Lake Plain Research Articles

Ecological risk of heavy metals in lake sediments of China: A national-scale integrated analysis

Intensive anthropogenic activities, specifically, industrial and agricultural production, have resulted in heavy metal enrichment in lake sediment and threats to aquatic ecosystems and human health. Evaluating the potential ecological risk of heavy metals in lake sediment is essential for promoting appropriate lake management in aquatic ecosystems. Large-spatial scale risk evaluations of heavy metal pollution in lake sediment in densely populated countries such as China are lacking. We compiled sediment heavy metal (Cu, Pb, Zn, Ni, Cr, As, Hg, and Cd) data from 190 lakes distributed across five geographic zones in China published between 2000 and 2019, evaluated the potential ecological risk and identified heavy metal sources through positive matrix factorization. Five conclusions were drawn. (1) Regarding the eight collected heavy metals, 6.1–40.4% of 190 lakes exhibited higher concentrations than the Chinese soil background value, and the concentration in 6.2% of lakes exceeded the probable effect concentration. (2) Based on the potential ecological risk index (PERI) and sum of toxic units (STU), Cd and Hg were the major pollutants. (3) The PERI value notably decreased with increasing lake surface area, and small lakes (<10 km2) generally yielded high PERI values. Among the five Chinese geographic zones, the Eastern Plain Lake Zone and Inner Mongolia-Xinjiang Lake Zone exhibited higher potential ecological risk. Compared to natural lakes, urban lakes and reservoirs posed higher ecological risks, while freshwater lakes yielded higher PERI values than saltwater lakes and saline lakes. (4) In all lakes, lake sediment pollutants Cu and Zn mainly originated from traffic sources; Cd originated from agricultural activities; Pb and Hg were related to industrial activities; and Ni, Cr and As indicated mixed sources. (5) In the Eastern Plain Lake Zone, Yunnan-Guizhou Plateau Lake Zone and Northeast Plain and Mountain Lake Zone, industry was the dominant source of heavy metals in lake sediment, while in the Tibetan Plateau Lake Zone and Inner Mongolia-Xinjiang Lake Zone, except for industrial sources, agricultural sources played an important role. Our national-scale integrated analysis provides valuable references for both macroscale policy formulation and polluted lake restoration.

Smallholder rice farming practices across livelihood strategies: A case study of the Poyang Lake Plain, China

In the past four decades, the livelihood strategies of Chinese smallholder farmers have become increasingly diversified and individualized, and consequently, their rice growing practices have diverged. However, few studies have identified how rice growing practices change with livelihood strategies. To address this challenge, this study employs an integrated smallholder livelihood strategy framework and uses crosssectional data in 2018 covering 250 smallholder farmers who belonging to 90 households in 10 villages in the Poyang Lake Plain, southern China. The results show that livelihood strategies were grouped into five categories based on the allocation of labor input, and the factors that differentiate the farmers adopting rice farming-dominated livelihoods from other farmers include age, sex, education level, health, annual income, the number of appliances and land area. Farmers who relied heavily on rice growing for their livelihoods grew larger area of rice paddy, invested more per unit area, applied more types of agrochemicals and obtained higher unit yields than those farmers spending most of their time on off-farm enterprises. However, the income of the former was much lower than that of the latter due to the low return of rice farming. There is no significant difference in the application weight of agrochemicals across livelihood strategies, which implies that farmers who do not heavily depend on rice growing excessively apply agrochemicals that cannot effectively increase rice yields. Based on these findings, we suggest that the government should implement measures to substantially increase the return of rice growing and educate rice farmers so they will adopt more environmentally friendly practices for applying agrochemicals.

Landscape controls of surface-water/groundwater interactions on shallow outwash lakes: how the long-term groundwater signal overrides interannual variability due to evaporative effects

The spatial and temporal controls on variability of the relative contributions of groundwater within and between flow systems to shallow lakes in the low-relief glaciated Boreal Plains of Canada were evaluated. Eleven lakes located in a coarse glacial outwash, of varying topographic positions and potential groundwater contributing areas, were sampled annually for stable O and H isotope ratios over the course of 8 years. It was demonstrated that landscape position is the dominant control over relative groundwater contributions to these lakes and the spatial pattern of the long-term isotopic compositions attributed to groundwater overrides interannual variability due to evaporative effects. Lakes at low landscape positions with large potential groundwater capture areas have relatively higher and more consistent groundwater contributions and low interannual variability of isotopic composition. Isolated lakes high in the landscape experience high interannual variability as they have little to no groundwater input to buffer the volumetric or isotopic changes caused by evaporation and precipitation. An alternative explanation that lake morphometry (area and volume) control long-term isotopic compositions is tested and subsequently refuted. Landscape position within coarse outwash is a strong predictor for relative groundwater input; however, surface-water connections can short circuit groundwater pathways and confound the signal. A hydrogeological case study for three of the study lakes is used to contextualize and further demonstrate these results.

Total suspended solids characterization and management implications for lakes in East China

In this study, we empirically developed a robust model (the Root Mean Square Error (RMSE), bias, NSE and RE were 26.63 mg/L, −4.86 mg/L, 0.47 and 16.47%, respectively) for estimating the total suspended solids (TSS) concentrations in lakes and reservoirs (Hereinafter referred to as lakes) across the Eastern Plain Lake (EPL) Zone. The model was based on 700 in-situ TSS samples collected during 2007–2020 and logarithmic transformed red band reflectance of Landsat data. Based on the Google Earth Engine (GEE), the TSS concentrations in 16,804 lakes were mapped from 1984 to 2019. The results demonstrated a decreasing tendency of TSS in 82.2% of the examined lakes (72.5% of the basins) indicating that the pollutants carried by TSS flowing into the lakes were decreasing. Statistically significant variation (p < 0.05) was found in half of these lakes (28.6% of the basins). High TSS level (>100 mg/L) was observed in 0.31% of lakes (1.1% of the basins). The changing rates of TSS in 47.8% of the lakes (52.7% of the basins) ranged between −50 mg/L/yr and 0. We found high and significantly increased relative spatial heterogeneity of TSS in 4.6% and 6.5% of lakes, respectively. Likewise, the environmental factors, i.e., fertilizer usage, domestic wastewater, industrial wastewater, precipitation, wind speed and Normalized Difference Vegetation Index (NDVI) exhibited a significant correlation with interannual TSS in 38, 21, 20, 11, 17 and 15 of the 91 basins, respectively. This analysis indicated that only precipitation and fertilizer usage were significantly (p < 0.05) related to the spatial distribution of TSS. The relative contributions of the six factors to the interannual TSS changes were varied in different basins. Overall, the NDVI (the representation of vegetation cover) had a high mean contribution to the interannual TSS changes with an average contribution of 7.2%, and contributions of fertilizer were varied greatly among the basins (0.01%–68%). Human activities (fertilizer usage, domestic wastewater, industrial wastewater) and natural factors (precipitation, wind speed and NDVI) played relatively important roles to TSS changes in 14 and 15 of the 91 basins, respectively. Beyond the six factors in this study, other unanalyzed factors (such as lake depth and soil texture) also had some impacts on the distribution of TSS in the study area.

Characteristics of Dissolved Organic Carbon in Boreal Lakes: High Spatial and Inter‐Annual Variability Controlled by Landscape Attributes and Wet‐Dry Periods

AbstractConcentration and chemical composition of dissolved organic carbon (DOC) influence several lake functions; greenhouse gas exchange, nutrient cycling, food webs, and water treatability. To assess spatial and inter‐annual controls on DOC characteristics, 34 lakes were sampled annually for 8 years on the Boreal Plains, Western Canada—a region with heterogeneous surficial geology, and a sub‐humid climate with pronounced inter‐annual wet‐dry periods. Large spatial variability in long‐term average DOC concentration (10–49 mg C L−1) and aromaticity (SUVA254: 1.2–3.9 L mg−1 C m−1) among lakes was found. Higher DOC concentrations and aromaticity were associated with lakes in watersheds with fine‐textured surficial geology and with relatively large contributions through shallow, organic‐rich flow paths. Lake DOC aromaticity was also higher in lakes with lower evaporative enrichment, regardless of surficial geology, indicating shorter lake water residence times and less within‐lake degradation of allochthonous DOC. High inter‐annual variability for both DOC and aromaticity was observed, with coefficients of variation at 10.9 ± 4.6% and 11.1 ± 2.5% among lakes, respectively. Inter‐annual variability in DOC concentrations had low synchronicity among lakes, with patterns of variability linked to surficial geology and primarily responsive to short‐term cumulative precipitation. Conversely, inter‐annual variability in aromaticity had high synchronicity among lakes, driven by longer‐term cumulative precipitation and shifts in lake water residence times. Our study shows it is necessary to consider lake hydrogeomorphic setting and climate to understand spatial and inter‐annual variability in lake DOC characteristics and associated lake functions, and that Boreal Plains lakes have high climate sensitivity.

Estimating the Gross Primary Production and Evapotranspiration of Rice Paddy Fields in the Sub-Tropical Region of China Using a Remotely-Sensed Based Water-Carbon Coupled Model

Rice serves as the staple food for over 50% of the global population. Remotely-sensed based estimation of the gross primary production (GPP) and evapotranspiration (ET) of rice paddy fields is essential to assess global food security. In this study, we tested the application of a recently proposed remotely-sensed based water-carbon coupled model (PML-V2) in the lower reaches of the Poyang Lake plain, which is one of the nine production bases for crops in China. Evaluation using the eddy covariance measurements showed that, after parameter localization, the model reproduced the seasonal variations of GPP and ET for both the early rice and the late rice. The model performed reasonably well in the validation period because the key parameters (e.g., the quantum efficiency and the stomatal conductance coefficient) exhibited predictable seasonal variations. At the regional scale, the spatial distribution in multi-year GPP of rice (1365 ± 326 gCm−2year−1) can be explained by the vegetation cover fraction (R2 &gt; 0.9); in comparison, the multi-year ET (1003 ± 65 mm/year) exhibits smaller spatial variations due to the high evaporation rate of the saturated soil surface of paddy fields. The water use efficiency of rice in this region varies around 1.35 gC/kgH2O with a standard deviation of 0.30. Our study shows that GPP and ET of rice can be estimated by remote sensing models without detailed crop management information, which is usually unavailable at regional scales.

Hydrochemical and hydrobiological characteristics of the Torey Plain lakes during the period of the lowest territory moisture

The largest salt lakes on the territory of Southeastern Transbaikalia and Northeastern Mongolia have been studied. It is shown that all lakes differ in hydrochemical and hydrobiological characteristics. According to the chemical composition of water, they belong to the soda type and sodium, carbonate, bicarbonate and chloride ions are predominant. Sulfates are in a subordinate meaning. The established relationship between abiotic and biotic parameters indicates the conjugation of biogeochemical processes involved in the formation of the soda type of lakes through the carbon cycle.

Spatiotemporal Evolution and Improvement Potential of Agricultural Eco-efficiency in Jiangsu Province

This study evaluated the agricultural eco-efficiency (AEE) of 77 counties and districts in Jiangsu Province from 1999 to 2018 using the slack-based measure (SBM) of efficiency in data envelopment analysis (DEA) (SBM-DEA) and analyzed its spatiotemporal evolution characteristics and influencing factors. We found that 1) the overall AEE, pure technology efficiency (PTE), and scale efficiency (SE) exhibited a fluctuating downward trend. AEE exhibited a significantly positive spatial association and an increasingly widening regional inequality. 2) AEE featured the “high south” and “low north” spatial pattern, with the high-value regions concentrated around the Taihu Lake plain region in southern Jiangsu Province (Sunan) and low-value regions scattered across most of the northern Jiangsu Province (Subei) cities. The high-high and low-low spatial association types further confirmed the existence of the north–south agglomeration pattern. 3) PTE and SE exhibited a similar “high south” and “low north” spatial pattern to that of AEE. The areas with the growth trends of AEE, PTE, and SE were clustered in Xuzhou and Nanjing city and in the bordering regions between Yangzhou and the Huai’an city, and also between Changzhou and the Wuxi city. 4) Excessive redundant input and use of pesticides, chemical fertilizers, agricultural diesel, labor, land, and agricultural carbon emissions, all have been the primary factors affecting Jiangsu’s AEE. Irrigation also considerably affected AEE, while mechanical power and agricultural film have minimal effects. The majority of counties and districts in the Subei, central Jiangsu Province (Suzhong), and Ningzhen Yang Hilly region experienced excessive usage of chemical fertilizers, pesticides, chemical fertilizers, agricultural diesel, labor, and land. The findings can improve understanding of the spatial association effect and underlying impediment of AEE and can further help policymakers promoting agricultural eco-efficiency.

Assessment of the values of science, education, tourism and the risk degradation of Pentadio geothermal areas to developing geotourism in the Limboto Lake Plain, Gorontalo

Geothermal areas are unique. Therefore, it can be developed to become a geotourism destination. Limboto Lake plain has geothermal potential which is indicated by the appearance of several points of manifestation. This study aims to assess the value of science, education, tourism and the risk of degradation in the geothermal area of the Limboto Lake plain unit. The method used is the assessment of the value of science, education, tourism and the risk degradation issued by the Geological Agency. The assessment was carried out in two geothermal areas located on the plain of Lake Limboto, namely Geothermal Pentadio. The research results showed that the weighting of the criteria for the values of science, education, tourism and the risk degradation in the Pentadio geothermal area were 73.75%, 73.75%, 75%, 65%, respectively.

Spatial variability and potential controls of soil organic matter in the Eastern Dongting Lake Plain in southern China

Spatial variability and potential controls of soil organic matter in the Eastern Dongting Lake Plain in southern China

An automatic classification algorithm for submerged aquatic vegetation in shallow lakes using Landsat imagery

Submerged aquatic vegetation (SAV) is one of the main producers in inland lakes. Tracking the temporal and spatial changes in SAV is crucial for the identification of state changes in lacustrine ecosystems, such as changes in light, nutrients, and temperature. However, the available SAV classification algorithms based on remote sensing are highly dependent on field survey data and/or human interventions, prohibiting the extraction of large-scale and/or long-term patterns. Here, we developed an automatic SAV classification algorithm using Landsat imagery, where the thresholds of two key parameters (the floating algae index (FAI) and reflectance in the shortwave-infrared (SWIR) band) are automatically determined. The algorithm was applied to eight Landsat images of four Yangtze Plain lakes and obtained a mean producer accuracy of 82.9% when gauged against field-surveyed datasets. The algorithm was further employed to obtain long-term SAV areal data from Changdang Lake on the Yangtze Plain from 1984 to 2018, and the result was highly consistent with lake transparency data. Numerical simulations indicated that our developed algorithm is insensitive to the Chl-a concentration of the water column. Yet, it has a detection limit of ~0.35 m below the water surface, and such a limit changes with different fractions of vegetation coverage within a pixel. The automatic classification algorithm proposed in this study has the potential to obtain the temporal and spatial distribution patterns of SAV in other shallow lakes where SAV grows in lakes sharing similar hydrological characteristics as the lakes in the Yangtze Plain.

Where there is smoke there is mercury: Assessing boreal forest fire mercury emissions using aircraft and highlighting uncertainties associated with upscaling emissions estimates

Abstract. Emissions from biomass burning are an important source of mercury (Hg) to the atmosphere and an integral component of the global Hg biogeochemical cycle. In 2018, measurements of gaseous elemental Hg (GEM) were taken on board a research aircraft along with a series of co-emitted contaminants in the emissions plume of an 88 km2 boreal forest wildfire on the Garson Lake Plain (GLP) in NW Saskatchewan, Canada. A series of four flight tracks were made perpendicular to the plume at increasing distances from the fire, each with three to five passes at different altitudes at each downwind location. The maximum GEM concentration measured on the flight was 2.88 ng m−3, which is ≈ 2.4× background concentration. GEM concentrations were significantly correlated with the co-emitted carbon species (CO, CO2, and CH4). Emissions ratios (ERs) were calculated from measured GEM and carbon co-contaminant data. Using the most correlated (least uncertain) of these ratios (GEM:CO), GEM concentrations were estimated at the higher 0.5 Hz time resolution of the CO measurements, resulting in maximum GEM concentrations and enhancements of 6.76 ng m−3 and ≈ 5.6×, respectively. Extrapolating the estimated maximum 0.5 Hz GEM concentration data from each downwind location back to source, 1 km and 1 m (from fire) concentrations were predicted to be 12.9 and 30.0 ng m−3, or enhancements of ≈ 11× and ≈ 25×, respectively. ERs and emissions factors (EFs) derived from the measured data and literature values were also used to calculate Hg emissions estimates on three spatial scales: (i) the GLP fires themselves, (ii) all boreal forest biomass burning, and (iii) global biomass burning. The most robust estimate was of the GLP fires (21 ± 10 kg of Hg) using calculated EFs that used minimal literature-derived data. Using the Top-down Emission Rate Retrieval Algorithm (TERRA), we were able to determine a similar emission estimate of 22 ± 7 kg of Hg. The elevated uncertainties of the other estimates and high variability between the different methods used in the calculations highlight concerns with some of the assumptions that have been used in calculating Hg biomass burning in the literature. Among these problematic assumptions are variable ERs of contaminants based on vegetation type and fire intensity, differing atmospheric lifetimes of emitted contaminants, the use of only one co-contaminant in emissions estimate calculations, and the paucity of atmospheric Hg species concentration measurements in biomass burning plumes.

Quaternary Geology of the Indiana Portion of the Eastern Extent of the South Bend 30- x 60-Minute Quadrangle

The Quaternary Geology of the eastern South Bend 30- x 60-Minute Quadrangle in Indiana represents landforms and near-surface sediments deposited during the Wisconsin Episode, Late Pleistocene. Sediments and landforms reflect the interplay between the Saginaw and Michigan Lobes of the Laurentide Ice Sheet. A relatively shallow, buried pre-Wisconsin and mid-Wisconsin morphology has been overridden by advances leading to the Last Glacial Maximum (LGM), ca. 24 ka. Between 24 and 17 ka, retreating ice fronts from the Michigan Lobe left a succession of ice-contact sediment ramps and associated pitted and collapsed fan-moraine complexes throughout the south and west of the map area. A sequence of stacked diamicton and sand and gravel fan heads appears at the hinged interlobate area north and northeast of South Bend. Ice margin positions are marked by distinct features like fans, kames and ice-walled lake plains, which are well developed on Michigan Lobe margins. The thicker glaciofluvial sand and gravel packages appear mostly interbedded with diamicton beds along fan heads, with relatively minor deposits in valley train units. Lowlands are mostly occupied by post-LGM (ca. 18 ka) valley-train outwash deposits, with interpreted flow toward the south and west, derived from an ice margin retreating first from south to north, near Mishawaka, then from southeast to northwest across the Kankakee valley. Sand and gravel colluvial and alluvial fans developed in a short span after ice retreated, along with incision of the ice-sculpted morphology. Late-glacial aeolian sand dunes sealed the landscape. Relatively minor modification of the landscape during the Holocene is indicated by alluvial and palustrine deposits.

Spatial Variation in Cadmium and Mercury and Factors Influencing Their Potential Ecological Risks in Farmland Soil in Poyang Lake Plain, China

Due to the irreversibility of heavy metal pollution, the presence of heavy metals in farmland soil is associated with severe ecological risks that endanger both the environment and human health. Cadmium (Cd) and mercury (Hg) are two toxic heavy metals found widely in polluted soil. Cd is not readily fixed in the soil and is therefore easily accumulated by plants, while Hg has a wide range of pollution sources. The aims of this study were to explore the spatial variation in Cd and Hg concentrations in farmland soil in Poyang Lake Plain, China, and to assess their potential ecological risks as influenced by natural and human factors. A total of 283 soil samples were obtained from Fengcheng city, central Jiangxi Province. Data were then analyzed using geostatistics, the potential ecological risk index, Pearson’s correlation analysis, and Geodetector. The results showed moderate variation in soil Cd and Hg concentrations, with a remarkable difference in their spatial distribution. Cd concentrations in the northwest and northeast of Fengcheng were below the regional background level in Jiangxi; in most remaining areas, Cd concentrations were between the regional background level and national risk screening value. Areas with Hg concentrations lower than the regional background level were largely concentrated in the south, east and north of Fengcheng, and gradually increased towards the central, where they exceeded the regional background level but were below the national risk screening value. Overall, the potential ecological risk level of Cd was predominantly low, while that of Hg was moderate. The comprehensive potential ecological risk was low in most areas for both Cd and Hg, with some scattered areas of moderate risk. Moreover, the comprehensive potential ecological risk index of both Cd and Hg was significantly correlated with soil pH, total phosphorous, elevation, distance from a river (p &amp;lt; 0.01), and distance from a road (p &amp;lt; 0.05). The most significant factor influencing the comprehensive potential ecological risk index of these two heavy metals was soil pH of 5.2–5.6, followed by total p ≤ 0.52 mg kg−1. In conclusion, moderate pollution of Cd and Hg occurred in farmland soil in Poyang Lake Plain where their comprehensive potential ecological risk level was generally low and mainly influenced by soil pH and total phosphorous.

Sources and hydrogeological conditions that cause high iodine concentrations in deep groundwater in the Zhangwei watershed, North China Plain

The sources and primary mechanisms of high iodine concentration in deep groundwater are rarely reported, thereby restricting the development and utilization of the related groundwater resources. To address these issues, 194 deep groundwater samples were collected from the Zhangwei watershed in the North China Plain, China, to analyze their constituents including iodine. Statistics, principal component analysis and hydrological methods were employed to determine the distribution of iodine concentrations and their controlling hydrogeochemical processes. The results show that the iodine concentration ranged from 2 to 446 μg/L and generally increased along the groundwater flow direction. Three zones with high iodine concentration (> 20 μg/L) were delineated as the alluvial–proluvial plain (Zone A, average 70 μg/L), alluvial–lake plain (Zone B, average 83 μg/L) and coastal plain (Zone C, average 199 μg/L), respectively. In Zone A, aquifer minerals weathering probably releases iodate ions into groundwater. The iodate is reduced with nitrate as the electron acceptor of iodine and transported with the precipitation infiltrating through the vadose zone to recharge groundwater, resulting in increasing the groundwater iodine concentration. In Zone B, the iodine concentrations depend on the contents of the organic matter, clay minerals, and iron aluminum oxide in the alluvial–lake sediments, due to that the deeply buried organic matter is rich in iodine which is released into groundwater through the biodegradation of organic matter, In Zone C, the iodine is probably derived from the sediments which were deposited in Quaternary marine transgression events, and its enrichment was controlled by the strong reduction condition of the deep aquifers. In one word, the iodine sources and hydrogeological conditions determined the high iodine concentrations of deep groundwater in the studied watershed. These findings can provide foundation for further insight into the high iodine concentration of deep groundwater in other hydrogeological units of the North China Plain and other similar units over the world, thereby ensuring drinking groundwater safety.

Cross-country ability of tracked vehicles

Research aims to determine conditions and parameters under which the tracked vehicle overcomes stone fields and separate blocks (boulders). Research methodology included the methods of analytical mechanics and mathematical analysis. Results. Mining and geological conditions of deposits gradually get more complicated, while mining moves to remote northern regions, which is a characteristic feature of the Holocene epoch. Road, weather, and natural conditions in arctic and northern territories differ markedly from other regions. Ridges, mounds, lake plains, and marshland are the predominant landscape. Stone fields, marshes, permafrost, marshy hollows, and deep ravines impede the traffic. Due to these factors it is particularly difficult to access and explore in arctic and northern territories. There are particular technical specifications for the exploration equipment, namely, increased cross-country ability for weak soil (snow and swamp), ability to overcome stone fields, increased haulage and towing capacity with the account of maximum possible environmental regulatory compliance, etc. The conditions of ascent and overturning are derived from geometry, while the sliding condition is derived from statics. Summary. A mathematical model has been created, which makes it possible to describe the tracked vehicle’s travel across the uneven ground and, under known design values of the vehicle, determine the limitary obstacle clearance.

Heavy metal contamination in surface sediments from lakes and their surrounding topsoils of China.

Due to rapid urbanization, industrialization, agricultural development, and mining activities, soil heavy metal pollution has become a severe issue in China. To explore the regional heavy metal ecological risk of lake sediment and surrounding topsoil, we analyzed 237 lakes, with 1797 lake sediment sampling points and 1164 surrounding topsoil sampling points. Lower mean concentrations were detected for most heavy metals in soils than sediment (except for Hg). Cd and Hg in sediments and soils showed a more significant variation, with the coefficient of variation exceeding 110%. Linear regressions and Pearson's correlation analyses demonstrated that sediments and soils exhibited significant positive correlations. The principal heavy metals exceeding the Agricultural Soil Control Standard (ASCS) in sediments and soils were As and Cd, respectively. The Yunnan-Guizhou Plateau Lake Region (YGPLR) was the most seriously affected, exceeding the ASCS for Cd. The lakes with the most severe pollution were located in YGPLR impacted by the high background concentration of heavy metals in soil and mineral development activities. The Eastern Plain Lake Region, the Southeast Lake Region, and the Northeast Plain and Mountain Lake Region showed a clear anthropogenic impact. Lakes in the Inner Mongolia-Xinjiang Lake Region and the Tibetan Plateau Lake Region were estimated to have relatively low ecological risks due to their sparse population and slight environmental disturbance. The impact of geochemical factors on the ecological risk of heavy metals in lake sediments is more substantial than that of human activities at the regional scale.

Recognizing the Aggregation Characteristics of Extreme Precipitation Events Using Spatio-Temporal Scanning and the Local Spatial Autocorrelation Model

Precipitation is an essential climate variable in the hydrologic cycle. Its abnormal change would have a serious impact on the social economy, ecological development and life safety. In recent decades, many studies about extreme precipitation have been performed on spatio-temporal variation patterns under global changes; little research has been conducted on the regionality and persistence, which tend to be more destructive. This study defines extreme precipitation events by percentile method, then applies the spatio-temporal scanning model (STSM) and the local spatial autocorrelation model (LSAM) to explore the spatio-temporal aggregation characteristics of extreme precipitation, taking China in July as a case. The study result showed that the STSM with the LSAM can effectively detect the spatio-temporal accumulation areas. The extreme precipitation events of China in July 2016 have a significant spatio-temporal aggregation characteristic. From the spatial perspective, China’s summer extreme precipitation spatio-temporal clusters are mainly distributed in eastern China and northern China, such as Dongting Lake plain, the Circum-Bohai Sea region, Gansu, and Xinjiang. From the temporal perspective, the spatio-temporal clusters of extreme precipitation are mainly distributed in July, and its occurrence was delayed with an increase in latitude, except for in Xinjiang, where extreme precipitation events often take place earlier and persist longer.

Controls on the stratal architecture of lacustrine delta successions in low‐accommodation conditions

AbstractLake‐delta deposits in low‐accommodation conditions are only a few metres thick and in some cases non‐existent. Fluvial channels occur in many cases directly on top of fine‐grained lacustrine deposits with delta deposits apparently missing. The geomorphology and stratigraphy of modern deltas in Lake Eyre, Australia, and Lake Chad in Africa indicate that delta shorelines can develop in lakes, but in many cases build out into low‐accommodation settings due to highly dynamic lake‐water levels. This work suggests that low‐accommodation is critical in the development of lacustrine delta deposits and that high (frequency and magnitude) rates of lake‐level change result in ’telescoping’ deltas, the deposits of which are thin but extensive. The telescopic deltas have conformable beds, but with abrupt vertical facies changes; this apparent stratigraphic contradiction is the result of long horizontal distance translation of the depositional system. Details of two lacustrine units, in Uinta Basin in the USA and Junggar Basin in China, both of which show characteristics of telescoping, are used to develop a process based stratigraphic model for the deposits of such lake deltas. Lacustrine facies comprise cross‐stratified, ripple cross‐laminated, structureless or graded and sharp‐based sandstone beds, mudstone (structureless, laminated, rippled, rich in organic content), carbonate mudstone, ooid packstone and stromatolites. Three facies associations are critical for lake delta stratigraphy: channelized distributary deposits that occur in the delta topset; lake plain deposits that represent the fluvial overbank deposits and the subaerially exposed (at low lake level) lake deposits; and fine‐grained, lacustrine deposits. A key corollary of the proposed low‐gradient, telescoping lacustrine delta model is that broad and shallow channels dominate the system, but that decimetre to metre thick, gently dipping delta‐front beds form subtle deposits along the margins of the lakes. These delta depocentres migrate basinward and landward at high rates (tens of kilometres each year), building thin (metres) but laterally extensive (tens of kilometres) sandstone units through multiple transgression–regression cycles.

Remote sensing estimation of water clarity for various lakes in China

Water clarity (expressed as Secchi disk depth (SDD)) reflects light transmission capacity of a water body and influences growth of aquatic plants, aquatic organisms, and primary productivity. Here, we calibrated and validated a general model based on Landsat series data for deriving SDD of various inland waters across China. The quality of remotely sensed reflectance products from different Landsat series images was assessed using in situ reflectance measurements. The results indicated that the products in the visible bands are the most robust and stable to estimate SDD for inland waters. Subsequently, a simple power function model based on red band was built using 887 pairs of in situ SDD measurements and concurrent Landsat images. The model was validated with an independent dataset of 246 SDD measurements, and the results showed that the mean relative error and normalized root mean square error were 34.2% and 55.4%, respectively. Finally, the model was applied to Landsat images acquired between 2016 and 2018 to investigate the SDD spatial distribution of all lakes with water area ≥ 10 km2 (total 641 lakes) in China. The estimation results demonstrated that the Eastern Plain Lake Zone and Northeast Plain Lake zone have relatively low SDD, with multiyear average SDD of 0.56±0.17 m and 0.47±0.29 m, respectively. The Yunnan‐Guizhou Plateau Lake Zone and Tibetan Plateau Lake Zone have relatively high SDD, with multiyear average SDD of 1.48 ± 0.86 m and 1.30 ± 0.83 m, respectively. The results indicated that the proposed model exhibits strong ability to accurately construct SDD coverage for various lakes.