Fróðskaparrit - 01.07.2004, Side 98

Fróðskaparrit - 01.07.2004, Side 98
96 MERCURY IN THE FAROE ISLANDS — A REVIEW OF AVAILABLE DATA The mercury concentration in brown trout is similar to the common level in Arc- tic Canada (Lockhart et al., 2001). It is still elevated above the level in Finland (AMAP 1998) where brown trout in Finnish Lapp- land was less than 0,1 mg/kg. Several studies have been undertaken to elucidate the factors influencing the uptake of mercury from a watershed/lake. It ap- pears that apart from the magnitude of the áctual atmospheric mercury deposition, a wet and boggy upland with high organic matter content is a driving force for elevat- ed fish mercury concentration in a lake (Fjeld, 1993), and than the mobilization is increased by disturbances not only from flooding in connection with electricity pro- duction, but also from other erosion-creat- ing activity like agriculture and the use of heavy terrain-going machinery (Gustin, 2002; St.Louis et al., 2004). This indication that what would be termed moderate watershed erosion in oth- er circumstances could render the water less suitable in monitoring the long range transported (also called “background lev- el”) pollutants is bad news for monitoring in the Faroe Islands where there is no fish- containing water where the watershed is not being used for some sort of erosion- creating activity like sheep grazing and growing of crops. The natural erosion how- ever, i.e. that driven by wind, temperature and wet deposition, is significant and may overshadow the anthropogenic initiated erosion. Sedimcnts from freshwater lakcs During the summer-period of 2000, sedi- ments were collected from different Far- oese fresh water lakes as part of the Nor- Lake project (Landkildehus et al., 2002). Some cores were made available for retro- spective mercury analyses where the sedi- ments are cut in sections representing a cer- tain time period as defíned by radiological analyses, and where the mercury concen- tration is measured in each slice (Table 4). Sediment cores were taken from Sørvágs- vatni and Leynavatni and each core was sliced in 5 cm thick segments. Knowledge about mercury concentration and the age of the various sediment slices allows the drawing a profile of the mercury pollution from the time of the sedimentation of the oldest slices in the core to the present time. The uppermost slices of the sediment from Leynavatni could not be dated because of extensive bioturbation in these sections, so the estimated sedimentation rate applies only to the two slices at the bottom of the core. Fig. 3 shows the mercury concentra- tion in the sediment profile sampled in Sørvágsvatn. To eliminate variability stem- ming from the tendency of mercury to bind to the organic fraction, the mercury con- centration in the figure has been corrected for the organic content of the actual seg- ment by dividing with the loss on ignition (in g/kg dw). Comparing the mercury concentration in the segments of two cores that corresponds to sediments deposited approx. 100 years ago, shows that the concentration in lake Sørvágsvatn sediments was approx. twice as high as in the Leynavatn sediments. Cor- recting, however, both mercury concentra- tions for the organic material content, ex-
Side 1
Side 2
Side 3
Side 4
Side 5
Side 6
Side 7
Side 8
Side 9
Side 10
Side 11
Side 12
Side 13
Side 14
Side 15
Side 16
Side 17
Side 18
Side 19
Side 20
Side 21
Side 22
Side 23
Side 24
Side 25
Side 26
Side 27
Side 28
Side 29
Side 30
Side 31
Side 32
Side 33
Side 34
Side 35
Side 36
Side 37
Side 38
Side 39
Side 40
Side 41
Side 42
Side 43
Side 44
Side 45
Side 46
Side 47
Side 48
Side 49
Side 50
Side 51
Side 52
Side 53
Side 54
Side 55
Side 56
Side 57
Side 58
Side 59
Side 60
Side 61
Side 62
Side 63
Side 64
Side 65
Side 66
Side 67
Side 68
Side 69
Side 70
Side 71
Side 72
Side 73
Side 74
Side 75
Side 76
Side 77
Side 78
Side 79
Side 80
Side 81
Side 82
Side 83
Side 84
Side 85
Side 86
Side 87
Side 88
Side 89
Side 90
Side 91
Side 92
Side 93
Side 94
Side 95
Side 96
Side 97
Side 98
Side 99
Side 100
Side 101
Side 102
Side 103
Side 104
Side 105
Side 106
Side 107
Side 108
Side 109
Side 110
Side 111
Side 112
Side 113
Side 114
Side 115
Side 116
Side 117
Side 118
Side 119
Side 120
Side 121
Side 122
Side 123
Side 124
Side 125
Side 126
Side 127
Side 128
Side 129
Side 130
Side 131
Side 132
Side 133
Side 134
Side 135
Side 136
Side 137
Side 138
Side 139
Side 140
Side 141
Side 142
Side 143
Side 144
Side 145
Side 146
Side 147
Side 148
Side 149
Side 150
Side 151
Side 152
Side 153
Side 154
Side 155
Side 156
Side 157
Side 158
Side 159
Side 160
Side 161
Side 162
Side 163
Side 164

x

Fróðskaparrit

Direkte link

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

Link til denne avis/magasin: Fróðskaparrit
https://timarit.is/publication/15

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.