陸地水碳酸鹽CO水生光合生物相互作用產(chǎn)生碳匯的重要性英文

1、Sci. Bull. (2015) 60(2):182191DOI 10.1007/s11434-014-0682-yReview Significance of the carbon sink producedby H2OcarbonateCO2aquatic phototroph interaction on landZaihua Liu Wolfgang DreybrodtReceived: 17 June 2014 / Accepted: 10 September 2014 / Published online: 23 December 2014© Science China

2、 Press and Springer-Verlag Berlin Heidelberg 2014Abstract One of the most important questions in the science of global change is how to balance the atmospheric CO2 budget. There is a large terrestrial missing carbon sink amounting to about one billion tonnes of carbon per annum. The locations, magni

3、tudes, variations, and mech- anisms responsible for this terrestrial missing carbon sink are uncertain and the focus of much continuing debate. Although the positive feedback between global change and silicate chemical weathering is used in geochemical models of atmospheric CO2, this feedback is bel

4、ieved to operate over a long timescale and is therefore generally left out of the current discussion of human impact upon the carbon budget. Here, we show, by synthesizing recent findings in rock weathering research and studies into biological carbon pump effects in surface aquatic ecosystems, that

5、the carbon sink produced by carbonate weathering based on the H2OKeywords Carbon sink · H2OcarbonateCO2 aquatic phototroph interaction · Carbonate weathering · Biological carbon pump · Land aquatic ecosystem · Global change1 IntroductionOne of the most important questions in

6、 the science of global change is how to balance the atmospheric CO2 budget 14. According to Melnikov and ONeill 3, there is a large terrestrial missing carbon sink as follows:The (terrestrial) missing carbon sink = sources (emissionsfrom fossil fuels ? net emissions from changes in land use)- sinks

7、(oceanic uptake ? atmospheric increase), i.e., 2.8 = 7.9 (6.3 ? 1.6) - 5.1 (1.9 ? 3.2) (all values in Pg C/a,15carbonateCO2aquatic phototroph interaction on land not1 Pg = 10g).only totals half a billion tonnes per annum, but also dis- plays a significant increasing trend under the influence of glob

8、al warming and land use change; thus, it needs to be included in the global carbon budget.Z. Liu (&)State Key Laboratory of Environmental Geochemistry, Instituteof Geochemistry, Chinese Academy of Sciences,Guiyang 550002, Chinae-mail: liuzaihuaW. DreybrodtFaculty of Physics and Electrical Engine

9、ering, University of Bremen, 28334 Bremen, GermanyThe locations, magnitudes, variations, and mechanismsresponsible for the terrestrial missing carbon sink, how- ever, are uncertain and continue to be debated. The pre- vailing dogma has focused on carbon sinks in soil and vegetation 58. The preferred

10、 explanation for the missing carbon sink is the effect of CO2 and/or nitrogen fertiliza- tion 57. For example, Kheshgi et al. 7 found that*25 % of CO2 emissions are sequestered by the terrestrialbiosphere. Therefore, there is still a *0.8 Pg C/a missing sink (or net terrestrial flux) to be determine

11、d.Although the positive feedback between global change and the silicate chemical weathering of rocks is used in geochemical models of atmospheric CO2 9, this effect is believed to operate over a long timescale and therefore is generally left out of the current discussion of human impact upon the car

12、bon budget 10. For example, current global carbon budgets assume that pre- and post-anthropogenic riverine carbon fluxes are equal 11.Sci. Bull. (2015) 60(2):182191 183Here, we show, by synthesizing recent findings in rock weathering research and studies into biological carbon pump effects in surfac

13、e aquatic ecosystems, that the carbon sink produced by carbonate weathering based on the H2O carbonateCO2aquatic phototroph interaction on land not only totals one half billion tonnes per year 12, but also displays a significant increasing trend under the dual influence of global warming and land us

14、e change 1215, comparable with those in the worlds forests 8. Therefore, the atmospheric CO2 sink produced by the H2Ocarbon- ateCO2aquatic phototroph interaction on land needs to be included in the global carbon budget due to both its large quantity and its changing characteristics.2 Significance of

15、 weathering of trace carbonates in silicate rock watershedsHimalaya. They found that carbonate dissolution provided more than 90 % of the weathering-derived HCO3-, Ca2? and Sr for at least 55 ka following initial exposure of rocksurfaces, although carbonate may represent only*1.0 wt% in fresh glacia

16、l till; this significantly increases the ratios of HCO3-/Na? and Ca2?/Na? in the so-called silicate end-member reservoir. Jacobson et al. 20 alsofound the following: (1) Carbonate bedrock in the Hima- laya has a wide range of ratios of Ca/Sr and 87Sr/86Sr that cannot be adequately defined by a singl

17、e end-member in conventional mass balance equations; and (2) Ca2?behaves non-conservatively during transport in Himalayan stream waters. The removal of up to 70 % of the dissolvedCa2? by calcite precipitation appears to be a pervasive-process in the Himalaya that drives dissolved Ca/Sr ratios toward

18、 values much lower than those measured in car- bonate bedrock. Therefore, they concluded that, without taking these factors into account, stream water Ca/Sr andAlthough primarily known in carbonate rocks, carbonate87Sr/86Sr ratios, and hence HCO3, can be erroneously(mainly CaCO3) is also commonly as

19、sociated with silicate rocks, such as shales, calcareous sandstones, metamor- phosed gneisses and schists, hydrothermally altered gra- nitic rocks 16, and pristine granitoids, which probably form CO2-rich fluids associated with the final cooling of batholiths as well as during later periods of hydro

20、thermal activity 17, 18. Therefore, the CO2 consumed in silicate rock terrains does not necessarily result primarily from silicate weathering: It may be chiefly due to the contribu- tion of rapid calcite dissolution in the silicate rocks 16 18. For instance, Blum et al. 16 investigated the major ele

21、ment and strontium (Sr) isotope geochemistry of bed- rocks, surface waters, and river sands in the Raikhot watershed within the High Himalayan Crystalline Series (HHCS) of northern Pakistan. Mass balance calculations of mineral-weathering contributions to the flux of dissolvedions from the watershed

22、 showed that 82 % of the HCO3-flux is derived from the weathering of carbonate minerals and only 18 % from silicate weathering, even if the bed- rock in the watershed is predominantly silicate rocks (quartzofeldspathic gneiss and granite) with only *1 % carbonate. This indicated the significance of

23、small amountsof bedrock carbonate in controlling the water chemistry of silicate rock watersheds. It also suggests that the flux of Sr with high 87Sr/86Sr ratios in major Himalayan rivers may be derived mainly from the weathering of small amounts of calcite within the HHCS silicates. Therefore, mode

24、ls using the flux of radiogenic Sr from the Himalaya as a proxy for silicate weathering rates may overestimate the amount of CO2 consumption attributable to reactions with silicates there. Similar results were obtained by Jacobson et al. 19, 20, who showed that the conventional application of two- c

25、omponent Ca/Sr and 87Sr/86Sr mixing equations overes-timated silicate-derived Sr2? and HCO3- fluxes from theinterpreted as representing the dominance of silicate dis- solution. We think similar problems could arise with the inversion method if ratios of HCO3/Na and Ca/Na are used. This may explain w

26、hy Gaillardet et al. 21 obtained such high estimates of CO2 consumption from silicate weath-ering despite the fact that its weathering rates are 102108times lower than those of carbonates 22, 23. They cal- culated CO2 consumption vis-a -vis silicate weathering by measuring the bulk chemistry of larg

27、e rivers and underes- timated the carbonate weathering contributions that occur in predominantly silicate areas.In a more recent study, Moore et al. 24 tracked the relation between mountain uplift, silicate weathering, and long-term CO2 consumption by the use of Ca isotopes in the Southern Alps, New

28、 Zealand. Although rocks in the sampled watershed contain only *3 % hydrothermal and metamor- phic calcite, these authors found that riverine Ca largelyoriginates from carbonate weathering and that the fraction of Ca from carbonate weathering increases with increasing tec- tonic activity, from *50 %

29、60 % in regions experiencing the lowest uplift rates to as high as 90 % in regions experi- encing the highest uplift rates. Therefore, they concluded that silicate weathering in the HimalayanTibetan Plateau is also not a major sink for atmospheric CO2.It should be noted that present results are main

30、ly fromthe uplifted silicate areas, which are conventionally thought to have stimulated CO2 consumption by silicate weathering. Research results from other areas are needed in future.To summarize, the contribution of carbonate weathering to the atmospheric CO2 sink may have been greatly underestimat

31、ed in these previous studies 21, 25, 26 due to ignorance of the important role played by trace calcite in silicate rock areas.184Sci. Bull. (2015) 60(2):1821913 Photosynthetic uptake of DIC by aquatic phototrophs (the biological carbon pump effect)DIC (dissolved inorganic carbon, DIC=CO2(aq) ? HCO3-

32、 ? CO32-) in surface waters is consumed by aquatic photosynthesis on the continents and in the ocean2730. Some of it, of course, will return to the atmo- sphere due to the CO2 pressure difference between water and the atmosphere. Aquatic ecosystems, such as rivers, lakes, wetlands, and the oceans, p

33、lay an important role in the carbon cycle by means of the so-called biological pump 31. Aquatic phototrophs occupy the well-mixed surface layers of a given river, lake, wetlands, or ocean and grow by photosynthesis at a rate which varies according to the nutritional state of the water. Dead biota an

34、d feces fall down through the water column, thus removing carbon from the surface layers, hence reducing the partial pressure of CO2 there. This reduction enables the uptake of new DIC from the surface waters and/or of new CO2 from the atmosphere.Our argument that the H2OcarbonateCO2aquaticphototrop

35、h interaction serves as an important atmospheric CO2 sink that depends on the carbonate dissolution, and theuptake rate of DIC (CO2 and/or HCO3-) by aquaticphototrophs differs from the generally accepted view that the consumption of atmospheric CO2 resulting from car- bonate weathering on the contin

36、ents is balanced over a relatively short timescale by carbonate precipitation in the oceans and that all of the CO2 involved is released back to the oceanatmosphere system 10. This latter contention is at least partly problematic because it does not consider the large uptake of DIC by the photosynth

37、esis that produces organic carbon in the aquatic systems of both oceans and continents. For instance, Ternon et al. 32 found that the fertilization of oceanic waters by the Amazon River around its outflow enhances the biological pumping effect of CO2, contributing up to 30 % of the measured lowering

38、 of pCO2 there, and so, increasing the atmospheric CO2 sink in the Atlantic Ocean. Einsele et al. 33 investigated atmospheric carbon burial in modern lake basins and its significance for the global carbon budget. They found that, although the area of lake basins is only about 0.8 % of the ocean surf

39、ace (or 2 % of the land surface), a surprisingly large amount of atmospheric carbon is buried in them, amounting to0.07 Pg C/a, or more than one-fourth of the annual atmo- spheric carbon burial in the modern oceans. This burial is accomplished mainly by the rapid accumulation of lacus- trine sedimen

40、ts and a very high preservation factor which is, on average, 50 times higher than that observed in the oceans. Lerman and Mackenzie 34 found that the primary production and net storage of organic carbon counteract the CO2 released by carbonate precipitation, leading to lower CO2 emissions from the s

41、urface layer through the reaction:Ca2? ? 2HCO3- ) CaCO3 ? CH2O ? O2. Wang et al.35 found that the flux of CO2 into the atmosphere from the Changjiang (Yangtze River) has decreased dramatically (*75 %) during the past four decades (*19602000) due to a marked increase in nutrient (e.g., NO3-) concentr

42、a- tions. This may show the importance of CO2 uptake by phototrophs in river systems due to the importance of elemental fertilization for phototroph growth. Yang et al.36 investigated the carbon source/sink of a subtropical, eutrophic lake by investigating the overall mass balance expressed as a bal

43、ance between gas exchange and carbon burial. They found that the ratio of carbon emission into the atmosphere to carbon burial in the sediment was only 0.08, indicating that this lake is an effective carbon sink.All of these findings show the significance of photo- synthetic uptake of DIC by aquatic

44、 phototrophs (the bio- logical carbon pump effect) in stabilizing the carbon sink produced by carbonate weathering through the transfor- mation from DIC to organic carbon.However, most researches were done in the un-con- taminant rivers or streams. For the situation in the con- taminant rivers or st

45、reams (such as dark water, in which low light will limit the amount of photosynthesis), more work has to be done in future.4 Net carbon sink produced by H2OcarbonateCO2 aquatic phototroph interaction on landIn a recent attempt to balance the atmospheric CO2 budget, Liu et al. 12 considered the combi

46、ned effects of carbonate dissolution, the global water cycle, and the photosynthetic uptake of DIC by aquatic phototrophs. They found that the net atmospheric CO2 sink produced by the H2Ocarbonate CO2aquatic phototroph interaction on the land (for the expression of carbonate weathering based on H2Oc

47、arbon- ateCO2aquatic phototroph interaction, see the new con- ceptual model in Fig. 1) could be as large as 0.477 Pg C/a (CFR1 ? CFR2 ? CFS-AL in Fig. 2), which accounts for about 17 % of the terrestrial missing carbon sink and is comparable with the carbon sink in the worlds forests 8.This is much

48、larger (by a factor of about three) than the estimate of 0.148 Pg C/a obtained by Gaillardet et al. 21, who underestimated the carbonate weathering sink in sili- cate areas and did not consider the photosynthetic uptake of DIC by land aquatic phototrophs or the burial of part of theresulting organic

49、 matter on the continents (CFR2 ? CFS-AL = 0.233 Pg C/a, Fig. 2). This latter value of 0.233 Pg C/a has been confirmed by the independent work of others 37, 38. For instance, Waterson and Canuel 37 haveshown that the contribution of autochthonous organic carbon (AOC) derived from DIC transformed by

50、aquatic photo- synthesis in the Mississippi River system (the largest river system in North America) can constitute 20 %57 % of theSci. Bull. (2015) 60(2):182191 185Fig. 1 Conceptual model of the carbon cycle produced by carbonate weathering (karst processes) based on H2OcarbonateCO2aquatic phototro

51、ph interaction (drawing in reference to Lerman and Mackenzie 34 and Liu et al. 12). Notes: 1. CSF (net carbon sink flux produced by H2OcarbonateCO2aquatic phototroph interaction) = 0.5 9 Q 9 (DIC2 ? AOC)/A ? FSAOC where the ratio 0.5 indicates that only one half of the HCO3- generated by carbonate d

52、issolution is of atmospheric origin; Q is the discharge from the surface water system; DIC2 is the concentration of dissolved inorganic carbon in the surface water system; and AOC is the concentration of total organic carbon in the surfacewater system transformed from DIC1 (dissolved inorganic carbo

53、n in the groundwater system) by submerged aquatic phototrophs via photosynthesis in the surface water system. FSAOC is the sedimentary flux of autochthonous organic carbon (OC) in the surface water system over the catchment area (A). 2. Unlike the conventional carbonate weathering carbon cycle model

54、 9, 10, 25, which considers H2OcarbonateCO2 interaction and ignores organic matter formation produced by the aquatic photosynthetic uptake of DIC, this new conceptual model helps to answer important questions such as whether carbonate weathering could be contributing to the long-term carbon sink (e.

55、g., through sedimentation, burial of autochthonous organic matter, FSAOC), and thus, to a proportionate degree, controlling long-term climate changetotal organic carbon (TOC). If the lower value, 20 %, is multiplied by the sedimentary deposition of organic carbon in inland waters (0.6 Pg C/a) plus riverine TOC discharge to oceans (0.5 Pg C/a) 38, a similar value of 0.22 Pg C/a AOC is obtained. Therefore, the atmospheric CO2 sink due to carb