OpenStem

@openstem · Joined Jul 2026

7420 public items8 groups

Note~256 words · 1 min

Primary vs Secondary Pollutants Not all air pollution is emitted directly. Primary pollutants come straight out of a source — a tailpipe, a smokestack, a burning field. Secondary pollutants form afterward, when primary pollutants react with

Environmental

Environmental · L2 · Air Pollution: Sources & Smog

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Note~255 words · 1 min

Point Source vs Nonpoint Source Pollution Water pollution is usually grouped by where it comes from. Point source pollution has one clear, identifiable origin — like a discharge pipe. Nonpoint source pollution is spread across a whole lands

Environmental

Environmental · L2 · Water Pollution & Treatment

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Note~350 words · 2 min

From Curbside Bin to Sorted Bale When a truck picks up a mixed recycling bin, everything — paper, plastic, glass, metal — usually travels together to a materials recovery facility (MRF). There, a combination of machines and human quality-co

Environmental

Environmental · L2 · Recycling Systems & Materials

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Note~376 words · 2 min

Why Farmers Fight Erosion Topsoil is the thin, nutrient-rich layer that almost all farming depends on — and it forms extremely slowly, often taking centuries to build up a single centimeter. Wind and rain can strip that same layer away in a

Environmental

Environmental · L2 · Soil Conservation & Erosion Control

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Note~290 words · 1 min

Three Ways Plates Meet Earth's crust is broken into large rigid plates that are always slowly moving — a few centimeters a year, about the speed a fingernail grows. Where two plates meet, they interact in one of three basic ways, and each p

Environmental

Environmental · L2 · Earthquakes & Plate Boundaries

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Note~377 words · 2 min

Earth's Sunscreen High in the stratosphere, between roughly 15 and 35 kilometers up, sits a layer where ozone (O₃) molecules are far more concentrated than elsewhere in the atmosphere. This ozone layer absorbs the large majority of the Sun'

Environmental

Environmental · L2 · The Ozone Layer & UV Protection

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Note~67 words · 1 min

Radioactive decay and half-life Radioactive isotopes decay at a constant fractional rate. If N₀ atoms are present at time zero, the number remaining at time t is N = N₀ · e^(−k·t), where k is the decay constant. The half-life t½ = ln(2)/k i

Environmental

Environmental · L3 · Half-Life and Radioactive Decay

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Note~271 words · 1 min

Energy Flows One Way, and Shrinks Every Step Unlike nutrients, which cycle endlessly through an ecosystem, energy flows through it only once — captured by producers from sunlight, then passed (mostly lost) up a chain of consumers until it i

Environmental

Environmental · L3 · Trophic Levels & Energy Pyramids

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Note~209 words · 1 min

Why Nitrogen Needs a Cycle Nitrogen gas (N₂) makes up about 78% of the atmosphere, but its two nitrogen atoms are locked together by an unusually strong triple bond that most organisms cannot break. The nitrogen cycle is the set of biologic

Environmental

Environmental · L3 · The Nitrogen Cycle

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Note~226 words · 1 min

A Cycle With No Sky in It Carbon and nitrogen both spend part of their cycle as atmospheric gases (CO₂, N₂), which lets them move around the planet quickly. Phosphorus has no biologically significant gas phase at all — it moves entirely thr

Environmental

Environmental · L3 · The Phosphorus Cycle

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Note~230 words · 1 min

Two Models of Growth Populations don't grow forever — but the two standard models ecologists use to describe growth differ sharply in whether they account for that limit. Exponential Growth When resources are effectively unlimited, a popula

Environmental

Environmental · L3 · Population Ecology & Carrying Capacity

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Note~252 words · 1 min

The Greenhouse Effect, Mechanistically Incoming sunlight is mostly shortwave (visible/UV) radiation, which passes through the atmosphere and warms Earth's surface. The surface then re-radiates that energy as longwave (infrared) radiation —

Environmental

Environmental · L3 · Climate Feedback Loops

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Note~312 words · 2 min

Capacity Factor: How Much of the 'Nameplate' You Actually Get A power plant's rated ('nameplate') capacity is the maximum output it can produce under ideal conditions. In practice, no plant runs at that maximum all the time — capacity facto

Environmental

Environmental · L3 · Renewable Energy Technologies

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Note~241 words · 1 min

The Pollutants Behind the Index An Air Quality Index doesn't measure one thing — it's built from several distinct pollutants, each with its own sources and health effects. PM2.5 vs PM10: Why Size Matters Particulate matter is classified by

Environmental

Environmental · L3 · Air Quality Index & Pollutants

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Note~214 words · 1 min

Eutrophication: A Chain Reaction, Not a Single Event Eutrophication starts with excess nutrients — mainly nitrogen and phosphorus from fertiliser runoff and sewage — but the water-quality damage it causes unfolds through several linked stag

Environmental

Environmental · L3 · Water Quality & Eutrophication

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Note~213 words · 1 min

Two Landmark Agreements, Two Structures International climate policy has largely moved from a top-down model to a bottom-up one. The Kyoto Protocol (1997) set legally binding emissions targets, but only for developed nations — the US never

Environmental

Environmental · L3 · Environmental Policy & International Agreements

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Note~215 words · 1 min

Two Starting Points, One Trajectory Ecological succession describes how an ecosystem's species composition changes predictably over time. What differs between primary and secondary succession is simply the starting condition — specifically,

Environmental

Environmental · L3 · Ecological Succession

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Note~224 words · 1 min

A Definition That Still Anchors the Field The 1987 UN report Our Common Future, chaired by Gro Harlem Brundtland, gave sustainable development its most widely used definition: development that meets the needs of the present without compromi

Environmental

Environmental · L3 · Sustainable Development & the Triple Bottom Line

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Note~235 words · 1 min

Two Thresholds, Not One A region only qualifies as an official 'biodiversity hotspot' (Conservation International's criteria) if it clears two thresholds at once: at least 1,500 endemic vascular plant species, and at least 70% of its origin

Environmental

Environmental · L3 · Biodiversity Hotspots & Extinction Rates

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Note~216 words · 1 min

Linear vs Circular A linear economy extracts raw materials, manufactures products, and discards them as waste once used — a one-way flow. A circular economy instead designs products and systems to keep materials in use as long as possible,

Environmental

Environmental · L3 · Waste Management & the Circular Economy

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Note~257 words · 1 min

Two Zones, One Balance Sheet Every glacier can be split into two zones. In the accumulation zone (typically higher up), snowfall exceeds melt and ice builds up. In the ablation zone (typically lower down), melting, sublimation, and calving

Environmental

Environmental · L3 · Glacial Mass Balance & Sea-Level Contribution

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Note~251 words · 1 min

The Ocean as a CO₂ Sponge The ocean has absorbed roughly a quarter to a third of all the CO₂ humans have emitted since the industrial revolution — a service that has slowed atmospheric warming, but at a chemical cost to the water itself. Th

Environmental

Environmental · L3 · Ocean Acidification

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Note~245 words · 1 min

A Partnership Under Stress Reef-building corals aren't just animals — each polyp hosts millions of photosynthetic algae called zooxanthellae in its tissue. This partnership supplies the coral with up to about 90% of its energy and gives the

Environmental

Environmental · L3 · Coral Bleaching Mechanism

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Note~266 words · 1 min

Two Jobs, One Cause: Low Oxygen Wetlands punch far above their weight as both carbon sinks and water purifiers — and both roles trace back to the same root cause: their waterlogged soils exclude oxygen, slowing the microbial processes that

Environmental

Environmental · L3 · Wetlands as Carbon Sinks & Nutrient Filters

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Note~271 words · 1 min

What an Aquifer Is An aquifer is an underground layer of permeable rock or sediment — sand, gravel, sandstone, fractured limestone — that can store and transmit meaningful amounts of water. Aquifers come in two broad types. Darcy's Law, Con

Environmental

Environmental · L3 · Groundwater Hydrology

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Note~256 words · 1 min

Why Cities Run Hotter The urban heat island (UHI) effect describes how cities measurably run warmer than their rural surroundings — typically by about 1–7 °C, with the gap usually widest at night. Three quantifiable drivers explain most of

Environmental

Environmental · L3 · Urban Heat Island: Quantitative Drivers & Mitigation

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Note~307 words · 2 min

Looking at the Whole Life, Not Just One Stage A life-cycle assessment (LCA) is a structured way of adding up a product's or material's total environmental impact across every stage of its existence, rather than judging it by just one part o

Environmental

Environmental · L3 · Life-Cycle Assessment (LCA)

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Note~227 words · 1 min

Predicting Impact Before It Happens An environmental impact assessment (EIA) is the formal regulatory process most jurisdictions require before approving major projects — mines, dams, highways, power plants — so that likely environmental co

Environmental

Environmental · L3 · Environmental Impact Assessment (EIA)

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Note~292 words · 1 min

What a Climate Model Actually Does A General Circulation Model (GCM) — often just called a global climate model — divides the atmosphere and ocean into a three-dimensional grid of cells. For each cell, the model solves physical equations go

Environmental

Environmental · L3 · Climate Models & Scenario Projections

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Note~244 words · 1 min

Demand vs Supply: PET and AET Deserts aren't simply defined by low rainfall — they're defined by a mismatch between how much water the atmosphere 'demands' and how much is actually available. Potential evapotranspiration (PET) is that deman

Environmental

Environmental · L3 · Desert Ecosystems: Water Balance & Adaptations

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