The Link Between Deforestation and the Darkening Seas

There is a strong link between land and sea, emphasizing the importance of understanding how human activities can impact both. We know that deforestation causes soil erosion, habitat loss, and aggravates climate change, but how do these destructive human actions affect the ocean? A recent study conducted in Belize found that deforestation changes the color and density of what otherwise would be regular, filterable run-off entering the ocean.


Organic materials from land can flow into the oceans from rivers, which play an important role in nutrient and carbon cycles around the world. Ecosystems in the ocean are suited to the consistent flow and have systems to capture and use the organic materials. Human activity has interfered with this natural process by altering the land in a way that then changes the general makeup and quantity of runoff entering the ocean.


The Belize Great Barrier Reef is the second largest coral reef in the world and is home to an incredible display of biodiversity. This area is home to many different reef types and is a United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage Site cumulatively comprised of seven marine protected areas. One of the biggest threats to the extensive reef systems is coastal development from farming and building. To create space for these projects, the land is cleared of vegetation, causing large amounts of organic matter runoff to enter river systems. A 2021 study found that “streams draining agricultural and urban land contained more land-derived material than those draining forested land, and that a substantial fraction of this material reached the coastal environment.”


The dissolved organic material from the Belizean coastline forms a dark film upon the water, significantly blocking sunlight from passing through. Ecosystems that live within the reef, seagrasses, and other photosynthesizing organisms depend on the sunlight filtering through the water to survive. As these are mostly autotrophic organisms at the bottom of the food chain, the entire ecosystem depends on their longevity for food and shelter. When they are deprived of sunlight, the entire ecosystem is at risk of collapsing.


The findings from this study are not unique to Belize, as deforestation is a worldwide problem affecting the photosynthesizers in our seas. To ensure the ocean’s preservation, we must understand the real connections between what is happening on land and how it impacts the oceans. Coastal communities, especially those that are in the midst of developing and clearing land, should integrate protection plans to prevent excessive runoff. The sooner we understand that the land and sea are not separate entities, the sooner we can realize how the protection of the ocean involves the protection of the land, and vice versa.



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