Lingdingyang Estuary Research Articles

Impact of Anthropogenic Activities on Sedimentary Records in the Lingdingyang Estuary of the Pearl River Delta, China

High-intensity anthropogenic activities have greatly altered the estuarine-shelf depositional processes of sediments, and the intensity and frequency of the impacts of human interventions have far exceeded the natural development of estuarine systems. Since the reform and opening up, human activities such as dams, sand mining, channel dredging, and reclamation have already caused anomalous changes in the dynamical–sedimentary–geomorphological processes of the Lingdingyang Estuary (LE). Analyzing the impact of high-intensity anthropogenic activities on sedimentary processes and the hydrodynamic environment through sedimentary records can provide a scientific basis for predicting the evolution of the estuary and the sustainable development of the Guangdong–Hongkong–Macao Greater Bay Area. The aims of this study are to reveal the impact of varying intensity human activities across different periods on depositional pattern and conduct a preliminary investigation into the spatial differences in sedimentary characteristic attributed to human activities. Two cores (LD11 and LD13) located in the LE were selected for continuous scanning of high-resolution XRF, grain size, and 210Pbex dating tests, and scrutinized with the previous studies of the historical process of human activities in the LE. The results show the following: (1) The abrupt alterations in 210Pbex, geochemical indices, and grain size in LD13 happened in close proximity to the 95 cm layer, suggesting a shift in the sedimentary environment during 1994. (2) In the context of the continuous reduction in water and sediment flux into the LE after 1994, the large-scale and high-intensity human activities like sand mining, channel dredging, and reclamation are responsible for the sedimentation rate increase rather than decrease, the coarsening of sediment fractions, the frequent fluctuations in Zr/Rb, Zr/Al, Sr/Fe, and Sr/Al ratios, and the increase in anomalous extremes. (3) Sedimentary records found in locations varying in anthropogenic intensities differ greatly. Compared with the nearshore siltation area, the grain size composition in the channel area is noticeably coarser and exhibits a wider range of grain size variations. The 210Pbex is strongly perturbed and the vertical distribution is disturbed; the phenomenon of multiple inversions from the surface downwards is shown, making it impossible to carry out sedimentation rate and dating analysis, and the geochemical indicators have changed drastically without any obvious pattern. The evidence of the human activities can be retrieved in the sedimentary record of the estuary and provide a different angle to examine the impacts of the human activities.

Combined effects of massive reclamation and dredging on the variations in hydrodynamic and sediment transport in Lingdingyang Estuary, China

Combined effects of massive reclamation and dredging on the variations in hydrodynamic and sediment transport in Lingdingyang Estuary, China

Long-term morphological evolution and its mechanism of Lingdingyang Estuary: Interferences from anthropogenic forcings

The long-term morphological evolution process and mechanism of estuaries driven by high-intensity human activities are a hot and frontier scientific issue in estuarine and coastal research. Lingdingyang Estuary (LE) has been disturbed in recent decades by high-intensity anthropogenic forcing. High-intensity human activities have played a major role in the dynamic and geomorphological evolution of the LE, predominantly over the long term. In this study, the morphological evolution pattern of LE from 1955 to 1998 was first simulated using the Telemac-2D long-term morphological evolution model, and the input reduction of the upstream river boundaries was discussed. Then, based on the long-term model, the contribution of different human activities on geomorphic evolution was identified. Finally, the mechanism of high-intensity reclamation on morphological evolution was analyzed. The main findings can be summarized as follows: i) the general geomorphic pattern of LE at the mouth bars and channels are represented reasonably well from 1955 to 1998 when the multiple river boundaries input are reduced to combined seasonal river discharge and the phased daily SSC. Ii) High-intensity reclamation significantly weakened the deposition of ILE (Inner-Lingdingyang Estuary) with the annual deposition volume decreased ~1.33 × 107 m3, resulting in the deposition area narrowing 6–8 km to the south. On the contrary, reclamation enhanced the deposition of OLE (Outer-Lingdingyang Estuary) with the annual deposition volume increased ~5.15 × 106 m3, which enlarged the deposition area. Iii) the sharp decline of sediment discharge in upstream decreased significantly the deposition from 1978 to 1998 with the annual net deposition volume decreased ~1.754 × 107 m3, and the total deposition area of LE narrowed significantly and moved 3–5 km upstream. Iv) the total annual net deposition volume of LE from 1978 to 1998 decreased obviously by 2.084 × 107 m3 under the combined impact of the sharp decline of sediment discharge in upstream and high-intensity reclamation, of which the contribution rate of the sharp decline of sediment discharge in upstream was 61%, and that of high-intensity reclamation was 16% for the whole LE. v) the equilibrium location between runoff and tide caused by high-intensity reclamation moved 4.4 km southward from 1978 to 1998, which was the dominant factor for driving the southward migration of the deposition area during this period. In addition, reclamation resulted in the changes of water surface slope and tidal dynamics, which significantly affected the local geomorphic evolution pattern. The results of this study can improve and enrich the methods of the reduction of river boundary in upstream for long-term geomorphic evolution, and provide reference for the long-term geomorphic simulation of other multi-input estuaries. Our findings are expected to improve the scientific comprehensive management of the Pearl River Estuary and guide the construction of the Guangdong-Hong Kong-Macao Greater Bay Area

Inference of emission history of neonicotinoid pesticides from marine sediment cores impacted by riverine runoff of a developed agricultural region: The Pearl River Basin, China

Neonicotinoids (NEOs), as the most-consumed pesticides on a global scale, have posed a serious threat to human health and ecological environment. Information regarding the emission history of NEOs is of great importance to improve the prediction of their environmental loading and biological risk potential. In the present study, contamination levels and compositions of 12 NEOs were identified in 8 sediment cores from the Lingdingyang Estuary, which was impacted by agricultural emissions in riverine runoff of the Pearl River Basin for centuries. The total concentration of 12 target NEOs (∑12NEOs) ranged from 0.02 to 69.5 ng/g dw along the sediment core profile, with a mean of 12.9 ± 15.9 ng/g dw. Net deposition fluxes and concentrations of 5 parent NEOs experienced a remarkable exponential increase in the vertical profile of sediment cores, except for imidacloprid (IMI). Despite the similar exponential growth before 2012, subsequent decreased levels of IMI in historical sediment indicated its gradual replacement by other NEOs. IMI was the NEO with the highest frequency of 80.3% and the highest mean concentration of 7.66 ± 8.76 ng/g dw. The ecological risk assessment of NEOs suggests that 65.1% of sediment samples exceeded the chronic threshold for aqueous organisms using equilibrium partitioning approach. Since downward diffusion of NEOs in the Lingdingyang Estuary was rectified by their rapid desorption, the sedimentary record probably provided an accurate illustration of agricultural NEO emissions in the Pearl River Basin, China. The recent NEO inventory in the adjacent waters of core sites was estimated with a mean of 76.8 tons/yr. This study provides insights into the role of agricultural emission in riverine runoff in the environmental loads of NEOs in the historical sediment.

Contamination of typical phthalate acid esters in surface water and sediment of the Pearl River, South China: Occurrence, distribution, and health risk assessment

The occurrence and distribution of six phthalate acid esters (PAEs) in surface water and sediment of the Pearl River were investigated, including Xijiang River (XR), Beijiang River (BR), Lingdingyang Estuary (LE), and Guangzhou River (GR) in South China. Six target PAEs were identified in surface water and sediment at almost all sites in the Pearl River, with di(2-ethyl-ethyl) phthalate (DEHP) and dibutyl phthalate (DBP) as dominant PAEs. Total 6 PAEs (ΣPAEs) in surface water and sediment ranged from 1,797.5 to 4,968.5 ng L−1 and 95.24 to 3,677.26 ng g−1 dw, respectively. In addition, the contamination levels of PAEs in the Pearl River are in the following order: XR > BR > GR > LE for surface water and BR > XR > GR for sediment. Local agricultural activities, industrial production, water confluence, and seawater intrusion are the probable sources of PAEs in the Pearl River. Based on correlation analysis, the possible collocation patterns of different PAEs were revealed. The risk assessment indicates that residual PAEs in the Pearl River pose a serious threat to the ecological environment. According to risk characterization of fish living in the Pearl River, the decreasing order of health risks was: GR > LE > XR > BR.

Characteristics and Exploration of the Geomorphological Evolution of Lingdingyang Estuary in Recent Decades

Based on the underwater topographic data of Lingdingyang since 1970s, the new characteristics of the evolution of the swale in Lingdingyang estuarine bay were analysed and the causes of the evolution were discussed. The results indicated that the West Shoal silts eastward and southward, and its spreading speed gradually slows down after 1985. Area in the north of the West Shoal decreases gradually and the in the south of the West Shoal the shoal area increases gradually. Recently, in the north of the Middle Shoal scour occurred, while in the south silt is the primary evolution. The - 5m contour line of East Shoal has little variation, and the swale surface area is also decrease gradually. The average annual erosion and deposition of the East, Middle and West Shoals of Lingdingyang has a certain correlation with the annual average sediment discharge of the main hydrological stations upstream. The correlation of the West Shoal is the best, Due to the high intensity of reclamation, the channels of in the west of Lingdingyang extends significantly to the sea. The runoff channels in the West moves downward, and the sedimentation center of the West Shoal tends to moves southward.

The Hydrodynamic Division of Lingdingyang Estuary and its Application in the Impact Analysis of Large Water-Related Projects

The dynamic environment of lingdingyang estuary is very complex due to the confluence of runoff and tide as well as the different characteristics of each entrance. Meanwhile, human activities are intensive. Taking the large bridge project of the Pearl River Estuary--Shenzhen-Zhongshan Bridge Project as an example, this paper divides the waters of Lingdingyang estuary where the project is located into tidal channel area, shoal area and two west flood discharge areas based on the differences of hydrodynamic and environmental characteristics. Combined with the one and two-dimensional tidal current model of estuary and delta, the paper discusses the dynamic response of different dynamic characteristic areas to the engineering construction, and carries out the construction scheme optimization and hydrodynamic influence demonstration. The project impact analysis based on dynamic zoning proposed in this paper not only rationally evaluates the hydrodynamic environmental impact of large water-related projects of Lingdingyang, but also is of great significance to the balance of protection and development of Lingdingyang Estuary.

Application of parameters and paradigms of the erosion and deposition for cohesive sediment transport modelling in the Lingdingyang Estuary, China

Suspended sediment and the surficial sediment in most estuaries throughout the world consist of fine particles. Modelling cohesive sediment transport is an important way to explore the morphological evolution of estuaries where cohesive sediment is dominant. Various values for critical shear stress and deposition paradigms for cohesive sediment transport were evaluated here by analysis of field samples combined with numerical simulation in the Lingdingyang (LD) estuary in China. A UMCES-Gust Erosion Microcosm System (U-GEMS) experiment using field samples suggests that the experimental average value of critical shear stress for erosion (τce) is 0.26 N/m2. Two conflicting paradigms, i.e. mutually exclusive versus simultaneous erosion and deposition, are commonly used for cohesive sediment transport. Simulations of tidal currents and sediment transport during the wet season of 2007 and dry season of 2016 in the LD estuary were conducted under these two paradigms using the TELEMAC-2D hydrodynamic module and the sediment module SISYPHE in the TELEMAC model. Model verification under these two paradigms was carried out, and the τce parameters in the TELEMAC model were revised based on a U-GEMS experiment. The results showed the following. (1) The simulation results of the model in the LD estuary were satisfactory when an experimental average τce value of 0.26 N/m2 was used. (2) The simultaneous paradigm using a τce value of 0.26 N/m2 well explained the changes in the field-observed depth-averaged suspended sediment concentrations under all tidal regimes during the dry season, whereas the simultaneous paradigm using a τce of 0.15 N/m2 was more similar to observations in the LD estuary during the wet season.

Depocentre transfer in the Lingdingyang estuary: Interferences from natural and anthropogenic forcings

Estuarine morphodynamic processes caused by the combined effects of global and coastal environmental processes and human activities significantly influence the sustainable development of estuaries. Based on the bathymetric and boundary data extracted from multi-year digital charts for the Lingdingyang estuary (LE), South China, and in situ observations of the main hydrological stations, the spatiotemporal variations of depocentres in the LE and possible contributing factors are analysed. The results indicate that the spatial evolution of the morphology of the LE features shoal-deposition and channel erosion, and that the temporal evolution (1955–2015) presents a general pattern of alternating erosion and sediment deposition. A pattern of multi-depocentres exists in the LE, and the evolution of the depocentres can be divided into three general stages: i) a stage dominated by natural processes (1955–1989), ii) a stage dominated by highly-intensive reclamation (1989–2006), and iii) a stage dominated by large-scale channel dredging or sand mining (2006–2015). The transfer path of depocentres in the eastern and middle shoals traversed mainly from a north-westerly to south-easterly direction, while the transfer path of depocentres in the western shoal shows a clockwise spiral transfer feature. The large reduction of sediment supply from upstream river after the 1980s, resulted in an overall decrease in the mean annual sediment deposition volume in the LE from ~0.61 million m3/year (1989–1998) to ~0.29 million m3/year (2012–2015). The mean annual sediment deposition rate of the LE over time (i.e. 1955–2015) fluctuates in an oscillating manner rather than a linearly declining trend. Large to extreme flood (e.g. flood events of ‘94.6’, ‘98.6’ and ‘08.6’) led to higher sediment deposition rates and larger deposition volumes in the LE during the periods 1989–1998 and 2006–2008. The position of the four outlets were significantly pushed outwards by highly-intensive reclamation between 1989 and 2006, thus resulting in the bifurcation of runoff (in the Jiaomen and Hengmen outlets) and the formation of new artificial ‘outlets’ in the new channels. These great variation of the outlets induced the depocentres to transfer southeast or southwest during the period 1989–2006. A large number of temporary depocentres formed as a result of large-scale sand mining, were located in the middle shoal from 2006 to 2015. In addition, the enhancement of tidal dynamics combined with the great reduction of sediment supply from upstream river, actuated the continued transfer of the depocentres in the eastern, middle, and western shoals to the northwest or northeast after 2006. It is expected that our findings can provide a scientific foundation for port engineering construction, channel development, and the use of the tidal flat zone in the LE. Our conclusions provide a reference for other estuaries that are subject to similar anthropogenic activities.

Remote sensing dynamic monitoring of the shoreline and the mangrove wetland in the Lingdingyang Estuary in the past 40 years

Remote sensing dynamic monitoring of the shoreline and the mangrove wetland in the Lingdingyang Estuary in the past 40 years

Delta changes in the Pearl River estuary and its response to human activities (1954–2008)

This paper is concerned with delta evolution in response to human activities in the Pearl River estuary. Utilizing more than 50 years data bathymetric data, together with simulation fluvial discharge data, the net accretion rate in the Lingdingyang subaqueous delta decreased from 16.6 mm/y over the period 1955–1964 to 1.6 mm/y for the period 1998–2008 because there was a dramatic downward trend in the sediment load. In particular, the closure of the Longtan Dam (LTD) in 2006 resulted in the sediment load entering the Pearl River falling from 75 Mt/y (annual average: 1954–2006) to 25.2 Mt/y, a decrease of ∼67%. Another reason may be sand mining in the Lingdingyang estuary. Based on the linear relationship between sediment load and accumulation rate, an annual average sediment load of 21.7 Mt/y carried into the Lingdingyang estuary is the critical threshold value that separates delta progradation from recession. However, the outer subaqueous delta in the Modaomen estuary underwent deposition in the same period, because there is no obvious change in sediment load into the area during 1954–2008. In the coming decades, ongoing human interferences will reduce the fluvial sediment load entering the sea, which probably will result in a phase of general delta recession replacing delta progradation.

Characteristics of Engineering Geological Environment at Lingdingyang Estuary of Pearl River Mouth, South China Sea

ABSTRACT Shi, Y.; Ma, S.; Zeng, N., and Xia, Z., 2013. Characteristics of Engineering Geological Environment at Lingdingyang Estuary of Pearl River Mouth, South China Sea. In: Harff, J., Leipe, T., Waniek, J.J., and Zhou, D. (eds.), Depositional Environments and Multiple Forcing Factors at the South China Sea's Northern Shelf, Journal of Coastal Research, Special Issue, No. 66, pp. 25–33. Coconut Creek (Florida), ISSN 0749-0208. The Lingdingyang Estuary is one of the most important estuaries in the Southern China. With the regional rapid industrialization and urbanization, the engineering geological environment at Lingdingyang Estuary has attracted growing attention. Total of 250 samples and about 1,420 km of high resolution seismic profiles were collected by the Guangzhou Marine Geology Survey (GMGS) in 2004 and 2005. First, the characteristics of engineering geological environment at Lingdingyang Estuary were studied regarding three aspects, including topography and morphology, shallow geology, the subm...

Classification of the Pearl River Estuary via Principal Component Analysis and Regionalisation

This paper deals with the subdivision of the LingDingYang Estuary of the Pearl River Estuary (South China at the South China Sea) using geostatistical methods. The division obtained is characterised by the dominating components and interpreted in terms of ruling environmental conditions. The mathematical procedures used are regionalised classification via hierarchical cluster analysis and principal component analysis. While regionalisation determines areas characterised by different sedimentological and geochemical parameters, principal component analysis identifies the influencing factors in the different parts of the estuary. Three main subareas within the LingDingYang Estuary were discriminated. Here, marine-influenced regions can be clearly separated from those determined by the geological catchment area and the ones dominated by river discharge. The samples for this work were taken during cruises in 2004 and 2005. This work has been integrated into a German–Chinese cooperation project between the Leibniz Institute for Baltic Sea Research (Warnemünde, Germany) and the South China Sea Institute of Oceanology (Guangzhou, China).

Distribution of dissolved organic matter in the Pearl River Estuary, China

Chromophoric dissolved organic matter (CDOM) fluorescence and dissolved organic carbon (DOC) were measured in the Lingdingyang Estuary, a major component of the Pearl River Delta, China, in May 2001 and November 2002. Measurements of CDOM and DOC suggest multiple sources of dissolved organic matter (DOM) in the low-salinity region of the estuary, due to the mixing of four freshwater outlets, Humen, Jiaomen, Honqimen and Hengmen, all with different freshwater endmembers and all flowing into the head of the Lingdingyang. Our 2002 cruise expanded efforts to characterize these four major outlets, allowing for the quantification of CDOM inputs within this complex watershed. DOC and CDOM appear conservative in mid-salinity (5–20) waters, suggesting that mixing dominates production and removal processes over time scales on the order of 3 days, the residence time of water in this region of the estuary. DOC and fluorescence are linearly correlated in the mid-salinity region of the estuary north of Shenzhen, suggesting that in this region, terrestrial inputs dominate both signals. However, this relationship does not continue out onto the shelf, where water masses of differing optical properties mix. The CDOM/DOC ratio decreases with increasing salinity as would be expected through phototrasformation of CDOM into non-fluorescent DOC. Additionally, this ratio at low salinity appears to vary seasonally, with a higher value in Spring (high flow) compared to Fall (low flow).

Polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides in water columns from the Pearl River and the Macao harbor in the Pearl River Delta in South China

Polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) were measured in suspended particles and dissolved phase from the Baiertang water column and the Macao water column samples as collected from the Guangzhou channel of the Pearl River and the Macao harbor, where the sediments were heavily contaminated with organic pollutants. Total OCPs concentration varies from 23.4 to 61.7 ng/l in Baiertang water column and from 25.2 to 67.8 ng/l in Macao column, while total PAHs concentration varies from 987.1 to 2878.5 ng/l in the Baiertang water column and from 944.0 to 6654.6 ng/l in the Macao column. The vertical distribution profiles of pollutants and the partition of pollutants between particles and dissolved phases indicate that the sediments in Baiertang act as an important source of selected pollutants, and the pollutants in water of this region were mainly originated from the release and re-suspension of contaminants residing in the sediments. The sediments in Macao harbor act as a reservoir for organochlorine pesticides, such as DDTs mainly introduced by river inflow from Xijiang and PAHs input by brackish water from the Lingdingyang estuary. Combustion of fossil fuels and petroleum input are the main sources of PAHs in the Macao water column, while combustion of fossil fuels and coal is responsible for the PAHs in the Baiertang water column. The ratios of DDT/(DDD + DDE) for the Macao water column samples demonstrate that such chemicals were input into this region in recent times.

The characteristic of marine environment in Lingdingyang Estuary

Hydrologic features, load of main pollutants and current condition of water quality in Lingdingyang Estuary are discussed by references and monitoring data. Affected by topography, runoff and tide, its dynamic condition is very complicated. Different water areas have different hydrologic features. The topography under the water of Lingdingyang Estuary is higher in the northwest than that in the southeast. The shoal alternates with the deep trough within the bay. The distribution of the salinity and the contents of the mud and the main pollutants tally with the topography tendency. Change in water quality goes through four stages. Current condition of water quality is fairly good. Inorganic nitrogen is the primary pollutant, and then phosphorus. Rich in nutrition of nitrogen and phosphorus become a more and more prominent problem.

Preliminary study on the dissolved and colloidal organic carbon in the Zhujiang River estuary

This paper reports data on the dissolved and colloidal organic carbon in the Zhujiang (Pearl) River estuary. DOC concentration was 142 to 239 μmol/L in the freshwater taken in March 1997 from the four Zhujiang River tributaries flowing into the Lingdingyang estuary. High concentration was observed in the Humen tributary located near Guangzhou. The rapidly increased DOC concentration at low salinities (∼5) may be attributed to the exchange between macroparticulate and dissolved organic matter during the early stage of estuarine mixing. DOC concentration overall followed the mixing line until salinity 25, where the Deep Bay is located and where DOC was elevated. This elevated DOC may suggest a local organic matter source from Shenzhen. Using a cross-flow ultrafiltration (CFF) system equipped with a Millipore Prep-scale CFF 1 kD regenerated cellulose membrane, we also separated the colloidal organic matter from the truly dissolved fraction (<1 kD). CFF membranes were carefully evaluated for their applicability (retention characteristics, blank level and mass balance) to separate colloidal organic matter. COC in the study area ranged from 5 to 85 μmol/L, representing 3%–32% of DOC. The highest COC percentage was found at low salinities (<5) in both winter and summer. Evidence suggests in-situ production of colloidal material at this salinity range. Beyond this point, a very modest removal was observable until high salinities. Again, an increase in COC concentration was shown in the samples taken from the Deep Bay.