Application of Biotic Indices and Pollution Tolerance Index in Assessing

Copyright: © 2015 Andem AB, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Application of Biotic Indices and Pollution Tolerance Index in Assessing Macro-Invertebrate Assemblage of Ediba River, Cross River State, Nigeria


Introduction
Macro-invertebrates communities are widely used as indicators of river ecosystem health status because they include a wide range of species, each with relatively well-known sensitivity or tolerance to river conditions [1]. They are useful in understanding the ecological health of an aquatic ecosystem, rather than using chemical and microbiological data, which at least give short-term fluctuations [2]. Macro-invertebrates are considered important because they reflect the cumulative effects of the present and past conditions; also they have low mobility (i.e. are sessile or nearly) and life cycles of several weeks or years [3]. Benthic invertebrates range in sizes from 0.2 mm to 15 cm in length as in the case of a fully grown fresh water crayfish, while most are larvae of insects, others are aquatic snails and worms [4].
Bio-monitoring studies and the use of macro-invertebrates to rate the quality of water bodies of both lotic and lentic types have been widely reviewed elsewhere [5,6]. The use of pollution tolerance index (PTI) as a method of measuring the overall health status of aquatic bodies through the use of macro-invertebrates remains the most reliable and effective method [7][8][9]. Macro-invertebrates which are utilized in aquatic pollution studies include: Mayflies (Ephemeroptera), caddisflies (Trichoptera), stoneflies (Plecoptera), beetles (Coleoptera), crayfish and amphipods (Crustaceans), aquatic snails (Mollusca), biting midges (Chironomids) and leeches (Hirudinea) [10][11][12]. This study is undertaken to investigate the composition, abundance and distribution of macro-invertebrate community and using pollution tolerance index to assess the health status of Ediba River.

Study area
The Ediba River in Abi Local Government Area of Cross River State, Nigeria is located in latitude 05˚ 52" 49.7" N and longitude 07˚ 59'56.7E'' (start point) and latitude 05˚ 53'29.0"N and longitude 07˚ 58'41.3"E (end point) ( Figure 1). The river is the second largest of Southern Nigeria, with a width of 1000 yards during flood. It reaches its greatest depth in September -October with an average of 30 ft at the bank. The river is subjected to various anthropogenic activities. Three sampling stations were selected using geographical positioning system (GPS) and base on effluent discharge, land use patterns, human impacts, solid wastes disposal and bank type.

Diversity Indices
The diversity index for the three Stations is shown in Table 3. Taxa richness or Margalef's index (d) was highest in Station 1 (2.985) and lowest in Station 3 (1.008). Station 1 had the highest diversity index value of 0.947, while, Station 3 recorded the lowest diversity index value of 0.604. Evenness ranges from 0.337 in Station 3 to 0.362 in Station 2. Margalef's index (d) and Shannon wieners show insignificant difference across station (p>0.05) while evenness show significant difference across stations (p<0.05).

Pollution Tolerance Index (PTI)
PTI was utilized to assess the overall health status of the study area and to ascertain the extent of human impact on the river is shown in Table 4. Unpolluted water would have values between 23 and above as excellent, 17 -22 as good, while the polluted water would have 11 -16 as fair and <10 as poor. The PTI values for Stations 2 and 3 were 6 and 4 respectively indicating a poor water quality status.

Discussion
The abundance of macro-invertebrates encountered in the study area was generally low. Ephemeroptera and Zygoptera were poorly represented accounting for 0.82% and 1.44% respectively of the relative abundance [6] reported high diversity of Ephemeroptera which includes Ademophleboides sp., Baetis sp., Centroptillum sp., Cloeon sp., Cloeon bellum and Ephemerella ignita in Edion and Omodo Rivers in Southern forceps into different groups and preserved in 4% Formalin. Then, they were identified and counted, using standard keys according to [13][14][15][16].

Statistical analysis
Statistical data were subjected to analysis of variance (ANOVA) to compare the differences in species composition and abundance with Microsoft Word Excel 2007. Biological indices, such as taxa richness, evenness (E) and Shannon-Weiner diversity, were determined using version 3 of PAST Software Design.

Determination of Pollution Tolerance Index (PTI)
Pollution tolerance Index (PTI) was determined by utilizing the methods [17,18]. Three groups of macro-invertebrates were assigned a multiplication factor of 3 for the pollution sensitive group (Ephemeroptera, Trichoptera and Plecoptera), 2 to the facultative tolerant group (Anisoptera, Zygoptera and Decapoda) and 1 to the pollution tolerant group (Gastropods, Oligochaetes and Hirudinea). Values obtained were thereafter compared with established standard values in accordance with [7].

Results
A total of sixteen genera belonging to nine orders and 289 individuals were encountered. The relative abundance of macroinvertebrates taxa encountered at the different sampling stations is presented in Table 1, while Table 2 shows the percentage composition of macro-invertebrate taxa in the Ediba River.   Where S = indicates significant difference at a probability level less than 5%, (P<0.05) NS = indicates not significant difference at a probability level greater than 5% (P>0.05) Where S 1 = Ruhura Station, S 2 = Itumudea Station , S 3 = Enoe Station  Nigeria and the high abundance of these species is an indication of good water quality. Odonata are known to be facultative species as they are mostly associated with moderately polluted waters and this order was well represented, with the highest diversity of species encountered during the study period. The diversity of Odonata was encountered in Station 1 with species such as; Trithermis arteriosa, Crocothemis erythra, Palpopleura pleura and Macromia sp. None were recorded in Station 2 and only Palpopleura pleura in Station 3. The high abundance of Odonata in Station 1 maybe due to food availability or habitat preference of this species [19] also reported high abundance of Odonata in Awba Reservoir in Ibadan, Oyo State. Diptera was the second largest taxa after Oligochaetes in relative abundance. Three species of Helius sp., Anopheles sp. and Palpamyia sp. were encountered. Helius sp. was encountered in Stations 1 and 2, with 13 and 10 species respectively. Anopheles sp., was not recorded in Station 1, but occurred in Stations 2 and 3, with 10 and 11 species respectively. The relative abundance of these taxa has been reported by [20] who showed that conditions such as substrates and the alkaline pH of the water body have favoured their abundance. Lower number of Trichoptera (Caddis fly) was recorded, accounting for 2.97% of the relative abundance. According to [21] the larva of caddis fly does not tolerate polluted water, hence the lower number in this study. Hemiptera were fairly represented with two species (Hydrometria sp. and Physopella malanoptera), while only one species each of Oligochaetes and Polychaetes were represented (Tubifex sp., and Capitella sp,). Oligochaetes and Polychaetes were completely absent in Station 1, but present in Stations 2 and 3, with 53 and 94 individuals respectively. This may be due to the fact that Annelids are mostly pollution tolerant species and can survive wide range of pollution in water [20][21][22][23] recorded several species of Oligochaetes in Warri River including Nais sp. and this was due to the richness of the immediate substrate in organic matter, their feeding habits as they are deposit feeders, their tolerance to silting, decomposition and flow rate than other macrobenthic groups. Among the Decapoda, only one species of fresh water prawn was encountered (Macrobrachium vollenhovenii). A high pollution tolerance index of 39 was recorded for Station 1, where organisms, such as Ephemeroptera and Trichoptera, were encountered, which indicates Oligosaprobic in quality. However, Odonata, Decapoda and Oligochaetes were high in Stations 2 and Station 3, indicating that the waters were relatively polluted or mesosaprobic in quality. The relatively low diversities of Ephemeroptera and Trichoptera as encountered in this study may be due to habitat preference. Trichoptera are mostly present in upland streams or rivers which are well oxygenated when compared to low land fresh waters as encountered in this study.

Conclusion
Pollution sensitive taxa such as Ephemeroptera and Trichoptera were completely absent in Stations 2 and 3 indicating the poor quality status and the low PTI values in this stations. The need for long-term hydro-biological investigation, with elaborate emphasis on water quality monitoring and the ecology of macro-invertebrate fauna is so much recommended for the safety and conservative use of Ediba River and other fresh water bodies and their resources.