Introduction
Materials and methods
Lake and watershed properties
Iso Kivijärvi (reference) | Martinjärvi (peat extraction impacted) | |
---|---|---|
Surface area (ha) | 190 | 105 |
Mean depth (m)a
| 1.6 | 1.0 |
Maximum depth (m) | 4.5 | 2.0 |
Volume (Mm3)a
| 3.08 | 1.08 |
Catchment (km2) | 38 | 178 |
Residence time (d) | 90 | 7 |
Mean thickness of gyttja (m)a
| 1.99 | 1.37 |
TOT P (µg/l) | 29 | 30 |
TOT N (µg/l) | 720 | 651 |
pH | 5.8 | 6.0 |
Alkalinity (mmol/l) | 0.07 | 0.05 |
Conductivity (mS/m) | 3.2 | 3.0 |
Color (mg Pt/l) | 207 | 182 |
Iron (µg/l) | 1338 | 1287 |
Sediment sounding, coring, and dating
Chemical and physical analyses
Chironomid analyses
Diatom analyses
Numerical methods
Historical records on stressors
Year | External stressor/event |
---|---|
Early 1870s | Commercial loggings begin in Keuruu |
1885–1890 | First permanent settlements and agricultural fields in Lake Martinjärvi watershed |
1920 | First permanent settlements by Lake Suojärvi (immediately upstream from Lake Martinjärvi) |
1920 | First permanent settlements in Lake Iso Kivijärvi watershed |
Late 1920s | Old growth forests largely logged |
1929 | Land owners advised to drain their forests for better growth |
1960s | Agricultural fields more widespread than at present |
1960 | First preparations for a peat extraction area begin in the upper part of Lake Martinjärvi watershed |
1960s–1970s | Intensive drainage ditching in the watershed |
1960s–1970s |
K and P fertilization of peatlands for forestry common in Finland |
1970s–1980s | Clear-cut loggings of most forests on mineral soils in the area |
1972–1976 | First peat extraction areas start production |
1978 | Preparations begin at the peat extraction area closest to Lake Martinjärvi (Kalmuneva; 56 ha) |
Early 1980s | Forest ditching largely completed |
1982 | Production begins in Kalmuneva |
2000s | Construction of summer houses |
2000s | Maintenance (clearing) of old drainage ditches (mainly 2004–2007) |
Results
Artificial radionuclides
Natural radionuclides
Lab code | Site/core | Mid depth (cm) | d13C (‰) | C-14 age (BP) | ± |
---|---|---|---|---|---|
Hela-3391 | Iso Kivijärvi 1 | 100 | −30.9 | 4741 | 53 |
Hela-3392 | Iso Kivijärvi 1 | 150 | −31.5 | 6005 | 63 |
Hela-3393 | Iso Kivijärvi 1 | 180 | −31.8 | 6284 | 63 |
Hela-3394 | Iso Kivijärvi 1 | 220 | −31.8 | 7439 | 55 |
Hela-3387 | Martinjärvi 2 | 100 | −30.4 | 3583 | 69 |
Hela-3388 | Martinjärvi 2 | 190 | −30.4 | 5033 | 70 |
Hela-3389 | Martinjärvi 2 | 275 | −31.1 | 6008 | 69 |
Hela-3390 | Martinjärvi 2 | 350 | −31.4 | 7499 | 57 |
Depth range (cm) | Time span (a) | Average density (g/cm3) | Average DM (%) | Average C (%) | DM accumulation (g/m2/a) |
C accumulation (g/m2/a) |
---|---|---|---|---|---|---|
Iso Kivijärvi
| ||||||
100–150 cm | 1264 | 1.113 | 12.7 | 12.9 | 72.7 | 6.2 |
150–180 cm | 279 | 1.109 | 16.5 | 8.5 | 192.0 | 16.7 |
180–220 cm | 1155 | 1.124 | 16.1 | 8.7 | 69.8 | 5.3 |
100–220 cm | 2698 | 1.115 | 16.7 | 8.3 | 82.8 | 6.9 |
SD | 0.008 | 2.1 | 8.3 | 69.7 | 6.3 | |
Martinjärvi
| ||||||
100–190 cm | 1450 | 1.106 | 17.9 | 7.5 | 123 | 9.3 |
190–275 cm | 975 | 1.103 | 17.7 | 8.2 | 170 | 14 |
275–350 cm | 1491 | 1.137 | 22.4 | 7.4 | 128 | 9.5 |
100–350 cm | 3916 | 1.112 | 18.9 | 7.7 | 134 | 10.3 |
SD | 0.018 | 2.6 | 0.4 | 25.8 | 2.7 |
Carbon and dry matter accumulation
Lake | Time span (a) | Thickness (cm) | Avg dens. (g/cm3) | Avg DM (%) | Avg C (%) | DM (g/m2/a) |
C (g/m2/a) |
---|---|---|---|---|---|---|---|
Post-1986 section (impacted)
| |||||||
Iso Kivijärvi | 28.4 | 7 | 1.08 | 11.6 | 12.34 | 334 | 42 |
Martinjärvi | 25.8 | 6 | 1.06 | 10.0 | 11.90 | 492 | 49 |
~1820–1900 section (recent reference)
| |||||||
Iso Kivijärvi | 73.9 | 6 | 1.08 | 11.7 | 12.75 | 84 | 11 |
Martinjärvi | 72.2 | 7 | 1.10 | 18.4 | 9.54 | 169 | 16 |
Lake | ΔDM acc. (from 1820 to 1900) (%) | ΔDM acc. (from long term) (%) | ΔC acc. (from 1820 to 1900) (%) | ΔC acc. (from long term) (%) |
---|---|---|---|---|
Relative changes
| ||||
Iso Kivijärvi | 296 | 302 | 291 | 499 |
Martinjärvi | 191 | 267 | 203 | 388 |