Journal of Conference Abstracts

Relationships Between Mineral Nitrogen in Soils and Nitrate in Surface Water in a Watershed
in Southwestern Michigan

Stephen S. Aichele (aicheles@pilot.msu.edu)

315 Natural Science Building, Department of Geography, Michigan State University,
East Lansing, Michigan 48824-1115, U.S.A.

Excess N can cause eutrophication of streams, and nitrate in drinking water has been linked to infantile methemoglobinemia. Waste disposal from hog farming is a problem in southwestern Michigan. It has resulted in very high N and P loadings to both soils and water. This study investigates the transformations and transport pathways of nitrogen in a rural watershed, as a step toward better understanding of the processes that result in nitrate loadings to streams and lakes.

The study site is a small (<20 ha), sandy watershed with organic soils in toeslope positions. The watershed is predominantly owned by one farmer, who has been practicing responsible waste management for four years, without any perceptible change in the quality of the water leaving the watershed. Nearby sites have seen noticeable improvement within the same time frame. Research methods applied at this site included; (1) testing for mineral N (NO₃^- and NH₄⁺) in soils to a depth of 1.5 m on a 30 x 30 m grid, (2) testing for mineral N in surface water at various depths, and (3) monitoring shallow groundwater for mineral N in transit from recharge areas to the stream system.

Preliminary results suggest that, while modification of application practices has brought soil N loads back to conventional levels, this change has had little effect on the surface water. Residual organic matter, resulting from either dumping of waste or erosion off of fields, is slowly mineralising in an anaerobic environment in the wetland to form NH₄⁺, which is nitrified near the water's surface. This site may continue to release N into streams and lakes downstream for decades.

Investigating Long Term Sulphur Dynamics at the
Hubbard Brook Experimental Forest with
Stable Isotope Measurements

Christine Alewell¹ (calewell@mailbox.syr.edu), Myron Mitchell¹ (mitchell@mailbox.syr.edu),
Nenita Lozano² & Roy Krouse²

¹ ESF, College of Environmental Science and Forestry, SUNY, Syracuse, New York 13210-2788, U.S.A., Fax: 315-470-6996.

² Department of Physics, University of Calgary, Calgary, Alberta T2N 1N4, Canada.

The ecosystem study at Hubbard Brook Experimental Forest (HBEF) has been in operation for more than 30 years. At the HBEF archived samples of bulk precipitation and stream water from 1969 through 1995 were analysed for ³⁴S values of SO₄^2-. Since the early 1970s the anthropogenic emissions and deposition has been declining in eastern North America. The longterm changes of the ³⁴S values in bulk precipitation should be useful in ascertaining the relative contribution and temporal changes of natural biogenic versus anthropogenic emissions in contributing to sulphur deposition. From the Na⁺ concentration in bulk precipitation and the known SO₄^2-/Na ratio of the sea water, the marine SO₄^2- contribution can be calculated. This information will be used in subtracting out the relative contribution of marine SO₄^2- (³⁴S = +20.7 per mil) and a non-marine ³⁴S value will be determined.

During earlier periods of higher S deposition, we hypothesize that SO₄^2- adsorption was likely enhanced. This adsorbed SO₄^2- should desorb as SO₄^2- loading decrease. Changes in the ³⁴S values of stream water can be used to evaluate this desorption of SO₄^2- from mineral soil.