Effects Of Omnivorous Fish On Competition Of Benthic-planktonic Algae Under Background Of Radiation Reduction

Radiation reduction is one of the main characteristics of climate change,which directly affects the primary productivity.In shallow waters,planktonic algae and benthic algae distribute in different habitats and compete asymmetrically for light and nutrients.The results of the competition determine the key characteristics of shallow aquatic ecosystem.In order to evaluate the effect of solar radiation reduction and omnivorous fish on the competition between planktonic algae and benthic algae,aquatic mesocosms were constructed.Treatment of control without shading,shading,and shading with crucian carp were designed.By measuring nitrogen and phosphorus,planktonic algal biomass and benthic algal biomass i.e.chlorophyll a,dissolved oxygen,total suspended solid in the mesocosms,the effects of solar radiation reduction and benthic omnivorous fish on the competition between plankton and benthic algae were studied.The results showed that:(1)The light intensity in the surface and bottom water were decreased by 33% and 39%respectively,and chlorophyll a of planktonic algae was reduced by 14.7% in the shading treatment as compared with the controls.While chlorophyll a of benthic algae was increased by 47.9% under shading conditions.The DO and SD was increased respectively by 8.7% and 8.1%,and the concentrations of TN and TP were increased by 30.0% and23.9%,respectively as compared with the control group.The results showed that solar radiation reduction increased nitrogen and phosphorus in water column,promoted the growth of benthic algae,and improved the transparency of water.Therefore,was not conducive to the growth of planktonic algae,but conducive to the competition of benthic algae under the condition of reduced radiation.(2)Under the shading condition,crucian carp significantly decreased the surface pH by2.5%,the bottom pH by 3.9%,SD by 24.9% and the bottom light intensity by 56.3%.The Chl a of planktonic algae and benthic algae were reduced by 25.6% and by 29.1%.And the concentrations of TP and TSS were increased by 49.6% and 64.0%,respectively.The TSI were increased by 3.3%.The results showed that omnivorous fish increased TSS and TP in water column,decreased SD in water,and reduced planktonic algae and benthic algae biomass under the condition of reduced radiation.Therefore,it was not conducive to the growth of algae by crucian carp under the condition of reduced radiation.(3)Under the conditions of combined shading and crucian carp,the light intensity in the surface and bottom water were decreased by 39.4% and 60.6% respectively,and the bottom pH in water were decreased significantly by 2.9%,planktonic algae Chl a by36.5% and SD by 18.3%.The concentrations of TN and TP increased by 49.4% and 96.5%,respectively,and the concentrations of TSS and TSI increased by 44.2% and 3.6%,respectively.However,there was no significant difference of DO concentration,SPC,the surface pH and Chl a of benthic algae between treatments.The results showed that the combined effect of solar radiation reduction and omnivorous fish reduced the light intensity significantly in water,decreased the planktonic algae Chl a and SD,increased the content of TSS and TN and TP in water column,but had no significant effect on the benthic algae Chl a.Therefore,it was not conducive to the growth of planktonic algae under the conditions of combined solar radiation reduction and crucian carp.