According to Belgian researchers, dogs provide considerable amounts of extra nitrogen and phosphorus in nature reserves through their faeces.

Poo on the sidewalk is bloody irritating – but a dog turd or pee in a nature reserve can do little harm, you might think. However, this is indeed a problem, according to Belgian researchers new scientific article† The nutrients that dogs leave behind in nature reserves in their feces can have a negative effect on local biodiversity.

tally dogs

To determine how much poop and pee dogs leave behind in nature, we focused Pieter De Frenne and colleagues from Ghent University in four areas near the Flemish city. There they peated how many leashed and unleashed dogs passed by.

Next, De Frenne and his team delved into the scientific literature to determine the average amount of nitrogen and phosphorus in dog feces. They also estimated the amount of poo (100 grams) and urine (184 milliliters) that the animals produced during an average walk.

More green, less diversity

It follows from these figures that dogs leave behind about 11.5 kilograms of nitrogen and about 4.8 kilograms of phosphorus per hectare in a year. “That is a substantial amount of nitrogen and a very large amount of phosphorus,” says Wim de Vries, professor of environmental systems analysis at Wageningen University & Research, was not involved in the research himself. Because, he continues: an average of 20 to 25 kilograms of nitrogen and about half a kilogram of phosphorus ends up in one hectare of land from the atmosphere in the Netherlands and Belgium.

But why would more nitrogen and phosphorus – in principle substances that make plants grow better – a bad thing? Because, according to De Frenne and colleagues, this extra growth is mainly due to a handful of plant species, which outcompete other species. For example, dog poop and pee are at the expense of biodiversity.

big differences

Now there is something to criticize about the study and how it is brought to the attention. This is how the accompanying press release that “dogs that are walked in nature reserves contribute a significant amount of nutrients to the environment”. But, so notices Rik Leemans op, also professor of environmental system analysis in Wageningen: the researchers only looked at four fairly small nature reserves near Ghent. “Are they representative for nature reserves in general, or for larger areas further away from the city?”

The number of dogs also differs enormously per nature reserve. In one area, according to the researchers, there were an average of 11 dogs per hectare every day, in another area there was only one per hectare. As a result, the amounts of nitrogen and phosphorus left behind will also differ considerably per area.

clear message

Furthermore, says De Vries, the nitrogen and phosphorus from dog feces and pee are “naturally highly concentrated around the places where the dogs defecate”. As a result, they will have less effect on the entire area than the nitrogen and phosphorus from the atmosphere.

Moreover, in many areas there is a lack of phosphorus, notes De Vries. “Some extra phosphorus supply could therefore also improve the situation.” Still, Leemans calls the study a “nice, interesting little study”, which “has a clear message and fills a gap in our knowledge.”

Dog ban?

And what if we want to do something about all that extra nitrogen and phosphorus? Conservationists could encourage dog owners to take their pet’s poop with them, the researchers suggest. This means that the majority of the phosphorus and more than half of the nitrogen would not remain in the area. (The urine, which you don’t just scoop up and put in a bag, of course, contains hardly any phosphorus, but does contain 44 percent of the nitrogen.)

It would also be better to ensure that dogs are kept on a leash. Then turds and puddles mainly end up around the paths. The advantage of this is that you spare the rest of the terrain. The disadvantage is that in the places where the dogs still defecate and urinate, the amounts of nitrogen and phosphorus can become extremely high.

A third option is to create more off-leash areas where the dogs can run their course. And in areas that are particularly vulnerable, you could even ban dogs altogether, write De Frenne and colleagues. There goes your weekly nature walk, with Fido bouncing enthusiastically through the greenery.