Week 3- Chemical processes in estuaries

What is fluorines behaviour like

Conservative

What is fluorine conc like in seawater v riverwater

Higher conc in seawater

What is irons behaviour like in seawater

Non conservative

Why is irons behaviour non conservative

Lost in upper estuary

Why is irons loss unlikely due to oxidation of Fe(II) to Fe(III)

As river water contain oxygen at rate of Fe(II) oxidation is fast

What is irons loss more likely to be due to

Coagulation of colloidal Fe(III) as river water mixes with seawater

What is the makeup of iron like in the solution

Most Fe lost is Fe(III)

Conc of Fe (II) is still high

When does concentration of Fe(II) decrease

With increasing stability

How do ligand affect iron concentrations

Fe (III) is stabilised by ligands and stop it from dissolving

Fe(II) is more stable

• Effects the ratio of different irons

What behaviour does silicon show

Conservative and non-conservative

What evidence is there for the behaviour of silicon

Danshuei estuary

• Conservative behaviour in March

Elbe estuary

• Evidence for removal of dissolved silicon in early autumn

What do areas of silicon removal lead to

Diatom blooms

Give an example of a estuary with extreme silicon removal

Charlotte Harbour (Florida)

How can you trace large river plumes

Using the conservative behaviour of silicon

In Narragansett Bay what are a source of dissolved silicon in spring bloom and a net sink of dissolved and biogenesis silica

Marshes

Are anthropogenic inputs usually a source of silicon

No

In the rappahannock estuary what is the input of dissolved silicon due to

Desorption and dissolution

How can Si isotopes be used to study nutrient utilisation and remineralisation of biogenic silicon

Even though dissolved silicon shows conservative behaviour, silica preferentially use lighter Si isotopes to form frustules so the remaining dissolved silicon is enriched by heavier isotopes

What does behaviour of dissolved silicon changing over the year reflect

Rate of biological uptake/ remineralisation

Residence time of water within estuary

Turbidity

How does turbidity affect the behaviour of dissolved silicon

Particle loading may affect light penetration= River biological production is inhibited by turbidity

Why does manganese undergo intensive cycling in estuaries

Chemistry is linked to changes in redox

How do you describe the oxidising and reducing behaviour in manganese

Both takes place

Oxidising- Mn4+ thermodynamically stable, as MnO2 it has low solubility and Mn4+ forms particles or coats them

Reducing- Mn2+ thermodynamically stable, as Mn2+ it is soluble and can diffuse and advect in solution

Why are many estuarine sediments reducing

Due to high rates of burial of organic carbon

What takes place to manganese in anoxic sediment

Mn5+ is reduced to Mn2+ which is soluble

When is max concentrations of dissolved manganese seen

Intermediate sediments

What is the lifetime of manganese like

Long enough to be observed

What is a change in Mn oxidation state accompanied by

Phase change

What is the overall cycling of manganese like

What are the kinetics of Mn2+ like

Slow= can persist at concs higher than predicted by thermodynamics

Where can high concentrations of Mn2+ be found

Water column if circulation is restricted e.g. fjord

In bottom waters with low oxygen

Describe the tamar river and estuary

6km from north Devon coast

Main freshwater input to Plymouth

Catchment: agriculture, woodland, abandoned mines

Upper estuary: tidal mudflats and reed beds

Lower estuary: inhabited, dockyards, military port, mudflats

What is gauged daily flow like in Tamar river like

Variable but is a seasonal cycle

What do the 10 surveys show about estuarine mixing in the Tamar

Large seasonal variability due to runoff, residence times and point source

Nitrate shows conservative behaviour

Silicon shows conservative behaviour but not in summer

Phosphate has non conservative behaviour

What is the behaviour of nitrate and nitrite in 2018/19

Behaviour similar but concentrations different

What was the behaviour of phosphate like in 2019

Not conservative

All addition

How does nitrate behave in Tamar

Conservatively

What does student data show about nitrate

Does not show conservative behaviour in summer

How does phosphate behave in Tamar estuary

Non conservative manner