Changes in pH Measurements Relative to Algae Blooms


The waterfront location in Biscayne Bay is part of a diverse estuary on the west coast of Florida. pH was measured there using an OctaSlide viewer, and the data showed that it had been rising over the last six years of testing. Research showed that ocean basification could be caused by algae blooms that block out sunlight for the marine plants and through photosynthesis these algae lower pH. When the algae decompose, the process uses oxygen but leaves fewer marine plants to continue photosynthesis, so dissolved oxygen levels are lower.


pH, measured with a scale ranging from 0 to 14, represents the hydrogen ion concentration. Relative to water, a solution can have higher or lower [H+], determining its alkalinity. Generally, ocean pH over millennia has been slightly basic, averaging at 8.2, but recent CO2 emissions are absorbed by oceans and have been making the water surface more acidic (National Geographic, 2017).

In this experiment, pH was measured at the Ransom Everglades waterfront at Biscayne Bay over six years, starting in 2014, on different dates and times.

Biscayne Bay is a large estuary on the west coast of Florida that approximates 428 square miles (Discover Biscayne Bay, n.d.). The pH at the waterfront location was largely affected by algae blooms and climate change, resulting in rising pH levels.

Materials and Methods

pH was measured using OctaSlide Viewer. The Wide Range pH Octa-Slide Bar was inserted into the OctaSlide Viewer. Then a test tube was filled to the 10 mL line with the water sample. Then 8 drops of Wide Range pH Indicator were added, and the test tube was capped and mixed.

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The test tube was then inserted into OctaSlide Viewer. The last step was to match the sample color to the color standard and record it as pH. In the analysis, the mean was used.

Results, including graph(s)

The pH levels measured in the last six years show that they have been rising, specifically at the waterfront location. The average pH for 2014 was 6.5, 7.7 for 2015, 7.9 for 2016, 7.9 for 2017, 7.7 for 2018, and 7.9 again for 2019. This shows that the pH levels have been rising with a dramatic rise between 2014 and 2015. Nitrate levels also rose, with the 2015 average level being 0.10, 0.26 for 2016, 1.51 for 2017, 1.10 for 2018, and 0.52 for 2019.


Algae blooms are a problem that has been affecting Florida for some time. These blooms are detrimental to the growth of seagrass and impact the ecosystem negatively. Put simply, the algae blooms block out light that destroys ecosystems and causes plants and other organisms on the seafloor to die out. All of Florida struggles with these algae blooms, especially lakes, but Biscayne Bay has had its share of issues. Blue-green algae blooms, which are the ones that affect Florida, are caused by a combination of factors, most if not all of which are prevalent in Biscayne Bay. Algae blooms can grow in areas with high levels of nutrients, and estuaries like Biscayne Bay have a lot of nutrients from external sources and runoff, especially after hurricanes (Indiana University, n.d.). This runoff can be polluting. The data shows that nitrate levels rose dramatically in the 2016-2018 testing and remained higher than in the first tests after that, which could be connected. Another factor is warm temperatures, above 25ºC, which the waterfront is usually near or above (Indiana University, n.d.). During an algae bloom, the light can’t reach seagrass on the bottom of estuaries, and the aquatic plants’ growth is suppressed (Havens, Krimsky, Burton, Zimmerman, n.d.). The algae blooms are directly connected to the rising pH levels because they use the excess carbon dioxide for photosynthesis. DO levels weren’t up from 2014 data because the algae kill off the seagrass, but in its bacterial decomposition process, it uses oxygen (eXtension, 2011). Sampling could have been improved if it were more consistent since entire years of data were missing or never taken.

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Changes in pH Measurements Relative to Algae Blooms. (2022, Apr 27). Retrieved from

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