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14. THE NORTHEAST

Situated within the geographical ordinates, 21° to 29° 30' N and 89° 46' to 97° 30' E, the Northeastern Region consists of seven States, viz., Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland and Tripura, popularly known as the seven sisters. The region, surrounded almost on all sides by Bhutan, China, Myanmar and Bangladesh, is divided into five physiographic units, the Assam Himalayas, the Brahmaputra valley, the Shillong plateau, the Barak valley and the Southeastern hill region. Except the Brahmaputra and Barak valleys in Assam and the Imphal valley in Manipur, the terrain is hilly and mountainous, only making 65% of the northeast an undulating land with elevations ranging from 200 to 900 m above MSL.

14.1 RESERVOIR FISHERIES RESOURCES OF THE NORTHEAST

The northeast has a copious rainfall during March to May, when precipitation is minimal in the rest of the country. Cherrapunji and Mawsyngram, recording highest rainfall in the world, are situated in the northeastern India, the annual rainfall of the region ranging from 100 to 1142 cm. The tall hills, punctuated by deep valleys receiving abundant drainage make the region ideally suited for tapping the hydro-electric power potential of water. It is estimated that Brahmaputra and Barak basins together constitute 50% of the total hydel power potential of the country (Sinha, 1990). However, very little of the potential is presently being utilised. Only eight reservoirs have so far been created, six of them for power generation under four hydro-electric projects. This, together with small irrigation impoundments, makes the total area under man-made lakes 8 206 ha (Table 14.1: Fig. 14.1). No organised fishing is practised in any of them except on the Gumti reservoir in Tripura.

Table 14.1. Reservoirs of the northeastern region
Name of the reservoirStateArea
  (ha)
Barapani (Umiam)Meghalaya500
Kyrdemkulai-do-90
Nongmahir-do-70
Khamdong-do- & Assam1335
UmrongAssam979
GumtiTripura4 500
KhoupumManipur100
PalakMizoram32
Others-600
TOTAL 8 206

(Anon., 1991 and Sinha, 1990)

Figure 14.1

figure 14.1. Reservoirs of the North Eastern States

14.2 GUMTI RESERVOIR

Gumti reservoir is located at 23° 25' 45" N and 91° 49' 20" E, across the river Gumti in the South Tripura district. The 4 500 ha watersheet draws water from Barak, Raima and Sarma river basins. Completed in the year 1977, the 103 m long, 30 m high, straight gravity dam is made of brick and stone concrete, holding a storage of 235.62 million m3 at the FRL. The river at the dam site has a catchment area of 547 km2 receiving rainfall of 173 cm. The maximum capacity of spillways is 381.38 m3 sec-1 and the power intake tunnel has a maximum capacity of 31.15 m3 sec-1. Very little is known about the water and soil quality of the reservoir. Raha and Sarkar (1980) describe the soil as red to light yellowish brown and dark brown with a medium water holding capacity of fine loamy texture. Turbidity of water is very high due to soil erosion on account of denudation of forests in catchment area by shifting cultivators (jhoom). The soil is acidic (pH 5 to 6) but the water is alkaline within the pH range of 7.5 and 9.

Chaudhari (1992) reports a rich macrophytic community in the reservoir, comprising Eichhornia crassipes, Nymphaea sp., Lymnanthemum sp., Trapa natans, Vallisneria spiralis, Hydrilla verticillata and Potamogeton nodosus. The phyto- and zooplankton exhibit strong seasonal and spatial cycles with a domination of blue-green algae and copepods.

Details on the indigenous ichthyofauna of the river before the impoundment are not available. More than 47 species have been reported from the reservoir, commercially important among them being Aorichthys aor, Channa marulius, C. punctatus, Mastacembelus pancalus, M. guentheri, Puntius stigma, P. ticto, P. sarana, Xenentodon cancila, Amblypharyngodon mola, Chanda ranga, Heteropneustes fossilis, Clarias batrachus, Notopterus notopterus, Tor tor and Labeo gonius. Besides, the Indian and exotic carps, viz., Catla catla, Labeo rohita, Cirrhinus mrigala, Hypophthalmichthys molitrix, Ctenopharyngodon idella and Cyprinus carpio, have been introduced successfully in the reservoir. Catla-rohu and rohu-catla hybrids are also reported from the reservoir (Raha and Sarkar, 1980). Indian major carps breed in the upper reaches of the river at Ultacherra, Chitrajhari, Gandacherra, Rangajhari, Sarmacherra, Thakurcherra and Raimacherra. However, this isolated breeding success does not seem to lead to recruitment to the populations (Chaudhari, 1992).

Fish production

The highest fish production of 246.6 t was reported in 1981–82, with a steep decline thereafter (Table 14.2). The average production for the last 15 years was 141.74 t (31.5 kg ha-1). Variations in fishing effort, in terms of the number of licenses issued, have been erratic for the last 15 years with an increasing trend after the mid- eighties. The mean catch per licence is 379 kg.

Fishes caught from Gumti reservoir are graded into five categories (Table 14.3) for pricing and marketing. Notopterus spp., non-airbreathing catfishes and minnows dominated the catch till 1987–88. The share of Group IV, comprising the Indian and exotic carps, has been increasing since 1988–89.

Despite a species spectrum dominated by minnows and catfishes, the fish yield as per the official records is much higher than the national average. Although sustained stocking is often attributed to the high rate of productivity, it is clear from the catch data that the stocking has made some impact on fisheries only after 1988– 89 and the yield was high even during the earlier periods. The growth performance of introduced species in the reservoir is reported to be very impressive with silver carp growing to 12.9 kg within a period of 3 years. Very high growth rates have also been recorded for catla (10.5 kg), catla-rohu and rohu-catla hybrids (6.7 kg), and for the common carp (6.5 kg) for the same time span.

Table 14.2. Fish production from Gumti reservoir
YearFishing intensityStocking ofFish harvest
 (No. of licencesissued)fish seed (x 105)(t)
1978–792851.64169.000
1979–802936.89191.708
1980–814300.45193.398
1981–823792.50246.611
1982–833830.1590.891
1983–843525.00117.552
1984–852107.0441.124
1985–861983.05105.064
1986–871977.70133.986
1987–8858813.45322.043
1988–8944212.03138.693
1989–9049518.21137.393
1990–9130022.22121.331
1991–9243336.66101.630
1992–9362028.4815.731
Total5 605165.472 126.155
Average37411.03141.740
Average yield (kg ha-1): 31.50 
Average catch licence-1: 379 

(Anon., 1994b)

Table 14.3. Grade-wise fish catch composition in Gumti reservoir
YearTotal catch (t)Percentage composition of grades
IIIIIIIVV
1978–79169.0-----
1979–80191.726.2-56.50.60.2
1980–81193.415.412.167.05.30.2
1981–82246.635.022.837.83.90.5
1982–8390.946.318.631.71.21.1
1983–84117.525.123.234.413.93.3
1984–8541.148.611.231.17.30.8
1985–86105.135.014.041.98.20.9
1986–87134.037.17.645.79.10.5
1987–88322.050.64.628.915.30.5
1988–89138.734.310.520.732.32.1
1989–90137.438.42.442.116.50.5
1990–91121.328.63.443.523.90.6
1991–92101.64.63.226.665.50.1
1992–9315.74.05.162.128.70.1

Grade I - All minnows and weed fishes except Puntiusspp.
II - Puntius spp., eels and murrels (Channa spp.)
III - Notopterus spp. and non-airbreathing catfishes
IV - Indian and exotic major carps
V - Clarias batrachus and Heteropneustes fossilis

Stocking

In the absence of any recruitment of major economic species in the reservoir, sustained stocking assumes greater importance as a management measure to improve the fisheries, both qualitatively and quantitatively. Although stocking was initiated as early as 1978–79, it picked up momentum only after 1987–88, when the fish seed farm was commissioned adjacent to the reservoir. Detailed species-wise break-up of seed stocked is not available. So far, 16.5 million seed have been stocked in the reservoir over a period of 15 years at an annual average of 1.1 million and a stocking rate of 245 ha-1. During 1992–93, the stocking rate stood at 632 ha-1. The stocking did make an impact on the catch structure by increasing the share of Indian major carps (Fig. 14.2), but it did not increase the yield.

Figure 14.2

Figure 14.2. Stocking (in numbers x105) and major carp catches from Gumti reservoir

Craft and Gear

Gill nets of three different mesh sizes, ranging from 5 to 20 cm, are the most commonly used gear, followed by long lines, hook and line, traps, drag nets and cast nets. Hook and line and traps are targetted at murrels and Mastacembelus spp., while drag nets with 0.8 cm mesh are commonly employed for catching small fishes. A locally fabricated fishing boat usually 6 m × 1.25 m, with a V shaped hull, is used by the fishermen. One motor launch and two speed boats, owned by the Fisheries Department, are operated for transport of fish from landing to assembly centres.

Organization of fisheries

Organised fishing was initiated in Gumti in 1978–79. At present, more than 1 000 families, belonging to the Scheduled Caste and Scheduled Tribe communities, are engaged in fishing under seven cooperative societies. Fishing inputs are supplied to the fishermen under various welfare schemes. Boats, nets and nylon twines are distributed either free of cost or at a subsidy upto 50%. In 1990–91, 580 fishermen have benefitted from the welfare schemes (Table 14.4).

Table 14.4. Free distribution of fishing inputs to fishermen in Gumti reservoir
YearBoats (number)Nets (number)Nylon twine (kg)Total number of beneficiaries
1986–87108575140
1987–887105100212
1988–8927213100340
1989–9050333125508
1990–912040520580

(After Chaudhari, 19992)

Post-harvest arrangements

The licensed fishermen are required to hand over the catch by 0800 hrs to the officials of the Fisheries Department at any of the 5 assembly centres along the reservoir. The Department pays remuneration to the fishermen at the rates fixed on the basis of categories of fish. During 1991–92 the fishermen got Rs. 3.00 to 20.00 per kg of fish belonging to groups I to V. After paying the fishermen, the Department hands over the catch to the respective cooperative societies which sell it to retail outlets through an Apex Cooperative. The Fisheries Department levies a royalty ranging from Re. 1.00 to Rs. 3.00 per kg of fish sold by the society. The small fish, especially Puntius spp. harvested from the reservoir, support a flourishing dry-fish trade.

14.3 KYRDEMKULAI

Kyrdemkulai and Nongmahir are two pick-up reservoirs created below the Sumer power station of the Umtru-Umiam stage I hydroelectric project. They are the only two reservoirs in the region subjected to some investigations. The Central Inland Capture Fisheries Research Institute, under a consultancy assignment with the North Eastern Council, conducted feasibility studies for fisheries development in the two reservoirs (Sugunan and Yadava, 1991a). The salient findings of the study follows.

Kyrdemkulai reservoir, formed in 1979, is a part of the Umtru-Umiam Hydro-electric Project Stage III. River Umiam has a catchment of about 150 km2. The immediate catchment of the reservoir comprises forested hills, rarely exceeding the elevation of 700 m above MSL. The 106.7 m concrete gravity type diversion dam with three drainer gates has a height of 27.5 m and is provided with a 42.7 m long spillway having a capacity of 1 700 m3 sec-1. The river downstream is known as Umtru. The 167.7 m long diversion tunnel carries water from Kyrdemkulai to Nongmahir, another downstream reservoir.

The reservoir is elongated, with 10 major and minor pockets (bays). Besides the river Umiam, the reservoir receives 10 to 15 creeks, draining the forested catchment. With a total surface area of 80 ha, the reservoir maintains a full storage level (FSL) of 3.7 million m3 and a minimum storage level (DSL) of 2.78 million m3 It has a shoreline of 19.6 km. The water level in the reservoir fluctuates between 675.0 and 683.4 m above MSL. The level fluctuation is primarily determined by the requirements of the Nongmahir forebay. The water regime is also governed by incursion of Umiam waters, precipitation and runoff from the catchment. The mean depth of the reservoir at FRL is estimated at 4.63m.

Kyrdemkulai reservoir is situated in the low slopes of the East Khasi Hills, where climate varies from warm sub-tropical to cool and bracing. The region has a high rainfall, the average daily rainfall (calculated on monthly basis) varying from insignificant to 35.43 mm during 1987 and 1988.

The bottom sediments of the reservoir are fed by sand and clay fractions with average organic carbon content of 1.13%. Soil pH is on the alkaline side. Average values of organic matter (3.91%), available phosphorus (0.83 mg 100g-1), available nitrogen (21.56 mg 100 g-1) and specific conductivity (105.55 μmhos) reflect a low soil productivity.

Kyrdemkulai has a deep profile and its pockets with large littoral zones add considerably to the shoreline (Fig. 14.3). Limnological investigations do not portray significant sectoral differences, although there is a well expressed vertical profile of some physico-chemical parameters.

Water temperature, ranging from 19.5°C in November -December to 27.0°C in July, depicts moderate seasonal variations. Water pH, in consonance with the underlying soil, is alkaline. Dissolved oxygen and free carbon dioxide in the sub-surface have optimum values with a normal trend in their seasonality. Low alkalinity characteristic of the north-eastern waters is observed in Kyrdemkulai. Low hardness (18.56 to 27.84 mg 1-1) places the reservoir in the soft water category. In contrast to the low nutrient status of the sediments, optimum availability of nutrients in the water phase is a significant indicator of the reservoir's productive nature. However, total dissolved solids and specific conductivity are low (Table 14.5).

Physico-chemical characters governing the productivity of Kyrdemkulai reservoir, indicate favourable conditions for fish yield optimisation. Vertical profiles of temperature, pH, dissolved oxygen, free carbon dioxide and total alkalinity reflect the formation of thermocline and chemical stratification during the summer months. During winter (December-January) and monsoon months, especially August, this thermal stratification is disturbed, resulting in a turnover and subsequent water mixing. River Umiam, draining a sizeable catchment, contributes richly to the allochthonous nutrient enrichment. The nutrient flux and its optimum availability in the water phase can play a pivotal role in sustaining optimum levels of biotic communities.

Biotic communities

The low standing crop of net plankton is an indicator of a poor community, both in numerical and gravimetric terms. The dry weight of the total plankton estimated from different sectors covering three seasons varies from 0.21 to 0.40 mg 1-1 with an average of 0.31 mg 1-1. The average plankton density in numerical terms is 8 420 units 1-1. Despite a low plankton density, the primary carbon synthesis rate is high, suggesting a high nannoplankton concentration in the reservoir and a possible channelisation of production process through the nannoplankton chain. There is no significant difference in the plankton concentration and composition among various sectors. Chlorophyceae account for the bulk of the plankton (5 220 units 1-1), represented mainly by Staurastrum, Chaetophora and Dinobryon. Cyanophyceae are well represented in Kyrdemkulai, strongly indicating that the reservoir is at a more advanced phase of eutrophication. The blue–greens form nearly 36% (3 030 units 1-1) of the total plankton. The plankton species diversity is high.

Figure 14.3

Figure 14.3. Kyrdemkulai reservoir, Meghalaya

The reservoir is marked by the absence of aquatic macrovegetation, except for some isolated patches. The benthic macrofauna is rather poor, oligochaetes forming a sizeable component, followed by insect larvae. Gastropods are present in the shallows, especially th eprotected bays. Those parts of the bays receiving forest creeks, characterised by accumulation of detritus, harbour oligochaetes, larvae of Chironomus and Chaoborus, other insect larvae and nymphs. The density of benthos in the reservoir is 134 individuals m-2. The acidic nature of the soil might inhibit the colonisation of benthic communities.

Primary productivity

The reservoir has moderate rate of photosynthesis with the gross carbon production ranging from 39.37 to 56 mg C m3 hr-1. The net productivity is 18.75 to 20 mg C m3 hr-1. These productivity figures are equivalent to an average of 1 464.58 mg C m2 day-1 (gross) and 583.55 mg C m2 day-1 (net).

Table 14.5. Soil and water quality of Kyrdemkulai reservoir
 WINTERSUMMERMONSOONAV.
Soil    
pH5.907.606.206.57
Organic carbon (%)1.630.291.461.13
Organic matter (%)2.816.492.423.91
Available phosphorus (mg 100 g-1)0.791.120.590.83
Available nitrogen (mg 100 g-1)24.647.7032.3321.56
Spec. cond. (μmhos cm-1)121.6487.70107.30105.55
Water    
Temperature (°C)19.5023.5027.0023.30
Transparency (m)2.842.442.202.49
pH6.707.006.706.80
Dissolved oxygen (mg 1-1)7.107.106.706.80
Free carbon dioxide (mg 1-1)2.002.002.602.20
Total alkalinity (mg 1-1)28.0022.0032.0027.33
Total hardness (mg 1-1)18.5627.8423.2023.20
Chlorides (mg 1-1)18.8012.7213.1614.89
Iron (mg 1-1)0.16*tr.0.08
Ammoniacal nitrogen (mg 1-1)0.163.80.901.62
Nitrate nitrogen (mg 1-1)0.183.610.021.27
Silicates (mg 1-1)1.003.002.8010.67
Phosphate (mg 1-1)tr.0.020.020.01
Calcium (mg 1-1)14.84*9.2812.06
Magnesium (mg 1-1)3.72*13.928.62
Total dissolved solids (mg 1-1)32.00*62.0047.00
Spec. cond. (μmhos)**102.00102.00

* Values not recorded (Sugunan and Yadava, 1991b)

Fish fauna

In the absence of regular fishing, it was not possible to prepare a complete list of fish species of the reservoir. The following fish are reported. Cyprinus carpio, Acrossocheilus hexagonolepis, Tor putitora, Puntius sophore, Clarias batrachus, Dania rerio. Dania acquipinnatus, Dania dangila, Heteropneustes fossilis, Aplocheilus sp., Noemacheilus multifasciatus, Tor tor, Catla catla, Labeo rohita and Cirrhinus mrigala. Large murrels and Wallagu attu are either absent or their number is too low to create any serious problems. Similarly, there seems to be a poor population of weed fishes in the reservoir, which would a compete with the commercial carps, if introduced into the system.

Present status of fisheries

There is no organised fishing inthe reservoir. Tribals living in the neighbouring villages and the employees of the Meghalaya State Electricity Board (MeSEB) are engaged in subsistance or recreational fishing. Gill nets and long lines are the popular fishing tackle. The lake also attracts anglers who catch common carp, A. hexagonolepis and small fishes. Five to ten people angle in a day, each having 4 rods, on an average. No catch statistics are available. The villagers make improvised pen enclosures on the periphery of the reservoir to entrap fishes. A trap, locally called roh, is set in the pens which attracts common carp, H. fossilis, and small prawns. Six to seven pen enclosures are erected in the reservoir. There is only one fisherman who is engaged in full time fishing. He has gill nets, long lines and cast nets, his catch varying from 2 to 20 kg per day during the monsoon season.

There are five to six locally made boats in the reservoir, in the size range of 3 to 3.5 m, costing Rs. 500 to Rs. 1000 apiece. Excepting the one used by the lone full time fisherman, these are primarily used for collecting forest wood and for carrying anglers. Experimental gill netting yielded chocolate mahseer and common carp, while cast nets brought in a good number of mahseer juveniles which were released back into the reservoir.

Productivity status

The temporal and spatial variations in the limno-chemical parameters and the biotic communities offer vital clues to the productivity status of water bodies. A probe into the above parameters in respect of Kyrdemkulai reservoir suggests a combination of positive and negative characters. The temperature regime of the reservoir is relatively conducive to the production processes and the ambient dissolved oxygen in water is high in all seasons, which points towards high photosynthetic activity. The high shoreline development index of 11.65 denotes a highly irregular shoreline, a positive indicator to productivity. Whereas dissolved oxygen, water temperature and shoreline index suggest productive nature of the water body, the average pH, total alkalinity and specific conductivity are not in the productive range. However, the moderately high rate of carbon synthesis is a clear signal of productivity potential at the basic level. The other supporting limnological evidence for the high productivity of the water body are the oxycline and chemocline observed during the warmer months. Low pH of water and soil is an indicator of low productive nature, but the small size of the reservoir offers opportunities to adopt corrective measures to overcome this constraint. Bottom soil is rich in organic matter and this clearly suggests scope for detritivorous fishes in the reservoir. The poor benthic communities despite rich soil quality may be the result of the low soil pH. Notwithstanding a few discouraging limnological features, there is enough scope for fish yield optimisation in the reservoir through efficient management.

Fish yield potential

Based on the quantity of carbon produced, the reservoir can sustain a fish yield of 534 kg ha-1. In terms of calories, the average energy produced at primary level is 14 382 cal m2 day-1. At a conversion rate of 1% from carbon to fish, this primary productivity has the potential to yield 570.6 kg of fish (fish weight) ha-1 year-1. Considering the scope for increasing the fertility status of the reservoir through manuring, the target of production can be initially fixed at 600 kg ha-1, with considerable scope for gradual increase up to 1 000 kg ha-1 in due course.

Reservoir management

With the main accent of fisheries management in Kyrdemkulai on the yield optimisation, emphasis should be also placed on the conservation of the natural populations of chocolate mahseer in the river Umtru. The high primary production rate in Kyrdemkulai can be channelled to fish production. Apart from the usual reservoir management measures like regular stocking, population management through gear selection and maintaining a stocking and the harvesting schedule, there is enough room for increasing the productivity of the reservoir through artificial eutrophication. The small size of the reservoir and the fact that it does not form a source of drinking water make the option of fertilization easy. The fertilization can push up the fish production potential to much higher levels than what is calculated on the basis of primary productivity.

The management strategy formulated for the Kyrdemkulai reservoir (Sugunan and Yadava, 1991) falls broadly under the following lines :

Conservation and management of mahseer fisheries

  1. Establishment of a sanctuary for mahseers

  2. Banning the capture of mahseer juveniles

  3. Artificial breeding of chocolate mahseer for stocking the reservoir

Management of carp fisheries

  1. Fertilization

  2. Staggered stocking of carps

  3. Harvesting schedule

  4. Monitoring of fishing effort

  5. Post-harvest management.

Conservation and management of mahseer fisheries

The chocolate mahseer, Acrossocheilus hexagonolepis, the golden mahseer, Tor putitora and T. tor are the important mahseer species of the region. These fish are highly preferred by the sport enthusiasts as well as commercial fishermen. Among them, the chocolate mahseer is specially liked as food fish by the local people. Mahseers, in general, are enlisted as endangered and threatened species in the country. Unlike their counterparts in the Himalayas, the North Eastern mahseers are least subjected to the anthropogenic environmental pressures. This makes the job conservation of these species easier. Mahseers in the North East command a premium price and attract anglers from far and wide. The fisheries development plan for Kyrdemkulai, therefore, should have an in-built component of conserving the indigenous ichthyofauna, especially the chocolate mahseer.

Sanctuaries for mahseers

The lotic sector of the reservoir merges into the sandy river course of Umiam which traverses thick virgin forests of East Khasi Hill district of Meghalaya. This river stretch and its further upper reaches are ideal habitats for mahseer breeding and recruitment. One of the main factors that contributed to the decline in the mahseer populations elsewere in the country is the destruction of such habitats. Therefore, this habitat needs to be protected by declaring an 8 km stretch upstream the reservoir as mahseer sanctuary. In the sanctaury, all human activities leading to environmental degradation like deforestation and agricultural operations need to be prohibited. Special care should be exercised to preserve the sandy shores which provide clear water rich in dissolved oxygen for the breeding of mahseers. Removal of sand from the area should be totally prohibited. A complete ban is suggested on catching any fish from the sanctuary. The State Departments of Environment and Forests have a pivotal role to play in managing the sanctuary by implementing the regulations.

Artificial recruitment of mahseers

During the post-monsoon months, the juvenile mahseers of 5 to 10 cm size abound in the reservoir. They become easy prey to the cast net and small meshed gill nets. They can also be caught easily by operating drag nets in the shallow bays where they congregate for feeding. The investigating team, while operating cast nets in the vicinity of the tunnel intake tower and shallow bays of the reservoir in the month of July, captured 10 juveniles of chocolate mahseer per cast net. Tor putitora andT. tor were also caught occasionally in the cast nets. Fortunately, there is only one fisherman in the reservoir who operates cast nets. In future, if more fishermen employ cast nets and drag nets to catch the juveniles of mahseers, it may have disastrous effects on the mahseer stocks. A strict ban on the capture of juvenile fish should be a part of the management programme. Conservation measures as suggested above are expected to result in substantial recruitment to the mahseer populations. However, as an additional precautionary and supplementing measure, breeding and stocking of chocolate mahseer are recommended. The State Fisheries Department has a mahseer breeding farm at Barapani, where attempts to breed and rear the chocolate mahseer are going on.

Management of carp fisheries

Since the environment of Kyrdemkulai is suitable for Indian major carps, they should be introduced in the reservoir to constitute the main fishery. The carp fisheries management strategy for the reservoir should include fertilization, regular stocking and harvesting, monitoring the number of fishing units and post-harvest management.

Fertilization

Since the energy produced at the primary level in Kyrdemkulai is transformed to higher trophic levels through nannoplankton chain, there is an urgent need to enhance the microplankton community through artificial eutrophication. This will enable diversification of the pathway of energy tranfer through plankton chain. Basic objectives of fertilizing the reservoir are to increase the plankton density and to enhance primary productivity. The plankton biomass of Kyrdemkulai, based on the dry weight, is estimated at 0.31 mg 1-1, far below the ideal range for planktophagous fishes. A plankton density of 7 to 10 mg 1-1 is considered to be ideal for a reservoir, where the major fisheries depend on filter feeders. A higher plankton biomass of 30 mg 1-1, if achieved, can substantially increase the fish yield.

With a view to increasing the standing crop of plankton, a fertilization programme has been prepared for the reservoir, which envisages application of poultry manure at the rate of 10 t ha-1 yr-1, along with urea and superphosphate at the rates of 40 and 20 kg ha-1 yr-1. After a high standing crop of plankton is established, there is a fair possibility that the community may sustain itself without artificial eutrophication. In that event, it may even be possible to scale down and ultimately discontinue the application of fertilizers.

There is a need to lime the reservoir at the bays in order to increased the pH water and soil. The lime application also acts as a prophylactic cover against the outbreak of fish diseases like epizootic ulcerative syndrome.

Stocking

The basic purpose of stocking in Kyrdemkulai is to establish the quick growing carp populations into the ecosystem. The other important fish species, the mahseers are mainly carnivorous and do not directly compete with the carps for food. A breeding population of common carp is already available in the reservoir. Common carp is a well known detritivore and it has good market value in the region (unlike in many other parts of the country, common carp is not at discount in Meghalaya). Stocking of other bottom feeding detritivore is not recommended.

Since the fertilization is expected to increase the phytoplankon production, the stocking emphasis should be on filter feeders and the natural choice falls on the indigenous species, Catla catla, which has a proven track record. The other species suggested for stocking is rohu which is a versatile feeder. The reservoir needs to be stocked annually at the rate of 150 000 advanced fingerlings (above 100 mm) of catla and rohu in the ratio 3:2.

A circular hatchery (concrete, synthetic or metallic), a nursery farm for transit rearing and pen enclosures are the infrastructure needed for seed raising. Bay sectors of the reservoir provide ideal location for installing pens. The site lies between 675 to 679.7 m above MSL, which dries up during extreme summer, when the pens can be erected with ease. They would gradually fill up with the onset of monsoon and retain at least 1 to 2 m of water for sufficient duration to facilitate seed rearing (Fig. 14.4).

Harvesting schedule

Continuous stocking and harvesting system is suggested for Kyrdemkulai. In the beginning, the stocked carps need to be allowed to complete two years without fishing. Commercial exploitation may start from the third year onwards, but catla and rohu less than 400 g in size are required to be protected from fishing and if capture, to be released. On an average, 65 fishermen together can operate 390 units of gill nets (a unit being 50 m hung length). Average daily carp harvest is expected to be around 167 kg (calculated on the basis of 240 fishing days).

June 15 to August 15 may be declared as closed season and a complete ban on fishing strictly enforced during this period. A fishing party, comprising two fishermen, can share a boat and operate 12 units of gill nets of assorted mesh size but not less than 35 mm bar. Gill nets of less than 35 mm bar should be strictly prohibited, except for weed/trash fish population control (if necessary). Use of such nets could, however, be allowed if:

  1. Nets are operated in the presence of State officials

  2. All the juveniles of commercially important fishes, specially the stocked ones, are released back into the reservoir.

Figure 14.4

Figure 14.4. Site for pen nursery (diagrammatic sketch) in Kyrdemkulai

After a couple of years of such management, larger mesh size nets should be introduced in order to exploit fishes of 2 year plus age groups. The nets with head rope, breast line and foot rope with floats only should be used with a recommended hanging coefficent 0.5 horizontal and 0.87 vertical.

It is important to monitor the fishing effort both qualitatively and quantitatively. A low fishing effort may result in under-exploitation. Similarly, lower mesh size and excessive effort may have harmful effect through catching fish of an uneconomic size, thereby rendering the system unremunerative. In order to keep track of the fishing effort in terms of nets, boats and manpower, it is essential to register the units with State Fisheries Department. It is also suggested that a licence fee be levied. This will partially defray the cost incurred by the State for development and act as a check to keep the fishing units within the desired level. Experience shows that free fishing often leads to licentiousness and irrational proliferation of units which is detrimental for a sustainable capture fisheries management.

Post-harvest and other management

As the gill nets are usually lifted in the morning, the fishermen should get facilities to dispose off their catch instantly, at a reasonable price. State Government may have to look after this aspect. Preferably, a cooperative society may be formed to undertake marketing functions so that fishermen do not have to waste time and resources on post-harvest operations. Such facilities should be common for Nongmahir and Kyrdemkulai. Such arrangements, however, need to be worked out in close association with the fishermen, to prevent middlemen siphon away a good part of profits. The State Government may provide a boat which will serve to transport fish from fishing areas the landing centre. The same boat can be used for patrolling the reservoir to check unauthorised fishing activities.

Provision of fishery guards is very essential to ensure that all regulations are strictly implemented. They should act in close liaison with the security staff of MeSEB and the law enforcing authorities to implement the ban during the breeding season and to curb dynamiting, poisoning etc., and to ensure that mesh regulations are adhered to. They will also guard the mahseer sanctuary. A total of 10 fishing guards have been suggested for Kyrdemkulai, in view of the need to patrol the sanctuaries. Provision for two additional country boats for the guards' movement in the riverine stretch is also made. The State Departments of Environment and Forests have pivotal role to play in managing the sanctuary and therefore their active cooperation may be sought to implement the regulations.

Mahseer fisheries

The expected mahseer fishery is 8 000 kg a year. Assuming that half of this will come from gill nets, the 65 member gillnet fishermen may remove 4 000 kg mahseers from the system, leaving the rest as the anglers' quota. Angling may be regulated by issuing a licence fee. Assuming 50 angling days per year, a total of 1 200 angling mandays can be allowed i.e., at the rate 24 anglers a day on an average. An angling fee of Rs. 20/- can be realised from each angler per day. The bag limit may be at 6–8 fishes per angler, with the minimum size of fish of 250g.

Total Catch

Taking both carps and mahseers into consideration, Kyrdemkulai may yield an annual catch of 48 t, comprising 8 t of mahseer and 40 t of carps. The gill net catch will comprise 40 t of carps and 4 t of mahseers (total 44t). The anglers' share of mahseers will be 4 t per year.

Benefits

The two major objectives of fisheries development programme of Kyrdemkulai are fish yield optimisation and conservation of mahseer fisheries. The increased fish productivity from the lake is expected to improve the availability of fish in the state. Fish is a very costly commodity in Meghalaya. The scientific management of Kyrdemkulai reservoir can produce at least 48 t of fish per year which will considerably ease the availability position of fish in the local markets as well as in Shillong. It is estimated that fishing activities take place for 240 days a year with an average daily catch of about 184 kg. Apart from this, the project envisages to provide sport fishery for 50 days in a year with 24 anglers per day. Anglers' catch is expected to be 80 kg per day.

Employment

The reservoir can provide direct employment for 65 fishermen who will share a total annual fish harvest of 44 t of fish comprising 40 t of carps and 4 t of mahseers. Each fisherman will catch 615 kg of carps worth Rs. 18 450 at the rate of Rs. 30/- per kg and 61.5 kg of mahseers worth Rs. 2 460, at the rate of Rs. 40/- per kg. These sixty-five fishermen represent sixty-five families and, at an average of four members per family, the scheme offers direct benefits to 260 people. The mahseers in the reservoir are expected to provide sporting delight and additional income to 1 200 anglers. Many more will benefit indirectly. Boat building, net making and their maintenance are the main ancilliary activities. The reservoir is directly connected to the main centres of fish consumption, like Zero Point, Shillong and Guwahati. This eliminates the chances of exploitation by traders.

Remunerativeness of fishing operations

Fishermen of Kyrdemkulai will require assistance from financial institutions to meet their capital requirements. The overall remunerativeness of the fishing activities has been projected (Sugunan and Yadava, 1991a), based on a fishing unit comprising two fishermen, who share a boat and 12 units of gill nets (50 m hung length each). The initial outlay for boat and net is Rs. 10 500 involving an annual capital cost of Rs. 2 250. The variable cost, including the imputed value of wages that the two fishermen would have earned, is Rs. 11 600. The total annual cost including interest on capital, annual capital cost and all variable costs is estimated at Rs. 19 625. The two fishermen net out 1 230 kg of carps and 123 kg of mahseers which would earn them Rs. 41 820, at the rate of Rs. 30 per kg for carps and Rs. 40/- for mashseer (the sale price is kept at the lower side. Rs. 40 to 45 is the current market price for carp and Rs. 50 to 60, for mahseers).

Even after meeting the repayment obligations, and paying interest on capital and licence fee, the two fishermen between themselves can earn a net profit of Rs. 27 585, i.e., each fisherman gets Rs. 13 792/– per year, a comfortable income indeed. A fisherman of Kyrdemkulai will spend Rs. 7 117.50 for a catch worth Rs. 20 910 in a year. In other words, he gets a daily catch of 2.8 kg worth Rs. 87.00 from which he earns nearly Rs. 57.50 as net profit. This clearly shows remunerativeness of fishing in Kyrdemkulai, provided proper management measures are taken and the fishing units are regulated as per scientific norms.

14.4 NONGMAHIR

Nongmahir is a pickup reservoir (forebay), formed in the year 1979 by conduiting the waters of the Kyrdemkulai reservoir into a steep gorge through a 2 839 m long tunnel. The main earthen dam is 150 m long with a height of 50 m above the bed level of 638.72 m above MSL. The reservoir level is maintained by a series of five saddle dams, varying from 33 to 68.5 m in length. The Ogive spillway has a clear waterway of 12.2 m with the designed flood water discharge of 158.4 m3 sec-1. The reservoir is more or less circular in shape with a number of islands. It has a total surface water of 70 ha with a storage capacity of 5.8 million m3 at FRL and 2.16 million m3 at DSL. The small local catchment comprises hillocks bearing loose laterite soil. A conspicuous feature of the deep and steep basin is the limited littoral zone restricted to the embayments. The shoreline is 13.25 km long. The water level fluctuates between 669.20 and 672.07 m above MSL. After the power house became functional, there is a regular outflow of water from the reservoir. The level fluctuation is thus determined by the outflow, inflow from Kyrdemkulai, evaporation, and the runoff from the local catchment. The mean depth of the reservoir at FSL is estimated at 5.28 m.

One of the important morphometric characteristics of the reservoir is the deep drawdown. The elevation at outflow point is just 3 m above the bed level i.e., at a depth of 10.4 m (at FRL). This prevents stagnation and keeps the water in slow circulation. The conventional demarcation of lotic, intermediate and lentic sectors is not of much relevance in case of Nongmahir, since it is a pickup reservoir storing the Kyrdemkulai waters. The only sectoral distinction having any limnological significance is between the central sector and the bays (Fig. 14.5). Sugunan and Yadava (1991b) have described the reservoir and discussed the feasibility for fisheries development.

Habitat variables

The sediments in the reservoir are dominated sand and clay fraction with organic carbon percentage varying from 1.74 to 2.13. The soil, is acidic (pH 4.6 to 6.0), contains low to moderate concentrations of available nitrogen (29.91 to 44.59 mg 100 g-1, and phosphorus (0.38 to 1.12 mg 100 g-1). The specific conductivity is of low order (107.3 to 367.3 μmhos) and organic matter ranges within 2.3 to 3.61%.

Water temperature is marked by seasonal variation from 25.0° in November-December to 31.0°C in April. The water pH is largely governed by the underlying sediments, i.e., it remains mostly acidic, except during the summer when pH is slightly higher than neutral. Oxygen saturation in the sub-surface columns of the reservoir water remains fairly high with minor drop during monsoon months, coinciding with the increase in turbidity. The water has low total alkalinity, ranging between 11.20 and 25.52 mg l-1. Based on hardness values (16.84– 25.52 mg l-1). Nongmahir is a soft water body. Specific conductivity and total dissolved solids, notwithstanding seasonality, are low (Table 14.6). However, the concentrations of phosphate, nitrate and silicate indicate the productive potential of the reservoir.

There is a distinct vertical thermal gradient in summer, when the temperture decreases from 23.5°C at the surface to 22.5°C at 3 m and 21.0°C at 6 m respectively. The dissolved oxygen declines from 7.4 mg l-1 at 9 m with concomitant increase in free carbon dioxide values, suggesting klinograde tendency in the reservoir. The prevailing duration of warm and cold phases appears conducive for the annual turnover and subsequent mixing of nutrients in the lake. This is amply reflected by the availability of phosphate, nitrate and silicate in water. Although the total alkalinity is low, the omnipresence of free carbon dioxide contributes to the photosynthetic activity. However, low concentrations of ions and total dissolved solids prevent a higher productivity of Nongmahir reservoir.

Figure 14.5

Figure 14.5. Nongmahir reservoir, Meghalaya

Table 14.6. Soil and water quality of Nongmahir reservoir
 WINTERSUMMERMONSOONAV.
Soil    
pH4.605.26.005.30
Organic carbon (%)1.742.131.921.93
Organic matter(%)2.303.613.273.06
Available phosphorus (mg 100 g-1)1.111.120.380.87
Available nitrogen (mg 100 g-1)33.6044.5929.9136.03
Spec. cond. (μmhos)133.40367.30107.30202.67
Water    
Water temperature(°C)25.0031.029.0028.33
Transparency (m)2.602.401.002.00
pH6.607.406.706.90
Dissolved oxygen (mg 1-1)6.907.286.907.03
Free carbondioxide (mg 1-1)2.000.165.002.38
Total alkalinity (mg 1-1)28.0020.0012.0020.00
Total hardness (mg 1-1)16.8425.5223.0019.90
Chlorides ((mg 1-1)6.6612.7422.5613.98
Iron (mg 1-1)0.09*0.300.19
Ammonical nitrogen (mg 1-1)0.140.24*0.19
Nitrate nitrogen (mg 1-1)0.200.820.020.35
Silicates ((mg 1-1)1.004.006.603.86
Phosphate (mg 1-1)tr0.020.080.03
Calcium (mg 1-1)14.8420.8813.9014.37
Magnesium (mg l-1)2.564.649.103.60
Total dissolved solids (mg 1-1)26.0022.1014.0020.70
Spec. cond. (μmhos)150.21104.4069.60108.07

* Values not recorded (Sugunan and Yadava, 1991b)

Biotic communities

The dry weight of total plankton, estimated from various sectors covering the four seasons, varies from 0.20 mg 1-1 to 0.45 mg 1-1, with an average of 0.32 mg 1-1, is the result of low densities of plankton. The average plankton density by number is 5 440 units 1-1. Despite a low plankton population, the primary productivity of the reservoir is high, suggesting high nannoplankton density in the reservoir.

The phytoplankton constitutes more than 96% (by number) of the total plankton in the main reservoir. It is dominated by Chlorophyceae (70.86%), represented mainly by Staurastrum sp; Chaetophorasp. and Dinobryon sp. The bay plankton is characterised by a higher density of the blue-greens, indicating eutrophic character of the shallows. The bays represent the trophogenic zone of the reservoir which has a rich and diverse plankton community, represented by 24 genera.

Macrovegetation is absent. The main reservoir and the areas with high percentage of sand yield little benthic fauna. The bays receiving forest creeks and characterised by accumulation of detritus, harbour oligochaetes, Chironomus spp., Chaoborus, other insect larvae and nymphs are also observed in the bay areas. Molluscs are conspicuous by their absence in the reservoir. The density of benthic fauna in the reservoir is 38 individuals m-2.

Primary productivity

Estimates of the gross carbon production range from 34.38 to 68.0 mg C m3 hr-1. Corresponding figures for net productivity fluctuate from 25.0 to 43.62 mg C m3 hr-1. These figures are equivalent to an average of 1 187 mg C m2day-1 (gross) and 817.44 mg C m2 day-1 (net).

Fish fauna

Cyprinus carpio, Acrossocheilus hexagonolepis, Tor putitora, Puntius sophore, Dania rerio, D. acquipinnatus, D. dangila, Clarias batrachus and Heteropneustes fossilis are the fish species encountered in experimental fishing. Besides, Indian major carps (Catla catla, Labeo rohita and Cirrhinus mrigala) and the exotic silver carp are reported to be occasionally caught by the local fishermen. There is a total absence of large murrels and predatory catfishes (Wallago attu, etc.) and poor population of weed fishes. The fact that weed/trash fishes have not been able to gain foothold in the reservoir can be ascribed to the absence of macrophytes and an insignificant littoral zone. Their small population favours the stocking of Indian major carps, since the commercial carps would face less competition food.

Present status of fisheries

There is no commercial fisheries and the pressure is restricted to angling and seasonal use of bamboo traps. Angling is a favourite past time in Meghalaya. Apart from the local inhabitants, domestic toursists, from as far as Shillong, frequent the reservoir for angling. It is estimated that two to six people angle every day. The catch is very low and mostly comprises small specimens of common carp.

Traps, lures and snares form the basic capture gear. The most common is the use of bamboo split mat pens, erected in the marginal areas of the reservoir. The pen forming a semi-circle, extends its arms beyond the water phase, completely barricading the littoral zone. The pen facilitates entry of fish from the reservoir through a trap door, but prevents their return. Normally, the fish trapped in the pen during the night are harvested in the morning, using hand nets, cast nets, etc. Weed/trash fishes and H. fossilis are commonly caught in these pens. Common carp is caught in the pens during monsoon months.

Productivity status of the water body

The water temperature favours all biotic communities, except during the peak of winter (December to February). Of the morphometric attributes, the shoreline development index of 8.93 indicates productive nature of the lake. High values of ambient dissolved oxygen during all seasons suggest prolific photosynthetic activity and an unstressed aquatic environment. The average pH, total alkalinity and specific conductivity values, lying in the unproductive range, do depict deficiency in the aquatic phase. However, the optimum rates of carbon synthesis denominate productive potential at the primary level. The other supporting evidence for this potential is the presence of oxycline and chemocline during warmer months. Notwithstanding the few discouraging limnological features, the lake leaves enough room for yield optimisation through fisheries management both at the environmental and biotic communities levels.

Fish yield potential

At a conversion rate of 1%, primary productivity could support a yield of 433 kg of fish per hectare per year. Considering the scope for increasing the fertility status of the reservoir through manuring, the target of production has been fixed at 500 kg ha-1, with a scope for steady increase up to 1 000 kg ha-1 in due course.

Nongmahir being a forbay of Kyrdemkulai, does not receive runoff from any watershed. This deprives the reservoir of allochthonous nutrient loading which might have acted as a catalyst for trophogenic activities at the lower trophic levels. However, the small size of the reservoir and the fact that it does not form a source of drinking water, enables the fisheries manager to adopt the option of fertilization. A fertilizer and liming schedule similar to Kyrdemkulai has been recommended for Nongmahir.

Stocking

Stocking is the most important management tool for Nongmahir reservoir fisheries for the following reasons:

  1. There is a negligible native fish stock (since the reservoir is a forebay of Kyrdemkulai).

  2. The common carp is the only major commercial species present.

  3. The ‘log guard’ provided at the intake tunnel restrics the Kyrdemkulai fish fauna to gain entry into Nongmahir.

  4. In the absence of any streams and rivulets joining the reservoir and coupled with a deep basin without littoral formations, chances of natural recruitment of stocked fish (except free spawners) are very remote.

Common carp is already present in the reservoir. It is reported to breed there. Hence, no stocking of bottom feeding detritivore is recommended. Since the fertilization promises a good standing crop of plankton, emphasis is on filter feeders, Catla catla and rohu. Annual stocking of 110 000 advanced fingerlings (>100 mm) of catla and rohu in 3:2 ratio is recommended for the reservoir. Experience in other small reservoirs indicates the desirability of phased stocking and multiple harvesting. Harvesting schedule and other management measures similar to those for Kyrdemkulai are recommended for Nongmahir (Sugunan and Yadava, 1991b).

14.5 OTHER RESERVOIRS

Barapani (Umiam), the oldest reservoir in the region was commissioned in 1965 by damming the river Umiam as stage I of the Umtru-Umiam Hydro-electric Project. Located within 25°39'30" N and 91° 43'51" E, at an elevation of 900 m above MSL, the reservoir has a waterspread of 500 ha. It stores 182.72 million m3 of water to feed the turbines of hydro-electric power station at Sumer. The river Umiam eventually joins a tributary of Brahmaputra. No fisheries development activities have been reported from the reservoir, except for stocking Cyprinus carpio in early 1970s. The reservoir is under the jurisdiction of East Khasi Hill District Council, an autonomous local self government. Presently the fishing is limited to angling, which is not organised. It is reported that the common carp in the lake has a slow growth due to overpopulation (Sinha, 1990). The city wastes emanating from Shillong find their way into the reservoir through various streams, causing eutrophication. Denudation of forest in the catchment, mainly due to the practice of shifting cultivation(jhoom) is accelerating the siltation rate in the reservoir.

Khandong and Umrong are two reservoirs created under the Kopili Hydro-electric Project. Presently, the lakes are under the jurisdiction of the North Eastern Electric Power Corporation (NEEPCO) and fishing has not been initiated in either of them. The NEEPCO and CICFRI have started feasibility studies for fisheries development in the reservoirs. Khandong is a 1 335 ha reservoir across the river Kopili situated at an elevation of 719.0 m above MSL, receiving drainage from an extensive catchment of 1 256 km2, comprising thickly wooded forests. The reservoir has a maximum storage of 16.6 million m3 at full level. The water is reported to be productive. Umrong is a pick-up reservoir, receiving and storing the water coming from the Khandong Power House. Situated at an elevation of 602 m above MSL, the 90 ha impoundment also receives drainage from the local catchment of 62 km2. The reservoir has a capacity of 78.5 million m3 with a mean depth ranging from 2.58 to 8.0 m. The reconnaissance survey conducted by CICFRI suggests that the water body is reported to be productive.

14.6 STATUS OF RESERVOIR FISHERIES IN THE NORTHEAST

Among the existing six reservoirs in the region, only Gumti has an organised fishing activity, the remaining ones are either under-exploited or remain unexplored. Even at a modest yield of 150 kg ha-1, the reservoirs can contribute 1 211 t to the total fish production. The present level of yield, however, is not known.

Keeping in view the long-term solutions to the recurring flood problems in the region and tapping the enormous hydel power potential, a large number of projects are on the anvil. A total of 19 projects are envisaged in the Brahmaputra basin alone, with a colossal storage capacity of 9.33 million ha m. Of these, three are under construction and are expected to be completed during the VIII Five Year Plan (1996 to 1997). In the Barak basin, the proposed Taipaimukh dam at 24° 14' N, 93° 1' 36" E, is expected to create a waterspread of 6 455 ha with a gross storage of 0.18 million ha m. Five more projects in the basin are under various stages of planning. According to available projections, 68 760 ha of man-made lakes will soon appear in four States (Table 14.7). The region, poised for a quantum jump in the resource size, needs a well-conceived fisheries development strategy to tap the fish production potential from the proposed reservoirs.

Table 14.7. Projected increase in reservoir area during the VIII Plan
StateExisting area (ha)Projected additional area (ha)
Arunachal Pradesh-160
Assam2 314-
Manipur10040 000
Meghalaya660-
Mizoram32-
Nagaland-27 100
Tripura4 5001 500
Others600-
Total8 20668 760

(Anon., 1991;Sinha, 1990)

Table 14.8. Salient features of Kyrdemkulai and Nongmahir reservoirs of the northeast
 KyrdemkulaiNongmahir
Date of closure19791979
Area at FRL (ha)8070
Mean depth (m)4.635.28
Volume (million m3)3.75.8
Catchment area (km2)3.75.8
Elevation (m above MSL)150-
Length of shoreline (km)19.613.25
Shore dev. index11.658.93
Annual level fluctuations (m)8.42.9
Inflowing riverKyrdemkulaiTunnel
  (Kyrdem-kulai)
Outflowing riverUmtru-
Maximum outflow (m3 sec.-1)1 700-
Latitude (N)25° 43'-
Longitude (E)91° 47'-
Soil  
Sand (%)49.1955.10
Clay (%)39.2933.65
Silt (%)11.5211.25
Organic carbon (%)0.3–1.61.74–2.13
Available P (mg 100 g-1)0.6–1.10.38–1.12
Available N (mg 100 g-1)7.7–32.329.9–44.6
Spec. cond.(μmhos)87.7–121.6107–367
pH5.9–7.64.6–6
Water  
Water temperature (°C)19.5–2125–31
pH6.7–706.6–7.4
Transparency (cm)2.2–2.81.0–2.6
DO (mg l-1)6.7–7.16.9–7.3
CO2(mg l-1)2.0–2.60.16–5.0
Total alkalinity (mg l-1)22.0–32.012–28
Spec. cond. (μmhos)10269.6–150.2
Total hardness (mg l-1)18.6–27.816.8–25.5
Calcium (mg l-1)9.3–14.813.9–20.8
Nitrate (mg l-1)3.7–13.90.02–0.82
Phosphate (mg l-1)tr.–0.02tr–0.02
Silicate (mg l-1)1.0–3.0
Chlorides (mg l-1)12.7–18.86.6–22.6
GPP (mg C m-3 hr-1)39.4–56.034.4–68.0

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