Effect of Water Quality on Benthic Macro Invertebrates in Dikhu River, Nagaland, India

Water is essential for life. However there are reports of increased eutrophication in water bodies due to anthropogenic activities ultimately affecting its quality (Temjen and Singh, 2018). The effect of land use on water bodies can be understood by studying the water quality status (Hakamata et al., 1992). Water quality monitoring is therefore vital for the sustainable conservation of water resources and involves the regular and continued monitoring of physico-chemical parameters of water bodies. Variations in the quality of water are mirrored within the biotic community with certain sensitive species acting as indicators of water quality (Barbour et al., 1999). Biological agents that are utilised as indicators provide an exact measures of anthropogenic effects on aquatic ecosystems (Camargo et al., 2004). Benthic macro invertebrates have been documented as the best indicators of water quality in urban fauna stream (Mutonkole, 2015). Such composition of the benthic fauna are considered as a good indicator of water quality as they form relatively stable communities persistently and reflect characteristics of both sediments and upper water layer (El-shabrawy and Khalil, 2003). This community serve as a vital link in the aquatic food web (Siraj et al., 2010). Therefore, keeping in view the importance of benthic macro invertebrates as biological indicators and the subsequent lack of data in the region, the present investigation attempts to report physico-chemical properties of water and various benthic macro invertebrates in the Dikhu River, Nalagand, India.

Study area
 
Dikhu is one of the most prominent rivers of Nagaland, North East India. It has a total length of about 160 km. It originates from Nuroto Hill area in Zunheboto district. The river flows across Mokokchung and Longleng districts in Nagaland. The main tributaries of River Dikhu are Yangyu of Tuensang district and Nanung in the Langpangkong range in Mokokchung district. For the present investigation, two sampling sites were selected on the basis of accessibility and vegetation. Sampling site 1: Longmisa Noksen (N 26° 31’ 30.953" E 94°41’ 13.429") is located upstream and has a stretch of 2.18km and width varying from 9.56 to 40.29 m. The human settlement nearest to this site is Changtongya Town, Mokokchung, Nagaland. Sampling site 2: Longmisa- Chuchu (N 36°32’ 4.68" E 94°41’ 46.027") has a stretch of 898.87 m and width varying from 12.56 to 32.29 m. Both sites are adjacent to agricultural farmland and plantations during the study period. This water body is vital for the population living in the district of Mokokchung, Nagaland. The water body is utilised for domestic purposes such as irrigation for the adjacent farmland areas and also for domestic purposes. The water, however, is under the effect of a several anthropogenic factors such as sewage, chemical runoff and fishing activities.
 
Sampling procedures and analysis of water
 
Physico-chemical characteristics of water were investigated on a seasonal basis. The seasons included winter (Nov 2015-Jan 2016), spring (Feb-April 2016), summer (May-July 2016) and autumn (Aug-Oct 2016). Water temperature was recorded on the sampling sites. The water samples were collected from the sampling sites by dipping one litre polyethylene bottle just below the surface of water. For estimation of dissolved oxygen, samples were fixed at the sampling site in accordance with modified Winkler method (Iso, 1983). The analysis of water samples was done by adopting standard methods (Adoni et al., 1985; Apha, 1985; Trivedy and Goel, 1986). Water sample for other physico-chemical parameters were stored and carried to the laboratory for analysis. Turbidity was measured using an electronic turbidity meter (submersible turbidimeters, USGS, 2013). pH was measured with the help of portable digital pH meter (OAKTON). The water quality was also compared against the drinking quality standards of water (Who, 1995).
 
Sampling for benthic macro invertebrates
 
The macroinvertebrates colonizing the substrate and surface were collected with the help of the Surber sampler (0.50 mm mesh net) and by hand-picking from beneath the stones and macrophytes. The macroinvertebrates were preserved in 5% formalin at the sampling sites and were examined using inverted microscope for identification up to genus level with the help of standard monographs and identification keys.
 
Statistical analysis
 
Pearson’s correlation analysis was performed to determine the statistical relationships between the different water parameters and also examine the effect of water parameters on benthic macro invertebrates at the sampling stations. All statistical operations were performed by using IBM SPSS package 16.0.

Physico-chemical parameters of water
 
Table 1 shows the seasonal variation in physico-chemical parameters of water at sites 1 and 2. The water temperature (°C) ranged between a minimum of 10.61°C -27.5°C at site 1 and 10.01°C to 28.8°C at site 2 during the study period. Water temperature has been observed to follow the general atmospheric temperature. Temperature constrains the various processes in aquatic ecosystems differently and therefore, a general warming of the water column will change trophic interactions and ecosystem functioning (Alheit et al., 2005). Water Turbidity ranged from 9.97-77.56 NTU at site 1 and 10.42-78.92 NTU at site 2. The water turbidity levels were found to increase with the onset of the rainy season. Verma and Shukla (1969) believed that the pH would prove to be an ecological factor of major importance in controlling the activities and distribution of aquatic flora and fauna. During the study, pH ranged from 7.72-8.23 at site 1 and 7.59-8.21 at site 2. Dissolved oxygen is essential for the respiratory metabolism of organisms. The dissolved oxygen ranged between 8.33-12.45 mg/L at site 1 and 8.39-12.06 mg/L at site 2. The effects of waste discharge in the water body are largely determined by the oxygen balance of the system (Trivedy and Goel, 1986). It directly affects the survival and distribution of fauna and flora in an ecosystem (Vijaykumar et al., 1999). Higher values of dissolved oxygen were found during the winter season at both sites which may be due to decreased algal bloom as compared to that in summer season (Temjen and Singh, 2018). The carbon dioxide ranged between 5.33-9.33mg/L at site 1 and 5.25-9.21 mg/L at site 2. The primary source of inorganic carbon for photosynthesis and the organic substances in an aquatic ecosystem are largely in the form of dissolved carbon dioxide and bicarbonates (Wetzel, 2001). Water velocity values ranged from 0.196-0.518 m³/s at site 1 and 0.192- 0.520 m³/s at site 2. Alikunhi (1957) considered alkalinity as a measure of productivity. In present study, the values ranged from 72.95-134.55 mg/L at site 1 and 73.50-135.65 mg/L at site 2. The concentration of alkalinity in water bodies shift the pH levels of water bodies to the alkaline side (Wetzel, 1983). The higher values of alkalinity at both sites during the spring season in the present study might be attributed to higher rate of decomposition of nutrients by microbes and subsequent increase in temperature. Cole (1975) recorded calcium and magnesium to account for most of the hardness. Total hardness of water in present study ranged from 14.20-38.5 mg/L at site 1 and 14.35-39.6 mg/L at site 2. A trend of lower values in rainy season and maximum during winter was observed. Similar observations have been reported by Temjen and Singh (2018) who worked on Milak River at Mokokchung district, Nagaland. During the study, it is recorded that all the water quality parameters were within the permissible limit of Who (1995) except for alkalinity which had a value of 134.55 mg/L at site 1 and 135.65 mg/L at site 2. The increased alkalinity might be attributed to anthropogenic forces such as improper sewage disposal and run offs from the adjacent farmlands near the water body.


 
Diversity of macro invertebrates
 
During the study, a total of 19 species of benthic macroinvertebrates belonging to 3 taxa were identified at site 1 (Table 2). The species were identified only at generic level. Under Annelida, four species found were Enchytraeidae sp, Haplotaxida sp, Lumbriculida spand Tubificidae sp. 9 Arthropod species were Astacidae sp, Baetidae sp, Caenidae sp, Chaoboridae sp, Chironomini sp, Coenagrionidae sp, Ephemerellidae sp, Heptageniidae spand Leptohyphidae sp. A total of 6 species identified under Mollusca were Bothynidae sp, Corbiculidae sp, Lymnaeidae sp, Physidae sp, Pleuroceridae spand Sphaeriidae sp. It was observed that the Athropoda had the maximum diversity followed by Mollusca and Annelida (Fig 1). At site 2, a total of 18 species belonging to 3 taxa of macro inverteberates were recorded (Table 3). The species were identified only at generic level. Only 3 species were observed under Annelida namely, Haplotaxida sp, Lumbriculida spand Tubificidae sp. 9 species found under taxa Arthropoda, were Astacidae sp, Baetidae sp, Caenidae sp, Chaoboridae sp, Chironomini sp, Coenagrionidae sp, Lesidae sp, Psephenidae sp and Tanypodinaesp. Lastly, 6 species under Mollusca, namely Lymnaeidae sp, Physidae sp, Pleuroceridae sp, Sphaeriidae sp, Valvatidae sp and Viviparidae sp were recorded. Site 2 also possessed maximum diversity of Arthopoda, followed by that of Mollusca and Annelida (Fig 2). Fig 3 displays the seasonal variation of macro benthic invertebrate composition at site 1 and 2. We observe that summer had the highest number of taxa for all the 3 genera while winter had the lowest number of taxa at both the study sites.

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Pearson’s test for correlation showed that at site 1 (Table 4), dissolved oxygen was negatively correlated with water temperature(r=-.973, p=0.027). At site 2 (Table 5) a similar trend was observed between dissolved oxygen and temperature (r=-.988, p=0.022). We observe that with the increase in temperature, there is a significant decrease in the levels of dissolved oxygen present in the water body. This can be attributed to increased metabolic activities of biota consuming increased levels of dissolved oxygen due to increased temperature (Uehlinger et al., 2000). Water velocity was positively correlated with turbidity at both sites (r=998, p=0.002) and (r=.996, p=0.004) for site 1 and site 2 respectively. The increased influx of water during the rainy season, may increase the turbidity in the water body. Total hardness was negatively correlated with water temperature at both site 1 and 2, (r=-.992, p=0.008) and (r=-.997, p=0.003), respectively. The higher value of total hardness during winter seasons may be due a number of factor. Firstly, a decreased water level increases the ratio of calcium and magnesium salts concentration in water as compared to other season. Secondly, with the lower water volume during winter, anthropogenic activities such as fishing, washing of clothes and domestic sewage which contribute calcium and magnesium salts, further increases value of hardness of water. Meanwhile, the lower value of total hardness during the warmer seasons may be due to increased water levels due to precipitation. Similar observation have been reported by (Singh and Gupta, 2009; Temjen and Singh, 2018).

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Arthropoda was found to be positively correlated with water temperature (r=.960, p=0.040). Water temperature controls both the supply of oxygen and metabolism of invertebrates (Ekau et al., 2010). Therefore the increase in the water temperature during the warmer season may favour the population of Arthopoda. Meanwhile, Arthropoda was found to be negatively correlated with total hardness (r=-979, p= 0.021). This indicate that the increased levels of water hardness at site 1 negatively impacts the population and diversity of Arthropoda. This may indicate the susceptibility of arthropod species to the increased levels of water hardness. No statistical correlation of macro benthic invertebrates with water parameters were observed at site 2.

Biodiversity is one of the most significant attributes of sustainable development and represents the biological wealth of a given nation. Flora and fauna are becoming extinct at an alarming rate because of habitat loss, overexploitation and global climate changes. The present study highlights the status of macro benthic invertebrate structure of Dikhu River of Nagaland. Further, we conclude that the water quality parameters were within the limits of WHO (1995) except for alkalinity. The sensitivity of Arthropoda to water hardness may indicate that it is a source of bio indicator. Future large scale work on inventorying of macro benthic fauna can shed more light on the effect of water quality on macro benthic invertebrates while also enabling workers to inventory the rich biodiversity of the region.

The Head, Department of Zoology, Nagaland University is duly acknowlegded for providing necessary laboratory facilities for conducting the experiments.

The authors declare no conflict of interest.