While hiking through a nature preserve, you notice a fresh deposit that was not made by a deer and raccoon. Not only are urine and feces from dogs unpleasant, but they can also negatively impact biodiversity.
Belgian researchers recently studied the effects that dogs have on nature preserves when they walk them. They were particularly interested in how dogs’ excrement affects the environment, as well as how it impacts the environment when they go outside to relieve themselves.
Treehugger hears from Pieter De Frenne, Ghent University in Belgium, who is the lead author of the research. Our lab studies the effects on grassland and forest biodiversity of enhanced nutrient accessibility (both nitrogen as well as phosphorus).
Our research and the work of many others working on similar topics in other countries shows that increased nutrients can cause vegetation change and biodiversity loss. We noticed that many people visit nature reserves near Ghent with their dogs. We wanted to find out how much they bring in to determine their potential effect.
Researchers counted the number and behavior of dogs that visited four nature reserves. They then created four scenarios to show how the dogs behaved, including whether they were on leashes or if their owners took care of them. Over 18 months, the counts were done on 487 occasions.
They searched scientific literature to find information about the nutrients found in dog urine and feces. They used that information together with the number of dogs to estimate the average volume in urine and feces as well as the amounts of nitrogen, phosphorous, and the amount of each.
They found that fertilization rates decreased in the largest part, but rose in the areas where people walked their dogs.
The input was as high as 386 lb (175 kg) of nitrogen and 161 lb (73 kg) of phosphorus in a year.
De Frenne said that all dogs were leashed in our case and that the nutrient inputs of phosphorus and nitrogen exceeded the legal limits for fertilization. This is astonishing, considering our study involved nature reserves!
The researchers tested scenarios in which dogs were kept on leashes but their owners picked up their dog’s feces. They found that nitrogen fertilization rates dropped by 56% and phosphorus fell 97% in the models. Because nearly all phosphorus is found in dog feces while the rest comes equally from urine and feces.
De Frenne states that this is already a significant decrease.
The journal published the results. Ecological Solutions and Evidence.
Why Nutrients are Important
The key nutrients phosphorus, nitrogen, and sulfur are found naturally in aquatic ecosystems and the atmosphere. These nutrients are vital for organisms’ growth, but too many can be dangerous.
Toxic nitrogen and phosphorus are two terms that refer to excessive levels of these nutrients in the environment. It can be caused by chemical fertilizer runoff, wastewater treatment plants, and the burning of fossil fuels.
Researchers believe that these previously unknown sources could have a negative effect on how the ecosystem functions.
We were shocked at how high the nutrient intakes from dogs can be. De Frenne states that while nitrogen inputs to the atmosphere from industry, agriculture, and traffic are worthy of a lot more policy attention, dogs are completely ignored in this regard.
It is difficult to distinguish the effects of increased inputs from dogs from, say, the nitrogen coming from the atmosphere. This is a key input in many ecosystems in Europe, the UK, and the source of the nitrogen is mostly from traffic and agriculture. Research has shown that higher biodiversity is often caused by extra nitrogen and/or phosphorus.
Similar results are likely to be seen in other areas where dog ownership is common. One variable that could influence the results is the rate at which dog feces in that area are cleaned up.
Researchers suggest that managers of natural areas should stress the negative impact dogs can have on the environment. They should encourage owners to remove dog deposits and enforce leash ordinances.
De Frenne says that policy makers and forest managers can decide which natural areas are best protected.
However, our data show that urine and dog faeces are an important fertiliser for ecosystems. Therefore it is a wise management move to not allow dogs to be allowed in the most sensitive areas of nature reserves (e.g. If sensitive plants are present or soils are low in nutrients, you can establish nearby dog parks and parts of nature reserves where dogs are permitted.