Invertebrate monitoring in Ghana

ocP/vculrrBTo/85.7 INVERTEBMTE MONITORING IN GHANA bY J. samman original : Engljsh 206 /vcu lTLcl4. s Srrnrrna r), 1. Introduction The rnstituE of Aquatic 84ology has been involved in the monitoring of macro-invertebrates in five y'ivers of the oCP area in Ghana. Conscious of the fact that this is the rdnth anniversary year of the oCp, the present report has been expanded to Mghlight some of the imporEant earlier findings in the monitoring. It is hoped that in 19'35, -with the assistance of the University of Salford, all the data c{lected since the monitoring commenced will be pub 1 ished. 2. Abiotic Factors Of all the abiotic factors recorded regularly in the rivers, river heighE and turbiditv showed much variation in a year. These factors appeared Eo conErol the populations of some species of invertebrates ("g. the Micro- crustacea and Caenidae) in the rivers. There \das a low rainfull in the Volta Basin area in l9g2/83. The river levels in all the rivers in Ghana hrere, therefore, low in the dry season as compared with the records of the previous years. 3. Invertebrate Fauna 3.1. Untreated rivers River pru (site 20) and River Asukawkaw (zz; "rr"ared to havesimilar ecological characters mainly because the rivers run through the semi-forest zones. Analysis of the data from 1980 to 1984 shows EhaE the predominant organisms are the Baetidae, caenidae, Hydropsychidae, Chironomini and the orthocladinae. Fluctuations in the numbers of some groups of Epheme- roptera do, however, occur. For example the canidae populations tended to be highest in rhe dry season (in Ehe monEh of Aprir) in each year. -2- The 1982/1983 drought appeared to reduce the population of some invertebrates (eg the Baetidae. caenidae, the Hydracarina). By the end of 1984, however' most of the orgarrisms had recovered from the effect of the possible ecological changes that night have been caused by the drought. 3.2. Black Volta TreaEed Rivers (Effects of remephos ) Sampling and larviciding on tha Black Volta 1974. Sampling was suspended in 1981 becuuse of the work at the sampling site.Sampling resumed in 1984. of 1984 show that no taxon has been elimin&teo. I^Ihite Volta commenced at the end of road bridge construction Records until 1981 and Sampling on the l{hite Volta was also suspended in 1981 because of the destruction of the site due to the damage to rhe road bridge at the site. Sampling also resumed in 1983. There i{as muph f lucttration in the numbers of organisms collected from the drift and Surber samples. It was, therefore difficult to identify the overall effect of temephos on any of the taxa. River Oti There was 1B months pre-treatment data on Oti. High mortalities occur among the invertebrafes (I"licrocrustacea, Chaoboridae, Baetidae, Lep- tophlebiidae, OdonaEa' Dytiscidae and some chironomid larvae) during larvi- ciding. Records unEil 1984 show that no taxon has been eliminated. ft appeared, however, that the numbers of Odonata population have been reduced.