A student investigates the effect of road salt (sodium chloride) runoff from a major highway on the density of wild orchids (Dactylorhiza fuchsii) in a roadside meadow nature reserve.
She uses a quadrat to sample the vegetation from two areas in the meadow:
She counts the number of wild orchid plants in multiple quadrats in each area.
The table below shows her results:
| Area | Average (mean) number of wild orchids per m2\text{m}^2m2 |
|---|---|
| Close to drainage ditch (high runoff) | 222 |
| Away from drainage ditch (low runoff) | 474747 |
Name the independent variable in this investigation.
Suggest an explanation for these results.
Suggest how the student made sure that her results were valid and reliable.
The student claims that all roadside meadows should have concrete barriers and closed drainage pipes installed to divert all highway runoff away from the reserve.
Discuss the advantages and disadvantages of using closed drainage systems to divert runoff away from roadside ecosystems.
