Ecology of urban streams

Development of a biotic index for assessing biological health in Singapore rivers and canals

Singapore is an autonomous island nation located at the southern tip of the Malay Peninsula, 137 km north of the equator. It has a diverse array of freshwater ecosystems ranging from natural, forested small streams to larger concrete canals and reservoirs.

Typical concrete canals (top) and forested streams (bottom) found around Singapore.

With a population of more than 4.5 million, Singapore is highly urbanised, and only 2,000 hectares of tropical forest remains in the island’s centre. Many of Singapore’s streams and waterways are highly modified concrete canals (above), which regularly receive heavy rainfall due to the tropical climate of Singapore. The effects of urbanisation on stream ecosystems are complex and linked to three broad impacts: inputs of pollutants and sediments, altered hydrological regimes, and the reduction of riparian and in-stream habitat heterogeneity.

Historically, the health of Singapore’s waterways has been assessed by measuring water chemistry. The use of water quality data to determine the condition of waterways is widely accepted internationally, however, relying solely on water quality information for assessments of stream health can have disadvantages. For example, water quality conditions can vary markedly naturally, both daily and seasonally and depending on the water quality parameters measured, episodic events can also be missed by a spot sampling program. It can also be time consuming and expensive to measure a wide enough range of water quality parameters to accurately determine stream health. On the other hand, stream invertebrates can be particularly useful indicators of the health of a waterway because they have wide-ranging tolerances to pollution and can provide a much longer-term picture of the water quality at a site, than spot water quality measurements.

Tanya Blakely and Jon Harding, funded by the Public Utilities Board, Singapore, are developing a biotic index using stream macroinvertebrates (e.g.., insects, snails, crustaceans) to measure the condition and health of Singapore’s running water ecosystems. In order to develop this biotic index, we first need to document the benthic invertebrate fauna of Singapore’s lotic ecosystems and better understand the impacts of urbanisation on the biological health of Singapore’s waterways.

Thus, we conducted a survey of 35 concrete canals and 12 forested streams across an urbanisation gradient, situated around Singapore (Fig. 1).

Figure 1. GIS derived map of the study canals and streams sampled around Singapore.

Taxonomic richness was much greater in natural streams than the urban canals (Fig. 2). Our preliminary results indicate marked differences in macroinvertebrate communities between forested streams and concrete canals. Moreover, these dissimilarities in community composition are largely driven by physico-chemical differences in waterways (Fig. 3), which may vary predictably across an urbanisation gradient.

Figure 2. Mean (± 1SE) macroinvertebrate richness in 12 natural streams and 35 concrete canals across an urbanisation gradient.

Figure 3. Canonical correspondence analysis (CCA) of urban canals (black circles) and natural streams (white circles) around Singapore, and the physico-chemical variables that were important in determining macroinvertebrate community structure.

Chironomid larvae and snails dominated communities in canals whereas dragonflies, waterstriders, freshwater shrimps, caddisflies and mayflies were more common in natural forested streams.

Some of the macroinvertebrates collected from streams and canals in Singapore. Top, left to right: Amerianna snail, Anisocentropis caddis, Chironmus midge, Cteniporcoris bug, Eophylla caterpillar, hydropsychid caddisfly, leech, Amphipterygidae dragonfly, Aeshindae dragonfly, Perlidae stonefly, Macrogomphus dragonfly, Ephydridae fly larva.

People involved in project

University of Canterbury
Tanya Blakely
Jon Harding
Mike Winterbourn

Public Utilities Board
Hans Eikaas

Publications

Blakely, Eikaas, Winterbourn, McIntosh, Harding 2008. Biodiversity of tropical streams in Singapore. Poster by the Freshwater Ecology Research Group, University of Canterbury (pdf, 1.2mb).