The Yangtze River Estuary is a hotspot for nitrogen activity. Human actions have led to a surge in nutrients flowing into this area, disrupting the natural nitrogen cycle. Two crucial processes in this cycle are nitrification and nitrogen uptake. These processes have not been studied together much in estuaries until now.

Scientists used special techniques to track these processes. They found that nitrogen uptake was more active at the surface, while nitrification was more active at the bottom. Light and dark conditions also played a role. Light hindered nitrification, while darkness slowed down the uptake of ammonia and nitrate.

Phytoplankton and nitrifiers compete for ammonia. Phytoplankton had the upper hand at the surface, while nitrifiers dominated at the bottom. This competition varied across the estuary. In areas with lots of phytoplankton and high turbidity, both nitrification and nitrogen uptake were high. This is because high nitrate levels support lots of growth, and high turbidity helps recycle ammonia.

The estuary's own ammonia was crucial for both nitrification and uptake. It was preferred by phytoplankton and had a quicker turnover than nitrate. Interestingly, the nitrification happening right there in the estuary could meet up to half of the phytoplankton's daily nitrate needs in the surface layer.

This study sheds light on how nitrogen cycles in the Yangtze River Estuary. It helps us understand how these ecosystems work and how they react to human influence. It's a reminder that our actions have consequences, even in the depths of river estuaries.

ESTUARINE ECOSYSTEMS

Nitrogen's Journey in the Yangtze River Estuary

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