Saanich Inlet

Question 1

Freshwater Input into Saanich Inlet

Answer 1

Most of the FW comes from the Fraser River
This is dominant in the spring/summer and fall

Fraser River (Summer) – 7000 m3s-1
Cowichan River (Winter) – 100
Shawnigan River (Winter) – 8
Goldstream (Winter) – 5

Question 2

Seawater and Freshwater Flow in Saanich Inlet

Answer 2

FW from the outside sill flows over the sill into the inlet
Subsurface flow of SW flows out
Causes downwelling inside Saanich (reverse estuary)
Pushes nutrient-rich waters deep
Occurs at neap tide

FW inside inlet flows out, subsurface SW flows in over the sill and causes upwelling
Brings nutrients to surface
Occurs at spring tide

Question 3

Spring Tide

Answer 3

Solar and lunar tide aligned

Question 4

Neap Tide

Answer 4

Solar and lunar tide opposite

Question 5

What areas have strongest tidal mixing

Answer 5

Areas of narrow straits and narrow sills amplify the current induced by the tide

Our sites S5, S8 and S12

Question 6

Spring Tide Mixing

Answer 6

Strong mixing partially homogenizes the water over the sill and increases salinity over the sill

Question 7

Neap Tide Mixing

Answer 7

Weak mixing preserves the FW at the surface
Reverse estuary

Question 8

Mini Blooms in Saanich Inlet

Answer 8

Every 14-28 days a Spring tide occurs that is strong enough to cause mixing over the sill and push the FW out causing upwelling of nutrient rich salt water
This causes phytoplankton bloom

Question 9

Saanich Inlet Circulation Depth

Answer 9

The circulation in the inlet only affects shallow waters that are above the sill 70-100 m

Question 10

Saanich Inlet Oxygen Concentration

Answer 10

The euphotic zone is net photosynthesis so many parts of the shallow waters are oversaturated in oxygen

The deeper waters have net respiration and are often anoxic due to breakdown of organic matter

Question 11

Types of Respiration at depth

Answer 11

In the anoxic zones, bacteria use NO3 and SO4
But even at deep enough depths the NO3 is completely used

Question 12

Deep Oxygen Renewal

Answer 12

During late summer and early fall, you can find oxygen at depth in the Saanich Inlet because it is renewed

Dense oxygen-rich water flows over the sill and sinks to depth and flushes out the anoxic water
This oxygen is consumed in 2-3 weeks and occurs during the weakest neap tide where there is little mixing to preserve the dense water

Question 13

Productivity in Saanich Inlet

Answer 13

High productivity in very shallow waters, near zero under 20m
Due to the self-shading of all the phytoplankton
Most productive in spring summer and fall
Monthly measurements are always biased based on the tidal cycle, but no evidence that some months are more productive

Question 14

Dominant Phytoplankton in Saanich Inlet

Answer 14

During the spring/summer and fall larger phytoplankton dominate and these are primarily centric diatoms

In the winter smaller phytoplankton like nanoflagellates are dominant
Use their flagella to find light during winter months

Question 15

Explain the difference between the dominance of different groups in different parts of the year

Answer 15

In the summer there is high light near its Pmax and in winter very low light, below K

Nanoflagellates have high growth at low light, but have a lower max growth rate
Diatoms have low growth at low light, but have a higher max growth rate

Question 16

Unique Zooplankton trends

Answer 16

Euphausiids concentrate just above the anoxic layers
Amphipods are more tolerant to anoxia

Outside of Saanich inlet the species are much more broadly distributed than they are inside the inlet

Euphasiids are very common but hard to catch

Question 17

Which factors do you expect to be important in controlling zooplankton distributions in Saanich Inlet and surrounding regions?

Answer 17

The major factor that distributes zooplankton is oxygen concentration

They require certain levels of oxygen to respire, and many parts of the ocean can be anoxic so that control their distribution the most