Decrease in ammonium uptake at the pristine site with increasing exposure time on.

Eq. 2 fitted well (r² = 0.99) for the uptake data for both 10 µM (black circles) and 100 µM (grey triangles). The half-time value ‘b’ was 2.1 hours for both concentrations. The constant (C) was lower in the 10 µM treatment (0.22 µmol N gDW⁻¹ h⁻¹) compared to the 100 µM treatment (0.88 µmol N gDW⁻¹ h⁻¹). Dashed line indicates critical N-uptake to maintain biomass production (0.8 µmol N gDW⁻¹ h⁻¹). Note that uptake rates at 24 hours and later were based on the depletion of ammonium in the experimental solution, whereas other rates presented in this paper are average rates calculated from ¹⁵N uptake.