E7 NITROGEN CONCENTRATION Total-N [mg l-1] Mean of 4 sampling stations, 1981-1990 Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Surface 7.2 7.4 5.8 5.4 5.0 4.4 4.7 4.5 4.9 4.3 5.8 5.7 NH4-N [mg l-1] Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Surface 0.15 0.16 0.15 0.14 0.14 0.11 0.23 0.25 0.12 0.10 0.10 0.11 NO2-N + NO3-N [mg l-1] Mean of 4 sampling stations, 1981-1990 Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Surface 0.06 0.07 0.03 0.06 0.06 0.05 0.77 1.10 0.84 0.22 0.12 0.15