Dogs peeing and pooping in nature reserves disrupt ecosystems, Belgian study finds

Wandering through the forest or grassland of a nature reserve may be an ideal afternoon for dogs, but the urine and feces they leave behind can cause serious harm to these fragile ecosystems, a new study by Belgian researchers finds.

Dog excretions are high in nitrogen and phosphorus, a dangerous mix for ecosystems in nature reserves in Belgium and across Western Europe and parts of the United States that rely on low-nutrient soil. According to the study, overnutrition can harm wildlife and biodiversity. It attracts nitrogen-loving plants like hemlock, hogweed, and nettles. These are fast spreaders.

One main takeaway, said Pieter De Frenne of Ghent University, the lead author, is that owners should pick up their dog’s feces and keep their animal leashed to limit the possible spread of damage.

“Picking up poo would be an important message to dog owners based on this study,” he said. If dogs are leashed and kept to paths, he said, “95 percent of the other spots are spared.”

Scientists have documented how nitrogen pollution given off by cars or fertilizers can negatively affect an area’s biodiversity by upsetting the soil’s nutrient balance. High pH levels found in dog urine can also cause damage to grass, trees, and other plants.

But how dog excretion affects nature reserves, which increasingly abut urban or populated areas, had yet to be analyzed.

In the study, published Sunday in Ecological Solutions and Evidence, a British journal, researchers found that in the four Belgian nature reserves they observed, domesticated dogs excreted an extra 24 pounds of nitrogen and 11 pounds of phosphorous yearly per hectare. In comparison, De Frenne said, northern Belgium sees a yearly average of 48.5 pounds of non-naturally occurring nitrogen pollution — just about double the amount from dogs.

“This is really substantial,” he said.

In cases where dogs are leashed and walking along a specific path, the nitrogen and phosphorous levels spike up along the track to levels that are “higher than legal limits allowed on agricultural lands,” De Frenne said. However, the nutrient levels in other parts of the reserve are much lower.

Similarly, De Frenne said, when dog feces is removed, nitrogen levels fall by about a half and 97 percent less phosphorous is added to the soil.

Unlike a small park in a city, nature reserves in Belgium and across Western Europe are managed in a way to reduce levels of nutrients in soil to protect the area’s biodiversity and wildlife. These techniques can include top soil removal, phytoextraction (or the use of plants to eliminate impurities) and mowing.

“By also allowing dogs in them, especially if the poo is not picked up, these management efforts, which a lot of effort and money goes to, are to some extent counteracted,” De Frenne said.

The Ghent University team spent 18 months counting the number of dogs in four nature reserves around Ghent. Each dog was classified according to its ability to be walked on a leash. They also monitored the frequency with which people were picking up their waste.

In total, the team observed 1,629 dogs during 487 visits to the nature reserves.

It is clear that the levels of fertilization by dogs estimated here can potentially exert negative effects on biodiversity and ecosystem functioning of species-rich vegetation that are often pursued in forest and nature management,” the study concluded.

The ecosystems of the reserves studied are similar to environments across Europe, where there are around 87 million dogs.

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