Aquatic ecosystemAn aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems. Freshwater ecosystems may be lentic (slow moving water, including pools, ponds, and lakes); lotic (faster moving water, for example streams and rivers); and wetlands (areas where the soil is saturated or inundated for at least part of the time).
River sourceThe headwater of a river or stream is the farthest point on each of its tributaries upstream from its mouth/estuary into a lake/sea or its confluence with another river. Each headwater is considered one of the river's source, as it is the place where surface runoffs from rainwater, meltwater and/or spring water begin accumulating into a more substantial and consistent flow that becomes a first-order tributary of that river. The tributary with the longest course downstream of the headwaters is regarded as the main stem of that river.
Chemical compositionA chemical composition specifies the identity, arrangement, and ratio of the chemical elements making up a compound by way of chemical and atomic bonds. Chemical formulas can be used to describe the relative amounts of elements present in a compound. For example, the chemical formula for water is H2O: this means that each molecule of water is constituted by 2 atoms of hydrogen (H) and 1 atom of oxygen (O). The chemical composition of water may be interpreted as a 2:1 ratio of hydrogen atoms to oxygen atoms.
Drainage basinA drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, the drainage divide, made up of a succession of elevated features, such as ridges and hills. A basin may consist of smaller basins that merge at river confluences, forming a hierarchical pattern. Other terms for a drainage basin are catchment area, catchment basin, drainage area, river basin, water basin, and impluvium.
Southern HemisphereThe Southern Hemisphere is the half (hemisphere) of Earth that is south of the Equator. It contains all or parts of five continents (the whole of Antarctica, the whole of Australia, about 90% of South America, about one-third of Africa, and some islands off the continental mainland of Asia) and four oceans (the whole Southern Ocean, the majority of the Indian Ocean, the South Atlantic Ocean, and the South Pacific Ocean), as well as New Zealand and most of the Pacific Islands in Oceania. Its surface is 80.
BiogeographyBiogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, isolation and habitat area. Phytogeography is the branch of biogeography that studies the distribution of plants. Zoogeography is the branch that studies distribution of animals. Mycogeography is the branch that studies distribution of fungi, such as mushrooms.
HumusIn classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Latin word for "earth" or "ground". In agriculture, "humus" sometimes also is used to describe mature or natural compost extracted from a woodland or other spontaneous source for use as a soil conditioner. It is also used to describe a topsoil horizon that contains organic matter (humus type, humus form, or humus profile).
Organic chemistryOrganic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms. Study of structure determines their structural formula. Study of properties includes physical and chemical properties, and evaluation of chemical reactivity to understand their behavior.
Humic substanceHumic substances (HS) are coloured recalcitrant organic compounds naturally formed during long-term decomposition and transformation of biomass residues. The colour of humic substances varies from yellow to brown to black. Humic substances represent the major part of organic matter in soil, peat, coal and sediments and are important components of dissolved natural organic matter (NOM) in lakes (especially, dystrophic lakes), rivers and sea water.
United StatesThe United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America and consisting of 50 states, a federal district, five major unincorporated territories, nine Minor Outlying Islands, and 326 Indian reservations. It is the world's third-largest country by both land and total area. It shares land borders with Canada to its north and with Mexico to its south and has maritime borders with the Bahamas, Cuba, Russia, and other nations.
DataIn common usage and statistics, data (USˈdætə; UKˈdeɪtə) is a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted formally. A datum is an individual value in a collection of data. Data is usually organized into structures such as tables that provide additional context and meaning, and which may themselves be used as data in larger structures.
Western HemisphereThe Western Hemisphere is the half of the planet Earth that lies west of the Prime Meridian (which crosses Greenwich, London, England) and east of the 180th meridian. The other half is called the Eastern Hemisphere. Politically, the term Western Hemisphere is often used as a metonym for the Americas, even though geographically the hemisphere also includes parts of other continents.
