Hayes, Werner, Worrell Group project

THE EFFECTS OF GREEN ROOFS ON NUTRIENTS IN RUNOFF 1
Ericka Hayes, Andrew Werner, & Christopher Worrell EES 450*01 Spring 2016
1. Introduction:
Green roofs (roofs with a vegetated surface and substrate) provide ecosystem services in
urban areas, including improved storm-water management, better regulation of building
temperatures, reduced urban heat-island effects, and increased urban wildlife habitat
(Oberndorfer et al. 2007). Over the years the U.S. Government has been encouraging companies
to use green roofs because, of their benefits to the environment. The starter cost for green roofs
can be pricey, but they result in a lower overall cost compared to a normal roof (Malcolm et al.
2014). In other studies green roofs have been proven to reduce noise pollution from urban traffic
and construction (Czemiel Berndtsson et al. 2006).
Ten years ago, the roof on Smithdeal Hall at Virginia Wesleyan College was transformed
into a green roof (Malcolm et al. 2014). The roof is on a two-story building which is an overall
T-shape with trees taller than the rooftop and a small tree growing in the green roof media. The
green roof consists of seven layers: a base sheet fastened to a plywood base, roof membrane with
a copper root barrier, a drainage layer, a water retention layer, a filter fabric, and a growing
media planted with Sedum (Fig. 1). When the roof was first put in, they planted thirteen species
of Sedum, but now there are an unknown amount species of Sedum and other unknown
vegetation. The original green roof had three sections, but one of the sections has since been
removed due to water damage. A roof adjacent to the green roof on Smithdeal Hall was used as
our gravel roof and the awning of the new Blocker entrance was used as our “normal” or
“control” roof.
The professors at Virginia Wesleyan College wanted to observe if pollutants and
nutrients could be significantly reduced by green roofs. They used fifteen one-square-meter test
roof plots and two green roofs to measure if green roofs reduce pollutants and nutrients in

stormwater (Malcolm et al. 2014). Five configurations were used on the test plots (all green
plots had Sedum), green roof , green roof with a water-retention layer, green roof with a drainage
layer, green roof with both water-retention and drainage layers, and conventional tar and gravel-
covered buildup roof. They found a large percentage of high nitrogen concentrations in the
samples that were in the form of soluble nitrate (1.0 mg/L to 19.4 mg/L), possibly due to the
fertilizer previously used to promote plant growth (Malcolm et al. 2014). They also found that
the nitrogen concentration in the precipitation were typically at or below the detection limit and
the gravel roofs typically lower than 1.0 mg/L (Malcolm et al. 2014).
The goal of our study was to see if green roofs would decrease nutrient runoff. Since our
study took place 10 years after the installation of the green roof, the fertilizer has had a chance to
be absorbed by the Sedum and the natural addition of other plants may have helped to decrease
the volume of runoff. Excess nutrients caused by anthropogenic sources has been a major issue
in the Chesapeake Bay Watershed, because high levels of nitrogen and phosphorus can cause
algal blooms and anoxic zones, which can kill fishes, invertebrates, and subaquatic vegetation.
Fig. 1. Green roof configuration (Malcolm et al. 2014).

Hypothesis:
Our null hypothesis is that the green roof will not alter the concentration of nutrients
runoff. Our alternative hypothesis is green roof will decrease nutrient concentrations in runoff.
2. Methods:
In our experiment, we only collected data from four drains (green 1, green2, gravel,
Blocker) and one rain gauge (precipitation) to investigate the concentration of nutrients in runoff.
To collect the runoff, we used pie pans that we placed inside the four drains before a rain event,
and then we collected the samples in clean 125 mL polyethylene bottles (Malcolm et al. 2014).
We analyzed anions (phosphate, nitrate, nitrite, chloride and sulfate) in each water sample using
ion chromatography (Dionex ACS-2100) to test the effects of nutrient runoff. Single factor
ANOVA was used in Excel to analyze the runoff samples from the three storms, to determine if
the green roof caused any significant variation in nutrient concentrations.
In (Table 2) percent recovery for the SPEX check standards showed that nitrite and
chloride calibration was incorrect because the values we not within the ideal 90-110% range. By
having values outside the ideal range (90-110%), we are unable to be confidence in the
concentrations of the nitrite and chloride samples. In (Table 3) the percent difference in our
replication for nitrite was 23.9%, 14.2% nitrate, 9.6% phosphate, 1.0% chloride, and 2.7%
sulfate, which showed further uncertainty in the nutrient concentrations.

Fig. 2. Aerial image of the roof drains, Blocker drain, and the
pans in the drains.
3. Results:
There was no significant difference in the nutrient concentrations between sample types
(precipitation, green roof 1, green roof 2, and gravel) (ANOVA nitrate (p=0.3473), nitrite
(p=0.6818), phosphate (p=0.4464), chloride (p=0.1498), sulfide (p=0.6301)). The gravel and
Blocker roof drains had the highest concentrations of nitrite with 0.7295 ppm and 0.6717ppm,
respectively (Table 1). The highest nitrate concentrations were found in gravel and green roof 2
with 3.6887 ppm and 1.6235 ppm, respectively (Table 1). The phosphate concentrations were
mostly 0.000 ppm with gravel having the highest amount 0.5658 ppm (Table 1). Gravel also had
the highest chloride concentration 8.7915 ppm and green roof 1 had the highest sulfate
concentration 11.0210 ppm (Table 1). The average nutrient concentrations in the blanks were
0.000 ppm nitrite, 0.0001 ppm nitrate, 0.000 ppm phosphate, 0.3994 ppm chloride, and 0.0403
ppm sulfate. The R2 values for the calibration curves were 0.9972 nitrite, 1.0 nitrate, 1.0
phosphate.
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Ericka Hayes
Ericka Hayes

Table 1. Volume of samples, weather data, concentrations in ppm for nitrite, nitrate, phosphate,
chloride, and sulfate. “n.a” in the 3/13/16 Blocker samples is for unavailable data.
Volume (mL) 3/13/2016 3/15/2016 4/2/2016
Rain 119.94 44.50 145.53
Gravel Roof 138.27 32.17 146.23
Blocker n.a. 28.36 65.49
Green Roof 1 140.50 164.90 146.63
Green Roof 2 137.95 140.29 135.36
Antecedent Dry Period (days) 8 1 4
Mean Air Temp ºC 65 58 61
Precipitation (mm) 16.51 6.604 17.78
Nitrite Concentration (ppm)
Precipitation <DL <DL 0.5879
Gravel Roof 0.5793 0.7295 <DL
Blocker n.a. 0.6717 0.5861
Green Roof 1 0.5542 <DL 0.5530
Green Roof 2 0.5708 0.3506 0.5510
Nitrate Concentration (ppm)
Precipitation 0.9410 1.2458 0.6306
Gravel Roof 0.4916 3.6887 0.6714
Blocker n.a. 2.9893 0.6450
Green Roof 1 0.7933 0.0095 0.4240
Green Roof 2 1.6235 0.0170 0.1245
Phosphate Concentration (ppm)
Precipitation <DL <DL <DL
Gravel Roof <DL <DL 0.5658
Blocker n.a. 0.0566 <DL
Green Roof 1 <DL <DL <DL
Green Roof 2 0.0115 <DL <DL
Chloride Concentration (ppm)
Precipitation 1.5201 0.8491 5.0309
Gravel Roof 3.2103 8.2569 8.7915
Blocker n.a. 2.3139 1.8684
Green Roof 1 3.7863 4.9675 1.9955
Green Roof 2 3.5621 2.4374 4.4015
Sulfate Concentration (ppm)
Precipitation 0.5672 0.5084 6.7662
Gravel Roof 1.3068 5.9695 2.7312
Blocker n.a. 1.6268 1.2027
Green Roof 1 5.6286 11.0210 0.4991
Green Roof 2 1.9396 3.3533 1.6511

Fig. 3. Nitrite concentration (ppm) for all three storms and roof drains. Not significantly different
(p= 0.6818).
Fig. 4. Nitrate concentration (ppm) for all three storms and roof drains. Not significantly
different (p= 0.3473).

Fig. 5. Phosphate concentration (ppm) for all three storms and roof drains. Not significantly
Fig. 6. Chloride concentration (ppm) for all three storms and roof drains. Not significantly

Fig. 7. Sulfate concentration (ppm) for all three storms and roof drains. Not significantly
different (p=0.6301).
Table 2. The minimum, maximum, and mean of the SPEX percent recovery.
Nitrite Nitrate Phosphate Chloride Sulfate
Min
(ppm) 0.0000 0.0000 81.4344 97.9086 91.5975
Max
(ppm) 0.0000 1.4440 87.1935 145.6222 95.7126
Mean
(ppm) 0.0000 0.1904 84.7477 107.6280 93.8328
Table 3. The minimum, maximum, and mean of the percent difference.
Nitrite Nitrate Phosphate Chloride Sulfate
Min
(ppm) 0.0000 0.1276 0.0000 0.1767 0.2023
Max
(ppm) 100.0000 100.0000 93.9482 2.3722 12.1264
Mean
(ppm) 23.9009 14.2036 9.5870 1.0267 2.7193

Table 4. Comparison of phosphate and nitrate concentrations to Malcolm et al.
2007-2009
Total P
2016
PO4
2007-2009
Total N
2016
NO3
Green roof 0.33-0.7 <DL-0.015 1.37-3.33 <DL-0.57
Gravel <DL-0.61 <DL-0.57 <DL-0.35 <DL-0.7
Precipitation <DL-0.05 <DL <DL-0.29 0.63-1.25
4. Discussion:
Over the past decade green roofs have been a topic of interest and debate on whether
they work on improving environmental quality. Green roofs have proven to have effect on the
cycling of nutrients, like phosphorus and nitrogen. In our study, we looked at green roofs ability
to effect anions that are naturally found in runoff. Overall we looked at phosphate, nitrate, nitrite,
sulfate, and chloride, which are important components in biogeochemical cycles. Equilibrium of
these ions are important, because if ions such as nitrogen or phosphorus are limited in the
environment it may result in stunted plant growth and if there is too much it can result in harmful
effects. This is one of the reasons that led a group of VWC professors to conduct a study
measuring the concentrations of nutrients and heavy metals in runoff of the newly installed green
roof. Our hypotheses were to first compare our nutrient levels to the previous study.
4.1. Nitrate/Nitrite
One of the main reasons we chose to study nitrogen in runoff is due to it being an
essential nutrient in organisms and fluxes in biogeochemical cycles. Nitrogen concentrations can
fluctuate due to an increase of natural and anthropogenic sources, and changes in local and
global climate. Higher nitrogen levels in surface runoff can lead to algal blooms and dead zones
in nearby aquatic zones (Hessen et al. 1997). We were limited by the “7-ion standard” we used in
our ion chromatography analysis, so we were only able to analyze the concentrations of nitrate

and nitrite, instead of all forms of nitrogen. Nitrogen ions are highly reactive in the environment,
so to calculate the total N we would need a different ion standard or a different concentration
analysis method. If we were to compare the total N to only nitrate and nitrite there would be
misrepresentation (Cowen et al. 1976). We found that the nitrate and nitrite levels were not
significantly difference between the sample types when we analyzed the samples with a single
factor ANOVA in Excel. In (Fig. 3), we saw that the average nitrite levels were between 0.5 and
0.7 mg/L and the nitrate levels in Blocker and gravel have higher concentrations than the two
green roof samples.
4.2. Phosphate
Similar to nitrogen, phosphorus is a chemical that is essential to life and an abundance of
phosphorus can become a harmful to an ecosystem by causing a rapid growth in algae.
Phosphorus is often found in low levels and can be an important resource to many species
(Wymer et al. 1980). Phosphate might have a lower concentration in the green roof samples, due
to the abundance of vegetation which readily uptake any available phosphorus. Unlike nitrogen
which is highly reactive, the main form of phosphorus is phosphate, which is a reliable
representation of the total P concentration (Howard 2016). Ideally, the roofs on Blocker and
gravel should have the same concentrations as the regional average (0.5ppm, NADP 2014), and a
reduced concentration of phosphate from the green roofs. In (Fig. 5) we found that the
concentrations for phosphate were below the detection limit in a majority of the samples, which
might be a result of the fact that the atmosphere is not a major source of phosphate. Nixon et al
found that the majority of total flux of phosphorus comes from DIP [dissolved inorganic
phosphorus] and 15% of the total P is particulate phosphorus.

4.3. Sulfate
Sulfate can be a harmful ion in the atmosphere and aquatic reservoirs, it is also an
important component in many redox reactions that stimulate many biogeochemical cycles,
important processes are sulfur reduction, pyrite formation, metal cycling, salt-marsh ecosystems,
acid rain, and sulfur emissions. Sulfate is not directly harmful when found in terrestrial
environments, like green roofs (Luther et al. 1986). Atmospheric deposition of sulfate can
become dissolved and enter aquatic ecosystems after a rain storm occurs since it is not used by
terrestrial organisms, the concentrations of the sample type should reflect the regional average
(0.5ppm, NADP 2014). This is seen in (Fig. 7), there is no real trend that can be found. We had a
p-value that was higher than 0.05 which means that we had no difference between sites. It is also
possible for there to be deposited buildup of atmospheric sulfate in between rain events. There
will be increased sulfate deposition when there are more days between rain events.
4.4. Chloride
Chloride is an ion that can be harmful in aquatic systems, because it is highly reactive
and can potentially for dangerous compounds. Urban areas can cause an increase of runoff,
potentially increasing the amount of chloride in aquatic systems. Green roofs are a way to slow
down or prevent the transport of chloride, by allowing the chlorine ions to settle in the
environment without being harmful in mass quantities (Sonzogni et al. 1983). There is an
estimation that 45% of chloride is deposited from rainfall, and a small amount of it comes from
dry deposition alone. The amount of chloride that is not deposited directly into a stream is
transported through as groundwater (Peters and Ratcliffe. 1998). The chloride concentrations in
some of our samples were at or below the regional average (0.6ppm, NADP 2014), however the
higher concentrations may have resulted in poor acid washing methods.

4.5 Comparison to Malcolm et al. 2014
Our experiment was continuation and comparison to a study done by Malcolm et al.
2014, by measuring the nutrient concentrations from the green roof on Smithdeal Hall from their
study. The only nutrients we were able to compare were nitrate, nitrite and phosphate, because
the previous study did not analyze chloride or sulfate (Table 4). Several years ago there were
high concentrations of phosphorus about <DL- 0.7 (Table 4), dependent on the sample type
(Malcolm et al. 2014). In Table 4, the concentrations of phosphate are lower the Malcolm et al.
2014 in our study for all sample types. The main causes for the high concentrations of
phosphorus in the previous study may have been from the fertilizer needed to promote growth of
Sedum when it was first installed (Malcolm et al. 2014). Since the installation fertilizer has not
been reapplied to the green roof, which supports the reduction of phosphorus concentrations in
our samples.
4.6. Sources of Uncertainty
There are many sources of error that could have skewed our results since the data was not
significantly different between the types of samples. We were only able to collect samples from
three rain events, which may have prevented a significant difference due to the small sample
size. Bottle storage and contamination might have also played a role in how the chemistry of the
water may have changed after samples were collected. Our collection design allowed for
precipitation and runoff from the roof media to be caught in the collection pans, therefore our
samples were not purely runoff from the roofs. In a future study, we would design a cover to
prevent direct precipitation so that all water collected would have flowed on or through the roof
media. After the first storm there was an influx of pollen, leaf litter and soil in the runoff that
may have leeched nutrients into the samples. If we could change our experiment it might be

different if we used different methods for analyzing samples. We used ion chromatography in
order to look at individual anions, instead of spectrophotometric analysis using molybdenum
blue (Malcolm et al. 2014), which does not have a precise measurement of total P or total N to
compare to the previous study. We could instead look at only total N and total P to measure how
runoff on green roofs affects nutrients, which would have allowed us to further analyze the
fluxes and reservoirs within the biogeochemical cycling of nutrients.
4.7. Conclusion
Overall we found that even thought our graphs suggested a significant difference, our
ANOVA determined that there was no significant difference between sample types. We were
able to determine how our anions reacted with a green roof by gaining ideas and knowledge from
other studies. Green roofs are helpful because the transport of most nutrients is slowed or the
nutrients are absorbed by sedum on the roof, therefore it is better than other roof types at
mitigating the influx of nutrients. However there is a need for more studies and sampling fully
conclude if the green roof on Smithdeal Hall is effective at reducing the volume of nutrients in
runoff.
Acknowledgments:
VWC Physical Plant, Susan (Jake) Quigley
Dr. Howard for assistance with the Ion Chromatography
Dr. Malcolm for assistance and guidance throughout the study

References:
Czemiel Berndtsson, J., Emilsson, T., Bengtsson, L., 2006. The influence of extensive vegetated
roofs on runoff water quality. Sci. Total Environ. 355, 48–63.
Cowen, W. F., Sirisinha, K., Lee, G. F. 1976. Nitrogen Availability in Urban Runoff.
Journal (water Pollution Control Federation), 48(2), 339–345.
Howard, M. 2016. Personal conversation
Hessen, D. O., Atle Hindar, Gjertrud Holtan. 1997. The Significance of Nitrogen Runoff for
Eutrophication of Freshwater and Marine Recipients. Ambio, 26(5), 312–320.
Luther, G. W., Church, T. M., Scudlark, J. R., Cosman, M.. 1986. Inorganic and Organic
Sulfur Cycling in Salt-Marsh Pore Waters. Science, 232(4751), 746–749.
Malcolm, E.G., Tran,L.M., Reese, M.L., Schaus, M.H., Ozmon, I.M., 2014. Measurements of
nutrients and mercury in green roof and gravel roof runoff. Ecological Engineering 73,
705-712.
National Atmospheric Deposition Program (NADP). 2014. NADP Annual Maps.
http://nadp.sws.uiuc.edu/ntn/annualmapsByYear.aspx#2014
Nixon, S. W., Granger, S. L., Nowicki, B. L. 1995. An Assessment of the Annual Mass
Balance of Carbon, Nitrogen, and Phosphorus in Narragansett Bay. Biogeochemistry,
31(1), 15–61.
Oberndorfer, E., Lundholm, J., Bass, B., Coffman, R.R., Doshi, H., Dunnett, N., Gaffin, S.,
Köhler, M., Liu, K.K.Y., Rowe, B., 2007. Green Roofs as Urban Ecosystems: Ecological
Structures, Functions, and Services. BioScience 57, 823-833.
Sonzogni, W. C., Richardson, W., Rodgers, P., Monteith, T. J. 1983. Chloride Pollution of
the Great Lakes. Journal (water Pollution Control Federation), 55(5), 513–521.
Peters, N. E and Ratcliffe, E.B. 1998. Tracing hydrologic pathways using chloride at the
Panola mountain research watershed, Georgia, USA. Water, Air, and Soil Pollution, 105,
263-275
Wymer, P. E. O., Thake, B. 1980. The Importance of Phosphorus in Microalgal Growth and
Species Composition in Mixed Populations: Experiments and Simulations. Proceedings
of the Royal Society of London. Series B, Biological Sciences, 209(1176), 333–353.

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