Examkin

Question

Difficulty: MediumEcological Factors and Their Measurement

An ecologist measuring light penetration in a freshwater lake lowers a Secchi disc into the water and notes that it disappears at a depth of 2.5 m2.5\text{ m}. Upon slowly retrieving the disc, it reappears at a depth of 2.7 m2.7\text{ m}. What is the light transparency depth of this aquatic habitat?

  1. 2.6 m2.6\text{ m}Answer
  2. B
    5.2 m5.2\text{ m}
  3. C
    0.2 m0.2\text{ m}
  4. D
    2.5 m2.5\text{ m}

Answer

The light transparency depth of the aquatic habitat is 2.6 m2.6\text{ m}.
To determine the Secchi disc transparency limit in an aquatic ecosystem, the depth at which the disc vanishes (2.5 m2.5\text{ m}) and the depth at which it becomes visible again during ascent (2.7 m2.7\text{ m}) are averaged together: 2.5 m+2.7 m2=2.6 m\frac{2.5\text{ m} + 2.7\text{ m}}{2} = 2.6\text{ m}.

Step-by-Step Solution

1
Identify the depth of disappearance (d1d_1) and depth of reappearance (d2d_2) of the Secchi disc.
d1=2.5 md_1 = 2.5\text{ m} and d2=2.7 md_2 = 2.7\text{ m}.
Standard ecological protocol for Secchi disc measurement requires recording both depths.
2
Calculate the average (mean) depth using the formula Transparency Depth=d1+d22\text{Transparency Depth} = \frac{d_1 + d_2}{2}.
Transparency Depth=2.5+2.72=5.22=2.6 m\text{Transparency Depth} = \frac{2.5 + 2.7}{2} = \frac{5.2}{2} = 2.6\text{ m}.
Averaging accounts for parallax error and subtle light fluctuations at the water surface.

Key Concept

Secchi Disc Measurement of Aquatic Turbidity and Light Penetration
Rate this question

Topics

Ecological Factors and Their Measurement

More questions from this topic