Abstract
PHYTOGENIC mounds (nebkhas) formed by halophytes are widely distributed in coastal and desert environments. Such nebkhas provide loci for geochemical and biological activities that influence ecosystem processes and function. Seasonal variation in soil and bacterial properties were investigated within the nebkhas under the canopy of Halocnemum strobilaceum and in the surrounding unvegetated sites at salt marshes of Lake Manzala. The parameters measured include soil moisture, organic matter, total nitrogen and phosphorus, pH, electrical conductivity (EC), and bacterial community and enzyme characteristics. Enrichment ratios for soil salinity and nutrients were evaluated to indicate the salinity and fertility islands within nebkhas. Soil moisture content showed significant differences between the different seasons with the highest value in winter (16.55%) at unvegetated control site. Soil electrical conductivity, total nitrogen and phosphorus had their significantly higher values in nebkhas during autumn. The enrichment values for the measured soil parameters ranged from 0.31 to 4.09 in the four seasons which indicates a clear accumulation effect for soil nutrients and salts within the nebkhas under the canopy of H. strobilaceum. Bacterial abundance was consistently higher in nebkhas through all seasons. Eleven genera of bacteria belong to Firmicutes, Actinobacteria and proteobacteria phyla were recorded in nebkha and unvegetated sites. These genera varied in their occurrence between the two locations and the four seasons. It can be concluded that the formation of nebkhas by halophytic vegetation have noticeable effects on accumulation of soil salinity and fertility during different seasons that affect bacterial abundance and activity in coastal environment.