| 其他摘要 | The Loess Plateau is the most serious region in soil and water loss in China and even
in the world. By increasingly drier climate and human activities, the region Loess Plateau
where is also one of the important regions requiring ecological restoration for severe
ecological degradation. Soil erosion and solute transport on loess slope is a complicatedly
physicochemical process. It is affected by many factors and mutually intersected with
multi-discipline, such as soil science, ecology, hydrology, hydraulics, environmental
science and so on. The mechanisms and predictions of water and nutrient transport in soils
on a slope during rainfall have played important roles in the research on the degradation of
soil quality and the expansion of non-point source pollutions in recent years, which also
have been an interdisciplinary field focused in soil erosion, hillslope hydrology, dryland
agriculture and related environmental sciences.
Investigating the mechanism and model of soil water and nutrient transport could
predict and prevent effectively soil nutrient loss at intensively-eroded area on the loess
section. And it’s good for understand and master the nature and mechanism of erosion and
internal law of solute transport during the process of erosion on loess slope. This is very
important in ecological environment management of the Loess plateau. The main works
and detailed results of this study are as following:
(1) The initial soil moisture content influences solute loss by virtue of its impact on
infiltration, which suggests that if infiltration could be facilitated, the loss of solutes could
be reduced. Rainfall intensity increases the mass of sediment carried away by the runoff
and decreases the time required for runoff formation; the latter in turn increases the solute
concentration in the surface layer. The slope gradient also has a significant influence on the
masses of solute and sediment in the runoff; both increase as the slope gets steeper between
0 to 25 gradient. Treatment with PAM effectively increased the soil’s resistance to
raindrops and water flow-induced detachment. For the soil examined in this work, the
optimal PAM loading was 3g/m2. Solute concentration in the runoff at the first minute when runoff take place and the average solute concentration in the runoff were positive
linear correlation with solute concentration in the soil surface when runoff take place.
(2) Plant cover effect the runoff erosion ability by controlling the hydraulic
characteristics of flow. It’s different both the soil and water conservation effects and the
influence of the nutrient loss from slope from different vegetation types under the same
vegetation coverage. For the experimental area, the Stipa bungeana was better than alfalfa
for soil and water conservation. The vegetation coverage increased the soil surface
roughness, slower down the flow velocity and increase the time of water infiltration. The
vegetation coverage influenced the soil sediment in the runoff by controlling the hydraulic
characteristics of flow and the soil cohesion. The relationship between the average
sediments in the unite width of runoff and vegetation coverage could be expressed by
negative linear equations. The relationship between the average solute concentration in the
unite width of runoff and the vegetation coverage could be described by density function.
The average sediments in the unite width of runoff decreased 36.7 percentage and the
average solute concentration in the unite width of runoff decreased with 33.2 percentage
with the coverage of alfalfa increased 15 percentage between 30 and 60 percentage. The
stone cover decreased the runoff volume, soil sediment in the runoff, the solute loss with
runoff by increasing the surface roughness of soil surface, decreasing the flow velocity of
overland flow, increasing the time of water infiltration and the volume of infiltration. The
relationship between the average sediments in the unite width of runoff and the stone
coverage could be expressed by density function. The relationship between the average
solute concentration in the runoff and stone coverage could be expressed by linear equation.
For the experimental area, the average sediments in the unite width of runoff decreased
27.2 percentage and the average solute concentration in the unite width of runoff decreased
with 14.3 percentage with the coverage of stone increased 10 percentage between 10 and
30 percentage.
(3) We developed the average solute concentration in the unite width of runoff model
which expressed by the runoff shear stress under the infiltration excess condition on the
Loess plateau. The model expressed as Drs=a·k·(τ-τ0), where Drs was average solute
concentration in the unite width of runoff; a was empirical parameter and which changed
with solute types and the solute concentrated in the soil. The other parameter the same with the average sediments in the unite width of runoff. The model made the modeling solute
transport with runoff easier. The developed model to control the soil and water loss,
non-point pollution has a very important role.
(4) The method we used to refine power functions solute transport model developed
by Wang Quanjiu et al was change the exchange rate km with the raindrop-induced water
transfer rate er, which make the model physically-based and without the km calculation.
The refined model was more suitable for modeling the solute loess with runoff on the
Loess plateu. Test the model with experimental date. The model fitted the experimental
data very well. Our results also showed that when the slope gradient was 15° or larger than
15°, the constant parameter, ρ was equal to 2, ρ was equal to 1while when the slope
gradient was less than 15°.
(5) We have developed a physically-based solute transport model for estimating the
solute concentration in runoff originating from the soil surface under the infiltration excess
condition on the Loess plateau. To test the model, we carried out laboratory experiments
that used two soil types (loam and sandy loam) and exposed them to simulated rainfall.
The results simulated by the model were highly correlated with the experimental data. The
simulated data showed a high level of correlation with the measured data for soil water,
solute transport in the soil profile and runoff volume, solute concentration in the runoff.
This demonstrates that the model captured the temporal behavior of the runoff and solute
transport in the runoff. The model could not predict the solute concentrations in the runoff
under severe soil erosion conditions accurately.
KEY WORDS：Loss slope, soil erosion, solute transport, nutrient loss, model |
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