He animals in the food web release into the environment, which plants then use for

carbon dioxide:photosynthesis

Explanation:

carbon dioxide:photosynthesis During respiration, oxygen is used to breakdown glucose and produce energy. One waste product of respiration is carbon dioxide. Plants use carbon dioxide during photosynthesis and release oxygen as a by-product. Plants also need water for photosynthesis, but they get the water through roots or root-like structures.

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.