Long-term Environmental Impacts and Energy Balance of Lawn Removal and Conversion to Alternative Landscapes (2021-23, $30,000)
As population growth in urban areas continues to rise, water conservation is becoming a key priority for many municipalities. In recent years many municipalities have begun to offer rebate programs which incentivize removal of natural turfgrass areas and conversion to alternative ‘water- efficient’ landscapes, with the goal of reducing outdoor water use. In fact, the environmental impacts and changes to ecosystem services associated with such landscape alterations are still not well understood. As a result, ‘Ecosystem Services and Impacts’ of lawns was recently identified as one of the top research priority areas through the NTF/FFAR National Turfgrass Stakeholder Summit.
A two-year Te Lawn Institute/Scotts Miracle-Gro funded research project was conducted at the Urban Landscape Runoff Research Facility at Texas A&M during 2018 and 2019. Te results of the initial two-year study highlighted many differences in rainfall capture and runoff dynamics, surface temperatures, and management requirements between natural turfgrass lawns, xeriscapes, mulched, and artificial turf landscapes. However, as these landscape treatments continue to mature, there is a need to evaluate longer-term environmental impacts/runoff dynamics, and to characterize energy balance, greenhouse gas emissions, and soil nutrient pools. Tis progress report provides a summary of results of the first year of the currently funded project.
Tis two-year study is being conducted at the Urban Landscape Runoff Facility located at the Texas A&M University Soil and Crop Sciences Field Research Laboratory, College Station, TX. Te facility consists of 24 individually irrigated 13-foot by 27-foot (3.962-m by 8.229-m) plots originally established in 2012 with ‘Raleigh’ St. Augustinegrass. Each plot has its own runoff collection system composed of an ISCO flow meter and sampler, which provides full documentation of the amount of water lost to runoff as well as collection of water samples for subsequent measurement of the chemical content of the runoff. In August 2018, 16 of the formerly natural grass plots were converted to the following alternative water- efficient landscapes. Te treatments were then:
1. St. Augustinegrass Lawn: Original ‘Raleigh’ St. Augustinegrass (non-converted)
2. Water Efficient Landscape: Xeriscape: Native plants (covers 50 percent of the entire plots) planted on 3 inches (7.62 cm) of compacted decomposed granite following sod removal.
TPI Turf News September/October 2022
3. Water Efficient Landscape: Mulch: Native plants (covers 50 percent of the entire plots) planted on 2 inches (5.08 cm) of dark shredded wood mulch following sod removal.
4. Artificial Turf: Synthetic turf installed atop of compacted decomposed granite base, with grit silica sand infill following sod removal.
5. Sand-Capped Lawn: Washed Raleigh St. Augustinegrass sod laid atop of a 4-inch (10.16-m) sand- cap layer following sod removal.
Data collection for this project was initiated in April 2021 and will continue until June 2023. Parameters of interest in this study include:
Runoff and Rainfall Capture Dynamics - (pH, electrical conductivity (EC), Nitrogen (Total N, NO3
-N, NH4 -N, organic N) and orthophosphate-P concentrations),
Nutrient losses through denitrification and volatilization
Energy Balance – Net radiation, albedo, spectral irradiance (400 to 1100 nm), spectral reflectance, surface temperature, soil heat flux density, atmospheric humidity, and wind speed). Sensible heat flux density (rate of heating or cooling of air) and latent heat flux density (rate of evapotranspiration) will be estimated by energy balance theory.
Soil nutrient dynamics - Soil nitrate-N, ammonium-N and total Carbon will be analyzed on the soil cores to understand the long-term implications on soil nutrient pools.
Runoff dynamics have been continually monitored since the start of the study. To date, 10 runoff events have been measured in the study. Total and cumulative runoff volumes for each date and landscape type are shown in Figure 1. Not surprisingly, runoff volumes have been highly correlated to rainfall depth, and a minimum of 20 mm (.787 in.) of rainfall has been required to generate noticeable runoff from most of the landscapes. Te effect of landscape type on total runoff volumes from treatments appears to be consistent with the prior two-year study with Artificial turf (AT) and Xeriscaping (XE) consistently generating the most runoff among all landscapes (Figure 1).
St. Augustinegrass lawn plots occasionally show similar volumes of runoff as AT and XE, but usually only when rainfall occurs within 24 hours of irrigation. However, when rainfall amounts are greater than 60 mm (2.362 in.), differences in runoff volumes between St. Augustinegrass lawn and AT and XE become more apparent. Also
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