ArcGIS Based Regional Estimation Of Nitrogen And Phosphorus Loss Loads In Surface Runoff From Rice Paddy Fields

Nitrogen (N) and phosphorus (P) losses via surface runoff from paddy fields is one of the main causes of agricultural non-point source pollution in China, thus, the research related to its loss mechanism and characteristics is of great importance for environment protection. Field experiments of four typical paddy soils were conducted in this paper to study the dynamic changes and predict N and P concentrations in surface water under different fertilizer rates. Afterwards, the monitoring results were combined with mathematical simulation to construct a surface runoff loss loads estimation method. The main results were as follows:1) TN and TP concentrations reached maximum value on the first day after fertilization, and there was a linear correlation between fertilization rates and the maximum value (R2> 0.97). The maximum values, especially that of TP, were significantly influenced by soil type. Thereafter, the TP and DRP concentrations decreased by exponential equations, and finally kept at a relatively stable level. Dynamic change of TN and TP could be expressed by y= (A×P+b) ×e-k/ +c and y= (A×P+b) ×e-kt +(c×p+d),respectively.2) A N and P loss estimation method was established for field-scale loss loads simulation based on the field experiment results and the "rain-runoff’model. Verification experiments conducted in Jiaxing and Yuhang showed that simulation values of runoff volume, TN loads and TP loads matched obersevation data very well except for some samples. Besides, model quality evaluation also indicated that simulation values,though some samples’ errors were relatively high, coincided well with observed values,. Therefore, this estimation method could be used to calculate the runoff loss loads from paddy fields.3) Surface runoff loss loads analysis system (SRLAS), based on ArcEngine, was developed for regional scale runoff loss loads estimation. Furthermore, some input parameters were optimized according to investigation data, like fertilizer rate, fertilizer time, and so on. The SRLAS software was applied to calculate the nitrogen and phosphorus loss loads in Hangjiahu region between 2008-2012.The results showed that the five-year average TN loss loads was 19.66 kg N/hm2, and N fertilizer loss rate by runoff was 6.69%; the five-year average TP loss loads was 0.84 kg P/hm2, and P fertilizer loss rate by runoff was 4.23%. Scenario analysis indicated that from 2008 to 2012, when the fertilizer reduction rate was 10%,20%,30% and 40%, the regional average TN loss reduction amounts were 393.1 t.786.2t、1179.3 t and 1572.4 t, and the corresponding average reduction rates were 6.38%、12.76%、19.15% and 25.53%, relatively; while the average TP loss reduction amounts were 15.3 t、 30.5 t、 45.7 t and 61.1 t, and the corresponding average reduction rates were 3.12%、6.24%、 9.29% and 12.48%, relatively. Improving irrigation mode has a more positive influence on controlling the runoff loss loads of TN and TP from paddy fields than reducing fertilizer rates.