TY - JOUR
T1 - Characterization of acid sulfate soils and assessing their impact on a humic boreal lake
AU - Toivonen, Janne
AU - Österholm, Peter
PY - 2011/8
Y1 - 2011/8
N2 - Due to acidity and metals from acid sulfate soils (a.s. soils), many watercourses in midwestern Finland have since 1960s regularly experienced short but intensive periods of poor water quality during high water flow. This has led to occasional massive fish kills and a significant decline in fish populations.However, many watercourses in northern Europe are often also characterized by low pH caused by naturally occurring organic acids, non-carbonate bedrock and previously a large input of acid rain. Therefore the role of acid sulfate soils has not always been properly addressed.This study was done on Larsmo and Öja Lake, a freshwater reservoir embanked from the alkaline Bothnian Bay in the 1960s. Since that, events of severe acidity and fish kills have been documented on several occasions. Severe but heterogeneous a.s. soils with relatively coarse grain sizes were found in the catchment. These soils were found to leach metals typical for a.s. soils such as Al, Cd, Co, Ni and Zn to recipient streams, but in contrast to other a.s. soils studied in Finland, some of them even seem to be leaching large quantities of Fe. Patterns of acidity, sulfate, sulfur isotopes, organic carbon and metals in rivers, streams and the lake revealed that (1) a.s. soils in the catchment are by far the most important source of acidity and metals in the lake i.e. the main reason for fish kills, (2) the load from discharge of organic (humic) acids and dredging operations is insignificant on the lake as a whole, (3) young near-field sediments comprising only 7% of the whole catchment accounted for roughly 20-30% of the total acidic load, (4) most of the acid/metal load entered the lake system from the south, and (5) by regulating outlets to the sea it seems to be possible to prevent this load from dispersing into the northern part of the lake system.
AB - Due to acidity and metals from acid sulfate soils (a.s. soils), many watercourses in midwestern Finland have since 1960s regularly experienced short but intensive periods of poor water quality during high water flow. This has led to occasional massive fish kills and a significant decline in fish populations.However, many watercourses in northern Europe are often also characterized by low pH caused by naturally occurring organic acids, non-carbonate bedrock and previously a large input of acid rain. Therefore the role of acid sulfate soils has not always been properly addressed.This study was done on Larsmo and Öja Lake, a freshwater reservoir embanked from the alkaline Bothnian Bay in the 1960s. Since that, events of severe acidity and fish kills have been documented on several occasions. Severe but heterogeneous a.s. soils with relatively coarse grain sizes were found in the catchment. These soils were found to leach metals typical for a.s. soils such as Al, Cd, Co, Ni and Zn to recipient streams, but in contrast to other a.s. soils studied in Finland, some of them even seem to be leaching large quantities of Fe. Patterns of acidity, sulfate, sulfur isotopes, organic carbon and metals in rivers, streams and the lake revealed that (1) a.s. soils in the catchment are by far the most important source of acidity and metals in the lake i.e. the main reason for fish kills, (2) the load from discharge of organic (humic) acids and dredging operations is insignificant on the lake as a whole, (3) young near-field sediments comprising only 7% of the whole catchment accounted for roughly 20-30% of the total acidic load, (4) most of the acid/metal load entered the lake system from the south, and (5) by regulating outlets to the sea it seems to be possible to prevent this load from dispersing into the northern part of the lake system.
KW - Acid sulfate soils
KW - Dredge spoils
KW - Metals
KW - Organic acids
KW - Sulfur isotopes
KW - Acid sulfate soil
KW - Metals/chemistry
UR - http://www.scopus.com/inward/record.url?scp=79960645810&partnerID=8YFLogxK
U2 - 10.1016/j.gexplo.2011.04.003
DO - 10.1016/j.gexplo.2011.04.003
M3 - Article
AN - SCOPUS:79960645810
SN - 0375-6742
VL - 110
SP - 107
EP - 117
JO - Journal of Geochemical Exploration
JF - Journal of Geochemical Exploration
IS - 2
ER -