Food web structure in an agricultural drainage channel through an urbanized zone in Japan

Hiramatsu, Ken; Yonebayashi, Koyo; Ichion, Eiji; Nishimura, Shinichi; Onishi, Takeo

Food web structure in an agricultural drainage channel through an urbanized zone in Japan

2014

Hiramatsu, Ken | Yonebayashi, Koyo | Ichion, Eiji | Nishimura, Shinichi | Onishi, Takeo

Channels and streams flowing through urbanized areas are often modified by lining the channel bed with concrete to prevent flooding caused by land-use changes in the catchment area. Even when eco-friendly works, such as fish pools and fish habitat blocks, are incorporated into the modification to accommodate aquatic ecosystems, there will be impacts on the food web and, consequently, the amount of food available for fish. In this study, the food web structure of the Ooe drainage channel, a small concrete-lined stream through an urban area, was investigated using stable isotope ratios of carbon and nitrogen. We compared the characteristics of the Ooe channel to those of several other aquatic systems. We found a single trophic transfer line, from particulate organic matter (POM) to benthic fish (Rhinogobius sp.) and crustaceans (Palaemon paucidens) via swimming fish (Squalidus chankaensis and Pseudorasbora. parva). However, the highest trophic level (benthic fish) was only 2.6–2.8 because few planktonic arthropods occurred in the web between POM and fish, unlike in more natural bodies of water. In addition, neither terrestrial plants nor periphyton were major sources of POM. Instead, organic matter from domestic wastewater appeared to be the major source of POM in the Ooe channel. Thus, the food web structure of this concrete-lined stream flowing through an urbanized zone proved to be strongly affected by its non-natural surroundings and extremely vulnerable to changes in those surroundings.

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