Economic and Environmental Geology (자원환경지질)

The Korean Society of Economic and Environmental Geology (대한자원환경지질학회)
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Geochemical and Isotopic Study of the Kumho River

금호강 하천수의 지구화학 및 동위원소 연구

  • Published : 2009.12.28
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Abstract

The Kumho River flows through volcanic and sedimentary rocks at upstream and downstream regions and also through industrial district including dyeing complex before it meets the Nakdong River, and as a result, many factors can influence the geochemistry of river water. The concentrations of dissolved ions generally increased as it flows downstream. The concentrations of cations are in the order of Ca>Na>Mg>K, and those of anions are $HCO_3$>$SO_4$>Cl>$NO_3$. These results show that the weathering of sandstone and shale containing carbonate including calcite caused the enrichment of Ca and $HCO_3$. At first 4 sampling sites, Si contents are relatively high mainly due to the weathering of silicate minerals of volcanic rocks. However, Na and $SO_4$ contents are higher at downstream sites due to the industrial and municipal sewage. Piper diagram also shows that the geochemical patterns changed from Ca-$HCO_3$ to Ca-Cl/Ca-$SO_4$ and Na-Cl/Na-$SO_4$ type. When comparing the samples collected in May and July, the concentrations of dissolved ions in July are generally lower than those in May, which indicates that dilution by precipitation played an important role. In July the relative concentration of Ca increased, indicating that Ca in soils probably from fertilizer were mixed into the river water by precipitation. The river waters are mainly from precipitation. The dissolved ions are mainly from weathering of carbonate minerals and pollutants from municipal sewage and discharged water from industrial complex. The composition of oxygen and deutrium isotope in July showed higher values, which is contrary to the amount effect, maybe due to Youngchon Dam. The nitrogen isotope showed lower values in July than those in May, which can be interpreted to indicate mixing of nitrate from soils and fertilizer in the cultivated land by the heavy rain. The isotope composition of nitrate increased downstream, indicating that the influence of sewage and animal manure also increased downstream.

금호강의 하천수는 상류의 화산암 지대와 하류의 퇴적암 지대를 지나며 낙동강과 합류하기 전 대구의 염색공단과 같은 산업시설을 유하하여 지구화학적으로 다양한 영향을 받는다. 금호강 하천수는 상류에서 하류로 갈수록 풍화와 오염물질의 유입에 의해 전반적인 용존 이온의 증가를 보여주고 있다. 하천수에 용해된 양이온은 Ca>Na>Mg>K 순으로, 그리고 음이온은 $HCO_3$>$SO_4$>Cl>$NO_3$ 순으로 높게 나타났다. 이는 방해석과 같은 탄산염암을 함유하고 있는 사암과 셰일의 풍화에 의하여 Ca와 $HCO_3$가 다른 원소들보다 우세하게 나타난 것으로 보인다. 그러나 하류지역에서는 공단 폐수와 생활 하수의 영향으로 Na와 $SO_4$가 Ca와 $HCO_3$보다 높게 나타났다. 또한 상류 시료 채취점 네 곳에서는 Si의 함량이 상대적으로 높게 나타났는데 이는 화산암 내의 규산염광물의 풍화의 의한 것으로 해석된다. 하천수의 화학적 유형을 알기 위하여 파이퍼도에 도시해본 결과 금호강은 상류에서 하류로 흘러감에 따라 Ca-$HCO_3$, Ca-Cl/Ca-$SO_4$, Na-Cl/Na-$SO_4$ 유형 순으로 나타났다. 5월 갈수기와 비교하였을 경우 7월 우기시 용존 이온의 농도가 전반적으로 감소하였는데, 이는 강우에 의한 희석의 영향을 받은 것으로 해석된다. 그러나 7월의 경우 Ca 함량이 상대적으로 증가하였는데, 이는 토양내 Ca과 비료에서 유래된 Ca가 빗물에 의하여 강물에 섞인 결과로 해석된다. 금호강 하천수의 물은 주로 강수에서 직접 기인하며 용존 이온들은 탄산염 광물의 풍화와 생활 하수, 공장 폐수와 같은 오염물질에 의해서 공급되는 것으로 보인다. 산소와 수소 동위원소의 조성은 7월의 경우 5월에 비하여 일반적으로 높게 나타났는데 이것은 아마도 상류에 있는 영천댐의 영향일 것으로 생각된다. 질소 동위원소의 경우 전제적으로 7월의 값들이 5월에 비하여 낮은 것으로 나타났다. 이는 7월의 다량의 강수에 의하여 토양내의 질산염이나 경작지의 질산염 비료 등이 혼입되어서 나타난 결과로 해석된다. 전체적으로 하류로 가면서 질소 동위원소의 값은 증가함을 보여 오수와 가축분뇨 등의 영향이 하류에서 증가함을 보인다.

Keywords

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