Which test is used to measure the presence of chlorophyll in water samples?

The Chlorophyll-a Test is designed specifically to measure the concentration of chlorophyll-a in water samples. Chlorophyll-a is a pigment found in algae and is an important indicator of algal biomass in aquatic ecosystems. This measurement is crucial for assessing water quality, as high concentrations of chlorophyll-a can indicate productive water bodies that may support algal blooms, which can have negative environmental impacts, such as oxygen depletion and toxicity.

The other tests listed serve different purposes. The Primary Productivity Test assesses the rate at which organic matter is produced in a water body, often related to photosynthesis, but does not specifically quantify chlorophyll itself. The Coliform Test is used to detect the presence of coliform bacteria, which serve as indicators of potential pathogenic contamination. The Nutrient Analysis Test evaluates the levels of nutrients like nitrogen and phosphorus but does not directly measure chlorophyll. Thus, the Chlorophyll-a Test is the only choice that specifically targets the measurement of chlorophyll presence, making it the correct answer.