Water Quality

Water Quality asks you to explain how chemistry, living things and watersheds fit together in aquatic systems, and to read the data that describes them. Under the 2027 rules the event is set in marine and estuary environments: the brackish water where rivers meet the sea, the open coast, and the coral reefs that depend on both. Expect scenarios built around estuary or reef data, comparisons of macroinvertebrate and water-quality results between sites, and pictures of reef organisms. Your job is to say what the evidence means, why it is happening and what a manager should do about it. A fourth part is hands-on: you bring a salinometer you built and use it to measure an unknown salt solution.

Event format

The 2027 rules manual sets the same format for Division B and Division C.

The test has four parts with fixed weights. High score wins.

Class II means a stand-alone, non-programmable, non-graphing scientific calculator (a TI-30X or Casio fx-260 type); a four-function calculator is also fine. Graphing calculators and programmable non-graphing models (those with PROG or EXE keys) are Class III and not allowed. Category C eye protection means indirect-vent chemical splash goggles marked Z87; a face shield or ordinary safety glasses do not count.

What the rules cover

Everything in this table applies at every level unless it is marked otherwise. Division C adds two topics that Division B does not have.

Water chemistry and monitoring

Part III is about 11 parameters. For each one, know what it measures, its units, how it is tested, what raises and lowers it, and how it affects organisms. The table is your summary; the subsections give the mechanisms.

Dissolved oxygen

Dissolved oxygen (DO) is oxygen gas dissolved in water, reported in mg/L (equal to ppm for dilute water). Oxygen enters by diffusion from the air, sped up by wind and waves (reaeration), and by photosynthesis. It leaves through respiration and decomposition.

How much oxygen water can hold depends on temperature, salinity and pressure. Solubility falls as temperature rises and as salinity rises, so seawater holds less oxygen than fresh water at the same temperature. Approximate freshwater saturation values at sea level are 14.6 mg/L at 0 °C, 11.3 mg/L at 10 °C, 9.1 mg/L at 20 °C and 7.6 mg/L at 30 °C (USGS; seawater values are roughly 20% lower).

The key chain: ↑ temperature → ↓ oxygen solubility and ↑ metabolic rate → ↑ oxygen demand → ↓ DO. Warm, stagnant summer water is the usual setting for low-DO events.

DO also cycles over the day. Photosynthesis adds oxygen only in daylight, but respiration removes it around the clock, so DO peaks in the afternoon and bottoms out near dawn. A large daily swing signals a lot of algal biomass; a flat record suggests well-mixed water with less biological activity.

Hypoxia is low DO; NOAA and many agencies use about 2 mg/L as the working threshold, below which most fish and bottom animals cannot stay. Anoxia means no measurable oxygen. Hypoxic zones form where blooms die and decompose on the bottom and where layering (stratification) keeps surface oxygen from mixing down.

The Winkler titration is the classic DO test: the sample is "fixed" in the field with manganese sulfate and an alkaline iodide reagent so the oxygen is locked into a precipitate, then acidified and titrated with sodium thiosulfate. Electronic probes are faster but need calibration. A question asking why the sample is fixed immediately wants the answer that oxygen would otherwise exchange with air or be consumed before analysis.

pH and aragonite saturation

pH is a logarithmic measure of hydrogen ion concentration and has no units.

pH 5 has ten times the [H⁺] of pH 6 and one hundred times that of pH 7. Most fresh waters fall between about 6.5 and 8.5; surface seawater sits near 8.1, and marine organisms tolerate only narrow swings. Potentiometry with a pH electrode is the most precise method; indicator dyes and strips are quicker but coarser.

Ocean acidification is the long-term drop in seawater pH as the ocean absorbs CO₂. CO₂ + H₂O forms carbonic acid, which releases H⁺. The extra H⁺ combines with carbonate ions (CO₃²⁻) to form bicarbonate, so carbonate becomes scarcer. NOAA reports surface ocean pH has fallen by about 0.1 unit since preindustrial times. Because 10^0.1 ≈ 1.26, that is roughly a 26–30% rise in [H⁺].

The carbonate loss is what matters to reef builders. Corals, giant clams and many plankton build skeletons and shells of aragonite, a form of calcium carbonate. The aragonite saturation state (Ω) compares the ion product in seawater with the solubility product of aragonite.

Calcium barely changes in seawater, so in data questions Ω tracks carbonate ion, which tracks pH. Lower pH → less CO₃²⁻ → lower Ω → slower reef growth. Ω is also lower in cold water, which is one reason reef-building corals are mainly tropical.

Salinity and temperature

Salinity is the mass of dissolved salts per mass of water. Open-ocean water averages about 35 g/kg (35 ppt, or 3.5%). Estuaries are brackish: their salinity lies between fresh water and seawater and changes with the tide and river flow. Hypersaline lagoons, where evaporation exceeds inflow, can exceed open-ocean salinity.

Salinity changes density, electrical conductivity, freezing point and oxygen solubility, and it sets the osmotic challenge organisms face. Euryhaline organisms (oysters, many estuarine fish) tolerate wide salinity ranges; stenohaline organisms (most corals) do not, so a flood of fresh water can stress a reef as surely as heat.

Temperature quietly controls the other parameters: oxygen solubility, metabolic and reaction rates, and stratification. When a question ranks influences on DO, temperature is among the largest.

Desalination is one route to potable water in dry coastal nations: reverse osmosis pushes seawater through a membrane against its osmotic pressure, and multi-stage flash distillation boils and condenses it. Both leave a concentrated brine that must be discharged, which raises local salinity.

Turbidity and total solids

Turbidity is cloudiness caused by suspended particles such as silt, clay, organic matter and plankton, reported in nephelometric turbidity units (NTU). A Secchi disk is lowered until it disappears; a shallower Secchi depth means cloudier water.

Particles block light → less photosynthesis by zooxanthellae and seagrass → less growth and less daytime oxygen. Settling sediment also smothers coral polyps, which must spend energy producing mucus to clear it.

Total solids are everything left when a measured volume is evaporated (typically at 103–105 °C) and the residue weighed. Filtering first splits it into total suspended solids (caught on the filter) and total dissolved solids (passing through). In seawater the dissolved part is mostly salt, so a rise in the suspended part is the usual sign of sediment pollution.

Nutrients and fecal coliform as tests

Nitrate and phosphate are measured by colorimetric tests: a reagent produces a color whose intensity, read by eye against a chart or with a spectrophotometer, is proportional to concentration. Phosphate tests use the ascorbic acid method (a blue complex); nitrate tests often reduce nitrate to nitrite with cadmium and then form a pink dye. Rising nutrients predict algal growth; the next section explains why.

Fecal coliform bacteria live in the guts of warm-blooded animals. They are an indicator: they usually do not cause disease themselves, but they show that sewage or animal waste, and possibly pathogens, has reached the water. In the membrane filtration test, 100 mL of sample is passed through a filter, the filter is incubated on a selective medium at 44.5 °C (which favors gut bacteria), and the colonies are counted as colonies per 100 mL. Shellfish beds in estuaries are closed when counts rise, because filter-feeding oysters and clams concentrate bacteria.

Biochemical oxygen demand

Biochemical oxygen demand (BOD) is the oxygen microbes use to decompose the organic matter in a sample. In the standard BOD₅ test, a sample (often diluted) is sealed in a bottle, initial DO (D₁) is measured, the bottle is incubated in the dark at 20 °C for five days so no photosynthesis adds oxygen, and final DO (D₂) is measured.

How the parameters connect

Part III asks how the parameters relate, so learn the chains rather than isolated facts.

• ↑ nitrate and phosphate → algal bloom → ↑ turbidity, ↑ daytime DO and pH, then die-off → ↑ BOD → ↓ DO at night and near the bottom.
• ↑ temperature → ↓ DO solubility and ↑ respiration → ↓ DO; also ↑ bleaching risk.
• ↑ dissolved CO₂ → ↓ pH → ↓ carbonate → ↓ Ω.
• Heavy rain → ↓ salinity, ↑ turbidity and total solids, ↑ nutrients and fecal coliform from runoff and overflowing sewers.
• ↑ salinity → ↓ DO solubility, ↑ conductivity and density.

Reading monitoring data

Three habits earn most data points. Check units and whether a value is a concentration or a load. When comparing sites or dates, check whether flow, tide, season or time of day differs. State the mechanism in one sentence before you choose an answer.

A load is the mass of a substance moving past a point per unit time. A river with a low concentration can still deliver a large load if its flow is high.

Comparing macroinvertebrate data

Supervisors are asked to use comparative macroinvertebrate data alongside chemistry. Benthic macroinvertebrates (worms, clams, snails, crustaceans and insect larvae big enough to see) live in the sediment for months or years, so they record conditions over time rather than on the sampling day. In estuaries, pollution-tolerant taxa such as some small polychaete worms and oligochaetes dominate where organic enrichment and low DO occur, while sensitive amphipods, larger bivalves and diverse crustaceans dominate clean sites.

Three summary numbers compare sites: taxa richness (how many kinds), abundance (how many individuals) and diversity, which combines richness with evenness. An enriched site often has high abundance but low richness: a few tolerant species booming.

Marine and estuary ecology

An estuary is a partly enclosed coastal water body where river water mixes with seawater. It is brackish, its salinity changes with tide and river flow, and it ranks among the most productive ecosystems on Earth.

Why estuaries matter

The rules list the importance of estuaries as an applied topic, so be ready to name services and the mechanism behind each.

• Nursery habitat. Shallow, food-rich, sheltered water lets juvenile fish and shellfish grow with fewer large predators; NOAA estimates that a large share of U.S. commercial fish and shellfish depend on estuaries at some life stage.
• Filtering. Marsh plants slow water so sediment settles, and oysters filter large volumes of water, lowering turbidity and removing particles.
• Nutrient processing. Marsh and seagrass sediments take up nutrients and host denitrifying bacteria that return nitrogen to the air.
• Storm buffering. Marshes and mangroves absorb wave energy and storm surge and hold the shoreline.
• Economy. Fisheries, shipping, recreation and tourism.

Common estuarine habitats are mudflats, salt marshes, mangroves, seagrass beds and oyster reefs. Mangrove roots trap sediment, stabilize the shore and shelter juvenile fish. Draining, filling and dredging destroy these habitats directly and stir up buried sediment and contaminants.

Estuary types and mixing

Classic estuary classifications use two bases: how the basin formed (geology) and how the water circulates.

Water cycle and nutrient cycling

The water cycle moves water by evaporation and transpiration, condensation, precipitation, runoff and infiltration. Every step is also a pollutant pathway: runoff carries surface contaminants to the estuary, infiltration moves them toward groundwater, and evaporation leaves salt behind.

Nutrients are elements needed in quantity, mainly nitrogen and phosphorus. The one in shortest supply relative to need is the limiting nutrient (Liebig's law of the minimum). Coastal marine waters are most often nitrogen-limited; many fresh waters are phosphorus-limited; estuaries can switch between the two with season and salinity.

Nitrogen exists mostly as unreactive N₂ gas. Its cycle has five steps:

1. Nitrogen fixation: bacteria (including cyanobacteria) convert N₂ to ammonia/ammonium.
2. Ammonification: decomposers release ammonium from dead matter and waste.
3. Nitrification: aerobic bacteria oxidize ammonium to nitrite, then nitrate. Needs oxygen; slowed by low pH.
4. Assimilation: algae and plants take up nitrate or ammonium.
5. Denitrification: in low-oxygen sediment, bacteria convert nitrate back to N₂.

Phosphorus has no significant gas phase. It is stored mainly in sedimentary rock, enters water by weathering and runoff, and is taken up as orthophosphate (PO₄³⁻ and its protonated forms), the bioavailable form.

Eutrophication

Eutrophication is excess nutrients driving excessive algal growth, followed by oxygen loss. Sources are point sources (wastewater outfalls, combined sewer overflows, feedlots) and non-point sources (farm and lawn runoff, septic leakage, atmospheric deposition).

Nutrients → bloom near the surface (where light is) → shading kills seagrass below → bloom dies and sinks → decomposers consume oxygen → bottom hypoxia. The seasonal "dead zone" off the Mississippi River mouth in the Gulf is the standard example. Do not confuse eutrophication (oxygen loss via decomposition) with acidification (pH loss via CO₂).

Food webs and energy flow

Producers in marine systems are mainly phytoplankton, seagrasses, macroalgae and the zooxanthellae inside corals. Marine autotrophs take their carbon from inorganic sources: dissolved CO₂ and bicarbonate. Consumers eat producers or each other; decomposers recycle nutrients.

Removing one species ripples through a web. Removing grazers lets algae spread; removing predators lets prey boom. Write these as cause → effect chains: overfished parrotfish → less grazing → fleshy algae overgrow coral → fewer coral recruits.

Populations and community interactions

Populations grow exponentially when resources are abundant and level off near carrying capacity (K) as food, space or predation limit them. Predator numbers track prey numbers with a lag.

Learn the sign pattern, because questions describe new species pairs.

Life history strategies (Division C, State & National)

A life history strategy is how an organism allocates energy among growth, survival and reproduction across its life.

Real species fall along a continuum. The practical point: K-leaning species (slow-growing, late-maturing fish) recover slowly from overfishing, which is why they serve as overfishing indicators.

Survivorship curves plot the number surviving (log scale) against age. Type I stays high until old age, then drops (large mammals). Type II declines at a steady rate (many birds, some reptiles). Type III drops steeply early and flattens for the few survivors (corals, oysters, most fish with planktonic larvae).

A life table follows a cohort. Key columns: nₓ (alive at the start of age x), lₓ (proportion surviving to x), dₓ (dying during x), qₓ (death rate during x), and mₓ (offspring per individual at age x).

Age structure diagrams show the share of a population in each age class. A broad base means many young and growth; a narrow base with large older classes means decline. In fisheries, an age structure missing the oldest classes is a sign of overfishing, since fishing removes large, old fish first.

Succession is the change in community composition after disturbance. Primary succession starts on new surface (a fresh lava flow or a new shipwreck); secondary succession follows disturbance that leaves substrate (a hurricane-flattened reef). On reefs, bare or recently killed coral is colonized first by turf and filamentous algae, then crustose coralline algae (which help coral larvae settle), and finally new corals. Heavy grazing pressure keeps the sequence moving toward coral; loss of grazers can stall it at fleshy algae.

Traditional ecological knowledge (Division C)

Traditional ecological knowledge (TEK) is the knowledge, practice and belief about local ecosystems that Indigenous and local communities build through long observation and pass between generations. It is place-based, often expressed through practice and story, and frequently paired with rules about who may harvest what, where and when.

Coastal examples you can reason with:

• Hawaiian loko iʻa (fishponds) built with stone walls and sluice gates in estuaries and on reef flats let small fish in and kept grown fish from leaving; they depend on knowing tides, freshwater inflow and fish behavior.
• Seasonal and area closures (for example kapu in Hawaiʻi and tabu areas in parts of the Pacific) rest a fishing ground or protect spawning times, which works like a modern marine protected area.
• Local observation records, such as when a fish aggregates to spawn or where seagrass has retreated, can extend scientific monitoring back decades.

To apply TEK in a scenario, ask what long-term observations the community holds, what harvest rules they already follow, and how those can be combined with scientific data in co-management. Credit knowledge holders, involve them in decisions, and treat TEK as evidence with its own methods, not as anecdote.

Applied issues: pollution, harmful species and watershed management

Watersheds and their management

A watershed is the land that drains to a common water body; everything done on the land eventually reaches the estuary. Management tools include riparian buffers (vegetation strips that filter runoff), wetland protection and restoration, stormwater ponds and permeable pavement, nutrient management on farms, upgrading wastewater plants, and limits on development in sensitive areas. A good answer names the pollutant and the step in its path the tool interrupts.

Sedimentation

Erosion from farms, construction and cleared land sends sediment downstream. It raises turbidity, cuts light, smothers benthic animals and polyps, carries attached nutrients and contaminants, and fills channels. Prevention works at the land surface: keep vegetation cover, plant buffers along banks, avoid overgrazing, and use silt fences on construction sites.

Harmful algal blooms

A harmful algal bloom (HAB) is a bloom that produces toxins or causes harm through sheer biomass (shading, oxygen depletion). Common marine and estuary examples:

Nutrients, warm water and calm stratified conditions favor HABs. Filter feeders concentrate the toxins, so shellfish beds are closed during blooms.

Harmful species

Harmful species include invasive species introduced outside their range and native species that become harmful when the system is out of balance. Lionfish, native to the Indo-Pacific, spread through the western Atlantic and Caribbean, eat large numbers of small reef fish and have few predators there. Ballast water carries larvae of many estuary invaders. Native crown-of-thorns starfish become harmful during outbreaks. Invaders succeed because they lack their home predators and parasites and often reproduce quickly.

Recently killed coral

Reef surveys sort the bottom into categories, and recently killed coral is one of them: coral that has died within about the past year, with the skeleton still white or lightly fuzzed and the polyp structure still visible, before algae fully cover it. It is a snapshot of recent stress. A rise in recently killed coral after a heat wave points to bleaching mortality; patches with feeding scars point to crown-of-thorns or snail predation; a broken, scattered pattern points to storms, anchors or blast fishing.

Emerging contaminants

Emerging contaminants are chemicals now being detected whose effects are not yet fully regulated. Pharmaceuticals and personal-care products pass through wastewater plants, which were not designed to remove them, and some act as endocrine disruptors that can feminize male fish. PFAS (per- and polyfluoroalkyl substances) are used in nonstick coatings, water-repellent fabrics and firefighting foams. Their carbon–fluorine bonds are extremely stable, so they persist ("forever chemicals"), travel in water and bioaccumulate. In 2024 the EPA set drinking-water limits for PFOA and PFOS of 4 parts per trillion each. Expect questions on sources, why treatment misses them, and bioaccumulation up food webs.

The five ocean garbage patches

The five major subtropical gyres, in the North Pacific, South Pacific, North Atlantic, South Atlantic and Indian Ocean, collect floating debris into garbage patches. The best known is the Great Pacific Garbage Patch between Hawaii and California. The patches shift with the currents and are mostly microplastics suspended in the upper water rather than a solid island. Cleanup is hard because the pieces are small and dispersed, collection can harm wildlife, and new plastic keeps arriving unless inputs are cut. Plastic harms through entanglement, ingestion and absorbing other pollutants.

Water treatment

Potable water

Drinking-water treatment typically runs: screening and aeration → coagulation (a chemical such as alum makes fine particles clump) → flocculation (gentle mixing grows the clumps) → sedimentation → filtration → disinfection, most often with chlorine. Coagulation and settling target particles, filtration removes finer material, and disinfection targets microbes.

Wastewater

• Primary treatment screens out large solids and grit, skims fats and oils, and settles the rest in a primary clarifier.
• Secondary treatment is biological: in an aeration (activated sludge) basin, microbes consume dissolved organic matter with oxygen, then settle out in a final clarifier. Most BOD is removed here.
• Tertiary treatment removes nutrients or remaining pathogens where needed, then the effluent is disinfected before discharge.

Sludge is thickened and digested, often anaerobically, which stabilizes it and produces biogas. Trace the water and the sludge as two separate paths when a diagram asks you to order stages.

Coral reefs

Part II is worth 30% and has two halves: reef ecology and threats, and the 23 listed organisms.

Coral biology

A reef-building (stony, or scleractinian) coral is a colony of polyps. Each polyp secretes an aragonite skeleton beneath it. Most reef builders host zooxanthellae, dinoflagellates living in the polyp's tissue that photosynthesize and pass most of their sugars to the coral; the coral supplies CO₂, nutrients and shelter. Polyps also feed at night by catching zooplankton with stinging cells (nematocysts) on their tentacles.

Coral bleaching is the loss of zooxanthellae, usually under heat stress (about 1 °C above the usual summer maximum for several weeks). The white color is the skeleton showing through clear tissue. Corals can recover if conditions ease, but long bleaching starves them. NOAA's Coral Reef Watch tracks the heat stress.

Most corals reproduce by broadcast spawning, often in mass spawning events a few nights after a full moon; some brood larvae internally. Fertilized eggs become free-swimming planula larvae that settle on hard surfaces and bud into colonies. Fragmentation is asexual reproduction that helps after storms.

Reef types: fringing reefs hug the shore, barrier reefs sit offshore behind a lagoon, and atolls are reef rings around a lagoon with no central island. Darwin's 1842 subsidence model ran fringing → barrier → atoll as an island sinks; later work showed sea-level change also matters, so treat the sequence as a model with exceptions. Calcareous (coralline) algae help cement the reef; filamentous and fleshy algae compete with coral.

What harms reefs

Healthy reefs shelter a large share of marine species, absorb wave energy, and support fisheries and tourism. Management uses marine protected areas, size and gear limits, bans on destructive fishing, cutting land-based runoff, and monitoring programs such as Reef Check.

The 2027 organism list

The rules list 23 organisms. Identification is by common name only, but you also need each one's ecology, life cycle and feeding habits, and why surveys count it. Most come from the Reef Check indicator list, where each organism tracks a particular pressure: fishing, the aquarium or curio trades, the live food fish trade, or nutrient pollution.

Global (found in both regions)

Indo-Pacific only

Atlantic only

The salinometer task

Part IV is worth 10%: 5% just for bringing a salinometer, and 5% for an accurate reading.

Device rules

Mass/volume percent means grams of salt per 100 mL of finished solution. A 3.5% m/v solution has 3.5 g of NaCl in every 100 mL.

Two designs

A hydrometer is a weighted, sealed float. By Archimedes' principle it sinks until it displaces its own weight of liquid, so in denser salt water it rides higher. Mark a scale on its stem and calibrate it. Density rises roughly in step with salinity: about 1.00 g/mL for fresh water at 20 °C, about 1.005 for 1% NaCl, about 1.025 near seawater salinity and about 1.07 near 10% (approximate; values depend on temperature). That is a total change of only about 7% across the whole range, so a thin stem gives the biggest movement per percent salt.

An electronic (conductivity) salinometer passes a small current between two electrodes. More dissolved ions → higher conductivity → more current. A battery, two stainless or graphite electrodes at a fixed spacing and an analog meter or a calibrated LED/resistor circuit meets the "simple, not programmable" condition. Conductivity rises with temperature (roughly 2% per °C), so calibrate and test at similar temperatures.

Calibrating with mass/volume standards

Because the range is in m/v, make standards by dissolving a weighed mass of salt and topping up to a known final volume.

Use at least five standards across 1–10% (for example 1, 3, 5, 7 and 10%). Plot reading against known salinity and draw the best-fit line or curve; a hydrometer is close to linear, while a conductivity cell bends at high concentration. Read unknowns off the curve, not a two-point line.

Getting the reading right

• Rinse the device with distilled water and blot it between samples so you do not carry salt across.
• Read a hydrometer at eye level at the bottom of the meniscus; tap it to release air bubbles.
• Let a conductivity cell settle and keep the electrodes at the same depth every time.
• Measure the sample temperature and compare with your calibration temperature.
• Practice the full routine with unknowns made by a teammate until you are inside ±0.5% every time.
• Bring Category C goggles, or you cannot test.

Common pitfalls

Strategy

The four parts favor different skills. One partner can lead Part I and the life history and TEK items, and the other Part II and the device; both should handle Part III, since it is data-heavy and worth as much as either. Bring two Class II calculators so you can work in parallel.

Build the one-page sheet around what is hard to memorize. Useful content: the Part III table with units, test methods and typical marine values; the formulas for pH, percent saturation, BOD₅, load, Ω, Shannon diversity and life-table columns; the circulation and geological estuary tables; and a compact list of the 23 organisms with region, feeding and indicator role. Pictures will not fit at a useful size, so drill organism identification separately with photo flashcards until you know each one by sight.

For Part III, practice turning every table or graph into a one-sentence mechanism before computing anything. For Part IV, finish building early, calibrate at least five points, and log every practice reading so you know your device's real error. With 50 minutes, budget roughly 5 minutes for the salinometer reading and divide the rest evenly across Parts I to III.

How tournaments test this

The public archive holds 2,782 Water Quality questions from the 2019–20 and 2020–21 seasons, and the event bank holds 3,511. These seasons used a mix of freshwater and marine content, so treat them as practice for mechanisms, not as a guide to the 2027 balance.

In the archive, free response is about 53% of questions, multiple choice about 31%, true/false about 8%, multiple select about 5% and numeric about 3%. About 61% are Division C. The largest task types are "explain why" and "which of the following" (about 10% each); calculations and data interpretation are each a few percent. Among tagged questions, pollutants, nutrients, pH, dissolved oxygen and salinity lead. "Coral" appears in about 600 prompts and "aragonite saturation" in about 80, so reef chemistry is well established.

The most common keyed answers are directions ("decrease," "increase") and interaction types ("mutualism," "commensalism"), followed by "calcium carbonate," "dissolved oxygen," "dinoflagellates" and "eutrophication." Practice predicting the direction of a change and naming the mechanism.

Several 2027 items (TEK, life history, PFAS, recently killed coral, HABs and the coral reef organism list) have little archive coverage, so practice them with the worked examples here and with current NOAA and EPA material.

Test yourself

These are archived questions with official keys, each re-solved by hand. Work each one before opening the link.

Test yourselfTest yourself: water chemistry and monitoring

0 / 0 correct

1. 1

   What are the units for pH?

   Question 1 options

   Amg/LBMCmMDmolesEg/LFIt is a unitless quantity

   From: MIT Invitational, 2020-21, Division C

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Test yourselfTest yourself: nutrients and the nitrogen cycle

0 / 0 correct

1. 1

   Poorly-treated sewage and runoff from garden fertilizer can cause eutrophication. This is due to what components in the sewage/runoff?

   Question 1 options

   AFecal coliformBSedimentCPhosphates/NitratesDOrganic molecules

   From: Sierra Vista Invitational, 2020-21, Division B

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Test yourselfTest yourself: estuaries, treatment and applied issues

0 / 0 correct

1. 1

   In a partially mixed estuary salt water is mixed ____ and freshwater is mixed ____.

   Question 1 options

   Adownward, upwardBupward, downwardChorizontally, verticallyDvertically, horizontally

   From: Case Western Reserve University Invitational, 2020-21, Division C

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Test yourselfTest yourself: reefs and marine life

0 / 0 correct

1. 1

   Which of the following are true about atolls?

   Question 1 options

   AThey are generally considered precursors to barrier reefsBTheir formation process is more complex than the theory put forward by DarwinCThe central lagoon was formed through a mass extinction eventDGenerally, calcareous algae are considered good for reef formation, while filamentous algae are not
   Check answer

   From: Troy Invitational, 2020-21, Division B

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References and further reading

• Science Olympiad, soinc.org: the 2027 rules manual, general rules (calculator classes, eye protection) and official clarifications.
• NOAA Ocean Service, oceanservice.noaa.gov: estuaries, ocean acidification, hypoxia and harmful algal blooms.
• NOAA Coral Reef Watch, coralreefwatch.noaa.gov: heat stress and bleaching alerts.
• NOAA Ocean Acidification Program, oceanacidification.noaa.gov: carbonate chemistry and aragonite saturation.
• Reef Check, reefcheck.org: the reef survey protocol, indicator organisms and substrate categories including recently killed coral.
• USGS Water Science School, usgs.gov: dissolved oxygen, pH, turbidity, conductivity and the water cycle.
• EPA, epa.gov/pfas and epa.gov/nutrientpollution: PFAS drinking-water standards and nutrient pollution.
• EPA, Volunteer Estuary Monitoring: A Methods Manual: field and lab procedures for estuary water-quality parameters.
• OpenStax, Biology 2e, openstax.org: population ecology (life tables, survivorship, r and K), community ecology and nutrient cycles.
• SciOly Wiki, scioly.org: community notes on the event; check them against the 2027 rules.