Analysis Center, University of New Mexico, Albuquerque, NM 87131, USA; ... image was used to evaluate the turfgrass area of Albuquerque, New Mexico, U.S.A. ...
Landscape Ecology vol. 10 no. 2 pp 121-128 (1995) SPB Academic Publishing bv, The Hague
Potential environmental and economic impacts of turfgrass in Albuquerque, New Mexico (USA) Carlos A. Blanco-Montero’, Teri B. Bennett2, Paul Neville2, Clifford S. Crawford’, Bruce T. Milne’ and Charles R. Ward 3 Department of Biology, University of New Mexico, Albuquerque, N M 87131-1091, USA; 2Earth Data Analysis Center, University of New Mexico, Albuquerque, NM 87131, USA; Department of Entomology, Plant Pathology and Weed Science and Cooperative Extension Service, New Mexico State University, 9301 Indian School Rd. NE, Suite 201, Albuquerque, NM 87112, USA Keywords: turfgrass, satellite imagery, environmental impact
Abstract
We estimated the ecological and economic impact of urban turfgrass production in a large city. A satellite image was used to evaluate the turfgrass area of Albuquerque, New Mexico, U.S.A. Turfgrass, the major vegetation component of the city, covers 7,650 ha and represents approximately 30.0% of the metropolitan area. Of the total grass area, 85.0% exists as home lawns, 8.3% occurs in parks, and 6.7% is on golf courses. We estimated that turfgrass uses an average of 475,000 m3 of water every day, yielding more than 4,575,000 kg of grass clippings going to the landfill in approximately 250,000 garbage bags each year. The approximate yearly cost of maintenance comes to more than $30 million which includes the potential purchase of 322,065 kg of nitrogen fertilizer, 286,110 kg of phosphorus fertilizer, 237,915 kg of potassium fertilizer, and 37,408 kg of active ingredients of insecticides. Our evaluation of the cumulative effects of domestic and municipal turfgrass production can guide the application of economically sound Integrated Pest Management strategies and enable planning for sustained use of potentially limiting resources, such as water, in semiarid environments.
Introduction
As the major component of urban vegetation, turfgrass covers an estimated 8 to 10 million hectares in the United States (Tashiro 1987) and represents the single largest ‘crop’ produced in the country (Bormann et al. 1993). Such areas are intensively managed in urban settings due to public demand for ‘perfect lawns’ on golf courses, athletic fields, and homes. Healthy turfgrass can act as a buffer to delay, or prevent, the movement of chemicals and soil from agricultural and urban areas to watersheds. Carefully managed turfgrass has 15 times less runoff than lower quality turfgrass. Lawns can also detoxify air pollutants; its capacity to do this is
comparable to that of the same leaf surface area contained in trees, and it can provide cooling effects as well (Leslie and Knoop 1989). High maintenance of lawns results in a high input of pesticides, fertilizers and water. In 1983, an estimated $15 billion were spent to maintain such areas in the United States, with the greatest expenditures being made in insecticides, herbicides, fungicides, and fertilizers (Tashiro 1987). Another important aspect of turfgrass is its biomass production. Turfgrass clippings can have a major impact on city’s waste disposal. According to Leslie and Knoop (1989), 30% of the total garbage volume of Plano, Texas consisted of grass clippings. An estimate of solid waste categories in
122 Albuquerque identifies grass clippings as more than 20% of the total garbage volume, the largest single waste product going to the city landfill (Anonymous 1992). We evaluated the turfgrass area and maintenance practices in Albuquerque, New Mexico in order to estimate the potential impact of its management in the urban environment. Our evaluation should enable planning programs to focus on how to alleviate excessive use of contaminants, estimate and/ or reduce water use and dispose of clippings in an environmentally sound manner. The purpose of this study is to provide, for Albuquerque, an estimate of turfgrass area, as well as data on water use, turfgrass biomass and clipping disposal, use of pesticides and fertilizers in turfgrass, and economic impacts of turfgrass maintenance. From the standpoint of landscape ecology (Forman and Godron 1986) this study incorporates humans as the central organizer of spatially extensive, and energetically expensive, landscapes.
Materials and methods Separate studies were established to estimate, (1) turfgrass cover via satellite imagery, (2) potential use of water on the turfgrass area, (3) biomass production of turfgrass and its potential impact in the city waste disposal system, (4) potential use of pesticides and fertilizers, and (5) the economic impact of turfgrass maintenance. Procedures involved in conducting these five studies are discussed below. 1. Turfgrass cover in Albuquerque, N.M. as estimated from a satellite image To estimate resource needs and environmental impacts for the Albuquerque urban area, an areal estimate of turfgrass coverage was needed. Satellite data collection was considered a rapid and relatively cost effective method for determining the areal extent and geographic distribution of turfgrass coverage. A portion of the Landsat Thematic Mapper (TM) scene acquired 2 July 1989 was available for this investigation. The image covered approximately 248
km2 and included Tramway Boulevard to the north and the Albuquerque International Airport to the south. It was bounded on the west by Interstate 25, and on the east by the base of the Cibola National Forest. The Universal Transverse Mercator (UTM) coordinates (Zone 13) of the corners of the study site were: (1) northwest, 350414 E, 3895245 N; (2) northeast 363524 E, 3895245 N; (3) southwest 350414 E, 3873870.5 N; (4) southeast 363524 E, 3873870.5 N. The TM sensor was designed to spectrally differentiate the biophysical properties of vegetation in order to aid in discriminating vegetation types and their spatial distributions (Lillesand and Kiefer 1987). The sensor has a nominal 28.5 x 28.5 m spatial resolution and spectral sensors in the visible and near-infrared portions of the spectrum (Goetz et al. 1985). All surface and plant reflectance within the 812.25 m2 area of each cell detected by the sensor is merged and assigned a digital number ranging from 0-255 for each spectral band. Since a gross estimated figure for surficial biomass was needed, the spatial resolution of the sensor was considered appropriate. TM channels were radiometrically corrected using the offsets and gains provided by the National Aeronautics and Space Administration (NASA), which reduced the likelihood of misclassification due to differences in sensor bias. Channels were also corrected for atmospheric effects using the solar irradiance, atmospheric transmittance, solar zenith angle, and background reflectance using a radiometric transfer code (RTC) based on the U.S. Air Force’s LOWTRAN software (Forster 1984, Kneizys et al. 1988). Moran et al. (1992) found that using a RTC with estimated data successfully reduces the overall error of reflectance in comparison to uncorrected data; the procedure compensates for band specific problems such as rayleigh scattering in TM1 and water vapor absorption in TM4. A geometric correction was performed whereby lines and elements of pixels on the image were matched to corresponding Universal Transverse Mercator (UTM) coordinates of these points on the ground, using the U.S. Geological Survey 1:24,000 scale Quadrangle Maps. The image was rectified to the map coordinates using a nearest neighbor routine.
123 All image processing was performed using the Earth Resource Laboratory Application Software (ELAS) program. A selective principal component analysis technique was applied to the data in the manner of Chavez and Kwarteng (1989), Crosta and McMoore (1989), and Loughlin (1991), to enhance the likelihood that properties of interest in a scene would most likely be identified in a subsequent classification. For this study, the TM channels selected for image processing were 2,4, 5 , and 7. Since there is a high degree of correlation between the visible bands (1, 2, 3), channel 2 was selected for its green reflectance peak for vegetation. Channel 4 records the near infra-red portion of the electromagnetic spectrum (EMS) where vegetation has its peak response. Both channels 5 and 7 record mid infra-red regions of the EMS and are useful for finding soil and vegetation features. These four channels were selected for the principal component analysis transformation. After applying the PC-transformation, the image was classified using an unsupervised Bayesian maximum likelihood classification in order to derive spectral classes for the scene. The derived turfgrass classes were identified by a two channel scatter plot, using principal components 1 and 2, as well as by visual interpretation of vegetated areas from the display screen and maps. Selected vegetated areas such as parks, athletic fields, golf courses, and lawns were visited. The vegetation composition was evaluated by 1 line-intersect transect across the most representative area at each of the 12 field sites.
3. Turfgrass biomass production and its potential impact on the city waste disposal system We estimated turfgrass biomass production for lawns of 6 homes (total area 1,461 m2) with different maintenance programs, grass species, and surface areas. Grass clippings were obtained weekly from May to November 1992 from the residents of each home in a plastic bags free from any other garbage. Grass clipping mass was recorded with a portable electronic scale (Pelouzetmmodel PE 125, capacity 60 kg x 0.2 kg).
2. Turfgrass potential use of water Daily readings of the 1990-1992 potential evapotranspiration ([PET], the amount of water that can be evaporated or transpired from a standard cover crop of low water resistance, e.g. a grass turf) during the active turfgrass growing season (April to October), were obtained from the New Mexico State University/U.S.D.A. Agricultural Science Center at Los Lunas, N.M. Such rates, extrapolated to the estimated turfgrass area, indicate the potential use of water by turfgrass during these growing seasons. Predominant grass species and tree cover on lawns were obtained by observations of the front lawns of 200 randomly chosen residences throughout the evaluated area.
Results and discussion
4. Insecticide and fertilizer use Potential fertilizer use for this turfgrass area was estimated by extrapolating from recommendations given by Watson (1983). Potential insecticide use was obtained by extrapolating rates of application of commonly used insecticides on turfgrass published in Insecticide & Acaricide Tests: 1992 and 1993. 5. Economic impact of turfgrass maintenance The maintenance cost per area for different kinds of grass utilization was obtained from estimates in Busey and Parker (1992). To standardize cost estimates through time, adjustments were made for changes in the value of the dollar according to the guidelines of the Consumer Price Index for All Urban Consumers (July 1992). A locality cost adjustment was performed with the ACCRA Cost of Living Index (1992).
The main implication of this study is that households should be the focus of attempts to reduce pollution stemming from over-fertilization and excessive use of pesticides. In Albuquerque, domestic lawns produce more waste than recreational turf areas. In this city, the majority of homeowners tend to dispose of their grass clippings in the weekly garbage, a situation that does not occur in the maintenance of parks, athletic fields and golf courses, where clippings are deposited in situ. Decreases in domestic use of water for turfgrass would provide the single largest drop in water consumption associated with turfgrass.
124 Table I . Principal component analysis information. Percent of variance represented by each component, cumulative percentages and eigenvalues. Principal component
Variance (070 of total)
Cumulative percentage
Eigenvalue
1
74.9 20.9 3.6 0.6
74.9 95.7 99.4 100.0
745.7 207.5 362.8 634.7
2 3 4
Table 2. Principal component analysis transformation matrix. TM Bands
PCI
PC2
PC3
PC4
2 4 5 7
0.2457 0.2402 0.6586 0.6695
- 0.0557
0.8809 0.0756 - 0.4567 0.988
0.4007 -0.1814 0.5979 - 0.6701
0.9506 - 0.0159 - 0.3049
1. Turfgrass cover estimated from a satellite image Principal component analysis and cluster analysis were used to derive five spectral classes of pixels representing the major utilization classes of turfgrass. As commonly occurs in the analysis of multispectral imagery, the major component of variation among the spectral bands, as represented by principal component 1 (PC l), was due to positive correlation among the spectral bands (Table 1, 2). Thus, the eigenvectors (i.e., correlations of bands with the principal components, Table 2) for PC 1 were all positive, indicating that pixels with high brightness in all four bands were at the high end of PC 1. Such responses are generally related to the presence of soil which reflects heavily in all bands. The second component, interpreted as a vegetation
response, was strongly and positively related to TM band 4 (Table 2). The third component enhanced the urban features in the scene while the fourth component, representing a small fraction of the variation (Table l), was attributed to sensor noise and was not included in further analysis. Cluster analysis revealed three classes of turfgrass; home lawns, parks and athletic fields, and golf courses (Table 3). These classes differed with respect to tree cover and grass species; however, for the purpose of this study, all turfgrass classes were grouped in the same category, because they all had a 90- 100% turfgrass cover (Table 3). The estimated total area covered by grass was 7,650 ha, which equals 30.76% of the evaluated surface of Albuquerque (24,863 ha), see Fig. 1. Of the homes surveyed, 91% had front lawns, in which Kentucky bluegrass represented slightly over half of the grass cover. Bermuda grass amounted to slightly over a third of the remaining cover, which tall fescue and undetermined grass species made up the rest (Table 4). 2. Turfgrass potential use of water From our estimate of Albuquerque's turfgrass area, we estimated that irrigation requirements are 474,300 m3 of water applied at 0.62 cm every day. This estimate is based on summed daily averages of PET values during 1990-1992. (89,994,600 m3 in 1990, 100,811,700 m3 during 1991, and 114,321,600 m3 in 1992), which is the amount needed to compensate for the potential evapotranspiration that occurred during those years (Table 5 ) . These water requirements represented 8.5% of the total energy necessary to maintain turfgrass (Busey and Parker 1992).
Table 3. Spectral classes representing different kinds of vegetation, mean principal component analysis values, area, utilization, and vegetation cover from a Landsat-5 Thematic Mapper of Albuquerque, N.M. acquired 22 July 1989. Spectral classes
PC 1 scores
PC2 scores
PC3 scores
Surface (ha)
Utilization classes
Field evaluation (vegetation cover) %grass / 070 tree
9 13 22 23 32
84.58 85.81 81.95 92.14 72.11
118.133 98.35 109.20 231.38 131.11
63.20 64.23 55.25 36.09 41.22
1,917.72 1,269.87 3,345.01 478.74 639.00
Homes Homes Homes Golf courses/parks Parks
90/40-80 90/40-80 90/40-80 100/40-80 100/40-60
126 Table 4 . Percentage of different classes of grasses present of front lawns of 200 residences in Albuquerque, New Mexico in 1993. Grass type
Cover (070)
Kentucky bluegrass Bermuda grass Tall fescue Undetermined
51.1 36.5 9.0 3.4
3. Biomass production and impact on waste disposal Weekly grass clipping production comes to 4,576,521 kg in a volume of 237,150 m3, representing approximately 250,000 plastic bags (Table 6). These calculations are similar to those of Leslie and Knoop (1989), and it has been calculated that grass clippings make up to 22.6% of the total garbage volume of Albuquerque during May 1992 (Anonymous 1992). The clippings disposal requirement represents 2.28% of the energy necessary to maintain turfgrass (Busey and Parker 1992). The total cost of maintenance of this turfgrass area is $2,544,381per month, as it was calculated by Busey and Parker 1992, and adjusted for current rates in Albuquerque (Table 7). 4. Insecticide and fertilizer use Assuming recommended application rates, single applications of nitrogen (in fertilizer) amount to 328,964 kg, phosphorus application amounts 286,122 kg, and potassium to 238,116 kg (Table 8). Fertilization energy requirements represent 7.48% of the energy necessary to maintain turfgrass (Busey and Parker 1992). Insect control for this area comes to 37,410 kg of active ingredients (AI) in a single application (Table 8), representing 1.75% of the turfgrass maintenance energy (Busey and Parker, 1992). It is evident that the potential impact of turfgrass in Albuquerque is considerable. Here we used a relatively conservative scenario that involved recommended fertilization doses and water conservation irrigation practices. Unfortunately, these recommendations are often not followed, which means that the impact of turfgrass in the community is probably greater than some of the figures given
Table 5 . Weekly potential evapotranspiration readings from the NMSUAJSDA Los Lunas Agricultural Science Center, Los Lunas, N.M., during growing seasons of 1990 to 1992. Date
07 April 14 21 28 05 May 12 19 26 02 June 09 16 23 30 07 July 14 21 28 04 Aug. 11 18 25 01 Sep. 08 15 22 29 06 Oct. 13 20 27 31
Weekly potential evapotranspiration (cm) 1990
1991
1992
Average
2.39 3.81 3.45 3.78 3.50 4.89 5.11 5.26 5.42 5.68 4.96 5.54 5.74 4.33 4.07 5.04 4.83 4.61 4.58 3.20 3.62 4.32 3.53 3.91 2.66 2.39 2.37 1.87 1.36 0.93 0.49
4.34 4.21 4.76 4.16 4.77 5.10 5.36 4.36 4.97 4.98 3.97 5.66 5.58 5.67 2.44 1.17 1.59 5.05 5.42 5.32 5.20 5.60 4.71 3.81 3.75 4.43 3.66 4.11 4.17 2.67 0.79
4.14 4.88 4.58 5.72 5.03 4.66 5.96 3.77 4.78 5.33 6.72 5.69 6.38 6.49 5.19 5.92 5.04 6.02 5.90 5.21 4.56 4.70 5.14 4.63 3.79 4.36 4.02 4.11 3.31 2.40 1.01
3.62 4.30 4.26 4.55 4.43 4.88 5.47 4.46 5.05 5.33 5.21 5.63 5.90 5.49 3.90 4.04 3.82 5.22 5.30 4.57 4.46 4.87 4.46 4.11 3.40 3.72 3.35 3.36 2.94 2.00 0.76
above would suggest. There are alternatives that reduce the use of pesticides and enhance the positive aspects of fertilization so as to contribute to turfgrass ‘health’ and reduce pest problems. Blanco-Montero, 1993 discusses this management strategy in the context of ‘integrated pest management’ (IPM). The positive aspect of turfgrass cultivation is its effect in reducing noise and erosion, cooling the city, providing income to hundreds of persons and conferring recreational benefits to the community. A well maintained lawn does not need excessive inputs, but in the case of heavily used areas, such as
127 Table 6. Turfgrass (grass clippings) biomass production from 6 different lawns (1,461.1 m2) during 1992 in Albuquerque, N.M. Grass clippings Date
Fresh weight g/m2
Dry weight g/m2
Volume 1 /m*
Accumulated fresh weight g/m2
01 May 08 16 23 30 06 June 13 25 02 July 09 16 23 30 06 Aug. 13 20 28 03 Sep. 10 17 24 30 07 Oct. 14 22 29
66.10 98.20 63.70 72.60 50.60 53.70 100.95 63.18 66.90 29.74 92.09 46.54 64.07 93.22 69.00 55.92 54.33 38.56 37.87 95.12 95.04 34.50 29.62 24.49 20.53 38.78
28.75 42.71 27.70 31.58 22.01 23.35 43.91 27.48 29.10 12.93 40.05 20.24 27.87 40.55 30.01 24.32 23.63 16.77 16.47 41.37 41.34 15.00 12.88 10.65 8.93 16.86
0.13 0.20 0.13 0.14 0.10 0.11 0.20 0.13 0.13 0.06 0.18 0.09 0.13 0.19 0.14 0.11 0.11 0.07 0.07 0.19 0.19 0.07 0.06 0.05 0.04 0.08
66.10 164.30 228.00 300.60 35 1.20 404.90 505.85 569.03 635.93 665.67 757.76 804.30 868.37 961.59 1,030.59 1,086.51 1,140.84 1,179.40 1,217.27 1,312.39 1,407.43 1,441.93 1,471.55 1,496.04 1,516.57 1,555.35
Accumulated volume 1 /m2 ~
0.13 0.33 0.46 0.60 0.70 0.81 1.01 1.14 1.27 1.33 1.51 1.60 1.73 1.92 2.06 2.17 2.28 2.35 2.42 2.61 2.80 2.87 2.93 2.98 3.02 3.10
Table 7. Economic cost of maintenance of different turfgrass property classes, as obtained from Busey and Parker (1992), and adjusted for Albuquerque, N.M. Grass utilization
Area in Albuquerque (ha)
Maintenance cost (1974) ($/m2/y)
Total cost as 1974 WY)
Consumer price and cost of living adjustment factor to Albuquerque, 1992
Total cost 1992 ($)
Home lawns
6,532.6
0.145
9,472,270.00
2.73365
25,893,870.00
Parkdathletics fields
639.0
0.082
523,980.00
2.73365
1,432,377.00
Golf courses
478.7
0.245
1,172,913.OO
2.73365
3,206,333 .OO
Table 8 . Fertilizer requirements for different grass species as recommended by Watson (1983) and potential insecticide use per hectare. Requirements (Kg available element/ha) Grass species
Nitrogen
Phosphorus
Potassium
Insecticide (Kg[AI]/ha)
Tall fescue
18.0-45.0
22.0-52.8
20.75-41.5
4.89
Kentucky bluegrass
27.0-68.0
22.0-52.8
20.75-41.5
4.89
Bermudagrass
27.0-68.0
22.0-52.8
20.75-41.5
4.89
128 parks and athletic fields, occasional extra inputs may be necessary. A well maintained lawn may attract relatively high use, bringing increased stress to the grass and consequently the need for extra maintenance. Turfgrass cultivation provides conditions valuable to the growth of other ornamental plants in the turfgrass area. The requirements for maintenance of such plants are less well known than the requirements for grass. Therefore, it is easier to calculate the environmental impact of turfgrass than to calculate the same for other ornamental plants (Beard 1992). Alternative ornamental vegetation should provide as many benefits as turfgrass provides. A better understanding of the interactions between abiotic and biotic factors associated with turfgrass cultivation is needed in order to reduce unnecessary use of water, fertilizer, and pesticide, and to decrease maintenance costs and environmental impacts. Public education, especially of the home owner, is also needed in order to enforce these practices and reduce the pressure for growing ‘perfect lawns’.
Acknowledgement We would like to thank the following persons for their help in various aspects of this study: Barbara and Ray Gaskill, Beverly Molo, Bob Grassberger, Brian W. Gordon, Curtis Smith, Ernestine Sawyer, Janie Chavez, Jim Clark, Lana Garcia, Philip Zuber, and Theodore Sammis.
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