Evaluation of multi-assemblage metrics and temperate indices as indicators of human impact in Lake Ziway, Ethiopia

Abstract

Lake bioassessment is routinely done using one biological community such as macro-invertebrates, diatoms, macrophytes or fish. The
use of at least two assemblages has been suggested as they are believed to be more robust indicators, because each community responds differently to potential stressors in waters. This study aimed to use macroinvertebrate and diatom assemblages to identify metrics and temperate indices that could discriminate between reference and impacted sites of the littoral zone of Lake Ziway, Ethiopia. The Lake Habitat Quality Assessment (LHQA) method was used to categorize the sites in the littoral zone of the lake. Lake water, macroinvertebrate, and diatom samples were collected from 3 reference and 6  impacted sites between September 2015 and April 2016 with standard methods and following the Ontario Benthos Biomonitoring Protocol. A total of 34 macroinvertebrate taxa and 39 diatom species were recorded. 32 macroinvertebrate and 18 diatom indices were tested for their ability to discriminate between the reference, intermediate and multiple-stressed sites using correlations between metrics, similarity values with SIMPER and boxplots overlaps. Further, correlation of the metrics with physico-chemical parameters extracted metrics and indices with high discrimination efficiency
(≥3). The indices remaining were 5 macroinvertebrate (NT, PTI, PETI, PDT and CLI) and 4 diatom (CEE, PTV, TDI, and IBD) indicators which clearly discriminated between the impacted (intermediate and multiple stressors) and reference sites, but not within the  impacted sites, in the lake. These data can also possibly serve as core metrics for multi-assemblage index development for this shallow, tropical lake.

Key words/phrases: Diatom, Discriminatory efficiency, Lake bioassessment, Macroinvertebrate, Multi-assemblage, Omnidia, SIMPER