Tidally induced changes in bacterial growth and viability in the macrotidal Han River estuary, Yellow Sea

The Han River estuary in the Yellow Sea is a macrotidal (tidal range of 3.5 m at neap tide and 8.0 m at spring tide) eutrophic environment. Changes in bacterial growth and viability at different NaCl concentrations as well as other physico-chemical environmental parameters were investigated at diffe rent tidal levels in order to elucidate the major environmental factors con trolling the bacterial community. Bacterial growth rates (mu) varied with t idal state; maximum (mu=0.159 h(-1)) at high tide, and minimum (mu=0.069 h( -1)) at low tide. Although bacteria play a substantial role in ammonia remo val and regeneration, growth was not controlled by the fluctuations of nutr ient concentrations in the high nutrient estuary. The low viable cell numbe r recorded with the increased NaCl concentration indicated that the salinit y changes with tidal state was a major environmental factor controlling the viability of the freshwater bacterial populations. Portions of freshwater bacterial CFU (colony forming units) during low tide accounted for approxim ately 30% of the total CFU, and decreased down to 10% during high tide. Ove rall, the results indicate that the microbial communities in the macrotidal Han River estuary can be divided into two distinct groups according to the variations in salinity and freshwater runoff: (1) autochthonous halotolera nt estuarine populations which are nourished by the high nutrient runoff; a nd (2) allochthonous halophobic freshwater populations which are adversely affected by salinity increase. (C) 1999 Academic Press.