Rapid urbanisation and industrialisation have resulted in sharp land cover changes. Urban change not only impacts on land cover but also on urban climate. Land surface and atmospheric modifications due to urbanisation generally lead to a modified thermal climate that is warmer than the surrounding, non‐urbanised areas. In this research remote sensing technology was used to evaluate urban growth patterns and its thermal characteristics through mapping impervious surfaces and evaluating thermal infrared images. The case study was carried out in the northern part of Ho Chi Minh City, which has experienced accelerated urban development since the late 1980s. Landsat and Aster images were used to calculate variations in urban impervious surfaces from 1989 to 2006. Thermal bands were processed to obtain radiant surface temperatures for investigating the urban heat island effect associated with increasing impervious surfaces, both spatially and temporally. Impacts of urban development on surface temperature were shown by investigating the surface urban heat island effect intensity. The results show that the built‐up area in the northern part of Ho Chi Minh City expanded by 6.5 times between 1989 and 2006. Urban development has altered the magnitude and pattern of the surface urban heat island, with the highest land surface temperature cores found in the industrial (greater than 45oC) and urban areas (within 36oC and 40oC). In suburban and rural areas, where agricultural land still remains with full vegetation cover, the land surface temperature is usually lower. Using remote sensing, the impervious surface was extracted with overall accuracy and a Kappa coefficient for all three years greater than 96%, and the retrieved land surface temperatures with variations from in‐situ measurements of less than 2oC. The results presented here indicate that remote sensing can help to spatially monitor urban development and land surface temperature changes over the whole area and over a long period of time.
Ceratophyllum spp., Callitriche spp., Zannichellia spp. and Potamogeton pectinatus L. are widespread submerged macrophyte species, often occurring at high abundance and forming an integral part of the vegetation of many types of shallow aquatic systems. Several species occur in both freshwater and brackish water habitats. Most have a mixed reproduction system and can reproduce sexually by seeds and propagate asexually by rhizomes, turions, root tubers or axillary tubers. It is hypothesized that sexual propagules are more important than vegetative fragments to ensure long-distancedispersal, which in case of frequent bird or water flow-mediated dispersal should lead to lowered genetic differentiation. At a regional level, we used dominant ISSR markers in a multi-species approach and observed the largest clonal differentiation between brackish water and freshwater populations of the western European lowland (Belgium). Differentiation was pronounced at taxon level (e.g. Zannichellia), as a salinity gradient (P. pectinatus) or as a coastal-to-inland conductivity gradient (Callitriche obtusangula). These differences and trends suggested a very limited dispersal at regional level across both habitats and regions. To test the hypothesis whether vegetative reproduction and dispersal may have an important function in maintenance of the species at local scale, we investigated the microsatellite diversity and clonal distribution within and between populations of P. pectinatus from a single catchment, representing upstream forest ponds and downstream river sites along the Woluwe (Brussels, Belgium). Clonal diversity was low on average, however, with a higher number of multilocus genotypes in upstream forest ponds than in downstream river sites. A few but abundant clones were present along various stretches of the river indicating clonal spread and establishment over larger distances within the river. Clonal dispersal at a local scale was more pronounced in river than in pond habitats, indicating a higher relative importance of water flow than birdmediated dispersal for establishment of P. pectinatus in river sites. Dispersal of seeds and establishment of seedlings were assumed more effective within ponds than in river habitats. Upstream forest ponds can be regarded as source populations and refuges of clonal diversity for recolonization of the more stressful downstream river habitat.
Abstract. Mui Ca Mau at the southern tip of Vietnam supports a large area of mangroves and has a high value for biodiversity and scenic beauty. This area is affected by erosion along the East Sea and accretion along the Gulf of Thailand, leading to the loss of huge stretches of mangroves along the East Sea and, in some cases, loss of environmental and ecosystem services provided by mangroves. In this study, we used remotely sensed aerial (1953), Landsat (1979Landsat ( , 1988Landsat ( and 2000 and SPOT (1992SPOT ( , 1995SPOT ( , 2004SPOT ( , 2008SPOT ( , 2009SPOT ( and 2011 images and the Digital Shoreline Analysis System (DSAS) to quantify the rate of mangrove shoreline change for a 58 yr period. There were 1129 transects sampled at 100 m intervals along the mangrove shoreline and two statistical methods, namely end point rate (EPR) and linear regression rate (LRR), were used to calculate the rate of change of mangrove shorelines and distance from 1953 to 2011. The study confirms that erosion and accretion, respectively, are significant at the East Sea and Gulf of Thailand sides of Mui Ca Mau. The East Sea side had a mean erosion LRR of 33.24 m yr −1 . The accretion trend at the Gulf of Thailand side had an average rate of 40.65 m yr −1 . The results are important in predicting changes of coastal ecosystem boundaries and enable advanced planning for specific sections of coastline, to minimize or neutralize losses, to inform provincial rehabilitation efforts and reduce threats to coastal development and human safety.
To help improve the well-being of the local people, a joint Vietnamese-UK team set out to establish a way of estimating soil and nutrient losses under different land management scenarios, using field data extrapolated through remote sensing and GIS, to obtain catchment-wide estimates of the impact of land cover change. Immigration from remote provinces to the Dong Phu District of Binh Phuóc Province, about 120 km north of Ho Chi Minh City, has led to disruption of soil surface stability on easily eroded clayey sandstones, creating rapid nutrient depletion that affects crop yields and siltation in the channel of the Rach Rat river downstream. The poor farmers of the areas see crop yields drop dramatically after two or three years of cultivation due to the fertility decline. Soil loss varies dramatically between wet season and dry season and with ground cover. Erosion bridge measurements showed a mean loss of 85.2 t ha − 1 y − 1 under cassava saplings with cashew nuts, 43.3 t ha − 1 y − 1 on uncultivated land and 41.7 t ha − 1 y − 1 under mature cassava. The rates of erosion were higher than those reported in many other parts of Vietnam, reflecting the high erodibility of the friable sandy soils on the steep side-slopes of the Rach Rat catchment. However, although the actual measurements provide better soil loss data than estimates based on the parameters of soil loss equations, a large number of measurement sites is needed to provide adequate coverage of the crop and slope combinations in this dissected terrain for good prediction using GIS and remote sensing.
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