7.4 Results and Discussion
105
conservation practices were in the following order: check dam farmland > terrace
farmland > forest land & grassland. The check dam was the most appropriate practice
to conserve soil and water. Its retention abilities for water, soil, TN, TP and SOM were
231–469, 786–1878, 871–1854, 805–1656, and 984–1982 times of other practices,
respectively. The retention ability of the forest land was approximately equal to that
of the grassland, and the former was a little larger than the later in the Nanxiaohegou
Catchment due to the flourishing trees.
7.4.3 Positive Effects of the Conservation Practices
Understanding the complexity of land-use and land-cover changes and their driving
forces and impacts on human and environmental security is important for the planning
of natural resource management and associated decision making (Garedew et al.
2009). Soil cover and rainfall intensity are considered to have significant impacts
on soil erosion, and close relationships exist among them (Jin et al. 2009). We have
previously described that four representative conservation practices have been built
in the Nanxiaohegou Catchment, namely, check dam farmland, terrace farmland,
forest land, and grassland. Vegetation cover can increase infiltration, reduce surface
runoff, and thus markedly retard sheet erosion (Woo and Luk 1990). The retention
ability of the forest land was influenced by many factors, including the slope gradient
and length, the tree variety and age, plant cover structure and density, and the same
case happened to the grassland. Terracing and contour ridges caused an increase
in infiltration rate, largely because water would need more time to infiltrate into the
ground (Al-Seekh and Mohammad 2009). Thus, terrace farmland can also effectively
relieve soil and water loss from the slope. Different to the measures controlling
slope erosion above-mentioned, some practices, e.g., check dams and gully head
protections, could control soil and water loss both from the slope and the gully. The
check-dam can slow down the velocity of the sediment-laden water, resulting in a
lower sediment transport capacity, and therefore some of the sediments could sink
down (Xu et al. 2006). The main factors affecting the retention ability of the check
dam are supposed to be the dam height and the reservoir capacity.
Data presented here can be used to explain the commonly observed phenomenon
that soil erosion and nutrient losses have been greatly decreased with the implementation of the various conservation practices. In the Nanxiaohegou Catchment during
the treatment period 1954–2004, about 510.5 × 10
3 m
3 of transported water, half of
the total, had been retained by the conservation practices every year. Simultaneously,
almost all soil and nutrients, 94.8% of the total transported soil and nutrients, had
been locally retained in the catchment. As indicated in Table 7.1, soil and water loss
was not only markedly controlled, but also kept at a relatively low level. It can be
assumed that hydro-sedimentologic balance had been realized in the Nanxiaohegou
Catchment, similar to relative stability of the check dam system (Xu et al. 2006). As
a result, the qualities of the runoff and ground water had been meliorated, the land
had become more fertile, and the eco-environment had been greatly improved.
105
conservation practices were in the following order: check dam farmland > terrace
farmland > forest land & grassland. The check dam was the most appropriate practice
to conserve soil and water. Its retention abilities for water, soil, TN, TP and SOM were
231–469, 786–1878, 871–1854, 805–1656, and 984–1982 times of other practices,
respectively. The retention ability of the forest land was approximately equal to that
of the grassland, and the former was a little larger than the later in the Nanxiaohegou
Catchment due to the flourishing trees.
7.4.3 Positive Effects of the Conservation Practices
Understanding the complexity of land-use and land-cover changes and their driving
forces and impacts on human and environmental security is important for the planning
of natural resource management and associated decision making (Garedew et al.
2009). Soil cover and rainfall intensity are considered to have significant impacts
on soil erosion, and close relationships exist among them (Jin et al. 2009). We have
previously described that four representative conservation practices have been built
in the Nanxiaohegou Catchment, namely, check dam farmland, terrace farmland,
forest land, and grassland. Vegetation cover can increase infiltration, reduce surface
runoff, and thus markedly retard sheet erosion (Woo and Luk 1990). The retention
ability of the forest land was influenced by many factors, including the slope gradient
and length, the tree variety and age, plant cover structure and density, and the same
case happened to the grassland. Terracing and contour ridges caused an increase
in infiltration rate, largely because water would need more time to infiltrate into the
ground (Al-Seekh and Mohammad 2009). Thus, terrace farmland can also effectively
relieve soil and water loss from the slope. Different to the measures controlling
slope erosion above-mentioned, some practices, e.g., check dams and gully head
protections, could control soil and water loss both from the slope and the gully. The
check-dam can slow down the velocity of the sediment-laden water, resulting in a
lower sediment transport capacity, and therefore some of the sediments could sink
down (Xu et al. 2006). The main factors affecting the retention ability of the check
dam are supposed to be the dam height and the reservoir capacity.
Data presented here can be used to explain the commonly observed phenomenon
that soil erosion and nutrient losses have been greatly decreased with the implementation of the various conservation practices. In the Nanxiaohegou Catchment during
the treatment period 1954–2004, about 510.5 × 10
3 m
3 of transported water, half of
the total, had been retained by the conservation practices every year. Simultaneously,
almost all soil and nutrients, 94.8% of the total transported soil and nutrients, had
been locally retained in the catchment. As indicated in Table 7.1, soil and water loss
was not only markedly controlled, but also kept at a relatively low level. It can be
assumed that hydro-sedimentologic balance had been realized in the Nanxiaohegou
Catchment, similar to relative stability of the check dam system (Xu et al. 2006). As
a result, the qualities of the runoff and ground water had been meliorated, the land
had become more fertile, and the eco-environment had been greatly improved.