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Seasonal Relationships Between Precipitation, Forest Floor, and Streamwater Nitrogen, Isle Royale, Michigan
Author(s) -
Stottlemyer Robert,
Toczydlowski David
Publication year - 1999
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1999.03615995006300020018x
Subject(s) - forest floor , snowpack , mineralization (soil science) , hydrology (agriculture) , environmental science , precipitation , taiga , watershed , snow , zoology , ecology , soil water , geology , soil science , biology , geography , geotechnical engineering , geomorphology , machine learning , meteorology , computer science
The Upper Great Lakes receive large amounts of precipitation‐NH + 4 and moderate NO ‐ 3 inputs. Increased atmospheric inorganic N input has led to concern about ecosystem capacity to utilize excess N. This paper summarizes a 5‐yr study of seasonal N content and flux in precipitation, snowpack, forest floor, and streamwater in order to assess the source of inorganic N outputs in streamflow from a small boreal watershed. Average precipitation N input was 3 kg ha ‐1 yr ‐1 . The peak snowpack N content averaged 0.55 kg ha ‐1 . The forest floor inorganic N pool was ≈ 2 kg ha ‐1 , eight times larger than monthly precipitation N input. The inorganic N pool size peaked in spring and early summer. Ninety percent of the forest floor inorganic N pool was made up of NH + 4 ‐N. Forest floor inorganic N pools generally increased with temperature. Net N mineralization was 15 kg ha ‐1 yr ‐1 , and monthly rates peaked in early summer. During winter, the mean monthly net N mineralization rate was twice the peak snowpack N content. Streamwater NO ‐ 3 concentration peaked in winter, and inorganic N output peaked in late fall. Beneath the dominant boreal forest species, net N mineralization rates were positively correlated ( P < 0.05) with streamwater NO ‐ 3 concentrations. Forest floor NO ‐ 3 pools beneath alder [ Alnus rugosa (Du Roi) Spreng] were positively correlated ( P < 0.01) to streamwater NO ‐ 3 output. At the watershed mouth, streamwater NO ‐ 3 concentrations were positively correlated ( P < 0.05) with precipitation NO ‐ 3 input and precipitation amount. The relatively small snowpack N content and seasonal precipitation N input compared to forest floor inorganic N pools and net N mineralization rates, the strong ecosystem retention of precipitation N inputs, and the seasonal streamwater NO ‐ 3 concentration and output pattern all indicated that little streamwater NO ‐ 3 came directly from precipitation or snowmelt.