Water diversion structures and river discharge dictate salinity dynamics on tidal flats of the Fraser River delta, British Columbia

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Language of the publication
English
Date
2023-09-30
Type
Submitted manuscript
Author(s)
  • Drever, Mark C.
  • Douglas, Tristan J.
  • Domalik, Alice D.
  • Balke, Eric
  • Scott, David C.
  • Johnson, Mark S.
  • Gurd, D. Brent
Publisher
Elsevier

Abstract

Salinity in estuaries affects numerous ecological processes, and is strongly driven by river outflow interacting with the tide. We used an exponential decay function to model the relationship between salinity and freshwater flow (i.e., river discharge) to characterize and map salinity dynamics over the tidal flats of the Fraser River delta, British Columbia, Canada. The model has three parameters: the horizontal asymptote Asym that represents the average weekly salinity at very high river flows; the theoretical intercept R0 that represents salinity conditions during very low river flows; and the natural log of the rate constant lrc that reflects the relationship between river discharge into the estuary and resultant average salinity. Using data from 47 salinity-monitoring stations deployed from 2015 to 2021, we found that Fraser River discharge had a strong and inverse relationship with average weekly salinity on the outlying tidal mudflats, which is expressed by the lrc value of -8.56. Model estimates indicate that weekly salinity (on the Practical Salinity Scale) at very low discharge rates (R0) had a value of 22.4, which decreased at high discharge rates (Asym) to a value of 3.7. This predictable decrease in salinity for increasing river discharge means that the salinity regime of the Fraser River delta tidal flats is poikilohaline, and undergoes a regular and biologically relevant transition from brackish to nearly fresh water as the river outflow increases and abates seasonally. The resulting spatial gradients in salinity dynamics were associated with distance to river outflows and existing water diversion structures (i.e., jetties and causeways), meaning the timing and extent of this transition varied across the tidal flats. As estuaries become increasingly modified by coastal development and climate change, this simple model can be used to evaluate management interventions and river discharge scenarios that affect salinity gradients over tidal flats.

Subject

  • Nature and environment,
  • Science and technology

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Pagination

38 pages

Peer review

No

Open access level

Green

Identifiers

ISSN
1096-0015
0272-7714

Article

Journal title
Estuarine, Coastal and Shelf Science
Journal volume
291
Article number
108436
Accepted date
2023-07-13
Submitted date
2022-07-25

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Water

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