SIGNIFICANCE OF BACTERIA IN UREA DYNAMICS IN COASTAL SURFACE WATERS

Bacterial urea production and decomposition were studied in samples fr om coastal waters in the Southern California Eight (the Eight), USA, a nd an estuarine system of the Mankyung and Dongjin rivers (MD estuary) in Korea. Bacterial urea production ranged from undetectable to 139 n M d(-1), and the mean value of bacterial urea production (58 nM d(-1), n = 6) was equivalent to 35-91% of the estimated phytoplankton N dema nd in the Eight. The rates of bacterial production of urea were 2 orde rs of magnitude higher than the bacterial urea decomposition rates. Co nsequently, bacteria were consistently net producers of urea in the eu photic zone. The concentration-dependence of urea decomposition showed the presence of a high affinity but low capacity system (K-t+S-n: 26 to 33 nM, V-max: 3 to 11 nM d(-1)). The low K-m values indicate that i n typical seawater samples, which have >100 nM urea, the bacterial ure olysis system is always near-saturated. The significance of bacteria a s urea producers should be incorporated into models of nitrogen regene ration in surface waters.