Using the Biological Condition Gradient Model as a Bioassessment Framework to Support Rehabilitation and Restoration of the Upper Tana River Watershed in Kenya

George G Ndiritu,Edward L Njagi,David Courtemanch,Taita Terer,Laban Njoroge,Dickens Odeny,Joseph Gathua,Veronica M Muiruri,Peter Njoroge,Mary Muchane,Gilbert Kosgei,Peris W Kamau,Patrick K Malonza

doi:10.3389/fenvs.2021.671051

Abstract

The biological condition gradient (BCG), a scientific framework that describes the change in ecosystem characteristics in response to human-induced levels of stressors, was modified and used to characterize watershed habitats in the Upper Tana River watershed, Kenya. The inbuilt utilities of BCG, including its simplicity, versatility, and its robust nature, allowed its use by seven taxonomic groups of macroinvertebrates, diatoms, fish, herpetofauna (amphibians and reptiles), plants, macrofungi, and birds to assess and monitor landscape conditions in both terrestrial and aquatic habitats. The biological data were described using taxa abundance distribution measures followed by multivariate analyses to determine their relationship with water or soil quality and thereafter assessment of taxa tolerant levels in response to environmental stress and disturbances. Preliminary findings reported that the taxonomic groups complemented each other, with each taxonomic group reliably assessing ecological conditions to a certain degree that supported assigning all 36 sampled sites into BCG tiers. The BCG models developed for all taxonomic groups assisted in the identification and selection of taxa indicating varying levels of landscape conditions. These taxa, referred to as flagship or indicator taxa, assist in simplifying the BCG model and, hence, are possible for use by parataxonomists or ordinary citizens to assess and monitor the ecological health of habitats under consideration. Furthermore, the capability of BCG models to assess landscape conditions shows how they can be used to identify important habitats for conservation, direct investment for restoration, and track progress.

Highlights

The development of a scientific-based environmental assessment and biomonitoring framework that is simple and robust enough for use by the general public remains a major limitation for sustainable management of ecosystems (Graham et al, 2004)
The initial biological condition gradient (BCG) metrics were developed based on aquatic taxonomic groups of fish, macroinvertebrates, and diatoms to support the objectives of restoring and maintaining the chemical, physical, and biological integrity of the USA’s water resources (Clean Water Act; CWA, 1972)
It was discovered during this exercise that there was a strong case that the BCG framework can be applied in terrestrial ecosystems using associated taxa such as birds, amphibians, macrofungi, and vegetation

Summary

Introduction

The development of a scientific-based environmental assessment and biomonitoring framework that is simple and robust enough for use by the general public remains a major limitation for sustainable management of ecosystems (Graham et al, 2004). The SS described the trophic state of a lake by classifying the ecological condition status along a disturbance response gradient due to pollution from human and natural influences Today, it has evolved into indices of biotic integrity (IBIs) that are based on indices including community structure, richness, dominance and abundances as measures of pollution effects (e.g., Wilhm and Dorris, 1966; Karr, 1981; Davis 1995; Hawkins, 2006), and multivariate indices that combine weighted effects of the variates to predict membership in different water quality classes (e.g., Davies et al, 2016). These ecosystem gradient models use undisturbed or pristine habitat conditions as a reference point against arrays of habitats or sites experiencing varying levels of disturbances and are validated by actual measurement of environment variables

Objectives

Methods

Results

Discussion

Conclusion