Inorganic nitrogen retention in acid-sensitive lakes in southern Norway and southern Ontario, Canada—a comparison of mass balance data with an empirical N retention model
✍ Scribed by Ø. Kaste; P. J. Dillon
- Publisher
- John Wiley and Sons
- Year
- 2003
- Tongue
- English
- Weight
- 232 KB
- Volume
- 17
- Category
- Article
- ISSN
- 0885-6087
- DOI
- 10.1002/hyp.1249
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✦ Synopsis
In-lake retention of inorganic nitrogen species (nitrate and ammonium) was estimated from mass balances in five acid-sensitive lakes in southern Norway and eight in southern Ontario, Canada, to evaluate an empirical in-lake N retention (R N ) model. This model is included in the First-order Acidity Balance (FAB) model, which currently is used for calculation of critical acid loads and exceedances in many countries. To estimate in-lake R N , the FAB model uses a recommended mass transfer coefficient (S N ) of 5 m year 1 , which mainly is derived from NO 3 mass balances in Canadian lakes. To date, the in-lake R N model has not been evaluated for large parts of Europe. At the Norwegian study sites receiving the highest N deposition (>120 meq m 2 year 1 ) the net in-lake retention of inorganic N (TIN) exceeded the corresponding terrestrial retention by a factor of 1Ð1-2Ð6. Despite differences in N loading and hydrology at the Norwegian and Canadian sites, both the mean mass transfer coefficients for NO 3 (S NO3 ; 6Ð5 versus 5Ð6 m year 1 ) and TIN (S TIN ; 7Ð9 versus 7Ð0 m year 1 ) were of comparable magnitude. Both mean values and ranges of S NO3 suggest that the default S N value presently recommended for FAB model applications seems valid over a large range in N inputs and areal water loads (q s ). However, owing to the relatively few data available for lakes with high q s values (15-150 m year 1 ), it is recommended that more lakes within this range be included in future studies to obtain a more precise prediction of in-lake N retention over a wide q s gradient. Also, when considering that the FAB model treats all inorganic N leaching from a catchment as NO 3 , it seems reasonable to use a default S TIN value instead of just S NO3 when estimating in-lake R N . In that case, the in-lake R N presently calculated by the FAB model might be slightly underestimated.