Measuring urease activity in environmental samples

C.M. Solomon, J.A. Alexander,P.M. Glibert

Limnol. Oceanogr. Methods 5:280-288 (2007) | DOI: 10.4319/lom.2007.5.280

ABSTRACT: The current published method for measuring urease activity in phytoplankton involves measuring the hydrolysis of urea into ammonium. The method was previously optimized for studies of phytoplankton cultures, not for natural assemblages of phytoplankton. We tested several steps of the method using water samples from two distinct sites to optimize the urease assay method for field studies. We found interference of NH4+ from extraction and assay reagents in the current published protocol, leading to inconsistencies in rates of urease activity. We recommend a reduction in the concentration or removal of two of these reagents. We also found a biomass effect and recommend collecting smaller sample volumes in field studies. These improvements lead to values that may be more reflective of rates of urease activity in situ, but unfortunately more variable due to the low volumes used.