Research On Phosphorus Environment Process And Its Influence Factors In Poyang Lake Basin

The migration,accumulation and distribution of anthropogenic phosphorus(P)import into the watershed are important factors affecting ecosystem health and security.With the increasingly prominent conflicts between economic and social development and the environment in the Poyang Lake Economic Zone,clarifying the process and mechanism of the “human-lake relationship” in the P cycle is of great significance to the understanding and evaluation of the evolution and development of aquatic environment in the Poyang Lake.It is also the key to protect the sustainable and healthy development of the Poyang Lake ecological environment.However,the quantitative response relationship of P emission-P migration and transformationriverine P export has not yet been fully established.Also,the trend of P pressure in the terrestrial system and aquatic ecosystem is not clear in the Poyang Lake basin.Furthermore,the characteristics of P transport have not been analyzed to reveal the response mechanism between of anthropogenic P emission-P legacy-P export at the watershed scale in the Poyang Lake basin.No study was conducted to reveal the characteristics of P distribution and accumulation among different medium during the development and evolution in terms of P balance in Poyang Lake.Particularly,how changes in the river-lake relationship regulating the occurrence of P in sediments of Poyang Lake were not explored.This study focuses on the environment process of P source-transport of land systems-riverine P export-P retention in lake-P export lake in the Poyang Lake basin.The watershed P environment process and its distribution among different medium were revealed from the macro-scale and micro-scale.The main conclusions were as follows:(1)Human activities are the main source of P in the environment,the intensification of anthropogenic nitrogen(N)and P inputs profoundly affects water environmental quality.Hence it is pivotal to clarify the response relationship between riverine TN/TP export and anthropogenic N/P inputs to provide strategies guidance in N/P management.Based on the variation of NANI(net anthropogenic N inputs)/NAPI in the Raohe basin from 1990 to 2018,we constructed the response relationship between NANI/NAPI and the riverine TN/TP export fluxes,which successfully predicted N and P export at the basin scale.We found N export ratio(ratio of TN export to NANI)increased with slight fluctuation and was mainly affected by the combined effects of Nfer and Ndep etc.,while the decrease of P export ratio(ratio of TP export to NAPI)was mainly due to intensive retention effect of the soil and sediment induced by anthropogenic influence to P transportation process.These results indicate that the downstream aquatic systems take a high risk of increasing N load pressure and the basin systems suffer a danger from rising P load pressure.Therefore,it is recommended to concentrate more on downstream aquatic systems during the N management strategy implementation and pay closer attention to the whereabouts of P in the basin system.(2)The watershed P retention and buffering is an important pivot for regulating P pressure and impact in aquatic ecosystems,and land use is a key factor in its regulation.However,the response mechanism of buffer capacity to land use changes has not yet been clarified.Based on the variation of watershed P buffering capacity in the Poyang Lake basin from 1990 to 2019,we explored the mechanism of the response relationship between land use and watershed P buffering capacity along with the quantified watershed retention P threshold,wetland P removal and cultivated land P loss.This study shown that the watershed P buffering capacity showed a downward trend,and the SBI decreased more dramatically in the Poyang Lake basin,and it is significantly affected by land-use types under a amount of NAPI.The decreases in agricultural land,grassland,and wetlands and artificial land increase explained the66.9% decrease of watershed P buffering capacity before reached the P retention threshold.The interpretation of land use for watershed P buffering capacity was decreased when watershed P retention exceeded threshold.Decreased in watershed P buffering capacity was closely related to the increased of P loss in the landscapes(cultivated land),and wetland P removal provides an optimized direction for restoring the watershed P buffering capacity.(3)The changes of P balance and the fate of P in lakes play a significant role in lake aquatic ecosystems.In this study,the dynamics of P balance and legacy were used to reveal the influence of lake’s evolution on change of the P balance steady-state,and to analyze the regulation of endogenous cycle on P from 1990 to2019 in the Poyang Lake.This study found that the annual P legacy showed a downward trend in Poyang Lake.The accumulation rate of P legacy was dramatically different before and after 2005.The first transition in the P balance steady-state of Poyang Lake in 2005,and the steady-state of P balance was relatively fragile after this transition,a cliff-like decline in the P legacy rate was observed after 2010.The P balance steady-state had undergone two transitions in 2011 and 2014,and the interval between the transitions was shorter.The sediments contributed mainly to net P sinks and the TP buries in sediments increased with the increase of TP in Poyang Lake,before the transition of P balance steady-state in 2010.We infer that the bioavailability of P decreased significantly and the TP buries decreased significantly in sediments after the third(2014)transition of P balance steady-state in the Poyang Lake,and the sediments become the P source for water environment.(4)The hydrodynamic and hydrological situation of have undergone great changes in the Poyang Lake,due to the change of river-lake relationship in recently.Result in new characteristics of the change trend of P occurrence in sediments.Based on the differences in the distribution of P existing forms in sediments at distinct elevations in Poyang Lake,this study explored the response mechanism of the distribution of P species in sediments to changes in river-lake relationship,with the flushing transition of Poyang Lake and the change of clear sediment exposure time taking into consideration.This study found that the more extraction rate of TOP in the higher elevation of the sediments.The TP buries of sediments decline with scour intension due to the impact of river-lake relationship change,and the Fe/Al-P and Ex-P accumulation weaken in the decrease of sediment particles adsorption capacity.The increase of LOP and MLPo cumulative burial were related to remain time of water prolonged during wet season in the impact of river-lake relationship change.The change of river-lake relationship caused sediment exposure time vary,the continental beach sediments longer exposure time,the OP increased while the LOP decreased,and the IP decreased but the EX-P and Ca-P increase.