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Determining the F-Ratio

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Determining the F-Ratio 11/16/2010 Plankton production is supported by 2 types of nitrogen: The f‐ratio 1) new production supported by external sources of N (e.g. NO ‐ and N ), Assumptions: 3 2 ‐ ‐ 2) recycled or regenerated production, sustained by recycling of N. 1) N2 fixation is low f = (VNO3 )/ (VNO3 + ∑VNR) 2) Steady state system 3) Euphotic zone nitrification is low Note NR includes regenerated forms of N N uptake (historically thought to include 2 + urea and NH4 ) regenerated Biological + MthMathema tiltical ditidescription linki ng new NH4 production production and organic matter export. At steady state, nitrogen input is balanced by export nitrogen export. ‐ NO3 Under steady state (i.e. nitrate input balanced by export/grazing loss), if export NO ‐ NH + is less than input, biomass accumulates. NO ‐ 2 4 N export This biomass must eventually be exported 3 to keep the system in steady state. ‐Why does this generalization apply to the open sea but not near shore environments? Determining the f‐ratio • Incubate seawater in the presence of trace 15 ‐ 15 + 15 NO3 , NH4 , and sometimes N‐urea 15N • Calculate NO3‐, NH4+, and “DON” uptake 15N • What makes this difficu lt for the oligotrop hic 15N ocean? Net Uptake 15N 1 11/16/2010 Autonomous sensing of nitrate 2 11/16/2010 Not all “new” nutrients are introduced to the euphotic zone from below… • Atmospheric deposition (both dry and wet) Johnson et al. (2010) Nature can form an important source of nutrients. • Advection: lateral input of nutrients • N2 fixation Assimilation of N by N2 fixation • N2 fixation is the primary mode of nitrogen introduction to marine and terrestrial ecosystems. • N2 fixation converts N2 to NH3; exclusively prokaryotic process • Requires significant energy expensive 3 11/16/2010 Each annual cycle at HOT and BATS has significant Dissolved At Station ALOHA, N Inorganic Carbon 2 (DIC) drawdown, fixation appears to but not enough contribute ~30‐84% of nitrate is present new production in surface water to support growth. 8 NO 6 3‐ from Karl et al. in 4 Fasham, Ocean (‰) 2 Biogeochemistry 0 N particulate N export N2 15 -2 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 Year Let’s look at dissimilatory nitrogen transformations Oxidized N Energy to be gained in oxidation Reduced N Global estimate of N2 fixation based on N‐DIC drawdown in NO3‐ depleted warm waters is equivalent to 0.8 0.3 Pg C yr‐1 (Sarmiento & Gruber, 2006) 4 11/16/2010 Nitrification Dissimilatory nitrogen transformations - •Biological oxidation of NH3 to NO3 using oxygen as terminal electron acceptor. NH2OH → NO → N2O + - - Nitrification: NH4 → NO2 → NO3 •Two step process; ammonia oxidation fllfollowe dbd by n itititrite ox idtiidation; bthboth reactions yield energy. - - Denitrification: NO3 → NO2 → NO → N2O → N2 - •NO2 serves as an important intermediate; incomplete nitrification also + Anammox: NO2 + NH4 → N2 + 2H2O yields N2O. Aerobic regeneration of nitrogen Complete decomposition of organic matter (CH2O)106(NH3)16H3PO4 + 138O2 106CO2 + 122H2O +16HNO3 + H3PO4 + Degradation of organic N to Multi-step process. First step is the breakdown of amino acids to NH4 ; this process ammonium occurs during is mediated by heterotrophic microorganisms heterotrophic metabolism. Nitrification: 2NH + + 3O 2NO - + 4H+ + 2H O Nitrification is a 2 step 4 2 2 2 predominately mediated by ppyrocess that is mediated by - - chemoautotrophic microbes 2NO2 +O+ O2 2NO3 different groups of (best studied are microbes. The first step These reactions yield energy (but not much…) Nitrosomonas and Nitrobacter) (termed ammonium + oxidation) oxidizes NH4 to - NO2 , and the second step - - converts NO2 to NO3 . 5 11/16/2010 Recent isolation and cultivation of an abundant archaeal ammonium oxidizer Archaea 20- 40% of total picoplankton in meso- and bathypelagic waters 0 Let’s look at dissimilatory nitrogen transformations 1000 Oxidized N 2000 Pacific Atlantic Depth (m) 3000 4000 Energy to be 0 1020304050 gained in NO - + NO - (mol L-1) 3 2 oxidation Reduced N (Sarmiento & Gruber, 2006) 6 11/16/2010 Denitrification Anaerobic ammonium oxidation - - The reduction of NO3 and NO2 to N2 during heterotrophic respiration of (anammox) organic matter. Occurs predominately in anaerobic or suboxic environments. + - • NH4 + NO2 2N2 + 2H2O - C106H175O42N16P + 104 NO3 106CO2 + 60N2 + H3PO4 +138 H2O • Anaerobic ammonium oxidation • Major source of N gas - - 2 NO3 and NO2 are (along with denitrification) used as terminal electron acceptors during heterotrophic • Anoxic sediments, marine respiration. water column, and sewage wastewater • Mediated by Planctomyces Oxygen concentrations along the 26.9 kg m-3 isopycnal surface (~500 m in the N. Pacific) High productivity in surface water due to upwelling of nutrients. High organic matter flux depletes O2 concentrations below the euphotic zone. Chlorophyll distributions 7 11/16/2010 Global Nitrogen Budget Process Nitrogen Flux (TgN yr-1) Sources Pelagic N fixation 120 50 N input by N2 Losses of N by 2 fixation denitrification Benthic N2 fixation 15 10 Atmosphere N2 N2 N2O River input (DON) 35 10 River input (PON) 45 10 Photosynthesis Atmospheric deposition 50 20 TtlSTotal Sources 265 55 Bacterial Nitrification - Organic NO2 degradation NH + - Sinks matter 4 NO3 Organic N export 1 N O 2 Benthic denitrification 180 50 Aerobic Suboxic Water column denitrification 65 20 Denitirifcation N2O Sediment burial 25 10 Bacterial + N O loss to atmosphere 4 2 Detritus NH 2 degradation 4 N 2 Total Sinks 275 55 1 Tg = 1012 g 8.
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