Study on non-point source pollution characteristics under different spatial scales: a case study of Hanjiang River Basin, China.

In recent years, the research on non-point source (NPS) pollution has been deepening, but it is focused on the large-scale watershed or region. There are a few studies on the scales of small watershed and runoff plot, and it is even less to analyze the characteristics and mechanism of non-point source pollution in certain watershed by combining three different scales. Based on the combination of natural rainfall monitoring and MIKE model simulation, the Shaanxi section of Hanjiang River Basin in China was taken as an example to study the characteristics of NPS pollution at different spatial scales. The results showed that there was an obvious correlation between rainfall and runoff/sediment yield. The order of runoff yield/sediment yield per unit area was as follows: woodland > forested and grassy land > arable land. There was a significant relationship between the loss of total phosphorus and the sediment yield in the runoff plots. The total nitrogen pollution was serious, with an average concentration of 3.8 mg/L. The nutrient loss was in the form of nitrate nitrogen, with an average proportion of 63.06%. For small watershed scale, the characteristics of rainfall runoff pollution generation were like runoff plot scale, both have obvious initial scour phenomenon. However, compared with runoff plot scale, the pollutant loss concentration increases with a strong lag. The MIKE model based on the coupling of hydrology, hydrodynamics, and pollution load had a strong applicability in the basin. The critical source areas of NPS pollution were identified, and five scenarios were laid out in the areas for the control of NPS pollution. Centralized livestock and poultry farming had the best reduction effect.

Risk assessment of non-point source pollution based on landscape pattern in the Hanjiang River basin, China.

Non-point source (NPS) pollution has become a vital contaminant source affecting the water environment because of its wide distribution, hydrodynamic complexity, and difficulty in prevention and control. In this study, the identification and evaluation of NPS pollution risk based on landscape pattern were carried out in the Hanjiang River basin above Ankang hydrological section, Shaanxi province, China. Landscape distribution information was obtained through land use data, analyzing the contribution of "source-sink" landscape to NPS pollution through the location-weighted landscape contrast index. Using the NPS pollution risk index to identify and evaluate the regional NPS pollution risk considering the slope, cost distance, soil erosion, and precipitation erosion affect migration of pollutants. The results showed that (i) the pollution risk was generally high in the whole watershed, and the sub-watersheds dominated by "source" landscapes account for 74.61% of the whole basin; (ii) the high-risk areas were distributed in the central, eastern, and western regions of the river basin; the extremely high-risk areas accounted for 12.7% of the whole watershed; and the southern and northern regions were dominated by forestland and grassland with little pollution risk; (iii) "source" landscapes were mostly distributed in areas close to the river course, which had a great impact on environment, and the landscape pattern units near the water body needed to be further adjusted to reduce the influence of NPS pollution.

Quantitative assessment of non-point source pollution load of PN/PP based on RUSLE model: a case study in Beiluo River Basin in China.

The runoff-sediment relationship in the Yellow River Basin of China is still grim. People pay more and more attention to non-point source (NPS) pollution caused by surface pollutants migrating into the receiving water body with rainfall runoff. The particulate load of pollutants adsorbed in the soil and sediment by erosion and denudation and migration into water is also quite serious. It is necessary to deeply analyze the quantitative relationship between particulate nitrogen and phosphorus (PN/PP) load and soil loss. The soil erosion estimation of different administrative units in the study basin is obtained by the revised universal soil loss equation (RUSLE). The spatial distribution and the variation characteristics at different slopes and different land use of PN/PP load are discussed. An empirical equation of particulate organic load is used to calculate the PN/PP load. The results show that the multi-annual average erosion modulus of the basin is 358.33 t/(km2∙a); the multi-annual average soil erosion reaches 9.62 million tons. The PN/PP load caused by soil loss reaches 11,107.1 t and 7909.3 t, and the export coefficients are 4.13 kg/hm2 and 2.94 kg/hm2, respectively. Spatial distribution of the PN/PP load is in step with the soil erosion distribution. Soil erosion is prone to occur in the region under the slope of 8 ~ 25°, the NPS load of PN/PP are relatively large, and the average export coefficients of PN/PP are 7.17 kg/hm2 and 5.06 kg/hm2. With the increase of the slope, the PN/PP load export coefficient increases first and then decreases. Agricultural land (AGRL), forest land (FRST), and pasture (PAST) are the land use types that contribute the most to the PN/PP load and soil erosion, and the average export coefficients of PN/PP are 4.54 kg/hm2 and 3.23 kg/hm2, respectively. The variability of natural elements, the unevenness and heterogeneity of spatial distribution, and the heavy involvement of human activities will have a conspicuous impact on the soil erosion and NPS pollution processes in the basin. The research on the influence of single factor and combined factors on NPS pollution process can be strengthen and provides scientific theoretical basis for formulating reasonable and efficient water and soil conservation measures and NPS pollution control scheme, so as to achieve effective control and scientific management of environment pollution.

Improvement and application research of the SRM in alpine regions.

The simulation of snowmelt runoff in alpine mountainous areas is of great significance not only for the risk assessment of snowmelt flood in spring and summer, but also for the development and management of water resources in the basin. An improved snowmelt runoff model (SRM) is constructed based on the analysis of change characteristics of climate, runoff, and snow and ice cover in the middle and upper reaches of the Taxkorgan River in Xinjiang Province, China. Because of the large evaporation in the study basin, the evaporation loss is added to the model. The SRM and the improved SRM are calibrated and verified by using data such as temperature, precipitation, water vapor pressure, and snow-covered area (SCA) ratio in the study basin from 2002 to 2012. The results show that, compared with the SRM, the average Nash-Sutcliffe coefficient (NSE) of annual runoff simulation increases from 0.80 to 0.86 in the calibration and increases from 0.74 to 0.83 in the validation through the improved model, and the average runoff error reduces from - 12.8 to 1.32% in the calibration and reduces from - 20.0 to - 11.51% in the validation. After adding the measured flow rate for real-time correction, the average NSE of annual runoff simulation increases from 0.91 to 0.93 and the average annual runoff error reduces from - 7.76 to - 3.91% in the calibration. The average NSE increases from 0.85 to 0.89 and the average runoff error reduces from - 12.35 to - 2.76% in the validation. It indicates that the SRM structure with increased evaporation loss is more in line with the actual situation. The short-term simulation effect of the model is greatly improved by adding the measured flow rate for real-time correction. At the same time, the improved SRM and the hypothetical climate change scenario are used to analyze the impact analysis of the snowmelt runoff simulation in the partial wet year. The results show that in the case of rising temperature, the ice and snow ablation period is prolonged, and the annual runoff also changes significantly in time distribution. It is of guiding significance for the influence of climate change on the runoff of recharged rivers with ice-snow meltwater in the other alpine regions.