Jökull


Jökull - 01.12.2007, Síða 41

Jökull - 01.12.2007, Síða 41
Rates of carbon ingrowth and nutrient release from young Icelandic basalts Because of the value of C and P in revealing bio- genic activity, we examined C ingrown and P content and forms in soils derived from Icelandic basalts of different ages. The primary objective of this studywas to use biogeochemical analyses of C and P to deter- mine the interplay between biogenic activity and soil formation in Iceland. We hypothesized that biologi- cal activity and weathering of parent rock will incre- ase with age of the soil and expected to find evidence to support this hypothesis in both the C and P ana- lyses. We further hypothesized that older soils will contain more organic C, higher concentrations of oc- cluded and organic P, and lower amounts of mineral P than younger soils. GEOLOGIC SETTING Iceland is located on top of the Mid-Atlantic Ridge at the divergent boundary between the North Ameri- can and Eurasian plates, above a mantle plume which greatly enhances the volcanic productivity (Sæmunds- son, 1979). Due to its tectonic location, the eruptive products of Iceland are mostly comprised of basalt (Jakobsson, 1979). Soil from lavas from three dif- ferent volcanic systems were examined in this study: Hekla, Eldgjá and Laki. Hekla is an active stratovol- cano whereas the Eldgjá and Laki are eruption fissu- res. The 1783 Laki eruption produced the second lar- gest amount of basalt in the last 2000 years, second only to the 934 AD Eldgjá fissure eruption (Thordar- son et al., 2001; Thordarson and Self, 2003). METHODS AND MATERIALS Four historically dated basalt flows were sampled in southern Iceland: the 934 AD Eldgjá flow, the 1300 AD Hekla flow, the 1554 AD Hekla flow, and the 1783 AD Laki flow (Figure 1). There were three sam- ple sites at the 934 AD flow, two sample sites at the 1300 AD flow, two sample sites at the 1554 AD flow, and one sample site at the 1783 AD flow. Soil and bedrock samples were taken at each sample site. In areas where there was well developed soil, a trench was dug and samples were taken along various depths of the trench. All of these soils can be classified into Andosols (Arnalds, 2004). Total organic C content of each unsieved soil sam- ple was analyzed. Two grams of each bulk sample was placed in crucibles and dried overnight at 106"C. The samples were removed from the oven andweighed the following day to determine the weight of the samples before ashing. After recording the weight of the sam- ple, the samples were ashed in a muffle furnace for 2.5 hrs at 550"C, with the combusted material re-weighed after ashing. Loss on ignition (LOI) was determined by subtracting the weight after ashing from the we- ight before ashing. The LOI can be used to determine the amount of organic C presenting the soil. Upon combustion, C, N, H, and O are released. Approxi- mately 40% of the mass lost during ashing is organic C. Therefore, LOI is multiplied by 0.4 to approximate the amount of organic C present. The resulting con- centration of organic C was multiplied by soil density from each sampling horizon and the depth of the sam- ple trench to obtain total C in the soil (Oke, 1987). In order to validate the LOI results, the organic C content of five samples, which were chosen to re- present the spectrum of organic C concentrations fo- und in the LOI results, was determined using a CHN Elemental Analyzer (FlashEA1112, Thermo Fisher Scientific, Waltham, MA, US). Prior to analysis, sam- ples were treated with dilute HCL for 24 hours and then with water for 48 hours before being oven dried (Midwood and Boutton, 1998). We found that the or- ganic C values calculated from LOI were higher than those determined by the CHN analyzer. However, the difference is consistent across samples and is there- fore not expected to affect the interpretation of the or- ganic C results. The P content of each sieved sample was deter- mined by a four part sequential extraction as descri- bed by Filippelli and Delaney (1996). This method is similar to those of Walker and Syers (1976) and Tiessen and Moir (1993). The steps of this procedure include: 1) adding a citrate-dithionite-bicarbonate re- ducing agent and magnesium chloride to acquire the occluded fraction; 2) dissolutions with sodium ace- tate+acetic acid solution and following dissolution in hydrochloric acid to recover the mineral fraction, and 3) dissolution with hydrochloric acid after ashing to obtain the organic fraction (Filippelli and Delaney, JÖKULL No. 57 39
Síða 1
Síða 2
Síða 3
Síða 4
Síða 5
Síða 6
Síða 7
Síða 8
Síða 9
Síða 10
Síða 11
Síða 12
Síða 13
Síða 14
Síða 15
Síða 16
Síða 17
Síða 18
Síða 19
Síða 20
Síða 21
Síða 22
Síða 23
Síða 24
Síða 25
Síða 26
Síða 27
Síða 28
Síða 29
Síða 30
Síða 31
Síða 32
Síða 33
Síða 34
Síða 35
Síða 36
Síða 37
Síða 38
Síða 39
Síða 40
Síða 41
Síða 42
Síða 43
Síða 44
Síða 45
Síða 46
Síða 47
Síða 48
Síða 49
Síða 50
Síða 51
Síða 52
Síða 53
Síða 54
Síða 55
Síða 56
Síða 57
Síða 58
Síða 59
Síða 60
Síða 61
Síða 62
Síða 63
Síða 64
Síða 65
Síða 66
Síða 67
Síða 68
Síða 69
Síða 70
Síða 71
Síða 72
Síða 73
Síða 74
Síða 75
Síða 76
Síða 77
Síða 78
Síða 79
Síða 80
Síða 81
Síða 82
Síða 83
Síða 84
Síða 85
Síða 86
Síða 87
Síða 88
Síða 89
Síða 90
Síða 91
Síða 92
Síða 93
Síða 94
Síða 95
Síða 96
Síða 97
Síða 98
Síða 99
Síða 100
Síða 101
Síða 102
Síða 103
Síða 104
Síða 105
Síða 106
Síða 107
Síða 108
Síða 109
Síða 110
Síða 111
Síða 112
Síða 113
Síða 114
Síða 115
Síða 116
Síða 117
Síða 118
Síða 119
Síða 120
Síða 121
Síða 122
Síða 123
Síða 124

x

Jökull

Beinleiðis leinki

Hvis du vil linke til denne avis/magasin, skal du bruge disse links:

Link til denne avis/magasin: Jökull
https://timarit.is/publication/1155

Link til dette eksemplar:

Link til denne side:

Link til denne artikel:

Venligst ikke link direkte til billeder eller PDfs på Timarit.is, da sådanne webadresser kan ændres uden advarsel. Brug venligst de angivne webadresser for at linke til sitet.