattern. β’ Applicable to undisturbed, canopydominated, temperate, forested streams in the eastern US. Extra Slides Recommended Further Reading Special Issue On Stream Organic Matter Budgets 1997 Jack Webster and Judy Meyer Calculating WSM
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