Reconstructing nutrient criteria for source water areas using reference conditions

Nutrient concentrations are of concern in most watershed areas that serve as source water for public drinking water due to the high cost of nutrient removal treatment. Yet all nutrients criteria for source watersheds in Taiwan are identical for quality standards and the specific conditions of each source watershed were not considered. Nutrient RCs estimated by statistical methods and land disturbance modeling were applied to the Tamsui River in Taiwan. The results were then used to evaluate the nutrient status of Taipei Water Source Domain, which is located near the upstream portion of Tamsui River. The estimated RCs of NH3-N, TP, and Total N were 0.03–0.04, 0.019 to 0.036, and 1.22–1.50 mg L−1, respectively. Comparing with current criteria of NH3-N (0.1 mg L−1), the estimated reference conditions are lower and the criteria could be stricter to maintain sufficient water quality. However, the reference condition of TP estimated by the disturbance modeling (0.03 mg L−1) is higher than current criteria (0.02 mg L−1), leading to a possible loosening adjustment.