Ecological Assessment of Mai Pokhari Wetland

Land use and land cover

The statistical analysis of land cover change of Mai Pokhari identifies three major type of land cover i.e. Forest, Agricultural land and Grassland and observed significant changes within a duration of 10 year from 2000A.D. to 2010A.D. Agricultural land was observed significantly increased where forest was found decreased significantly. Forest around Mai Pokhari was observed dense and increased in the interval of 10 years but decreased while moving outside. It might be because of conservation practices managed by wetland management committee in the surrounding of wetland.

There is no provision of collection of raw materials including woods and fodder from surrounding of wetland which have helped on growth of dense forest. While moving away from wetland, most of the forest was observed turned into agricultural land. There was also observed dense community forest in north and west of wetland and scattered forest on east and south which is mostly residential areas. Population of study area was found increasing (CBS 2014) and mostly females were found involving in farming practices. Instead of tradition practices, large agricultural farm with business purpose were found initiated. This might be the cause of decreasing coverage of forest area.

Most of the people close to wetland have established hotel and lodge for major source of income. In such cases, people plant timber trees on their private land for selling purpose which is making scattered forest areas in residential. Forest depletion along with massive construction has direct impact on ground water causing lowering of water level (Alam¹, Rashid, Bhat¹, & Sheikh, 2011).

Roads close to wetland and construction of houses and running of heavy vehicles might also adding impacts on wetland condition. Most of the males of this area move to India for seasonal. This present trend have is replacing traditional occupation especially animal herding, trading. Most of the grasslands are turning bare and invasion. With the less utilization of grassland, it is slowly turning into forest. The conversion of land from one form to another form provides huge negative impact on wetland resources (Alam, 2011) as well as local ecosystem services (Zhang, Zhao, Liu, Liu, & Li, 2015).

Water Quality

Physio-chemical parameters changes due to natural and human activities. Dissolution of bed materials, meteorological events are some of the natural causes and also climate change although being natural influenced by human activities. pH measured in both sampling season were found acidic. pH measured is below water quality guidelines for the protection of aquatic life (6.5-9.0) which might be because of acidic nature of lake water due to huge deposition of fallen parts of Pinus roxburghii in soil. There was large deposition of organic matter in the lake and decomposition of such organic matter releases carbon dioxide (CO2). Thus produced carbon dioxide combines with water and forms carbonic acid (H2CO3).

Carbonic acid is also responsible for low pH. pH is positively correlated with ammonia and nitrate. Decomposition of organic sediments also liberates nitrates and ammonium ions which enhance hydrogen ions (H+) making water acidic (Adeogun & Fafione, 2011). Decomposition of organic matter forms acid containing compounds and elevates hydrogen ions in water (Yimer & Mengistou, 2009). There might be flow of NO3- and PO¬4- in wetland from the agricultural and grassland. The optimum level of pH for the survival of the organism ranges from 5 to 9 and beyond these limit species suffers (Mesner & Geiger, 2010).

Water conductivity is always highly influenced by the surrounding geology (Light, Licht, Bevilacqua, & Morash, 2005). Water conductivity was measured very low in both sampling period this was due to the presence of graphite rocks as bed and bank materials. Graphite are mainly composed up of inert materials (Light et al., 2005).

Dissolved oxygen is highly reactive and changes quickly in very short period of time (Legesse, Giller, & O’halloran, 2000). Dissolved oxygen is one of the major factor affecting the existing of aquatic species (Giller & Malmqvist, 1998). Communities assemblages and distribution of aquatic organisms are directly related to Dissolved oxygen(Jackson & Myers, 2002).

As per USEPA guidelines (2000), DO more than 5mg/L is appropriate for growth of most of the aquatic organism and less than 3mg/L is stressful to aquatic organism. DO measured is less than 3mg/L indicating stressful environment. Similar result was displayed by Rai (2013) in his research. 5-8mg/L DO for aquaculture and 80-100% of DO saturation for balanced aquatic ecosystem is guidelines set by Nepal water quality guidelines.

Measured DO is below than Nepal water quality guideline indication unfavorable living condition for aquatic organisms. Result showed slightly increase in DO concentration in pre-monsoon but also overall concentration was low. Major nutrient i.e. total phosphate and nitrate were found higher in post-monsoon and pre-monsoon season respectively. These nutrients are major influencer for the growth of algae and aquatic weeds (Wetzel 2001).

Growth and decomposition of algae and macrophytes consumes more dissolved oxygen and hence lowers the concentration of dissolved oxygen. Similarly, microbial organisms consume more dissolved oxygen for decomposition of huge deposition of organic matter. These might be major factors for lowing concentration of dissolved oxygen in lake. Poor amount of DO is a good indicator of poor water quality of lake.

Simply, Alkalinity is an ability to resist the change in pH. Generally, most of the lakes and reservoirs maintain similar pH because of presence of carbonates which is one of the major components of alkalinity. Carbonate is formed in water after the reaction of carbon dioxide with water. Addition and reduction of carbon dioxide is simultaneous process in wetland where addition of carbon dioxide reduces pH where pH raises with the reduction of carbon dioxide.

Alkalinity of water is also associated with hardness. Higher the total alkalinity in water, harder will be water. Total hardness is a sum of calcium hardness and magnesium hardness. The major cause of hardness is a presence of calcium and magnesium which often produces by the dissolution of limestone. In most of the sampling there was presence of bed rocks which might release calcium and magnesium in water.

Water bodies contain nutrients but excessive nutrients are harmful. Nitrogen, Phosphorus and Ammonia are major nutrients in fresh water. These nutrients enters into the fresh water through various sources including bed rocks, atmospheric deposition, surrounding vegetation and land use practices and human activities. Overabundance of these nutrients makes lake polluted as it enhances the excessive growth of algae. Growth and decomposition of algae reduced dissolved oxygen making difficult for aquatic organism to survive. Some algae also produce toxins, which might be harmful aquatic organism and human too, if ingested.

Nitrogen and its various forms are highly concern in the study of water analysis as these are major cause of environmental pollution. Various amount of nitrogen enters to the water through natural and anthropogenic process. Nitrate being highly soluble in nature reaches to water from earth materials, organic matters and fertilizers (Schmitt, Randall, & Malzer, 2001).

Excess of nitrate have long term and long chain impact on aquatic ecosystem. It enhances the growth of macrophytes and wild plants. Death of these plants adds organic matter and micro-organism for decomposition. Decomposition of organic matter by micro-organism consumes more oxygen and deficit oxygen causing death of aquatic organism. Mai Pokhari is rainfall feeding lake with high content of organic matter.

Organic matter might be the major source of nitrate in lake. Because of gradual lowering of water level, water is being filled in lake from river water. River water moving to lake transports nutrient from external sources. Agricultural runoff, plant debris, animals feces were nitrate releasing sources in river which was observed. Oxidation of ammonia also forms nitrates naturally. Nitrate was measured in the range of 0.07mg/L to 3.2mg/L and found increased in pre-monsoon season. Water quality guidelines and FAO has set less than 300mg/L is tolerable quality range for aquaculture.

The change in concentration less than 15% from local unimpacted condition is tolerable for aquatic ecosystem according to water quality guidelines of Nepal. Ayers (1985) stated no impact on plants and aquatic organism below the concentration of 5mg/L. Measured nitrate was within the range of guideline set by water quality guidelines. Measured ammonia was in the range of 0.18mg/L to 2mg/L above the range of water quality guidelines for protection of aquatic ecosystem (<0.007mg/L) and for aquaculture (<0.03mg/L).

Unlike nutrient over-enrichment, excessive ammonia in water bodies adds toxicant or buildup toxic in the body of aquatic organism and finally leads to death. Ammonia might be enters into to the Mai Pokhari through breakdown of organic matter, nitrogenous animal feces and nitrogen fixation process.

Various forms of phosphorus arise from various sources. Some major sources of phousphorus in Mai Pokhari might be decomposition of organic matter, liberation from phosphorus containing minerals. In addition, soil erosion from the bank might help to enter phosphorus to the water. Water from the Paha Khola also adds phosphorus to lake water.

The need of phosphorus is to enhance the growth of aquatic organisms. Excessive phosphorus enhances eutrophication. Eutrophication reduces the concentration of dissolved oxygen making difficult to survive for aquatic organism. Concentration of Total phosphate was measured in the range of 0.25mg/L to 4.1mg/L. This measured value is higher than water quality guidelines for aquaculture (<0.6mg/L). For the protection of aquatic ecosystem, change in concentration of phosphorus less than 15% is allowable as per water quality guidelines.

Ammonia, nitrate and total phosphate was found positively correlated with each other (Table 7). Ammonia and nitrate are the two forms of nitrogen and both formed by the process of nitrogen fixation. In Mai Pokhari, Organic matter was found major stressor and liberates nitrate, ammonium and total phosphate ions after decomposition.

In addition, animal feces, liberation of nutrients ions from minerals and rocks and microbial releases also made positive correlation among nutrients. Because of higher nutrients concentration, DO is measured low. pH was measured positively correlated with nitrate and ammonia whereas negatively correlated with total phosphate. It reveals that acidic pH is a result of nitrogen ions in water (Yimer & Mengistou, 2009).

As water is measured acidic might be due to containing less carbonate and magnesium ions resulting low total hardness of water. There is negative correlation measured between pH and total hardness/total alkalinity. Total hardness and total alkalinity are positively correlated. The addition of calcium carbonate and magnesium carbonate from limestone and dolomite enhances total hardness and total alkalinity.

Ecological Assessment: Macroinvertebrate assemblages

Biological indicators are essential elements for water quality assessment, management and conservation (Lewis, Jüttner, Reynolds, & Ormerod, 2007). Fish, macroinvertebrates and diatoms are major faunal bio indicator. The distribution of these species is determined by the stressing factor to the water but most of the study reveals that poor habitat quality is also responsible for poor species richness, its composition and diversity (Griffith et al., 2005).

Similar kind of taxa was recorded in post and pre-monsoon season. This might be due to similar climatic condition, substrate type and almost similar concentration of nutrients in a lake. The largest number of taxa and ETO taxa were measured in L1. This was due to mixed substrate type containing clay, silt, pebbles and freshly fallen parts of plant. Site L1 was also observed more disturbed by human activities.

Taxa richness was low in sites L4, L5 and L6 because of clayey substrate type. Diptera and Oligochaeta were recorded dominant taxa in both sampling period. Three family of Diptera i.e. Chironomidae, Tabanidae and Simuliidae and two family of Oligochaeta i.e. Tubificidae and Naididae were recorded. The high abundance of Chironomidae and Tubificidae were recorded in littoral zone. The wide distribution of Chironomidae and Tubificidae could be their strength to exist in unstable substrate (Weatherhead & James, 2001). Generally unstable substrates were found on disturbed and polluted sites.

Mactoinvertebrate Metrices

Taxa richness was found increase with the increase in coverage of macrophytes and lowering of water level in pre-monsoon season. Macrophytes provide safe shelter to macroinvertebrates from the predators could be the reason of higher taxa richness. This statement is also supported by previous study (Merritt & Cummins, 1996).

Distribution of variety of macrophytes also enhance diverse abundance of macroinvertebrates and plays significant role in their existence (HANSON, 1990). Water level was also found more shifted towards center in pre-monsoon season which might make habitat more suitable for macroinvertebrates.

The number of ETO taxa found highly decreased in pre-monsoon season. ETO taxa are sensitive species to the pollution. The decrease in number of ETO taxa might be increase in the concentration of pollutants and chemicals. The chemicals parameters and nutrients were measured higher in pre-monsoon season which could restrict the distribution of sensitive taxa. Lowering of water level might cause unsuitable habitat for ETO taxa causing lowing the number of ETO taxa in pre-monsoon season. Higher abundance of ETO taxa represents higher ecological quality of wetland.

The number of facultative taxa was found higher than pollution tolerant and pollution intolerant taxa in pre and post-monsoon season. Pollution intolerant taxa were recorded in low number in both sampling period. This scenario reflects that concentration of pollution is rising in lake making unsuitable environment for sensitive species. With the tolerance score of each taxon, similar NLBI was measured in both pre and post-monsoon season.

Nepal Lake Biotic Index determines lake water quality class and degree of pollution, provided with a value ranges from 1 to 10. Similar NLBI value reveals similar ecological condition or no change in ecological condition of wetland in post and pre-monsoon season. NLBI value ranges from 0 to 10 where towards 10 provides indication of higher quality of lake water with none to minimal level of pollution whereas value towards 1 indicates poor to bad quality of lake water and extreme level of pollution (Shah et al., 2011). Measured NLBI value ranges from 4 to 4.9 which refers moderately polluted ecological condition of wetland with fair water quality (Shah et al., 2011).

Shannon diversity was measured almost similar and low in both sampling period. External stressor to the environment or ecosystem is a one of the major reason for low diversity (Odum, 1959). Similar kind of substrate type in sampling period, higher deposition of organic matter, dominance of single taxa could be the reason for low diversity. Shannon diversity depends upon taxa richness and evenness (Enger et al., 2013).

Lower the taxa richness and evenness, lower will be the Shannon diversity. Shannon diversity was negatively correlated with ammonia and total phosphate but no relation was observed with nitrate. Shannon diversity was observed decreasing with the increasing concentration of nutrients. ETO taxa were also negatively correlated with nutrients parameter. Nutrients parameter plays significant role in the distribution and abundance of species. Increase in concentration of nutrients enhances the growth of algae, macrophytes which lowers dissolved oxygen and limits growth and distribution of macroinvertebrates.

Transportation of river water to the lake is one of the major sources of nutrients of the Mai Pokhari. Higher consumption of dissolved oxygen for decomposition of organic matter, increasing concentration of chemicals, growth of macrophytes and algae, gradually lowering of water level, highly abundant fish species are hindering the growth and distribution of macroinvertebrates as well as degrading ecological quality of wetland.

Shannon Wiener diversity and ETO taxa richness was negatively correlated with nutrients parameters. There was unequally distribution of benthic macroinvertebrates (BMI). Chironomids and Tubuficidae were highly measured where ETO taxa were poorly recorded. This might be because of unsuitable habitat for all species and stressor. Poor DO measured might be responsible for low to no presence of ETO taxa and other sensitive species in different sites and periods whereas Tubificidae and Chironomids can resist or survive.

Chironomids and Tubificidae are pollution tolerant species have ability to survive, grow and reproduce in poor environmental conditions as well. The measured concentration of total phosphate was beyond the water quality guidelines for aquatic ecosystem. Total phosphate was responsible for the excessive growth and distribution of algae bloom and macrophytes which consumes more dissolved oxygen and adds organic matter in lake. Most of the species couldn’t grow and live freely in poor DO concentration. In addition, Ammonia and nitrate also supports on growth and distribution of macrophytes making habitat unsuitable for BMI.