Title: Comparative assessment of biotic indices for assessing water quality and habitat integrity
Author: Roland Prieler
Supervising Institution: IHE Delft - Institute for Water Education
Year: 2019
Abstract:
To maintain a good ecological status of wetlands and rivers is of major concern due to the high diversity of ecosystem services they provide. Especially in remote areas where people rely on natural waterbodies for drinking water, it is important to maintain a high water quality. Increasing anthropogenic pressures such as hydropower production and intensified agriculture, however, cause a major threat to natural waters. The aim of this study was to compare the performance of two biotic indices and metabarcoding for assessing water quality and habitat integrity. Further, it was assessed whether land use or flow interruption cause a higher impact on macroinvertebrate and dragonfly assemblages. This case study was conducted in the Kafue Flats, in Zambia. Two hydropower dams enclose this approximately 6500 km² covering river floodplain which possesses major ecological and economical value. The biotic indices used are the Zambian Invertebrate Scoring System (ZISS) and the Dragonfly Biotic Index (DBI). The ZISS is based on macroinvertebrate families and their specific sensitivity to water quality. The DBI is based on adult dragonfly species, it considers their specific sensitivity, geographic distribution and their threat status to assess the habitat integrity of a site. To determine whether land use or flow interruption possesses a higher influence on taxa richness, water quality parameter and environmental variable were measured at each sampling site. In total eight sites were sampled, four of them were sampled in three consecutive sampling trips. Dissolved oxygen (DO) concentration was found to follow a strong increasing trend for the first 45 kilometres after the dam, ranging from 1.03 mg/l to 5.90 mg/l in the main channel. The same pattern was found for temperature, with a range from 20.40 °C to 24.40 °C along the same stretch. DO saturation, instream human activities, distance to the dam and sampling month were found to have the highest effect on macroinvertebrate richness. While the ZISS score followed the same trend as DO concentration, there was no difference observed for the ASPT (Average Score Per Taxon). However, measured water quality parameter showed an increasing trend along the downstream gradient. Hence, it is assumed that the ZISS is not able to properly reflect water quality in this large flood plain river. Even though the DBI site score was fluctuating due to low species richness it was found that the DBI is more sensitive to activities in the surrounding area thus reflecting the habitat integrity of a site. There was no significant correlation found between ZISS and DBI metrics.