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60% phosphorus and 50% nitrogen of the total load (Wang, 1999). Approximately
1300 tons per day of litter can be generated. Whereas, the use efficiency of these
wastes to farming is lower than 60%. During rainfall events, surface run-off is often
seriously polluted through washing out these nutritional matters. Results from
sampling and pollutants surveillance of polluted run-off showed a serious pollution
with a TSS content of 6.6–14.8 g/L, TN of 91.7–252.3 mg/L, TP of 13.0–34.6 mg/L,
COD of 1128– 9124 mg/L, respectively.
Agricultural diffuse pollution is a landscape problem that requires an integrated
approach involving implementation of both on-field and off-field control measures
(Tim, 1995). Many studies have been conducted on the control of nutrients flow from
agricultural lands by landscape structures (Pomogyi, 1993; Uusi-Kämppä, 2000;
Kuusemets, 2002). But most of these studies are about control effect on nutrient
transport processes by a single type of structure, relatively few have documented
combination control effect of multiple buffer/detention structures. Furthermore,
in most previous studies, the focus was on the final effect of a treatment system
and treated the transport process of nutrients as a black or grey box. The objects
of this study were: (1) to explicate the detailed transport processes of diffuse P-
pollutants crossing a typical complex agricultural landscape in North China; and (2)
to compare control behaviors of different buffer/detention structures and to assess
their integrated effects under different hydrological conditions.
MATERIALS AND METHODS
Study Area and Monitoring Installation
Taohuasi watershed is in the north bank of Yuqiao Reservoir with a surface area
of 249 ha. The relief is strongly differentiated – there are many ridges, hills, and
depressions accompanying cliffs, channels, and ephemeral stream valleys. Land
use in this watershed is predominantly hilly land and cropland (Figure 1). Longterm
average precipitation is 749 mm, of which 80% falls from June to September.
Streams distributed in the watershed are almost all ephemeral streams. Most of the
rainfall events are storms. Surface run-off is the main mechanism by which nutrients
are exported from the watershed. During two study years, precipitations were lower
than the long-term average and we integrally monitored eight rainfall-run-off events.
Continuous flow generates only during a heavy rainfall event, of which water flow
can transport from the upstream to the mouth of the watershed. Discontinuous flow
usually generates during a gentle rainfall, of which water flow is intersected with
little or no outflow at the watershed mouth. Monitoring sites were composed of 28
sampling sites for surface flow (S1 to S28) and five for tributary (T1 to T5) flow from
various land uses along the stream channel. All analyses of pollutants were done
using standard methods (APHA, 1985).
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