Ó Springer 2006
Hydrobiologia (2006) 556:137–147 DOI 10.1007/s10750-005-1262-6
Primary Research Paper
A feasibility study to monitor the macroinvertebrate diversity of the River Nile using three sampling methods M. Reda Fishar1 & W. Peter Williams2,* 1
National Institute of Oceanography and Fisheries, Inland Water and Aquaculture Branch, 101 Kasr El Aini St., Cairo Department of Life Sciences, King’s College, University of London, Franklin Wilkins Building, 150 Stamford Street, SE1 9NN, UK (*Author for correspondence: E-mail:
[email protected]) 2
Received 9 March 2005; in revised form 17 June 2005; accepted 25 July 2005
Key words: benthic macroinvertebrates, sampling, biodiversity, river, Nile
Abstract The River Nile is one of the world’s major rivers. Its’ catchment in Egypt has a population of 75,000,000. River flow is highly regulated and there are known discharges of pollutants. 1035 km of the river downstream of the Aswan high dam was studied to test the hypothesis that representative qualitative samples can be used to estimate macroinvertebrate biodiversity. Benthic macroinvertebrates are difficult to sample in large rivers and a reliable sampling strategy is required to evaluate their ecological status. Three methods for sampling have been investigated. Ekman Grab, macrophyte sweep netting and Artificial Substrate Samplers (ASS) were used to sample 15 sites from Aswan to Cairo between September 2001 and June 2002. Organisms were identified to species level where possible. Taxon accretion curves indicated that the all taxa present at a site should be collected using either 15 grab samples, 10 macrophyte samples or 5 ASS. The best time to sample was May–June. The biodiversity of macroinvertebrates in the Nile was recorded as 50 taxa with values of 7–31 at individual bank-side sites. Mid-stream biodiversity was much lower (0–19). Lowest biodiversity occurred at sites with known pollution inputs whilst highest occurred at sites with high levels of sedimentation. A regular programme for biomonitoring is recommended which will allow current status to be confirmed and future changes detected.
Introduction Biological monitoring of rivers using benthic macroinvertebrates is accepted as a useful tool for the assessment of water quality (Hellawell, 1986; Rosenberg & Resch, 1992). However, most studies have investigated relatively small rivers and there is a pressing need to obtain biological information on the worlds largest rivers many of which are under pressure due to population growth and urbanisation (Petts et al., 1993). The River Nile is a case in point as it is one of the worlds largest rivers flowing a distance of over 6625 km from source to mouth (Zahran & Willis, 2003). The
catchment of the Nile in Egypt, has a population of over 75 million and the Nile receives industrial and domestic waste whilst water is abstracted for drinking water, irrigation and industry. Information on invertebrates of the River Nile prior to the Aswan Dam is sparse (Rzoska, 1976) and there have been few invertebrate studies at any time on the Nile in Egypt. Studies that do exist are often descriptive of the fauna of small areas (El Shimy & Obuid-Allah (1992), Abdel Salam (1995), Samaan et al. (1995), Habashy (2000), Abdel Gawad (2001) and Fishar et al. (2003). This paper tests the hypothesis that representative qualitative samples can be collected in order
138 to estimate the macroinvertebrate biodiversity of the River Nile. The longer term aim is to develop a biotic index for the Nile with a rapid bioassessment monitoring programme. The development of a sampling strategy is an essential precursor before such a programme can be implemented. This paper thus seeks to identify: 1. 2.
3.
4.
The method or methods that are capable of sampling the taxa present at a site. The number of samples that are required to obtain a representative sample of the taxa present in the river. The seasonal variation in taxon diversity and the best time of year for sampling using the different methods available. The current macroinvertebrate biodiversity at selected sites along the River Nile.
Methods The stretch of river of studied was from Aswan High Dam to Al-Kanater Barrage in Cairo (Fig. 1). It is lowland, meandering section of river which eventually enters the Nile Delta below Cairo. The banks are sedimentary and muddy with steep banks whilst mid-stream is more erosional with a coarse sand substrate. Varying levels of human domestic, agricultural and industrial activity occur along the river and some sections are significantly polluted. 15 sites were selected to provide a wide range of physical and chemical conditions (Table 1). The east and west banks and the mid-stream area of the river were sampled at each site. Several methods are available for sampling large rivers including dredges, grabs, cores and airlift pumps (Hellawell, 1986). These methods are limited because they only work well on soft substrates and the volume of the substrate sampled by corers, grabs and air-lift pumps is very small. An alternative sampling method is the Artificial Substrate Colonisation Sampler (ASS) (ISO, 1993). The ISO ASS consists of plastic units which are enclosed in a netlon bag and attached to a brick. The ASS provide hard surface areas for the colonisation of rock clinging forms which are often more diverse than those found in depositing sub-
strates. They have the disadvantage that 3– 4 weeks are recommended for colonisation during which time the samplers can be dislodged by extreme flows or vandalised. Invertebrates are often attached to weeds and sampling aquatic macrophytes is a further method available in lowland rivers. In this study three methods have been used in an attempt to obtain representative qualitative macroinvertebrate samples: Ekman grab, the ISO (1993) recommended ASS and macrophyte sweep net samples. Collection and analysis of macro invertebrates samples The sampling programme took place from September 2001 to June 2002. Three pairs of field collecting dates were selected September/October 2001, January/February 2002, May/June 2002. These dates provided autumn, winter and spring/ summer samples within the available resource framework. On the first date of each pair 3 ASS were deployed and retrieved on the second date after 1 month immersion. A maximum of 2 ASS samples were subsequently analysed providing a maximum of six samples per site. Three Ekman grab samples (with opening area equivalent to 250 cm2 ) were taken from each bank and main channel on each visit providing a potential of 18 grab samples over the sampling period. Also, on each visit, two samples were taken from macrophyte beds at each bank giving a maximum of 12 samples over the whole period. The macrophytes within a 0.125 m2 quadrat were cut and thoroughly shaken and washed into a 500 lm mesh sweep net to dislodge associated macroinvertebrates. Where possible, collections were made from the two most abundant species of macrophyte at each site. Treatment of samples The macroinvertebrates (>500 lm) were separated from the substrates using 500 lm mesh sieves followed by hand picking and were stored in plastic jars in 7% formalin solution for a maximum of 5 days before identification. Invertebrates were identified to species level where possible. The
139
Figure 1. Map of sampling sites on the River Nile from Aswan to Al-Kanater Barrage in Cairo.
main references used for identification of the annelids were: Brinkhurst (1966) Brinkhurst & Jamison (1971) and Hussein et al. (1988). Mollusca: Walker (1959), Soliman (1972), Abdel Aal (1979), Brown (1980), Flemming (1983), Brown et al. (1984) and Ali (1989) and Ibrahim et al. (1999). Insect larvae and nymphs: Day (1956). Hydra vulgaris was identified using Ewer (1948), Smith (1959) and Campbell (1983, 1987, 1989).
Trichoptera were only identified as an order which underestimates the total taxon diversity to some extent although Trichoptera were not common. Chironomidae larvae and pupae were also recorded as a single taxon although there are several species which have been identified from collections of pupal exuviae (pers.com: Dr. L. Ruse (Environment Agency, Ecology Technical Team, Reading, UK).
140 Table 1. Location and nature of sampling sites on the River Nile from Aswan to the Al-Kanater Barrage in Cairo Site no
Key feature
Location
Distance from Aswan High Dam/km
1
Reference site
Aswan
20
2
Down stream of effluent from Kema
Aswan
25
3
factory for fertilisers and chemicals Up stream of sugar factory effluent
Armant
200
4
Down stream of sugar factory effluent
Armant
205
5
Tourist city
Luxor
220
6
Small city
Naja Hammady
340
7
Major city
Sohag
450
8
Major city
Assuit
620
9
Up stream of organic effluents
Minia
780
10 11
Down stream of organic effluents Up stream of industrial pollution
Minia Helwan
782 950
12
Down stream of industrial pollution
Helwan
13
Up stream of thermal pollution
Shoubra El-Kheima
1020
14
Down stream of thermal pollution
Shoubra El-Kheima
1025
15
End of main river before delta
Al-Kanater El- Khayria
1035
960
Results and discussion
Evaluation of sampling methods
Numbers of samples
There was considerable difference in the taxa collected per sample (Tables 2–4). The average number of taxa collected per sample from the banks by each method indicates that the ASS were by far most efficient with 7.2, followed by macrophytes with 3.4 and only 2.4 for the grab samples. These differences were found to be highly significant (p
