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

Abstract

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, O 2 , 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 was not. Faunal abundance was greater in litter bags at urban (mean = 72.6 animals/bag, 68% chironomids) than at forested sites (27.9 animals/bag; 33% chironomids), but species richness was higher in forested sites. Food webs at forested sites were more complex and differed from those at urban sites, which lacked shredders, and grazers differed in taxonomic composition and diet between urban and forested sites. At forested sites, insect larvae grazed biofilm, whereas at urban sites, snails consumed the organic mat. Leaf decomposition was fastest at the most disturbed site indicating rapid microbial decomposition caused by increased temperatures (+4.5°C) and nutrients, and possibly increased physical breakdown caused by rapid flow carrying abrasive sediment and garbage. Urbanization has had severe impacts on ecosystem function in Ampang River that could be alleviated by preventing pollution, restoring riparian vegetation, and providing natural substrate.

Trophic structure in a rapidly urbanizing planet

“…Yule et al. () suggested that urban development simplifies stream food webs, primarily by reducing richness, and decreasing abundances of some trophic guilds (e.g., shredders and predators). However, we do not know how the proliferation of synanthropes omnivores affects the stability and resilience of urban food webs, or how the availability of anthropogenic resources affects niche width.…”

“…It also affects how allochthonous subsidies are processed. Urbanization alters leaf decay, an important ecosystem process in stream ecosystems, through changes in riparian plant composition, hydrology, shredding insects, microbial diversity or nutrient concentration (Cook & Hoellein, 2016;Yule, Gan, Jinggut, & Lee, 2015). Human waste (sewage and garbage) might also directly subsidize aquatic organisms (Singer & Battin, 2007).…”

“…The effects of urban development on biodiversity are relatively well studied and reviewed Forman, 2014;McKinney, 2008). In general, there is a decline of diversity with urbanization, although there are considerable differences among cities and taxa (Aronson et al, 2014;Faeth et al, 2011;Johnson et al, 2013;Yule et al, 2015). Earlier studies suggested that urbanization increases overall abundance even as richness declines, but recent studies suggest a more variable response Faeth et al, 2011;Aronson et al, 2014;Saari et al, 2016;Marzluff, 2017).…”

Tropical freshwater sciences: an overview of ongoing tropical research

“…The relative importance of temperature and litter quality is explored across elevation gradients by Jinggut and Yule (2015). Martins et al (2015) and Yule et al (2015) use leaf-litter breakdown as a tool to understand how urbanization affects ecosystem function of tropical streams. Last, Boyero et al (2015) present the results of a pantropical study that highlights the large amount of variability in this process within and among tropical regions.…”

Trophic dynamics of macroinvertebrate communities of a subtropical river in China

“…Furthermore, benthic macroinvertebrates can also be used to monitor environmental deterioration. Taxa composition, abundance, diet, and many other characteristics of the macroinvertebrate community can be affected by anthropogenic disturbances (Yule, Boyero, & Marchant, ; Yule, Gan, Jinggut, & Lee, ). Macroinvertebrates have been used in water biomonitoring due to their high biodiversity, simplicity of sampling, and relatively longer life cycles than those of periphyton, fungi, and bacteria, which enables macroinvertebrates to reflect long‐term stress (Al‐Shami, Rawi, Ahmad, Hamid, & Nor, ; Hofmann, Hürdler, Ibisch, Schaeffer, & Borchardt, ; Morse et al, ).…”