Ecological Effect Of (Stupid & Ridiculous) Lawns

Abstract

Lawns are ubiquitous in the American urban landscapes. However, little is known about their impact on the carbon and water cycles at the national level. The limited information on the total extent and spatial distribution of these ecosystems and the variability in management practices are the major factors complicating this assessment. 

In this study, relating turf grass area to fractional impervious surface area, it was estimated that potentially 163,812 km2 (± 35,850 km2) of land are cultivated with some form of lawn in the continental United States, an area three times larger than that of any irrigated crop. 

Using the Biome-BGC ecosystem process model, the growth of turf grasses was modelled for 865 sites across the 48 conterminous states under different management scenarios, including either removal or recycling of the grass clippings, different nitrogen fertilization rates and two alternative water irrigation practices. The results indicate that well watered and fertilized turf grasses act as a carbon sink, even assuming removal and bagging of the grass clippings after mowing. The potential soil carbon accumulation that could derive from the total surface under turf (up to 25.7 Tg of C/yr with the simulated scenarios) would require up to 695 to 900 liters of water per person per day, depending on the modeled water irrigation practices, and a cost in carbon emissions due to fertilization and operation of mowing equipment ranging from 15 to 35% of the sequestration.

Conclusion

The analysis indicates that turf grasses, occupying about 2% of the surface of the continental U.S., would be the single largest irrigated crop in the country. The scenarios described in this study also indicate that a well-maintained lawn is a C sequestering system, although the positive C balance discounted for the hidden costs associated with N-fertilizer and the operation of lawn mowers comes at the expense of a very large use of water, N, and, not quantified in this study, pesticides. 

If the entire turf surface was well watered following commonly recommended schedules there would also be an enormous pressure on the U.S. water resources, especially when considering that drinking water is usually sprinkled. At the time of this writing, in most regions outdoor water use already reaches 50-75% of the total residential use. Because of demographic growth and because more and more people are moving towards the warmer regions of the country the potential exists for the amount of water used for turf grasses to increase.

- Full paper here