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RETENTION OF POLLUTANTS BY THE SINK
STRUCTURES IN CATCHMENTS – STUDIES TO REDUCE
DIFFUSE POLLUTION IN CHINA’S RURAL AREAS
C Yin, X Wang and B Shan
State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Ecoenvironmental
Sciences, P. O. Box 2871, Beijing 100085, China, E-mail: cqyin@mail.
rcees.ac.cn
SUMMARY
Eutrophication of lakes and reservoirs is a serious problem in China. Diffuse sources
from agricultural lands account for a large portion of the load. Besides reducing the
pollution from the sources, the retention strategy during the transport process is
important and it plays an important role in Best Management Practice in China. The
retention strategy consists of using different sink landscape structures in watershed
scales, such as multipond systems, small stone dams, swales, vegetative belts, dry
ponds, waterside buffer zones and others. During continuous run-off events, the
concentration reductions of total suspended solids (TSS), total phosphorus (TP),
total dissolved phosphorus (TDP) and dissolved reactive phosphorus (DRP) by the
system ranged from 40% to 70%. During discontinuous run-off events, removal rates
of pollutants by the whole system were higher as there was no or little surface water
and pollutants exported from the watershed; removal rates of pollutants all exceeded
99%. The statistical analysis results of run-off events indicated that a dry pond was
the steadiest structure for controlling diffuse pollutants export. A multipond system is
a wetland system composed of many tiny ponds connected by ditches and the ponds
are scattered among the villages and crop fields. We discovered many mechanisms,
such as decreasing the flow velocity with volume change, settling particulate matters
using sedimentation, removing dissolved pollutants using adsorption and recycling
nutrients back to the crop fields. These structures can effectively reduce diffuse
pollution and enhance nutrient cycling in rural watersheds with wet and dry weather.
These structures are made of natural materials and are very environmentally friendly.
They are cheap to construct and usually do not need energy for operation.
INTRODUCTION
Eutrophication in regional water bodies is being attributed to increased nutrients
inputs (Artola, 1995; Sharpley, 1998). Diffuse sources of sediment and nutrients,
primarily from agricultural lands, have been identified as the major cause of water
quality degradation (Carpenter, 1998; Arheimer, 2000; Dzikiewicz, 2000; Sharpley,
2000). Village area, farmland and breed industries in agricultural watersheds may be
the cause of main sensitive sources for nutrients loss. When unsuitable management
measures of these lands are employed, contamination of water resources may result.
Thus, elevated concentrations of nutrients from rural areas pose a potential hazard of
eutrophication and a consequent cost for water treatment (Sanderson, 2001).
Yuqiao Reservoir is the major source of drinking water to Tianjin City. Preliminary
research has identified diffuse polluted run-off from agriculture as the largest
contributor of nitrogen and phosphorus to the reservoir, which accounts for about
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