Historical nitrogen content of bryophyte tissue as an indicator of increased nitrogen deposition in the Cape Metropolitan Area, South Africa.
Information on changes in precipitation chemistry in the rapidly expanding Cape Metropolitan Area (CMA) of South Africa is scarce. To obtain a long-term record of N deposition we investigated changes in moss foliar N, C:N ratios and nitrogen isotope values that might reflect precipitation chemistry. Tissue from 9 species was obtained from herbarium specimens collected between 1875 and 2000 while field samples were collected in 2001/2002. There is a strong trend of increasing foliar N content in all mosses collected over the past century (1.32-1.69 %N). Differences exist between ectohydric mosses which have higher foliar N than the mixohydric group. C:N ratios declined while foliar delta(15)N values showed no distinct pattern. From relationships between moss tissue N and N deposition rates we estimated an increase of 6-13 kgNha(-1)a(-1) since 1950. Enhanced N deposition rates of this magnitude could lead to biodiversity losses in native ecosystems.
Wilson
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Botany Department, University of Cape Town, Rondebosch 7701, South Africa.
Stock
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Hedderson
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D000393:Air Pollutants / Q000032:analysis*; D044002:Bryophyta / Q000737:chemistry*; D004784:Environmental Monitoring / Q000379:methods; D009584:Nitrogen / Q000032:analysis*; D009587:Nitrogen Isotopes / Q000032:analysis; D013019:South Africa; D013997:Time Factors
D000393:Air Pollutants; D009587:Nitrogen Isotopes; D009584:Nitrogen