Deluge of dog pee and poop harms nature reserves, study finds | Biodiversity
According to a new study, dog feces and urine are deposited in nature reserves in such quantities that they risk harming wildlife.
The analysis found that the resulting over-fertilization of the soil with nitrogen and phosphorus by the trails could reach levels that would be illegal on farmland.
The scientists reached their conclusions by counting the number of dogs over 18 months in four nature reserves on the outskirts of Ghent in Belgium. They said the situation would be similar across Europe, which is home to around 87 million dogs.
The dogs are fed at home and then excrete nutrients on their walks, leaving an annual average of 11 kg of nitrogen per hectare and 5 kg of phosphorus, according to the research. This is a similar level of pollution known to be carried through the air by fumes from agriculture, industry and traffic, which ranges from 5 kg to 25 kg of nitrogen, which means that the impact of dog feces and urine is significant.
Many dog walkers believe that leaving their pet’s excretions in the wild will do them no harm. But most ecosystems are naturally nutrient-poor environments, and over-fertilization reduces biodiversity by allowing a few thriving plants, such as nettles and giant hogweed, to crowd out others and the wildlife that depend on them.
“We were surprised at how high the nutrient intakes of dogs could be,” said Professor Pieter De Frenne of Ghent University, who led the research. “Atmospheric inputs of nitrogen from agriculture, industry and traffic rightly receive a great deal of political attention, but dogs are entirely neglected in this respect.”
The researchers estimated illegal levels of nitrogen and phosphorus in situations where dogs must be on a leash and can only stray 2 meters on either side of a path. “These levels are quite staggering, because our study was in nature reserves,” he said. “Of course, there are many beneficial effects [to walks in nature]both physically and psychologically, for owners and their dogs, but the downside is providing significant amounts of nutrients.
De Frenne said the level of dog ownership is very similar in many Western European countries, so he saw no reason why the situation would be different anywhere else than Ghent. UK charity Plantlife has warned that nitrogen pollution is “one of the greatest threats to our wild plants, lichens and fungi, yet little is being done to address it”.
The research, published in the journal Ecological Solutions and Evidence, counted more than 1,600 dogs on 500 visits to nature reserves, at all times of the day and every day of the week. They combined this data with known levels of nitrogen and phosphorus excreted by the dogs to estimate the total nutrients deposited.
The scientists had recorded whether the dogs were kept on a leash or not and taking this into account, 126kg/ha/year of nitrogen was deposited by the paths and 4kg/ha/year on the rest of the nature reserves. If the dogs were all leashed, the amount jumped to 175 kg/ha/yr through the trails, with a similar increase in phosphorus.
Picking up and taking away all the dog feces removed almost all the phosphorus, but only half the nitrogen, because dog urine contains a lot of nitrogen but little phosphorus. “Urine is, of course, difficult to wash away,” De Frenne said. Previous research has found that high nutrient levels can persist even three years after dogs are banned.
“An important first step is to educate dog owners about this fertilization effect,” De Frenne said. “I think a lot of people will just pick up the feces.” But the urine would remain and he said managers of nature reserves with sensitive ecosystems could consider banning dogs, which is already happening in some places to protect birds and other wildlife.
Rob Stoneman, Director of Landscape Restoration at The Wildlife Trusts, UK, said: “Nature reserves are prime places for nature conservation, where wildlife and fragile habitats are protected. Obviously, poop is part of nature, but dog poop contains nutrients that can damage the ecology of vulnerable habitats. Wherever you walk your dog, it’s important to pick up, bag and dispose of the poop, to ensure the continued protection of these wild areas for all of us to enjoy.
De Frenne said the next steps in the research could involve soil testing to verify the estimates made in the current study and extending the analysis to pet cats.