Is Dog Pee Destroying the Urban Environment?
Some researchers worry that dog urine has negative effects on city landscapes
Posted Jun 13, 2019
Because I write about current research into dogs, their behavior and their relationship to people, there is a tendency for people to assume that when I report the conclusions of researchers I am merely expressing my own opinions. Therefore over this past year, I have been accused of being a pitbull hater, a pitbull lover, a cat hater, a lobbyist for the pet food industry, and someone who values the life of a dog over that of a person among other things. However, this was the first time that I found myself being accused of someone who was deliberately destroying the environment.
I had just completed giving a talk on dog history to a group of seniors when a small, older woman confronted me. Her fists were balled beside her and she was shaking with emotion when she said to me "You and your encouragement for people to have dogs as pets are destroying the environment. There is scientific evidence that dog piss is toxic to the soil and all growing things in the city and it is causing an environmental disaster. I am so upset about this that I recently joined the Green Party and am trying to get them to campaign for a total ban of the keeping of dogs in cities."
I tried to calm her down and told her that I knew of no such evidence, but if she could send it to me, and if it had scientific merit, I promised I would write about it in one of my columns. I then gave her my personal email address. I must admit that I was somewhat surprised when the next morning I had an email from her which contained a scan of a short, alarmist, article from some magazine, claiming scientific proof that dog urine was harmful to the urban environment.
From the information in that article, I eventually tracked down the original scientific report in the journal Urban Ecosystems. The senior researcher was Krista McGuire, who is currently in the Biology Department at the University of Oregon at Eugene. At the time that this particular research project was started, she was at Barnard College, part of Columbia University in New York City. She and several colleagues were studying the "green infrastructure" in New York City. Green infrastructure refers to the use of natural means (such as plots of soil and plants) to help control aspects of the urban environment (such as stormwater).
Most people don't recognize that things like trees growing along the streets, and plants in medians, are not there just to make the city center look good. Cities are generally built on hard surfaces, like concrete and asphalt, which don't absorb water and don't allow rainfall to enter the soil. So that means that cities require a sewer system to keep water off of the roads and to keep your basement from flooding.
However, when it rains too much for this sewer system to handle, the green infrastructure starts to play its part by helping to absorb that extra water. Ultimately, the stormwater combines with raw sewage in the belowground channels, but when the capacity is exceeded it gets discharged into local waterways. To keep this from happening, major cities like New York City invest a lot of money in order to build and maintain the green infrastructure. This includes street trees and deliberately designed water capture features called bioswales. You can think of these bioswales as slightly depressed strips of landscape filled with earth and vegetation which capture the water running off of the streets and pavements. These might look like ornamental strips of earth with plants near buildings, alongside streets, and also in the medians and roundabouts.
McGuire noticed that in certain sites, like unfenced areas around trees, the soils seemed barren and compacted, and the water from rainfall didn't seem to penetrate very well. That observation concerned her since it might highlight a serious problem. She thought that if something is happening to affect the soil in the city, this might be defeating the attempts to keep the environment of New York City healthy through the use of green infrastructure.
McGuire's team suspected that the soil characteristics they were observing had something to do with all of the dogs which urinated on those sites, so they set out to explore that possibility. This was an ambitious project, and as a first step, they sought the help of the New York City Department of Parks and Recreation to acquire soil typical of the city's landscape for their experiment. Next, they planted lilyturf (Liriope muscari), a plant with pretty purple flowers on a spike, which is commonly used as groundcover in the city, in landscaping, and in bioswales.
Getting the dog pee turned out to be the most difficult part. The experiment was going to require something like 40 gallons of dog urine. Although the researchers approached several animal shelters, all but one refused to help them. Visiting the one shelter which offered assistance gave them only a dribble of urine due to difficulty in predicting when the dogs would urinate and the tendency for dogs to refuse to continue urinating when the collecting bowl was brought near them. So ultimately they decided to use coyote urine since coyotes are closely related to domestic dogs and their urine is commercially available. (Yes, you can easily purchase gallons of coyote urine which gardeners use to keep deer away from the vegetation.)
The study was conducted in a greenhouse over a period of four weeks, with the plants watered at regular intervals with either unadulterated water or water mixed with different concentrations of urine. Meanwhile, the composition of the microbiome (the mixture of microbes, fungus, etc., in the soil) was measured, the acidity of the soil (pH) was determined, as well as the amount of water runoff (the opposite of water absorption by the soil).
There were some statistically significant changes over the course of the study, but unfortunately, the environmental significance of these seems to be difficult to evaluate. There were changes in the composition of the microbiome, however, the only effect that these changes seemed to have on the vegetation was to reduce the size of the root ball of the plants by a small amount. This effect could just as well happened because the plants were receiving regular watering and there was no necessity for the roots to extend out further to search for needed moisture.
In terms of the average water runoff, there was an increase in the third week of the study, but it seemed to have returned pretty much back to baseline by the fourth week.
The pH of the soil did change slightly, becoming slightly more acidic. In general, pH readings between 6 and 8 are considered to be neutral (in the normal range of stream water), and despite the application of acidic canine urine, the soil readings remained in that neutral range throughout the entire investigation.
Given the fact that it is unlikely that many patches of soil in the city are going to receive the sustained application and concentration of canine urine that the plants in this study were subjected to, it appears to me that the environmental effects of dogs on the green infrastructure of the city's environment, although real, can be projected to be relatively minor, certainly not the clarion call of Gabriel's trumpet announcing the end of urban life as we know it. It seems likely that a simple solution to any possible problems caused by dog urine interacting with the soil is to use inexpensive, low height garden fencing around sensitive areas involving the green infrastructure. Such fencing need only be about 18 inches high to discourage the average dog from crossing it.
That is not to say that dog urine has not caused problems for other cities in the past. About a decade ago, the issue of the effects of dog urine on the environment received a good deal of media attention in the UK. As a response, in Derbyshire, England, the city Council spent approximately £75,000 to check all of the lampposts in the district. This survey was commissioned after a report found that years of exposure to the highly acidic urine from dogs can cause the base of the posts to crumble away. This was part of a national campaign which was triggered after someone died when a lamppost collapsed.
Similarly, the Municipal Council of the City of York said dog urine was one of several things that had been causing corrosion at the base of both steel and concrete lampposts. The council claimed that it has to replace 80 street lights a year, at a cost of £1,000 for each, and they noted that the public would have to continue to foot the bill for this until a solution could be found.
However, these urban crises involve dog urine interacting with the built environment in the cities, rather than negative interactions with the green infrastructure affecting soil composition.
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Jee Min Lee, Jenny Tan, Aman S. Gill & Krista L. McGuire (2019). Evaluating the effects of canine urine on urban soil microbial communities. Urban Ecosystems, https://doi.org/10.1007/s11252-019-00842-0