TY - Generic T1 - Observations on the changes in nitrate concentrations in seven upland moorland catchments in north eastern Scotland Y1 - 1993 A1 - Black, K.E. A1 - Lowe, J.A.H. A1 - Billett, M.F. A1 - Cresser, M.S. JF - Water Research VL - 27 ER -