Dog pee and poop could be harming the soil in nature reserves, study suggests

• Dogs relieving themselves in nature are overfertilizing complex environments, a study suggested.
• The contamination can knock the environment out of balance, favoring one plant over others.

Dogs relieving themselves in nature may be overfertilizing ecosystems and causing a damaging loss of biodiversity, a new study has found.

The study, published Monday in the peer-reviewed journal Ecological Solutions and Evidence, relied on surveys of pet density over time in four nature reserves around Ghent, Belgium.

Though the findings were made in Belgium, the situation is likely similar in other reserves close to cities in Europe and in the US, Pieter De Frenne, a bioengineer of the University of Ghent and an author on the study, told Insider.

Dog feces and urine are "more than likely" contributing substantial levels of phosphorus and nitrogen — which are potent fertilizers — to the environment, De Frenne said.

The amount of nutrients that could be released in the environment was assessed from an estimate of how often the dogs poop and pee, and how phosphorus and nitrogen-rich the feces and urine are on average.

"When there is an excess of nitrogen available in the soil, only a selection of competitive plants are able to cope," De Frenne said.

These plants then overtake the environment and smother other plants.

"Orchids are a typical example. These are outcompeted and lost from the ecosystem," said De Frenne.

Assuming pet owners don't pick up the feces, dogs could be contributing about 24 lbs (11 kg) of nitrogen and 11 lbs (5 kg) of phosphorus per 2.47 acres (1 hectare) per year to the soil.

That means dogs could be pushing the environments well beyond the "critical load" — the amount of nitrogen that can enter an ecosystem without affecting biodiversity.

"For most of the ecosystems that we worked in, that level is 20 kg per hectare (44 lbs per 2.47 acres) per year," said De Frenne.

Air pollution from agriculture and traffic already contributes another 11 to 55 lbs (5 to 25 kg) of nitrogen per 2.47 acres (1 hectare) a year to soil contamination, the study authors said in a statement accompanying the study.

To reduce the load on environments, park managers could introduce more off-leash dog parks in areas with less sensitive ecosystems, De Frenne said.

Dog owners could also try to encourage their dogs to go before entering the park, or keep them on a leash to avoid spreading the contamination, he said.

"At least pick up the feces, because then you remove 97% of the phosphorus and half of the nitrogen," De Frenne said.