Alpha diversity: Alpha diversity describes the species diversity within a community at a small scale or local scale, generally the size of one ecosystem. When we casually speak of diversity in an area, more often than not it refers to alpha diversity.
Beta diversity: Beta diversity describes the species diversity between two communities or ecosystems. It is at a larger scale, and looks to compare the species diversity between two separate entities that are often divided by a clear geographical barrier like a river or a mountain ridge.
Gamma diversity: Gamma diversity is studied at a very large scale—a biome—where species diversity is compared between many ecosystems. It could range over areas like the entire slope of a mountain, or the entire littoral zone of a sea shore.

1 and 3 are correct.
Ecological succession, the process by which the structure of a biological community evolves over time. The time scale can be decades (for example, after a wildfire), or even millions of years after a mass extinction.
The community begins with relatively few pioneering plants and animals and develops through increasing complexity until it becomes stable or self-perpetuating as a climax community.
Two different types of succession—primary and secondary—have been distinguished. Primary succession occurs in essentially lifeless areas—regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. Secondary succession occurs in areas where a community that previously existed has been removed; it is typified by smaller-scale disturbances that do not eliminate all life and nutrients from the environment.
Increased niche development is the characteristic feature of Ecological succession.

1, 2 and 3 are correct.
Peatlands are wetlands that contain a mixture of decomposed organic material, partially submerged in a layer of water, lacking oxygen. The complex biodiversity of peatlands means they are home to variety of species. Their high carbon content makes them uniquely vulnerable to incineration if they are drained.
They are globally important carbon store. The unregulated exploitation of peatlands can potentially be detrimental to environment and to climate, as it could release carbon emissions that have been locked in for millennia.

Only 1 is correct.
Estuaries and their surrounding wetlands are bodies of water usually found where rivers meet the sea. Estuaries are home to unique plant and animal communities that have adapted to brackish water—a mixture of fresh water draining from the land and salty seawater.
An ecotone is a transition area between two biomes. It is where two communities meet and integrate. It has some of the characteristics of each bordering biological community and often contains species not found in the overlapping communities.
For e.g. the mangrove forests represent an ecotone between marine and terrestrial ecosystem. Other examples are grassland (between forest and desert.
Estuaries are subject both to marine influences—such as tides, waves, and the influx of saline water—and to riverine influences—such as flows of fresh water and sediment.
The inflows of both sea water and fresh water provide high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world. The banks of many estuaries are amongst the most heavily populated areas of the world.

The intertidal zone, also known as the foreshore and seashore and sometimes referred to as the littoral zone, is the area that is above water at low tide and under water at high tide.
Water is available regularly with the tides but varies from fresh with rain to highly saline and dry salt with drying between tidal inundations. It is very rich in nutrients and hence supports the growth of Mangroves the best.