What is an Ecosystem?

An ecosystem includes all of the living things in an area, plus their surroundings, plus all the ways in which they interact with each other.
Ecosystems exist on many different scales. You can consider the ecosystem of a rotting log in the forest, of a pond or a lake, of an alpine meadow, or of an entire range of mountains.
Earth’s ecosystems and its peoples are bound together in a grand and complex symbiosis. We depend on ecosystems to sustain us, but the continued health of ecosystems depends, in turn, on our use and care. Ecosystems are the productive engines of the planet, providing us with everything from the water we drink to the food we eat and the fiber we use for clothing, paper, or lumber. Yet, nearly every measure we use to assess the health of ecosystems tells us we are drawing on them more than ever and degrading them, in some cases at an accelerating pace. Our knowledge of ecosystems has increased dramatically in recent decades, but it has not kept pace with our ability to alter them. Economic development and human well-being will depend in large part on our ability to manage ecosystems more sustainably. We must learn to evaluate our decisions on land and resource use in terms of how they affect the capacity of ecosystems to sustain life — not only human 

GRASSLAND ECOSYSTEM

Grasslands exist in many parts of the world and are often influenced by humans. At southern latitudes, arid conditions may limit grass growth, sometimes resulting in competition among grasses for water. 
Grasslands are often grazed by domestic animals or mown by farmers and this may influence the distribution and abundance of plants in the sward. However, natural herbivores, for example, mammals, birds and insects, may also feed on grasslands. 
At northern latitudes, local disturbance patterns as well as larger scale land management may influence species interactions in the grasslands. In Iceland and elsewhere in northern Europe, grasslands are much influenced by lifestock grazing. Grasslands are often semi-natural, for example, cultivated grasses and legumes are frequently sown into grasslands to increase their production.

DESERT ECOSYSTEM

In ecology, desert ecology is the sum of the interactions between both biotic and abiotic processes in arid regions, and it includes the interactions of plant, animal, and bacterial populations in a desert habitat, ecosystem, and community. Some of the abiotic factors also include latitude and longitude, soil, and climate. Each of these factors have caused adaptations to the particular environment of the region. The biotic processes include animals and plants and the way they interact. Although deserts have severe climates, some plants still manage to grow. In hot deserts plants are called xerophytic meaning they are able to survive long dry periods. They may close their pores in daytime; they store water in their stems and leaves. Some of these plants include popcorn flower, barrel cactus and Saguaro cactus.

OCEAN ECOSYSTEM

Marine biology is the scientific study of organisms in the ocean or other marine or brackish bodies of water. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather than on taxonomy. Marine biology differs from marine ecology as marine ecology is focused on how organisms interact with each other and the environment, and biology is the study of the organisms themselves.
Marine life is a vast resource, providing food, medicine, and raw materials, in addition to helping to support recreation and tourism all over the world. At a fundamental level, marine life helps determine the very nature of our planet. Marine organisms contribute significantly to the oxygen cycle, and are involved in the regulation of the Earth's climate. Shorelines are in part shaped and protected by marine life, and some marine organisms even help create new land.

POND ECOSYSTEM

An aquatic ecosystem is an ecosystem in abody of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems.

Freshwater ecosystems cover 0.80% of the Earth's surface and inhabit 0.009% of its total water. They generate nearly 3% of its net primary production. Freshwater ecosystems contain 41% of the world's known fish species

Dobson unit

The Dobson unit (DU) is a unit of measurement of the columnar density of a trace gas in the Earth's atmosphere. It originated, and continues to be widely used, as a measure of total-column ozone, which is dominated by ozone in the stratospheric ozone layer. One Dobson unit refers to a layer of gas that would be 10 µm thick under standard temperature and pressure, sometimes referred to as a 'milli-atmo-centimeter.' For example, 300 DU of ozone brought down to the surface of the Earth at 0 °C would occupy a layer only 3 mm thick. One DU is 2.69×1016 ozone molecules per square centimetre, or 2.69×1020 per square metre. This is 0.4462 millimoles of ozone per square metre.

A baseline value of 220 DU is chosen as the starting point for an ozone hole since total ozone values of less than 220 Dobson Units were not found in the historic observations over Antarctica prior to 1979. Also, from direct measurements over Antarctica, a column ozone level of less than 220 Dobson Units is a result of the ozone loss from chlorine and bromine compounds.

The Dobson unit is named after Gordon Dobson, who was a researcher at the University of Oxford. In the 1920s, he built the first instrument to measure total ozone from the ground, now called the Dobson ozone spectrophotometer.