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Abstract
This study is highly important in order to trace and evaluate the fundamental change that has taken place in Manzala Lake, Egypt the subject of present study, after the construction of new Boughaz El-Gamil and dredging of El-Salam canal. Manzala Lake is the largest of five Egyptian Delta lakes. It has an original area of about 904,785 km² and is located in the northeastern quadrant of the delta. Two main goals of community ecology are to recognize patterns in species composition and to understand the processes affecting those patterns. This study aims to identify spatial and temporal patterns of macroinvertebrate composition between lotic and lentic waters and to asses the conditions of macroinvertebrate community in relation to physico-chemical condition in Manzala Lake. To address the goal of this study, macroinvertebrate samples and associated environmental data were collected from four sites (Ashtum El-Gamil, El-Boghdady, Bahr El-Baquar and El-Matariya). Each site divided into two different stations representing different water ecosystems (lotic and lentic) and habitats, except El-Matariya site has (lotic) water ecosystem only between January 2003 and December 2003. Taxonomic key to aquatic macroinvertebrate; diagnosis based on field and ecological observations were constructed after conducting this study as well as diagnosis with pictured keys and coloured photographs were given to the adult and immature stages of the collected aquatic macroinvertebrates. Surveying all lotic and lentic stations revealed the existence of 47 species of aquatic macroinvertebrates species belonging to 44 genera and 30 families of 6 classes. The communities were dominated by aquatic insects, about 74.47% of all representatives. Lentic taxa encountered in the study area are more frequent than the lotic one. Seven biological metrics were calculated from the macroinvertebrate data. Water samples were picked up from the four sites and analyzed monthly during the investigation period to determine the most important physical and chemical properties. The seasonal abundance, biotic metrics and physicochemical parameters in the four sites were compared by using paired t-test, one-way ANOVA and cluster analysis. Correlation analysis indicated that spatial change of the macroinvertebrate community in Manzala Lake was related to the environmental factors. An assessment of water quality indicates that it ranges from fair, fairly poor & very poor. In the field, a multitude of species can be exposed to numerous toxicants; thus, the sensitivity of individual species to particular toxicants must be known to predict effects and to analyze changes in species composition. The field study was conducted to determine the concentrations of fourteen heavy metals in water and biota samples. The concentrations of metals in the soft tissue of both bivalve; Cerastoderma glaucum and insect; Enchrous testaceus from four stations of Manzala Lake were determined by digestion of the whole body tissue in acid and determined using Plasma Optical Emission-Mass Spectrometer (POEMS III), Desert Research Center, Cairo, Egypt. C. glaucum and E. testaceus were used as test animals for ecotoxicological research as they were the widespread species in the lake. Moreover, laboratory studies were conducted to evaluate Zn, Cd and Pb toxicity in C. glaucum and E. testaceus in two ways. In the first method, the sub-chronic toxicity test was run for seven days using different concentrations (1, 5, 10 mg l-1). More marginal concentrations and time effects (LC10, LC90, LT10 and LT90) were also estimated for metals using probit analysis. In the second method, histopathological response to metals was studied using the midgut. Accumulations of some metals in C. glaucum differed by different seasons in the same station. Heavy metals values in water and biota tissue samples displayed significant variations (P < 0.05) with respect to different seasons and sites. There was significant difference between the bioaccumulation of metals in C. glaucum and E. testaceus tissues. Correlation analysis showed a significant relationship between bioaccumulation of metals in biotic tissues and physico-chemical parameters of each station. The LC50 for heavy metals decreased with increasing time of exposure. Heavy metals caused noticeable alternation in histological architecture of the epithelium midgut, which was represented by hyDROPic degeneration of columnar epithelial cell, increasing the number of goblet cells, increasing the number of Cd-containing granules and focal necrosis that could be used for monitoring environmental pollution.