T6 soil base cation weathering rates julian aherne :: trent university FORFLUX :: biogeochemistry of irish forests [RSF 07510] Advisory Group Meeting [5 6 December 2011]
objective (a) to determine the release of base cations (calcium, magnesium, potassium and sodium) from weathering at the Level IIi plots, and (b) to develop a simplified regional approach to estimate weathering rates. the promise (a) new measurements of soil mineralogy, total analysis and particle size analysis, and (b) test inference of soil mineralogy from total analysis at the Level IIi plots. the reality (a) analysed all mineral biosoil samples for total oxides [n = 85], (b) filled quantitative mineralogy gaps at Level IIi plots, (c) carried out direct estimates of soil surface area and particle size at Level IIi plots, and (d) applied a regional site specific approach to determine weathering rate for all biosoil plots weathering total oxide analysis and mineralogy weathering @ the sites
Level I and II Forflux Level II intensive
weathering is the physical and chemical breakdown (weathering) of rock and soil minerals and release of soil base cation (Ca 2+, Mg 2+, K + and Na + ) factors geology (mineralogy) of parent material, acidity of soil solution, temperature and surface reaction rates
the weathering rate top nine 1. skokloster assignment 2. soil type texture approximation 3. zirconium method 4. total base cation content correlation 5. PROFILE model 6. steady state water chemistry model 7. catchment mass balance 8. isotopic approaches 9. dynamic models
PROFILE multi layer steady state soil geochemical model widely used for the determination of weathering rates (Warfvinge and Sverdrup 1992). Key input data are quantitative soil mineralogy, soil surface area, bulk density and moisture (weathering reactions occur on the wetted mineral surface) mineralogy quantitative soil mineralogy is expensive [$$$], as such, data are available for only ~25 sites (including Level IIi [ballinastoe, brackloon, roundwood and ballyhooly]). However, normative procedures can be used to estimate idealised quantitative soil mineralogy based on the whole rock geochemistry of the soil (i.e., total analysis, which is cheap [$])
analysis to mineralogy (A2M) a computer program to determine, for given total chemical analyses, all possible mineral modes from an arbitrary but pre specified set of minerals (Posch and Kurz, 2007) total analysis for biosoils (analysis for all mineral soil layers). biosoil data [particle size, bulk density, etc] A2M weathering of base cations quantitative mineralogy PROFILE
step one send off soil samples for total oxide analysis (n ~ 85 samples, plots ~ 33, 1 4 mineral horizons per site) SiO2 Al2O3 Fe2O3 MnO MgO CaO K2O Na2O TiO2 Ballinastoe 49.9833 21.8467 5.1467 0.1000 0.7633 0.1033 3.8467 1.0233 1.3200 Brackloon 67.8700 10.8880 4.7320 0.0880 1.3440 0.3380 2.3360 1.2560 0.8540 Dromahaire 74.4954 7.1113 3.8998 0.1992 0.5463 0.1961 1.0005 0.1745 0.5905 Kilworth 73.2120 9.4000 4.1360 0.3120 0.6140 0.0100 2.7380 0.1600 0.7560 Mountrath 86.5025 3.7900 2.4275 0.0350 0.0925 0.0100 1.3500 0.0200 0.4150 Taughboy 54.3000 10.5067 6.0033 0.0367 0.8800 0.4633 2.3067 1.7200 0.5900 Thomastown 52.6700 13.3040 5.6700 0.0400 0.4420 0.0180 2.1700 0.4840 0.8400 step two determine the typical mineralogy for irish forest soils, based on available quantitative soil mineralogy (n ~25): quartz, muscovite (paragonite, Illite), chlorite, plagioclase (albite), k feldspar, rutile, hematite, kaolinite, calcite, dolomite
!FORFLUX minerals: Si Ti Al Fe2 Mn Ca Mg Na K P qtz 1 0 0 0 0 0 0 0 0 0 NA quartz kfs 3 0 1 0 0 0 0 0 1 0 K-Feldspar K-feldspar or50 3 0 1 0 0 0 0 0.5 0.5 0 K-Feldspar anorthoclase ab 3 0 1 0 0 0 0 1 0 0 Plagioclase albite an 2 0 2 0 0 1 0 0 0 0 Plagioclase anorthite lab50 2.5 0 1.5 0 0 0.5 0 0.5 0 0 Plagioclase labradorite ms 3 0 3 0 0 0 0 0 1 0 Muscovite muscovite par 3 0 3 0 0 0 0 1 0 0 Muscovite paragonite ill 3.5 0 1.3 0.1 0 0 0.3 0 0.6 0 Muscovite illite ill2 1 0 1.3 0.3 0 0 0.3 0 0 0 Muscovite illite-2 cli 3 0 2 0 0 0 5 0 0 0 Fe-Chlorite clinochlore cha 3 0 2 5 0 0 0 0 0 0 Fe-Chlorite chamosite pen 3 0 2 0 5 0 0 0 0 0 Fe-Chlorite pennantite ap 0 0 0 0 0 5 0 0 0 3 Apatite apatite dol 0 0 0 0 0 1 1 0 0 0 Calcite dolomite cal 0 0 0 0 0 1 0 0 0 0 Calcite calcite ant 0 1 0 0 0 0 0 0 0 0 NA anatase klt 1 0 1 0 0 0 0 0 0 0 NA kaolinite gbs 0 0 1 0 0 0 0 0 0 0 NA gibbsite hem 0 0 0 2 0 0 0 0 0 0 NA hematite step three tell A2M which minerals exist in each total oxide sample and let it solve for mineralogy
Site: Ballinastoe (67.9068 g): grams Si Al Fe2 Mn Mg Ca K Na K-Feldspar 0.8446 3.00 1.00.... 0.75 0.25 Muscovite 60.6133 2.63 2.67 0.06. 0.06. 0.59 0.22 Plagioclase 1.2325 2.51 1.49... 0.49. 0.51 Fe-Chlorite 5.2165 3.00 2.00 4.71 0.20 0.08... ------------------------------------------------------------------------ Site: Dromahaire (23.7648 g): grams Si Al Fe2 Mn Mg Ca K Na K-Feldspar 1.0664 3.00 1.00.... 0.70 0.30 Muscovite 16.4577 2.11 2.17 0.14. 0.15. 0.49 0.04 Plagioclase 1.9526 2.44 1.56... 0.56. 0.44 Fe-Chlorite 4.2881 3.00 2.00 4.43 0.47 0.10... ------------------------------------------------------------------------ Site: Kilworth (33.7653 g): grams Si Al Fe2 Mn Mg Ca K Na K-Feldspar 3.8646 3.00 1.00.... 0.87 0.13 Muscovite 24.4422 2.94 2.41 0.05. 0.10. 0.77 0.03 Plagioclase 0.5464 2.90 1.10... 0.10. 0.90 Fe-Chlorite 4.9121 3.00 2.00 3.73 0.62 0.65... ------------------------------------------------------------------------ Site: Taughboy (57.8454 g): grams Si Al Fe2 Mn Mg Ca K Na K-Feldspar 15.4575 3.00 1.00.... 0.62 0.38 Muscovite 20.9966 2.95 1.82 0.10. 0.21. 0.46 0.17 Plagioclase 13.7760 2.79 1.21... 0.21. 0.79 Fe-Chlorite 7.6153 3.00 2.00 4.20 0.06 0.75... ------------------------------------------------------------------------ Site: Thomastown (37.3963 g): 4 Groups grams Si Al Fe2 Mn Mg Ca K Na K-Feldspar 9.8665 3.00 1.00.... 0.81 0.19 Muscovite 18.7281 2.86 2.29 0.07. 0.12. 0.62 0.13 Plagioclase 1.9599 2.94 1.06... 0.06. 0.94 Fe-Chlorite 6.8418 3.00 2.00 4.59 0.07 0.34... how well does it work? Level IIi sites have both total oxides and mineralogy, also available for a few other sites (n = 8). Comparison of A2M mineralogy with quantitative is good (eyeball statistic)
step four apply PROFILE with site specific mineralogy, mineral stiochemistry, bulk density, surface area, etc base cation weathering rates (mol c ha 1 year 1 ) site base cations calcium magnesium potassium sodium tauboy 380 54 103 81 142 dromhaire 1010 15 501 327 167 ballinastoe 772 15 354 272 131 thomastown 502 21 217 150 114 kilworth 257 4 126 84 43
conclusions (a) base cation weathering rates determined for biosoil plots using PROFILE in conjunction with A2M mineralogy, (b) procedure can be streamlined to one oxide sample per soil profile, and (c) it is a relatively simple approach to estimate regional weathering rates. deliverables (a) database of total oxides and mineralogy, and (b) data source to input output budget publication