Remote sensing of ocean color is used to detect phytoplankton blooms and oceanic eddies. In this study, satellite remote sensing was used to detect an eddy-like phytoplankton bloom in the western South China Sea in early September, 2007. The eddy-like phytoplankton bloom formed in the middle of August, before the formation of a cyclonic eddy. The time series reveals a lag period of about 1 week between maximum chlorophyll (Chl a) and maximum eddy intensity. This lag may have been related to the Mekong River discharge and its subsequent mixing by the cyclonic eddy. The spatial distribution of the bloom was characterized by a jet of high Chl a. Our data provide evidence that a significant proportion of south-westerly monsoon driven nutrients are used by phytoplankton. We also determined that phytoplankton blooms may support the large-scale advective spreading of high biomass waters to the open ocean by large surface currents. These biomass rich waters are probably important in the food chain dynamics of the outer south-eastern shelf and the coral islands or atolls in the open ocean.
Summer phytoplankton blooms appear frequently off the Somali coast in the southwestern Arabian Sea (AS), where strong reversal monsoon and summer upwelling is prevailing. Distinct high chlorophyll-a (Chl-a) concentrations in summer were displayed in the western AS, especially in the region off the Somali coast. The spatial and inter-annual variations of the summer high Chl-a were studied using satellite data including ocean color and wind vectors. Under ocean conditions including monsoon winds, Ekman transport (ET) and Ekman pumping velocity (EPV), as well as geostrophic current and aerosol precipitation, the possible mechanisms of high Chl-a was investigated. The summer high Chl-a presented strong inter-annual variations in the southwestern AS. The results of simple correlation analysis indicated that there were good correlations between the ET and Chl-a, as well as between EPV and Chl-a. These implied that the ET and EPV may cause uplift of nutrients into the upper layer of the western AS from subsurface or coastal regions, inducing high Chl-a in the southwestern AS, especially in the region off the Somali coasts in summer. The multiple/partial correlation analysis implied further that EPV-induced upwelling may be more helpful than the ET-induced upwelling in the coastal region off Somalia, leading to probably more significant influence of EPV upwelling on the phytoplankton bloom than upwelling by ET. Aerosol precipitation in the southwestern AS also played an important role in high Chl-a in the deep offshore AS (i.e., Section B in Fig. 1(a)), as second only to ET and sea surface temperature (SST), and even higher than EPV. A novel finding is that the influence of aerosol optical thickness (AOT) is evident in the offshore region and the dust precipitation is more important sources to oligotrophic water. Both the stability of the upper ocean and the aerosol precipitation may play more evident roles in the open regions of the southwestern AS off Somali.
Lakes in the Hanoi urban areas are highly vulnerable to serious eutrophication and algae bloom due to anthropogenic pollution and climate change. This study aims at monitoring the trophic state of lakes in Hanoi by developing an empirical model for directly estimating the trophic state index (TSI) from Landsat 8 (L8) level 2 data, which has been atmospheric corrected by the Land Surface Reflectance Code (LaSRC) algorithm and provided freely by the US Geological Survey (USGS). Regression analysis of a 138-point data set of in situ TSI measured in 13 lakes in Hanoi on seven dates in the 2015–2020 time period with the simultaneously acquired L8 reflectance data set showed a significant correlation between TSI and L8 spectral ratio of the near-infrared band (band 5) versus the green band (band 3) by a logarithmic equation (the coefficient of determination,
Poyang Lake is a freshwater lake in China which is a vital winter habitat for many kinds of wildlife and a critical component of the regional ecology. Here, we use Landsat satellite imagery to systematically assess habitat characteristic changes from 1990 to 2021. Four machine learning methods including random forest (RF), gradient boosting tree (GBT), support vector machine (SVM) and classification and regression trees (CART) are analyzed by comparing the overall accuracy and Kappa coefficients. The results show that the accuracy of random forest is higher than that of the other three machine learning methods. The long-term characteristics of Poyang Lake winter habitat types are extracted from Landsat satellite images using the RF method. These results show that the mudflat area was larger than water surface and sand. After 2012, more mudflat area had been converted into grassland, which is related to the early onset of the winter dry season in the Poyang Lake area. The habitats were scattered and fragmented from 1990 to 1998; after 1997−1998, however, the degree of landscape patch density and interference decreased, indicating a decreased impact of human-related interference and natural factors on the evolution of habitats in and around Poyang Lake.
This research focuses on analyzing land use and cover changes in Metropolitan Area of Wuhan between 1988 and 2023, utilizing a comprehensive data set from Landsat remote sensing and machine learning techniques to understand their implications for carbon storage. It finds that the Random Forest (RF) algorithm outperforms others like Support Vector Machine (SVM), Gradient Boosting Trees (GBT), and Classification and Regression Trees in identifying land use types, achieving high accuracy and a Kappa coefficient exceeding 0.98. Significant changes in Wuhan’s landscape have been noted, especially the marked decrease in arable land and increase in urban construction, reflecting the pressures of economic development and urban expansion on natural resources and their impact on the ecosystem. The study uses the InVEST model to assess how these land use transformations affect carbon storage, revealing a significant decrease in carbon storage from 1988 to 2023, with a total reduction of approximately 428.59 × 104 t from 1988 to 2023, largely attributed to the conversion of key carbon sequestering lands such as arable lands and forests into urban areas. This transition, particularly from arable land to urban construction land, underscores the challenges faced in managing land use changes without compromising environmental sustainability and carbon storage capacities.
Absence of reliable hydro-climatic information is among the bottlenecks for inadequate and improper management of stormwater runoff in rapidly-urbanizing catchments. This paper explores the influence of catchment heterogeneity in understanding the proneness of urban catchments to stormwater-borne hazards. Using GIS techniques, satellite images, and field surveys, geomorphological features and hydrologic characteristics of the Mbezi River catchment in Dar es Salaam-Tanzania were modeled to understand variations in their influence on flood hazards occurrence throughout the study catchment. The findings reveal that with GIS techniques public, domain Digital Elevation Models (DEMs) can provide preliminary but useful insights to inform stormwater management decisions in cities with limited hydrological data. Specifically, the heterogeneity characterization of the case study catchment indicates that Mbezi River is fern-leaf-shaped: it has a well-drained catchment (drainage density= 1.9 km/km2), with total relief and elongation ratios of 265 m and 0.25, respectively. Results further revealed that the catchment is comprised of many natural sinks (blue spots) that, upon enhancement, can retain about 18 percent of stormwater runoff that could otherwise contribute to downstream runoff challenges. About 68 per cent of the major sinks (with potential volume>2.4 m3) are located along the river flood plain where land is publicly owned. Additionally, more than 11.6 ha of land (as property) and 168 buildings are in areas that were mapped to have large natural sinks and they are at risk to flooding when the sinks get filled.
Traditional villages are precious historical and cultural heritage. Here, we investigate Fuzhou area of Jiangxi Province, China, and consider 114 national-level and provincial-level traditional villages, applying fieldwork, historical document searches, GIS spatial analysis, spatial syntax analysis, and other methods to explore the spatial form characteristics of traditional villages in this area on a macroscopic and microscopic (individual) level, and the relationships between scales. It is found that on a macroscopic regional level, the spatial distribution of traditional villages is unevenly distributed at a low altitude and at a close proximity to water systems; while on a microscopic level, traditional villages are mainly small and medium-sized, with landscape environments mainly determined by eight different types of waterfront hills. Among the four types of village boundaries, there are more villages with finger-like characteristics, including finger-like villages with banded features and finger-like villages with cluster characteristics. The living environment patterns mostly determined by four different types of comb settlements due to the limitations of regional environments as well as the topographic and cultural factors. Our results are significant for the improved evolution, protection, and development of traditional villages such as those found in the Fuzhou area.
This study reveals the superimposing ecological risk of chemical form and total amount of heavy metals (HMs) and their source in the sediments of Baiyangdian Lake, also provides important scientific basis for environmental protection and sustainable development of the Xiong’an New Area. The total amount and distribution of typical HMs (As, Cd, Cr, Cu, Pb, and Zn) in the sediments of Baiyangdian Lake and its peripheral rivers were analyzed. Moreover, five chemical forms (F1−F5) of HMs in the sediments of Baiyangdian Lake were identified by an improved Tessier five-step method. Risk Assessment Coding Method (RAC) and mean sediment quality guideline quotient (SQG-Q) were used to assess ecological risk. In addition, the improved enrichment coefficient and statistical methods were used to identify the sources of HMs. The contents of HMs in the lake sediment is about 1 to 3 times the background values, with higher concentration in the central area and lower concentration in the northern and southern areas. The pH and organic matter concentrations were 6.99 to 7.28 and 3.98% to 5.69%, respectively. The chemical form of HM in the lake sediments is mainly in residue form. Ion-exchangeable form and carbonate bound form of Cd account for the highest proportion (19% to 42% and 17% to 25%, respectively); Pb and As have a higher proportion of iron and manganese oxidation form (21% to 51% and 15% to 31%, respectively); Cu and Zn have a higher proportion of organic bound form (11% to 39% and 8% to 25%, respectively). RAC indicates a high potential risk for Cd, Pb, and As, and the SQG-Q indicated a high ecological risk for As, Cr and Pb. The form and behavior of HMs, such as bioavailability and toxicity, are largely influenced by the physicochemical properties of the sediments. Organic matter and pH mainly affect the ion exchange form of HMs, while the total amount of HMs mainly affects the binding form and residual form of HMs with organic matter. Changes in the content and morphology of Cu, Zn, and Cd in Baiyangdian sediments are mainly influenced by inflow river, which are mainly from human industrial activities, such as wastewater discharge. There are various sources of HMs, such as Pb, which mainly comes from human life activities such as domestic waste, leaching, aquaculture, and tourism in Baiyangdian village, influenced by lead and natural environment and related to the spatial location of the lake; while the source of chromium is more complex.
Internal lakes are considered as the ecological environments and the monitoring and evaluation of which can be considered as a matter in the national development and natural resources management (Rasouli et al., 2008). The changes in the water levels of lakes and the variations of the land use and cover along with the margins and the association of these changes with natural and human factors in Urmia Lake and Aral Lake are much-discussed and taken into consideration. In this study, a comparison was made between Urmia Lake and the Aral Lake over a period of 28 years, and the first one being suffered from declining water levels and drastic changes due to many factors, including, most specifically, human intrusion and mismanagement. For this purpose, Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat 5 and 8 satellite images were utilized for 1988 and 2018 and object-based image classification was applied in six classes, i.e. water body, arid, agriculture, salt marsh, salt wet and built with the acceptable accuracy of 89.23 (1988) and 85.8 (2018) percent for land use maps of the Urmia Lake and 92.46 (1988) and 95.15 (2018) percent for the Aral Lake. The overall accuracy of classification which represents the functioned credit classification for the maps should be more than 85% (Anderson et al., 1976). The classification showed that during the study period both of the lakes faced declination of water and increasing of salt levels. The trend of agricultural and built-in lands has been rising especially in Urmia Lake. Results indicated that the creation of the agricultural lands and human levels in recent decades has caused the increase in water consumption which in turn has reduced the amount of water entering to the Urmia Lake and has created hard conditions such as the dryness of the lake today.
This study employed the three-dimensional MIKE model to simulate the hydrodynamic properties of Poyang Lake from October 2020 to December 2021. The model demonstrated high accuracy, with the coefficient of determination (R2) exceeding 0.96 for water level and 0.98 for water area comparisons, indicating its efficacy in replicating the lake’s hydrodynamics. Notably, the highest pressure gradient forcing was observed in March and April, aligning with increased flow rates in the Ganjiang River, affecting the east side of Poyang Lake. This period saw a distinctive pressure gradient front in the lake’s central channel, potentially influencing material distribution. Eddy kinetic energy, calculated from model velocity data, peaked in May and June, and again in September and October, corresponding to changes in river flow rates. This energy was predominantly influenced by local dynamics in the lake’s central area, with low frequencies and extended periods, differing from other lake regions. Furthermore, the study found a strong correlation between eddy activities and the spatial distribution of water materials, as indicated by the consistency of turbidity patterns in satellite imagery and eddy kinetic energy distributions. These findings highlight the significant impact of hydrodynamic behaviors, particularly eddy movements, on the distribution of suspended materials within Poyang Lake.
The coastal sediments are sensitive carriers that reveal climate change, sea-level fluctuations, and monsoon evolution. A large number of sedimentary sequences developed along the coast of the Shandong Peninsula in the Last Glacial Period. Previous studies mainly focused on material sources and climate characteristics, but seldom mention the ten-thousand-year timescale monsoon evolution and its relationship with sea level fluctuations. The Liukuang section (LKS) is adjacent to the North Yellow Sea, which is mainly composed of alternations of dune sand and paleosol of the Last Glacial. Based on the chronological framework constructed by AMS 14C and optically stimulated luminescence (OSL) dating, we measured grain size, geochemistry, and heavy minerals to reconstruct the evolution of the East Asian winter monsoon (EAWM) and climatic fluctuations during the Last Glacial Period. The variations of the climate proxy indicators show that the degree of dry-cold climate and EAWM strength are indicated by different sedimentary facies in dune sand > sandy paleosol > lacustrine > silty paleosol. On a ten-thousand-year timescale, we detected episodes of EAWM strengthened in the LKS4 (78.9－59.5 ka), LKS3b (50.5－39.6 ka) and LKS2 (29.7－13.1 ka), which correspond to Marine Isotope stage (MIS) MIS4, MIS3b and MIS2, respectively, and EAWM weakened in the LKS3c (59.5－50.5 ka) and LKS3a (39.6－29.7 ka), which correspond to MIS3c and MIS3a, respectively. These climatic events were essentially synchronous with climate changes recorded in the geological carriers such as the cave stalagmites of southern China, loess from the Chinese Loess Plateau (CLP), and sea-level fluctuations in the Yellow-Bohai Sea. It is believed that the external driving factor is from the changes of solar radiation, and the internal factor is mainly from the combined effect of monsoon changes and sea-level fluctuations.
