11:00 AM - 1:00 PM
[MIS15-P10] Water quality characteristics of stream water and their formation processes in alpine and subalpine areas of the Northern Alps, Japan
Keywords:alpine and subalpne areas, stream water, water quality, topographical and geological characteristics
Understanding hydrological systems in mountainous regions are important because mountainous regions have been recognized as a principal water resource recharge area. Previous studies have shown that the water quality of streams in headwater is associated with the geology and topography of the catchment. However, the hydrological systems in mountainous regions with steep topography due to continuous orogenic activities have not been sufficiently investigated; hence, many aspects including water quality formation processes remain unresolved. Therefore, the objective of this study was to clarify the relationship between the water quality of streams and geomorphological/geological conditions in catchments in alpine and subalpine zones of the Northern Alps, Japan. For this, stream water samples were collected, and major inorganic dissolved ion concentrations and oxygen/hydrogen stable isotopic compositions of water were analyzed.
There was a significant negative correlation between the elevation at stream water sampling locations and total dissolved solids (TDS) in water. The topographic characteristics (catchment area, catchment elevation, maximum channel length, catchment slope, etc.) would not be major factors for determining TDSs in water because no strong correlations were found. Then, slope direction lengths of catchments reflecting transit times of water since the water input into the catchment were calculated. The slope direction lengths had a stronger correlation with the TDS of water, indicating that the TDS of water is more strongly influenced by the time contact with the geology after precipitation than by the topographic characteristics of the catchment.
The relationship between dissolved cation concentrations in water and slope direction lengths of catchments was analyzed for each grouped catchment based on the geological feature. The concentrations of sodium and magnesium ions were higher in the stream water from marine sedimentary rocks than in other geology although the concentrations varied among samples. This suggests that the cation composition of stream water in marine sedimentary rocks geology is dominated by cation exchange by clay minerals unevenly deposited in different locations in catchments. It could be since marine sedimentary rocks are heterogeneously distributed in geology due to selective erosion, transport, and sedimentation during their geological formation. In addition, the concentrations of calcium and bicarbonate ions in the stream water showed compositions indicating the influence of calcite weathering. Moreover, the magnesium ion concentration in the stream water was linearly related to their bicarbonate ion concentrations, except for about half of the stream water samples in the marine sedimentary rock geology. This indicated that the source of magnesium ions in water was also calcite. All results in this study could suggest that stream water quality in alpine and subalpine areas, as in other areas, reflects the geological and rock characteristics of the catchments.
There was a significant negative correlation between the elevation at stream water sampling locations and total dissolved solids (TDS) in water. The topographic characteristics (catchment area, catchment elevation, maximum channel length, catchment slope, etc.) would not be major factors for determining TDSs in water because no strong correlations were found. Then, slope direction lengths of catchments reflecting transit times of water since the water input into the catchment were calculated. The slope direction lengths had a stronger correlation with the TDS of water, indicating that the TDS of water is more strongly influenced by the time contact with the geology after precipitation than by the topographic characteristics of the catchment.
The relationship between dissolved cation concentrations in water and slope direction lengths of catchments was analyzed for each grouped catchment based on the geological feature. The concentrations of sodium and magnesium ions were higher in the stream water from marine sedimentary rocks than in other geology although the concentrations varied among samples. This suggests that the cation composition of stream water in marine sedimentary rocks geology is dominated by cation exchange by clay minerals unevenly deposited in different locations in catchments. It could be since marine sedimentary rocks are heterogeneously distributed in geology due to selective erosion, transport, and sedimentation during their geological formation. In addition, the concentrations of calcium and bicarbonate ions in the stream water showed compositions indicating the influence of calcite weathering. Moreover, the magnesium ion concentration in the stream water was linearly related to their bicarbonate ion concentrations, except for about half of the stream water samples in the marine sedimentary rock geology. This indicated that the source of magnesium ions in water was also calcite. All results in this study could suggest that stream water quality in alpine and subalpine areas, as in other areas, reflects the geological and rock characteristics of the catchments.