Freshwater ecosystems 

• Freshwater bodies have a very low salt concentration, typically less than 5 parts per thousand (ppt). Common examples include lakes, ponds, pools, springs, – – – – – – – – 
• – – – – – – – – – – – – – – – – – – – – – – – — – – – – – – – – – – – – – – – – – – – – – – –

Marine ecosystems

• On the other end of the spectrum, marine water bodies—like the open ocean and shallow seas—contain salt levels of 35 ppt or higher, comparable to – – – – – – – – – – – – – – – – – –
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Brackish water ecosystems 

• In between these two extremes are brackish water bodies, where the salt content ranges from 5 to 35 ppt. These include estuaries, salt marshes, mangrove swamps, and mangrove forests, which serve as transition zones between freshwater and – – – – – – – – – – – – – – – – – –
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