Agricultural and Food Science, Vol. 14 (2005): 44–56. 44 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 14 (2005): 44–56. © Agricultural and Food Science Manuscript received March 2004 Assessment of aquatic pollution, remedial measures and juridical obligations of an acid sulphate soil area in western Finland Peter Österholm Åbo Akademi University, Department of Geology and Mineralogy, FI-20500 Åbo, Finland, e-mail: peter.osterholm@abo.fi Mats Åström Kalmar University, Department of Biology and Environmental Science, SE-39182 Kalmar, Sweden Robert Sundström Åbo Akademi University, Department of Geology and Mineralogy, FI-20500 Åbo, Finland Reclaiming of Holocene sulphide-bearing sediments, widespread in the coastal areas of Finland, has ena- bled oxidation of sulphides to a depth of 1–3 m and the subsequent development of acid sulphate soils (pH < 4). This work is concerned with spatial hydrogeochemical patterns, remediation measures and the juridi- cal obligation to improve water quality in one such area, i.e. the Rintala plain (23 km2) in mid-western Finland. Streams draining acid sulphate soils in Rintala are more acid (pH ~ 4 and acidity ~ 4 mmol l-1) and carry significantly higher concentrations of SO4 2-, Al, Ca, Cd, Co, Cu, F, Mn, Ni, Pb, Se, Sr and Zn than those draining forest and rural areas in the vicinity of the Rintala plain and organic-rich soils located on the plain. The juridical obligation to improve the water quality is inappropriate as it does not consider the main reason for the poor water quality, i.e. drainage by subsurface drainage pipes, and because of the equality principle (other acid sulphate soil areas have just as poor water quality but do not have such an obligation). Groundwater management, i.e. keeping the groundwater level as high as possible, is recommended as the best management practice. Key words: acid sulphate soils, sulphur, metals, acidity, pH, hydrogeochemistry, drainage, groundwater management Introduction Holocene sulphide-bearing marine sediments are common on the coastal plains of Finland. Drainage of these by open ditches started in the 18th century and was strongly intensified after 1950 when agri- cultural machines and the use of subsurface drain- age became more common. As a consequence, the groundwater level has dropped considerably, ena- 45 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 14 (2005): 44–56. bling oxygen to penetrate and oxidise metal sul- phides. This oxidation process, which produces large amounts of acidity (e.g. van Breemen 1973), has resulted in the development of more than 1 m deep acid soils (pH 2.5–4), referred to as active acid sulphate (AS) soil, in an area covering up to 3000 km2 of the coastal plains of Finland (Palko 1994). In these acidic soils, a number of chemical elements are mobilised and ultimately washed away with runoff, resulting in low pH (< 5) and strongly elevated concentrations of major and trace elements in adjacent streams (Weppling 1993, La- hermo et al. 1996, Åström and Åström 1997, Eden et al. 1999, Åström and Spiro 2000, Åström 2001, Sundström et al. 2002). This causes severe hydro- biological harm, including occasional fish death and disturbance in fish reproduction (e.g. Hildén et al. 1984, Urho et al. 1990, Kjellman et al. 1994). The Rintala plain, that is in the focus of this study, is 23 km2 of which about 70% (17 km2) con- sists of AS soil (pH < 4; Fig. 1) that has developed on parent sediments with S concentrations between 0.2% and 1.1%. Almost all of the AS soil in Rinta- la are Sulfic Cryaquepts in Soil Taxonomy (Soil Survey Staff 2003) and, as elsewhere in Finland, only a small minority (~5%) of the AS soil are Typic Sulfaquepts. The clay content is between 25–35% below the plough layer (hydrometer anal- ysis; data from Österholm and Åström 2002). The remaining area consists of moderately acidic soils (pH 5–6.5) with either low S-concentrations (< 0.1%) or very high concentrations of organic mat- ter (C > 4%; Fig. 1). The development of active AS soil and the subsequent discharge of acid- and met- al rich waters from Rintala did not start until the early 19th century (and even then only on a rela- Ky rö nj ok i r iv er Sot aoj a Moderately acid soil, tot S <0,1% Moderately acid soil, tot S 0.2-0.3% and tot C >4% in the B-horizon Embankment and/or border of the Rintala area Acid sulphate soil (pH <4), tot S 0.2-1.1% Dam Se5 So4 So3 So2 So1 So5 So8 So7 So6 Se4 Se3 Se2 Se1 Se7 Se6 Se8 Se9 Se10 Pumping station A rtificial channel Seinäjoki Old-Seinäjoki Fi nl an d Study area 2 km Fig. 1. The Rintala area (study area) located in western Finland. 46 A G R I C U L T U R A L A N D F O O D S C I E N C E Österholm, P. et al. Aquatic pollution caused by acid sulphate soils tively small scale) when Sotaoja stream was dug through the central and southern parts of the area (Fig. 1) and the peat cover was burned (Österholm and Åström 2004). Thereafter a network of surface ditches have successively been dug denser and deeper throughout the area. To make the drainage efficient enough for modern agricultural activities, subsurface drainage was introduced in the1950s and became the main drainage type in the 1970s. Since 1982, most of the water in Seinäjoki stream has been redirected into an artificial channel, al- lowing only ca. 120 l s-1 (Aarno Halttu, personal communication) into old-Seinäjoki stream through the dam. This water consists of natural water from the Seinäjoki stream (ca. 80%; Fig. 1) and artificial water from a purifying plant (not indicated on the map). In order to even more efficiently control the hydrology of the Rintala plain, in the early 1980s embankments were raised along the Kyrönjoki river to prevent flooding and a pumping station was built at the old-Seinäjoki outlet (Fig. 1) to maintain stable water levels. Another pumping sta- tion was built in the northernmost part of the area but its capacity is only a few percents of the former. Hence, it has a small impact for the area as a whole, and because it is operated in a similar manner as the other pumping station, no further attention has been paid to it in this study. The Finnish Environ- ment Institute (Finnish state) applied for the envi- ronmental permit for building of the embankments and pumping stations and the water-rights court granted it in 1984. The water-rights court, howev- er, considered that these procedures could increase the metal- and acid load on Kyrönjoki river. In connection with the renewal of the environmental permit in 1992, the Finnish Environment Institute was obliged to improve the quality of the drainage water either by preventing the oxidation of the soils or by treating the water before letting it into Kyrönjoki river. The Finnish Environment Insti- tute which regarded this obligation (among others) as unreasonable, appealed against the decision to the water-rights court of appeal in 1994. The ap- peal did not result in any changes regarding the obligation to improve the water quality. The envi- ronmental permit needs to be renewed by the end of year 2005 and in connection with this, the ful- fillment of the above mentioned obligation will be examined. Rintala is the only AS soil area in Fin- land which is under such an obligation. In this paper, we characterise the surface-water quality of the Rintala plain, and based on that char- acterisation and other available information and field experiences, we discuss how the water quality of the area should be improved and how the juridi- cal obligation of the area should be answered. Methods Stream-water samples were collected in October 1997 (autumn) and May 1998 (spring) at eight sites along Sotaoja stream, ten sites along old-Seinäjoki stream and 15 sites (in spring only) in low-order streams (small ditches), which includes 6, 4 and 5 streams draining AS soils, organic rich soils and forest & rural areas (in the vicinity of Rintala) re- spectively. At ten sites in autumn and at seven sites in spring samples were taken in duplicate. The samples were filtered (0.45 μm) and acidified with ultrapure HNO3 and then analysed for Al (6.9%), As (2.7%), Ba (6.0%), Ca (5.8%), Cd (2.0%), Co (2.0%), Cr (5.1%), Cu (4.1%), Fe (4.1%), K (7.8%), Mg (5.8%), Mn (13.1%), Ni (7.3%), Pb (24.7%), Se (6.7%), Sr (4.0%), V (4.0%) and Zn (3.8%) con- centrations with the inductively-coupled-plasma mass-spectrometry (ICP-MS) and inductively-cou- pled-plasma atomic-emission-spectrometry (ICP- AES). The relative standard deviation (analytical precision), calculated from the duplicates, is indi- cated in brackets above. The electric conductivity, pH, acidity (SFS 3005) and concentrations of (NO2 - + NO3 -)-N (concentrations as nitrite-nitrogen + ni- trate-nitrogen and indicated below as NO2_3-N; SFS 3030), NH4 +-N (concentrations as ammonium-ni- trogen; SFS 3032), P (SFS 3026), Cl (SFS 3006), SO4 2- (concentrations as sulphate; SFS 5738), F (SFS-EN ISO 10304-1) and total organic carbon (TOC; SFS-EN 1484) were determined in the labo- ratories of the West Finland Regional Environment Centre. Runoff data was obtained from the meas- uring weir, monitored and maintained by the Finn- 47 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 14 (2005): 44–56. ish Environment Institute, at the nearby Kainas- tonluoma reclaim area. Results and discussion Hydrochemistry of low order streams In spring 1998, the low-order streams draining AS soils were more acid (median pH 4.0), had signifi- cantly higher electric conductivity (median 136 mS m-1) and carried significantly higher concentra- tions of SO4 2-, Al, Ca, Cd, Co, Cu, F, Mn, Ni, Pb, Se, Sr and Zn than those draining forest and rural areas in the vicinity of the Rintala plain and or- ganic-rich soils located on the plain (Table 1). With the exception of Pb, this suite of elements is also clearly elevated in other similar streams draining Boreal AS soils (Åström and Björklund 1995, Åström and Åström 1997) and, with the exception of Al, depleted in the B-horizon in AS soil in Rintala (Cd, Se and F not determined; Österholm and Åström 2002). On the contrary, elements that Table 1. Hydrochemistry of low-order streams draining acid sulphate soils, organic-rich soils and forest & rural areas in Rintala in May 1998, and of headwater streams in Finland (Lahermo et al. 1996). Acid sulphate soil n = 6 Organic-rich soils n = 4 Forest and rural n = 5 Headwater streams n = ca. 1150 min med max min med max min med max med Temperature (°C) 2.8 7.5 7.7 3.5 6.4 9.4 3.2 4.6 9.1 – pH 3.7 4.0 4.2 5.5 5.7 A 6.0 5.1 5.5 A 6.6 5.9 EC (mS m-1) 108 136 TF 194 51 60 F 63 6 10 27 4 Acidity (mmol l-1) 2.0 4.0 TF 8.0 1.0 1.4 F 2.2 0.2 0.2 0.3 – SO4 2- (mg l-1) 510 700 TF 1200 76 97 F 130 13 15 63 3 NO2_3-N (mg l -1) 2.7 6.7 F 8.3 11.2 15.3AF 19.0 0.1 0.2 0.8 0.5 NH4 +-N (mg l-1) 0.1 1.0 F 2.6 0.4 0.4 0.5 0.0 0.2 0.8 – P (µg l-1) 18 31 72 58 79 A 98 30 81 A 181 – Cl (mg l-1) 23 39 F 53 42 56 F 65 3 10 27 1 F (mg l-1) 0.6 1.5 TF 3.5 0.2 0.3 F 1.2 0.1 0.1 0.1 0.1 TOC (mg l-1) 6 10 25 25 31 AF 45 16 24 A 26 – Al (mg l-1) 3.3 11.8 TF 59.5 0.0 0.1 0.1 0.1 0.5 0.6 0.1 As (µg l-1) 0.4 0.7 2.0 0.3 0.7 1.1 1.2 1.7 AT 2.9 0.4 Ba (µg l-1) 12 23 28 55 85AF 98 16 24 27 10 Ca (mg l-1) 22 50 TF 139 10 25 F 28 5 5 22 4 Cd (µg l-1) 0.6 1.0 TF 3.5 0.1 0.2 0.3 0.1 0.1 0.1 < 0.02 Co (µg l-1) 58 110 TF 363 2 4 5 2 4 10 0.2 Cr (µg l-1) 1.1 2.2 5.9 1.6 2.3 2.8 1.2 1.6 2.4 0.5 Cu (µg l-1) 7.7 17.0TF 150.6 2.4 4.8 5.5 5.5 7.5 T 8.6 0.6 Fe (mg l-1) 0.37 0.90 3.54 0.12 0.36 0.56 0.39 0.59 0.92 0.68 K (mg l-1) 5.0 7.8 F 21.0 2.6 5.3 6.6 1.7 3.2 6.8 0.7 Mg (mg l-1) 16 25 F 106 8 22 F 26 2 2 6 1 Mn (mg l-1) 3.1 5.7 TF 17.2 0.2 0.8 F 0.9 0.1 0.1 0.2 0.03 Ni (µg l-1) 87 156 TF 554 5 8 9 5 11 44 0.5 Pb (µg l-1) 0.4 0.8 TF 10.3 b.d. 0.2 0.3 0.1 0.3 0.4 0.2 Se (µg l-1) 0.7 2.2 TF 6.5 b.d. 0.3 0.4 b.d. 0.2 0.3 0.1 Sr (µg l-1) 185 361TF 807 71 192F 217 27 28 82 22 V (µg l-1) 0.1 0.3 0.5 0.4 1.2 A 1.7 1.7 1.8 AT 2.3 0.5 Zn (µg l-1) 170 329 TF 1103 10 18 36 12 26 71 4 A Significantly (α = 0.1) higher than for streams draining acid sulphate soil (Mann Whitney) T Significantly (α = 0.1) higher than for streams draining organic-rich soils (Mann Whitney) F Significantly (α = 0.1) higher than for streams draining forest & rural areas (Mann Whitney) EC = electric conductivity TOC = total organic carbon 48 A G R I C U L T U R A L A N D F O O D S C I E N C E Österholm, P. et al. Aquatic pollution caused by acid sulphate soils are not enriched in the AS soil-waters (Ba, Cr, V) are not depleted in the soils (Österholm and Åström 2002). There is, thus, no question that the acidity and high metal concentrations of the Rintala sur- face waters originate in the zone of active oxida- tion and weathering in the AS soil. A characteristic feature of streams draining or- ganic-rich soils is high TOC, NO2_3-N and Ba con- centrations, and of those draining forest and rural areas weakly but significantly elevated As and V concentrations (Table 1). Both stream types also have significantly higher P concentrations than those draining AS soil. Because these two streams types have higher conductivity and concentrations of SO4 2- and several metals than what can be con- sidered as ”background concentrations” in the country (headwater streams; Table 1, last column), some unknown small patches of AS soil are likely to exist in the drainage areas of at least some of the streams of these groups. Hydrochemistry of the Sotaoja stream In the upper Sotaoja stream (So1-So3; Fig. 1) in autumn 1997, the concentrations of the AS soil related determinants occur in high concentra- tions: those of SO4 2-, Al, Ca, Cd, Co, Mn, Ni, Se and Zn were similar to the maximum concentra- tions and those of Cu, Pb, F and H3O + similar to the median concentrations in the low-order streams (Table 1 and 2). In the lower Sotaoja stream (So4-So8, Fig. 1), the concentrations of these determinants were approximately half as high as those in upper Sotaoja (Table 2). A similar downstream pattern exists for NH4 +-N, Fe, K and Mg (Table 2). There are three reasons for this pat- tern: (1) in the area that drains to upper Sotaoja, widespread fresh AS soil deliver large quantities of elements into drainage, (2) downstream of So3, Sotaoja merges with a relatively big stream (twice as large as upper Sotaoja; not indicated in the map) which rises in the forest and rural areas east of the Rintala plain (Fig. 1) and contains relatively low element concentrations, resulting in dilution of the Sotaoja stream water (Table 2), and (3) the lower reaches of Sotaoja stream (So4- So8) receives discharge both from AS soils and organic-rich soils (Fig. 1). In spring 1998, there was a similar spatial pat- tern, i.e. the concentrations of the AS soil related determinants including K and Mg (Table 2) were approximately twice as high in the upper (So1- So3) as in the lower Sotaoja (So4-So8), indicating similar sources, hydrological pathways and con- trols in the two seasons. However, in spring the overall concentration level was only approximate- ly half as high as that in autumn, and in upper So- taoja, as expected, the concentration level was overall similar to the median of the water samples collected on the same occasion from low-order streams draining AS soil (Table 1 and 2). Two pos- sible explanations for the lower element concen- trations in spring are: (1) different hydrological conditions indicated by the higher runoff (16 l s-1 km-2) than in autumn (6 l s-1km-2) resulting in dilu- tion, and/or (2) the acidity and elements released by oxidation and weathering in the AS soil in the summer were primarily leached in autumn (Palko and Yli-Halla 1993), leaving behind a minor pool of mobile compounds which were leached the fol- lowing spring. Hydrochemistry of the old-Seinäjoki stream In autumn 1997, pH was circumneutral and the concentrations of elements were overall low at Se 1 (Table 3; Fig. 1). This is due to discharge of larger quantities of circumneutral dilute water from the dam (probably up to 250 l s-1). From Se1 to Se10 (Fig. 1) there was an overall increase in the concentrations of many variables (Table 3), ex- plained by the downstream increase in the propor- tion of AS soil. In spring 1998, the downstream variations in the concentrations of V, As, P and TOC were small and unsystematic (Table 3). In contrast, the con- centrations of all other variables increased through the upper reaches (from Se1 to Se3), decreased through the middle reaches (from Se4 to Se7) and increased again through the lower reaches (from 49 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 14 (2005): 44–56. Table 2. Analytical results for samples collected in Sotaoja stream and the main inflow ditch. OCTOBER 1997 Sample So1 So2 So3 Inflow ditch So4 So5 So6 So7 So8 Temperature (°C) 1.2 1.5 2.1 0.9 1.3 1.6 1.5 1.4 1.4 pH 3.9 3.9 3.9 4.3 4.1 4.1 4.2 4.2 4.2 EC (mS m-1) 206 205 176 64 100 126 118 117 114 Acidity (mmol l-1) 5.9 5.5 6.4 1.1 2.4 3.2 2.8 2.8 2.7 SO4 2- (mg l-1) 1170 1300 1240 223 600 685 650 600 600 NO2_3-N (mg l -1) 6.6 7.3 8.0 2.8 4.1 6.6 5.7 5.7 5.8 NH4 +-N (mg l-1) 0.33 1.53 1.65 0.16 0.54 0.86 0.69 0.68 0.65 P (mg l-1) 0.02 0.03 0.05 0.02 0.03 0.02 0.02 0.03 0.03 Cl (mg l-1) 41 43 41 28 32 35 35 33 35 F (mg l-1) 2.20 2.15 2.30 0.55 1.05 1.27 1.19 1.12 1.14 TOC (mg l-1) 13 12 12 22 23 19 18 20 19 Al (mg l-1) 20 39 46 6 14 25 16 17 17 As (µg l-1) 1.08 1.67 1.73 1.53 1.55 1.49 1.33 1.29 1.49 Ba (µg l-1) 24 30 27 34 41 35 35 39 Ca (mg l-1) 94 146 159 41 60 92 72 71 70 Cd (µg l-1) 2.81 4.44 4.98 1.07 2.13 2.35 1.82 1.72 2.08 Co (µg l-1) 257 416 477 89 172 215 175 163 171 Cr (µg l-1) 1.5 2.4 3.1 1.7 2.0 2.6 1.9 1.9 2.4 Cu (µg l-1) 22 36 42 19 24 29 22 21 23 Fe (mg l-1) 1.41 1.78 1.48 0.81 0.97 1.00 0.81 0.77 0.81 K (mg l-1) 18 32 34 10 14 18 14 15 15 Mg (mg l-1) 83 142 167 31 58 88 64 66 68 Mn (mg l-1) 20 21 20 4.6 12 17 13 13 13 Ni (µg l-1) 335 560 645 176 274 334 250 257 258 Pb (µg l-1) 1.1 2.0 2.4 0.6 1.0 1.5 0.8 0.8 0.8 Se (µg l-1) 4.5 7.0 7.5 1.7 3.3 4.6 3.9 3.6 3.8 Sr (µg l-1) 781 1205 1244 522 685 585 557 602 V (µg l-1) 0.22 0.34 0.35 1.06 0.79 0.76 0.60 0.61 0.70 Zn (µg l-1) 842 1241 1349 334 598 729 601 557 631 Se8 to Se10; Table 3). The strong increase in the upper reaches is due to the moderate contribution of circumneutral dilute water from the dam (ap- proximately 120 l s-1), and the impact of high run- off (16 l s-1 km-2) from the agricultural fields un- derlain mainly with AS soil (Fig. 1). The decrease in concentrations in the middle reaches is ex- plained by the contribution of dilute water mainly from forest and rural areas and to some extent from S-poor agricultural soils (non AS soils) to the north (Fig. 1). In the lower reaches, below the low-S area (Se8-Se10), the increase in concentrations was due to high inputs from agricultural fields underlain mainly with AS soil (catchment of Sotaoja stream in particular). At the outlet (Se10), the water was more acidic and had higher concentrations of ele- ments than in autumn, despite the fact that the So- taoja stream, which drains extensive areas of AS soils, was more acidic and had higher element con- centrations in the latter season (Table 2). This re- verse trend is explained mainly by two factors: (1) overall lower pH and higher element concentra- tions in the water exiting the AS soil in autumn, resulting in deterioration of the water quality in Sotaoja stream in that season, and (2) the propor- tion of water exiting AS soil relative to that dis- charged from the dam was considerably higher in spring, resulting in deterioration of the water qual- ity in old-Seinäjoki stream in that season. Hence, the temporal and spatial variations in water quality 50 A G R I C U L T U R A L A N D F O O D S C I E N C E Österholm, P. et al. Aquatic pollution caused by acid sulphate soils Table 2. (Continued) MAY 1998 Sample So1 So2 So3 Inflow ditch So4 So5 So6 So7 So8 Temperature (°C) 7.4 7.1 6.7 6.5 6.6 7.1 6.0 6.0 6.1 pH 3.9 4.0 4.0 4.5 4.3 4.4 4.4 4.4 4.4 EC (mS m-1) 146 142 137 47 82 88 91 88 86 Acidity (mmol l-1) 5.1 4.8 4.4 0.8 2.0 1.5 2.5 2.2 2.0 SO4 2- (mg l-1) 710 670 690 170 360 360 420 410 410 NO2_3-N (mg l -1) 10.0 10.6 11.4 4.2 3.1 9.3 9.3 9.5 9.7 NH4 +-N (mg l-1) 1.31 1.32 1.30 0.18 0.63 0.74 0.65 0.64 0.65 P (mg l-1) 0.04 0.04 0.04 0.04 0.05 0.05 0.05 0.05 0.05 Cl (mg l-1) 29 31 30 28 25 33 30 30 29 F (mg l-1) 1.70 1.70 1.50 0.39 0.81 0.88 0.87 0.86 0.84 TOC (mg l-1) 14 14 15 20 19 20 19 19 20 Al (mg l-1) 25 17 16 1 5 7 4 6 7 As (µg l-1) 0.92 0.70 0.68 0.59 0.56 0.74 0.48 0.60 0.74 Ba (µg l-1) 27 17 21 26 41 35 28 43 Ca (mg l-1) 92 65 58 13 27 41 24 33 32 Cd (µg l-1) 2.13 1.57 1.76 0.33 0.74 1.04 0.60 0.81 1.04 Co (µg l-1) 233 165 173 29 69 94 55 76 96 Cr (µg l-1) 3.3 2.0 2.5 1.0 1.4 1.9 1.4 1.3 2.0 Cu (µg l-1) 29 21 21 7 10 13 8 10 13 Fe (mg l-1) 1.51 1.10 0.97 0.25 0.49 0.58 0.32 0.41 0.44 K (mg l-1) 13 10 12 4 6 9 4 7 7 Mg (mg l-1) 53 39 42 8 19 29 16 23 25 Mn (mg l-1) 13 9 10 1.4 4 5 3 4 5 Ni (µg l-1) 329 226 241 49 98 129 77 108 134 Pb (µg l-1) 1.0 0.9 0.8 0.2 0.4 0.6 0.4 0.5 0.5 Se (µg l-1) 2.7 1.8 2.0 0.3 0.7 0.9 0.7 0.8 1.2 Sr (µg l-1) 609 437 433 200 303 185 254 335 V (µg l-1) 0.33 0.26 0.25 0.50 0.40 0.51 0.34 0.40 0.56 Zn (µg l-1) 623 467 488 94 209 281 167 230 280 EC = electric conductivity TOC = total organic carbon in the area are complex, but overall the water qual- ity is very poor and typical for AS soil affected waters. Appropriate methods for improvement of water quality In stream liming, i.e. applying lime in the streams in Rintala, is not motivated because of the great amounts of lime needed (> 100 t CaO per year) to reduce the acidity and the huge amounts of metals leached (e.g. 50 kg Al ha-1 a-2 in upper Sotaoja; Österholm and Åström 2004) which, if neutralisa- tion would be successful, would create a big prob- lem with metal precipitates in the drains. If, despite its limitations, in-stream liming would be used in Rintala, a choice of conventional limestone (CaCO3) powder might be appropriate in the old- Seinäjoki stream while the high acidity in the So- taoja stream (> 2 mM L-1; Table 2), in accordance with recommendations by Weppling (1997), would require the use of easily-dissolved hydrated lime or quick lime (CaO) in order to optimize the neu- tralisation effect and costs. 51 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 14 (2005): 44–56. Table 3. Analytical results for samples collected in Seinäjoki stream. OCTOBER 1997 Sample Se1 Se2 Se3 Se4 Se5 Se6 Se7 Se8 Se9 Se10 Temperature (°C) 4.3 3.4 3.2 2.9 3.2 3.2 3.5 3.4 3.4 3.2 pH 6.6 5.6 5.5 5.7 5.6 5.3 5.5 5.3 5.3 4.6 EC (mS m-1) 11 15 14 17 25 25 23 21 21 31 Acidity (mmol l-1) 0.1 0.2 0.2 0.2 0.3 0.4 0.3 0.4 0.4 0.6 SO4 2- (mg l-1) 14 30 34 41 62 67 64 51 63 106 NO2_3-N (mg l -1) 2.2 1.2 1.2 1.8 3.6 3.2 3.1 1.9 2.1 2.0 NH4 +-N (mg l-1) 0.06 0.11 0.08 0.08 0.11 0.11 0.10 0.06 0.08 0.13 P (mg l-1) 0.12 0.07 0.06 0.08 0.08 0.06 0.05 0.05 0.05 0.06 Cl (mg l-1) 8 10 10 12 16 14 14 11 11 13 F (mg l-1) 0.11 0.16 0.17 0.18 0.23 0.24 0.23 0.18 0.22 0.30 TOC (mg l-1) 20 19 20 22 18 18 17 22 25 22 Al (mg l-1) 0.03 0.30 0.44 0.37 0.29 0.63 0.53 0.82 0.93 2.56 As (µg l-1) 1.14 0.72 1.05 1.24 0.80 1.12 0.99 1.48 1.18 1.03 Ba (µg l-1) 11 11 13 15 13 16 14 16 17 20 Ca (mg l-1) 7 7 10 10 13 16 17 14 16 18 Cd (µg l-1) 0.03 0.07 0.11 0.10 0.15 0.23 0.20 0.22 0.21 0.66 Co (µg l-1) 0.3 5 7 7 9 14 13 13 16 32 Cr (µg l-1) 0.7 0.5 0.8 0.9 0.7 1.0 0.9 1.2 1.0 1.3 Cu (µg l-1) 10.0 6.7 8.5 6.9 5.5 8.7 7.8 8.3 8.4 9.5 Fe (mg l-1) 0.23 0.14 0.26 0.30 0.16 0.28 0.29 0.62 0.50 0.51 K (mg l-1) 3.1 2.5 3.4 3.6 4.9 5.3 5.4 4.6 4.8 5.0 Mg (mg l-1) 2.2 3.3 4.7 4.8 5.8 7.2 7.2 6.7 8.1 12.9 Mn (mg l-1) 0.02 0.27 0.42 0.39 0.54 0.76 0.78 0.71 0.97 1.97 Ni (µg l-1) 4 10 16 15 20 30 29 28 33 53 Pb (µg l-1) 0.2 0.1 0.1 0.1 0.1 0.2 0.2 0.3 0.3 0.2 Se (µg l-1) 0.2 0.4 0.5 0.3 0.4 0.6 0.7 0.6 0.6 0.8 Sr (µg l-1) 34 41 59 65 69 90 83 78 86 126 V (µg l-1) 0.25 0.15 0.28 0.33 0.25 0.44 0.46 0.84 0.65 0.57 Zn (µg l-1) 19 38 47 47 58 79 88 70 80 158 Passive treatment methods which utilize bio- logical and chemical processes that traditionally have been used for treatment of mine drainage, are tested on AS soil drainage in Rintala (Successive Alkaline Passive Treatment) and in McLeods creek, Australia (Closed Tank Reactor; Desmier et al. 2002). In the method used in Rintala, water is infiltrated through a 0.5 m thick layer of organic material on top (removing O2 and Fe 3+, and retain- ing metals through sulphate reduction and adsorp- tion) and a 0.5 m thick layer of limestone below (reducing acidity). Thereafter, metals not yet re- tained are precipitated as hydroxides in a settling pond by aeration. While these methods can signifi- cantly increase the pH and remove metals from the treated water, the volume of water which can be treated will be too low to have a significant impact on the overall water quality in an area like Rintala with 17 km2 of AS soil and an average runoff of about 7 l s-1km-2. Furthermore, as this study shows, the Rintala streams are in most parts diluted by non-AS soil drain waters which further increases the amounts of waters that would have to be han- dled. If these passive treatments were to be used on a large scale in the area, although not recommend- ed by the authors, the hydrochemical data of this study shows that upper Sotaoja, where the AS soil waters are undiluted and of very poor quality, is the best choice of location (Table 2). Soil surface liming (about 10–30 t ha-1 5 years) on AS soil keeps the pH above 5 in the plough layer and turns these otherwise rather unfertile 52 A G R I C U L T U R A L A N D F O O D S C I E N C E Österholm, P. et al. Aquatic pollution caused by acid sulphate soils Table 3. Continued MAY 1998 Sample Se1 Se2 Se3 Se4 Se5 Se6 Se7 Se8 Se9 Se10 Temperature (°C) 9.7 8.8 9.0 9.1 8.7 7.7 7.7 7.3 6.9 7.2 pH 5.7 4.2 4.2 4.3 4.3 4.4 4.4 4.3 4.3 4.4 EC (mS m-1) 10 82 90 76 68 56 54 59 61 70 Acidity (mmol l-1) 0.2 2.4 2.6 2.0 1.7 1.3 1.2 1.2 1.4 1.5 SO4 2- (mg l-1) 25 380 410 350 250 220 230 220 250 260 NO2_3-N (mg l -1) 0.8 3.6 4.1 3.5 3.6 3.2 3.2 3.5 3.9 6.6 NH4 +-N (mg l-1) 0.23 1.17 0.98 0.74 0.51 0.42 0.32 0.26 0.26 0.46 P (mg l-1) 0.07 0.03 0.03 0.03 0.03 0.04 0.04 0.04 0.04 0.04 Cl (mg l-1) 7 27 32 28 27 23 21 22 22 25 F (mg l-1) 0.13 1.10 1.20 0.93 0.79 0.68 0.56 0.57 0.66 0.77 TOC (mg l-1) 20 12 11 12 13 16 15 16 16 18 Al (mg l-1) 0.32 10.4 12.2 10.6 8.21 3.3 2.9 3.12 4.43 5.86 As (µg l-1) 0.74 0.72 0.74 1.04 0.90 0.66 0.63 0.61 0.80 1.02 Ba (µg l-1) 24 22 29 31 25 22 16 17 19 33 Ca (mg l-1) 6 36 46 46 39 20 16 18 26 38 Cd (µg l-1) 0.08 0.70 0.95 0.89 0.79 0.38 0.35 0.40 0.60 1.01 Co (µg l-1) 5 70 93 86 73 35 30 36 55 87 Cr (µg l-1) 1.1 2.1 2.1 2.1 1.8 1.4 1.1 1.0 1.4 1.7 Cu (µg l-1) 4.0 17.7 21.1 19.7 15.1 8.4 8.0 8.1 11.1 14.3 Fe (mg L-1) 0.31 0.86 1.05 1.01 0.83 0.44 0.39 0.39 0.57 0.60 K (mg l-1) 2.2 7.0 9.5 9.8 8.7 4.8 3.4 4.4 5.9 8.5 Mg (mg l-1) 2.6 20.6 25.9 25.4 22.3 10.9 9.4 10.9 16.0 24.9 Mn (mg l-1) 0.24 3.39 4.56 4.35 3.77 1.74 1.54 1.95 2.93 4.65 Ni (µg l-1) 10 127 165 152 127 62 53 59 90 135 Pb (µg l-1) 0.2 0.5 0.6 0.6 0.4 0.4 0.3 0.4 0.4 0.6 Se (µg l-1) - 2.1 2.8 2.5 1.9 0.9 0.7 0.7 1.1 1.3 Sr (µg l-1) 38 256 339 328 282 137 113 127 186 296 V (µg l-1) 0.47 0.35 0.33 0.50 0.64 0.52 0.50 0.51 0.66 0.81 Zn (µg l-1) 22 257 331 309 258 123 106 125 173 266 EC = electric conductivity TOC = total organic carbon lands into some of the most productive farm lands in Finland. However, the lime (in at least short term) does not penetrate below the plough layer where most of the acidity is stored (Weppling 1997, Österholm and Åström 2002) and does therefore not have a notable impact on drainage waters (Palko 1994, Puustinen 2001). Even if the lime would penetrate into deeper soil layers, the amounts needed to neutralise the soil acidity are unrealistically high in an area like Rintala where the chemical drainage depth is about 1.8 m (Öster- holm and Åström 2002). Lime filter drainage is a relatively new technique in Finland where lime is applied around the subsurface pipes (Weppling 1997). This method seems to significantly reduce the drain water acidity and precipitates metals into the soils around the drain pipes. However, since the method is basically based on neutralisation of acidity by lime, the lime reservoir is depleted in a few years in AS soil areas like Rintala (Triipponen 1997, Puustinen 2001) and there is an obvious risk that remobilisation of metal precipitates around the drain pipes will then occur. Nonetheless, at one test site in W. Finland (Ilmajoki), it seems that by combining lime filter drainage and controlled drainage (method described below) the neutralisa- tion capacity is both prolonged and increased (Bär- lund et al. 2004). Hence, it would be worthwhile to 53 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 14 (2005): 44–56. monitor that test site for some more years in order to make a better judgement on the functionality of the combination of the two techniques. Groundwater management, i.e. keeping the groundwater table as high and as stable as possi- ble, hampers soil oxidation, and thus, acidity pro- duction and metal mobilisation is reduced. It might also reduce the upward movement of acid waters, by retarding capillary forces, during dry periods (Pelanteri 1998). Furthermore, maybe the most important factor with groundwater management, which has received little or no attention when eval- uating environmental measures on ASS, is that it seems to reduce the amount of drain outflow very effectively. On (non AS soil) farmlands in Sweden (Wesström et al. 2001, 2003) and North Carolina (Gilliam et al. 1997) it has been observed that con- trolled pipe drainage (CPD) can reduce the drain outflow by 30% or more due to increased eva- potranspiration and crop growth. The reduction in runoff is highest in dry years, while in rainy years it may have little or no effect on runoff (Gilliam et al. 1997). Consequently, even if groundwater man- agement would not affect the water quality from AS soil to a large extent, it is likely to have a great impact on the total amount of metals and acidity being leached from these soils per unit of time. Controlled pipe-drainage is suitable for agricul- tural lands with a low relief (< 2%) and a high hy- draulic conductivity (> 0.5 m d-1, Evans and Skagg 1989), and is becoming increasingly popular in western Finland (Rainer Rosendahl, personal com- munication). Technically, the subsurface drainage pipes are lead into a well where the height of the groundwater can be controlled by adjusting the height of the output valve (riser). The idea with CPD is to enable trafficability by keeping drainage intensity high (low riser and/or bottom valve open) during cropping and harvesting and to minimise drainage at other times in order to prevent over- drainage. Besides from its potential ability to re- duce S oxidation and metal release, it is claimed to increase the crop yield. Promising results (regard- ing water-quality) have been obtained with CPD at an AS soil site in Ilmajoki, western Finland (Jou- kainen and Yli-Halla 2003, Bärlund et al. 2004), which is an area close to Rintala and with rather similar soil properties. However, at another test site in western Finland (Korsholm) where the groundwater is naturally high, the groundwater could not be further raised by CPD, and conse- quently the water quality was not improved (Bär- lund et al. 2004). There are also maintenance prob- lems at several other CPD sites (i.e. very low groundwater level), possibly due to (1) evapotran- spiration, (2) bypass seepage to the main ditch and (3) the bottom valve is kept open (enabling maxi- mum drainage) for too long in connection with field work, resulting in overdrainage. It has been suggested (e.g. Joukainen and Yli-Halla 2003) that it may be necessary to pump water into the control wells in order to maintain the high groundwater level. But, if the groundwater is artificially raised (not just maintained on a fixed level), it can not be excluded that this would increase rinsing of acidity and metals from the soils. For the Rintala area we thus recommend, without having considered the economical aspects, groundwater management with CPD preferably combined with construction of one or several dams in Sotaoja and stricter regu- lation of the water level at the pumping stations. Raised bed drainage, a method used on AS soils in Australia and Vietnam, could be a potential method on Finnish AS soils in combination with conventional groundwater management (Ian White and Mike Melville, personal communication). The advantage is that the field is trafficable even at high groundwater levels and that crop yields are good, while one of the disadvantages is that all farming machines need to have the same wheel shaft width. Furthermore, as the soil structure is permanently destroyed below the wheel lanes, the width between the lanes can not be changed later. This technique has not yet been trialed on Finnish AS soils. The use of the traditional open ditches instead of subsurface drainage on AS soil areas would have a significant positive effect on the water qual- ity (Palko and Yli-Halla 1993), but due to several agricultural drawbacks and the fact that most of the Rintala area is already drained by subsurface pipes, it can not be considered as a potential meth- od for Rintala. 54 A G R I C U L T U R A L A N D F O O D S C I E N C E Österholm, P. et al. Aquatic pollution caused by acid sulphate soils The juridical obligation to improve water quality The juridical obligation to improve the water qual- ity in the Rintala area is based on the assumption that the embankment of Kyrönjoki river and the construction of the pumping stations might have a negative effect on the water quality in Kyrönjoki river. Above it is clearly demonstrated, that the ac- ids and metals are derived from the acidic subsoil horizons, which have developed because of water table drawdown caused by extensive ditching op- erations over the last two hundred years (the last few decades in particular). Hence, the control of the water quality of the area is the groundwater level of the area and therefore we argue above that better ground water management (rise in ground- water table) is the key to a better water quality in the future. As a result of the embankment of Kyrönjoki river and the construction of the pumping stations, it has been possible to release excess water (and lower the groundwater table) earlier in the spring. On the other hand, prior to these engineering ma- nipulations, the water level in the Old-Seinäjoki stream was occasionally much lower than at present (Vesihydro 1992) as there was no pumping station and associated dam to prevent outflow dur- ing dry periods. Because of these contrasting ef- fects and the fact that long-term data on water quality and ground water levels does not exist for the area, it is not possible to determine whether the highlighted works have forced the ground water to drop and concomitantly the water quality to dete- riorate. The opinion of the authors is therefore, in line with the Finnish Environment Institute appeal in 1994, that the juridical obligation of the Rintala area is unreasonable. Considering the present-day expectations of surface water quality highlighted e.g. in the EU Water Framework Directive (CEC 2000), the sur- face water originating from the Rintala AS soil have unacceptable loads of acidity and potentially toxic metals. In this sense, a juridical obligation would be justified, but it should, unlike the present one, focus on the source of the problems (water table drawdown caused by ditching). Also, due to the equality principle, any water-quality related ju- ridical obligation should not focus specifically on Rintala, because the AS soil of this area do not supply more acids and metals than other typical AS soils of the region (Åström 1996) and they comprise only 1–2% and 5–10% of all cultivated AS soil in Finland (Yli-Halla et al. 1999) and the Kyrönjoki catchment (Erviö 1975) respectively. Conclusions The concentrations of AS soil related determinants in the runoff from the Rintala AS soil are similar to that of other AS soil areas in western Finland. The chemistry of the water emptying from the Rintala pumping station into Kyrönjoki river is controlled by the extent of release of acids, metals and other compounds from the AS soils, and by the extent to which the AS soil runoff is diluted (and neutral- ised) by water from the dam, the forest & rural ar- eas and the organic-rich soils. At a runoff similar or lower than that in October 1997 (≤ 8 l s-1km-2), the water from the dam is the most important dilut- ant. In order to improve water quality in Rintala, groundwater management by controlled pipe drainage, preferably combined with a dam in So- taoja and possibly stricter regulation at the pump- ing station, is recommended because: (1) the relief and soil type are suitable for controlled pipe drain- age, (2) it would reduce temporal overdrainage common in the area, (3) the amounts of metals and acidity released with current drainage practices is too high to be cleaned ex situ, (4) it has the poten- tial to improve the water quality and reduce amount of runoff and (5) it has the potential to be accepted by farmers. The current juridical obligation for Rintala is not justified, because it fails to address the reason for the poor water quality, i.e. previous and current drainage works. Acknowledgements. 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Lahermo, P., Väänänen, P., Tarvainen, T. & Salminen, R. 1996. Geochemical atlas of Finland, Part 3: Environ- mental geochemistry – stream waters and sediments. Geological Survey of Finland, Espoo, Finland. 149 p. Österholm, P. & Åström, M. 2002. Spatial trends and losses of major and trace elements in agricultural acid sulphate soils distributed in the artificially drained Rintala area, W. Finland. Applied Geochemistry 17: 1209–1218. Österholm, P. & Åström, M. 2004. Quantification of current and future leaching of sulfur and metals from Boreal acid sulfate soils, western Finland. Australian Journal of Soil Research 42: 547–551. Palko, J. 1994. Acid sulphate soils and their agricultural and environmental problems in Finland. Ph.D. thesis, Univer- sity of Oulu. Acta Universitatis. Ouluensis. C 75. 58 p. Palko, J. & Yli-Halla, M. 1993. Assessment and manage- ment of acidity release upon drainage of acid sulphate soils in Finland. In: Dent, K.L. & Mensvoort, M.E.F. (eds.). Selected papers of the Ho Chi Minh City sympo- sium on acid sulphate soils. International Institute for Land Reclamation and Improvement, Publication 53. p. 411–418. Pelanteri, K. 1998. Säätösalaojitus happamilla sulfaattimail- la. In: Joukainen, S. Happamien sulfaattimaiden ympä- ristöongelmat. Finnish Environment Institute, Helsinki. 44 p. Puustinen, M. 2001. Management of runoff waters from ar- able land. Final report of the EU/LIFE Project (LIFE97 ENV/FIN/335). The Finnish Environment 477. 56 p. SFS 1484 Water analysis. Guidelines for the determination of total organic carbon (TOC) and dissolved organic carbon (DOC). Helsinki: the Finnish standardization organisation, 1997. 16 p. SFS 3005 Alkalinity and acidity in water. Potentiometric ti- tration. Helsinki: the Finnish standardization organiza- tion, 1981. 5 p. SFS 3006 Determination of chloride concentration in water. Potentiometric titration. Helsinki: the Finnish standardi- zation organisation, 1982. 6 p. SFS 3026 Determination of total phosphorous in water. Di- gestion with peroxide sulfate. Helsinki: the Finnish standardization organisation, 1986. 5 p. SFS 3030 Determination of the sum of nitrite and nitrate nitrogen in water. Helsinki: the Finnish standardization organisation, 1990. 5 p. SFS 3032 Determination of ammonia nitrogen in water. Helsinki: the Finnish standardization organisation, 1976. 6 p. SFS 5738 Determination of sulfate in water. Nephelometric method. Helsinki: the Finnish standardization organi- sation, 1992. 5 p. References 56 A G R I C U L T U R A L A N D F O O D S C I E N C E Österholm, P. et al. Aquatic pollution caused by acid sulphate soils SFS-EN ISO 10304-1 Water quality. Determination of dis- solved fluoride, chloride, nitrite, orthophosphate, bro- mide, nitrate and sulfate ions, using liquid chromatog- raphy of ions. Part 1: Method for water with low con- tamination (ISO 10304-1:1992). Helsinki: the Finnish standardization organisation, 1995. 22 p. Soil Survey Staff 2003. Keys to soil taxonomy. 9th ed. USDA. Natural Resources Conservation Service. U.S. Government Printing Office. 332 p. Sundström, R., Åström, M. & Österholm, P. 2002. Compari- son of the metal content in acid sulfate soil runoff and industrial effluents in Finland. Environmental Science and Technology 36: 4269–4272. Triipponen, J.-P. 1997. Sirppujoen valuma-alueen tutkimus. Lounais-Suomen ympäristökeskus. 43 p. (in Finnish). Urho, L., Hilden, M. & Hudd, R. 1990. Fish reproduction and the impact of acidification in the Kyrönjoki River estuary in the Baltic Sea. Environmental Biology of Fishes 27: 273–283. van Breemen, N. 1973. Soil forming processes in acid sul- phate soils. In: Dost, H. (ed.). Acid sulphate soils. Pro- ceedings of the International Symposium on Acid Sul- phate Soils. International Institute for Land Reclamation and Improvement, Publication 18. p. 66–130. Vesihydro 1992. Rintalan pengerrysalueen kuivatusvesien pumppaamisen vaikutus Kyrönjoen veden laatuun, veden hankintaan ja kalatalouteen. Report. 44 p. (in Finnish). Weppling, K. 1993. Hydrochemical factors affecting the neutralization demand in acid sulphate waters. Vatten 49: 161–170. Weppling, K. 1997. On the assessment of feasible liming strategies for acid sulphate waters in Finland. Ph.D thesis, University of Tartu, Estonia. 81 p. Wesström, I., Ekbohm, G., Linnér, H. & Messing, I. 2003. The effects of controlled drainage on subsurface out- flow from level agricultural fields. Hydrological Proc- esses 17: 1525–1538. Wesström, I., Messing, I., Linnér, H. & Lindström, J. 2001. Controlled drainage - effects on drain outflow and wa- ter quality. Agricultural Water Management 47: 85– 100. Yli-Halla, M., Puustinen, M. & Koskiaho, J. 1999. Area of cultivated acid sulfate soils in Finland. Soil Use and Management 15: 62–67. Rikkipitoiset maat ovat yleisiä Suomen länsirannikolla. Näiden maiden kuivatus on johtanut rikin hapettumiseen ja ns. happamien sulfaattimaiden (pH < 4) muodostumi- seen. Mailta huuhtoutuu runsaasti happamuutta, rikkiä ja metalleja, mikä aiheuttaa merkittävää ekologista hait- taa monissa Länsi-Suomen vesistöissä. Tässä työssä kä- sitellään alueellista vesigeokemiaa, keinoja vähentää ympäristökuormitusta ja juridisia velvoitteita Rintalan pengerrysalueella. Rintalan pengerrysalue (23 km2) sijaitsee Kyrönjo- en varrella Seinäjoen lounaispuolella. Happamia sul- faattimaita kuivattavat ojat ovat huomattavasti happa- mampia (pH = 4 ja happamuus = 4 mmol l-1) ja niissä on paljon suuremmat SO4 2--, Al-, Ca-, Cd-, Co-, Cu-, F-, Mn-, Ni-, Pb-, Se-, Sr- ja Zn-pitoisuudet kuin ei-happa- man (korkea humuspitoisuus) alueen ojissa sekä pen- gerrysalueen ulkopuolelta tulevien metsä- ja asutus- alueiden ojissa. Nämä ei-happamat ojat ja Seinäjoen vanhaan uomaan päästetty vesi voivat laimentaa Rinta- lasta Kyrönjokeen johdettavan veden happamuutta ja metallipitoisuuksia jopa yli 90 %, mutta veden laatu on silti huono. Alueen pengerryksen ja rakennettujen pumppaus- asemien vuoksi Rintalan alueelle on asetettu velvoite parantaa ulosjohdetun veden laatua. Velvoitetta on pe- rusteltu sillä, että mainitut rakennelmat voivat huonon- taa veden laatua. Kun otetaan huomioon nykypäivänä pintaveden laadulle asetettuja odotuksia (mm. EU:n ve- sipuitedirektiivi), sulfaattimaiden aiheuttamaa ympäris- tökuormitusta olisi aiheellista käsitellä oikeudessa. Vel- voitetta ei kuitenkaan voida pitää tarkoituksenmukaise- na, koska salaojitusta, joka on pääsyy veden huonoon laatuun Rintalan ja muun Suomen sulfaattimaa-alueilla, ei oteta lainkaan huomioon. Tämän lisäksi Rintala on ainoa pengerrysalue, jolle tällainen velvoite on asetettu, vaikka alueen veden laatu laimentamattomissa ojissa ei ole huonompi kuin muiden vastaavien alueiden veden laatu. Pohjaveden tarkempi kontrolli, ensisijaisesti sää- tösalaojituksella, olisi todennäköisesti paras keino hap- pamuuden ja metallipäästöjen pienentämiseksi. SELOSTUS Vesistön saastumisen arviointi, parannustoimenpiteet ja juridiset velvoitteet happamalle sulfaattimaa-alueelle Länsi-Suomessa Peter Österholm, Mats Åström ja Robert Sundström Åbo Akademi Assessment of aquatic pollution, remedial measures and juridical obligations of an acid sulphate soil area in western Finland Introduction Methods Results and discussion Conclusions References SELOSTUS