Field survey and analysis of influence of suspended sediment on algae growth

A field survey was carried out in Neijiang that is an oxbow lake located within the Zhenjiang-Yangzhou segment in the lower reach of Yangtze River.Sediment concentrations,water transparency,underwater light intensity,algae species and biomass in the oxbow lake were monitored periodically.The observed data were analyzed.Results show that fine suspended particulate matters with the granular size less than 75 μm can constitute more than 80% of the total suspended sediment load in the lake; among which,clay grains account for 20%-50% of the fine suspended sediment.The mean values of sediment concentration in the lake are 40mg/L and 70mg/L for low and high water period,respectively.The gross algae biomass is basically within 100×10⁴ cell/L and dominated by green algae species.The light attenuation resulting from the suspended sediment load in the lake obeys the exponential law,and the relationship of green algae biomass and sediment concentration is also exponential.The diffuse attenuation coefficient appears to be linearly correlated to the sediment concentration.We thus conclude that the suspended sediment can inhibit the algae reproduction process through indirectly declining the underwater light intensity.Such an inhibition can be quantified by the relationship of algae cell density and sediment concentration.