The effect of water quality on the distribution of macro-benthic fauna in Western Lagoon and Timsah Lake, Egypt.I

Abstract

Macro-benthic fauna are considered the good bio-indicators for the environmental changes of any aquatic ecosystems. Samples of macro-benthos, sediments and surface water were collected from 13 stations representing different conditions in the Western Lagoon (10 stations) and Timsah Lake (3 stations) from autumn 2014 to summer 2015. Macro-benthic density and diversity in Timsah Lake were higher than those in the Western Lagoon; the density at Timsah Lake encompassed 167,649 individual/m2 representing 42 species from the total of 46 species recorded in the investigated area. While species density in the Western Lagoon constituted 12,008 individual/m2 presenting only 16 species. Winter recorded the highest density (74,854individual/m2); the highest dominance (CDI=0.858) and the lowest Equitability (0.293) due to the dominance of the opportunistic species. Spring harvested both the highest diversity (28 species) and species richness (SR=2.917). While autumn and summer procured both the lowest density and diversity (34,021 and 29,544individual/m2 and 23 and 25 species respectively). The equitability index (E′) showed its highest values within the Western Lagoon (>0.90) owing to the species poorness relative to Timsah Lake. The water quality data showed that the Western Lagoon and Timsah Lake had significant high oxygen influx in spring (11.00 and 9.35mg/l, respectively) and oxygen depletion in summer (1.00 and 3.00mg/l, respectively). Reactive phosphorus and ammonia in the Western Lagoon exceeded the world averages. Timsah Lake sediments were highly affected by the sediment drifts from the Western Lagoon. The highest influx of the fine sediment group (FSG) was estimated during spring with an average of 62.77% and 61.18% in Timsah Lake and Western Lagoon, respectively. Total organic matter (TOM) in Western Lagoon recorded the highest average of 17.05% in spring accompanied with the high biological productivities.