Applications of AnnAGNPS Model for Sediment and Nutrient Loadings for Funiu Mountain Area, China

The main goal of this study was to evaluate the performance of AnnAGNPS(Annualized AGricultural NonPoint Source)pollution model,in calculating runoff,sediment loading and nutrient loadings for Funiu Mountain area.Most of the model input parameters were sourced from Luanchuan Forest Ecology Station(LFES)in Funiu Mountain area.The data on 23 storms in 2018 was used to calibrate the model and the data on 33 storms in 2019 for validation.The whole evaluation consisted of determining the coefficient of determination(R^(2)),Nash-Sutcliffe coefficient of efficiency(E),and the percentage volume error(VE).Results showed that the runoff volumes were underpredicted by 5.0%with R^(2) of 0.93(P<0.05)during calibration and underpredicted by 5.3%with R^(2) of 0.90(P<0.05)during validation.But sediment loading was able to produce a moderate result.The model underpredicted the daily sediment loading by 15.1%with R^(2) of 0.63(P<0.05)during calibration and 13.5%with R^(2) of 0.66(P<0.05)during validation.Nitrogen loading was overpredicted by 20.3%with R^(2)=0.68(P<0.05),and phosphorus loading performance was slightly poor with R^(2)=0.65(P<0.05)during validation.In general,the model performed well in simulating runoff compared to sediment loading and nutrient loadings.

Growth and nutrient accumulation of Phragmites australis in relation to water level variation and nutrient loadings in a shallow lake

Shallow lake eutrophication is a global environmental issue. This study investigated the effects of water level variation and nutrient loadings on the growth and nutrient accumulation of Phragmites australis （reed） by field samplings in Baiyangdian Lake, the largest shallow lake of northern China. The field samplings were conducted in two sites of different nutrient loadings during the whole growth period of reeds, and three types of zones with different water depths were chosen for each site, including the terrestrial zone with water level below the ground, the ecotone zone with the water level varying from belowground to aboveground, and the submerged zone with water level above the ground. The result showed that reed growth was more limited by water level variation than nutrient loadings. The average stem lengths and diameters in terrestrial zones were about 26.3%-27.5% and 7.2%-12.0% higher than those in submerged zones, respectively. Similarly, the terrestrial status increased the aboveground biomass of reeds by 36.6%-51.8% compared with the submerged status. Both the nutrient concentrations and storages in the aboveground reeds were mainly influenced by the nutrient loadings in surface water and sediment rather than the water level variation of the reed growth environment, and the nutrient storages reached their maxima in late August or early September. It was observed that the maximum nitrogen storage occurred in the terrestrial zone with higher nutrient loadings, with the value of 74.5 g/m2. This study suggested that water level variation and nutrient loadings should be considered when using reeds to control and remediate eutrophication of shallow lakes.

Effects of Nitrogen Exponential Fertilization on Growth and Nutrient Concentration of Hydrangea macrophylla Seedlings

Slow growth rate restricts the development and growth of seedlings due to nutrients deficiency or nutrient imbalance.Exponential fertilization can enhance the internal nutrient reserves in seedlings at the nursery-stage and strengthen their resistance to adverse conditions.In this study,nitrogen requirements for producing Hydrangea macrophylla‘Hanatemari’that robust seedlings,nutrient dynamics,biomass and growth,was examined utilizing exponential fertilization.The potted seedlings were fertilized with urea under exponential regime at rates of 0.5,1.5 and 2.0 g nitrogen/plant(EF1,EF2,and EF3),respectively.In addition,an unfertilized group treated with equal volume of deionized water was used as control.The results showed that seedlings under 1.5 g N/plant(EF2)had the highest plant growth index and total biomass.The nutrient concentrations of different organs varied in different fertilization treatments.Based on the results of current study,it is concluded that 1.5 g N/plant(EF2)is suitable exponential fertilization treatment for the culture of hydrangea seedlings.Our treatments results showed that 2.0 g N/plant is not suitable for seedling culturing,because of serious nutrient toxicity.These findings will help to improve seedling quality and strengthen the production of H.macrophylla for plantation.

Coupling effects of hydrological characteristics and nutrient load in sediments on the trophic state of reservoirs

Currently,lakes and artificial reservoirs are increasingly threatened by eutrophication,which is the result of the combined action of many natural and anthropogenic factors.In the past,the effect of nutrient load on the trophic state of water bodies has attracted much attention,while few studies have addressed the effect of hydrological characteristics.Therefore,to reveal the coupling effects of hydrological characteristics and nutrient load in sediments on the trophic state of water bodies,this study collected relevant data from 36 lakes and reservoirs across China.Pearson correlation analysis showed that trophic level index was positively and significantly correlated with nutrient load in sediments and hydraulic retention time,while it was negatively correlated with mean depth and hydraulic load.The principal component analysis showed that the nutrient load was the first major component that influenced the trophic state of water bodies,followed by the mean depth and hydraulic retention time.Eutrophication was prone to occur in water bodies with mean depth less than 7 m and hydraulic retention time greater than 14 d,and the trophic level index regression equation with hydrological characteristics and nutrient load in sediments was derived by multiple regression analysis.This study revealed that the trophic state of water bodies influenced by both nutrient load and hydrological characteristics.It provides a new idea to reduce the occurrence of eutrophication in reservoirs by using the artificial hydrological regulation capacity of reservoirs.

Effects of sediment dredging on water quality and zooplankton community structure in a shallow of eutrophic lake

Effects of suction dredging on water quality and zooplankton community structure in a shallow of eutrophic lake, were evaluated. The results showed that a decreasing trend for levels of phosphorus, organic matter, total suspended solids, Chlorophyll a and Secchi transparency in the water column was found, while levels of water depth, electrical conductivity, total dissolved solids and NO3^--N concentration increased markedly post-dredging. The effects of dredging on dissolved oxygen, pH value and temperature were almost negligible. The zooplankton community structure responded rapidly to the environmental changes caused mainly by dredging. As a result, the abundance of rotifers decreased, while the density of zooplanktonic crustaceans increased markedly. The representative taxa were Brachionus angularis, B. budapestinensis, B. diversicornis, Synchaeta spp. and Neodiaptomus schmackeri. A distinct relationship between zooplankton taxa composition and their environment, unraveled by a redundancy analysis, indicating that the measured environment contributed to the variations in the zooplankton community structure to some extent. The first four synthetic environmental variables explained 51.7% of the taxonomic structure. Therefore, with the reduction of internal nutrient load and a shift in dominance by less eutrophic species, it inferred that dredging might be one of effective measures for environmental improvements of such lakes.

Interactive effects of irrigation and exponential fertilization on nutritional characteristics in Populus 3 euramericana cv. ‘74/76' cuttings in an open-air nursery in Beijing, China

Nutritional characteristics determine tree stock quality to a considerable extent. Exponential fertilization can induce nutrient reserves within juvenile trees, but its validity on poplar is contingent on interaction with a scientific irrigation regime due to limited water resources under global warming. In the present study, we raised 3200 Populus 9 euramericana cv. ＇74/76＇ cuttings under four irrigation regimes of 0（I0）, 60 %（I60）, 80 %（I80）, and100 %（I100） of field capacity for soil moisture content with or without（control） the employment of nitrogen（N） addition delivered as exponential fertilization at the rate of 8 g N cutting^（-1）（E8） in an open-air nursery in Beijing, China. Both height and diameter increased with the increment of soil moisture ratio or in response to exponential fertilization（EF） without any interactive effects. In general, concentrations of N, phosphorus（P）,and potassium（K） declined with time in stem but foliar N concentration did not change. Under the I100 regime, EF increased foliar N concentration relative to the control but failed to affect N concentration in stem in September, when both N concentration and N content were increased by EF under the I80 regime. Stem-K content and concentration by EF under the I80 regime also increased in September,therefore EF-treated cuttings had a higher ratio of K content in stem to that in whole plant（%ANAR）. Vector diagnosis for nutritional status indicated that EF resulted in dilution of K concentration but induced a steady-state P uptake in leaves under all irrigation regimes. Therefore, EF of N addition could promote N uptake to leaves of P. 9 euramericana cv. ＇74/76＇ cuttings, but it had a null effect on N and P reserves in stem and impaired K reserves.In conclusion, the irrigation regime of 80 % field capacity of soil moisture content was suggested for the culture of juvenile P. 9 euramericana cv. ＇74/76＇ cuttings. As the interactive meaning, EF was also suggested for its excellent promotion on both N and K uptakes.

Environmental effects of mariculture in China:An overall study of nitrogen and phosphorus loads

Eutrophication in coastal area has become more and more serious and mariculture potential is a main cause.Although there are some quantitative research on nutrient loads in national and global perspective,the calculation method problems make the results controversial.In this paper,the farming activities are divided into fed culture types(include cage culture and pond culture)and extractive culture types(e.g.seaweed,filter-feeding shellfish culture).Based on the annual yield of China in 2019 and feed coefficient of fed culture types and carbon(C),nitrogen(N),and phosphorus(P)content of extractive culture types,the annual nutrient loads was estimated.The results showed that to coastal region of China(1)annual nutrient released by fed culture types were about58451 t of N,9081 t of P,and annual nutrient removed by harvest of extractive culture types were 109245 t of N,11980 t of P and 1.86×10^(6)t of C.Overall,the net amount of nutrient removed annually by mariculture industry were 50794 t of N and 2901 t of P.(2)The nutrient released from mariculture industry influenced nutrient stoichiometry.Pond farming and seaweed farming had the potential of increasing the molar concentration ratio of N and P(N:P),while cage farming and bivalve farming decreased the N:P.(3)Due to different mariculture types and layouts in the coastal regions in China,N and P loading were regional different.Among the coastal regions in China,net release of nutrient from mariculture occurred only in Hainan and Guangxi regions,while in the other regions,N and P were completely removed by harvest.We suggest decrease the amount of fed culture types and increase the amount of integrated culture with extractive culture types.This study will help to adjust mariculture structure and layout at the national level to reduce the environmental impact.

THEORETICAL ESTIMATION OF GROUNDWATER DISCHARGE AND ASSOCIATED NUTRIENT LOADING TO A LAKE WITH GENTLE SLOPE BOTTOM

A simple estimation model of groundwater discharge and nutrient flux from nearshore unconfined aquifer to lake was studied. It was supposed that the aquifer was permeable isotropic homogeneously and its thickness approximated to the depth of lake. Distribution of the hydraulic gradient and the specific discharge along the transect of the discharge zone were discussed. Results show that the groundwater discharge patterns vary with the inclination angle of lakeshore bottom. For a shallow lake with gentle slope bottom, the rate of discharge of groundwater to lake is not constant across a discharge zone, but the discharge is concentrated in a narrow portion of the littoral zone where the Dupuit assumptions are invalid. The width of the discharge zone is correlative with aquifer thickness and slope of the lake bottom. The distribution functions of hydraulic gradient and groundwater discharge rates accord exponentially with offshore distance.

What drives the change of nitrogen and phosphorus loads in the Yellow River Basin during 2006-2017?

The Yellow River Basin (YRB) plays a very important role in China’s economic and social development and ecological security.In particular,the ecosystem of the YRB is sensitive to climate change.However,the change of nutrient fluxes in this region during the past years and its main driving forces remain unclear.In this study,a hydrologic model R System for Spatially Referenced Regressions on Watershed Attributes (RSPARROW) was employed to simulate the spatio-temporal variations in the fluxes of total nitrogen (TN) and total phosphorus (TP) during the period of 2006-2017.The results suggested that the TN and TP loads increased by 138%and 38%during 2006-2014,respectively,and decreased by 66%and 71%from 2015 to 2017,respectively.During the period of 2006-2017,the annual mean fluxes of TN and TP in the YRB were in the range of 3.9 to 591.6 kg/km^(2)/year and 1.7 to 12.0 kg/km^(2)/year,respectively.TN flux was low in the upstream area of the Yellow River,and presented a high level in the middle and lower reaches.However,the flux of TP in Gansu and Ningxia section was slightly higher than that in the lower reaches of the Yellow River.Precipitation and point source are the key drivers for the inter-annual changes of TN loads in most regions of the YRB.While the inter-annual variations of TP loads in the whole basin are mainly driven by the point source.This study demonstrates the important impacts of climate change on nutrient loads in the YRB.Moreover,management measures should be taken to reduce pollution sources and thus provide solid basis for control of nitrogen and phosphorus in the YRB.