Surface Sediment Distribution Research Articles

Microplastics (MPs) distribution in Surface Sediments of the Freidounkenar Paddy Wetland

There is an urgent need to increase knowledge on the distribution of microplastics (MPs) in wetlands because these are sites of special ecological value and the ever-growing use of plastic can threaten such fragile ecosystems. This research assesses, for the first time, the occurrence of MPs in surface sediment of the Freidounkenar International Wetland (Northern Iran), a valuable habitat for migratory birds. A total of 1368 MP/kg were identified in the surface sediments of the wetland. The distribution of MPs in sediments per area was Ezbaran (36.5%), Western Sorkhrood (32.0%), Freidounkenar (20.1%) and Eastern Sorkhrood Ab-bandans (11.4%). The most contaminated sites were located close to agricultural fields, Damgahs (agroecosystems for birds), fishing areas and roads. Fibers and white-transparent and black-grey MPs constituted the dominant MPs in the surface sediment. The most abundant MPs were < 250 μm and these were made of nylon, polypropylene-low density polyethylene copolymer, polystyrene, low density polyethylene and polypropylene. The identification of MPs was carried out visually and supported with Scanning Electron Microscopy (SEM)-Energy Dispersive X-Ray (EDX) and micro-Raman techniques. There were weathering signs in large proportion of the MPs, according to SEM analysis, which evidences their formation from the degradation of other plastics. This is a comprehensive study on MPs in surface sediment of this sensitive internationally recognized ecosystem with high ecological value.

Diatom and dinoflagellate cyst distribution in surface sediments of the Chukchi Sea in relation to the upper water masses

Diatom and dinoflagellate cyst analyses were performed on 22 surface sediment samples from the Chukchi Sea to document their geographical distributions in one of the most understudied sections of the Arctic Ocean and to examine the influence of upper water masses on these two major groups of phytoplankton. Total concentrations vary from 0.9 to 5.9 × 106 valves g−1 for diatoms and from 0.8 to 12.5 × 103 cysts g−1 for organic-walled dinoflagellate cysts, with the highest values for both groups observed in the southern part of the Chukchi Sea and away from the Bering Strait. Well-preserved microfossils were recovered, with a total of 35 and 88 taxa of dinoflagellate cysts and diatoms, respectively. The most abundant diatoms are Paralia sulcata, Thalassiosira antarctica, Thalassiosira nordenskioeldii, and resting spores of Chaetoceros spp., whereas cysts of phototrophic Alexandrium spp., Operculodinium centrocarpum sensu Wall and Dale (1966), and heterotrophic Islandinium minutum and Brigantedinium spp. were most common in the dinoflagellate cyst assemblages. Cysts of HAB-causing Alexandrium spp. were found in most of the samples, with the highest abundances in Herald Canyon where they contribute ∼56.6% to the cyst assemblage. As expected, cysts produced by heterotrophic dinoflagellates were more abundant where sedimentary diatom concentrations were the highest.Statistical analysis identified three major diatom and dinoflagellate cyst clusters: 1. Sites influenced by the Alaska Coastal Current in the eastern part of the Chukchi Sea are characterized by high abundances of P. sulcata and O. centrocarpum sensu Wall and Dale (1966); 2. The western part and Herald Canyon in the northern part of the Chukchi Sea are distinguished by diatoms Chaetoceros spp., T. antarctica and dinoflagellate cysts of Alexandrium spp. and affected by the Siberian Coastal Current and Bering Shelf Water; and 3. Assemblages in the southern part of the Chukchi Sea are recognized by noticeable abundances of T. nordenskioeldii and cryophilic diatom taxa, and dinoflagellate cysts I. minutum, as well as by overall lower percentages of cysts of Pentapharsodinium dalei and Brigantedinium spp. This work revealed the potential applicability of the combined use of diatoms and dinoflagellate cysts for reconstructions of past dynamic water mass changes in the Chukchi Sea.

Utilization of Remote Sensing Images for Compiling The Characteristics Map of Indramayu Beach, West Java

The beach has an important role in the development and economy of a region. Therefore, it is important to understand the condition and characteristics of the coast so that it can be managed and developed wisely. One way to understand the condition of the beach is through making a map of the characteristics of the beach. A coastal characteristic map is a graphical representation of the conditions and characteristics of the geology, geography, and hydrology of a coast. Making a coastal characteristic map with remote sensing requires several steps, namely: 1). satellite data collection: Pre-processing satellite data; 2). classification of satellite data; 3). satellite data analysis; and finally 4). making a coastal characteristic map. The area that is the fabric material is the beach of Indramayu Regency, West Java. Based on the analysis and interpretation of 2015 Landsat 8 (LDCM) image data, 2020 Sentinel 2 Image data, BATNAS, and DEMNAS data, it is known that the characteristics of the Indramayu beach are that it has geo-quaternary building materials which include: (a) coastal bunds, ( b) swamp deposits, (c) shallow marine deposits, (d) sand deposits, (e) flood plains, (f) river deposits, and (g) floodplain deposits. The morphology includes: (a) beach sand plains, (b) concave coastal swamps, (c) old beach bunds, (d) young beach bunds, (e) alluvial plains, (f) flood plains, and (g) fan plains delta. Finally, it has a distribution of surface sediments on the seabed which includes: (a) sand, (b) silt, gravelly sand, (d) slightly gravelly silt, (e) slightly gravelly sandy mud, and (f) gravelly mud.

Ecotoxicology and geostatistical techniques employed in subtropical reservoirs sediments after decades of copper sulfate application.

Spatial distribution linked to geostatistical techniques contributes to sum up information into an easier-to-comprehend knowledge. This study compares copper spatial distribution in surface sediments and subsequent categorization according to its toxicological potential in two reservoirs, Rio Grande (RG) and Itupararanga (ITU) (São Paulo-Brazil), where copper sulfate is applied and not applied, respectively. Sediments from 47 sites in RG and 52 sites in ITU were collected, and then, copper concentrations were interpolated using geostatistical techniques (kriging). The resulting sediment distributions were classified in categories based on sediment quality guides: threshold effect level and probable effect level; regional reference values (RRVs) and enrichment factor (EF). Copper presented a heterogenic distribution and higher concentrations in RG (2283.00 ± 1308.75mg/kg) especially on the upstream downstream, associated with algicide application as well as the sediment grain size, contrary to ITU (21.81 ± 8.28mg/kg) where a no-clear pattern of distribution was observed. Sediments in RG are predominantly categorized as "Very Bad", whereas sediments in ITU are mainly categorized as "Good", showing values higher than RRV. The classification is supported by the EF categorization, which in RG is primarily categorized as "Very High" contrasting to ITU classified as "Absent/Very Low". Copper total stock in superficial sediment estimated for RG is 4515.35Ton of Cu and for ITU is 27.45Ton of Cu.

Mercury Sources and Processes Implied by Other Pollutants Distributions in Surface Water and Sediments of a Subtropical Estuary in Southern China

Mercury Sources and Processes Implied by Other Pollutants Distributions in Surface Water and Sediments of a Subtropical Estuary in Southern China

The broad-scale microplastic distribution in surface water and sediments along Northeastern Mediterranean shoreline

Plastics manufactured to fulfil the unique demands of civilization accumulate in the sea due to their durability. Microplastics (MP) pose a greater threat than macroplastics as they can easily enter the aquatic environment and be hard to detect. MPs potentially impact several components of the marine life and food chain. This study determined MP distribution and characterization by collecting sediment from 47 different stations and surface seawater (SSW) from 29 stations in 2019 along the Turkish coast of the Eastern Mediterranean Sea. Potential MP particles were stained with Nile-Red and verified using ATR-FTIR. While MP abundance in the sediment ranged between 118 ± 97 and 1688 ± 746 MPs kg−1, it varied between 0.18 ± 0.10 MPs m−3 and 2.21 ± 1.75 MPs m−3 in SSW. The MP abundance showed significant spatial variation (p < 0.05). The polymer type in the samples was determined by ATR-FTIR. In both water and sediments, polyethylene was the most common MP type (>59 %), while fragment was the most common MP form (>57.6 %), and >65 % of overall MPs were <1500 μm. The spatial pattern of MPs in the sediments and SSW was affected by the population, the magnitude of the tourism sector, the rim current, and circulation. The monitoring data presented here can provide a remarkable projection of the current trend and form a basis for future MP pollution prevention.

Heavy Metal Distribution in Surface Sediments of the Coastal Pearl Bay, South China Sea

Six heavy metals (As, Cu, Cd, Zn, Cr, and Pb) in surface sediments (0–5 cm) from the twenty selected sites of the coastal Pearl Bay (South China Sea) were analyzed to assess the distribution pattern and potential ecological risk. Overall concentrations (mg/kg, dw) in the sediment samples were: As (10.88 ± 6.50), Cu (24.16 ± 18.63), Cd (0.55 ± 0.78), Zn (48.53 ± 30.06), Cr (35.78 ± 28.66), Pb (31.28 ± 18.50). Results showed that the overall mean values of Cd concentrations exceeded the standard of China Marine Sediment Quality, caused by significantly high levels of Cd contents in five sites (S8, S11, S13, S16, and S17) at the offshore area of Pearl Bay. Generally, the metal concentrations showed a decreasing trend from the offshore area to the inner bay. Various index values such as the geo-accumulation index (Igeo), the ecological risk index (Eri), and the contamination factor (CF) demonstrated that the coastal Pearl Bay was not polluted by the examined metals except for Cd, which might cause contamination and ecological risk in the region. Principal component analysis (PCA) results indicated that Cu, Zn, and Cr might originate from natural sources inland, and Pb and As might come from the gasoline and diesel fuel from engine boats. It is recommended that further research should focus on detecting the acute source and transferring mechanisms of the toxic metal Cd.

Effects of river inputs on particulate organic matter composition and distributions in surface waters and sediments of the Mersin Bay, Northeastern Mediterranean Sea

Terrestrial inputs-induced eutrophication in the P-depleted Northeastern (NE) Mediterranean shelf waters has led to changes in particulate organic matter (POM) composition and distributions in the water column and surface sediments. The present study aimed to understand the impacts of terrestrial nutrient and POM inputs on coastal eutrophication, bulk POM composition and concentrations in surface waters and sediments of the Mersin Bay, located at the Cilician Basin of NE Mediterranean Sea. The present results showed that the regional rivers and wastewater discharges markedly increased nutrient concentrations, leading to enhanced eutrophication and POM concentrations surface waters of the Mersin inner bay. The C/N and C/P molar ratios derived from the regressions of POM data in surface waters were 6.92 and 129, respectively. The higher C/N and C/P molar ratios in the surface sediments of productive Mersin Bay indicated selective decay of N, P-containing organic matter buried in muddy sediments. Close positive correlations were found in sediment organic matter and mud contents, indicating the crucial role of fine particles in transport and enrichment of organic matter in the muddy shelf sediments of NE Mediterranean Sea.

Microplastic Distribution and Influence Factor Analysis of Seawater and Surface Sediments in a Typical Bay With Diverse Functional Areas: A Case Study in Xincun Lagoon, China

Microplastics come directly or indirectly from human activities. The bay and coastal areas are constantly under pressure from human activities, including tourism, fishing, and aquaculture. Microplastic pollution is now recognized as a great threat to bay environments. In this study, we assessed microplastics in the Xincun Lagoon Bay, which had multiple human activities, to understand whether human activities could directly reflect the pollution level of microplastics. The results showed the dominant microplastics were small (100–500 μm, 45.2%) and transparent (57.0%), mainly consisting of fibers (95.7%), and cellophane (54.4%) was the dominant polymer. The color, type, and component indicated that wastes from aquaculture, laundry wastewater in the Tanka fishing raft area, and domestic wastes from tourism were the primary sources of microplastics in Xincun Bay. During the rainy season, microplastic abundances in surface water and surface sediment at the outer bay were found to be significantly higher (108.8 ± 37.1 item/L and 250.4 ± 92.0 item/kg, respectively) than those found at the inner bay (34.3 ± 12.9 item/L and 167.6 ± 71.7 item/kg, respectively), which presented a reverse trend in the dry season (p &amp;lt; .01). Although Xincun bay has a relatively closed environment and diverse human activities, concentrated rainfall and strong winds could cause microplastic abundance inside the bay during the rainy season to be lower than that outside the bay. Furthermore, the comparison of microplastic abundances in the areas with intensive human activities and non-human activity areas indicated that the intensity of human activities could not directly reflect the pollution of microplastics in the lagoon bay. It is also necessary to consider the geographical and seasonal characteristics in order to explain the pollution degree of microplastics in a bay.

Quantifying Importance of Macrobenthos for Benthic‐Pelagic Coupling in a Temperate Coastal Shelf Sea

AbstractBenthic oxygen fluxes consist mostly of advective and diffusive terms. Both terms in the German Bight exhibit a prominent annual cycle but with opposite variation patterns. To understand the driving mechanisms quantitatively, a novel 3‐D benthic‐pelagic coupled model resolving interactions among macrobenthos, bioturbation, oxygen consumption, and carbon early diagenesis was applied to reconstruct the benthic states. Simulation results show a satisfactory agreement with field data and reveal that the benthic oxygen flux is determined by not only pelagic drivers but also by internal dynamics associated with the interaction between organic carbon and macrobenthos, and bedform morphodynamics. Variation of advective flux, characterized by summer‐low and winter‐high, is mainly driven by hydrodynamics and bedform morphodynamics, while variation of diffusive flux, featured by summer‐high and winter‐low, is a compound effect of pelagic and benthic drivers with a dominant control by macrobenthos through bioturbation. The role of bioturbation in benthic oxygen consumption is twofold: (a) on the one hand, it alters the particulate organic carbon (POC) distribution in surface sediments, thereby changing the availability of POC to oxygen consumption; (b) on the other hand, it mixes oxygen down into sediments, thereby facilitating oxygen consumption. Our results indicate that the first role prevails in sandy seafloor characterized by energetic hydrodynamics, while the second role becomes increasingly important along with a weakening of bottom currents. We found that bioturbation contributes up to 87% 4% and 55% 8% of the total benthic oxygen fluxes in muddy seabed and at a regional scale (the German Bight), respectively.

Environmental implications of the distribution and physical characteristics of surface sediments in the northern Persian Gulf

Environmental implications of the distribution and physical characteristics of surface sediments in the northern Persian Gulf

Changes in the distribution of surface sediment in Pearl River Estuary, 1975–2017, largely due to human activity

In recent decades, the surface sediments in the Pearl River Estuary (PRE), China, have been intensely disturbed by human activities. Data from 1975 to 2017 show that the mean surface sediment grain size in PRE is distributed between 5 and 8 ϕ, while the sorting coefficient of the sediments vary between 0.39 and 4.53, and the skewness is between −0.31 and 0.55. From 1975 to 1994, sandy sediment was mainly distributed near the outlets. However, sandy sediments have been present in the south of the West Shoal and Middle Shoal, and north of Lantau Island, and have had a patchy distribution since the 2000s. From 1975 to 2017, the average total grain size of the surface sediments in PRE changed from 6.4 to 5.3 ϕ, indicating a coarsening trend. This was mainly caused by the sharp reduction in upstream sediment load since the 1980s, as well as channel dredging and sand mining in PRE. On the one hand, the decrease in the sediment load caused an increase in the erosion area, which caused a large amount of fine-grained sediment to be eroded and transported to the open sea. On the other hand, channel dredging and sand mining resulted in coarse-grained sediments in the paleo-sedimentary layer being stirred to the surface, thus making a significant contribution to the coarsening of the average grain size. Channel dredging and sand mining are also the main reasons for the patchy distribution of sediments in PRE. In the future, with further reductions in the sediment load and the persistence of reclamation, channel dredging, and sand mining, the grain size of surface sediments in PRE will continue to show a coarsening trend.

Phosphorous fractionation distribution in surface sediments of the Jobokuto Bay

Phosphorus (P) is an essential nutrient that can limit primary productivity in waters. Phosphorus has significant impact on the biogeochemical cycle in marine ecosystems. Surface sediments play an important role in the nutrient dynamics. Riverine input is sources of P to the ocean and sediment plays an important role as a source or sink of P in the coloumn of water. Phosphorous (P) availability is regarded as the most important factor for determining the water quality in coastal waters. However, not all of the P fractions can be released from the sediment. This study was conducted to identify the distribution of phosphorus (P) fractionation in the sediment surface of Jobokuto Bay. Samples were collected from ten locations. Percentage of sedimentary parameters such as sand, silt, clay, and organic carbon were analyzed to find out their relation with various P fractions. The sediment found was mostly sand at the station near to the coast and mud (silt and clay) at offshore stations. The results showed that Ca-P dominant (56.03%) and percentages of Fe-P, OP, and Ads-P were 23.43, 17.41, and 3.2% respectively. Terrestrial inputs and biological deposits cause Ca-P dominant. The bioavailability of P fractions were ranged from 34.45 to 56.1% of the total P (TP) content. The high concentrations of the Ads-P was found in the mud fraction and located at offshore stations. The order of abundance of the major forms of P in the surface sediments of Jobokuto bay is as follows: Ca-P &gt; Fe-P &gt; OP &gt; Ads-P

Assessing heavy metals in surface sediments of the Seomjin River Basin, South Korea, by statistical and geochemical analysis

We investigated particle size distribution and heavy metal concentrations in surface sediments of streams and lakes in the Seomjin River Basin by comparison with Sediment Quality Guidelines (SQGs). Origins were identified using statistical and geochemical approaches. Sand was prevalent in mean particle size of surface sediments (except lakes). Mean concentrations of Pb, Zn, Cd, and Hg were similar for the Seomjin and Boseong rivers, while those of Cu, As, Cr, and Ni were approximately 1.5–2.0 times higher in the Boseong. SQGs revealed no serious pollution in the basin's site concentrations, although As and Ni levels in the Boseong had some potential for benthos toxicity. Correlation and principal component/factor analysis showed that concentrations of Cu, As, Cr, and Ni were dominant from geological origins rather than anthropogenic. The reducible fraction bound to Fe and Mn-oxides was prevalent in Pb, while the water- and acid-soluble fractions were easily exchangeable or bound to high Cd carbonates. The fraction bound to the highest lattice in residual prevailed in Zn, Cu, Cr, and Ni, accounting for 64%, 65%, 87%, and 86%, respectively. Similarly, results indicated geological origins. Risk assessment to benthos based on labile fractions (F1 + F2 + F3) were Cd (72%) < Pb (66%) < Zn (36%) ≈ Cu (35%) < Ni (14%) ≈ Cr (13%). While Cd and Pb showed the highest risk, their concentrations were relatively lower. However, Cr and Ni showed the highest concentrations but low risk levels, suggesting their pollution is unlikely to have adverse effects on benthos.

Mapping of Sediment on the Waters Around Panjang Island, Banten Bay, Indonesia

This study was conducted to map the surface sediment conditions in the waters around Panjang Island, Banten Bay. The survey method was conducted in February 2015 by taking sediment samples using a grab sampler at 15 stations. Sediment analysis was conducted to determine the grain size using the granulometry method which was then processed using the KUMMOD-SEL software to obtain the composition and texture of the sediment. The results of processing sediment samples at each station obtained that the grain size of sediments in the waters around Panjang Island ranged from -0.7 to 2.6 in the phi (φ) scale. Sediment composition consists of sand and gravel, with sand dominance of 89.1 %. Sediment textural classification consists of only 4 categories i.e. very coarse sand, coarse sand, medium sand, and fine sand. In general, the pattern of sediment distribution follows the pattern of water depth, where fine sand occupies deeper areas. Meanwhile, medium sand dominates surface sediment distribution in the study area.

Characteristics of morphodynamic conditions in the shallows of Puck Bay (southern Baltic Sea)

Abstract Puck Bay is an unusual and thus interesting coastal water region, as it combines two different environments – a lagoon and the sea. They differ from each other in their seabed morphology, salinity, dynamics and water exchange. Their common elements are the extensive shallows and the vicinity of the Hel Peninsula. The shallows of Puck Bay have developed at various stages of its evolution, which began several thousand years ago and continues to this day. They have been shaped by varying morphogenetic factors resulting from changes in sea level and accompanying evolution phases of sand barriers, e.g. washover fans, as well as the intensity and directions of sediment transport. At present, the shallows cover more than 35% of the seabed area and are influenced by hydrodynamic factors and availability of sediments. The study area was divided into five fields, taking into account morphological and genetic criteria as well as recent hydrodynamic conditions. This study provides an updated map with classification and distribution of surface sediments and describes grain size parameters for sediment samples collected in the selected fields. Based on a comprehensive assessment of grain size parameters, lithodynamic equilibrium zones were determined and areas of sediment deposition and redeposition were identified.

Heavy metal pollutants and their spatial distribution in surface sediments from Thondi coast, Palk Bay, South India

BackgroundThe concentration of heavy metals and their spatial distribution in surface sediments collected from the Thondi coast, Palk Bay, South India were analysed in this study. The sediment grain size, pH, EC, and major elements (Fe, and Al), heavy metal concentrations (Mn, Cr, Zn, Cd, Ni, Cu, and Pb) were determined and the values for the geoaccumulation index (Igeo), enrichment factor (EF), potential contamination index (Cp), potential ecological risk index (RI), contamination factor (CF), modified contamination degree (mCd), degree of contamination (Cd), and potential contamination factors (Cp) were calculated based on their background values to determine the pollution level of the study area. Multivariate analysis such as Pearson’s correlation coefficient, principal component analysis/factor analysis (PCA/FA), cluster analysis, and regression analysis are a versatile method for identifying heavy metal sources and determining the relationship between pollutants in marine sediment.ResultsThe pollution indices, namely EF, CF, Cd, mCd, CP, RI, and Igeo, revealed that the heavy metal contamination was due to Cd, while a moderate level of contamination was caused by Cu, Zn, Pb, and Cr. The principal component analysis and correlation matrix analysis showed a strong positive loading for Cd due to its high level of contamination in the study area. Anthropogenic inputs such as municipal wastewater, domestic sewage discharge, fishing harbour activities, and industrial and aquaculture wastes led to the increased Cd concentration in the study area. Moreover, the pollution load index revealed that the sediments were polluted by heavy metals.ConclusionThe findings of this study revealed that the increased concentration of heavy metals in the study area increases the toxicity in the marine environment, thus affecting the ecosystem.

Response of mercury accumulation to anthropogenic pollution in the past 1000years based on Lake Huguangyan sediments, Southern China.

A new 210Pb-dated record of Hg accumulation derived from a sediment core from a Hg-enriched area in Huguangyan Lake (HGY) in South China is presented. Based on synthetic analyses of multi-proxy records including chemical composition, total organic matter, and grain-size distribution in surface sediments and nearby soil samples, it is inferred that the influx of Hg into the lake is mainly a result of atmospheric deposition, with no or minor hydroclimate-induced lithogenic input from the catchment and limited adsorption effects of organic matter and clay. Significantly enhanced anthropogenic input of Hg started in the early 1900s. Since then, several anomalies of Hg accumulation have been the results of wars or intensified economic activities in China. HGY sediments provide a rare and reliable natural archive for detecting atmospheric Hg deposition, which is closely related to anthropogenic activities.

Dinoflagellate cyst distribution in surface sediments of Ambon Bay (eastern Indonesia): Environmental conditions and harmful blooms

The present study aimed to document dinocyst ecological preferences in Ambon Bay, Eastern Indonesia, and to investigate if the bay sediments serve as a seedbank for toxic bloom events. To this end, dinocyst and geochemical analyses of surface sediment samples were performed, along with physicochemical water column parameters. Twentythree dinocyst species were identified, and high dinocyst concentrations (up to ~12,000 cysts g−1 dry sediment) were found in the inner bay. Environmental factors such as surface water temperature and salinity generally played an important role in dinocyst distribution. The concentration of Polysphaeridium zoharyi cysts showed a strong positive correlation with phosphorus. A statistically significant correlation was also found with the concentration of other autotrophic dinocysts in the sediments, and an inverse correlation was observed with the sediment C/N ratio. Cysts may serve as seedbanks for Pyrodinium bahamense blooms in the area.

Temporal and Spatial Distribution of Surface Sediment and Its Implications in the Yangtze Subaqueous Delta

Characteristics of sediments vary significantly temporally and spatially in the Yangtze subaqueous delta and adjacent East China Sea shelf due to complicated dynamic conditions. Magnetic properties of sediments are sensitive to hydrodynamics and provenance, and therefore can indicate sediment transportation and deposition. High-resolution surface sediments collected in different seasons and years from the Yangtze subaqueous delta and neighboring East China Sea shelf were subjected to environmental magnetic analyses. In combination with granulometric analysis, this paper discusses temporal and spatial variations of magnetic properties and their implications for indicating sediment transportation, sediment source identification, and hydrodynamic response. The results show that magnetic parameters SIRM and XARM/SIRM suggest sediment transportation path from the Yangtze River into the East China Sea, with majority migrating to the south and southeast and then deposited to the west of 123°E, while a little fine sediment delivered to the northeast in summer. Cluster analysis demonstrates three sedimentation districts according to magnetic properties and particle size in the study area, which represent modern Yangtze sediment, late Pleistocene relict sand, and their mixture, respectively. Temporal-spatial changes in particle size of sediments suggests erosion outside the North Branch in the past few years, while opposite trend of changes on particle size of surface sediment in the adjacent area might reflect different degrees of erosion.