GROUP
Plymouth Field Course 2019
4
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Nutrient Mixing Diagrams
ESTUARY
Silicate:
Nitrate:
Silicate in the Tamar Estuary showed non-conservative behaviour, represented by a deviation from the Theoretical Dilution Line (TDL). Since this deviation was below the TDL, the change in silicate concentration with salinity was not a case of simple dilution and mixing, but active removal from the system. This removal was most likely due to the high abundance of diatoms throughout the estuary, as they have an obligate requirement for silicate in the production of their frustules.
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Nitrate in the Tamar Estuary showed conservative behaviour over most of the estuary, with a slight removal in the low salinity range (0-5). Most samples’ concentrations were very close to the TDL which indicates that there was no significant removal or addition of nitrate to the system. Therefore, change in concentration was a result of mixing down the estuary.
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Phosphate:
Phosphate in the Tamar Estuary also showed strong non-conservative behaviour, but differed from silicate in that almost all the sample concentrations lie above the TDL. This means that phosphate was being added along the course of the estuary, which was likely due to the resuspension and/or desorption of sediment phosphate or from pollution inputs along the estuary such mine waste.
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