Abstract
The survival of Formosan landlocked salmon has been threatened by the change of habitat ambience. Because of the potential
toxicity of nitrite (NO2
-) and ammonium (NH4
+) to salmonid fisheries, we studied the evolution of nitrogen compound
distributions in stream water and their relationship with ambient abiotic factors. The water was sampled at five sites surrounded
with various land-use types in bi-monthly intervals for seven years. The results indicated that a high NO2
- concentration occurred
in summer, especially in the Yushan Stream (Site # 5), which borders intensive agricultural farms. By contrast, a high NH4
+
concentration typically occurs from winter to early spring, even though the Taoshanshi Stream (Site # 1) is surrounded by a
primitive forest. Multiple stepwise regression analyses indicated that, in Site # 5, the accumulation of NO2
- positively correlated
with NO3
- concentration, C/TIN ratio, and temperature (p < 0.05), which could be attributed to the domination of dissimilatory
nitrate reduction to ammonium (DNRA). In Site # 1, the statistical regression model revealed that NH4
+ elevation positively
correlated with DO (p < 0.05) and negatively correlated with temperature (p < 0.1), suggesting the suppression of nitrification by
low temperature.