What TWO factors do scientists track and monitor in all types of freshwater ecosystem?
A: light availability
B:nutrients
C:water flow rate
D: Biodiversity

A: light availability

B: nutrients

Explanation:

Both nutrients and light availability affect the primary productivity of the freshwater ecosystem, therefore, scientists study both factors to track associated changes. This is because photosynthesis is driven by sunlight and nutrients availability. It is suggested that the abundance of autotrophs (e.g. phytoplanktons) in an aquatic ecosystem increases as light and nutrients availability increase. Thus, there will be more food available for secondary and tertiary consumers to feed upon. Resultantly, the aquatic environment will turn a biodiversity hotspot where many species of living organisms start dwelling. Thus, scientists mainly ecologists would focus on these two parameters at first that lead to consideration of other parameters.

For more information, you may want to read this scholarly article

https://aslopubs.onlinelibrary.wiley.com/doi/abs/10.4319/lo.2006.51.1.0288

The answer is Selective permeability