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United States Department of Agriculture

Agricultural Research Service

Title: Phosphorous and Greenhouse Gas Dynamics in Drained Calcareous Wetland Soils of Minnesota

Authors
item Berryman, Erin - UNIVERSITY OF IDAHO
item Venterea, Rodney
item Baker, John
item Bloom, P -

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 6, 2009
Publication Date: September 1, 2009
Repository URL: http://hdl.handle.net/10113/36042
Citation: Berryman, E.M., Venterea, R.T., Baker, J.M., Bloom, P.R. 2009. Phosphorous and Greenhouse Gas Dynamics in Drained Calcareous Wetland Soils of Minnesota. Journal of Environmental Quality. 38(5):2148-2159.

Interpretive Summary: Artifical drainage via ditch construction or other means has been commonly used as a means of creating productive farmland in many areas of the upper midwest over the past several decades. The resulting land, depending on how it is used and managed, can become a potential environmental risk. A freshwater marsh, created about one hundred years ago by artificially draining a 105-ha shallow lake (Rice Lake), is a suspected source of phosphorus (P) to the Detroit Lake watershed, a major recreational destination in northwestern Minnesota. P loadings to the main drainage canal increase during the summer months, when the water table typically declines. Restoration efforts have been proposed that would elevate the water level as a means of inhibiting the release of P during mineralization of soil organic matter. Studies were conducted in the laboratory using intact soil cores from two different areas of the wetland to examine the impacts of water table control on P release, and also its effects on greenhouse gas emissions during 6 to 23 wk of incubation. Cores from one of the sites displayed high rates of P release from the highest water table treatment, while the other site showed only trace levels of P in the porewater. P release was attributed largely to the chemical reduction and dissolution of P bound to iron (Fe) hydroxides. P mineralization may also play an important role in slower organic inorganic P transformations. Field porewater monitoring and soil sampling supported the hypothesis that P release is controlled by Fe. Significant differences in greenhouse gas fluxes were also observed among treatments. At both sites, the highest water table treatment displayed lower cumulative nitrous oxide flux and higher methane flux than the lowest water table treatment, resulting in a net increase in total carbon dioxide greenhouse gas equivalents. Thus, the proposal to increase water levels has the potential to increase both P release and total greenhouse gas emissions, although issues related to process variability across the wetland were difficult to assess. These results have important implications for the local watershed district and other agencies (e.g., NRCS) which are charged with ameliorating this problem and others similar to it. The results of this study have in fact been considered by these agencies as they move forward with restoration efforts for the Upper Pelican River Watershed.

Technical Abstract: A freshwater marsh, created about one hundred years ago by artificially draining a 105-ha shallow lake (Rice Lake), is a suspected source of phosphorus (P) to the Detroit Lake watershed, a major recreational destination for northwestern Minnesota. P loadings to the main drainage canal increase during the summer months, when the water table typically declines. On the assumption that increased aeration causes P release through mineralization of organic matter, local authorities have proposed that the water level in the marsh be maintained at a higher level. To test this assumption, and to examine the impacts of water table control on greenhouse gas emissions, intact soil cores from 2 sites in the wetland were subjected in the laboratory to three water table levels and incubated for 6 to 23 wk. Dissolved reactive P, reduced Fe, pH, dissolved organic carbon (DOC), and oxidation reduction potential (Eh) were monitored in the pore water. Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes were determined from headspace gas samples. Gas fluxes were converted to global warming potentials in CO2 equivalents. DRP dynamics differed between sites. One site displayed high DRP flux from the highest water table treatment, while the other site showed only trace levels of porewater DRP, with no significant differences among treatments. Additionally, the effect of transition from low to high water table yielded significantly higher mean DRP under fooded conditions than during the drained conditions, but did not show different mean DRP than continuously fooded conditions. DRP release in wetland soil was attributed largely to reduction and dissolution of P bound to Fe hydroxides, but P mineralization may play an important role in slower organic inorganic P transformations. Field porewater monitoring and soil sampling supported hypothesis that DRP solubility is controlled by Fe. Greenhouse gas fluxes were similar at both sites, and significant differences were observed among treatments. At both sites, the highest water table treatment displayed lower cumulative N2O flux (p<0.05) than the lowest water table treatment. Cumulative CO2 equivalent data at one site indicates that the highest water table treatment has the greatest global warming potential (significant at p<0.05). Thus, the proposal to increase water levels has the potential to increase both P release and total greenhouse gas emissions, although issues related to process variability across the wetland were difficult to assess.

Last Modified: 4/20/2014