Litter Creates Habitat for Animals in Rivers

Researchers conclude we need to be improving habitat conditions in urban rivers.

Plastic litter in river
Plastic bags may mimic the structure of water plants. Esther Derksen / Getty Images

Litter may be an environmental hazard and eyesore – but for some animals, it provides a home.

In a study of local rivers, researchers at the University of Nottingham in the U.K. found more invertebrates like snails and insects living on litter than on rocks in the water.

In urban rivers where there aren’t a lot of natural alternatives, litter appears to offer a complex and stable environment for a wide variety of organisms. The findings, which were published in the journal Freshwater Biology, could offer insight into river management and how cleanups are performed, the researchers suggest.

Lead author Hazel Wilson, a PhD student in the School of Geography at the University of Nottingham, says the idea for the research came while she was removing litter in a local river.

“This study came out of conversations I had whilst volunteering at river cleanups in London where I was told about eels living in car tyres, fish shoaling around shopping trolleys, and crayfish living in drinks cans,” Wilson tells Treehugger.

“As I spoke to more people about this, I found that there was lots of anecdotal evidence that litter was providing habitat for animals in rivers. However, there hadn’t been much scientific study into litter as river habitat, and so we wanted to look into this by investigating what invertebrates lived on litter compared to the dominant natural habitat which was rocks.”

The researchers studied three local rivers: the River Leen, Black Brook, and Saffron Brook, in Leicestershire and Nottinghamshire. They collected samples of 50 rocks and 50 pieces of litter from the riverbeds at each site and took them back to the lab for comparison.

There they washed them individually to look for macroinvertebrates and then measured the surface area of each item. They found that the surfaces of the litter were inhabited by a more diverse group of invertebrates than those found on rocks.

Plastic, metal, fabric, and masonry samples of litter had the highest diversity of inhabitants, while glass and rock were much less diverse than other types of materials. Flexible plastic, like plastic bags, had the most diverse animal communities, causing the researchers to speculate that the plastic might be similar to the structure of plants found in water.

“There were five species we only found on litter (two snails, one damselfly larvae, one leech, and one fly larvae). Some of these species are normally found on aquatic plants, which suggests that flexible plastic might mimic the structure of aquatic plants,” says Wilson.

“However, we need more investigation to work out for sure which characteristics of litter mean it can support greater biodiversity. This could help us discover methods and materials to replace the litter habitat with alternative and less damaging materials when we conduct river cleanups.”

Replacing Litter with Better Biodiversity

While these invertebrates have found a use for discarded plastic bags and other trash, that obviously doesn’t mean that’s a good reason to leave litter in the environment. Instead, researchers say, their findings highlight the poor environmental quality in some rivers and point to the need for supporting better biodiversity.

“Although our results found litter could have a positive effect in terms of providing structure and habitat for invertebrates, the effects of litter are overall negative,” Wilson says.

“Therefore, as well as continuing to push for correct disposal of waste and clearing litter from the environment, we should be improving habitat conditions in urban rivers. Ideally, we need to replace the habitat lost during removal of litter, with alternatives that don’t harm the environment like wood branches or aquatic vegetation.”

View Article Sources
  1. Wilson, Hazel L., et al. "Anthropogenic Litter is a Novel Habitat for Aquatic Macroinvertebrates in Urban Rivers." Freshwater Biology, 2020, doi:10.1111/fwb.13657