The role of land use on phosphorus release and longitudinal changes of pollution in an agricultural watershed, Bostankar river, Iran

Abstract

AbstractPhosphorus in surface waters accelerate algal growth and eutrophication, considerably influencing water quality. Spatiotemporal changes in phosphorus concentration are crucial for environmental issues. We aimed to study the temporal and spatial changes in water quality in a river and in a drainage water system considering different land uses. To this aim, 15 water samples were collected from the origin of the river to the estuary, in the Bostankar River watershed (N-Iran), during spring and winter. Further samples were collected from agricultural drainage water in rice fields, tea, flower, orange as well as kiwi gardens, and forests during spring and winter. EC, pH, TDS, and three forms of phosphorus (total, particulate, and soluble) were measured in the water samples. The results showed that water quality changes in agricultural drainage water were time-dependent; the average total phosphorus was 0.4 mg l-1 lower in the spring than in the winter. The highest phosphorus concentration (1.29 mg l-1) occurred in the winter in the drainage water of the orange gardens. Temporal and spatial changes of the river showed that water quality reduced from the river upstream (jungles and grasslands) towards the downstream (different agricultural land uses), and the amount of phosphorus increased from 0.25 to 0.5 mg l− 1. The TDS increased from 60 to 220 mg l− 1 in the river in the winter. Finally, the results showed that human activities were the main factor in river water quality reduction due to agricultural activities.