Effects of Long-Term Heavy Metal Contamination on Diversity of Terricolous Fungi and Nematodes in Egypt - A Case Study

Abstract

Internationally there is a gradual decline in availability of fresh water to be used for irrigation. As a consequence, the use of drain water for irrigating agricultural lands is on the rise particularly in urban areas of developing countries especially Egypt. On the other hand, there is increasing concern regarding the exceedance of statutory and advisory food standards for trace metals throughout the world. A study was undertaken to assess the long-term effect of irrigation with drain water on heavy metal content in soils and diversity of terricolous biota. An agroecosystem in Bahr El-Baqar area, south of Port Said, Egypt were selected where various cereals, vegetable and fodder crops have successfully been grown. During the period from September (2004) to February (2005), 25 soil profiles, 100 soil and 30 water samples were collected from cultivated soil and drain of Bahr El-Baqar. Soil heavy metals content (Zn, Pb, Cd, Co, Mn and Cu), gypsum, organic matter, total calcium carbonates, cations, anions, electric conductivity and pH were determined. Water samples has been subjected to various analyses including water temperature, pH, total soluble salts, electric conductivity, total nitrogen, total phosphate, heavy metals and organic loads (chemical oxygen demand and biological oxygen demand). For isolation and examination of total mycobiota, arbuscular-mycorrhizal fungi (AMF) and nematodes from rhizosphere soils, samples were collected from dominant plant species in the study area. Obtained data were subjected to multivariate analysis by using Canonical Correspondence Analysis to find out the relationship between biota and environmental variables. Results indicated that concentrations of heavy metals exceeded the maximum allowable limits while water analyses showed that organic load values are slightly increase in all examined samples and samples were not complying with the standard value given by law 48/1982 for ambient water quality in the drain. It was possible to encounter as many as 43 fungal species belonged to twenty-one genera from five sites in the agroecosystem in south Port Said. The results show that Zygomycota represented by six species (7.59% of the total isolate number), teleomorphic Ascomycota (3 species, 3.78%), anamorphic Ascomycota (31 species, 86.96%) and mitosporic fungi (3 species, 1.67%). The AM fungal spores obtained belonged to the three genera namely Acaulospora, Gigaspora, and Glomus and eight species. While family Glomeraceae accommodates the greatest range of species (6 species), the other family Gigasporaceae accommodate the lowest range (two species). Twelve species belonging to eight genera and six families of plant-parasitic nematodes were identified throughout the study. Total levels of heavy metals showed a trend relationship between metal concentration in soil and long term of irrigation assuming that there is a continuous deposition of heavy metals on the soils due the continuous use of Bahr El-Baqar drain in watering soil for many years in which both living and non-living components of ecosystem are hazardly affected. Detailed studies to minimize the quantity and improve the quality of wastewater discharged should be carried out for each industry. Research must take the objective of sustainability into consideration. Legislation sensible to environmental control should depend on a thorough knowledge of the existing situation and careful assessment of its likely impact on the development. On the other hand activation of law 4/1994, for the protection of environment in Egypt, is urgently needed.