Analysis of environmental factors determining the abundance and diversity of macroinvertebrate taxa in natural wetlands of Southwest Ethiopia

Abstract

In Ethiopia, wetland resources play a vital role in the lives of adjacent communities by helping them to achieve food security and livelihoods. However, many wetlands throughout the country are facing degradation as high population growth rate increases the need for more fertile agricultural land. Lack of awareness and logistic constraints are important reasons for the weak consideration of wetland ecosystems by the country's development planners. In this paper, we set out to develop methods for predicting species–environment relationships. Decision tree models and Canonical Correspondence Analysis (CCA) were used to identify factors influencing macroinvertebrate community structure in natural wetlands of Southwest Ethiopia. The models were based on a dataset of 109 samples collected from 57 sites located in eight different wetlands. Sixteen macroinvertebrate taxa were selected based on their frequency of occurrence to determine the status of the wetlands. It was found that Corixidae, Baetidae and Hydrophilidae had the highest predictive model performance. This indicates that these taxa have clear requirements regarding their environmental conditions. The low Kappa value combined with the high number of Correctly Classified Instances of Chironomidae may be related to their high frequency of occurrence, so that their presence is of little predictive power. This was also further illustrated by the Canonical Correspondence Analysis (CCA) where the family of Chironomidae, common at nearly every sampling station in the wetlands, was plotted in the centre of the CCA axis. Vegetation cover, water depth, and conductivity were the most important variables determining the presence or absence of macroinvertebrate taxa. These variables were selected in more than 80% of the classification tree models and played a critical role in the ordination analyses. The sensitivity analysis, based on the regression tree models, also showed that vegetation cover and conductivity were affecting the abundance of some macroinvertebrate taxa. Information on habitat quality and environmental factors preserving a high diversity are essential to develop conservation and management programs for wetlands and their related ecosystem services in Ethiopia, where wetland resources are being lost at a high rate, and continue to be at high risk due to expansion of agricultural and other development activities.