Abstract
A Beijing paddy field, along with in-situ experiments, was used to validate and refine the in-situ observation (IO) method to describe nonpoint source pollution (NPS) in paddy fields. Based on synchronous observed rainfall, water depth, and water quality data at two locations (1# (near inlet) and 2# (near outlet)) with large elevation differences, the evapotranspiration and infiltration loss (ET+F), runoff depth and NPS pollution load were calculated according to IO, and a common method was used to calculate ET+F. Then, the results of the different methods and locations were compared and analyzed. The results showed that 1# observation point was located at a lower position compared with 2# observation point. According to 1# observation point, there were 5 days of dry field in the drying period, which was consistent with the actual drying period, and there was a dry period of 9 days based on 2# observation point. The ET+F estimated by IO fit well with the calculated values. In the experiment, 6 overflows and 1 drainage event were identified from the observed data at locations 1# and 2#. The relative deviation of the NPS pollution of total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), nitrate-nitrogen (NO3−-N) and ammonia nitrogen (NH4+-N) was between 0.6% and 2.0%. The water level gauge location had little influence on IO but mostly affected the water depth observations during the field drying period. The mareographs should be installed in low-lying paddy field areas to monitor water depth variation throughout the whole rice-growing season.
Highlights
IntroductionMost rice planting areas in China use excessive chemical fertilizers and pesticides
China is the largest rice producer and consumer in the world [1,2]
Using the in-situ observation (IO) methods in different locations with large elevation differences to study nonpoint source (NPS) pollution in paddy fields, 1# observation point was located at a lower position compared with 2# observation point
Summary
Most rice planting areas in China use excessive chemical fertilizers and pesticides. Except for a small portion absorbed by rice, are mostly lost to the environment through gaseous loss, leaching, or surface runoff, causing pollution to the environment [3,4]. Due to the large rice planting area, severe nitrogen and phosphorus losses cause nonpoint source (NPS) pollution [5,6]. Reducing runoff pollution has become a necessary measure to control nonpoint source pollution [9,10]. Verifying paddy fields’ nonpoint source pollution load is significant for reducing chemical fertilizers and formulating a total pollution control system [11,12]
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