Lab 5: Nutrient Cycling
Team Grey Van: Eric North, Andrew Testo, James Werner
Abstract
Nutrient cycling is the processes by which elements are extracted from their
mineral, aquatic, or atmospheric sources or recycled from organic forms, are used by
plants and eventually returned to the environment. Nutrient cycling data has been
collected At Hubbard Brook, NH for over thirty years. In this experiment, nitrate and
sulfate concentration levels in Hubbard Brook were measured from 1963 to 1983 and
compared to the establishment of the Clean Air Act of 1970. Nitrate and sulfate
concentrations were found to decrease after 1970.
Introduction
Nutrient cycling is the processes by which elements are extracted from their
mineral, aquatic, or atmospheric sources or recycled from organic forms, are used by
plants and eventually returned to the environment. Nutrients required in relatively large
quantities by plants are called macronutrients. The macronutrients are sodium, potassium,
calcium, magnesium, sulfur, phosphorus and chloride. Of these seven, sulfur and
nitrogen, in the form of sulfate and nitrate respectively, are input into the environment in
significant amounts through pollution. Sulfate and nitrate in the atmosphere reach the
terrestrial environment through wet deposition. Wet deposition is the process by which
particles are removed from the atmosphere through precipitation. By measuring the
nutrient concentration in Hubbard Brook the amount of nutrients deposited and leeched
from the soil can be determined. The Clean Air Act of 1970 mandated a decrease in
pollutants in air emissions from stationary and mobile sources. We believe that as an
effect of the regulations of the Clean Air Act, nitrate and sulfate levels in Hubbard Brook
will begin to decrease after 1970.
Methods
Nutrient cycling data was retrieved from the Hubbard Brook website,
(http://www.hubbardbrook.org/). From the data, the levels of sulfate and nitrate
deposited into the stream were monitored from 1963 to 1983 for watershed 6.
Results
Fig 1.
Hubbard Brook Nitrate concentration
140
2.5
2
120
1.5
1
100
0
mm
80
-0.5
60
-1
-1.5
40
-2
-2.5
20
-3
0
-3.5
1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983
year
Concentration %
0.5
flow
NO3
Fig. 2
Hubbard Brook sulfate concentration
140
7
6
120
5
4
100
80
mm
2
1
60
Concentration %
3
flow
SO4
0
40
-1
-2
20
-3
0
-4
1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983
year
NO3 and SO4 stream concentrations have been gradually decreasing since the early
seventies at watershed 6. Nitrate concentration shows direct correlation with stream
flow. These concentration values are only significant when they are positive values, as
the negative values are just place holders given for years where no measurements were
taken.
Discussion
The results show that concentrations of sulfate and nitrate begin to decrease in the
early 1970’s, concurring with the Clean Air Act of 1970 and therefore supporting the
hypothesis. Because fewer pollutants were able to enter the atmosphere, fewer pollutants
were deposited into the Hubbard Brook area and entered the stream. However, there may
be other factors that have influenced nitrate and sulfate concentrations in the system, such
as increased uptake by plants if density is increasing over time, or shifting weather
patterns (Santiago 2005). Its possible that because watershed 6 was the reference
watershed and no trees were removed, plant density was increasing and therefore more
nutrients were being taken up by plants, leaving less in the stream.
Conclusion
The results show a correlation between the enforcement of the Clean Air Act of
1970 and a decrease in stream concentrations of sulfate and nitrate, following the original
hypothesis. However, it is not known with strong certainty that the Clean Air Act is the
cause of the decrease. Through further studies of more sites, the influence of variables
other than the Clean Air Act could be reduced. This would provide stronger evidence for
the effect of pollution regulations on deposition. An additional improvement would be to
measure nutrient levels in wet deposition, rather than runoff, to gain a more direct route
of determining the amount of pollution in the atmosphere. The results of this study,
combined with others, could be used to evaluate the effectiveness of The Clean Air Act
and possible changes that could be made to improve the regulations.
Works Cited
Santiago, Louis S. Edward Schuur, Katia Silvera. Nutrient cycling and plant-soil
feedbacks along a precipitation gradient in lowland Panama. Journal of Tropical
Ecology. Vol 21. p.461.