The primary objective of this study was to make a deep investigation on the concentration of chlorophyll a and ash-free dry mass (AFDM) estimates for algae growing on stones in Urumqi River located in an arid region of northwest China. The study was conducted on three sites. A highly improved method for measuring primary productivity in situ was used to estimate the primary production of algae growing on rocks (or algae epilithic) deposited in surface water. The results showed a low biomass with mean chlorophyll a content that was estimated at 5.9 mg/m2in the Urumqi River. Of the three sites studied, the mean gross primary productivity of periphyton was 394.89 mgC/m2 day and AFDM 344.75 mg/m2. The analysis of correlation between chlorophyll a and altitude was found to be a curve of anti- hyperbola. Total phosphorus and chlorophyll a was in equilibrium with that between chlorophyll a and total nitrogen.
Key words: Epilithic algae, phytoplankton productivity, chlorophyll a, ash-free dry mass (AFDM).
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