%0 Journal Article %J Marine Chemistry %D 1998 %T Measuring 15N-NH4 in marine, estuarine, and freshwaters: an adaptation of the ammonium diffusion method for samples with low ammonium concentrations. %A Holmes, R.M. %A McClelland, J. %A Sigman, D.M. %A Fry, B. %A Peterson, B.J. %K ammonium %K analytical methods %K diffusion %K estuarine %K fresh water %K inorganic nutrients %K N-15 %K PIE LMER %K sea water %B Marine Chemistry %V 60 %P 235-243 %G eng %M PIE3 %R 10.1016/S0304-4203(97)00099-6 %F Journal Article