Which of the following is the best example of long-term environmental monitoring?

a. measuring soil carbon content in a 200-year-old forest in 10 locations
b. testing stream water nitrate concentrations weekly throughout a summer
c. collecting ocean surface water temperatures monthly for four decades
d. analyzing contaminant concentrations from every well in a county

Option C is correct

Explanation:

Long term environmental monitoring is done with the objective to observe  rapid and continuous changes occurring in any component of nature such as air, water, land etc. in order to make informed planning decisions.

This also helps us to set long term environmental management and rehabilitation   goals.

Thus, option C is correct as ocean surface water is being monitored regularly with objective of managing it properly for four decades.