Improving our understanding of the impacts of urbanization on tropical island streams is critical as urbanization becomes a dominant feature in tropical areas. Although the “urban stream syndrome” has been successful in summarizing urban impacts on streams, the response of some island streams is different to that expected. Here we review available information on urban impacts to tropical island streams and describe unique responses to urbanization. We identified three key aspects that play particularly important or unique roles in determining tropical-island stream integrity: biotic response to water pollution, movement barriers along the stream network, and altered geomorphology that results in habitat loss. As expected, water pollution negatively impacts stream ecosystems in tropical islands and in some regions impacts can be severe, as untreated wastewaters are directly discharged into streams. While aquatic insects show the expected responses to pollution, other native fauna (e.g., shrimps and fishes) appear to be less impacted by moderate levels of pollution. Movement barriers along the stream network are especially important as much of the tropical island fauna have diadromous (either amphidromous or catadromous) life histories. Most native freshwater mollusks, shrimps, and fishes inhabiting tropical islands are diadromous and depend on unimpeded connections between freshwater and marine environments to complete their life cycles. The presence of these species in urban streams is best explained by longitudinal connectivity rather than by the degree of urban impact. Finally, in streams that remain connected to marine environments, the presence of native shrimps and fishes is strongly related to the physical habitat. Fish assemblages in channelized and severely altered stream reaches are almost completely devoid of native fauna and tend to be dominated by non-native species. In contrast, relatively diverse shrimp and fish assemblages can be found in reaches that retain their physical habitat complexity, even when they are impacted by urbanization. Our understanding of urban impacts on tropical island streams remains limited. However, the identification of key aspects can help us better understand urban impacts on streams in tropical islands, and best focus our management and research efforts to protect these unique ecosystems.

Urban impacts on tropical island streams: Some key aspects influencing ecosystem response

Urbanization is occurring rapidly in southeastern Asia where streams are increasingly pressured. We assessed the ecological integrity of Ampang River in Kuala Lumpur by comparing structural and functional measures between forested and urban sites. We assessed 4 forested, 1 intermediate (deforested, not channelized), and 5 urban, channelized sites. Urbanization altered substrate (concrete at urban sites), riparian vegetation, light, temperature, O2, conductivity, nutrients, and major ion levels, and simplified food webs. Invertebrate composition shifted from pollution-intolerant taxa at forested sites to tolerant taxa at urban sites. Richness in Surber samples was 56 species at forested sites and 27 taxa at urban sites. Basal food sources at forested sites were leaf litter and biofilm, whereas at urban sites they were a sediment mat comprising organic matter, cyanobacteria, iron bacteria, and algae. Organic matter biomass on ceramic tiles was greater at urban than forested sites, but chlorophyll a ...

https://www.jstor.org/stable/10.1086/681252

Urbanization affects food webs and leaf-litter decomposition in a tropical stream in Malaysia

Increasingly, land is a scarce resource which is much sought after in Penang Island, Malaysia. This is because Penang is largely made up of steep topography and much of the lowland areas are already developed. Penang is one of the many rapidly industrialising states in Malaysia with a largely urban populace. In recent decades, efforts at industrialisation and the development of other economic sectors have been intensified, leading to greater urbanisation and greater pressures on land. Although land reclamation has eased the pressures somewhat, it is not enough to satisfy the high demand for land on the island. As such, developers have turned to the remaining hill land on the island. Many hills and their environs are already being developed and many hill projects are in the pipe line. This has led to many environmental problems such as deforestation, decimation of water catchments, destruction of endangered fauna and flora, soil erosion, landslides, water pollution, sedimentation and downstream flooding. S...

Environmental hazards associated with hill land development in Penang Island, Malaysia: some recommendations on effective management

Seasonal patterns of water quality and phytoplankton dynamics in surface waters in Guangzhou and Foshan, China.

Over the years, urban growth models have proven to be effective in describing and estimating urban development and have consequently proven to be valuable for informed urban planning decision. Therefore, this paper investigates the implementation of an urban growth Cellular automata (CA) model using a GIS platform as a support tool for city planners, economists, urban ecologists and resource managers to help them establish decision making strategies and planning towards urban sustainable development. The area used as a test case is the River Shannon Basin in Ireland. This paper investigates the spatio-temporally varying effects of urbanization using a combined method of CA and GIS rasterization. The results generated from Cellular automata model indicated that the historical urban growth patterns in the River Shannon Basin area, in considerable part, be affected by distance to district centres, distance to roads, slope, neighbourhood effect, population density, and environmental factors with relatively high levels of explanation of the spatial variability. The optimal factors and the relative importance of the driving factors varied over time, thus, providing a valuable insight into the urban growth process. The developed model for Shannon catchment has been calibrated, validated, and used for predicting the future land use scenarios for the future time intervals 2020, 2050 and 2080. By involving natural and socioeconomic variables, the developed Cellular automata (CA) model had proved to be able to reproduce the historical urban growth process and assess the consequence of future urban growth. This paper presented as a novel application to the integrated CA-GIS model using a complicated land use dynamic system for Shannon catchment. The major conclusion from this paper was that land use simulation and projection without GIS rasterization formats cannot perform a multi-class, multi factors analysis which makes high accuracy simulation is impossible.

/pdf/land-use-scenarios-and-projections-simulation-using-an-21eccm7zop.pdf

Low Kwai Sim

Papers

Urbanization and urban water problems in Southeast Asia a case of unsustainable development