Temporal Variability of Nutrient Budgets in a Tropical River Estuary
: the Bangpakong River Estuary, Thailand
Thanomsak Boonphakdee a* and Tateki Fujiwara b
a Graduate School of Environmental Science, Burapha University, Chonburi, 20131, Thailand
b Fisheries and Environmental Oceanography Laboratory, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
Received 16 September 2007; Accepted 18 NOvember 2007
Abstract
Water, salt, dissolved inorganic nitrogen (DIN), and dissolved inorganic phosphorus (DIP) budgets in the Bangpakong Estuary were conducted by repeated observations and multiple box modeling. Water samples for inorganic nutrient analyses were collected monthly from June 2000 to May 2001. Flushing time at the estuary depicts high variations ranging from 1.4 (October 2000) to 80 days (February 2001) with an annual mean of 15.2 days. Seasonal variation in salinity gradients and estuarine Richardson numbers show the Bangpakong Estuary was partially stratified during the wet season and a well-mixed estuary in the dry season. Riverine nutrient inputs and distributions of nutrient concentrations within the river estuary varied in space and time. Temporal variations in fluxes were strong within inter-seasonal scales owing to water fluxes and system concentrations. The increase of DIN and DIP fluxes in the estuary may be the results of degradation of particulate organic matter. The Bangpakong Estuary appears to be a heterotrophic system where respiration exceeds photosynthesis (p-r < 0) and a denitrifying system. Seasonal variations in biogeochemical rates were attributable to differences in magnitude of freshwater inputs.
Keywords: nutrients budget; nutrient distribution; nonconservative flux; the Bangpakong River or Estuary, Thailand
* corresponding author : nuiosk@yahoo.com