Ecological Responses of Macroinvertebrates to an In-Stream Ecosystem Restoration Technique in a Tropical Stream in Eastern Uganda

Abstract

A field experiment was conducted to examine the ecological responses of macroinvertebrates to an in-stream ecosystem restoration technique called woody debris introduced in a stream in different arrangements to show how they (woody debris) affected the macroinvertebrate ecology, specifically assemblage composition and biometrics in River Nabongo. The experiment was carried out in two heterogeneous stream environments i.e., i) in a riffle found in the middle reaches of the river at a higher altitude and ii) a pool in the lower altitude and reaches of the river. Each of these two treatments had a control plot for comparison purposes. Four macroinvertebrate sampling campaigns were launched in experimental sites from September 2019 to April 2021. All restoration structures had more macroinvertebrates than control and pre-treatment sites. The introduction of simple structures at the riffle site led to an increase in collector-filterers from 9-128 individuals, while at the pool site all the structures increased macroinvertebrates by 1151 individuals. Taxon richness was highest in the complex plot with 14±0.41 which significantly differed from the rest of the sampling plots at P<0.05. The relative abundance of taxa at the pool site varied significantly from one sampling plot to another at P<0.05 with the highest mean abundance registered in complex and simple structures having 61.3±0.10 and 23.5±0.11 respectively. It was concluded that complex woody debris structures increase the diversity, abundance and richness of aquatic macroinvertebrates by providing hard substrates for colonization by algae and microorganisms on which macroinvertebrates feed. We recommended that other researchers should study the impact of other in-stream ecosystem restoration techniques such as floating islands, constructed wetlands, D-deflectors, a comparison of which with restored woody debris will enable ecologists to choose the most suitable technique to apply at different stream points.