Aquatic Environment & Health Mgmt

The word 'Tsunami' is of Japanese origin, derived from two kanji characters: 'tsu' (津) meaning 'harbour' and 'nami' (波) meaning 'wave'. It refers to a series of extremely long-wavelength ocean waves generated by sudden tectonic displacement of water (subsea earthquakes, landslides, or volcanic eruptions).

Option analysis:

• Tsunami: Correct, literally translates to 'harbour wave' from Japanese.
• Hurricane: Derived from Taino word 'Huracan', meaning evil spirit of wind.
• Cyclone: Coined from Greek 'kyklos', meaning coiled snake or wheel.
• Seiche: French-Swiss term for standing waves in enclosed water bodies.

By definition, one percent ($1\%$) represents 1 part in 100 parts, which equals $10,000$ parts in one million parts ($1\% = 10,000\text{ ppm}$). Therefore, a concentration of $0.1\%$ is calculated as:

Option analysis:

• $1\text{ ppm}$: Equivalent to $0.0001\%$.
• $10\text{ ppm}$: Equivalent to $0.001\%$.
• $100\text{ ppm}$: Equivalent to $0.01\%$.
• $1000\text{ ppm}$: Correct, equivalent to $0.1\%$.

In physical limnology, Holomictic lakes are lakes where the water column undergoes complete circulation and destratification (overturn) from the surface to the maximum bottom depth at least once a year, establishing complete isothermal and uniform density conditions throughout. This contrasts with Meromictic lakes, where a dense bottom saline layer (monimolimnion) never mixes with upper waters.

Option analysis:

• Polymictic Lakes: Mix frequently or continuously due to shallow depth and wind.
• Dimictic Lakes: Specific subgroup of holomictic lakes that mix twice a year (spring and autumn).
• Monomictic Lakes: Subgroup of holomictic lakes that mix once a year.
• Holomictic Lakes: Correct, standard broad limnological classification for lakes that achieve completely uniform temperature and density throughout the entire water column during mixing periods.

Water hardness is caused by multivalent metallic cations (primarily $Ca^{2+}$ and $Mg^{2+}$). It is divided into:

• Temporary (carbonate) hardness: Caused by calcium and magnesium bicarbonates ($Ca(HCO_3)_2$ and $Mg(HCO_3)_2$), which decompose and precipitate as insoluble carbonates upon simple boiling.
• Permanent (non-carbonate) hardness: Caused by chlorides ($CaCl_2, MgCl_2$), sulfates, and nitrates/nitrites, which cannot be precipitated by boiling and require chemical softening (such as soda ash or ion-exchange).