Context: I am an undergraduate student who just started out in my first year and semester. For one of my units (a intro stats unit), I am tasked with a group project to conduct a simple statistical study and write a report on it, with my group choosing to study the diurnal pH of a lake. (Is there any correlation between the pH of the lake and the time of day). My friend stated that his one of his lecturer taught him that turbidity has no effect on pH (which i agree chemically). I agree to not measure turbidity for my group project and not cause conflict, but would like to pose my thinking and reasoning here purely for my own learning and understanding.
Condensed question:
I am curious and would like to enquire about the following concept. In an observational field study of diurnal lake pH (open system, not a lab), can turbidity be used as a statistically valid proxy for light attenuation and biological activity, which are factors that indirectly influence pH through photosynthesis and respiration? Even though turbidity itself has no direct chemical effect on pH?
Elaboration/more context:
I completely agree that turbidity does not change water pH chemically, and thank you for clarifying that previously. But would like to further expand on the usage of turbidity for our specific statistical field study.
We are conducting a group project for a statistics class to research daily pH fluctuations in a lake. I believe that our independent variable (Time of Day) is ultimately a proxy for sunlight intensity. Thus, I would expect the true drivers of our diurnal pH curve to be the biological and ecological processes that cycle throughout the day (photosynthesis, respiration, and decomposition).
Because this is a simple statistical project with no funding or specialised resources, we are heavily constrained in our testing methods. We are unable to directly measure DCO₂, DO, BOD₅, nutrient loading (orthophosphates/nitrates), chlorophyll-a, alkalinity, or continuous ion mobility.
As such, we thought to employ simple, low-cost proxies to capture the behaviour of the ecosystem and account for statistical anomalies. We are tracking water temperature (to account for gas solubility, autoionization equilibrium, and metabolic rates) alongside standard weather observations (sunlight, wind, and precipitation), and using vegetation density as a crude proxy for potential biomass that affects photosynthesis.
Given these heavy resource constraints, would it be statistically valid to include turbidity as a physical covariate to help explain data anomalies? Specifically, I thought to use it to flag the following scenarios:
Light attenuation: Explaining why an afternoon pH spike fails to occur on a clear day due to physical sediment shading blocking photosynthesis.
Runoff vs. Dilution: Combining turbidity with precipitation data to infer whether a storm introduced an influx of organic material/nutrients or simply caused pure rainwater dilution.
Biomass tracking: Coupling a sudden spike in turbidity during a calm, sunny week with high daytime pH values to speculate a localised algal bloom.
We would explicitly acknowledge the limitations of turbidity in our final report and recommend further chemical studies, but I am wondering if it is a good addition to a constrained dataset since we are testing in an open system with many biological and ecological processes rather than a closed lab system where only chemical processes are at play. May I kindly hear your thoughts regarding this?"
Follow-up questions:
If Yes: A major pitfall would be that turbidity would not differentiate biological mass from inorganic mass, how can this ambiguity be best handled, and are there other major pitfalls to take not of?
If No: Apart from turbidity not having a direct chemical effect on pH, what other factors prevent it from being a useful proxy in our scenario, and are there other simple variables you'd recommend tracking instead?
Ps: Apologies for the long post. I initially phrased the question for my friend to relay to his lecturer, but I decided to post here first to not cause any social conflict and better understand the topic/not ask a stupid question and waste my friend/his lecturer's time.
