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

cmurray1@lakeheadu.ca

Thank You!