What is the Risk to Runoff Water Quality Posed by Fertilization of Turfgrass?
Dr. Chris Murray,Department of Interdisciplinary Studies
Outline
• What motivated this project?
• Runoff and pollution
• Turfgrass as a water quality management tool
• The problem: excess nutrients
• Experiments and studies of the effect of fertilization
• Best Management Practices
• Conclusions
Project motivation
• A collaboration between Landscape Ontario’s Lawn Care Commodity Group and Lakehead University
• Two factors initiated this project:
1. Source water protection agencies and similar organizations are considering fertilizer bans as a means of protecting water quality
2. Several studies had reported results contradicting this approach: where fertilizer is stopped, N,P in runoff increases
Why might this be a problem?
• As was the case with pesticide use, fertilization of lawns is often cited as a purely cosmetic practice
• While lawns provide aesthetic and recreational value, these benefits are considered non-essential
• Much more emphasis is placed on the risk of water contamination than these “soft” benefits of turfgrass
• If there is little or no value and significant risk, why not ban fertilizers and eliminate that risk?
• Is this a quantitatively appropriate response?
What do I mean by quantitative?
• Not all situations require numerical information to make an informed decision
• Example: how much gasoline should I drink in a day?
• There is no benefit to drinking any amount of gasoline
• Answer: don’t ever drink gasoline!
• Don’t need to consider body weight, age, or any other quantity to make this decision
Another example
• How much water should I drink every day?
• Q: Can you drink too much water?
• LD50 in rats: 90 g/kg
• A: Yes.
• Q: Do I need to drink any water?
• A: Yes, at least 2 L a day
• So, drink somewhere between 2 and 10 L
• Numbers are important to consider, because there are competing factors
Turfgrass Fertilization
• How much should one fertilize a lawn to obtain the best water quality?
• Q: Can you reduce water quality by fertilizing too much?
• A: Yes.
• Q: Can you improve water quality by fertilizing?
• A: Yes.
Risks of ignoring competing factors
• If fertilization can improve water quality, restricting fertilization can damage water quality
• Ignoring impact on turfgrass management industries, the implication is that such regulation could achieve the opposite of its intended effect
• Even in Canada, we cannot afford to make very many mistakes where water quality is concerned
General research questions
• What is the true state of scientific information regarding this issue?
• Is there consensus within the scientific community?
• If so, does it support a ban on fertilization of turfgrass?
• A primary focus of this study is the effect, both positive and detrimental, fertilization of turfgrass may have on the nutrient pollution through runoff.
Stormwater / runoff
• My background: stormwater and wastewater (not biology, ecology or turfgrass science)
• Most critical to understand: what dominates water pollution
• Why is runoff a problem?
• Runoff is “natural”, and would exist without human intervention
• Human activity dramatically increases runoff and the pollution it carries.
• As runoff increases, pollution increases
From SUNY College of Environmental Science and Forestry
Clean water is pollution
• What?
• How do stormwater management devices work?
• Quality: Sedimentation, filtration, sometimes chemical absorption
• Quantity: Dry wells, ponds, detention tanks
• Simple example: gravity separator
Velocity the same all along pipe, little settling occurs.Pollutants in = pollutants out
Velocity reduced in expanded sectionMore time to settle, bigger particles drop fasterSlower flow, bigger tank = more captured, less pollution
“Self-cleaning” pollution trapsScouring: high-velocity water stirs up sediment andresuspends captured pollutionPollution out > pollution in
Too much water is pollution, even if it is pure.
Reduced runoff = reduced pollution
Combined Sewer Overflow
Photo credit: Christopher Zurcher
Experimental considerations
• Need to measure quantity and quality
• Apples-to-apples comparison requires measurement of input as well as output
• Difficulty measuring small volumes introduces bias
• A mass balance approach is needed: what are all the paths nutrients may follow?
Bias
• Large events are easy to measure, carry more pollution
• If you don’t measure small events, you may skew results towards higher pollutant count
• Many small events can account for more pollution than a few large events, in total
• Small amounts of runoff stretched out over long periods of time are difficult to measure
“Laboratory” vs. FieldExperimental plot
• Controlled fertilization
• Controlled rainfall
• Events observed by researchers
• Can characterize all input/output water and nutrients
• Unrealistic
• Always includes worst case scenario
Real lawns
• Realistic
• Not as controlled
• May rely on assumptions such as homeowner behaviour
• Relies on automatic samplers
• Realistic rainfall, lawn use
From Yu et al., J. Hydrology, 434-435(2012) p.1-6
From Garn, USGS Water Investigation Report 02-4130 (2002)
Nutrients• Macronutrients required by
turfgrass:
• H2O, CO2, O2
• Nitrogen (e.g. as NO3-)
• Phosphorous (e.g. as H2PO4-)
• Potassium (K)
• Calcium (Ca)
• Magnesium (Mg)
• Sulphur (S)
Nutrient Cycles, Role in plants
• Nitrogen:
– Ingredient in proteins, DNA, chlorophyll, etc.
– Affects shoot-root growth, density, color, disease resistance, and stress tolerance.
• Phosphorous:
– Ingredient in cell membranes, energy transfer molecules, DNA, etc.
– Affects rate of seedling development and root growth.
• Why are these of primary concern?
Department of Geology, University of Illinois
Algal Blooms, Eutrophication
From Ministry of the Environment , Northwest Pacific Region Environmental Cooperation Center
Terminology
• Surface water/stormwater/runoff
• Infiltration/leachate
• In general, we aim to increase infiltration and decrease runoff to decrease pollution
• Why?
• Sediment and associated chemical pollutants
Erosion
• Wherever development occurs, risk of increased runoff velocity and erosion
• More sediment is carried into water
Dissolved/particulate pollution
• Nutrients such as phosphorous are soluble in water, but will bind with minerals in sediment
• A very small concentration of sediment may be responsible for most of the nutrient loading
• For a given mass, fine particles carry more pollution than large particles, and carry it further
How can adding fertilizer help?
• Turfgrass is, in general, a non-native groundcover that requires maintenance to thrive
• Without human intervention, it will not outcompete indigenous plants (weeds) which are better-suited to harsh conditions (especially drought) but not suited to human-scale runoff
• In general, healthier turfgrass increasingly reduces runoff and increases infiltration/evapotranspiration
• Runoff can be completely eliminated by turfgrass, and a lawn is often the only barrier between impervious surfaces and waterways
Runoff, Infiltration and Erosion Control
• How might reducing fertilizer increase the concentration of N, P in water?
• Small effect: increased decay of plants
• Large effect: less healthy turfgrass cannot hold water as effectively, so runoff increases
• Filtering is not enough: the amount of water must be reduced
Competing Factors
• The contamination of runoff by nutrients (both dissolved and particulate) found in fertilizer contributes to eutrophication of lakes causing negative impacts on the aquatic flora and fauna.
• Healthier turfgrass systems improve surface water quality through natural filtration and absorption of water, which reduces runoff intensity.
Summer/Fall 2012 Review
• More than 150 articles
• Aim: collect every piece of information regarding the impact of turfgrass fertilization on water quality
• Examined turfgrass versus alternative groundcovers
Some simple questions
• Under controlled conditions, what is the effect on the amount of nutrients output due to fertilization of turfgrass?
• What evidence is there turfgrass is a good choice for limiting runoff?
• What recommendations might be made, based on scientific consensus (if one exists)?
Reports worth examining
• Garn, 2002: – No runoff other than that due to rain on lawns– Increase P in runoff for fertilized lawns– The site with the best turf stand had the least runoff,
though quantitative measurements not made.– No effect of fertilization on nitrogen in runoff
• Kussow, 2002, 2004, 2008:– Fertilization with P leads to more P in runoff – Accounted for runoff volume– Most (runoff, nutrients) recorded when soil frozen– Without fertilization for two years, runoff, nitrogen and
phosphorous increased – Whether soil is frozen is dominating factor
• Easton and Petrovic, 2004
– Examined both synthetic and organic fertilizer
– P losses higher from P-containing fertilizer, highest for organic types (P applied very high)
– Fertilization increased infiltration, decreased runoff
– Frozen soil runoff accounted for majority
– Fertilization during establishment created most pollution
– In many cases, equal or higher N,P losses from unfertilized control due to overall increased runoff
• Soldat and Petrovic, 2008
– Review of various studies of runoff versus fertilization
– Worst-case scenario studies where water is added to plots following P fertilization showed P in runoff directly related to P applied
– Realistic rainfall events yielded results that included higher P from non-fertilized sites
– Sediment loss from turfgrass very low, or zero
• Beirman et al., 2010
– Examined no fertilization, P-free, P and triple-P fertilization
– Runoff highest for non-fertilized plots
– P in runoff from non-fertilized site highest in year 1, the same as from site receiving P in fertilizer in subsequent four years
– Frozen soil runoff dominates P loading, and recommended that no P used in Fall where runoff potential is high
Overview
• No studies perfectly controlled, perfectly realistic, but…
• Usually, nutrient concentrations in runoff higher where fertilization is applied
• Usually, amount of runoff is lower where fertilization is applied
• Most often, the total nutrient loss in runoff is decreased by fertilizing
• Where applicable, nutrient loss when ground is frozen dominates annual pollution
Turfgrass vs. other vegetative groundcovers
• Comprehensive studies are lacking.
• Most lawn alternatives are composed of non-native ornamental plant species
• The use of turfgrass reduces yearly runoff volume much more than native grass species
• Much more nitrogen may be leached from ornamentals than turfgrass
Best Management Practices: timing
• Worst: fertilization before the rain
• Avoid fertilization when soil is going to freeze or is already frozen
• Frequent, small applications better
Design
• Avoiding soil disturbance, or limit disturbances to one area at a time, always with turfgrass separating it from the waterways
• Avoid fertilization of turfgrass on high silt or clay content soil near the bottom of hills, near water’s edge
Clippings
• Mow at high cut height, frequently and when grass is dry
• Leaving clippings can greatly reduce runoff, but contributes (as much as 50% of required) nitrogen (though not phosphorous)
• As with any nutrient source, keep clippings away from impervious surfaces where they may be washed away
Watering• Irrigate in the morning
• Watering in recommended, as long as there’s no runoff
• Water pollution is less likely with more frequent, smaller volumes of watering… there is less likelihood of runoff.
• Another issue of competing factors? Better roots are supposed to be supported by the infrequent, high-volume watering, and these will reduce runoff… but short-term increased runoff
• Research lacking on effect of irrigation
Monitoring
• Every three years, soil test for P
• Until a test can be performed, use P-free fertilizer
• Especially during establishment, monitoring of soil needs is important
• Some reasons why soil testing is not enough: soil levels do not determine runoff potential
• Need to also measure: bulk density of soil, compactness
Conclusions
• The majority of studies examining the effect of fertilization on turfgrass show reduced runoff (and reduced nutrient loading) when lawns are fertilized
• Turfgrass is more effective than most alternative groundcovers
• Frozen soil, like any impervious surface, increases runoff potential and can be responsible for most of the pollution
Take-away’s
• Too much water (even when clean) is pollution
• Development
= impervious surfaces
= high volume, high velocity runoff
= erosion
= pollution
• Turfgrass (which is improved by careful maintenance) is one of the only “band aids” we have to treat this problem
Acknowledgements
• Student researchers:
– Kayla Snyder, Diane Mitchell, Lindsey Jaanussen, Brooke Marion, Kristyn Madrick
• Thanks to Mr. Ken Pavely, Mr. Gavin Dawson and Landscape Ontario’s Lawn Care Commodity Group
For more information contact:Dr. Christopher Murray
Department of Interdisciplinary StudiesLakehead University
Thank You!
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