Dog poo and pee degrading nature reserves, study finds

New research has shown that dogs being walked in nature reserves contribute a significant amount of nutrients to the environment through their faeces and urine, which experts warn could negatively impact local biodiversity.

Researchers at Ghent University have estimated that dog faeces and urine add an average of 11 kg of nitrogen and 5 kg of phosphorous per ha to nature reserves near the Belgian city of Ghent each year. The researchers say that the nutrients added through this neglected form of fertilisation are substantial and could be detrimental to the local ecosystem and biodiversity.

The estimates for the amount of nitrogen being added by this previously unrecorded source are particularly significant when compared to the total levels of nitrogen being added across most of Europe through fossil fuel emissions and agriculture, which range from 5-25kg of nitrogen per ha.

Professor Pieter De Frenne of Ghent University, lead author of the research, said: "We were surprised by how high nutrient inputs from dogs could be. Atmospheric nitrogen inputs from agriculture, industry and traffic rightfully receive a lot of policy attention, but dogs are entirely neglected in this respect."

A sign prohibiting dogs at one of the Ghent nature reserves included in the study (Pieter De Frenne).

The researchers call for land managers, especially in low-nutrient ecosystems, to emphasise the negative fertilisation effects of dogs to visitors, encouraging them to remove their dogs' faeces. They also call for leash use to be enforced more stringently and the establishment of more off-leash dog parks to reduce pressure on nature reserves.

In the experiment, which calculated the amount of nutrients dogs were adding to the environment by recording the number of dogs present in four nature reserves, the researchers modelled different scenarios including if the canines were on or off leashes and if owners picked up faeces.

Professor De Frenne explained the findings: "In our scenario where all dogs were kept on leashes, we found that in these concentrated areas around paths, nutrient inputs of both nitrogen and phosphorus exceeded legal limits for fertilization of agricultural land. Which is quite staggering as our study concerned nature reserves!"

In a scenario where dogs were on leashes, but all owners picked up their dogs' faeces, the researchers found that this reduced fertilisation levels by 56% for nitrogen and 97% for phosphorus. This is due to dog faeces accounting for nearly all phosphorous being deposited, whereas nitrogen is deposited equally by both faeces and urine.

The addition of nutrients to nature reserves might sound beneficial as these lead to increased plant growth; however, this mostly occurs in a limited number of nutrient-demanding species that outcompete rarer specialists, reducing biodiversity.

"In many nature reserves, management is specifically directed towards lowering soil nutrient levels to enhance plant and animal biodiversity. This can be done through methods like mowing and hay removal," explained Professor De Frenne. "Our findings suggest that the currently neglected inputs of dogs in nature reserves could delay restoration goals."

The researchers say that their data could be improved by recording breeds of dogs, as well as their size, weight and the number of urine and faecal deposits, for instance, by asking owners. The team also added that georeferencing dog faeces and urine locations could further help to detect fertilisation 'hot-spots'.

 

Reference

De Frenne, P , Cougnon, M, Janssens, G P J & Vangansbeke, P. 2022. Nutrient fertilization by dogs in peri-urban ecosystems. Ecological Solutions and Evidence. DOI: https://doi.org/10.1002/2688-8319.12128