Southampton University Falmouth 2015

Group 13

© B Carter

Disclaimer: The views and opinions expressed are those of the individual and not necessarily those of the University of Southampton or the National Oceanography Centre, Southampton.

Nitrate

Phosphate

Silicon

At the mouth of the Fal Estuary there is a waste management plant.  Waste management adds a high level of dissolved phosphate into the water that the plant flows into (Oram, 2015).  Measurements taken within the estuary show non-conservative behavior and the removal of phosphate.  However, due to the addition of phosphate from the waste management plant, dissolved phosphate levels increase dramatically at the mouth of the estuary and into Fal Bay, especially when measured at depth.  As a result of the rising tide at the times of sampling, the incoming tide brought increased dissolved phosphate levels further up the estuary from the mouth as reflected in our sample measurements.

The Fal Estuary is fed by the Truro and the Falmouth Rivers, both of which flow over large granite bedforms, which contain high amounts of Silicon (Smith and Rogers, 1999).  Because of this, it is expected that there will be high dissolved Silicon contents in the water samples collected along the estuary due to erosion of the underlying granite.

References

Oram, B. (2015). Phosphate in Water. [online] Water-research.net. Available at: http://www.water-research.net/index.php/phosphate-in-water

Smith, N. and Rogers, J. (1999). Fluvial sedimentology VI. Oxford: Blackwell Science.

Maps.environment-agency.gov.uk, (2015). Environment Agency - What's in your backyard?. [online] Available at: http://maps.environment-agency.gov.uk/wiyby/wiybyController?x=181500.0&y=29500.0&topic=pollution&ep=map&scale=9 &location=Falmouth%20Bay,%20Cornwall&lang=_e&layerGroups=default&distance=&textonly=of f#x=182778&y=33720&lg=1,6,&scale=7

Figure  50- TDL for nitrate against salinity at stations

Figure 55-Silicon concentration against depth at stations

Figure 56 - TDL for silicon against salinity at stations

Figure 57 - Zoomed TDL for silicon against salinity at stations

Figure 51 - Zoomed TDL for nitrate against salinity at stations

Figure 54 - Zoomed TDL for phosphate against salinity at stations

Figure 53 - TDL for phosphate against salinity at stations

Figure 52 - Phosphate concentration against depth for various stations

Figure 49 - Nitrate concentration against depth for stations

Silicon appears to be behaving non-conservatively in the estuary with very few of the points following the TDL. This could be due to its removal by silicon utilising organisms, such as diatoms. Silicon is removed and is used in the form of SiO2 as skeletal material. The concentration is higher at the riverine head, due to most silicon being transported to the estuary by riverine inputs. Removal may also be lower where there are higher levels of primary productivity by diatoms and other silicon utilising organisms. The Geology of the estuary is also important in determining silicon concentration. Granite is high in silicic compounds and dominates throughout Cornwall; contributing to the high levels in the estuary.

Nitrate is showing non-conservative behaviour in the estuary. This is due its seasonal depletion during phytoplankton blooms. Nitrates enter the estuary via leaching of fertilisers and other agricultural and industrial processes. Concentrations are also higher at the riverine end due to increased inputs through extensive tributaries and agricultural lands.

Oxygen samples were collected and treated. They were then weighed and analysed by pipetting 1ml of sulphuric acid and stirred using magnetic bars. This removed any precipitates within the sample. Thiosulphate was introduced in millilitres to titrate sample. This continued until the solution ran clear. This was arbitrated by the potentiometric recorder reaching 50% light penetration. The same procedure was carried out for all 6 samples, from which oxygen % saturation could be calculated.

Oxygen

Theoretical Dilution Lines

For each of these elements it is expected that the riverine end member will be situated at lower salinities and at higher concentrations of the given element, this is usually because rivers are the main source of these elements to the oceans. From here it is possible to draw a theoretical dilution line between the riverine and marine end members. Where the data points lie above the theoretical dilution line it can be concluded that the element is behaving non conservatively and the given element is being added to the solution. Where the data points lie below the TDL the element is said to behave conservatively.

Chemical Analysis