This paper describes the design, construction, and function of a 1,000 m2 facility containing 24 individual 33.6 m2 field plots equipped for measuring total runoff volumes with time and collection of runoff subsamples at selected intervals for quantification of chemical constituents in the runoff water from simulated home lawns.
As the urban population increases, so does the area of irrigated urban landscape. Summer water use in urban areas can be 2-3x winter base line water use due to increased demand for landscape irrigation. Improper irrigation practices and large rainfall events can result in runoff from urban landscapes which has potential to carry nutrients and sediments into local streams and lakes where they may contribute to eutrophication. A 1,000 m2 facility was constructed which consists of 24 individual 33.6 m2 field plots, each equipped for measuring total runoff volumes with time and collection of runoff subsamples at selected intervals for quantification of chemical constituents in the runoff water from simulated urban landscapes. Runoff volumes from the first and second trials had coefficient of variability (CV) values of 38.2 and 28.7%, respectively. CV values for runoff pH, EC, and Na concentration for both trials were all under 10%. Concentrations of DOC, TDN, DON, PO4-P, K+, Mg2+, and Ca2+ had CV values less than 50% in both trials. Overall, the results of testing performed after sod installation at the facility indicated good uniformity between plots for runoff volumes and chemical constituents. The large plot size is sufficient to include much of the natural variability and therefore provides better simulation of urban landscape ecosystems.
Four of the most rapidly growing, highly populated metropolitan areas are located in the southern U.S. in subtropical climates1. In addition, the largest percent change in urbanized land between 1982 and 1997 occurred in southern USA1. With increased urban areas comes a concomitant demand for potable water, much of which is used for outdoor use during summer months2. With new construction, programmable in-ground irrigation systems are often installed. Unfortunately, these systems are often programmed to deliver irrigation to urban landscaping more frequently and/or in volumes that exceed evapotranspiration demands of the landscape2. This results in a significant volume of runoff from urban landscaping to receiving waters, which contributes to what has been termed urban stream syndrome3. Symptoms of the urban stream syndrome include increased frequency of overland flow and erosive flow, increased nitrogen (N), phosphorus (P), toxicants, and temperature in addition to changes in channel morphology, freshwater biology, and ecosystem processes3.
Losses of N and P from agricultural ecosystems have been extensively studied and found to be primarily dependent on four factors: nutrient source, application rate, application timing, and nutrient placement4. While fewer published data currently exist on off site movement of nutrients from urban landscapes, these principals can be directly applied to turfgrass culture, whether in home lawns, sod farms, parks, or other green spaces. Additionally, improper irrigation practices which result in runoff from the landscape can exacerbate these losses.
Nutrient losses can be further altered by irrigation water quality. Areas in the southwest US often utilize more saline or sodic water for irrigation of home lawns and urban landscapes5,6. The chemical composition of the irrigation water may significantly alter soil chemistry causing a release of carbon, nitrogen, calcium, and other cations to runoff water. Recent work showed that increased sodium absorption ratio (SAR) of the extracting water significantly increased the amounts of carbon (C) and nitrogen (N) leached from St. Augustinegrass clippings, ryegrass clippings, and other organic materials7. Furthermore, water extractable soil C, N, and P losses from recreational turfgrass soils were significantly correlated with irrigation water chemical constituents6.
Washbusch et al. studied urban runoff in Madison, WI and found that lawns were the largest contributors of total phosphorus8. In addition, they also found that 25% of the total P in “Street Dirt” originated from leaves and grass clippings. In a typical rural setting, leaf litter falls onto the ground and then decomposes slowly releasing nutrients back to the soil environment. However, in urban environments, significant quantities of nutrient-rich leaves and grass clippings may fall on or get washed or blown onto hardscapes such as driveways, sidewalks, and roadways, subsequently making their way into the streets where they contribute to “street dirt”, much of which gets washed directly into receiving waterways.
Urban landscape soils are often disturbed and highly compacted during construction, which can also increase amounts of runoff due to reduced infiltration rates9. Kelling and Peterson reported that both total runoff volume and the nutrient concentrations in runoff from home lawns are increased from lawns that are compacted or have severely disturbed soil profiles due to previous construction activities10. Edmondson et al. on the other hand, found that urban soils were less compacted compared to surrounding agricultural soils in the urban and suburban region of Leicester, UK11. They attributed this to heavy agricultural machinery used, but they also noted that lawns had a greater soil bulk density than soil under trees and shrubs which was attributed to grass mowing and greater human trampling.
It would appear that in many situations, urban and suburban stream syndromes are significantly impacted by runoff and point-source discharges3,12. While point-sources can be manipulated through permits and recycling, additional research is needed to develop and test best management procedures for home lawn establishment and management to minimize nutrient losses to runoff. Past research efforts in this regard have often been centered along coastal areas where there are high sand content soils, due to concerns related to the effects of leaching and runoff losses of nutrients to coastal waters. However, when working with very sandy soils, one must have steep slopes and high rainfall rates to be able to generate any runoff13,14. In contrast, many of the soils in the central United States are fine textured and have low infiltration rates that result in significant amounts of runoff from even small rainfall events. Thus, it was desired to design and construct a runoff facility on native soil and slope typical of those that may occur on residential landscapes.
This paper describes the design, construction and function of a 1,000 m2 facility containing 24 individual 33.6 m2 field plots for measuring total runoff volumes at relatively small temporal resolutions and simultaneous collection of runoff water subsamples at selected volumetric or temporal intervals for measurement and quantification of chemical constituents of the runoff water.
1. Site Selection
2. Retaining Wall Construction
3. Installation of Instrumentation
4. Plot Area Preparation
5. Planting and Initial Runoff Event
6. Sample Analysis
Plot characteristics
The average slope for all 24 plots was 3.7% and ranged from a low of 3.2% for plot 17 to a high of 4.1% for plot 2 (Table 1). Average topsoil thickness was 36 cm and ranged from a low of 25.0 cm for plot 24 to a high of 51.5 cm for plot 10 (Table 1).
Runoff volumes
Runoff volumes from the first trial on 09 August 2012 had a mean of 213.5 L and ranged from a low of 95.6 L to a high of 391 L with a coefficient of variability (CV) of 38.2% (Table 2). It should be noted that prior to sodding, these plots had been well irrigated to ensure good function of the irrigation and runoff collection systems, measure irrigation distribution and similar activities. Thus, much of the applied irrigation was collected as runoff.
In contrast, the soil was much drier prior to the 13 September 2012 runoff event which resulted in lower average runoff volume of 52.6 L. Volumes ranged from a low of 27.5 L to a high of 70.8 L with a CV of 28.7%. In this case, much of the applied water infiltrated into the soil beneath the sod resulting in lower amounts of total runoff.
Chemical concentrations
Irrigation was done using the local potable water. A composite sample of the irrigation water was collected from the irrigation heads during the irrigation event and was analyzed for its chemical composition. The water had a pH of 8.5, an electrical conductivity (EC) of 1,030 dS/cm and contained 0.19 mg/L NO3-N, 0 mg/L NH4-N, 3.26 mg/L DOC, 0.38 mg/L TDN, 0.19 mg/L dissolved organic nitrogen (DON), 0.14 mg/L orthophosphate-P, 220.9 mg/L Na, 2.0 mg/L K, 0.87 mg/L Mg, and 4.27 mg/L Ca.
The pH values for all 49 water samples collected after the first runoff event the morning of 09 August 2012 after laying sod the previous day averaged 8.4 standard units with a minimum of 8.1 and a maximum of 8.9 units (Table 3), resulting in a very low CV of 1.5%. The EC and Na+ concentration of the runoff samples had fairly large means and CV values below 10% (Table 3). Concentrations of DOC, TDN, DON, PO4-P, K+, Mg2+, and Ca2+ had CV values in the range of 10.3-32.9%. Concentrations of NO3-N and NH4-N had means of 0.58 mg/L and 0.12 mg/L. However, these two parameters were the most variable and had the highest CV values of 85.0% and 63.5%, respectively.
The pH values for the 40 water samples collected on 13 September 2012 from the second group of plots averaged 8.5 standard units with a CV of 2.9% (Table 4). As with the first trial, pH, electrical conductivity (EC), and Na+ measurements for the first runoff event after laying sod on 12 September 2013 had the highest means and lowest CV values of 2.9, 4.9, and 6.5%, respectively. Concentrations of NO3-N, DOC, TDN, DON, PO4-P, K+, Mg2+, and Ca2+ had CV values in the range of 33.0-49.7%. Ammonium-nitrogen had the lowest mean value of 0.39 mg/L but was the most variable with the highest CV of 107.5%.
The above data for the first runoff event from newly sodded plots will serve as a baseline for future measurements. We expect the CV values between plots to decrease as the turfgrass becomes better established and there is less opportunity for channel flow of water between sod blocks and more uniform overland flow of water through the grass canopy. Plot size is adequate to allow for soil-water-chemical interactions to occur before runoff reaches the collection devices and thus, chemical concentrations in the runoff should be representative of what would be found in a similar urban landscape. We anticipate the facility to be of use in developing science based best management procedures for fertilization and irrigation of urban landscapes.
Figure 1. Contour map of hillside showing the locations for the three blocks of runoff plots. Please click here to view a larger version of this figure.
Figure 2. Schematic diagram of the retaining wall showing placement of the collection troughs and pads for measurement devices. Please click here to view a larger version of this figure.
Plot Number | Topsoil Depth (cm) | Surface Slope (%) | pH (Std. Units) | NO3-N (mg/kg) | P (mg/kg) | K (mg/kg) |
1 | 34.8 | 4.0 | 4.7 | 43 | 215 | 334 |
2 | 35.3 | 4.1 | 5.0 | 40 | 204 | 273 |
3 | 39.5 | 4.0 | 5.1 | 44 | 190 | 302 |
4 | 35.3 | 3.8 | 5.0 | 59 | 184 | 300 |
5 | 30.5 | 3.7 | 4.9 | 56 | 205 | 325 |
6 | 31.5 | 3.6 | 5.0 | 26 | 223 | 271 |
7 | 33.5 | 3.8 | 5.1 | 30 | 224 | 243 |
8 | 40.5 | 3.9 | 4.8 | 13 | 218 | 208 |
9 | 36.0 | 3.4 | 5.1 | 26 | 263 | 343 |
10 | 51.5 | 3.6 | 5.4 | 49 | 229 | 348 |
11 | 32.5 | 3.5 | 5.6 | 34 | 262 | 352 |
12 | 50.5 | 3.6 | 5.4 | 32 | 235 | 339 |
13 | 48.5 | 4.0 | 5.0 | 54 | 261 | 318 |
14 | 26.0 | 3.3 | 5.6 | 23 | 252 | 322 |
15 | 36.5 | 3.4 | 5.1 | 37 | 247 | 292 |
16 | 28.0 | 3.6 | 5.4 | 20 | 279 | 291 |
17 | 38.1 | 3.2 | 5.5 | 13 | 319 | 256 |
18 | 36.4 | 3.3 | 5.3 | 15 | 316 | 220 |
19 | 40.8 | 3.9 | 5.3 | 31 | 329 | 223 |
20 | 33.5 | 4.0 | 5.1 | 40 | 321 | 271 |
21 | 39.0 | 3.6 | 5.0 | 24 | 283 | 269 |
22 | 31.0 | 3.3 | 5.0 | 30 | 311 | 314 |
23 | 31.0 | 3.4 | 5.0 | 30 | 287 | 259 |
24 | 25.0 | 3.8 | 5.2 | 13 | 301 | 292 |
Table 1. Mean depth of topsoil, surface slope, soil pH, nitrate-N, P, and K for the 24 runoff plots. Values for pH, NO3-N, P, and K reported by the Texas AgriLife Extension – Soil, Water and Forage Testing Laboratory. Soil pH was measured on a 2:1 soil:water extract, NO3-N by Cd reduction, P and K by Mehlich 3 extraction followed by ICP analysis.
Date | Units | Mean | Minimum | Maximum | CV (%) |
9-Aug | L | 213.5 | 95.6 | 391.6 | 38.2 |
13-Sep | L | 52.6 | 27.5 | 70.8 | 28.7 |
Table 2. Mean, minimum, maximum, and coefficient of variation (CV) for the runoff volumes collected on 09 August 2012 and 13 September 2012 from 12 runoff plots one day after laying sod.
Parameter | Units | Mean | Minimum | Maximum | CV (%) |
pH | Std. Units | 8.4 | 8.1 | 8.9 | 1.5 |
EC | µS/cm | 1,137 | 1,080 | 1,220 | 3.7 |
NO3-N | mg/L | 0.58 | 0.08 | 2.93 | 85 |
NH4-N | mg/L | 0.12 | 0.04 | 0.37 | 63.5 |
DOC | mg/L | 22 | 16.3 | 30.1 | 13.4 |
TDN | mg/L | 1.89 | 1.16 | 4.42 | 32.9 |
DON | mg/L | 1.2 | 0.8 | 2.26 | 23.3 |
PO4-P | mg/L | 1.05 | 0.59 | 1.76 | 31.9 |
Na | mg/L | 213 | 201 | 222 | 2.3 |
K | mg/L | 11.9 | 6.4 | 19.1 | 29.3 |
Mg | mg/L | 4.65 | 2.64 | 5.69 | 13.2 |
Ca | mg/L | 18.4 | 13 | 22.1 | 10.3 |
Table 3. Mean, minimum, maximum, and coefficient of variation (CV) for 49 measurements each of 12 parameters of water samples collected on 09 August 2012 from 12 runoff plots one day after laying sod with no fertilizer additions.
Parameter | Units | Mean | Minimum | Maximum | CV (%) |
pH | Std. Units | 8.5 | 8.1 | 9 | 2.9 |
EC | µS/cm | 1,514 | 1,310 | 1,630 | 4.9 |
NO3-N | mg/L | 1.68 | 0.28 | 3.95 | 49.7 |
NH4-N | mg/L | 0.39 | 0.08 | 2.59 | 107.5 |
DOC | mg/L | 27.6 | 7.08 | 54.6 | 33.7 |
TDN | mg/L | 3.73 | 0.81 | 6.6 | 33.0 |
DON | mg/L | 1.67 | 0 | 4.97 | 48.0 |
PO4-P | mg/L | 1.34 | 0.33 | 2.32 | 40.5 |
Na | mg/L | 206 | 188 | 241 | 6.5 |
K | mg/L | 10.4 | 3.58 | 21.8 | 35.9 |
Mg | mg/L | 3.17 | 1.02 | 5.02 | 41.3 |
Ca | mg/L | 12.7 | 3.72 | 21 | 40.1 |
Table 4. Mean, minimum, maximum, and coefficient of variation (CV) for 40 measurements each of 12 parameters of water samples collected on 13 September 2012 from 12 runoff plots one day after laying sod with no fertilizer additions.
Water flow over, into, and through soils is greatly affected by the topography, vegetative cover, and the soil physical properties. Excessively compacted soils and soils with high clay contents will exhibit reduced infiltration rates and increased amounts of runoff. Therefore, when building a facility of this nature, every effort should be made to use native soils with uniform slopes and minimize compaction from all types of traffic on the experimental areas during construction. In addition, compaction from post construction maintenance activities should be minimized. These factors also need to be considered when interpreting the data from a given experiment and comparing them to data from other sites where site conditions may be very different.
All natural soils have a high amount of inherent spatial variability. This may be a result of biological activity such as worm holes, insect activities, etc. or basic soil properties such as texture and shrink-swell potential of the clays. The large plot size used in this facility was selected to include as much of this spatial variability as possible and thereby minimize the total variability between plots.
The irrigation spray nozzles in this facility were selected for use to provide a high precipitation rate with improved drift reduction. An irrigation audit resulted in a mean precipitation rate of 4.04 cm/hr and a uniformity of 79.5%. Other nozzles may be used if lower precipitation rates are desired, however this may result in less uniform water distribution and increased spray drift due to wind. Forced runoff events in which the irrigation system was used as the water source were conducted between 7-9 a.m. to minimize wind effects.
Use and operation of the facility thus far has shown a need for careful observation of the spray nozzles and replacement of damaged ones. Damaged nozzles alter the amount and distribution of water which may bias data. Although not a problem in this initial work, it is evident that periodic cleaning of the channel drains and H flumes will be required to remove accumulated organic and inorganic sediments. Such sediments may affect flow rate measurements particularly at low flows as well as contribute chemical constituents to runoff water samples.
The mean NO3-N concentrations of 0.58 and 1.68 mg/L for the August and September trials are high compared to the 0.0-0.4 mg/L reported by Kelling and Peterson for unfertilized control lawns which served as check plots in their WI study10. A large part of this increase may be due to the fact that our study was conducted on freshly planted sod. This allowed water to come into direct contact with soil in seams between sod blocks and likely increased both soil erosion and N removal from the fertile soil. Effects of flow along seams will be diminished in future experiments as the turf matures and knits together into a tight, dense turf canopy. Furthermore, disturbance of the soil during construction and raking prior to sod installation did effectively aerate the soil which provided optimum conditions for nitrification in the soil. The measured NO3-N concentrations are similar to the mean of 1.54 mg/L reported by Gobel for rainfall runoff from gardens, grassed areas and cultivated land19.
Phosphorus losses from unfertilized turfgrass typically range from 0.5-5.5 mg/L 10,17,18. Mean phosphorus losses were 1.05 and 1.34 mg/L for the August and September trials, respectively, and were within the range of 0.5-1.7 mg/L reported by Kelling and Peterson10 and within the range of 0.5-5.5 mg/L reported by Vietor20. Higher P losses from unfertilized plots reported by Vietor were likely due to the higher slope of 8.5% and different grass species used in their study20. Mean P losses in the present study were higher than the mean P concentration of 0.09 mg/L reported by Gobel for rainfall runoff from gardens, grassed areas and cultivated land19. A large part of the P loss from the current study was likely due to soil erosion from the first runoff event on a newly planted site. It is also likely that the high sodium content of the irrigation water used in the present study may have affected the concentrations of P in the runoff water7.
In comparison to the first trial, the measured concentrations of parameters in the second trial were more variable. This increased variability was attributed to the drier initial soil moisture content prior to planting which resulted in fewer samples. The extra 30 days of hot, dry weather allowed more nitrification to occur. In addition, there was more dust at planting time which may have been on the vegetation and subsequently washed off in the runoff event. It is also possible that some of the increased variability may be due to differences in nutrient content of the purchased sod, although every effort was made to minimize this source of error.
Overall, the runoff facility has numerous benefits for future research concerning runoff from turf covered areas such as home lawns, sports fields, parks and similar green spaces. Primary among these is that the facility is large enough to be maintained on a long term basis using full sized equipment common to the turf industry. Mowing can be done using either walk behind or riding mowers. Fertilization can be done using commercially available drop spreaders. The large size of the individual plots should help include similar amounts of natural variability and microclimate effects in each. The facility was built on relatively undisturbed native soil so results are not biased by anthropogenic effects. The facility has individual plot control over irrigation using equipment that is typical of homeowner irrigation systems. Thus, the need for a rainfall simulator is eliminated thereby allowing up to all 24 plots to be run simultaneously if so desired. Runoff measurement and sampling is automated allowing data and sample collection from unscheduled storm events.
Future studies investigating the effects of irrigation volumes, ground cover, nutrient sources, application rates, and application timing are planned. As urban greenscape acreage continues to increase, facilities of this nature offer the potential for intensive studies of irrigation and nutrient movement from urban landscapes. Data of these type can be used for development of scientifically-based best management practices that minimize off-site movement of water and nutrients under various climatic regimes.
The authors have nothing to disclose.
The authors gratefully acknowledge financial support from The Scotts Miracle-Gro Company for this facility. We are also appreciative to the Toro Co. for assistance with providing the irrigation controller. The vision and planning by the late Dr. Chris Steigler in the early stages of this project is also gratefully acknowledged. The authors would also like to thank Ms. N. Stanley for her technical assistance with sample preparation and analysis.
Flow meter | Teledyne Isco | Model 4230 | Bubbling flow meter that measures and records water flow through flume |
Portable Sampler | Teledyne Isco | Model 6712 | Works in conjunction with the flow meter to collect water samples at predetermined intervals. |
Flow Link Software to collect data | Teledyne Isco | Ver 5.0 | Allows communication between flow meter and computer |
Pre-sloped trench drain | Zurn Industries, LLC | Z-886 | |
Irrigation Controller | Toro Company | VP Satellite | Controls irrigation to each plot individually |
Electric Valves | Hunter | 2.5 cm PGV | Opens or closes water flow to individual plots based on signal from irrigation controller |
Spray nozzles | RainBird | HE-Van 12 | Sprays irrigation water in predetermined pattern and rate |
Irrigation heads | Hunter | Pro Spray 4 | 4 inch pop up spray heads |
6 inch slotted drain pipe | Advanced Drainage Systems | 6410100 | single wall corregated HDPE – slotted |
6 inch plain drain pipe | Advanced Drainage Systems | 6400100 | single wall corregated HDPE – plain |
Filter Paper | Whatman GF/F | 1825-047 | 47mm diameter, binder-free, glass microfiber filter |
pH Meter | Fisher | Accumet XL20 | |
Combination pH probe | Fisher | 13-620-130 | |
Automatic Temperature Compensating Probe | Fisher | 13-602-19 | |
Electrical conductivity probe | Fisher | 13-620-100 | Cell constant of 1.0 |
TOC-VCSH with total nitrogen unit TMN-1 | Shimadzu Corp | TOC-VCSH with TMN-1 | dissolved C and N analyzer |
Smartchem 200 | Unity Scientific | 200 | Discrete Analyzer for P measurement |
ICS 1000 | Dionex | ICS 1000 | Ion Chromatography for Ca, Mg, K and Na measurment |
Portable Soil Moisture Meter | Spectrum | FieldScout TDR 300 | 7.5 cm long probes |
Totallizing Water Meters | Badger | 3/4 inch water meters | standard homeowner water meters |