March, S., Miller, A. J., Zhang, X-H. and Pearson, J. 2004. Tree leaf biomarkers for atmospheric nitrogen deposition. Water, Air, & Soil Pollution: Focus. 4 (6), pp. 241-250. https://doi.org/10.1007/s11267-005-3034-8
Murray, P. J., Hatch, D. J., Dixon, E. R., Granger, S. J., O'Prey, C., Stevens, R. J., Laughlin, R. J. and Jarvis, S. C. 2004. Transformations of nitrogen at the interface between the topsoil and an impervious clay subsoil. Water, Air, & Soil Pollution: Focus. 4 (6), pp. 45-52. https://doi.org/10.1007/s11267-005-3012-1