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What are the differences between low-nutrient areas and high-nutrient areas? How do their food chains work?
In marine ecosystems, the distinction between low-nutrient, low-chlorophyll (LNLC) and high-nutrient, low-chlorophyll (HNLC) affects the operation of the food chain of the entire ecosystem. This article will explore the characteristics of these regions, the operating mechanisms of their food chains, and the impact of these phenomena on the global carbon cycle.
Low-nutrient areas are those waters that have low levels of important nutrients such as nitrogen, phosphorus or iron, which results in low primary productivity, manifested as low chlorine concentrations. These areas exist across 75% of the world's oceans.
Characteristics of low nutrient areas
Low-nutrient areas are often referred to as oligotrophic areas, where primary production is limited by the availability of nutrients. They are mostly found in subtropical gyres, but may also appear in the Mediterranean Sea or in some inland lakes. These areas have relatively few sources of nutrients compared to coastal areas, mainly due to nutrient runoff from land and the influence of ocean circulation.
Composition of the food chain
In these low-nutrient areas, producers are mainly small phytoplankton. These phytoplankton efficiently absorb limited nutrients and form the basis of the food chain. Primary production of phytoplankton forms a food source for other organisms in the water, such as small zooplankton. These small zooplankton in turn become food for larger fish and other predators.
Primary production is the process of converting carbon dioxide and other elements into organic compounds, which mainly relies on photosynthesis by phytoplankton. About half of the Earth's carbon fixation comes from this process.
Characteristics of high nutrient areas
In contrast, high-nutrient areas are often defined as HNLC areas, where nutrient levels are high but primary production and chlorophyll concentrations are still low. This phenomenon is often caused by a lack of micronutrients (such as iron), which limits the growth of phytoplankton even when sufficient macronutrients are available.
Effectiveness of the food chain
In high-nutrient areas, biodiversity is higher due to higher primary production, coupled with an adequate supply of nutrients. The food chain structure in these areas is relatively sound and can support the prosperity of various fisheries and other marine life. At the same time, the low nutrient state promotes the nutrient cycle among phytoplankton. Although its total output is small, its overall efficiency cannot be underestimated due to the relatively closed ecosystem.
In low-nutrient areas, the main productivity comes from the efficient use of resources, and especially in these areas, microbial circuits play a key role in cycling and converting inorganic nutrients into organic matter.
Future Challenges and Prospects
As the impact of climate change intensifies, the global supply pattern of nutrients such as nitrogen and phosphorus will change, which may cause the boundaries between low-nutrient and high-nutrient areas to become unclear. The scientific community is closely watching these changes because they will affect the global carbon cycle and the health of the ecosystem as a whole.
To date, despite lower primary productivity in low-trophic areas, they still account for 40% of global ocean productivity due to their widespread presence. Therefore, we must ask: How will these fragile ecosystems adapt to changing environmental challenges under future climate scenarios?
