Title: Influence of Application of Agrochemicals on the Benthic Macroinvertebrate Species Diversity and Abundance in Ahero Irrigation Scheme, Kisumu County, Kenya
Authors: Mr. Walter Abwao Akeyo , Dr. Paul Otieno Abuom (PhD.) , Dr. Albert Elim Long'ora (PhD.)
Volume: 9
Issue: 4
Pages: 55-79
Publication Date: 2025/04/28
Abstract:
Irrigated rice fields are considered temporary wetland agro-ecosystems managed with variable degree of intensity. They are dynamic environments with high biological diversity compared to other agro-ecosystems and are highly disturbed with routine rice farming practices such as ploughing, rotavation, puddling and application of agrochemicals. There is little information on the influence of these practices on benthic macroinvertebrates in lentic agro-ecosystems such as rice fields. Therefore, the main objective of this study was to establish the influence of application of agrochemicals on the benthic macro-invertebrate species abundance and diversity in Ahero Irrigation Scheme. The study adopted descriptive longitudinal research design. The benthic macroinvertebrate community were sampled using Ekman grab, washed through a 1 mm mesh sieve, fixed in 5% buffered formaldehyde, then sorted, identified and counted using a dissecting stereo microscope. Results indicated that total mean abundance for benthic macroinvertebrates varied significantly (One-Way ANOVA at ? =0.05, F (5,114) = 100.440, p = 0.000) during various operations in the rice fields. The highest value (245.60±40.674) was recorded immediately after fertilizer application at flowering stage and the lowest value (81.3±15.26) was recorded during land preparation. There was a moderate effect size (Eta2 = 0.183 or after fertilizer application at flowering stage and the lowest mean value (81.3±15.26 18.3%) in plots A, B, D and G, as well as in plots K, L, M and N (Eta2 = 0.192 or 19.2%). A total of 22,414 individuals distributed among 29 taxa were recorded for the two crop cycles. The most abundant macroinvertebrate orders were Hemiptera 30% (5,632), Diptera 28% (5,199), Coleoptera 27% (5,158), Ephemeroptera 9% (1,630) and Odonata 6% (1,157). Order Hemiptera had the highest families (6) while Ephemeroptera had the least (2). Chironomidae (2186 individuals) were the most abundant family present in all the sites since they were capable of living in condition of total oxygen depletion for some hours and present greatest environmental plasticity, living where other more sensible organisms are absent. High biodiversity indices were observed with Shannon Diversity (H') values ranging between 3.059 to 3.16, Pielou's evenness (J) ranged between 0.910 to 0.937 and taxon richness (S) ranged between 27 to 29. The findings for benthic macro invertebrates will be used to monitor ecological integrity of the rice agroecosystems.