GROUP
Plymouth Field Course 2019
4
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Oxygen concentration clearly varied with depth, but this variation differed by station. At Stations C-1 and C in the upper estuary, oxygen concentration peaked at 5m, decreasing below this at Station C. Stations D, F and H all exhibited an oxygen minimum at medium depths. Stations E and G increased in oxygen concentration with depth. Stations I and J near the breakwater both decreased in oxygen concentration with depth. Various physical, chemical and biological factors may have been responsible for different patterns observed, such as biological uptake through aerobic respiration or from stratification of the water column, reducing vertical mixing.
Oxygen Concentration
Oxygen Concentration Depth Profile:
Oxygen Concentration against Salinity:
Click on graph to enlarge
Click on graph to enlarge
Oxygen concentration broadly increased with salinity (R2=0.29, P=0.0029), and was seen to increase down the estuary from 238.41μmol l-1 at Station C-1 to 249.47μmol l-1 at Station J. There was some deviation, with the lowest oxygen concentration of 232.51μmol l-1 observed at Station C and the highest value of 258.31μmol l-1 at Station G. Station G had higher oxygen concentration than expected at all three depths, suggesting a localised oxygen influx. A potential explanation for the increase in oxygen with salinity was the high biological oxygen demand of estuarine waters due to the high input of organic carbon.
ESTUARY
