An ecosystem is a community of plants and animals associated with specific climatic conditions and abiotic (nonliving) features. In the grand scheme of things, there are only two types of ecosystems: terrestrial (land) and aquatic (water) ecosystems. However, these ecosystems can be broken down into a variety of smaller, more regional and specialised ecosystems, which are sometimes referred to as biomes.
Terrestrial ecosystems encompass Earth's land area. Most authorities, like the Department of Biodiversity and Conservation Biology of the University of Western Cape, agree on a system of smaller ecosystems within the large terrestrial ecosystem that includes grasslands (also known as savannahs), which typically have arid, hot climates; deserts, which are composed of hot, dry sand dunes; tropical rainforests, which are wet, humid and hot and contain millions of different plant and animal species; alpine and arctic regions, which are cold, harsh climates where only animals adapted to those conditions can survive; and forests---both coniferous and deciduous---which are home to enormous trees and a wide variety of other life forms.
According to the University of California, water covers approximately 75 per cent of our planet, meaning that the aquatic ecosystem is much larger than the terrestrial. Like the terrestrial ecosystem, and can be broken down into several smaller categories, with the marine ecosystem, which comprises the world's saltwater bodies, being the largest. Within the marine ecosystem you'll find wildly diverse ecosystems, from coral reefs in warm waters filled with a rich variety of colourful life to the cold polar seas teeming with whales and seals. The littoral ecosystem (also known as the littoral zone) is the shallow water environments found close to shores and is home to numerous marine creatures. Finally, a lentic ecosystem has still waters, such as pond or swamp, whereas an ecosystem of flowing waters, like rivers or streams, is referred to as a lotic ecosystem; according to Mrs. O's House, which provides projects for students regarding these ecosystems, there are approximately 80,000 miles worth of rivers in the state of Pennsylvania alone.
Artificial ecosystems are those that are created by human beings and are often referred to as urban ecosystems by sites offering projects and information on the subject, such as Science NetLinks. These include cities, towns, villages and any area that has been wholly constructed by humans. These large communities, strung together, may collectively be referred to as the human ecosystem.