Aquatic Layers
Water Density
• Water is odd in that it becomes less dense when
forms a solid
• Water, like
other liquids,
gets more
dense as it
gets cold until
4 °C.
• This results in
water
stratification.
Thermohaline Circulation
• epilimnion
– near O2 saturation
– high biological activity
– oxidized=stable (CO2 , NO3- , SO42-, etc.)
• hypolimnion
– near anaerobic
– decay processes rule
– reduced=stable (CH4 , NH3 , H2S, etc.)
Thermohaline Circulation
• Density is affected by
– Temperature: as T↓ density ↑
– Salinity: as S↑ density ↑
• Salinity: equiv. g of solute per 1 kg of
seawater
– Given a unit of ‰, which is parts per
thousand
– Salinity varies widely from freshwater to
seawater.
Solute Distribution
Salinity
• Rain dissolves ionic and covalent compounds
while on land and delivers them to the oceans.
– Salinity remains relatively constant because of Ksp
– The ocean has a limitless supply of carbonate, so
as more Ca, Mg, Fe enter the ocean they
precipitate and form sediment.
CaCO3(s) ⇌ Ca2+(aq) + CO32-(aq)
• ocean (30 - 40 ‰ salinity)
• surface/ground water (5 ‰ salinity)
Salinity Calculation on CAPA
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Dissolved oxygen
Thermal Pollution
• One of the most important parameters of water
quality is dissolved oxygen (DO)
• Henry’s law governs the DO level in solution
• Because DO goes↓ when T goes ↑, industrial
facilities that use surface water for cooling
machinery cause thermal pollution even though
the water is “clean” when it leaves the facility.
• North Anna nuclear power plant is an example.
– they built an artificial lake, and use half of it
• DO solubility depends on temperature and
salinity
– As T ↑ DO ↓
As S ↑ DO ↓
USGS DO table
DO worksheet
The Carbon Cycle
The Carbon Cycle
• Atmosphere: you already know this
• Form groups and draw a picture of the three
sectors of the environment
– Identify the major reservoir in each
– Identify major reactions/transformations in each
• Both biotic, abiotic, and anthropogenic
– Identify how each sector interactions via carbon
transport
The Carbon Cycle
• Atmosphere & Lithosphere
– Respiration, decomposition, plant emissions, fires,
anthropogenic combustion
• lithosphere → atmosphere
– Photosynthesis
– All carbon (HCs, VOCs, etc.) all get oxidized by OH
to become CO2.
• Lithosphere: you already know this
– Microbes decompose organic matter
• Acidogenesis, acetogenesis, hydrolysis, respiration
• large biomolecules → small biomolecules → CO2
– Inorganic carbon in limestone, representing about
99% of the total carbon on Earth.
The Carbon Cycle
• Hydrosphere & Lithosphere
– Decomposition, Ksp , anthropogenic pollution
• lithosphere → hydrosphere
– Sedimentation, anthropogenic pollution
• hydrosphere → lithosphere
• atmosphere → lithosphere
• Atmosphere & Hydrosphere
– Respiration, decomposition, biotic emissions
• hydrosphere → atmosphere
– Photosynthesis, diffusion (KH)
• atmosphere → hydrosphere
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Carbon in Water
The Carbon Cycle - Hydrosphere
• Organic carbon: 3% of hydrospheric total
– Similar to lithosphere: biomolecules of various size,
microbial processes
• Inorganic carbon (CO32- and HCO3-) 97%
40-45% of anthro. emissions stay in atmosphere
20-35% get absorbed in the hydrosphere
20-40% get absorbed by the biosphere
– Thus, the enhanced greenhouse effect is half muted
by about 150-200 ppm (280 is pre-industrial, 400
ppm is current)
– Oceans convert CO2 to carbonic acid
• terms
– OC: organic carbon
– OM: organic matter
– TOC: total organic carbon
– NOC: natural organic carbon
– DOC: dissolved organic carbon
– POC: particulate organic carbon
– BOC: biodegradable organic carbon
• Most carbon adds BOD to the water
• Inorganic C (+4 ox. state); Organic C (-4,-2 ox.)
Humic Acids – just like soap
• OM allows the retention of other molecules
– it is hydrophilic enough to complex metals with its
carboxylate, oxygen, and nitrogen groups making
metals much more soluble
– they have large hydrophobic regions in which retain
hydrophobic chemicals
– if the HM is soluble, then retained molecules are also
– if the HM is in the sediment, then retained chemicals
are there
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