Why Look at Marsh Soil Nutrients?
The purpose of this project was to evaluate changes in carbon (C), nitrogen (N), and phosphorus (P) in samples from identical locations taken ten years apart from Horicon Marsh in Dodge County, Wisconsin.
The area surrounding the marsh is primarily agricultural and has the potential to contribute nutrients to the marsh, affecting the fertility of the soils and changing the ecosystem.
What did we do?
We hypothesized that carbon, nitrogen, and phosphorus would show significant increases over the ten-year interval between samplings.
Sample sites were positioned every ¼ mile along east-west transects throughout the marsh. A soil core was obtained at each sample site in the winter of either 2002 or 2003. The same sites were revisited and new samples collected in winter of either 2012 or 2013, ten years after the initial visits. The top five centimeters of each soil core were oven dried at 105°C for 72 hours.
Total carbon and nitrogen were analyzed by combustion using a PerkinElmer 2400 series II CHNS/O Analyzer. Total phosphorus was analyzed by the Olsen P-extraction method on a QuikChem FIA+ 8000 series Lachat analyzer.
A paired t-test (α=0.05) was used to compare nitrogen and phosphorus values. Carbon data were compared with a Mann-Whitney ranked sum test at the 95% confidence interval.
What have we learned?
Carbon and nitrogen did not increase significantly over the time period. Carbon is generally bound in soil organic matter; in histic wetland soils, changes attributable to land use might be difficult to detect due to the already high organic matter content. Nitrogen accumulation was likely mitigated by denitrification processes.
Phosphorus concentrations were greater in the second set of samples. Phosphorus adsorbs tightly to sediment and organic material, which would prevent its removal by flowing water. Changes in land use, especially row crop agriculture in the Horicon marsh area, could contribute runoff inputs of soil particles carrying phosphorus with them. This may explain significantly increased phosphorus levels between the start and end of the study period.
Future studies might quantify land use changes, their extent, and their impacts on the marsh ecosystem; analyze spatial patterns of phosphorus accretion to determine if it is cycling equally throughout the marsh; and determine the impact of denitrifying bacteria and anaerobic conditions on nitrogen accumulation. Additional research could include testing the water column of the marsh for dissolved nutrients; and sampling the Rock River at its inlet to and outlet from the Horicon Marsh to determine nutrient flux to the stream from the marsh.
Ashley Hansen, University of Wisconsin-Stevens Point firstname.lastname@example.org
Anna Radke, University of Wisconsin-Stevens Point; Sarah Shawver, University of Wisconsin-Stevens Point
Dr. Robert Michitsch
Soils Professor and Research Advisor
Dr. Kyle Herrman
Water Resource Professor and Research Advisor
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