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.
Fig. 2
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.