Effects Of Different Anthropogenic Disturbance On Carbon Sources Of River Benthic Food Webs

Research on the energy flow and nutrients cycle within food webs can provide important references for the study of the structure and function of river ecosystems.At present,rivers all over the world are affected by human disturbances to varying degrees.Whether human disturbances affect the food web pattern of rivers,such as the sources of carbon and the relative contribution of carbon sources to consumers,is still not well understood.In this study,the Xuerongzangbu Catchment and Jinshui Catchment of similar latitudes were taken as the research objects.The differences of the distal environmental factors i.e.land use,the proximate environmental factors such as water physical and chemical factors and riparian vegetation coverage,the stable carbon and nitrogen isotope values of food web components,and the contribution rate of food sources in the two catchments with different human disturbance intensity regions were analyzed.The influence mechanism of the distal environmental factors and the proximate environmental factors on the stable carbon and nitrogen isotope values of food web components and the contribution rate of food sources was studied.The main results are as follows:(1)Vegetation was the main type of land use in the Xuerongzangbu and Jinshui Catchments.The vegetation in the Xuerongzangbu Catchment was mainly composed of grassland,and the vegetation in the Jinshui Catchment was mainly composed of forest.Except for conductivity and turbidity,there were significant differences in the proximate environmental factors between the two catchments.The proportion of bare land in the severely disturbed area in the Xuerongzangbu Catchment was smaller than that in the lightly disturbed area,and the concentration of total nitrogen,ammonia nitrogen,total phosphorus and total organic carbon was higher than that in the lightly disturbed area.The proportion of urban and agricultural land in the severely disturbed area in the Jinshui Catchment was higher than that in the lightly disturbed area,and the concentration of nitrate nitrogen,ammonia nitrogen,total organic carbon and permanganate index was higher than that in the lightly disturbed area.In Xuerongzangbu and Jinshui Catchments,nitrogen and phosphorus nutrients(total nitrogen,nitrate nitrogen,ammonia nitrogen and total phosphorus),organic pollution index(total organic carbon and permanganate index),water temperature and turbidity were negatively correlated with vegetation area,and positively correlated with urban and agricultural land area.In the Xuerongzangbu Catchment,dissolved oxygen concentration was positively correlated with vegetation area,and negatively correlated with urban and bare land area.In the Jinshui Catchment,dissolved oxygen concentration and global horizontal irradiance were negatively correlated with vegetation area,and positively correlated with agricultural and urban land area.(2)The variation range of?¹³C of the basic food sources in the Xuerongzangbu and Jinshui Catchments were-28.96‰?-18.10‰and-32.94‰?-18.55‰,and the variation range of?¹⁵N were-9.51‰?12.65‰and-9.16‰?15.58‰,respectively.In the Xuerongzangbu Catchment,the?¹³C of most basic food sources between the lightly disturbed area and the severely disturbed area was similar,and the?¹⁵N of most basic food sources in the severely disturbed area was higher than that in the lightly disturbed area,but the difference was not significant.In the Jinshui Catchment,the?¹⁵N of most basic food sources in the lightly disturbed area was significantly lower than that in the highly disturbed area.The?¹³C of benthic algae in the Xuerongzangbu and Jinshui Catchments was positively correlated with water temperature,p H and total phosphorus,and negatively correlated with the flow velocity,and the?¹³C of macrophytes was positively correlated with water temperature.The?¹⁵N value of benthic algae and macrophytes was negatively correlated with annual accumulated temperature,global horizontal irradiance and vegetation area,and positively correlated with urban,agricultural and bare land areas.The variation range of?¹³C of the feeding functional groups in the Xuerongzangbu and Jinshui Catchments were-27.68‰?-22.11‰and-28.39‰?-17.43‰,and the variation range of?¹⁵N were 2.80‰?11.52‰and-2.61‰?12.95‰,respectively.Most of the feeding function group?¹³C between the lightly disturbed area and the severely disturbed area in the Xuerongzangbu and Jinshui Catchments was similar,and the feeding function group?¹⁵N in the lightly disturbed area was significantly lower than that in the severely disturbed area.In the Xuerongzangbu Catchment,only the predator?¹³C and benthic algae?¹³C values were significantly positively correlated.In the Jinshui Catchment,the correlation between the stable nitrogen isotopes of the feeding functional group and most of the basic food sources was significant.(3)River organic matter was the most important food source for each feeding function group in the Xuerongzangbu Catchment,and terrestrial carbon sources were the most important food source for each feeding function group in the Jinshui Catchment.There was no significant difference in the contribution rate of aquatic carbon source,river organic matter and terrestrial carbon source to the feeding functional groups between the lightly disturbed area and the severely disturbed area in the Xuerongzangbu and Jinshui Catchments.In the Xuerongzangbu Catchment,riparian vegetation coverage promoted the contribution of terrestrial carbon sources to predators.In the Jinshui Catchment,total nitrogen,annual accumulated temperature,global horizontal irradiance and urban land area promoted the contribution of aquatic carbon sources to the feeding function group,and water temperature,riparian vegetation coverage and vegetation area reduced the contribution of aquatic carbon sources to the feeding function group.Vegetation area promoted the contribution of river organic matter to the feeding function group,and urban and agricultural land area reduced the contribution ratio of river organic matter to the feeding function group.Water temperature and vegetation area promoted the contribution of terrestrial carbon sources to the feeding function group,and the urban land area reduced the contribution ratio of terrestrial carbon sources to the feeding function group.Except for collector-gathers in the Xuerongzangbu Catchment,allochthonous carbon was the main carbon source for the feeding functional groups of the two catchments.The changes of land use and environmental factors in Xuerongzangbu and Jinshui Catchments had significant bottom-up effects on the basic food sources and functional feeding groups?¹³C and?¹⁵N value,but had no significant effect on the contribution rate of each food source.This study will deepen the understanding of the impact of human disturbance on river food web structure and carbon source,and provide important scientific basis for river ecosystem restoration.