Abstract

This study was undertaken to explore the diversity of macrophytes and their utilization pattern in Rudrasagar Lake of Tripura, which is a Ramsar site in India. We identified 31 species of macrophytes from the study site. Important Value Index (IVI) and Total value Index (TVI) of these plants were estimated to know their diversity and utilization pattern. Some of the dominant species included Nymphoides indica (L.) Kuntze, Eichhornia crassipes (Mart.) Solms, and Vallisneria spiralis L. The majority of local households using the macrophytes for domestic purposes. Macrophytes most preferred by the local people were Euryale ferox Salisb., Trapa natans var. Bispinosa and Ehnydra fluctuans Lour. We found that the dominant species of the lake were not always preferred by the community. Thus awareness and cultivation of the preferred species can reduce pressure on the availability of the highly preferred species and also improve the livelihoods of the wetland-dependent people of the area.

1. Introduction

Wetlands, the most productive ecosystems on Earth ¹, house the majority of floral and faunal groups and act as a base of our environment ². These ecosystems are saturated with water, either permanently or seasonally, as well as at low tides less than 6 m deep ³. Ponds, lakes, marshy places, and shady moist areas are ideal for the growth of macrophytes. Macrophytes are submerged, free floating and emergent in nature and sometimes grow on moist or even semi-dry soils. Macrophytes are an important part of wetland ecosystems. Plants are an essential factor in fixing energy that powers all other components of the system. Macrophytes play an important role in the structure of freshwater wetlands and have been targeted for wetland restoration and conservation ⁴. Macrophytes have significant effects in terms of the physical and chemical environment of wetlands ⁵.

India has more than 757,000 wetlands, 26 of which have been designated as Ramsar sites or wetlands of international importance ⁶. Rudrasagar Lake is a Ramsar site situated in Tripura state of northeastern India. This lake was declared a Ramsar site in 2005 and is considered a wetland of international importance. This wetland has a maximum area of about 8.16 km². The total catchment area is 13,336 ha, which includes 716 ha of small hillocks with human habitation, 4,942 ha of crop land, 175 ha marshy land, 178 ha shifting cultivation area, 466 ha of government orchard land, 215 ha of pasture land, 1,340 ha of reserve forest area, and 4,534 ha of scrub/bamboo/degraded forest ⁷.

Studies on macrophytes have been conducted by many researchers [8-17] ⁸, but no work has been carried out to understand the diversity of macrophytes or their seasonal patterns of utilization in this region. Rudrasagar Lake is a great source of biodiversity, providing many services to the local human population ¹⁸. However, this wetland ecosystem is degrading day by day due to various anthropogenic stresses, necessitating urgent measures for wetland conservation and restoration. This study focused on the diversity of macrophytes in Rudrasagar Lake and the pattern of their utilization by local communities, information that will be helpful for developing management strategies and a restoration plan for the ecosystem. IVI is an ecological index which helps to understand the diversity of plants in an area and TVI help to understand the utilization pattern of plants by local people. So IVI and TVI is use in this research to understand the diversity and utilization pattern of macrophytes.

2. Materials and Methods

Tripura is a landlocked state in that experiences a monsoonal climate with the main seasons being winter (Dec-Feb), pre-monsoon or summer (Mar-Apr), and monsoon (May-Nov). Rudrasagar Lake is located at Melaghar in the Sepahijala district of Tripura. The wetland is at 23°29′N, 90°01′E (Figure 1). The lake has a total area of 240 ha; Neermahal (Water Palace) is situated in the middle of the lake. In the area surrounding the lake, a mostly Bengali community resides. The main occupation of the community people is fishing, supplemented by earnings from ecotourism and agriculture.

The study was carried out during three seasons (winter, summer, and monsoon) from January 2017 to March 2018. The initial survey was done visually by boat covering the whole lake to study various species and distribution of macrophytes. A total of 112 quadrats (1 × 1 m) were laid out at 12 sampling stations during the study period. Macrophyte specimens were collected, photographed, and taken to the laboratory for further identification. Macrophytes were identified to the species level using standard literature ^{19, 20}.

Ecological indices measuring composition, abundance, richness, evenness, and diversity provide a quantitative approach to patterns among macrophyte distribution. However, 6 metrics (density, frequency, abundance, relative density, relative frequency, and relative abundance) were selected to ensure comparability with existing literature and low redundancy. An Importance Value Index (IVI) was calculated by following the methodology described by Misra ²¹ and Curtis ²² as follows:

For measuring diversity, the Shannon-Weaver index ²³ as follows were used

Where, ni is the total density value for species, i, and N is the sum of the density values of all the species in that site.

For estimating dominance species, Simpson index ²⁴ were calculated.

Where, N = total number of species and n = number of species in a given community.

In order to identify the pattern of macrophyte utilization by the local community, free listing ²⁵ was done, which is the listing of macrophytes that a research participant can cite at a given time. For this free listing 64% of total households were covered in the study area. A total of 146 household heads (male = 49.6%, female = 50.4%) agreed to participate in the free listing. These plant species lists were used for the determination of ethno-cultural importance of macrophytes.

An ethno-cultural survey was made to understand the cultural behavior of local people regarding the utilization of macrophytes. The cultural value (CV_e) of a species was determined by using the methodology of Reyes-Garcia et al. ²⁶:

where CV_e is the cultural value of species e, Uc_e is the total number of uses reported for species e divided by the total number of potential uses (e.g., food, fodder, construction), Ic is the number of participants who listed species e as useful divided by the total number of people participating in free listing, and IUc is the number of participants who mentioned each use of species e divided by the total number of participants. To calculate the practical value of a species, a similar formula was used, following Reyes-Garcia et al. ²⁶:

where PV_e is the practical value of species e, UP_e is the number of different uses observed for species e divided by the potential uses of a species considered in the study, P_e is the number of times species e was brought to a household divided by the total number of informants participating in observation, and DUp_e is the duration of use for each item brought to the household. Economic value (EV_e) of a species was calculated by the local market price of a species and the number of times it was brought to any household using the formula of Benz et al. ²⁷. Total value index (TVI) of a species was enumerated by summing of cultural value (CV_e), practical value (PV_e), and economic value (EV_e) as described by Byg and Balslev ²⁸:

3. Results

The survey revealed the occurrence of 31 plant species belonging to 20 taxonomic families (Table 1). The different parts of macrophytes (Figure 2) were used for various purposes (Table 1).

The most dominant species of the lake were Nymphoides indica (L.) Kuntze (IVI=41.14), Eichhornia crassipes (Mart.) Solms (IVI=38.60), Vallisneria spiralis L. (IVI=36.69), Amischophacelus axillaris (L.) R.S.Rao & Kammathy (IVI=31.11), and Trapa natans var. Bispinosa (Roxb.) Makino (IVI=28.27) (Table 1). The least dominant species were Ipomoea fistulosa Mart. ex Choisy (IVI=6.80), Pennisetum polystachyon (L.) Schult (IVI=8.02), Azolla pinnata R.Br. (IVI=8.76), Salvinia cucullata Roxb. (IVI=9.69), and Polygonum hydropiper L. (IVI=10.60). The most dominant species during summer was Eichhornia crassipes, whereas Pennisetum polystachyon was the least dominant. Nymphoides indica and Ipomoea fistulosa were the most dominant and least dominant species, respectively, during monsoon season. However, in winter Eichhornia crassipes was the most dominant and Ipomoea fistulosa was the least dominant (Figure 3).

The macrophytes most preferred by the local people were Euryole ferox Salisb. (TVI=202.93), T. natans (TVI=163.13), Enhydra fluctuans Lour. (TVI=92.47), A. axillaris (TVI=81.43), and Ludwigia adscendens (L.) H.Hara (TVI=73.44). TVI value was high for these plants due to their preferred utilization by the community. The local people get huge profits by selling these macrophytes, which increases their TVI value. The least preferred macrophytes were Salvinia cucullata (TVI=0.74), Grangea maderaspatana (L.) Poir. (TVI=0.76), Hygroryza aristata Nees (TVI=0.78), Pistia stratiotes L. (TVI=0.78), and Ceratophyllum demersum J.G.Klein ex Cham. (TVI=0.90) due to their lower levels of utilization (Table 1).

The management and conservation of the lake has been taken care by the Rudrasagar Udbastu Fisherman Samabaya Samity (local community body) for several years. It is on record that after every five years period the community creates a new group consist of nine people with the mechanism of voting, and hands over the responsibilities of the lake to them for the purpose of management and conservation. One of the astonishing fact about the entire process has been that male and female members of the community are entrusted to work with shoulder to shoulders in the management and conservation of wetlands. Another fact remains that people belonging to the local community who doesn’t have any stakes are not allowed to take participate in any kind of management activities of the lake. The community generates revenues through issuing licenses for fishing in the lake, cultivation of crops in surrounding areas, and boating. Paddy (Oryza sativa) is usually cultivated in the adjacent areas of the wetland during winter. Farmers wield fertilizers and pesticides during the period of cultivation and especially during rainy season. It is believed that runoff from agricultural land to water body causes degradation of water quality in Rudrasagar Lake. The community allows the growing of several aquatic plants to provide shelter to fingerlings and for the nesting of aquatic birds. Plants such as Eichhornia crassipes renders shield to small fishes from predators. Every year during monsoon season, Euryale ferox is auctioned by the cooperative society. As a result of the auction, the highest bidder is given the privilege to harvest all the plants and in addition garners fruits to sell in the local market. During summer, Trapa natans is harvested. The fruit is known for its nutritional value and for its thirst-quenching properties. It has been widely recognized as one of the favorite fruits of local people and moreover the fruit has been known for a good chunk of revenue return for the community. During winter, aquatic plants are harvested and the lake turns out to be a carnival for boat racing festival. The selling of these harvested edible macrophytes has become a source of additional income for the local people. Some of the major hurdles of Rudrasagar lake are siltation from three inlets (Noachora, Kamtalichora and Durlav narayanchora), weed infestation (uncontrolled growth of Eichhornia crassipes), encroachment for agricultural land and households, pollution from open swage, illegal fishing by poisoning water and hunting of migratory birds in winter season. Runoff of fertilizers and pesticides from agricultural land during rainy season, mixing poison for fishing, oil and grease from boat, open swage are the main cause of water pollution in Rudrasagar lake.

4. Discussion

Among the 31 macrophytes, Nymphaeaceae and Poaceae were represented by 4 species and Araceae, Asteraceae, Hydrocharitaceae, Onagraceae, and Polygonaceae were represented by 2 species each. One species each was recorded from Alismataceae, Azollaceae, Ceratophyllaceae, Commelinaceae, Convolvulaceae, Cyperaceae, Lentibulariaceae, Marsileaceae, Menynthaceae, Najadaceae, Pontederiaceae, Salviniaceae, and Trapaceae (Table 1). Bhowmik et al. ²⁹ reported 65 hydrophytes from wetlands in West Tripura, India. Some of the species have already been reported by him, but 16 species are newly reported in our study.

Eichhornia crassipes was the dominant macrophyte of Rudrasagar Lake during summer (IVI=43.36) and winter (IVI=47.23); Nymphoides indica (IVI=41.14) was dominant during monsoon season. The dominant macrophytes throughout the year were Nymphoides indica (IVI=41.13), Eichhornia crassipes (IVI=38.60), and Vallisneria spiralis (IVI=36.69) (IVI=31.10) (Figure 3). Saluja and Garg ⁴ also reported IVI of 28 macrophyte species from Bhindawas Lake, Haryana, in which the dominant species was (IVI=64.11). A few plants, such as Nymphaea micrantha Guill. & Perr., Nymphaea pubescens Willd., and Nymphaea stellata F.Mueller, were only found in the monsoon season. These species are highly utilized by local people, so in summer and winter when the water level is low, these plants are rarely available in the lake. Eichhornia crassipes is hardly visible in the monsoon season, but during summer and winter its vigorous growth reduces the surface area of open water and creates problems for boating. However, according to local people, this plant is able to absorb oil from motor boats, which helps to maintain water quality.

Shannon’s index had maximum values in the monsoon season (3.15) and summer (2.72), whereas a minimum value during winter (2.60) due to low atmospheric temperature effect plant growth. The mean diversity of macrophytes was much higher in monsoon season than during summer and winter. Simpson’s value was high during the monsoon season (0.10) and winter (0.09) and lowest in summer (0.07). Overall, macrophyte diversity of Rudrasagar Lake was at its maximum during monsoon season and minimum in winter. According to Suluja and Garg ⁴, the maximum value of Shannon and Simpson indexes was 2.28 and 0.86, respectively, in Bhindawas wetland, India. This indicates that Bhindawas wetland ecosystem has lower diversity but higher dominance than the present study, which might be due to water-related variables (dissolved oxygen, pH, and phosphorus levels) or soil nutrient factors (soil carbon and phosphorus levels).

Macrophytes were found to be used for various purposes such as food, fodder, medicine, and fencing. It was also observed that whole plant or different parts of plants such as roots, stems, leaves, fruit, and seeds were used for various purposes (Figure 2). We found that 35% of macrophytes were used as a whole plant for medicine, food, and fodder, whereas in the case of 5% of the macrophytes only the seeds were used.

Total value index of these 31 species was calculated on the basis of cultural value, practical value, and economic value. The cultural values range from 0.51 to 2.4; the practical and economic values range from 0.23 to 2.23 and 0 to 200, respectively. High TVI indicates macrophytes that were highly preferred by the community and low TVI indicates less preferred. According to TVI, Euryale ferox (202.93), Trapa natans (163.13), Enhydra fluctuans (92.47), Amischophacelus axillaris (81.43), and Ludwigia adscendens (73.44) were the most preferred macrophyte species (Table 1). This might be due to easy availability, easy harvesting method, and high utilization value of those macrophytes. The economic values of these macrophytes were also much higher than the values of the other macrophytes we found.

After determining the IVI and TVI ranks of the macrophyte species, the data were compared. For most of the macrophyte species the rank by IVI differed from the TVI ranking (Table 2). Nymphoides indica, Eichhornia crassipes, and Vallisneria spiralis were the most dominant species as per IVI, whereas Euryale ferox, Trapa natans, and Enhydra fluctuans were considered the most useful macrophytes based on TVI. Macrophytes with high IVI are dominant in nature due to their high relative abundance but the TVI value depends on the utilization pattern. High TVI values indicate high practical and economical values. In the community, one macrophyte was highly utilized but the people are not concerned about its relative abundance. This is why plants with high TVI value but low IVI value are facing threats. Plants with high IVI increase after harvesting as disturbance sometimes increases the vegetation. So in both cases TVI is directly or indirectly controlling the IVI, especially by relative abundance. Note that Nymphoides indica, which was ranked first by IVI value, was 17th in the TVI ranking as its economic value was less than that of other species. Trapa natans was the second most preferred macrophyte species according to TVI and ranked 5th as per IVI because it was easily available. Salvinia cucullata is only used as fodder and least preferred macrophyte species as per TVI. It was reported by other worker that wetland conservation should be based on traditional knowledge and resource priority by the community that will eventually aid in fostering biodiversity and preserving key ecosystem services in cost effective and sustainable way ³⁰.

Correlation between the IVI and different parameters of TVI was calculated (Table 3). Positive correlations were found between TVI and cultural value (r = 0.603; P < 0.01) and between TVI and economic value (r = 0.975; P < 0.01). Cultural value also showed a positive correlation with practical value (r = 0.434; P < 0.05). The high correlation between the cultural value and practical value was also reported by Reyes-Garcia et al. ²⁶. IVI values had a positive correlation with cultural value (r = 0.357; P < 0.05), which indicates that easily available macrophytes are culturally important for the local people. But practical value of the macrophytes does not show any relation with the availability of those macrophytes in the lake. Therefore if a macrophyte has high practical value it means it is highly used by the community.

5. Conclusion

This study determined the influence of macrophyte species on utilization pattern in wetland ecosystems of India. We showed that the cultural value of a macrophyte depends on its dominance, but the practical value of the macrophyte depends on its easy availability. Since practical value is not dependent on dominance it creates a threat for overutilized macrophytes. Overutilization of dominant macrophytes reduces the relative abundance of those macrophytes in nature, which ultimately reduces their dominance. A few macrophytes, such as Euryale ferox, Trapa natans, and Enhydra fluctuans, may be cultivated in water bodies to reduce stress on selected species.

Acknowledgments

The authors deeply acknowledge the fishing community people for their kind support in research work.

Funding

The authors’ assistance from NMHS-SG, MoEF & CC is thankfully acknowledged.

References