Mai lives in Beijing. Sonya lives in Singapore and Kris lives in Sydney. The three friends often chat online. Mai thinks it's amazing that Kris swims in the ocean in December. In Beijing, December days are short and it's freezing outside. Sonya goes to the beach all year round and can't understand why Kris finds the beach too cold in July. Describe the positions on the Earth's surface where the friends live.

estuaries are the partially enclosed coastal bodies of brackish water formed at the mouth of sea where river meets an ocean. it is a transition zone between river and sea water so estuaries are influenced to both marine environment such as tides, waves and to riverine such as flow of fresh water and sediments. the mixing of sea and fresh water provide high level of nutrients, making estuaries a high product habitats.

many estuaries suffers degradation from a variety of human activities like erosion from deforestation, overgrazing, overfishing, drainage and eutrophication.

so from the above statement answers will be

1. false as estuaries are formed due to both brackish and freshwater.

2.true, due to high productivity estuaries are breeding ground for many marine species.

3. direct and indirect activities of man that contribute to pollution and deposition of sediments.