Search

Abstract  We investigated the chromophoric dissolved organic matter (CDOM) of river water in the Sakawa River and of surface water in the vicinity of the river’s mouth in Sagami Bay, Japan, during the period from July 2003 to July 2004. Absorption by CDOM was modeled as a logarithmic function. As a qualitative index of CDOM, the slope (S) of this function was estimated for a wavelength range from 280 to 500 nm. As a quantitative index of CDOM, the integration of absorption was determined between 280 and 500 nm (Σ 280 500 a CDOM). High seasonal variability of S values was observed at the marine station. The S values at the upstream stations were related to chlorophyll a concentrations but not to bacterial abundance, whereas the integrated values at upstream stations were correlated with precipitation. Seasonal variability in the integrated values was low at the downstream stations, where the effect of effluent from nonpoint sources and sewage treatment plants was strong. Anthropogenic CDOM at the downstream stations appeared to be degraded by microbial utilization and photodegradation, whereas terrestrially derived CDOM at the upstream stations was less degraded. These qualitative differences in CDOM and the marked effect of dilution by seawater near the Sakawa River mouth suggest that the dynamics of CDOM in riverine and coastal environments should be studied with careful consideration of both spatial and temporal variations, particularly in small estuaries. [ABSTRACT FROM AUTHOR]

Abstract??The seasonal abundance of the dominant dinoflagellate,Ceratium fusus, was investigated from January 2000 to December 2003 in a coastal region of Sagami Bay, Japan. The growth of this species was also examined under laboratory conditions. In Sagami Bay,C. fususincreased significantly from April to September, and decreased from November to February, though it was found at all times through out the observation period.C. fususincreased markedly in September 2001 and August 2003 after heavy rainfalls that produced pycnoclines. Rapid growth was observed over a salinity range of 24 to 30, with the highest specific rate of 0.59 d?1measured under the following conditions: salinity 27, temperature 24?C, photon irradiance 600?mol m?2s?1. The growth rate ofC. fususincreased with increasing irradiance from 58 to 216?mol m?2s?1, plateauing between 216 and 796?mol m?2s?1under all temperature and salinity treatments (except at a temperature of 12?C). Both field and laboratory experiments indicated thatC. fusushas the ability to grow under wide ranges of water temperatures (14?28?C), salinities (20?34), and photon irradiance (50?800?mol m?2s?1); it is also able to grow at low nutrient concentrations. This physiological flexibility ensures that populations persist when bloom conditions come to an end. [ABSTRACT FROM AUTHOR]