Abstract
We surveyed the water quality of irrigation reservoirs in a tea field catchment. The study area was located in Shizuoka Prefecture, Japan. Water in some of the reservoirs showed alkalinity because of the photosynthesis of aquatic plants. On the other hand, water in one irrigation reservoir showed acidity because of nitrogen fertilizer. The NO3-N concentration increased how many times owing to large runoff from a watershed when rainfall was strong and heavy accumulation. The Changes in NO3-N concentration were small throughout the season when was light rainfall. The average of NO3-N concentration in the irrigation reservoirs was about 5 mg·l-1.
