We love our pet dogs. Many of us, as children, have been lucky enough to own a family dog, with maybe the dog acting as a pillow while watching a favourite television show, both stretched out in luxury in front of the fire. Or the time the dog licked you inside your mouth but it wasn’t really that yucky because it was your pet dog. Or the first time the dog brought the ball back and actually dropped it at your feet! Good dog!
But our much-loved dogs all come with regular deposits of dog faeces. These contain large amounts of nitrogen and phosphorous and in an urban watershed situation, much of the nutrients can find their way into drains and creeks and then into coastal seas. A human caused excess of nutrients can result in declining water quality and cultural eutrophication, that is a depletion of dissolved oxygen in lakes and sea water.
The nutrients cause too much algae growth which eventually dies and the bacteria breaking down the dead algae use the water body’s dissolved oxygen, with the resulting low oxygen levels causing the death of fish and many other aerobic aquatic organisms. In other cases, anaerobic noxious cyanobacteria (photosynthetic bacteria) produce hydrogen sulphide making any freshwater undrinkable.
Nitrogen from dog faeces finds its way into the atmosphere by volatilization as ammonia NH3 and is leached into groundwater as ammonium NH4. Phosphorus as phosphate PO4 is not as soluble and easily leached as nitrogen and is relatively stable in the soil, it is erosion of soil particles from exposed soil and the impervious hard surfaces common in urban areas preventing entry into the soil that result in phosphorous entering waterways (Hobbie et al. 2017; Suprihatin et al. 2003).
Urban area watersheds including dog faeces, along with household lawn fertilizers, account for a large percentage of nutrient pollution and eutrophication in lakes and coastal waters (Duan et al. 2012; Dubrovsky et al. 2010; Driscoll et al. 2003). We all need to take responsibility for the amount of nutrients that leave our properties. Nitrogen and phosphorus production have both greatly exceeded the planetary boundary ‘Biochemical Flows’. This along with biodiversity destruction in ‘Biosphere Integrity’ are two planetary boundaries which have been exceeded, three more are at great risk, out of a total of nine (Campbell et al. 2017). See my article on Planetary Boundaries in Medium.com.
The Gulf of Mexico dead zone provides us with a large example of cultural eutrophication and in some summer seasons the dead zone extends from the Mississippi River mouth to the Texas border, about 500 kilometres. In spring the waters which flow out of the Mississippi into the Gulf are ladened with nitrates and phosphates from agriculture, sewerage and urban runoff with the dog faeces. They make an oxygenated freshwater layer over the colder and more dense saltwater, with little or no storms at that time of year, the waters don’t mix very much. This top layer is warmed by sunlight and together with the nutrient enables excessive growth of phytoplankton, mainly blue-green algae. As the algae dies it sinks into lower levels and is decomposed by bacteria which use the dissolved oxygen in the water. The resulting low oxygen level of 2 parts per million will kill some fish species and shell fish which can’t migrate to better water. Their death in turn results in the death of seabirds and marine mammals which depend on the fish and shell fish for food. The dead zone is dispersed with the start of autumn, cooler weather and storms and hurricanes mixing the water layers in the Gulf of Mexico (Miller & Spoolman 2016).
Effective strategies to reduce urban watershed nonpoint runoff nutrient impact on our creeks, lakes and coastal seas are, the protection of existing nitrogen and phosphorous sinks such as wetlands or the establishment of new wetlands, along with controlling the source of nutrients (Driscoll et al. 2003), that is in this case, picking up after your dog.
Dog faeces disposal can be by municipal refuge collection into landfill and if the faeces has been picked up in a polythene bag this may be the necessary solution.
Composting may be an option if collected in a cellulose bag or picked up from your own garden and placed directly into the compost heap. The dog faeces are high in nitrogen so will need to be mixed with carbon rich leaf litter, or similar to achieve a suitable carbon nitrogen ratio for effective decomposition.
Dog faeces contains large numbers of harmful pathogenic bacteria including Escherichia coli, salmonella and giardia and as such the composting process needs to reach temperatures of >55⁰C to reduce these microorganisms. Even so, ensure the decomposed faeces does not come into contact with any soil growing food crops in the garden. It also has a high salt content which will be detrimental to soil health (Martínez-Sabater et al. 2019).
Picking up your dog’s faeces to prevent it entering an urban watershed will help reduce nitrogen and phosphorous pollution and cultural eutrophication.
Campbell, B. M., Beare, D. J., Bennett, E. M., Hall-Spencer, J. M., Ingram, J. S., Jaramillo, F., … & Shindell, D. (2017). Agriculture production as a major driver of the Earth system exceeding planetary boundaries. Ecology and Society, 22(4).
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Duan, S., Kaushal, S. S., Groffman, P. M., Band, L. E., & Belt, K. T. (2012). Phosphorus export across an urban to rural gradient in the Chesapeake Bay watershed. Journal of Geophysical Research: Biogeosciences, 117(G1).
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Hobbie, S. E., Finlay, J. C., Janke, B. D., Nidzgorski, D. A., Millet, D. B., & Baker, L. A. (2017). Contrasting nitrogen and phosphorus budgets in urban watersheds and implications for managing urban water pollution. Proceedings of the National Academy of Sciences, 114(16), 4177–4182.
Martínez-Sabater, E., García-Muñoz, M., Bonete, P., Rodriguez, M., Sánchez-García, F. B., Pérez-Murcia, M. D., … & Moral, R. (2019). Comprehensive management of dog faeces: Composting versus anaerobic digestion. Journal of environmental management, 250, 109437.
Miller, G.T. and Spoolman, S.E. (2016). Living in the Environment, (19th Ed.) Canada.: Cengage Learning. Book.
Suprihatin, I., Fallowfield, H., Bentham, R., & Cromar, N. (2003). Determination of faecal pollutants in Torrens and Patawalonga catchment waters in South Australia using faecal sterols. Water science and technology, 47(7–8), 283–289.