Impacts of Water-Sediment Regulation Scheme on Chromophoric Dissolved Organic Matter in the Lower Yellow River

As a river with more than 3000 reservoirs in its watershed,the Yellow River has been affected by dams not only on the sediment load,but also on the water quality.Water-sediment regulation scheme(WSRS),which has been carried out annually in the Yellow River since 2002,is a typical human activity affecting river water quality.Chromophoric dissolved organic matter(CDOM)in river is susceptible to changes in ecological and environmental conditions as well as human activities.Here,we report variations in dissolved organic carbon concentrations,compositions and sources of CDOM in time series samples in the lower Yellow River during WSRS.In addition,a parallel factor fluorescence analysis(PARAFAC)method is applied to identify different fluorescent components in water samples during WRSR,showing four major components including tryptophan-like component(C1),microbial humic-like component(C2),terrestrial humic-like component(C3)and tyrosine-like component(C4).In general,C1 increased after water regulation,while C2 and C3 increased after sediment regulation,indicating that the water and sediment released by the dam have different effects on CDOM compositions.Under the impacts of the dam,source of CDOM in the lower Yellow River is mainly autochthonous related to microbial activities,and is regulated by the terrestrial input during WSRS period.Sediment resuspension inhibits microbial activities and reduces the production of autochthonous CDOM.Overall,human activities especially WSRS,as exemplified here,significantly alter the quality and quantity of CDOM in the lower Yellow River,affecting CDOM dynamics and biogeochemical processes in the estuarine environment.

Significant impacts of artificial regulation on nutrient concentrations and transport in Huanghe River

Human perturbations such as dam regulation have led to significant changes in nutrient flux,structure,and spatiotemporal distribution through rivers and have greatly influenced coastal and estuarine ecological environments.Based on the data from 2001-2019,the impacts of the water-sediment regulation scheme(WSRS)in the Huanghe(Yellow)River on nutrient concentrations,forms,fluxes,and potential ecological effects on the Huanghe River estuary and Bohai Sea were analyzed.Nutrient concentrations and forms were significantly influenced by the different regulatory modes and were associated with hydrological and biogeochemical processes.The concentrations and forms of nutrients were strongly influenced by the riparian floodplains and scouring process of the downstream riverbed at the water draining stage,while they were influenced mainly by the mixing process in the Xiaolangdi Reservoir at the sediment desilting stage.Compared with those in non-WSRS years,the seasonal distributions of water discharge and nutrient fluxes in WSRS years significantly changed,with peaks occurring at least one month earlier than those in non-WSRS years.Nitrate(NO_(3)-N),phosphate(PO_4-P),and silicate(SiO_(3)-Si)fluxes during the WSRS,which were strongly controlled by water discharge at Lijin(the nearest hydrological station to the river mouth),accounted for more than 20%of the annual fluxes;these fluxes were more than 5-9 times greater than those during the same period in non-WSRS years.WSRS exacerbated nutrient imbalances and increased Pyrrophyta/Bacillariophyta ratios by 231%in the Huanghe River estuary,resulting in chlorophyll-a peaks in the Bohai Sea shifting from spring to autumn in the 20~(th)century to spring-summer in the 21^(st)century.

Using Rn-222 to Study Human-Regulated River Water-Sediment Input Event in the Estuary

The implementation of the water sediment regulation scheme(WSRS)is a typical example of artificially controlling land-source input.During WSRS,the water discharge of the Yellow River will increase significantly,and so will the input of terri-genous materials.In this study,we used a natural geochemical tracer 222Rn to quantify terrestrial inputs under the influence of the 2014 WSRS in the Yellow River Estuary.The results indicated that during WSRS the concentration of 222Rn in the estuary increased by about four times than in the period before WSRS.The high-level 222Rn plume disappeared quickly after WSRS,indicating that 222Rn has a very short‘memory effect’in the estuary.Based on the investigation conducted from 2015 to 2016,the concentration of 222Rn tended to be stable in the lower reaches of the Yellow River.During WSRS,the concentrations of 222Rn in the river water in-creased sharply at about 3–5 times greater than in the non-WSRS period.Based on the 222Rn mass balance model,the fluxes of 222Rn caused by submarine groundwater discharge(SGD)were estimated to be(3.5±1.7)×10^(3),(11±3.9)×10^(3),and(5.2±1.9)×10^(3)dpm m^(-2)d^(-1)in the periods before,during,and after WSRS,respectively.This finding indicated that SGD was the major source of 222Rn in the Yellow River Estuary,which can be significantly increased during WSRS.Furthermore,the SGD-associated nutrient fluxes were estimated to be 9.8×10^(3),2.5×102,and 1.1×10^(4)μmolm^(-2)d^(-1)for dissolved inorganic nitrogen,phosphorus,and silicon,respectively,during WSRS or about 2–40 times greater than during the non-WSRS period.