There's Chemistry in our Rivers! Quiz

Answer: Oxygen (O2)

Oxygen is required by almost all organisms (e.g. mammals, fish, invertebrates) for respiration. Some bacteria actually thrive in oxygen-free conditions.

Answer: All three of these

ALL gases present in the atmosphere are in dynamic equilibrium with the aqueous phase. Gases diffuse across the air-water interface. All of these gases (plus many others) are in the atmosphere.

Answer: True

If oxygen is being produced by photosynthesis within the water column at a rate faster than the 'excess' can diffuse across the water-air interface, then concentrations much greater than 100% theoretical solubility can easily occur. Algal blooms can often generate this phenomenon.

Answer: IV and III

When O2 is present, metals are usually in their highest common oxidation states. For both metals, this results in solid substances - iron(III) oxide and manganese(IV) oxide.

Answer: N and P

Nitrogen and phosphorus are essential elements for biosynthesis of new cellular material. Much effort is directed towards restricting and reducing concentrations of these elements in order to mitigate excessive plant growth e.g. to control algal blooms.

Algal growth rate can occur at the physiological maximum allowed by their metabolism - this is usually temperature dependent, so they grow faster in warmer temperatures than colder temperatures but only up to a certain maximum above which protein denaturation starts occurring.
However, optimal growth at this physiological maximum often does not occur because one of the components needed for growth is simply too scarce. This then becomes the limiting feature/nutrient. By far the most common limiting nutrients are nitrogen and phosphorus. Why? Because these are essential for growth (to form DNA, proteins etc) but are not always present in abundant supply in the water. Carbon, hydrogen and oxygen are also essential, but the carbon comes from almost limitless dissolved carbon dioxide, and hydrogen and oxygen from the water itself.
If this sounds a little strange, perhaps the following analogy might help. Imagine you are creating an assembly line for building cars. You need a car body, an engine and wheels. There are lots and lots of engines and car bodies and a few wheels. You start the assembly line and the first few cars are made. However, soon, the assembly line grinds to a halt because the next car to be made doesn't have any wheels. Eventually some more wheels arrive from the supplier, and the assembly line starts up again creating more cars. But then once again, the wheels run out and the assembly line stops. In this instance the wheels are the limiting factor (or in the case of the algae, the limiting reagent).

Answer: ammonia or ammonium

Ammonia (or ammonium) is the preferred nitrogen substrate for cellular growth as it is readily converted in amino acids for protein synthesis. Urea and nicotine need to be converted to ammonia first (requiring energy). Some cyanobacteria can use N2 for synthesis but again this is energetically costly as it needs to be converted to ammonia first.

Answer: Hydrogen sulfide (H2S)

Rotten egg gas is produced from the anaerobic decomposition of organic matter by bacteria. It is much more common in coastal areas where there is a higher concentration of the starting material (sulfate) from sea water. Methane is also produced under such anoxic conditions but is generally suppressed when the sulfate concentration exceeds ca. 1 mM. I made nitrogen sulfide up!

Answer: A substance that minimizes change in pH when an acid or base is added

A buffer is a substance that typically has significant proportions of both acid and base forms present. When another acid or base is added to the water, this causes a change in the relative proportions of the buffer's forms which in turn minimizes induced change in pH. If the pKa of the buffer is 5 and an acid is added, then the final pH will be a little less than 5 (this is NOT closer to neutral).

Answer: No

This is tricky! While the bacteria change the rate of a reaction (as do catalysts), they do not fit the second part of the definition (to remain unchanged by the process). Bacteria use the energy derived from the reaction to perform metabolic functions including growth. Hence they change.

Answer: It will make the water more acidic (lower pH)

Increasing atmospheric CO2 will increase the concentration of CO2 in the water. This CO2 forms carbonic acid (H2O + CO2 -> H2CO3). The carbonic acid dissociates to H+ (acid) and bicarbonate (HCO3-). Higher H+ concentrations equate to lower (more acidic) pH. The effect might sound small but scientists are already concerned about increasing acidity causing loss of coral reefs.

For more information see http://www.ocean-acidification.net/FAQeco.html