Spatial and temporal distribution of inorganic nutrients and factors controlling their distributions in Gwangyang Bay

Abstract

In order to understand the spatial and temporal variations of nutrients and factors controlling their distribution in Gwangyang Bay, this study was carried out bimonthly from June 2001 to July 2003. Inorganic silicate and nitrate concentrations ranged from 0.04 μM to 69.5 μM (avg. 12.9 μM), and from 0.12 μM to 42.2 μM (avg. 7.83 μW), respectively. Silicate concentrations measured just after the typhoon were the highest with an average of 43.2 μM at the surface layer in June 2001, whereas the highest nitrate concentration (avg. 37.0 μM) was observed in the surface layer in July 2003. River runoff apparently influenced variations in silicate and nitrate concentrations (r-0.701 and 0.728, p<0.000, respectively) as well as salinity (r=-0.628, p<0.000). Phosphate concentrations ranged from 0.24 μM to 5.70 μM (avg. 1.34 μM) and were highest at stations 5, 6, and 7, near a fertilizer plant with an average of 2.01 μM. On the basis of N/P and Si/ N molar ratios, limiting nutrients have varied temporary and spatially. During 2001-2002, nitrogen was a limiting nutrient in the study area, and phosphate was limited when a large volume of freshwater flowed into the bay. Silicate was limited when the high standing crops of phytoplankton occurred in the whole study area throughout 2003, and in the inner bay in February and August 2002. During the study period, factors controlling the distribution of nutrients might be summarized as follows; 1) inflow of freshwater by heavy rain accompanied by typhoons and frequent rainfall in summer, showing high concentrations of silicate and nitrate, 2) release of high phosphate concentrations from the fertilizer plant located in the south of Moydo to adjacent stations, 3) release of nutrients from bottom sediment, 4) magnitude of occurrence of phytoplankton standing crops.