FALMOUTH FIELDCOURSE

Group 5

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Click below for more data from the pontoon

Click below to see our biological data from offshore and the estuary

YSI probe

Sample 1

Temperature decreases relatively consistently as depth increases. Salinity increases with depth from 33.25 to 33.61. The chlorophyll (μg/L) is low at the surface but increases rapidly to 5.01 μg/L at 1m. This then remains relatively similar throughout the water column.

Sample 2

Temperature decreases at a fairly constant rate as depth increases. Salinity remains at 33.04 until 1m where it increases to 33.41. Chlorophyll increases from the surface to ~2m, it then remains relatively homogenous.

Sample 3

Salinity increases with depth from ~1 to ~2.75m, there is a minor decrease in the surface 1m. Temperature decreases with depth. Chlorophyll remains at ~5μg/L in the surface metre of the water column, it then increases to ~9μg/L. At the riverbed, the chlorophyll decreases dramatically to ~1.5μg/L.

Salinity increases at a relatively constant rate with depth. Temperature decreases as depth increases with only slight deviations in the surface water. The chlorophyll decreased with depth, there is a slight increase in the first 1m.

Temperature decreases as depth increases. Salinity increases with depth. Chlorophyll at this station decreases overall as depth increases. There is some variability between 0.5 and 2m.

Sample 4

Sample 5

Salinity increases with depth after 1m, it begins to level off at ~4m. Temperature increases slowly from 0-2m before increasing more rapidly to 4m where it levels off. Chlorophyll shows a dramatic increase from ~1-3m, it then decreases again to the riverbed.

Sample 6

Temperature decreases as depth increases to ~4m where is levels off. Salinity increases with depth after ~1m, high saline water remains at depth. Chlorophyll shows an initial increase before decreasing until ~4m where it levels off.

Sample 7

Current meter data

The figure shows the speed (ms-1) vs depth at different times throughout the day, this can be compared to the table showing current direction to determine the tidal state

Between 12:33 – 12:35 the tide was going out. At the surface, the speed is 0.203ms-1, decreasing with depth to 0.039ms-1, this is the result of increased shear at the riverbed. The current speed is lowest between 13:14 – 13:18, at this time the direction begins to change suggesting that this is slack water. At 14:16 the current speed is slowest at the surface (0.029ms-1) but increases with depth. At 4m, the speed the decreases again because of the shear created by the riverbed. Between 15:24 and 15:27 the speed at the surface had increased to 0.099ms-1, is again increases with depth until 5m where is decreases as it approaches the riverbed.

A current meter was used hourly to measure speed (ms-1) and direction (o) from the Pontoon. This aim of these measurements was to determine the direction and speed of the tidal currents.

Light data

The PAR data from the Pontoon was plotted as a P vs E curve showing Irradiance (PAR) against Depth (m). As we used a Transmissometer on the pontoon, we had accurate surface Irradiance (E0) and depth Irradiance (Ez) readings that could be used to calculate the Attenuation coefficient and 1% light depth. To get the Attenuation coefficient, we calculated and plotted the natural log of (Ez/E0) against depth and took the gradient of this now linear line as the Attenuation coefficient (K). From this, we could calculate the 1% light depth, and therefore the base of the Euphotic zone, using (ln(100)-ln(1)/K). Both of these were plotted over time throughout the day spent measuring on the Pontoon.

Click each graph to expand

The Pontoon data shows the Irradiance to decrease with the expected trend, however the lower end of the P vs E curve is not obtainable due to the shallow depth of the estuary. The Attenuation coefficient, and therefore the 1% light depth, decrease throughout the day. This is because the tide was flooding, and clearer seawater was pushing the sediment loaded riverine waters back up the estuary.

All the irradiance depth graphs show a decrease of irradiance with an increase in depth. The irradiace begins to decrease more gradually before decreasing at a faster pace the deeper you go. This means an exponetial decrease in irradiance occurs with depth.