Study of Seasonal Changes in Chlorophyll a Concentration in the Water of Chahnimeh Reservoirs in Sistan

Chlorophyll a is the main pigment of photosynthesis in water ecosystems. Measuring Chlorophyll a can indicate its biomass which is the real visible indicator for trophic level in water ecosystems. The objective of this study was to study the seasonal changes in chlorophyll a concentration in the water of Chahnimeh reservoirs in Sistan. The samples were collected from water of Chahnimeh reservoirs during four seasons, from March to October 2010. EC and pH of the samples were measured at the time of collecting the samples. In order to measure chlorophyll a, the samples were extracted and the absorption rate of the extract in different wavelengths was measured by a spectrophotometer model Unico 2100/visible/Uv visible according to standard method ASTM 8012. Then, concentration of chlorophyll a was calculated using the standard equation.     The range of mean pH and EC were obtained as 8.72-8.87 and 540-579 (μs/cm) respectively in the studied stations. The highest seasonal mean of chlorophyll a was obtained in summer in Chahnimeh 3 (2.17± 0.32 μg/L) and the lowest seasonal means of chlorophyll a were obtained in winter n in Chahnimeh 1 and 2 (0.82± 0.28 μg/L). The results of ANOVA test showed the statistical differences between the mean of chlorophyll a concentration in spring and summer seasons and the mean of chlorophyll a concentrations in winter and autumn (p<0.05). According to the Chlorophyll a concentration obtained and its comparison with EPA standard, it can be concluded that Chahnimeh reservoirs can not be classified in eutrophic lake groups of and they are oligotrophic reservoirs.