The accumulation of heavy metals in marine sediments poses a significant threat to marine ecosystems. This study utilized a 210Pb-dated sediment core from Laizhou Bay to reconstruct historical sediment variability, trace heavy metal sources, and evaluate their contamination at a centennial timescale. By intergrating Self-Organizing Map, Principal Component Analysis and Positive Matrix Factorization, we conducted a comprehensive analysis of the sources of heavy metal pollution in Laizhou Bay. Our results revealed four distinct periods of heavy metal distribution into: 1906-1930, 1930-1976, 1976-2000, and 2000-2020, corresponding to shifts in human activities and changes in the Yellow River course over the past century. This study is the first to introduce the SOM algorithm into the field of heavy metal source analysis in Laizhou Bay, exhibiting better classification robustness for non-linearly coupled combinations like Co-Cr-Ni-V. By combined with PMF, we identified four primary sources of heavy metals: natural sources, mixed anthropogenic and natural sources, agricultural activities, and industrial production, with contribution rate of 28.37, 28.86, 14.03 and 28.74%, respectively. Notably, Cadmium (Cd) was identified as the most enriched pollutant, demonstrating pronounced anthropogenic amplification. These results provide valuable insights for targeted pollution mitigation strategies, emphasizing the need for source-specific management approaches in coastal zones under increasing anthropogenic pressure.

Water quality degradation threatens macrophyte-dominated lake ecosystems, necessitating systematic analysis of spatiotemporal patterns and anthropogenic drivers. This study examines two macrophytic lakes (East Taihu and Liangzi Lake) using water quality monitoring data (2005–2023) through trophic state index (TSI), comprehensive pollution index (Pw), and dynamic change analyses. The results reveal divergent trends: East Taihu Lake exhibited an increase in chlorophyll α, total phosphorus (TP), and ammonia-nitrogen (NH3-N), while total nitrogen (TN), permanganate index (CODMn), and secchi depth (SD) exhibited a decline. Prior to 2018, the TSI and Pw of East Taihu Lake exhibited an upward trend; however, after 2018, they demonstrated a gradual decline. Notably, the TSI of East Taihu Lake persists at a relatively elevated level (TSI > 50), thus being classified as eutrophic, with TP identified as the predominant contributor to water pollution (p< 0.01). All water quality indexes, TSI, and Pw of Liangzi Lake have shown an upward trend, but its TSI and Pw are lower than those of East Taihu Lake, being mesotrophic (30< TSI< 50), but in some stages it is close to eutrophic. CODMn and TP dominated Liangzi’s pollution (p< 0.01). Correlation analyses have identified intensive anthropogenic activities, including population growth, agricultural/industrial expansion, fertilizer/pesticide use, wastewater discharge, and cage aquaculture expansion – as key drivers of water quality deterioration. Meanwhile, the increase in nutrient concentrations and the outbreak of cyanobacterial blooms caused by the release of endogenous pollutants should not be overlooked. Effective restoration requires integrated strategies. These include: 1) controlling external pollutant loads, especially phosphorus inputs, 2) optimizing aquatic vegetation and fish communities, and 3) strengthening lake management regulations. These measures are essential for the restoration of the clear and stable state of macrophyte-dominated lakes.

Small lakes on the Yunnan-Kweichow Plateau of Southwest China are significant carbon sinks, and highly sensitive recorders of global climate change and human disturbance. However, the lack of robust sediment chronologies makes it challenging to unravel the dynamics of dissolved organic matter (DOM) accumulation in these sedimentary successions, and the driving mechanisms of change over historical timescales. In this paper, we constructed a robust chronology (1850-2019 CE) based on radioactive lead (210Pb) for Xihu Lake, and used elemental analysis, optical spectroscopy, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and stable carbon isotopic measurements to evaluate long-term variations in the abundance, source and composition of sedimentary DOM. We found that DOM abundance increased after 2000 CE due to intensive socio-economic activities and climatic warming within the watershed. Stable carbon isotopic results are consistent with spectral parameters, suggesting the additional DOM abundance was mainly derived from annual input from autochthonous aquatic plants. These autochthonous sources shifted the DOM pool into saturated and S-containing aliphatic compound and protein-like fluorescence component, which had higher bio-lability and mineralization potential. After successive mineralization for hundreds of years, sedimentary DOM underwent a transition characterized by reduced bio-lability and increased persistence with time gradients. More oxygenated, aromatic and high-molecular-weight DOM fractions were preserved in deeper and older sediments, which became a key component of lake carbon sinks. Furthermore, massive diagenetic transformations resulted in an increasing tendency in diversity and richness of molecular assemblage. This work provides a comprehensive understanding of historical inputs, degradations and preservations of sedimentary DOM, and offers new insights into our understanding of DOM dynamics from a paleolimnological perspective.

The freshwater lakes in the middle and lower reaches of the Yangtze River (MLYR) have been affected by a multitude of factors, including climate change and human activities, and are currently facing a range of aquatic ecological environment problems. In order to establish restoration goals and paths, it is essential to have a scientific understanding of the historical process and pattern of long-term degradation of the lake ecological environment. This study focused on Shengjin Lake, a representative Yangtze River-connected lake in MLYR. Based on the analysis results of cellulose carbon isotopes (delta C-13(cellulose)) in modern aquatic macrophytes, the response characteristics of aquatic macrophytes delta C-13(cellulose) to lake environment evolution were revealed by high-resolution multi-proxy (delta C-13(cellulose) of plant residues and geochemistry indices) analysis of a sediment core. The study also reconstructed the ecological environment evolution process of Shengjin Lake over the past two hundred years. The primary research findings are as follows: Firstly, the results of the modern process survey demonstrated that the delta C-13(cellulose) of different modern species exhibited considerable variation. The submerged plants exhibited an enrichment of C-13, while the emergent plants exhibited an enrichment of C-12. Secondly, a comprehensive modern process investigation, coupled with palaeo-limnological records and literature data, led to the conclusion that the large plant residues of sediments were primarily derived from submerged plants. Concurrently, statistical analysis indicated that the content of total organic carbon in lakes was the primary factor influencing the changes in sediment delta C-13(cellulose). The composition of delta C-13(cellulose) may be indicative of changes in lake primary productivity. Finally, the paleo-limnological record revealed that the ecological environment of Shengjin Lake has undergone significant changes over the past two hundred years. In particular, since the 1970 s, the delta C-13(cellulose) has been significantly enriched by C-12, and the geochemical indexes of elements have shown an increasing trend (p < 0.01). This suggests that the ecological environment of Shengjin Lake is gradually deteriorating as a consequence of human activities such as enclosure aquaculture and the construction of Huangpen Sluice, which have occurred in the context of climate warming and regional wind speed decrease in recent decades. This study presents new indicators and evidence for the reconstruction of the evolutionary process of the nutrient environment of lakes in MLYR. Moreover, it provides a foundation for the protection and restoration of lakes.

The broad leaf, deciduous black locust ( Robinia pseudoacacia ) and needle leaf, evergreen Chinese pine ( Pinus tabulaeformis ) are the major afforestation species on the Loess Plateau of China, accounting for 29.5% and 15.9% of the afforestation area, respectively. The decay of black locust and drying of the forest land soil in this region have caused serious concerns among scientific community and local management authorities. Understanding the hydrological characteristics of the afforestation plantation may provide clues for choosing proper species. However, previous studies demonstrated diverse or even contradictory understandings due to incomplete observations of the water balance. We used a model to reconstruct the water balance based on 5 years (2015–2019) of incomplete soil water and transpiration observations at the field for these two species. The R ‐squares of linear regression analysis of simulated and observed soil water in black locust and Chinese pine plantations were 0.69 and 0.90, respectively; and transpiration was 0.62 and 0.69, respectively. Based on the reconstructed water balance components, we found that (1) black locust and Chinese pine had similar annual evapotranspiration in quantity. However, the Chinese pine transpired less and evaporated more water from the canopy than the black locust, with their ratios to the annual precipitation 50.7% and 69.7%, 26.3% and 17.2%, respectively; (2) the Chinese pine has higher evapotranspiration than the black locust in the non‐growing season, accounting for 19.5% and 9.2% of the annual evapotranspiration, respectively; and (3) the Chinese pine is more tolerable to soil water drought than black locust. The findings may suggest that the Chinese pine is a more favourable species for afforestation than the black locust from the point view of drought resistance in this region.

Context Freshwater lakes are still facing a series of problems, e.g. a decline in water quality, and a decrease in biodiversity. Thus, assessing the state of aquatic ecological health of the lake has drawn widespread attention from scholars both at home and abroad. Aims This study aims to assess the state of aquatic ecological health of Poyang Lake and analyse the influencing factors. Methods The long-term (2007–2018) site-monitoring data were analysed on the basis of the extension–evaluation method and correlation-analysis method. Key results The results showed that the aquatic ecological health was mainly ‘good’, and remarkable seasonal differences were observed. The seasonal order of relative aquatic ecological health could be expressed as the wet season being better than the dry season, whereas the rising season was similar to the retreating season. And the pollutant discharged into the lake was found to be the key factor, and the hydrological conditions led to seasonal differences in the state of aquatic ecological health of Poyang Lake. Conclusions Consequently, scholars and policymakers should focus on both nutrient concentrations and hydrological conditions, which are the key factors influencing the aquatic ecological health of Poyang Lake. Implications The results of this study have provided a theoretical and practical basis of the causes of ecological deterioration and should help with ecological-health protection of the large lakes connected with the Yangtze River.

Evaluating the effectiveness of sediment retention by comparing the spatiotemporal burial of sediment C, N, and P in a plateau lake and its affiliated reservoirs is critical in dealing with global eutrophication in freshwater ecosystems. The objective of the study was to estimate the spatial-temporal of C, N and P accumulation rates (CAR, NAR and PAR) in sediment cores of a plateau Lake Dianchi (DC) and its four affiliated reservoirs (Dashiba-DSB, Xibaisha-XBS, Baoxianghe-BXH, and Shuanlong-SHL). The results indicated that the average sediment accumulation rates (SARs) ranged from 0.040 to 1.187 g cm(-2) a(-1) in DC and 0.201 to 3.965 g cm(-2) a(- 1) in its affiliated reservoirs. Spatially, all of the values of CAR, NAR and PAR exhibited similar distribution character-istics, along with two high-value regions concentrated in the southern and northern parts of the lake DC. Temporally, these three values of Lake DC and its affiliated reservoirs showed upward trends from bottom to top over the past similar to 150 years, especially occurring in the 1950s. The change in the C/N ratio indicated that intensive anthropogenic factors promoted the CAR, NAR and PAR in sediments. Based on a developed proportional model, the ratios of sediment retention by each reservoir on TOC, TN and TP were calculated to be 2.15 %, 4.38 % and 9.01 % for DSB, 0.14 %, 0.18 % and 0.14 % for XBS, 1.61 %, 5.77 % and 1.23 % for BXH, and 0.97 %, 2.07 % and 0.46 % for SHL, respectively. Reservoirs located in the upper and middle reaches of the lake catchment play a critical role in sediment retention and prevent a potential risk from water deterioration of the downstream Lake DC. Linkages between reservoir-sources and lake-sinks not only provide valuable information for managing the environmental changes within the catchment, but also contribute to new insight into the regulation of water eutrophication in global lake ecosystem.

Investigating the impacts of climatic factors and human activities on sedimentary records of heavy metal (HM) contamination in lakes is essential for decision-making in global environmental monitoring and assessment. Spatiotemporal distributions of grain size (GS) and HM (Al, Cr, Mn, Ni, Cu, Zn, As, and Pb) concentrations have been conducted in core sediments that are collected from two adjacent plateau fault-bound lakes in southwest China with contrasting environments, i.e., deep oligotrophic Lake Fuxian (FX) and shallow hypertrophic Lake Xingyun (XY). Results showed that the average value of d 50 in FX (4.61 μm) was lower than that in XY (8.35 μm), but the average concentrations of HMs (except Cr and Mn) in XY were higher than those in FX. Heavy metal burial rates (HMBR) were mainly controlled by sediment accumulation rates (SARs) rather than HM concentrations. The correlation coefficients between GS and HM concentrations became strong as the increasing water depths were associated with a stable sedimentary environment. Time-integrated enrichment factors (EF) and source identification of HMs between FX and XY represented that Cr, Ni, and Cu originated from natural sources but Mn, Zn, As, and Pb from anthropogenic sources, respectively. Regardless of FX and XY, the transition times of HMs from natural to anthropogenic sources occurred in the mid-1960s. Comparison of qualification impacts of climatic factors and human-induced factors on increased anthropogenic HMBR by the partial least squares path modeling (PLS-PM) implied that socio-economic activities, such as population density (PD) and gross domestic product (GDP), provided higher contributors to increased anthropogenic HMBR in XY (0.23/0.71) than FX (0.11/0.18). The comparative results of this study provided new insights into environmental monitoring and management of HM contamination for adjacent lakes with contrasting environments.

At present, East Taihu Lake has been profoundly affected by human interventions. However, the earlier limnological conditions such as the occurrence of temporal nodes and the cause of eutrophication remain unclear due to the short temporal range covered by the instrumental record. The stable carbon isotope ratio of plant residue α-cellulose (δ13Ccellulose) is a sensitive proxy indicator of palaeoproductivity, but this proxy index is rarely used in Chinese lakes. In order to test whether δ13Ccellulose can be used as a lake ecological environment changes indicator, we investigated the relationship between the δ13Ccellulose and several geochemical proxies from a ∼ 30 cm core extending 100 years obtained from a shallow lake: East Taihu Lake, China. Here, the changes in δ13Ccellulose of plant residues in sediments from East Taihu Lake were coupled analysis with geochemistry indexes to identify the response of δ13Ccellulose from plant residues to the past environmental changes. Combined with the results of C/N ratios, δ13Ccellulose and other related studies, the big plant residues in the sediments of East Taihu Lake may be derived from autochthonous aquatic macrophytes. In addition, the δ13Ccellulose showed a significant negative correlation with total organic carbon, probably indicating the changes of primary productivity of the lake. The δ13Ccellulose and geochemical proxy records revealed that the environmental changes in East Taihu Lake have undergone three distinct periods. The first period (1900s-1960s) represented a natural state without intensive human disturbance. The acceleration of lake eutrophication from the middle period (1960s-1995s) was a consequence of intensive local human activities. The late stage (1995s-2010s) represented a minor decline in nutrient levels after the implementation of ecological protection and restoration. By comparing the results with historical documents and measurements from East Taihu Lake, we inferred that anthropogenic pressures were the primary cause of the changes in the aquatic macrophyte communities and environments. This study provides a unique approach to the ecological environment evolution of East Taihu Lake. At present, Taihu Lake still suffers from annual cyanobacterial blooms due to economic growth (urbanization and industrialization). There is an urgent need for interventions to reduce nutrient inputs in order to enhance ecosystem resilience. Finally, the results of study of East Taihu Lake in China reveal the potential of combining δ13Ccellulose and other geochemical proxies to study palaeoenvironmental change, which provides new perspectives for understanding lake ecological environmental change in lakes.

Discriminating the potential sources contributing to lacustrine sediment is helpful for decision-making for catchment soils and lake management strategies within lake-catchment systems. Using a sediment fingerprinting approach from the multivariate mixing model, the spatiotemporal sources of geology and land use were identified in a small agricultural catchment in southwest China. Results showed that sediment accumulation rates (SARs) were estimated to range from 0.002 to 0.065 g cm−2 a−1 (mean 0.015 ± 0.016 g cm−2 a−1), which has a positive correlation with instrumental Indian Summer Monsoon (ISM) precipitation. Time-integrated sources were divided into four zones in combination with the changes in SARs, which were qualitatively and quantitively interpreted by particle size, and precipitation, and historical land use polies over the past ~160 years. Spatially, Quaternary granite (QG) in geology and channel bank (CB) in land use were the dominant contributors to the lakeshore sediment, respectively. Two relatively higher contributions of abandoned land (AL) to lakeshore sediment were found during the periods of 1930s–1950s and post-1990s, which originated from the dual impacts of topographical factors of slope gradient and elevation, and socioeconomic factors of the gap of farmer’s expenditure to income. The results illustrate that restricting the farmland to be abandoned would be useful for reducing the soil erosion within the lake-catchment system.

The Aral Sea has been persistently shrinking in past decades, and the influence of the lake water level changes on vegetation in the lake retreat areas is uncertain. In this study, we quantitatively assessed the vegetation development due to relevant hydrological changes in the retreat area of the Aral Sea. The results showed that the normalized difference vegetation index (NDVI) in the retreat area displayed an overall increase from 1986 to 2020. The increasing vegetated area accounted for 84 % of the total area of the South Aral Sea, which was caused by an increase in the exposed lakebed area. However, about 40 % of the area in the North Aral Sea was the increasing vegetated area due to the improved water environment. When the depth to water table (DTW) was larger than 7-8 m, vegetation development was more dependent on precipitation than groundwater. When DTW was less than 7-8 m, groundwater had a more significant impact than precipitation on vegetation development. The negative impacts of groundwater salinity exceed the positive contributions of water supply on vegetation development, which differs to the common understanding under conditions of fresh or brackish groundwater in arid climates. Water level recovery is an effective option for improving vegetation establishment on the exposed seabed; otherwise, the exposed seabed area observed during the period 1990s-2010s in the eastern basin may remain a saline desert for a long period in the future. Finally, an empirical relationship between NDVI and water levels was established, which can be used for lake water level management that considers vegetation development in the retreated area of the Aral Sea.

The incredible drying of the Aral Sea has resulted in a large area of exposed seafloor with saline soils, which has led to catastrophic consequences. This study investigated ground-truth soil salinity data and used Landsat data to map the soil salinity distribution of the exposed seabed of the Aral Sea from 1960 onwards. The soil salinity distribution, with the depth from 0 cm to 100 cm, was analyzed. The correlation analysis was applied to find the best performance index in describing soil salinity changes. The results showed that ground-truth data of topsoil salinity (depth of 0−5 cm) exhibited a significantly strong correlation with soil salinity index 4 (SI4) among seven indices, where the Pearson correlation coefficient (r) was up to 0.92. Based on the relationship between soil salinity sampling data and SI4, a linear regression model was employed to determine the capability of evaluating the soil salinity distribution of the Aral Sea with the coefficient of determination (R2), root mean squared error (RMSE), and ratio of performance to deviation (RPD) values of 0.84 and 0.86 dS m−1 and 2.36, respectively. The SI4 performed well and was used to predict the soil salinity distribution on the exposed seabed. The distribution showed that soil salinity increased from the former to current shoreline. In the North Aral Sea, compared to 1986, the water area remained stable, accounting for 50.3% in 2020, and the soil salinization level was relatively low. However, the moderately and slightly saline areas dominated 73.8% and 7.5% of the South Aral Sea in 2020, with an increase of 53% and 6% transformed from the water area. The area of salinized soils dramatically increased. The strongly and extremely saline areas were mainly located in the northeastern part of the eastern basin and western part of Vozrozhdeniya Island, respectively, and were the main source of salt-dust storms. These results support the dynamic monitoring and distribution patterns of soil salinization in the Aral Sea.

The radionuclide, beryllium-7 (7Be) has been widely used as a nuclear trace element to study surface soil particle migration and identify sediment sources in short-term processes. In this study, we measured 7Be concentration in vegetation and its interception (7Be deposition intercepted by vegetation) and absorption from the atmosphere on the slopes of the Yangtze river delta. We report the concentrations of 7Be were highest in dry plants and lower in cultivated crops. 7Be interception amounts varied greatly among different plant species, with an average interception ratio of 7Be plant inventories to soil deposition of 13 ± 8%. There is a significant positive correlation between biomass and 7Be interception in natural and wild plants. The depositional 7Be was redistributed by the covering vegetation. This study provides an important basis for using 7Be as a tracer for soil erosion under vegetation cover.

通过测试南漪湖2008年、2014年和2015年沉积物柱芯中的环境放射性核素210 Pbex和137 Cs,辅以相互印证的210 Pb CRS计年模式和137 Cs定年时标方法,定量估算了南漪湖过去百余年间的沉积速率变化;基于遥感目视解译方法获得了南漪湖1985—2016年湖泊面积时空变化,结合构建的湖泊泥沙输移模型,定量估算了南漪湖出湖河流的年均泥沙输移量;基于此,进一步分析了湖泊沉积速率和泥沙输移通量与湖泊面积变化之间的相关关系.结果表明:南漪湖同一湖区不同年份沉积物柱芯剖面中210 Pbex和137 Cs比活度分布特征相近,210 Pbex比活度遵循随深度增加而减小的趋势,137 Cs则在24和16 cm左右分别记录了1954年首次沉降和1963年最大沉降蓄积峰值;南漪湖沉积速率整体呈现波动变化趋势,在20世纪50年代前后沉积速率出现极大值,随后至采样年份该沉积速率呈缓慢上升趋势,这种变化可能与不同历史时期的自然因素和人类活动密切相关;过去31年间,南漪湖湖泊面积整体上呈缩小趋势,减少了57.37 km2,主要集中于西北、东北和东南部等区域,湖泊周边过度围垦是影响湖泊面积变化的主导性因素;南漪湖出湖河流的年均泥沙输移量约为1904.60 t∕a,湖泊沉积速率和泥沙输移通量受湖泊面积变化影响较大,随着湖泊面积的增加,湖泊沉积速率和泥沙输移通量分别呈指数降低和线性增加的趋势.

Evaluation of the spatial and temporal composition of floodplain sediments and soils is critical in the creation of soil management strategies for impacted riverine catchments. The objective of this study was to determine the distribution, and to identify the sources, of particulate trace elements and fallout radionuclides in the catchment of the River Avon (SW England), where sedimentary processes had been altered by reservoir construction in the 1950s. The catchment was compartmentalized into its main functional units namely, cultivated land, pasture, woodland, wet moorland, and channel bank. Surface soils were collected in each unit, along with four strategically-placed cores, all of which were analyzed for particle size, fallout radionuclides and elemental concentrations. Sediment particle sizes and sediment accumulation rates were affected by the construction of the reservoir, specifically the distributions of silt and clay. The concentrations of fertilizer constituent Cr and P were highly correlated in the mid-catchment but were unrelated downstream due to elevated concentrations of Cr from geological deposits. Copper, As, Pb and Sn had variable down-core distributions, with pulses in concentrations due to mining inputs. The contributions of the end-member sources of particulate elements in the sedimentary mixtures were evaluated, quantitatively, using a Bayesian Mixing Model and the cultivated land was identified as a significant contributor to the mixtures, independent of space and time. The results contribute to advances in soil quality and conservation measures as components of a catchment management plan for the Avon, an approach maybe applicable to other small catchments in the UK and internationally.

Polymodal distributions and end-member modeling of grain-size in lacustrine sediments can reveal the changes in sedimentary processes, transportation mechanisms, and climatic changes. The temporal and spatial variation characteristics of grain-size were investigated in six sediment cores of the plateau deep-lake Fuxian, in southwest China, where the climate was driven by Indian Summer Monsoon (ISM). Results indicated that the size of the dominant grain-size exponentially decreased with the declining hydrodynamic condition towards the deep-water zones, with an exception of the maximum grain-size near the outlet of the lake. Measured grain-size distributions were classified into four end-members (EMs) with a basic end-member model algorithm (BasEMMA), of which could be linked to a distinct transport mechanism and source: EM1 (long-term suspended load from atmospheric dust) with the modal size of 0.3–11.2 µm, EM2 (off-shore suspended load from fine riverine input) with 7.9–14.2 µm, EM3 ((near-shore suspended load from coarse riverine input) with 15.9–31.7 µm, and EM4 (near-shore riverbed load from extremely coarse riverine input) with 35.6–70.9 µm, respectively. Temporal variation of EM2 + EM3 components of grain-size in Core F5 are responses to the changes in instrumentally recorded precipitation in Chengjiang (1961–2008) and ISM (1860–2006), which indicates that changes in river flow in response to changes in precipitation is the primary driver of clastic sediment deposition especially in the narrow section of the lake. Our findings indicate grain-size distribution and sediment compositions are significant tools for improving the understanding of the spatiotemporal heterogeneity in dry-humid transformation of ISM over the past 150 years.

Topographic factors such as slope and aspect are essential parameters in depicting the structure and morphology of a terrain surface. We study the effect of the number of points in the neighbourhood of a digital elevation model (DEM) interpolation method on mean slope, mean aspect, and RMSEs of slope and aspect from the interpolated DEM. As the moving least squares (MLS) method can maintain the inherent properties and other characteristics of a surface, this method is chosen for DEM interpolation. Three areas containing different types of topographic features are selected for study. Simulated data from a Gauss surface is also used for comparison. First, the impact of the number of points on the DEM root mean square error (RMSE) is analysed. The DEM RMSE in the three study areas decreases gradually with the number of points in the neighbourhood. In addition, the effect of the number of points in the neighbourhood on mean slope and mean aspect was studied across varying topographies through regression analysis. The two variables respond differently to changes in terrain. However, the RMSEs of the slope and aspect in all study areas are logarithmically related to the number of points in the neighbourhood and the values decrease uniformly as the number of points in the neighbourhood increases. With more points in the neighbourhood, the RMSEs of the slope and aspect are not sensitive to topography differences and the same trends are observed for the three studied quantities. Results for the Gauss surface are similar. Finally, this study analyses the spatial distribution of slope and aspect errors. The slope error is concentrated in ridges, valleys, steep-slope areas, and ditch edges while the aspect error is concentrated in ridges, valleys, and flat regions. With more points in the neighbourhood, the number of grid cells in which the slope error is greater than 15° is gradually reduced. With similar terrain types and data sources, if the calculation efficiency is not a concern, sufficient points in the spatial autocorrelation range should be analysed in the neighbourhood to maximize the accuracy of the slope and aspect. However, selecting between 10 and 12 points in the neighbourhood is economical.

Channelization significantly affects soil erosion in river floodplains. The object of this study was to use Cs-137 as a tracer to determine the Cs-137 inventory and derived soil erosion rates under various land use types in a catchment on channelized river floodplain in the lower reaches of Yangtze River, China. Sampling was carried out to establish a Cs-137 reference inventory in a 70-year old paddy field located on the shoulder-slope of a local hill. The mean reference inventory of Cs-137 was 1275 Bq m(-2), whereas the Cs-137 inventory within the catchment ranged from 284 to 1150 Bqm(-2) and the soil erosion rates from -33.3 to - 2.4 t ha(-1) yr(-1), respectively. The dominated land use of paddy in cultivated soils contributed relative low soil erosion. Bamboo and castanea mollissitna were preferential for local land uses in uncultivated soils in comparison with woodland and Pinnus massoniana. The rates of soil erosion rates in old tea garden were higher than that in new tea garden. Overall, severe soil erosion and no deposition in the entire catchment occurred in the entire catchment due to the human-induced channelization in the 1970s. Our results suggest that restricting farmland being returned to tea plantations, thereby maintaining the current land use types would reduce soil erosion in river floodplain in the future.