Contents of carbon, nitrogen and phosphorus in dissolved organic matter and humus in brownish spring waters in Hokkaido, Japan

Abstract

The springs of brownish-colored water called "moor hot springs" are force-pumped to the surface in various regions in Hokkaido, northern Japan. The color is due to the presence of dissolved organic matter, mainly humus, in water. The carbon, nitrogen, and phosphorus contents of the dissolved organic matter and humus were determined for the brownish-colored spring waters collected from seven regions in Hokkaido. The DOC, DON, and DOP concentrations ranged from 0.31-6.2 mmol L-1 , 0.004-0.80 mmol L-1 , and 0.001-0.060 mmol L-1 , respectively. Humus was extracted as hydrophobic acid using Supelite DAX-8 resin. The concentrations of carbon, nitrogen and phosphorus in the hydrophobic acid ranged from 0.15-3.5 mmol L-1 , 0.004-0.24 mmol L-1 , and 0.001-0.021 mmol L-1 , respectively. The concentrations of hydrophobic acid carbon were higher than those of hydrophilic acid carbon at the six sites. This implied that hydrophobic acid was main component of dissolved organic matter in most springs. Compared to the surface waters, DOC concentrations showed a wider range and the proportions of hydrophobic acid carbon to DOC also showed a wider range. These findings suggest that DOC and hydrophobic acid concentrations have remarkable variation among brownish springs in Hokkaido. In addition, the C:N and C:P ratios of hydrophobic acid were distributed across a wider range than those of the surface waters. High C:N ratios in DOM and hydrophobic acid were found at sites where well depth was shallowest. Spring water from deeper layers had a longer retention time in the ground. This suggested that for shallow springs, hydrophobic acid was solubilized from the source of DOM, such as peat, recently. Spring water at one site had remarkably high C:P and N:P ratios in DOM and hydrophobic acid. Detection of dissolved inorganic phosphorus indicates that mineralization was activated from organic to inorganic phosphorus. The C:N:P ratios in DOM and hydrophobic acid varied among the sites, suggesting that this ratio may be used as an index to provide a unique profile for each of the brownish-colored springs.