Lab 12.4

Lab 12.4 – Ash Plume and Algal Bloom

Fundamental concept: Examine biological response variables post ash deposition
Estimated time to complete: 30 minutes
Data skills Preparation: Lab 2
Materials needed: None

In lab section 12.3, we discovered that the arrival and deposition of the ash plume over the Endurance Array likely created a false signal of an algal bloom. We can now shift our focus to the days following the plume’s arrival—when it delivered carbon and other micronutrients—to look for evidence of a real increase in primary productivity.

Recall that during wildfire ash plume deposition in the ocean, dissolved nitrogen concentrations can increase significantly. Among lots of other chemical compounds, wildfire ash contains various forms of nitrogen, such as nitrate (NO₃⁻), which can dissolve into seawater when ash settles on the ocean surface. This sudden influx of nutrients can act as a fertilizer, potentially stimulating phytoplankton growth.

Now use the data below to help you explore the impact of the ash deposition event on the phytoplankton community. You can interact with the data by switching among productivity variables and nitrate.

Application Questions

Use the interactive graphs to answer the questions below.

Figure 12.4.1. Interactive time series graphs from the OOI Oregon Shelf Surface Mooring in September, 2020. Use the drop down menus to select parameters to include in Graph 1 and Graph 2. Use the “Zoom to” buttons or the slider bars between the graphs to zoom in and out.

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Select Chlorophyll-a as the parameter for Graph 1 and set Zoom to Post-depositional Period. You can use the sliders between the graphs to zoom in and out further if needed.

1. What is the date and time of the lowest chlorophyll reading at the start of the post-depositional period? Record the minimum chlorophyll concentration.
2. What is the date and time of the highest chlorophyll concentration in the post-depositional period? Record the maximum chlorophyll concentration.
3. Calculate the percent change in chlorophyll concentrations from the lowest to highest chlorophyll readings. Show your work.

Tip: Percent change = 100*(new value – original value)/ original value

Watch a video refresher on calculating percent change for more help

1. Now select dissolved oxygen as the parameter for Graph 2. Describe the correlation between DO and chlorophyll. Is this the result you would expect if phytoplankton are growing? Explain why or why not.
2. View the remaining parameters in Graph 2 (Fluorometric CDOM, Optical Backscatter, and Nitrate) in relation to chlorophyll. What additional evidence suggests that ash deposition stimulated phytoplankton growth?

Reflection Question

Are wildfires getting worse as Earth’s climate warms? Watch the following video to find out.

 

6. As stated in the video, the occurrence and severity of wildfires is increasing globally. Given what you learned about the result of the Oregon and Australia fires, make two predictions about how wildfires will impact the ocean environment.