751 articles
Diapycnal mixing
Diapycnal mixing is the turbulent transport of heat, salt, and tracers across density surfaces in stratified fluids, driven mainly by breaking internal waves and supplying the energy the ocean's overturning circulation needs.
Didymosphenia geminata
Didymosphenia geminata, commonly called didymo or rock snot, is a freshwater diatom native to northern Europe and North America that forms dense streambed mats in nutrient-poor rivers worldwide since the 1990s.
Diel vertical migration
Diel vertical migration is the daily movement of aquatic animals toward the surface at night and into deeper water by day, the largest synchronized movement of biomass on Earth.
Dirección General de Aguas (Chile)
The Dirección General de Aguas (DGA) is the Chilean state agency, created in 1969 under the Ministry of Public Works, that manages the country's continental waters.
Discharge (hydrology)
Discharge, also called streamflow or river discharge, is the volume of water passing a point in a channel per unit time, measured in cubic feet or meters per second.
Discrete fracture network model
A discrete fracture network (DFN) model simulates fluid flow and transport through fractured rock by representing each fracture explicitly, used in nuclear waste safety and hydraulic fracturing.
Dissolved inorganic carbon
Dissolved inorganic carbon (DIC) is the total inorganic carbon dissolved in seawater, mainly bicarbonate, carbonate, and carbon dioxide, and is the route by which human-made CO₂ enters the ocean.
Dissolved organic carbon
Dissolved organic carbon (DOC) is the organic carbon in water that passes a 0.45-micrometer filter, making up about 90% of total organic carbon in most waters.
Dissolved oxygen
Dissolved oxygen (DO) is the amount of oxygen gas dissolved in water and available to aquatic organisms, usually reported in mg/L, and a core measure of water quality.
Double-diffusive convection
Double-diffusive convection, first called thermohaline convection, arises when a fluid's density depends on two components, like heat and salt, that diffuse at very different rates.
DRASTIC
DRASTIC is a GIS-based overlay index method that rates seven hydrogeologic factors, named in its acronym, to assess groundwater vulnerability to contamination from surface pollutants.
Drift (stream ecology)
Drift in stream ecology is the downstream transport of benthic invertebrates in the water column, a primary food source for stream fishes and a means of dispersal.
Drifter (oceanography)
A drifter, also known as a Lagrangian drifter, is a satellite-tracked ocean buoy with a subsurface drogue at 15 m depth that follows currents while measuring temperature and position.
DSV Alvin
DSV Alvin, also known as RV Alvin, is a U.S. Navy-owned research submersible operated by Woods Hole Oceanographic Institution since 1964, reaching depths of 6,500 meters.
DSV Limiting Factor
The DSV Limiting Factor is a two-person submersible rated to 11,000 m, built for Victor Vescovo's Five Deeps Expedition and sold in 2022 to Gabe Newell's Inkfish.
Dual-porosity model
The dual-porosity model is a mathematical representation of a fractured porous medium treating rock as two overlapping continua, fractures and porous matrix, introduced by Barenblatt and colleagues in 1960.
Dye tracing
Dye tracing is a hydrogeology technique that injects fluorescent dye, typically uranine, into water and measures it downstream to reveal underground flow paths and velocities.
Dynamic topography
Dynamic topography is the height of the sea surface relative to the geoid, produced by ocean currents, or the solid-Earth deformation caused by flow in the convecting mantle.
East Australian Current
The East Australian Current is a major ocean current flowing south along Australia's east coast from the Coral Sea, known for large eddies and warming the Tasman Sea.
Echo sounding
Echo sounding, also called depth sounding, measures water depth by timing a sound pulse's return from the seabed; it replaced the lead line in the early twentieth century.
Ecological status
Ecological status is a five-class measure of surface water ecosystem quality under the EU's 2000 Water Framework Directive, rating rivers, lakes, and coastal waters from high to bad.
Ecosystem respiration
Ecosystem respiration is the oxidation of organic matter to inorganic carbon by all organisms in an ecosystem, measured in streams and rivers from daily dissolved oxygen records.
Edge wave
An edge wave is a surface ocean wave trapped against a sloping coast by refraction, propagating along the shoreline with an amplitude that decays rapidly offshore.
Effective rainfall
Effective rainfall, also called effective precipitation, is the portion of total rainfall useful for a stated purpose, most often crop water supply in the root zone.
Ekman layer
The Ekman layer is the wind-driven surface layer of the ocean, about 100 m deep, where the current spirals with depth due to Earth's rotation.
Ekman pumping
Ekman pumping is the vertical motion induced in a rotating fluid where a frictional boundary layer meets the interior, caused by friction turning the flow across isobars.
Ekman transport
Ekman transport is the net horizontal movement of wind-driven surface water in the ocean, deflected 90 degrees to the right of the wind in the Northern Hemisphere.
Electronic navigational chart
An electronic navigational chart (ENC) is a standardized vector chart database issued by a government-authorized hydrographic office for use with ECDIS, conforming to International Hydrographic Organization standards.
Environmental flow
An environmental flow is the quantity, timing, and quality of water flow and level needed to sustain aquatic ecosystems, a field of assessment with some 207 methodologies recorded worldwide by 2003.
Epikarst
Epikarst is the uppermost, intensely weathered zone of karstified carbonate rock, also called the subcutaneous zone, acting as a perched aquifer that stores rainwater and regulates recharge to deeper karst.