SALT-WEDGE INTRUSION OF SEAWATER AND ITS IMPLICATIONS FOR PHYTOPLANKTON DYNAMICS IN THE YURA ESTUARY, JAPAN

Kasai et al., (2010). Estuarine, Coastal, & Shelf Science 86; 408-414

Importance• Estuaries are highly biologically productive ecosystems

• Provide environmental services (e.g. water filtration)

• Economic value (e.g. tourism, fisheries)

• Irreplaceable natural resources

Study Objectives

1. Monitor hydrographic and biological trends in the Yura Estuary, Japan.

2. Determine if any correlation exist between trends

Yura Estuary, Japan

Methods

Fig. 1. Location and bathymetry of the YuraEstuary with standard hydrographic stations (●) and hydrographic stations where nutrient and chlorophyll concentrations were also assessed (○).

• Study period April 2006 to March 2008

• Chl, temp, salinity, nutrient concentrations, river discharge, and sea level

Results

Fig.?2 Longitudinal distributions of temperature, salinity and chlorophyll<ce:hsp sp="0.2"/> +<ce:hsp sp="0.2"/> pheophytin concentration measured on 25?26 February 2008 and 22?23 May 2007. Distance from the river mouth is represented as positive...

Winter Summer

Results

Fig. 4. Multiple regression analysis of observed salt-wedge distance as a function of river discharge and sea level. The regression equation is y = −0.16x1 + 0.09x2 + 6.5, where y is the salt-wedge distance, x1 the river discharge and x2 the averaged daily mean sea level on the sampling day and the previous day.

Fig. 5. Vertical profiles of salinity and chlorophyll + pheophytin concentration in the river (6 km upstream from the river mouth) on 22 September 2006

Fig. 6. Longitudinal distributions of nitrate + nitrite, chlorophyll + pheophytin concentrations and salinity on 22–23 August 2007.

Questions?

Questions• How does the Yura Estuary compare to other estuaries?

Questions• What other types of systems besides salt-wedge estuaries

typically exhibit sub-surface chlorophyll maxima?

Questions• How does the formation of subsurface chlorophyll maxima

in these systems differ? (i.e. the physical or biological mechanisms)

Questions• Are any estuaries in the Gulf of Mexico similar to the Yura

Estuary in Japan?

Questions• Would you expect a highly migratory salt-wedge to

increase or decrease primary productivity?