Question

How Does the Nitrogen Cycle Work in the Ocean?

Have you ever seen a dirty fish tank covered in green slime? Well, that’s the nitrogen cycle at work in an aquatic environment. In this unit, we learned about how nitrogen moves through both living and nonliving things and takes many different forms during its cycle through an ecosystem.

Now, it’s time to dive into the depths of the ocean to explore the journey that nitrogen takes in aquatic environments.


Video of Nitrogen Cycle: Understanding Our Soil: The Nitrogen Cycle, Fixers, and Fertilizer


To create this model, show the journey of a nitrogen molecule through the nitrogen cycle. Present your model in any way you’d like, it could be a diagram, a cartoon strip, a journal entry with pictures, in a video or your own way.


In your final product, make sure to include the following terms:

Atmospheric nitrogen

Soil

Ammonia

Nitrogen dioxide

Eat

Bacteria

Denitrification

Waves

Marine plants

Upwelling

Turnovers

Nutrients

Also, be sure to touch on the following concepts:

The interrelatedness of atmospheric (air), hydrological (water), and biological (life) systems in an aquatic environment

Feedback loops. You will need to add arrows to show the loops and possibly word/labels to the arrows to show what is happening.

Save your project and upload it below.

Nitrogen Model Criteria

Use of required terms


Included concepts of atmospheric, hydrological, and biological systems in aquatic environments.


Include positive and negative feedback loops


Presented in an organized and creative way.


(16 points)

Answer 1

Below is a ready-to-use model you can turn into a diagram, poster, cartoon strip, journal entry, or short video. It follows a single nitrogen molecule (or nitrogen atom) through the ocean nitrogen cycle and includes the required terms, the interactions among atmospheric, hydrological, and biological systems, and both positive and negative feedback loops. I also include a suggested visual layout and a short storyboard you can use.

Quick legend (forms & processes you can label on your visual):
- Atmospheric nitrogen = N2 (gas in the air)
- Ammonia = NH3 / ammonium NH4+
- Nitrite = NO2− (note: nitrogen dioxide = NO2, a gas often from atmosphere/pollution)
- Nitrate = NO3−
- Bacteria = nitrifiers, denitrifiers, decomposers, nitrogen-fixers
- Upwelling and Turnovers = movements that bring deep nutrients to the surface
- Waves = surface mixing & gas exchange
- Soil = seabed sediments / coastal soils
- Marine plants = phytoplankton, seaweeds, seagrass
- Eat = grazing/consumption by zooplankton and fish
- Nutrients = biologically available nitrogen (NH4+, NO3−, etc.)

Step-by-step journey (use arrows “→” between steps; label arrows with the process name):

1. Atmosphere (Atmospheric nitrogen: N2)
→ (Nitrogen fixation: by cyanobacteria or lightning, or deposition of NO2/NOx from the atmosphere)
→ Bioavailable nitrogen (nitrate NO3− or ammonium NH4+) enters the ocean surface.

2. Surface water / phytoplankton (Hydrological + biological interaction)
- Upwelling and Turnovers bring nutrient-rich deep water to the surface → increases available Nutrients.
- Waves mix the surface and enable gas exchange between water and atmosphere (label arrow: “mixing & gas exchange”).

3. Marine plants (phytoplankton, seaweed)
→ Assimilate NO3− or NH4+ to build proteins and grow (label arrow: “assimilation / uptake”).

4. Food web (Eat)
- Zooplankton and fish Eat marine plants, moving nitrogen into animal biomass.
- Predators Eat other animals; nitrogen moves through trophic levels.

5. Excretion and death (biological to chemical)
- Animals excrete waste and organisms die → decomposers (Bacteria) break down organic matter → produce Ammonia (ammonification).
- Arrow label: “excretion / decomposition → NH3/NH4+.”

6. Nitrification (microbial process)
- Bacteria convert NH3/NH4+ → NO2− (nitrite) → NO3− (nitrate).
- Note: NO2 (nitrogen dioxide) is also an atmospheric gas (often from combustion) that can enter water by deposition; nitrite (NO2−) is a dissolved intermediate in nitrification.

7. Sedimentation and Soil (seabed)
- Some organic nitrogen and particulate matter sink to the bottom and become part of the seabed Soil and sediments. Label: “sedimentation → benthic nitrogen pool.”

8. Denitrification (microbial return to atmosphere)
- In low-oxygen sediments, denitrifying Bacteria convert NO3− → N2 (and N2O/NO gases) → released back to the Atmosphere.
- Arrow labeled: “denitrification → N2 (back to atmosphere).”

9. Internal loading & diffusion
- Hypoxic conditions can cause sediments to release NH4+ and other Nutrients back into the water column (label: “internal loading / diffusion”).

10. Cycle repeats
- Upwelling and Turnovers bring those nutrients back to the surface where Marine plants can use them again.

Two feedback loops to draw and label (use arrows to show the loops):

- Positive feedback loop (eutrophication + internal loading):
Increased nutrient inputs (runoff, atmospheric deposition, or strong upwelling)
→ larger phytoplankton blooms
→ more organic matter sinks and decomposes
→ Bacteria consume oxygen while decomposing → hypoxia
→ hypoxia causes sediments to release more NH4+ (internal loading)
→ more nutrients available → bigger blooms
(Label arrows: “more nutrients → more algae → more decomposition → hypoxia → nutrient release → …”)

- Negative feedback loop (denitrification removing excess nitrogen):
Higher nitrate concentrations in low-oxygen sediments
→ increased denitrification by bacteria
→ conversion of NO3− to N2 gas
→ nitrogen removed from the water column and returned to atmosphere
→ reduces nutrient availability, limiting future algal growth
(Label arrows: “NO3− → (denitrification by bacteria) → N2 → atmosphere → fewer nutrients available.”)

Suggested visual layout (poster or diagram):
- Top: Atmosphere (clouds, label “Atmospheric nitrogen: N2” and “NO2 / NOx deposition”)
- Arrow down: “atmospheric deposition / nitrogen fixation (lightning & N-fixing bacteria).”
- Middle: Surface ocean box with waves (label “Waves: mixing & gas exchange”), phytoplankton/ marine plants.
- Arrow from deep to surface: “Upwelling / Turnovers → nutrients.”
- Right/above surface: Food web icons (zooplankton → fish) with “Eat” arrows.
- Bottom: Seabed / Soil box with sediments, bacteria icons.
- Arrows from organisms → seabed: “sedimentation.”
- Arrow from seabed up: “internal loading (when hypoxic).”
- Arrow from seabed to atmosphere: “denitrification → N2 (bacteria).”
- Side panels: show nitrification cycle (NH3 → NO2− → NO3− by bacteria) and label nitrogen dioxide (NO2) as atmospheric pollutant/deposition.
- Draw a big circular arrow around all boxes to show the overall cycle.

Short storyboard / single-molecule narrative (optional, for a creative submission):
- “I started as a calm N2 gas molecule floating in the atmosphere above the ocean. Lightning struck nearby and some NOx rained down, or cyanobacteria in the surface water fixed me into a usable form (NO3−). Upwelling carried me up to the sunlit surface, where a phytoplankton cell took me in to make protein. A tiny zooplankton ate that phytoplankton (Eat), so I joined the zooplankton’s body for a while. Later the zooplankton pooped and my nitrogen became ammonia (NH3). Nitrifying bacteria changed me into nitrite (NO2−) then nitrate (NO3−). Some of me settled into the seabed (soil) and was stored. In low oxygen, denitrifying bacteria turned me back into N2 and I drifted up into the atmosphere again to start the cycle over. Waves and turnovers shuffled me between air and water the whole time, and larger climate or pollution changes could speed up or slow down parts of my journey.”

Rubric checklist — make sure your final product includes:
- All required terms (Atmospheric nitrogen, Soil, Ammonia, Nitrogen dioxide, Eat, Bacteria, Denitrification, Waves, Marine plants, Upwelling, Turnovers, Nutrients) — place these labels clearly on your diagram.
- Clear arrows with labels showing processes (fixation, assimilation, nitrification, denitrification, sedimentation, upwelling, mixing, excretion).
- A labeled positive feedback loop (e.g., eutrophication → internal loading) and a labeled negative feedback loop (denitrification removing nitrogen).
- A clear statement or small paragraph connecting atmospheric (air), hydrological (water movement: waves/upwelling/turnovers), and biological (marine plants/animals/bacteria) systems.
- Organized and creative presentation — use colors (e.g., blue arrows for hydrological movement, green boxes for plants, brown for sediments), icons, or a short narrative.

If you want, I can:
- Produce a one-page printable poster layout in plain PDF (I can generate the text and exact labels; I can’t create image files directly here, but I can give a formatted text + ASCII map or SVG instructions you can paste into a drawing tool).
- Create a short 6-frame cartoon script with exact captions and panel art suggestions you can draw or animate.
- Convert the above into a slide-ready bulleted script for a short video narration.

Which format would you like help turning this into — a poster diagram, a cartoon strip, or a narration script for a video?