Effects Of Food Resource Availability And Hydrological Variation On Autochthonous And Allochthonous Carbon In The Irtysh River(Xinjiang)

Rivers are important bridges between the matter cycle and energy flow of land and ocean.Quantifying the food web structures and dynamics is a fundamental ecological research for the understanding of ecosystem structure and functioning,with implications for future management and rehabilitation of rivers.As the basic energy source of food web,carbon source is an important nutrient for biological growth,and also determines the structure and trophic relationship of food web.Xinjiang is an important region for the study of aquatic biodiversity in Northwest China.The rivers,lakes and reservoirs are rich in aquatic biological resources.However,there are few relevant studies in this area,especially for the systematic study of food webs.The Irtysh River is the second largest river in Xinjiang Province of China and the only Chinese river which ultimately flours into the Arctic Ocean.To study the structure of food web and the energy path,we characterized the availability of primary producers?epilithic algae and phytoplankton?and primary consumers?zooplankton and macrozoobenthos?.Meanwhile,we attempted to figure out potential effects of resource availability and flooding regime on food web trophodynamics and evaluatethe relative contributions of autochthonous and allochthonous production to aquatic consumers using the Bayesian stable isotope mixing model,and the response to resource availability and hydrological regime in the Irtysh River.The main results and conclusions were as follows:1.During the study period,the averaged cell density and biomass of epilithic algae in the Irtysh River were 914.19×10⁶ cell/m² and 1383.02 mg/m²,respectively.There were statistically significant differences in density and biomass at the three sampling seasons and river reaches?p<0.01?.The averaged cell density and biomass of phytoplankton were 0.40×10⁶ cell/L and 0.62 mg/L,respectively.The averaged biomass of zooplankton was 0.060 mg/L.There was significant differences in biomass at the three river reaches?p<0.05?.The averaged biomass of macrozoobenthos was 6.24 g/m².There was statistically significant differences in biomass at the three river reaches?p<0.01?.2.Pearson correlation analysis showed that the density of epilithic algae in the Irtysh River was correlated positively with total nitrogen.The biomass of epilithic algae was correlated positively with conductivity,total dissolved solids,total nitrogen and was significantly positively with salinity.The density of phytoplankton was correlated positively with ammonium.The biomass of phytoplankton was correlated positively with ammonium and significantly positively with water temperature,but significantly negatively with flow velocity.The biomass of zooplankton was correlated positively with ammonium.The biomass of macrozoobenthos was correlated negatively with water temperature and significantly negatively with transparency.3.The values of?¹³C in May,July and September varied from-31.99‰to-14.95‰,-29.11‰to-14.82‰,-28.22‰to-15.07‰,respectively.The values of?¹⁵N varied from 4.07‰to 13.04‰,1.54‰to 10.73‰,1.34‰to 11.16‰,respectively.?¹³C showed a great range in May than other months and the?¹⁵N was more enriched.?¹³C varied from-28.01‰to-28.01‰at the upper reach,-29.37‰to-15.07‰at the middle reach,and-28.76‰to-15.18‰at the lower reach.?¹⁵N varied from 1.61‰to 11.17‰at the upper reach,2.09‰to 10.55‰at the middle reach,and 1.34‰to 10.41‰at the lower reach.The upper reach had higher TPs and FCL.Among the five potential food sources?epilithic algae,aquatic plants,POM,terrestrial leaf and riparian plants?,there were significant differences for the?¹³C and?¹⁵N values?Kruskal-Wallis Analysis,p<0.001?.The averages of?¹³C and?¹⁵N values of the potential food resources were-22.62‰and 4.45‰,-14.95‰and4.83‰,-24.55‰and 4.99‰,-28.43‰and 1.99‰,-26.78‰and 8.37‰,respectively.4.The Bayesian stable isotope mixing model showed that terrestrial leaf was the dominant carbon sources to aquatic invertebrate during three sampling seasons.And fish fed on aquatic plants in May,but switched to riparian plants in July and September.Terrestrial leaf was the dominant carbon sources to aquatic invertebrate at the upper and lower reaches,but riparian plants dominated at the middle reach.Fish relied on aquatic plants at the upper reach,but switched to riparian plant at the middle and lower reaches.5.We divided the five potential food sources into autochthonous and allochthonous carbon,meanwhile,we assessed the proportional contribution of autochthonous?epilithic algae,aquatic plants and partial POM?and allochthonous carbon?riparian plants,terrestrial leaf and partial POM?to consumers.Aquatic invertebrates showed the reliance on riparian plant or terrestrial leaf?allochthonous?during three sampling seasons and at three river reaches.Fish relied on autochthonous production in May and at the upper reach but switched to allochthonous production in July,Septeber and at the middle and lower reaches.