PAST PAPER 2017

Question 1

Explain how you would construct a mixing diagram for an element, having determined the salinity and dissolved element concentrations. Explain how the TDL relates to the sea water & river water end members, & how conservative or non-conservative behaviour within the estuary can be identified.

Answer 1

• Plot the determined salinity and dissolved element conc’s on scatter graph
• River water end member is conc at salinity = zero.
• Sea water end member is conc at higher salinity.
• TDL is the line connecting the end members
• If the chem constituent plots follow along the TDL, then the constituent is said to display conservative behaviour in the estuary & the process of mixing controls distribution of the element.
• if the points lie above the tdl, there’s a source of addition of the element
• if the points lie below the line, there’s removal
• ^ these both indicate non-conservative behaviour

Question 2

What is the limitation of mixing diagrams?

Answer 2

They don’t provide any information about the processes causing addition or removal (biological processes, adsorption/desorption, coagulation/flocculation & redox processes)