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Unlock This CourseCoastal ecosystems are some of the most productive environments on Earth, supporting incredible biodiversity from tiny plankton to massive whales. But what makes these areas so rich in life? The answer lies in nutrient cycles - the continuous movement of essential chemicals like nitrogen, phosphorus and carbon through the environment.
Think of nutrient cycles like a giant recycling system. Nothing gets wasted - when plants and animals die, their nutrients get broken down and reused by new life. In coastal areas, this recycling happens incredibly fast because of the warm temperatures, abundant water and mixing of fresh and salt water.
Key Definitions:
Coastal ecosystems have unique conditions that make nutrient cycling incredibly efficient. The mixing of river water (carrying nutrients from land) with seawater creates nutrient-rich environments. Tides constantly stir up sediments, releasing stored nutrients. Warm temperatures speed up decomposition, whilst shallow waters allow sunlight to reach the bottom, supporting plant growth.
Nutrient cycle diagrams are like maps showing how chemicals move through an ecosystem. They use arrows, boxes and symbols to show the journey nutrients take from one place to another. Learning to read these diagrams is essential for understanding how coastal ecosystems work.
Every nutrient cycle diagram contains similar elements, regardless of which nutrient it's showing. Understanding these components will help you interpret any diagram you encounter.
These are shown as boxes or circles and represent where nutrients are held. Examples include soil, water, living organisms and the atmosphere. The size of the box often indicates how much nutrient is stored there.
Arrows show the movement of nutrients between stores. Thick arrows indicate large flows, thin arrows show smaller movements. The direction shows which way nutrients are moving.
Labels along arrows describe what's causing the nutrient to move. Examples include photosynthesis, decomposition, weathering and runoff. These explain the 'how' of nutrient movement.
Start by identifying the main stores, then follow the arrows to see how nutrients move between them. Look for cycles - nutrients should eventually return to where they started, completing the 'cycle'.
Nitrogen is crucial for all life because it's needed to make proteins and DNA. However, most nitrogen in the atmosphere (78%) can't be used directly by plants and animals - it needs to be 'fixed' into usable forms first.
The nitrogen cycle involves several key processes that transform nitrogen between different chemical forms. Each process plays a vital role in keeping the cycle moving.
Special bacteria convert atmospheric nitrogen gas into ammonia, which plants can use. In coastal areas, this happens in root nodules of plants like sea beans and by free-living bacteria in sediments and water.
Other key processes include:
Unlike nitrogen and carbon, phosphorus doesn't have a gaseous phase - it cycles entirely through rocks, soil, water and living organisms. This makes it often the limiting nutrient in coastal ecosystems.
Phosphorus enters coastal ecosystems mainly through weathering of rocks and human activities. Rivers carry dissolved phosphorus to the coast, where it's quickly taken up by marine plants and algae.
Rock weathering releases phosphorus slowly over thousands of years. However, human activities like agriculture and sewage discharge can add large amounts quickly, sometimes causing problems like algal blooms that use up oxygen and kill fish.
Carbon cycling in coastal waters is incredibly important for global climate regulation. Oceans absorb about 25% of all carbon dioxide released into the atmosphere, helping to slow climate change.
The ocean acts as a massive carbon store, holding 50 times more carbon than the atmosphere. Coastal areas are particularly important because they're where land and ocean carbon cycles meet.
Marine plants and algae absorb CO₂ from water to make food, just like land plants. This removes carbon from the water.
All marine organisms release CO₂ when they breathe, adding carbon back to the water.
CO₂ constantly moves between ocean surface and atmosphere. Cold water absorbs more CO₂ than warm water.
The Great Barrier Reef demonstrates efficient nutrient cycling in action. Coral polyps have a symbiotic relationship with algae - the algae photosynthesise and share nutrients with the coral, whilst the coral provides protection. However, excess nutrients from agricultural runoff have caused algal blooms that block sunlight and damage the reef, showing how human activities can disrupt natural cycles.
Human activities can dramatically alter natural nutrient cycles, often with serious consequences for coastal ecosystems. Understanding these impacts is crucial for managing and protecting these valuable environments.
Agricultural runoff, sewage discharge and coastal development all add extra nutrients to coastal waters. Whilst some nutrients are good, too much can cause eutrophication - excessive plant growth that depletes oxygen and kills marine life.
Excess nutrients cause algae to multiply rapidly, forming 'blooms'. When the algae die, bacteria decompose them, using up oxygen in the water. Fish and other marine animals suffocate, creating 'dead zones' where nothing can survive.
Creating your own diagrams helps you understand how nutrients move through ecosystems. Start simple and add detail as your understanding grows.
Follow these steps to create clear, accurate nutrient cycle diagrams that demonstrate your understanding of coastal ecosystem processes.
Steps to follow:
Chesapeake Bay in the USA was severely damaged by nutrient pollution from farms and cities. Scientists used nutrient cycle diagrams to understand the problems and design solutions. By reducing nitrogen and phosphorus inputs and restoring oyster reefs (which filter water), the bay's health is slowly improving. This shows how understanding nutrient cycles can guide conservation efforts.