A large proportion of the rural labor force in China will continue to transfer to non-agricultural sectors in the near future, which will inevitably lead to the transformation of the agricultural production mode and the structure of the farmers’ livelihood. The Chinese government is making great efforts to govern agricultural nonpoint source pollution (ANSP), and farmers' environmental behavior is a key factor that must be considered in the formulation of agricultural environmental policies. Based on a set of micro survey data on farmers in the study area and econometric methods, this study investigates the impact of agricultural labor transfer on ANSP by considering the substitution effect of agricultural factors and the effect of agricultural economies of scale. The results show that the increase of the agricultural labor force will not be conducive to reducing ANSP, while the income increase brought by agricultural labor transfer will improve the input structure of agricultural factors and have a positive impact on ANSP reduction. Government departments should provide subsidies or incentive measures to help agricultural social service organizations to expand their coverage and increase the frequency of socialized agricultural services, in order to guide farmers in the use of environment-friendly agricultural technology to reduce the ANSP caused by agricultural factors at the source. Furthermore, it is necessary to facilitate the development of small-sized agricultural machinery suitable for small-area land cultivation. 相似文献
To evaluate the effect of the tidal cycle on the pore water nitrate dynamics in intertidal sediment, concentrations of inorganic
nitrogen in water and sediment were monitored during tidal cycles in the mud flat of Tama Estuary, Japan. During submergence,
nitrate concentration was highest in the overlying water and decreased monotonically with increasing depth in the sediment,
suggesting that the primary source of nitrate in the sediment was nitrate transported from the overlying water. Pore water
nitrate decreased remarkably during the initial 3–4 hours after the onset of exposure. Thereafter, it was constant or slightly
increased until tidal flooding.In situ accumulation of nitrate at the end of exposure, however, did not exceed the nitrate concentrations in the overlying water.
The inhibition of nitrate reduction and the stimulation of nitrification would explain the change of nitrate concentration,
both consistent with the input of oxygen into the sediment following a 10 mm drop of the water table. In Tama Estuary sediments,
the effect of the tidal cycle on the removal of combined nitrogen is rather negative, because high nitrate concentrations
in the overlying water canceled the positive effect of nitrate accumulation by nitrification during exposure, while tidal
oxygen intrusion have an inhibitory effection sedimentary denitrification. 相似文献
Bioassesment by the use of the macroalga, Ulva lactuca L., was carried out in the Limfjord, Denmark, to assess the significance of nitrogen and phosphorus as limiting factors for primary production during 1985, 1993, 1994 and 1995 and for the detection of changes in eutrophication levels.
Minimum and critical tissue concentrations for nitrogen and phosphorus in macroalgae were identified. The concentrations of nitrogen were generally below the critical concentration level in June–October in 1985, 1993, and 1995 but in 1994 nitrogen was only limiting for primary production in short periods. Only in early spring in 1985 and 1993 were the tissue concentrations of phosphorus below the critical concentration level, whereas in 1994 up to 3–4 months showed phosphorus limited growth, indicating that significant changes in limitation patterns can occur between different years.
It was concluded that the use of biomonitoring techniques is well suited as a bioassessment method for direct detection and for providing a time-integrated measure of nutrient availability in coastal waters, and thus for assessing ecosystem health with regard to eutrophication. It is recommended that biomonitors and the concept of critical tissue concentrations should be used in environmental management and incorporated in future monitoring programmes. 相似文献