Wetland Ecology of Eastern Himalayas

Vol. 23 (4), 2017-18 ISSN: 0974 - 1364

Ministry of Environment, Forest & Climate Change, Govt. of India The ENVIS Team

Editors Prof. AL. Ramanathan Swati Singh (Programme Officer)

ENVIS Coordinator Prof. AL. Ramanathan (Dean, School of Environmental Sciences, JNU)

ENVIS Co-coordinator Dr. Usha Mina (Associate Professor, SES/JNU)

ENVIS Committee Members Prof. Paulraj R. (SES/JNU) Dr. Ramovatar Meena (Assistant Professor, SES/JNU) Dr. Amit Kumar Mishra (Assistant Professor, SES/JNU)

ENVIS Resource Person Swati Singh (Programme Officer) Sandhya Farswan (Information Officer) Vijay Kumar (IT Officer) Ruchika (Data Entry Operator)

Cover Page Photographs Bhagita Devi Mayanglambam (Research Scholar, SES/JNU)

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Disclaimer The ideas and views expressed in the articles and cover page design in this Newsletter are solely of the writers and information derived from various secondary sources. Hence the centre holds no responsibility to errors in any kind. ENVIS RP: Geodiversity & Impact on Environment, Vol-23 (4), 2017-18

School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110 067, India Email:[email protected]; [email protected]

Water being a vulnerable natural resource, maintaining its availability in adequate quantity and quality has become a major challenge to human civilization. In this paper, we present the results of our study on the morphometry, hydrodynamic processes, macrophyte distribution, the significant limnological characteristics of Loktak Lake and discuss their influence on lake water quality and suggest the strategies for its sustainable management. Morphometry of a lake has both positive and negative influence on sediment dynamics and macrophyte growth. Due to shallow nature of the lake, minor fluctuations in water level causes major changes in its water to land ratio and in turn drastic variations in nutrient loading, algal growth and water quality. Submerged macrophytes play a major role in minimizing resuspension of flocculent/unconsolidated lake bottom sediments and result in lowering turbidity. The lake has a characteristic macrophyte locally called as phum/phumdi (a floating mass of vegetation, soil and organic matter) of different shapes and sizes with thickness ranging from a few inches to several feet.

Phum/phumdi can act both as sink and source of various pollutants to improve water quality as well as enhance eutrophication of the lake. Therefore, improved understanding on the linkage between the morphometry and other limnological parameters as well as establishing the water level at which the macrophytes begin to grow and constant maintenance of that level is crucial for sustainable lake ecosystem.

Loktak Lake, Morphometry, Water Level Fluctuations, Macrophytes, Lake Management

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Lakes are important bodies of freshwater on earth and their ecosystem services are equally important for sustainable socio-economic development of any region. In recent years, however, a variety of anthropogenic activities have seriously deteriorated the health status of many lake ecosystems around the globe (Wetzel, 2001; Scheffer, 2004). Therefore, availability of freshwater resources in adequate quantity and quality is one of the global concerns of the 21st century society.

Eutrophication of lakes, with excessive development of phytoplankton and associated deterioration of water quality, causes socio-economic problems such as unsuitability of water for drinking, undesirable conditions for recreation, and fish kills due to lack of oxygen (Fulton and Paerl,

1987). Consequently, extensive research is being focused to get insights into the factors responsible for lake eutrophication and on the approaches for lake restoration strategies (Scheffer, 2004).

Loktak is the largest freshwater lake in north-eastern India and lifeline of the state of Manipur. It has been linked with the people of the region culturally and socio-economically since the historical times

(LDA and WISA, 1998). In recent decades, the lake is being contaminated by domestic and municipal waste waters from urban centers as well as agricultural runoffs from the catchment area.

Morphology of a lake is one of the most important factors controlling the trophic status, physico- chemistry, productivity and distribution of aquatic organisms (Scheffer, 2004). Morphometric factors related to water circulation such as fetch and wave-mixed depth are likely to make differences among lakes (Carpenter and Lodge, 1986).

Changes in area, volume and depth of a lake are linked with nutrient cycling and water chemistry.

Therefore, the aim of this study is to examine the possibility of using lake morphometry to understand the role of water level fluctuations on macrophyte distribution and water quality in Loktak Lake.

The Manipur Valley is an intermontane flat basin with approximately oval in shape in the Indo-

Myanmar Ranges of the north-eastern India. Geologically, the north-eastern India constitutes a part of the

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eastern syntaxial bend of the Himalaya emplaced as an imbricate thrust system during the subduction of the Indian plate below the Myanmar plate (Chakraborti et al., 2008). It is believed that Manipur Hills evolved as an accretionary prism due to this subduction (Soibam 2000; Soibam and Pradipchandra, 2006).

The rock formations are of Tertiary - Cretaceous age consisting dominantly of sediments of Dishang,

Barail, Surma and Tipam Formations along with minor amount of igneous and metamorphic rocks. The sediments were formed in a shallow marine environment (Tethys Sea) and uplifted during the Himalayan

Orogeny.

The Eocene Disang Formation comprises splintery shale with minor mudstone, siltstone, sandstone and limestone (Chakraborti et al., 2008). It is overlain by Oligocene Barail Formation with abundant carbonaceous shales, and is in turn succeeded by the Surma and Tipam Formations consisting predominantly of argillaceous sediments. Ultramafic igneous rocks of the ophiolite sequence are intruded into the Disang Formation (Chakraborti et al., 2008).

About 25% of the central valley of Manipur is occupied by lakes, wetlands and hillocks. The

North-North West–South-South East oriented valley slopes gently from the north to the south. The

Imphal or Manipur River meanders through the Manipur Valley in a North West–South East direction and passes through a gorge to flow out of the state/country to join the Chindwin River in Myanmar.

Loktak is a large, shallow natural freshwater ecosystem situated in Bishnupur district of the state of Manipur (Figure 1). It occupies southern part of the Imphal Valley, which is a flat basin covered with

Plio- Quaternary non-calcareous sediments of (150 m thick) fluvio-lacustrine origin (Environment and

Forests Department, 2007). It is one of the Ramsar sites of international importance which is also enlisted in Montreux Record. The Lake is located between 93° 46' to 93° 55' E longitudes and from 24° 25' to 24°

42' N latitudes at an altitude of ~760 m above msl (WAPCOS, 1993; Singh and Shyamananda, 1994;

Singh and Singh, 1994; LDA, 1996; LDA and WISA, 1998; Trisal and Manihar, 2004).

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Figure 1: Map showing the location of Loktak Lake. The lake is roughly oval in shape with irregular shorelines prominent on the eastern side along with several bays. Surface area of the lake is ~300 km2 comprising large pockets of marshy land. After the construction of the Ithai barrage the seasonal water level fluctuations had reduced drastically (Singh,

2010). However, being a shallow lake, the surficial water level changes is still evident and huge areas of the littoral zone get exposed during dry season. Water-level fluctuations are due to changes in seasonal discharge of rivers, surface evaporation, and pumping for irrigation.

Water depth of the lake varies between 0.5 to 4.6 m with an average depth of 2.7 m. The maximum length and width of the lake are 26 km and 13 km respectively (WAPCOS, 1993; LDA, 1996;

LDA and WISA, 1998). It has a direct and indirect catchment area of ~980 and ~7157 km2 respectively.

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The Nambul river that drains Imphal Valley and city flows into Loktak carrying the maximum amount of sediment load, in addition to inputs from other rivers such as Nambol, Thongjaorok, Merakhong,

Khujairok etc. The increased inputs of nutrients are mainly due to anthropogenic activities such as deforestation, urbanization, shifting cultivation etc. in the catchment area, and also the Ithai Barrage which minimizes the outflow of lake water, thus, make the water relatively stagnant resulting in further increased of nutrients (phosphorus and nitrogen) in the lake. Several rural and urban settlements around the lake also discharge their domestic waste materials.

Water movement in aquatic systems play a major role in driving resource distribution, resuspension and particle transport, which makes available the previously unavailable resources.

Interestingly, the morphology of the Loktak basin coincides with the orientation of local winds controlling the sediment distribution and vertical mixing of the water column that facilitate release of sediment phosphorus into the lake water. This is more so in Loktak Lake as it has almost one metre bed of unconsolidated sediments/flocculent which can be easily resuspended with minor turbulence in the lake water. In recent decades, the drastic changes in the land-use and land-cover pattern of the catchment region, resulted in increased inputs of sediments and nutrients into the lake from both natural and anthropogenic sources (Trisal and Manihar, 2002).

The very gentle slope of the Loktak Lake basin in general, and littoral zone in particular, not only allows the deposition of fine sediments but also modulate the wave action in favour of the growth as well as establishment of aquatic macrophytes. In a shallow lake, increased nutrient loading and substantial loss of macrophytes can cause a shift from a clear water to a turbid water state (Scheffer et al. 1993, Scheffer

1998). In addition to the nature of land use pattern, the type of rock formations and hydrology of the catchment region play an important role in determining and controlling the chemistry of the lake water.

In large shallow lakes such as the Loktak, hydrodynamics which control the structure of hydrophytes (macrophytes and phumdi) and water quality vary significantly from littoral to pelagic zones.

Hence, understanding the role of hydrodynamic processes in lake system in time and space is important in

ENVIS RP: Geodiversity & Impact on Environment, Vol-23 (4), 2017-18

controlling water quality for its sustainable management. Therefore, several parameters of lake morphometry influence aquatic habitat, water-level fluctuations, water temperature and circulation, and wind exposure (Bornette and Puijalon, 2011).

Aquatic macrophytes in Loktak Lake occur in three general categories viz., emergent, submerged and floating. Among these, the submerged macrophytes locally called as charang are relatively abundant and widespread and form colony like structures almost all over the lake (Figures 2A & B). They play a major role in the lake ecosystem by trapping and cycling of nutrients. Submerged macrophytes exist at the interface and act as a living link between bottom sediments and the overlying water (Carpenter and

Lodge, 1986). They provide cover, shade and well oxygenated safe shelter for fish and other aquatic life forms, and also minimise sediment resuspension, arrest sediment transport and thus improve water quality. The absence of macrophytes enhances sediment resuspension leading to increased turbidity and poor water quality. On the other hand, an overabundance of macrophytes results in increased nutrient concentrations leading to eutrophication causing hindrance to recreational activities such as swimming, fishing, boating etc., and unpleasant aesthetic appearance of the lake system. Therefore, the presence and/or absence of submerged macrophytes play a critical role in controlling water quality in the lake.

Loktak Lake is known for phumdi (floating mass of vegetation, soil and organic matter) of different sizes and geometrical shapes with thickness ranging from a few inches to several feet (Figures

2A & B) (Trisal and Manihar, 2002). Phumdi consists of live biomass belowground, dead organic material and sediments, held together by a meshwork of rhizomes and crisscrossing roots and stems. Its level rises and falls during the year consistent with seasonal fluctuations in water level of the lake.

Coincident with the draw down event during dry season, phumdi stays rooted on the periphery especially on the south eastern periphery of the lake. During lake draw down, especially during the month of May, water becomes very clear and lake bottom is seen in almost every part of the lake. The phumdi’s movement occurs along the direction of wind which indicates north to south wind movement during draw

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down. When the lake gets refilled, the phumdi will again come northward spreading in different parts of the lake.

Figure 2. Field photographs showing A&B) Charang (Submerged macrophytes) and Phumdi.

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Phumdi acts as both source and sink for the nutrients (P and N) in addition to heavy metals

(Kosygin, 2002; Meitei 2002; Santosh and Bidan, 2002). The clay particles and associated organic matter of the phumdi by virtue of their high ratio of surface area to size, scavenge large quantities of phosphorus and nitrogen from lake water making nutrients less available for algae and thus help improve water quality. On the other hand, the nutrient rich phumdi undergoes dessication and oxidation during lake draw-down and release the nutrients into the water when the lake gets refilled, thus enhance the growth of phytoplankton. Hence, its trophic state ranges from oligotrophic to mesotrophic (annual mean PO4 concentration is 0.035 mg/L, varying from 0.05 to 0.051 mg/L). In Loktak water colour changes in time and space that varies from blue to green to grey to black in the increasing order of phytoplankton growth respectively.

Figure 3. Field photograph showing Phumsang (hut) on phumdi.

Phumdi provides an important habitat for lake dwellers (including human beings) and migratory birds (Figure 3). They are ideal nursery for biodiversity. They also provide nutrients for the growth of

ENVIS RP: Geodiversity & Impact on Environment, Vol-23 (4), 2017-18

various aquatic flora and fauna and help in maintaining a balanced ecosystem of the lake habitat in addition to shade for fish population (Figure 4).

Figure 4. Schematic diagram showing the anatomy of floating phumdi (from creating habitat for natural solutions).

The Keibul Lamjao National Park (KLNP) is the only floating wetland park in the world. It is made up of the phumdi that aggregated and permanently stationed in the south-eastern part of Loktak

Lake in course of time. This swampy grassy wetland has an area of about 40 km2 and hosts a rich and diverse flora and fauna in addition to “Sangai”, the only deer species in the world (Figure 5).

ENVIS RP: Geodiversity & Impact on Environment, Vol-23 (4), 2017-18

Figure 5. Field photograph showing Sangai (deer) on Phumdi.

Compared to deep water lakes, in large shallow lakes such as the Loktak, minor variations in water level cause significant differences in water to land ratio (i.e., larger area of lake bottom sediments will be exposed when lake water level drops down) leading to drastic changes in nutrient loading, algal growth and water quality (Figure 6). Lake morphology (depth and volume) controls its eutrophication state. In shallow lakes, water draw-down has positive (sediment consolidation) and negative (sediment nutrient release) impacts on sediment dynamics and macrophyte growth.

Figure 6. Schematic diagram showing cross-section of A) Large Shallow Loktak Lake; B) Draw down; C) Refill.

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Growth of abundant submerged macrophytes minimizes sediment resuspension. Frequent water level fluctuations and winds result in macrophyte instability and loss causing a more turbid algal- dominant state. One of the ways of controlling water quality of large shallow lakes is the maintenance of stable submerged macrophytes. They have a stabilizing effect on lake ecosystems and their presence in abundant quantity can maintain clear water state even when there is high nutrient contents (Canfield et al.,

1984; Jeppesen et al., 1990b; Scheffer et al., 1993; Moss et al., 1994; Meijer et al. 1994 and Jeperson et al. 1997). In shallow lakes, at an intermediate nutrient level of ~0.1 mg/L of P, clear state of lake water depends on the presence and abundance of its submerged macrophytes (Jeppesen et al., 1990; Hargeby et al., 1994). In the absence of external loading, recolonization of submerged macrophytes can facilitate the recovery of eutrophic lakes (Søndergaard et al., 1996). Draw-down of lake water is one mechanism for inducing the growth of macrophytes in shallow systems. Desiccation and consolidation of exposed sediments due to lake draw-down can arrest resuspension potential and reduce turbidity after lake re-fill, thereby promoting greater light penetration for macrophyte growth. In contrast, after lake re-fill, a large pulse of nitrogen and phosphorus in sediments are mobilized during desiccation and oxidation to water column and promote excessive algal growth, which would compete for available light. Therefore, exploring the optimum water level conditions is important for maintaining a sustainable lake ecosystem.

The geological setting of the Loktak basin, its limnological characteristics and increased anthropogenic activities in recent decades in and around the lake caused deterioration of water quality and loss of biodiversity. Considering its unique ecosystem, precious freshwater resource and socio-economic significance, Loktak Lake needs immediate attention for its conservation and sustainable management. In this direction, following salient strategies, with no or minimal negative effects if any, are suggested as part of the conservation and maintenance of this unique ecosystem:

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1. Protecting lake shorelines from erosion and maintaining an adequate buffer zone around the lake is

recommended after providing necessary alternative arrangements if required, for the local

communities living there.

2. Reducing as well as pre-treatment of effluents from anthropogenic activities discharged into the lake.

3. Avoid the use of motorised boats for recreational activities to prevent churning/resuspension of

bottom sediments. Since the lake is shallow with thick layer of unconsolidated bottom sediments,

churning/resuspension can cause high turbidity and reduce penetration of light into the lake water.

Motorised boats can also reduce aquatic plants by cutting them off and/or scouring away bottom

sediments they need to grow in.

4. Restricted fishing with respect to time and space to reduce competition with migratory birds for food

especially during winter season.

5. Promoting the growth of submerged macrophytes to restrict resuspension of sediments by wave

action and thus minimising the turbidity of lake water.

6. Regulating the anthropogenic activities such as deforestation, urbanization and shifting cultivation in

the catchment region are critical for sustainable lake ecosystem. Checking waste disposal as well as

monitoring human activities by the villagers in the vicinity of the lake.

7. Removal of flocculent/unconsolidated organic rich bottom sediments exposed during lake draw-down

in order to minimize internal nutrient cycling when the lake gets refilled. The sediments thus removed

can be transported away from the upstream and utilized as a manure on agricultural fields for growing

crops and also in the reclamation of degraded soils after assessing pollutants such as heavy metal

abundances.

8. Improved understanding on the linkage between morphometry and other limnological parameters as

well as regular monitoring of water chemistry will help in conserving the rich biodiversity of the lake.

9. Establishing the water level at which the phytoplankton begins to grow and constant maintenance of

that level is crucial for sustainable lake ecosystem.

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10. Sensitisation and raising awareness among the local community as well as tourists on the significance

of Loktak Lake through print and electronic media.

We express our sincere thanks to the Dean, SES, JNU for keen interest and encouragement, DST

(Purse -II) & UGC (SAP-DSA-II and UPE-II) for financial support towards lab development. MBD thanks JNU for fellowship.

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