The Influence Of Omnivorous Fish On The Resource Competition Between Benthic And Planktonic Algae Under The Background Of Climate Warming

With the intensification of global environmental problems caused by global warming,the impact of elevating water temperature caused by global warming on shallow water ecosystem is also increasingly significant,and the expansion of omnivorous fish is also likely to cause water ecological environment problems.The outcomes of benthic algae and planktonic algae competition for light and nutrients resources determine the key characteristics of shallow aquatic ecosystems.In shallow aquatic ecosystems lacking macrophytes,the competition is influenced by water temperature and omnivorous fish.Mesocosm systems of climate warming,crucian carp and their combined action were constructed to study the effects of climate warming and crucian carp(Carassius auratus)on the competition for light and nutrient between benthic and planktonic algae.Planktonic algae biomass chlorophyll a(Chla),benthic algae biomass chlorophyll a(Chla),total nitrogen(TN),total dissolved nitrogen(TDN),total phosphorus(TP),total dissolved phosphorus(TDP),total suspended solids(TSS),transparency(SD),light attenuation and dissolved oxygen(DO)in each system and the controls were measured and compared.The main results were:(1)The elevated water temperature increased the biomass of planktonic algae(Chla)by 24.8%,and decreased the biomass of benthic algae(Chla)by 43.3%.In addition,the TN,TDN,TP and TDP were increased by 18.5%,18.4%,43.8% and 41.7% in the elevated water temperature treatments as compared with controls.The elevated water temperature also increased the TSS by 44.4%,but decreased the light intensity and SD by 36.7% and 23.9%.These results showed that the climate warming increases the nutrient concentrations,promotes the growth of planktonic algae,enhances the eutrophication,reduces the SD and light intensity limiting the benthic algae growth.Thus,the climate warming is conducive to the deterioration of water quality.(2)Crucian carp increased the Chla of planktonic algae biomass,TN,TDN,TP,TDP and TSS by 73.4%,20.4%,18.4%,50.0%,50.0% and 100.7% in the water body.However,the Chla of benthic algae biomass,DO,SD and light intensity of sediment surface were reduced by 36.7%,13.4%,29.8% and 35.6%.The results showed that the crucian carp increased nutrient concentrations,which is beneficial to planktonic algae growth and unfavorable to the benthic algae growth,aggravating the eutrophication.(3)Under the background climate warming,the crucian carp increased the planktonic algae Chla by 77.1% and TN,TDN,TP,TDP and TSS by 25.9%,24.5%,56.3%,55.8% and104.4%,but decreased benthic algae Chla by 57.9%.The light intensity on sediment surface and SD were decreased by 45.9% and 31.4%.The results showed that crucian carp are more conducive to the growth of phytoplankton,enhancing the eutrophication and deteriorating water quality under the background climate warming.