Potential Impacts of Exogenous Nitrogen Enrichment on Distribution and Transfer of Nitrogen in Plant-Soil System of Suaeda salsa Marsh in the Yellow River Estuary, China

To determine the potential impacts of exogenous nitrogen(N)enrichment on distribution and transfer of N in Suaeda salsa marsh in the Yellow River Estuary,the variations of N in plant-soil system during the growing season were investigated by field N addition experiment.The experiment included four treatments:NN(no N input treatment,0gNm^(−2) yr^(−1)),LN(low N input treatment,3.0 gNm^(−2) yr^(−1)),MN(medium N input treatment,6 gNm^(−2) yr^(−1))and HN(high N input treatment,12 gNm^(−2) yr^(−1)).Results showed that N additions generally increased the contents of total nitrogen(TN),ammonia nitrogen(NH_(4)^(+)-N)and nitrate nitrogen(NO_(3)^(−)-N)in different soil layers and the increasing trend was particularly evident in topsoil.Compared with the NN treatment,the average contents of TN in topsoil in the LN,MN and HN treatments during the growing season increased by 10.85%,30.14%and 43.98%,the mean contents of NH_(4)^(+)-N increased by 8.56%,6.96%and 14.34%,and the average contents of NO_(3)^(−)-N increased by 35.73%,45.99%and 46.66%,respectively.Although exogenous N import did not alter the temporal variation patterns of TN contents in organs,the N transfer and accumulation differed among tissues in different treatments.With increasing N import,both the N stocks in soil and plant showed increasing trend and the values in N addition treatments increased by 9.43%–38.22%and 13.40%–62.20%,respectively.It was worth noting that,compared with other treatments,the S.salsa in the MN treatments was very likely to have special response to N enrichment since not only the period of peak growth was prolonged by about 20 days but also the maximum of TN content in leaves was advanced by approximately one month.This paper found that,as N loading reached MN level in future,the growth rhythm of S.salsa and the accumulation and transference of N in its tissues would be altered significantly,which might generate great impact on the stability and health of S.salsa marsh ecosystem.

Distribution of polycyclic aromatic hydrocarbons in sediments from Yellow River Estuary and Yangtze River Estuary,China

Surface sediment samples collected from twenty-one sites of Yellow River Estuary and Yangtze River Estuary were determined for sixteen priority polycyclic aromatic hydrocarbons （PAHs） by isotope dilution GC-MS method. The total PAH contents varied from 10.8 to 252 ng/g in Yellow River Estuary sediment, and from 84.6 to 620 ng/g in Yangtze River Estuary sediment. The mean total PAH content of Yangtze River Estuary was approximately twofold higher than that of Yellow River Estuary. The main reasons for the difference may be the rapid industrial development and high population along Yangtze River and high silt content of Yellow River Estuary. The evaluation of PAH sources suggested that PAHs in two estuaries sediments estuaries were derived primarily from combustion sources, but minor amounts of PAHs were derived from petroleum source in Yellow River Estuary. PAHs may be primary introduced to Yellow River Estuary via dry/wet deposition, wastewater effluents, and accidental oil spills, and Yangtze River Estuary is more prone to be affected by wastewater discharge.

Potential Effects of Episodic Deposition on Nutrients and Heavy Metals in Decomposing Litters of Suaeda glauca in Salt Marsh of the Yellow River Estuary, China

Episodic deposition has been recognized as a major factor affecting the decomposition rate of detrital material in salt marshes. In this paper, three one-off burial treatments, no burial treatment(0 cm, NBT), current burial treatment(10 cm, CBT) and strong burial treatment(20 cm, SBT), were designed in intertidal zone of the Yellow River Estuary to determine the potential influences of episodic deposition on nutrient(C, N) and heavy metal(Pb, Cr, Cu, Zn, Ni, Mn, Cd, V and Co) variations in decomposing litters of Suaeda glauca. Results showed that although various burial treatments showed no statistical difference in decomposition rate of S. glauca, the values generally followed the sequence of CBT(0.002 403/d) > SBT(0.002 195/d) > NBT(0.002 060/d). The nutrients and heavy metals in decomposing litters of the three burial treatments exhibited different variations except for N, Cu, Cr, Ni and Co. Except for Mn, no significant differences in C, N, Pb, Cr, Cu, Zn, Ni, V and Co concentrations occurred among the three treatments(P > 0.05). With increasing burial depth, Cr and Cd levels generally increased while Cu, Ni and Mn concentrations decreased. Although episodic deposition was generally favorable for C and N release from S. glauca, its influence on release was insignificant. In the three burial treatments, Pb, Cr, Zn, Ni, Mn, V and Co stocks in S. glauca generally evidenced the export of metals from litter to environment, and, with increasing burial depth, the export amounts increased greatly. The S. glauca were particular efficient in binding Cd and releasing Pb, Cr, Zn, Ni, Mn, V and Co, and, with increasing burial depth, stocks of Cu in decomposing litters generally shifted from release to accumulation. The experiment indicated that the potential eco-toxic risk of Pb, Cr, Zn, Ni, Mn, V and Co exposure would be serious as the strong burial episodes occurred in S. glauca marsh.

Experimental Research on the Marine Hydrodynamic Action on the Consolidation Process of the Sediments in the Yellow River Estuary

Based on the in-situ measurements, the impact of the marine hydrodynamics, such as wave and tide, in the rapidly deposited sediments consolidation process was studied. In the tide flat of Diaokou delta-lobe, one 2 m × 1 m × 1 m test pit was excavated. The seabed soils were dug and dehydrated, and then the powder of the soil was mixed with seawater to be fluid sediments. And an iron plate covered part of the test pit to cut off the effect of the marine hydrodynamics, By field-testing methods, like static cone penetration test （SPT） and vane shear test （VST）, the variation of strength is measured as a function of time, and the marine hydrodynamics impact on the consolidation process of the sediments in the Yellow River estuary was studied. It is shown that the self-consolidated sediments＇ strength linearly increases with the depth. In the consolidation process, in the initial, marine hydrodynamics play a decisive role, about 1.5 times as much as self-consolidated in raising the strength of the sea-bed soils, and with the extension of the depth the role of the hydrodynamics is reduced. In the continuation of the consolidation process, the trend of the surface sediments increased-strength gradually slows down under the water dynamics, while the sediments below 50 cm are in opposite ways. As a result, the rapidly deposited silt presents a nonuniform consolidation state, and the crust gradually forms. The results have been referenced in studying the role of the hydrodynamics in the soil consolidation process.

Investigation on Water Pollution of Four Rivers in Coastal Wetland of Yellow River Estuary

[Objective] The study aimed at analysing water pollution of four rivers in coastal wetland of Yellow River estuary. [Method] Taking four seriously polluted rivers (Guangli River, Shenxian Ditch, Tiao River and Chao River) in coastal wetland of Yellow River estuary as study objects, water samples were collected from the four rivers in May (dry period), August (wet period) and November (normal period) in 2009 and 2010 respectively, then pollution indices like nutritive salts, COD, chlorophyll-a, petroleum, etc. were measured. Afterwards, the status quo of water pollution was assessed based on Nemero index and comprehensive trophic level index (TLI), so as to find out the integral status quo of water quality of wetland rivers and damages to aquatic ecological environment. [Result] On the whole, water pollution of four rivers in coastal wetland of Yellow River estuary was serious, in the eutrophication state, and the main pollutants were TN, TP, NH+4-N and petroleum. In addition, excessive N and P in the four rivers resulted in water eutrophication of Bohai Bay, so further leading to ride tide, which destroyed the coastal ecological environment of Bohai Sea. Moreover, compared with historical data, water pollution by nitrogen and phosphorus became more serious, while there was no obvious aggravation in the water pollution by petroleum. In a word, water pollution wasn’t optimistic on the whole. [Conclusion] The research could provide theoretical bases for the protection and utilization of river water in coastal wetland of Yellow River estuary and its coastal sea area.

The Derivation of Nutrient Criteria for the Adjacent Waters of Yellow River Estuary in China

Ecological protection and high-quality development of the Yellow River basin are becoming part of the national strategy in recent years.The Yellow River Estuary has been seriously affected by human activities.Especially,it has been severely polluted by the nitrogen and phosphorus from land sources,which have caused serious eutrophication and harmful algal blooms.Nutrient criteria,however,was not developed for the Yellow River Estuary,which hindered nutrient management measures and eutrophication risk assessment in this key ecological function zone of China.Based on field data during 2004-2019,we adopted the frequency distribution method,correlation analysis,Linear Regression Model(LRM),Classification and Regression Tree(CART)and Nonparametric Changepoint Analysis(nCPA)methods to establish the nutrient criteria for the adjacent waters of Yellow River Estuary.The water quality criteria of dissolved inorganic nitrogen(DIN)and soluble reactive phosphorus(SRP)are recommended as 244.0μg L^(−1) and 22.4μg L^(−1),respectively.It is hoped that the results will provide scientific basis for the formulation of nutrient standards in this important estuary of China.

Nitrogen cycle of a typical Suaeda salsa marsh ecosystem in the Yellow River estuary

The nitrogen（N） biological cycle of the Suaeda salsa marsh ecosystem in the Yellow River estuary was studied during 2008 to 2009.Results showed that soil N had significant seasonal fluctuations and vertical distribution.The N/P ratio（15.73±1.77） of S.salsa was less than 16,indicating that plant growth was limited by both N and P.The N absorption coefficient of S.salsa was very low（0.007）,while the N utilization and cycle coefficients were high（0.824 and 0.331,respectively）.The N turnover among compartments of S.salsa marsh showed that N uptake from aboveground parts and roots were 2.539 and 0.622 g/m2,respectively.The N translocation from aboveground parts to roots and from roots to soil were 2.042 and 0.076 g/m2,respectively.The N translocation from aboveground living bodies to litter was 0.497 g/m2,the annual N return from litter to soil was far less than 0.368 g/m2,and the net N mineralization in topsoil during the growing season was 0.033 g/m2.N was an important limiting factor in S.salsa marsh,and the ecosystem was classified as unstable and vulnerable.S.salsa was seemingly well adapted to the low-nutrient status and vulnerable habitat,and the nutrient enrichment due to N import from the Yellow River estuary would be a potential threat to the S.salsa marsh.Excessive nutrient loading might favor invasive species and induce severe long-term degradation of the ecosystem if human intervention measures were not taken.The N quantitative relationships determined in our study might provide a scientific basis for the establishment of effective measures.

Variation in reach-averaged bankfull discharge in the Yellow River Estuary in recent years

The Yellow River Estuary(YRE)alternatively experienced channel aggradation and degradation during the period 1990-2016.To study the variation in flood discharge capacity during the process of river bed evolution,bankfull characteristic parameters were investigated on the basis of measured hydrological data and surveyed cross-sectional profiles,which was crucial for comprehending the processes and the key factors to cause these rapid changes.A reach-averaged method was presented in this study in order to calculate the characteristic bankfull parameters in the YRE,and this method integrated the geometric mean using the logarithmic transformation with a weighted mean based on the distance between the two successive sections.The reach-averaged bankfull parameters in the tail reach of the Yellow River Estuary(the Lijin-Xihekou reach)during the period 1990-2016 were then calculated.Calculated results indicated that the adoption of a concept of reach-averaged bankfull discharge was much more representative than the cross-sectional bankfull discharge,and the results also indicated that bankfull discharges decreased during the process of channel aggradation,and increased during the process of channel degradation.Finally,an empirical formula and a delayed response function were established between the reach-averaged bankfull discharge and the previous 4-year average fluvial erosion intensity during flood seasons,and both of them were adopted to reproduce the reach-averaged bankfull discharges,and calculated results showed high correlations(R^(2)>0.8)of these two methods.

Assessing the benthic habitat quality in the Huanghe(Yellow River) Estuary and its adjacent areas using AMBI and M-AMBI

The protection of the biological diversity and the maintenance of the regional ecological integrity for the Huanghe （Yellow River） Estuary and its adjacent areas are practically significant and valuable. However, frequent human activities and natural climate changes have caused vigorous disturbances on the ecosystem in these sea areas. An objective assessment on the benthic habitat quality （BHQ） of the Huanghe Estuary and its adjacent areas is conducted, using AZTI＇s Marine Biotic Index （AMBI） and multivariate AMBI （M-AMBI） based on the data of macrobenthos in May and August 2011. The results show that both the indices do not correlate significantly, and their assessment results are greatly different. All of the samples assessed using the AMBI were ＂high＂ or ＂good＂, because the ecological group I （EGI） and the ecological group II （EGII） were dominant macrobenthic ecological groups in the research area. Owing to a low species＇ richness and a high individual abundance in some samples, the BHQ levels using the M-AMBI were worse than those of the AMBI. Significant correlations are observed between the M-AMBI, water depth, bottom water salinity and dissolved inorganic nitrogen, thus the M-AMBI could sensitively respond to environmental changes and distinguish influences from uninfluenced stations, but the AMBI could not. The consistent results between the AMBI and the M-AMBI mainly appeared in the uninfluenced （undisturbed or slightly disturbed） sta- tions. Therefore, the M-AMBI is more effective than the AMBI in assessing the benthic habitat quality in the Huanghe Estuary and its adjacent areas. Using the M-AMBI to assess the BHQ of the Huanghe Estuary and its adjacent areas, the results show that 3% of the stations are undisturbed and the BHQs are ＂high＂, and 61% of the stations are slightly disturbed and those of the BHQ are ＂good＂, and the rest are meanly disturbed and those of the BHQ are ＂moderate＂.

Distribution characteristics and controlling factors of typical heavy metals in Huanghe River estuary,China

The geochemical characteristics and potential controlling factors of colloidal Zn,Cd,and Pb in Huanghe(Yellow)River estuary(HRE),China were investigated.The three metals were highly variable over a range of spatiotemporal scales,comprehensively forced by various physical and biological processes.Total dissolved Zn,Cd,and Pb varied from 200.1 to 321.7,2.6 to 4.1,and 0.5 to 1.0 nmol/L,respectively.Only one near-estuarine station of Zn had contamination factor values>1,which indicate the lower contaminant levels.Five dissolved species of Zn,Cd and Pb were fractionated,namely<1 kDa,1-3 kDa,3-10 kDa,10-100 kDa,and 100 kDa-0.45μm.The<1 kDa truly dissolved phase was the main fraction of the three dissolved metals(50%-62%),while the 100-kDa-0.45-μm high molecular weight colloidal fraction was dominant in their respective colloidal phase.Territorial input and sediment acted as important sources of strong ligands and natural colloids for the HRE water system.<3-kDa Zn and Pb were susceptible to the dissolved oxygen,the behaviors of colloidal Zn and 3-10-kDa Pb were related to dissolved organic carbon(DOC).However,no significant correlation between each dissolved fraction of Cd and salinity,pH,temperature,colloidal organic carbon,and DOC was found in this study.Overall,these findings,completed by the evaluation of the dissolved species of Zn,Cd,and Pb at 10 sites over the river-sea mixing zone,provided new insights into the colloidal heterogeneity that affect metals geochemical features,migration and fate in estuaries.

Community characteristics of macrobenthos in the Huanghe(Yellow River) Estuary during water and sediment discharge regulation

The community characteristics of macrobenthos in the Huanghe（Yellow River） Estuary is influenced by a combination of natural and anthropogenic factors. Here, we investigated short-term changes（1-month） in macrobenthic community structure in response to water and sediment discharge regulation（WSDR） in 2011.Specifically, we sampled the macrobenthos at 18 sampling stations situated at four distances（5, 10, 20, and 40 km）from the mouth of the Huanghe Estuary before（mid-June）, during（early-July）, and after（mid-July） WSDR. The results showed that a total of 73, 72, and 85 species were collected before, during, and after WSDR, respectively.Then, 13, 1, and 16 dominant species were detected at this three periods. Four phyla were primarily detected at all three periods（Annelida, Mollusca, Arthropoda, and Echinodermata）. However, while Mollusca and Annelida were the most important phyla in our study, Echinodermata and Annelida were the most important phyla in 1982,demonstrating major changes to community structure over a 3-decadal period. All stations were of high quality BOPA index before WSDR, whereas two and three stations were of reduced quality BOPA index during and after WSDR, respectively. The results of ABC curves showed that had incurred disturbed conditions after human activities WSDR. Most important of all, multivariate analyses and RDA analysis indicated that the structure of the macrobenthic community was closely linked to environment factors, including that organic content factor caused the distribution of macrobenthic community mostly during WSDR, while water depth after WSDR affected the macro benthos community structure seriously, and during WSDR, the environment factor influencing it was not single, including organic content, sulfide content, Hg and As. These differences may have been due to changes in water transparency negatively impacting the growth and development of macrobenthos, due to specific lifehistory requirements. Our results demonstrate that anthropogenic activity is having both long-term（3 decadal）and short term（1-month） impacts on the structure of the macrobenthic community of the Huanghe Estuary. In conclusion, human activities WSDR influence the habitat environment of macro benthos, including the water temperature, nutrients, bioturbation, and so on. Therefore, we suggest the necessity to strengthen regulations of land-derived organic pollutant input to maintain the ecological balance of the Huanghe Estuary.

An Information Entropy-Based Methodology to Construct the Avulsion Threshold in the Tail Reach of the Estuarine Alluvial Plain

Channel avulsion is a natural phenomenon that occurs abruptly on alluvial river deltas,which can affect the channel stability.The causes for avulsion could be generally categorized as topography-and flood-driven factors.However,previous studies on avulsion thresholds usually focused on topography-driven factors due to the centurial or millennial avulsion timescales of the world’s most deltas,but neglected the impacts of flood-driven factors.In the current study,a novel demarcation equation including the two driven factors was proposed,with the decadal timescale of avulsion being considered in the Yellow River Estuary(YRE).In order to quantify the contributions of different factors in each category,an entropy-based methodology was used to calculate the contributing weights of these factors.The factor with the highest weight in each category was then used to construct the demarcation equation,based on avulsion datasets associated with the YRE.An avulsion threshold was deduced according to the demarcation equation.This avulsion threshold was then applied to conduct the risk assessment of avulsion in the YRE.The results show that:two dominant factors cover respectively geomorphic coefficient representing the topography-driven factor and fluvial erosion intensity representing the flood-driven factor,which were thus employed to define a two dimensional mathematical space in which the demarcation equation can be obtained;the avulsion threshold derived from the equation was also applied in the risk assessment of avulsion;and the avulsion threshold proposed in this study is more accurate,as compared with the existing thresholds.

Influence of bathymetry evolution on position of tidal shear front and hydrodynamic characteristics around the Yellow River estuary

A three dimensional numerical model based on the hydrodynamic module of finite-volume coastal ocean （FVCOM） was established for the Yellow River estuary. The model has been calibrated by observed data and proved to be suitable to reflect the hydrodynamic force in the research area. We employed the model to simulate the tidal shear front off the Yellow River estuary and analyzed the formation, spread and duration of two different types of shear front. To examine the effect ofbathymetry evolution on the position of tidal shear front, subaqueous bathymetry of the Yellow River estuary was changed according to the changing patterns obtained from the past few years. Tidal shear front was modeled on both the original and the changed bathymetry. The results show that the position of shear front moved from a shallow to a deep area due to the deposition of bathymetry. The influence of bathymetry evolution on hydrodynamic characteristics including the distribution of salinity and the movement of particles was studied. We found the dispersion areas of low salinity became larger after changing bathymetry and the particles on the surface, middle and bottom layer are able to move further both north and west of Laizhou Bay on the changed bathymetry.

Polychlorinated Naphthalenes (PCNs) in Surface Sediments of the Yangtze and Yellow River Estuaries,China

The concentrations and congener profiles of poly- chlorinated naphthalenes （PCNs） in surface sediment samples collected from the Yangtze and Yellow River Estuaries were inves- tigated. PCN congeners （from MoCNs to OCN） were determined by isotope dilution/high-resolution gas chromatography/high- resolution mass spectrometry （HRGC-HRMS）. The total concen- trations of PCNs were 34.3-303.0 pg/g （dry weight, dw） in the Yangtze Estuary samples and 6.2-408.0 pg/g （dw） in the Yellow River Estuary samples, which were lower compared with that in other sediments reported by previous studies. In addition, the re- markably different homologue or congener profiles of PCNs have been obtained in this study. Samples dominated with MoCNs to TrCNs might be attributed to atmospheric deposition and global fractionation, while in other samples taken from the surrounding industrial areas the enrichment of higher chlorinated homologues suggested that the industrial and human activities should be the main potential sources.

Assessment of heavy metal levels in surface sediments of estuaries and adjacent coastal areas in China

This article investigates the variations of contamination levels of heavy metals such as copper, lead, chromium, cadmium, zinc, arsenic, and mercury over time in surface sediments of the Changjiang River Estuary （CRE）, Yellow River Estuary （YRE）, Pearl River Estuary （PRE）, and their adjacent coastal areas in China. The contamination factor （CF）, pollution load index （PLI）, and geoaccumulation index （Igeo） are used to evaluate the quality of the surface sediments in the study areas. The results showed that the CRE, YRE, and their adjacent coastal areas were at a low risk of contamination in terms of heavy metals, while the PRE and its adjacent coastal area were at a moderate level. By comparison, the concentrations of heavy metals in the surface sediments of the YRE and its adjacent coastal area were relatively lower than those in the CRE, PRE, and their adjacent coastal areas.