Influence of zinc on periphyton Communities: laboratory interaction of Zinc and phosphate in River Garasou

Several studies based on laboratory experiments and field observations have reported high sensitivity of periphyton algae to selected environmental variables. However, very few studies have aimed to investigate complex interactions between these variables. The present study evaluate the long-term (24 day) influence of Zinc and Zinc combined with phosphate on productivity of algal periphyton communities. Periphyton communities developed from a relatively unpolluted water were exposed in indoor artificial streams with zinc concentration ( 1.2 mg.l-1) and 2 mg P.L-1 found at a polluted stream. The effects of zinc on community productivity were assessed by measuring biomass, ash-free dry mass (AFDM), chlorophyll-a. Results obtained from present study indicate that Zn alone cause a severe decrease in growth of the periphyton algae, but phosphate totally compensated for this Zn effect. Results indicated that an increase in P exposure causes, an increase of dry mass, AFDM and chlorophyll a. Furthermore the uptake of Zn will increase in Zn+P treatment, leading to higher concentration in the periphyton algae. This study implies that in systems rich in phosphorus, zinc exposure might not be a problem, but in systems with low phosphorus concentrations, net primary production might be affected.

Keywords:

Zinc , periphyton , phosphate , River Garasou , Kermanshah