Primary producers

Define allochthonous materials:

Materials that come from outside the system e.g. leaf litter

Define autochthonous materials:

Materials that come from inside the system e.g. algae

Give the simplified equation for euphotic depth:

euphotic depth = 4.6 / k

k = attenuation coefficient

Define mixing depth:

The lowest depth at which the water is mixed vertically e.g. by the wind.

How does the relationship between euphotic depth and mixing depth affect algal growth?

• If Z_m < Z_eu, growth occurs 

• If Z_m > Z_eu, decline occurs 

Give the equation for enrichment factor:

enrichment factor = abundance of element in plants / availability of element in water

What does a high enrichment factor indicate?

A high enrichment factor indicates that a nutrient is likely to limiting to phytoplankton growth.

What nutrients tend to be limiting in lakes?

Nitrogen and phosphorus.

What type of phytoplankton can silicon availability often be a limiting factor for?

Silicon can be a limiting factor for diatom growth.

What type of phytoplankton can vitamin availability often be a limiting factor for?

Vitamins can be a limiting factor for flagellate growth.

Give some key facts about the Lake District:

• High rainfall and variable temperatures 

• 30m max depth 

• Very clear water – k=0.18, Z_eu=25m 

• Oligotrophic 

How does light and temperature vary over a year?

They both follow a bell-like curve, with light peaking a bit before temperature.

When do diatom populations tend to grow most rapidly?

In the spring, when silicon is abundant.

When do cyanobacteria populations tend to grow most rapidly?

In the late summer-early autumn, when nitrogen and phosphorus have remineralised and become more abundant.