Agriculture Reference
In-Depth Information
Table 6. Estimated biomass of
Misgurunus anguillicaudatus
from each paddy field in 2001
Weight of population (g)
Amount of
increase
(g) (B - A)
Rate of
increase
(B / A)
Site
Swim up
to paddies
A
Swim down
from paddies
B
A
841.9
856.4
14.5
1.0
B
257.8
73.7
-184.1
0.3
C
43.8
184.7
140.9
4.2
D
36.3
1019.7
983.4
28.1
E
22.8
582.7
559.9
25.5
F
9.1
20.1
11.0
2.2
G
21.7
1113.6
1091.9
51.3
H
10.4
216.2
205.8
20.8
I
41.5
472.4
430.9
11.4
TOTAL
1285.4
4539.5
3254.2
3.5
Table 7. Total number of species verified in paddy fields and canals in 14 areas in Japan
Number of
species verified
in paddies
A
(Of which
endangered
species
)
Total number of species
in Japan
B
A
/
B
(%)
Mammals
28
(5)
Approx. 200
14
Birds
136
(37)
Approx. 700
19
Reptiles and amphibians
38
(17)
161
24
Fish (sweet water)
101
(36)
Approx. 300
34
Benthos
182
(24)
Approx. 5,200
4
Dragonflies
61
(9)
204
30
Plants
1379
(67)
Approx. 7,000
20
3.5 Recharging groundwater with water used in paddy fields
Irrigated paddy fields generally possess a superior function of recharging
groundwater because of the high rate of vertical and lateral permeation as described in
Figure 5. To quantify the amount of water recharged from paddy fields and other lands,
Ichikawa (2002) observed the amount of flowing water at nearly 300 monitoring points in
the middle-stream basin of the Shira river in Kumamoto prefecture in Japan. The
monitoring included the amount of water intake from six weirs in the region, the amount
of return flow to rivers, and the amount of down-flow to the lower basin. He also
surveyed the distribution of paddy fields and calculated the exact area for cropping
among the fields.
As a result, groundwater accumulation amounting to an average of around
90 mm/day, and a maximum of 150 mm/day was observed in this region.
Figure 21
shows a ground plan of the survey area and main directions of groundwater moving in the
area. Figure 22
shows that paddy fields upstream of the Kumamoto city area supply 45%
of the total groundwater recharge (281 million tons) of which the city requires around
226 million tons annually for drinking water, industrial water and air conditioning for
buildings.
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