EFFECT OF SHRIMP CULTIVATION ON LAND AND LAND COVER

EFFECT OF SHRIMP CULTIVATION ON LAND AND LAND COVER

6.1. Introduction

Evidence from the ground rather from statistics, shows that land degradation due to shrimp culture is a serious problem in the coastal area. Increased soil salinity in the land and water owing to shrimp cultivation is being reported on the various studies. The conflicts between shrimps cultivation and changing land use pattern also discussed in the previous chapter of this study. Siltation of river / canal and flooding the fields by saline water and year after year shrimp cultivation, blamed a serious consequences for agriculture, vegetation, grazing land livestock, fisheries and wildlife, drinking water, biodiversity, etc in this study. This chapter presents changes of land and land uses in respect of high siltation, long time waterlogging, change of soil quality, problem of salinity and depletion of vegetation. The schematic flow diagram (Figure 6.1) is used describe various functions and interrelationship of each sub-component.

6.2. Siltation

Siltation means gathering of silt. This occurs due to disturbance of normal flow of the river or canal. Shrimp cultivation needs to construct embankment and bound parallel to river or seashore. Channel closures are required whenever the embankment crossed a river or khal. Drainage sluices are constructed to drain excess rainwater from polders into adjacent channels or exchange saline water when they needed. The construction of large numbers of sluices required on the closure of many tidal channels.

Unfortunately, improper management of coastal embankment and haphazard construction of ghers embankment, traditional extensive shrimp cultivation in the study area is becoming vulnerable. It has been seen that most of the shrimp farms in the study area entered and drained saline water into the ghers through the holes of embankments named as sluice gate (Plate 6.1). The flow of water back and forth in the natural canal system are neither equal to quantity of actual flow nor enough for proper maintenance of the system and ultimately large scale siltation take place in front of the sluice gate resulted reducing depth and width of the river. Stream and creek sections were blocked normal flow of water as raising the level of their bed higher than shrimp farms enclosure. Ultimately caused the drainage congestion in the shrimp farm. Figure 6.2 shows the process of siltation in river/canal and shrimp farm/agricultural land.

Moreover, sedimentation carried by rainwater inside the polder cannot flow freely due to the embankment of the shrimp farms and siltated channels bed. This could especially affects the natural movement of fish species and decreased flow of nutrients those enrich the soil fertility help to enhance productivity of agriculture. Siltation also creates problems for communication as traditional navigation channels are blocked (Plate 2). On the other hand, blockage of drainage channel increases flood occurrence and in the long run, will lead to serious environmental hazards (Kalam 1992).

 6.2.1. Siltation in Agricultural Field / Shrimp ghers

Siltation in agricultural field occurred seriously. Floodwater of agricultural field can not drain out smoothly. The sluice gate in the embankment project also changed the water flow system with closing of the mouth of many channels. As a result, drainage water from the agricultural field becomes slow which enhance the silt gathering. Sedimentation also increases from erosion of earthen embankment (bund) due to rainfall in monsoon season. Table 6.1 revealed that siltation above 6 inches and above have been reported by 63.9 per cent and 65.8 per cent during the period of 1985-75 and 1999-75 respectively. Average siltation in the agricultural/shrimp farms have been increased to 2.35 inches from 1985-75 and 2.93 inches 1999-85 respectively. During the period 1999-75, average siltation in the agricultural/shrimp farms depicted  5.28 inches, which mostly doubled compared from the year 1985-75.

Table 6.1: Percentage of Siltaion on the Cropland

Siltation	Percentage of total siltation			Differences of Percentages
in Inch	1975	1985	1999	1985-75	1999-85	1999-75
<0.5	2.7	0.8	0.0	-1.90	-0.80	-2.7
0.5-1.0	30.7	3.2	0.0	-27.5	-3.20	-30.7
1.1-2.0	28.3	8.8	0.0	-19.5	-8.80	-28.3
2.1-3.0	36.9	17.4	0.8	-19.5	-16.6	-36.1
3.1-4.0	0.8	21.7	2.7	20.9	-19.0	1.9
4.1-5.0	0.3	31.0	6.7	30.7	-24.3	6.4
5.1-6.0	0.3	15.2	24.1	15.0	8.80	23.8
6.0+	0.0	1.9	65.8	1.90	63.9	65.8
Total	100	100	100	-	-	-
Average Siltation	1.83	4.18	7.11	2.35	2.93	5.28

Source: Field Survey, 1999

6.2.2. Siltation in River, Canals and Ponds

Construction of BWDB polder intended to control tidal water intrusion and protect agricultural land for raising the productivity of crops. Now, this polder are used as protection of shrimp farms from tidal flooding and intrude saline water as controlled way through construction of sluice gate for enhancing shrimp productivity. Thus, at present shrimp cultivation from tidal flooding, a new situation was created with respect to sedimentation and erosion. Originally the coastal rivers, creeks and canals were silted and eroded twice a day with tidal water. As a result, the creek and canal system was not stable and continuously subject to changes caused by sedimentation and erosion.

The siltation on the riverbed became a problem because of increase the elevation of the river gradient than the upstream branch of rivers and canals. As a result, the volume of upstream water cannot flow smoothly, which causes the speed of water flows in the adjacent rivers obstructed and taken time to flowing into the sea. Thus, drainage outlets as well as the sluice gates are not functioned and gradually blocked by siltation, causes drainage problems in the study area.

Similarly, sediment containing river water or rainfall enter inside the embankment are not drained out. As a result, creeks and canal inside embankment area silted up. The course materials settles near the inlet  while the finer parts settle further away. It is seen that most of the canal and riverbed silted and somewhere it raised 3 to 5 feet the depth during the period 1975-99. The present siltation rate on the river was accounted 3 inch per year. Table 6.2 shows the average siltation of different water bodies in the study area.

Table 6.2: Average Siltation in feet in Pond, Khal and River in respect of 1975

Type of water bodies	1975	1975-85	1985-99	1975-99
Pond	0	0.02	2.90	2.92
Khal	0	0.16	3.10	3.26
River	0	1.33	3.50	4.83

Source: Field Survey, 1999

6.3. Water Logging

The process of siltation in the river and canal, traditional ghers culture and lack of proper management of the embankment are the major causes for water logging in the study area. Water during the high tide enter into the shrimp farms / agricultural land for shrimp cultivation or the accumulated rainwater of the within the ghers area could not drained out due to higher elevation of the river/canal bed than the plan agricultural land. As a result, vast area has been suffering from permanent water logging.

However, the cuts in the BWDB embankments have aggravated flooding and salinity intrusion within the polder, expanded inundated areas. As a result the sweet stagnant water turned into saline and consequently leaded to an environmental disaster in the study area. Table 6.3 depicts the duration of saline water in the shrimp ghers. In 1975, most of the agricultural land (86.6%) in the study remained under water for six months while in 1985 and 1999, inundation of same period have reported 76.7% and 32.2% respectively. At present (1999), about 60 per cent of respondent reported, duration of inundation of saline water in the shrimp farms gradually increased to 9 months which was 12.3 per cent and 1.6 per cent in 1985 and 1975 respectively. About 11 per cent of the shrimp farm in the study reported permanent water logging.

Table 6.3: Duration of Saline Water Stored in the Shrimp Gher

Month	Percentage of Duration
	1975	1985	1999
3	11.8	0.0	0.4
6	86.6	76.7	32.2
9	1.6	12.3	57.0
12	0.0	11.0	10.5
Total	100	100	100

Source: Field Survey, 1999

6.4 Soil Quality

Soil in the coastal area, especially in the mangrove forest, contain a high amount of sulfide in the form of hydrogen sulfide and pyrite. When dried out, the sulfides are oxidized and the soils become acid sulfate soils (Eiumnoh, 1995). When these area are converted to shrimp pond, the pond water will high acidity levels which consequently results in decreasing decomposition rate of organic matter at the pond bottom. This situation causes harmful effects on shrimps (TESCO, 1994). Formation of hard pans below the soil surface also unsuitable for plant growth (Hussain, 96). The suitable soil for shrimp ponds should have clay and have slightly alkaline conditions.  In the study area, there are three major types of soils can be categorized:

a)       Acid Sulphate soil

b)       Rapidly permeable and saline soil and

c)       The Sundarbans soil.

Ganges floodplain including tidal floodplain have been producing fair to good crops for many decades with little or no use of manure or fertilizer (CEMP, 1987). About 6200 hectares of active acid sulphate soils in the coastal areas of Khulna, Bagerhat and Cox’s Bazar have been reported by the study Uddin & Islam, 1988. The texture of most saline soils varies from silty to clay dominated by 2 : 1 type clays, which develop wide cracks as the soil dries out. However, none of the soil mentioned above is naturally fertile enough to maintain sustain high yields due to extreme acidity, deficient of N, P, Zn and Cu. Upazila wise Soil Characteristics of Different Agroecological Regions are describe in Table 6.4.

Table 6.4: Upazila wise Soil Characteristics of Different Agroecological Regions

DISTRICT Upazila	AEZ	AEZ Sub-Region	Main soil Texture	Main General Soil Type	BAGERHAT1. BagerhatHigh Ganges River floodplain Ganges tidal flood plain

Nonsaline, calcareous and non calcareous

Saline, calcareous and non calcareous

		Loamy, Clayey		Calcareous Grey floodplain soil Calcareous dark Grey floodplain soil Noncalcareous Grey floodplain soil Acid sulphate soil
2. Fakirhat		Ganges tidal flood plain		Saline, calcareous and non calcareous		Clayey		Calcareous Grey floodplain soil Calcareous dark Grey floodplain soil Noncalcareous Grey floodplain soil
Kachua		Ganges tidal flood plain		Nonsaline, calcareous and non calcareous Saline, noncalcareous		Loamy, Clayey		Calcareous Grey floodplain soil Calcareous dark Grey floodplain soil Noncalcareous Grey floodplain soil Acid sulphate soil Peat
Mongla		Ganges tidal flood plain		Saline, noncalcareous Nonsaline, calcareous and non calcareous		Loamy, Clayey		Calcareous Alluvium Calcareous Grey floodplain soil Calcareous dark Grey floodplain soil Noncalcareous Grey floodplain soil Acid sulphate soil
Morrelganj		Ganges tidal flood plain		Nonsaline, calcareous and non calcareous Saline, noncalcareous		Loamy, Clayey		Calcareous Grey floodplain soil Calcareous dark Grey floodplain soil Noncalcareous Grey floodplain soil Acid sulphate soil Peat
Rampal		Ganges tidal flood plain		Nonsaline, calcareous and non calcareous Saline, noncalcareous Saline, calcareous and noncalcareous		Loamy		Calcareous Alluvium Calcareous Grey floodplain soil Calcareous dark Grey floodplain soil Noncalcareous Grey floodplain soil Acid sulphate soil Peat
Sarankhola		Ganges tidal flood plain		Saline, noncalcareous		Loamy		Calcareous Grey floodplain soil Noncalcareous Grey floodplain soil

               Source; BARC 1990

6.4.1 Fertility Status of Soil

The present study focused on whether the physical parameters and fertility status of soil and land have changed due to shrimp cultivation that might have adversely affected rice yields. From the Table 6.5, it is evident that fertility status of soil in respect of organic content, nitrogen and phosphorus tends to higher in areas where shrimp is being cultivated than areas where shrimp culture has not yet developed. The status of micronutrients like zinc and sulpher was medium to high in both shrimp and non-shrimp areas.

Table 6.5: Percentage of Nutrient Contents below Critical Level

District		Org. matter		N		K		Ca		Mg		P		Zn		B		Cu
Satkhira		36		100		2		0		0		48		89		2		50
Khulna		50		100		0		0		0		4		100		0		100
Bagerhat		45		100		0		0		0		14		100		5		100
Patuakhali		100		100		0		0		0		22		31		4		0
Barguna		40		100		4		0		0		50		50		-		64
Bhola		85		100		40		0		0		8		100		0		100
Chittagong		21		100		10		0		0		100		21		4		0
Noakhali		80		100		10		0		0		10		0		0		100
Laxmipur		25		100		50		8		0		0		100		0		100
Feni		50		100		0		0		0		50		100		0		100
Critical level		<1.7***		65*		0.18**		1.8**		0.70**		10.0*		1.8*		0.17*		0.85*

Source: BARC, 1990

               Note:

*               Critical level expressed in ug/g soil

                          

**

          Critical level expressed in meq/100 g soil

                          

***

         Not

critical level, low organic matter content (%)

                           

Yet there is evidence of declining trend of rice yields where shrimp cultivated in rotation with rice (Table 6.6). This is possibly due to higher level of salinity that is left in the soil because of incomplete leaching caused by inadequate monsoon rainfall or absence of drainage facilities for flushing salinity by fresh water. This is also landowner did not start cultivation of paddy right in time (Atiur, 1992). In certain sites in the shrimp culture areas there is evidence of higher level of salinity that supports the view that shrimp farming in rice fields leads to gradual built-up of soil salinity that may render a soil unfit for crop cultivation in the long run (Mahmood 1994).

Table 6.6: Trend of Rice Yields per acre from 1975-99

Types of		Production in maunds per acre		Difference in maunds per acre
Crops		1975		1985		1999		1985-75		1999-85		1999-75
Paddy		37.13		23.02		11.23		-14.1		-11.8		-25.9
Wheat		9.16		0.00		0.00		-9.2		0.0		-9.2
Jute		9.22		0.00		0.00		-9.2		0.0		-9.2
Oil Seed		7.90		6.17		3.93		-1.7		-83.7		-4.0
Sugarcane		10.77		0.00		0.00		-10.8		0.0		-10.8
Pulses		7.11		6.38		5.75		-0.7		-23.6		-1.4
Pepper		15.66		8.22		6.77		-7.4		-54.4		-8.9
Vegetables		29.67		13.00		8.97		-16.7		-150.2		-20.7
Fruits	27.54	12.94	8.43	-14.6	-168.1	-19.1

            Source: Field Survey, 1999

6.4.2 Soil Salinity

Soil of coastal areas is naturally more saline than other parts of the country. Figure 6.3 (a, b, c, d) shows the surface soil salinity in different parts of coastal region of Bangladesh. Soil salinity is the most limiting factor that affects certain crop production at different levels and in severe cases the total yield is lost. The main factors for the development of saline soils are: Tidal flooding during wet season, direct inundation by saline or brackish water and upward or lateral movement of saline ground water during the dry season (Uddin & Islam, 1998). Direct inundation of agricultural land and water bodies by saline water and keeping saline water several months on that land is a main cause to increased salinity rather than tidal flooding in the study area. Upward or lateral movement of saline ground water also influenced by direct inundation of saline water during the dry season. Thus, brackish water shrimp cultivation provokes significantly to increased salinity in the coastal area.

The areas where soil salinity exceeds 8 dsm^-1 micro-mhos/cm have good potential for shrimp farming rather than agricultural production (Karim, 1990). The tolerance range of water salinity for shrimp cultivation is 10 dsm^-1 to 30 dsm^-1. But depending on season and rainfall, this salinity level change from 5 to 40 ppt. Thus, salinity variation is considered an important factor in shrimp production. Optimal level of salinity varies from species to species. For instance, the tiger shrimp (penaeus mondon) grows faster at 15-30 ppt. The white shrimp (p. indicus and p. merguiensis) tolerate higher salinity ranges 25-40 ppt.  (Nuruzzaman, 1993).

The highest salinity, both in terms of intensity and extend (Ec dsm^-1>16), falls within Khulna, Satkhira and Bagerhat districts saline (SW Halcrow & Parners Ltd 1992) of the southwest region of Bangladesh. Table 6.7 Distribution and Extent of different categories of soil salinity in the coastal and offshore regions of Bangladesh. Salinity categories ranges from slightly to moderately saline in dry season (4-8 dS m^-1) having potential for brackish water shrimp aquaculture in the study area. The lands used for brackish water shrimp cultivation for several years, cumulative increment of salinity of soil resulting unusable for agricultural practices. Moreover, upward and lateral movement saline water, soil salinity in adjacent land also increases and attacked kitchen vegetable garden.

Table 6.7: Distribution and Extent Soil Salinity in the Coastal and Offshore Regions of Bangladesh

(‘000’ Hectares)

District	Salinity Categories dS m-1				Upazila
Upazila	S1	S2	S3	S4	Total
	2-4	4-8	8-16	>16
SATKHIRA
1. Asasuni	1.80	24.60	6.48	3.10	35.98
2. Debhata	3.40	7.50	1.30	0.00	12.20
3. Kaliganj	2.20	16.30	4.90	2.60	26.00
4. Satkhira	7.80	8.50	2.80	0.00	19.10
5. Shamnagar	0.00	18.10	15.27	5.20	38.57
6. Tala	1.30	10.60	2.60	0.00	14.50
District Total	16.50	85.60	33.35	10.90	146.35
KHULNA
7. Baitaghata	1.30	17.40	1.00	0.00	19.70
8. Dacope	0.00	17.60	3.40	2.10	23.10
9. Dumuria	0.00	16.30	3.60	2.80	22.70
10. Koyra	0.00	17.84	3.70	2.30	23.84
11. Paikgacha	2.60	23.10	2.10	2.60	30.40
12. Rupsa	0.00	0.30	0.00	0.00	0.30
District Total	3.90	92.54	13.80	9.80	120.04
BAGERHAT
13. Bagerhat	6.00	1.80	1.00	0.00	8.80
14. Fakirhat	2.60	0.00	0.00	0.00	2.60
15. Kachua	5.20	1.30	0.00	0.00	6.50
16. Mongla	0.00	15.50	0.00	0.00	15.50
17. Morrelganj	4.10	30.10	1.30	0.00	35.50
18. Rampal	10.40	16.10	0.30	0.00	26.80
19. Sarankhola	0.00	12.28	0.00	0.00	12.28
District Total	28.30	77.08	2.60	0.00	107.98

            Source: Karim,1990

From Table 6.8, it is seen that the coastal areas of Bangladesh have 7769.09 sq.mile of saline land (soil salinity more than 2 mmhos/cm.) which is 29.69% of the coastal area. Most of these lands are suitable for brackish water aquaculture (except Noakhali area where elevation is not favourable for tidal inundation). Land with more than 15 mmhos/cm. of salinity has no agricultural potentials (FAO 1986, & Karim 1990).

Table: 6.8 Surface Soil Salinity in the Coastal Area of Bangladesh                                   

District	Salinity levels : mmhos / cm				Total Saline area	District area
	2 - 4	4 – 8	8 - 15	15 +	(Sq. mile)	(Sq. mile)
Khulna	14.3 (1.10)	610.00 (46.00)	587.30 (44.30)	114.70 (8.60)	1326.30	4630.00 (28.64)
Barisal Patuakhali	56.70 (4.70)	333.00 (26.90)	847.90 (68.30)	-	1237.60	5540.00 (22.34)
Noakhali	-	907.20 (86.30)	143.10 (13.60)	-	1050.30	2033.00 (51.76)
Chittagong	78.89 (1.90)	1968.09 (47.40)	1855.99 (44.70)	248.92 (6.00)	4151.89	13953 (29.75)
Total	149.89 (0.57)	3818.29 (15.00)	3434.29 13.13	363.62 1.39	7766.09	26156.00 (29.69)

Source: MPO (TR - 18), Table 4, p. 15

Note:       i)              mili mhos/cm  (electrical conductivity value)

                                                1 mili mhos/cm = 1000 micro mhos/cm

                                                1.56 mili mhos/cm = 1 part per thousand (ppt) or

                                                1 mili mhos/cm = 0.64 ppt

                                ii)             Figures on parentheses in the last column are percentages of district area,                                                                           which is saline while the others are percentages total area for the relevant                                                                            district.

6.5 Surface Water Salinity

The advancement of the saline front in the Khulna, Bagerhat and Satkhira district has been a matter of alarm and concern. The investigations carried out since 1976 has established that the salinity intrusion, concentration and duration in the region depend mostly upon the quantity and duration of the upland flow received in the area, from the Ganges through the Gorai-Madhumati system. Owing to the decreasing trend of dry season flow in the Ganges, the Gorai-Madhumati is receiving a very low discharge in the dry months and, as a result the salinity and the tidal limit are penetrating further into the country. In November the water level in the Ganges falls very rapidly, shoals from at the take-off point. Efforts have been made to keep the Gorai as active as possible by dredging operations since 1982. This is not adequate and the Gorai becomes almost completely dry every year. Yearly maximum salinity at the monitoring stations for the lean period of 1982-83, the lines of equal salinity have been drawn over the affected area for 500, 1000 and 2,000 micro-mhos concentrations (Nishat, 1988). The area engulfed by the isoline of different concentrations during the years since 1976 has been shown in Table 6.9.

Table 6.9: Maximum penetration of salinity of 500 micro-mhos along different estuaries for several years

Name of	Distance	Distance in kilometer during the year
estuaries	from	1968	1976	1977	1978	1979	1980	1981	1982	1983
Shabazpur	Chorfession	105	116	120	118	133	115	120	116	115
lower Meghna
Biskhali	Patharghata			41	50	50	24	54	40	42
Baleshwar	Charduani			80	70	76	76	71	74	85
Sibsa	Opposit hiron Point			180	170	180	220	230	200	190
Passur	Hiron Point	147	247	160	142	170	205	200	277	287

Source: Coastal area resource development and management, p, 30

Table 6.10 shows the mean monthly salinity in different stations of Khulna Region.

Table 6.10: Mean Monthly Maximum Salinity in different Station (at 25-Degree Celsius)

Sl. No.	Station Name	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
2	Afrahat	558	607	999	2274	2991	369					369	460
3	Amasio	470	482	528	505	438	327					346	377
5	Arpara	518	552	586	541	480	399					365	470
8	Bagerhat	2050	4648	9382	13014	11320	7605					767	1623
15	Chalna	5890	10920	16313	21211	18739	11070					590	2215
25	Dumuria	3376	6688	13885	18006	19437	17790					925	1721
26	Gazirhat	495	577	1809	3993	3239	674					320	371
31	Haridaspur	480	426	437	378	288	240					367	391
33	Hironpoint	30632	34762	39195	41109	39804	28558					16034	22969
40	Kamarkhali	423	456	491	481	418	314					344	392
43	Khulna	380	440	1000	900	1300	190					280	280
44	Lohalia	245	250	250	200	200	185					200	220
45	Magura	420	400	520	420	440	250					280	440
48	Mongla	2300	3700	6000	6000	7900	1900					320	425
53	Paikgacha	5500	6800	8000	7500	8000	8000					675	1500
54	Patgati	360	300	360	260	230	195					240	280
57	Pirojpur	325	320	430	390	300	280					310	290
61	Satkhira	7500	8000	16500	24000	21000						3000	37000

Source: Southwest Area Water Resources Management Project, 1993.

All embankments for shrimp cultivation are made of earth. These embankments are temporary structures, which enhance saline water seepage from shrimp farm to adjacent pond and other water body. Increase of surface water salinity also creates problems for livestock husbandry because surface water is normally used as drinking water for livestock. The level of salinity in the river, canal and ghers water is not uniform across the season. As can see from Table 6.11 shows that surface water salinity is slightly less in shrimp pond than source of saline water and adjacent water bodies. Surface water salinity in Mongla River, canal adjacent to the shrimp farms and ghers were found 10, 9 and 7 ppt. respectively.

Table 6.11.  Surface water salinity in river, canal and gher during the month of May 1999

Upazila	River	Canal	Pond/ghers
Rampal	10	9	7
Mongla
Batiaghata
Paikgacha

                Upazila Fisheries Office, 1999

On the other hand, sometimes shrimp farmers create an artificial flow of saline water from tidal river through canal to supply saline water in their shrimp pond. It affects the level of salinity of surface water surrounding the canal in which formerly fresh water as available. Surface water salinity in the Rupsha River collected by News Print paper mills presented in the following Figure 6.4.

6.6 Ground-water salinity

Ground water is the primary source of potable water in the coastal region of Bangladesh. The position of the saline ground-water front is determined by the local rainfall recharge, the nature of saline/fresh-water flooding from estuarine tidal effect and subsurface flow from the north. In the shallow aquifers in the coastal zone, up to a depth of about 60-meter the salinity is extremely variable and changes rapidly over the short distances. In the deeper aquifer, the pattern of salinity distribution is more uniform on a regional basis, as is the continuity of the aquifer. Between the shallow and the deeper aquifers, there exist thick layers of clay. The fresh/saline-water interface lies 120-160 km inland in the western most part of the area, but swings sharply to the south and lies approximately at the coast over most of the rest of the area. This interface is sensitive to the availability of fresh recharge water (Nishat, 1988).

Underground water is used for drinking purposes both for man and livestock and also for irrigation purposes. Increase of salinity makes drinking water unusable and decrease agricultural yield. Table 6.12 illustrates the ground water quality recorded at a few stations near the Rampal Upazila. The quality of ground water throughout the coastal area is affected by salt-water intrusion. Reports also indicate that the sulphate content can be as high as 27-39 m.e./litre in the Ganges flood plain (Karim and et al. 1982).

Table 6.12: Ground water Quality, 1990 (ppm)

Nutrients	Daulatpur	Khalishpur	Khulna	Bagerhat	Chalna
	(Khulna)	(Khulna)
Ca	60.60	23.30	24.00	68.00	139.30
Mg	32.00	22.60	27.80	46.00	212.00
SiO2	35.50	30.00	30.00	37.50	48.00
Fe	5.60	0.07	0.64	11.60	6.90
B	-	-	0.05	0.18	0.13
Na	50.10	199.00	209.00	533.00	39.60
Free CO2	19.50	-	-	-	6.70
CO3	-	38.20	27.80	145.00	21.80
HCO3	400.00	320.00	282.00	755.00	222.00
Cl	43.00	170.00	226.00	450.00	765.00
SO4	39.20	16.10	30.80	26.50	8.30
TDS	487.00	683.00	741.00	1713.00	1365.00

            Source: IUCN, 1994

Underground water salinity increase due to inundation of vast land by saline water for shrimp cultivation and lifting of underground water to dilute the salinity of water in shrimp ponds in March and April when salinity of sea water exceeds the tolerance limit for shrimp cultivation.

6.7 Vegetation

It is observed that before starting shrimp farming, land are cleared if there are any bushes or forest. On the other hand, once shrimp cultivation has started, trees and vegetation may be disappeared due to excess salinity and inundation. In the farm areas, most of the trees and vegetation are completely cleared. Sometimes trees on the dyke and embankment are excluded but due to seepage and leakage of saline water these trees disappear subsequently. Vegetation outside of the shrimp farm also disappears due to saline water seepage.

Water logging can have negatively affect the growth of vegetation. Salinity with water logging adds more severity affecting for survival of vegetation in the study area. So reeds or grass used for fuel or for making mats and paper are lost gradually due to exceeding saline limit in water logged areas. Table 6.13 shows gradual encroachment of shrimp farms into the homestead area created water logging and causes serious problems for the survival of trees in and around homesteads kitchen garden. At present 46 per cent of the shrimp ghers encroached into the homestead land and very close to living room (less than 10 meters distance from homestead land). Since 1975, there was no shrimp farms found in this range. At that time most of the shrimp farm (81.4%) were available not less 500-meter far away from homestead areas.

Table 6. 13: Encroachment of shrimp to the Homesteads

Distance	Percentage				Differences of Percentages
In Meter		1975	1985	1999	1985-75	1999-85	1999-75
<10		0.0	0.9	46.0	0.9	45.1	46.0
10-24		0.0	3.4	24.1	3.4	20.6	24.1
25-50		0.3	7.8	15.8	7.4	8.0	15.4
51-100		0.0	4.0	5.3	4.0	1.3	5.3
101-300		0.7	5.6	3.5	4.9	-2.1	2.8
301-500		17.6	19.3	3.2	1.7	-16.0	-14.4
500+		81.4	59.0	2.1	-22.4	-56.9	-79.3
Total	100		100	100	-	-	-

Source: Field Survey, 1999

Shrimp cultivation is a land development process in which normally swampy forestland or agricultural land of low elevation is converted into shrimp pond by embankment construction. In ease of swampy forest or bushy land, at first trees and bushes are cleared totally or except trees on the land where dyke and embankment would be constructed. Table 6.14 shows the percentage of forestland and pasture, which have been converted to shrimps pond by clearing forest and pasture.

 

Table 6.14: Types of Land Use before Shrimp Cultivation

Types of	Percentage			Differences of Percentages
Land Use	1975	1985	1999	1985-75	1999-85	1999-75
Forest	1.5	2.9	2.2	1.3	-0.6	0.7
Paddy Land	74.1	91.9	89.9	17.8	-2.0	15.8
Vegetables Garden	18.9	4.0	2.2	-14.9	-1.8	-16.7
Other Crops	4.6	0.0	0.0	-4.6	0.0	-4.6
Grazing Land	0.4	0.6	1.1	0.2	0.5	0.7
Fish Culture Area	0.4	0.6	3.4	0.2	2.8	3.0
Total	100	100	100	-	-	-

            Source: Field Survey, 1999

The shrimp farming areas were found an adverse effect on natural vegetation. This was reflected in the erosion of genetic diversity of a wide range of plants, aquatic flora, agricultural crops, fruits, vegetables and tree species (Atiur 1994). Putting all the blame for the destruction of mangrove on the recent development of shrimp culture is far off the mark is not only in Bangladesh but also other shrimp producing countries of the country. In the Philippines, it was reported that 310 thousands hectares of mangroves were deforested since 1920 (Zamora, 1989). In the Thailand about 172 thousands ha of mangroves was destroyed as was reported since 1971 (Chantadessi, 1989). In Indonesia about 20% of the mangrove or 800 thousands ha are considered to be suitable for being converted of shrimp ponds (Andriwan, 1989). In Bangladesh about 8750 ha Chakaria mangrove forest were completely damaged due to shrimp cultivation and incurred the loss of income of 19 cores 61 laks taka (Daily Ittefaque, 16^th May, 1999).

The interviewees named several aquatic plants and weeds that become completely extinct now because of shrimp farming in the coastal area (Atiur 1994). They are Durba (Cynodon dactylon), Baju (Tamarix troupii), Chehur (Bauhnia vahlii), Thankuni (Centella asiatica), Ambalisak (Oxalis corniculata), Kachuripana (Eichhorina crassipes). But these species are still available in non-shrimp area.

A wide range of fruits trees and species was seen in the study areas. They are mango, jackfruit, guava, blackberry, datepalm, coconut, bamboo, betelnut, boroi, starapple, lemon, lichi, termarind, banana, sabeda, nim etc. The interviewees in the study area reported that only some tree species such as raintree, sobeda survived to a limited extent. In some homesteads betelnut, coconut, palmyra palm, date palm area seen to grow but they don’t bear fruits. Table 6.15 shows the status of major trees and their growth rate over different years.

Table 6.15: Status of vegetation in homestead garden and its growth rate over different years

Name of	Number of trees			Growth rate
Trees	1975	1985	1999	1985-75	1999-85	1999-75
Mango	3302	1833	928	-44.49	-49.37	-71.90
Jack Fruit	1369	629	197	-54.05	-68.68	-85.61
Guava	1752	771	603	-55.99	-21.79	-65.58
Barry	627	272	121	-56.62	-55.51	-80.70
Silk Cotton	440	160	321	-63.64	100.63	-27.05
Nim Tree	649	283	253	-56.39	-10.60	-61.02
Shirisha Tree	2087	1159	1224	-44.47	5.61	-41.35
Palm	2178	1090	792	-49.95	-27.34	-63.64
Date	11079	6607	3859	-40.36	-41.59	-65.17
Coconut	10525	6115	3953	-41.90	-35.36	-62.44
Bamboo	7682	2725	1598	-64.53	-41.36	-79.20
Nut	41960	15625	8603	-62.76	-44.94	-79.50
Boroi	1025	478	364	-53.37	-23.85	-64.49
Star Apple	422	164	94	-61.14	-42.68	-77.73
Lemon	827	249	168	-69.89	-32.53	-79.69
Lichi	310	75	20	-75.81	-73.33	-93.55
Tamarind	1272	444	510	-65.09	14.86	-59.91
Banana	19733	7617	3687	-61.40	-51.60	-81.32
Safeda	342	250	193	-26.90	-22.80	-43.57

Source: Field Survey, 1999

Note:       Growth rate = (Post project – Pre project) / Pre project

In addition to its effects on vegetation clearance, decrease of pastureland and disappearance of trees, shrimp cultures have some indirect effects on vegetation. Formerly, when land under shrimp culture and used as agricultural practices, agricultural residuals were used as fuel for cooking and as food for livestock and cow dung further used as fuel and manure. As a result fuel crisis become a common and profitable business which decrease in land vegetation and increase soil erosion and sedimentation in the river and agricultural field and creates problem in local ecosystem. Non-availability of cow dung manure decrease the organic matter and fertility of soil of agricultural land and garden prevent the scope for further growth of vegetation and decrease agricultural yield. Figure 6.4 shows the interrelationship of direct and indirect effects of shrimp farming in the study area.