Today…
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Hydrologic cycle
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General origins of solutes
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Reservoirs, fluxes, transient, steady state
processes
Atmospheric deposition, surface water,
groundwater
Other types of water…
Terminology - hydrologic cycle
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Reservoirs = location of mass:
H2O cycle: glacier, lake, ocean, river etc.
 Gases (atmosphere)
 Solutes in water etc.
Flux = transfer of mass between reservoirs
 Water, other fluids, solutes
 Units = mass per area per time ( e.g.,
m3/m2/yr)
 Requires physical transport – advection and
diffusion, both water and solutes
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Major H2O reservoirs
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Three phases (gas, liquid, solid)
Free H2O only (not hydrated minerals)
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97% in oceans
2% in ice (solid)
Melting would raise sealevel by 2% (about 80 m)
 Greenland alone would raise sealevel ~7 m
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1% in ground water
0.01% in streams and lakes
0.001% in atmosphere (vapor)
Continental ice sheets and sea level
East AAIS
(52 m)
Gainesville (your
house) elevation ~2030 masl
West AAIS
(5 m)
Greenland IS
(7m)
Modern Sea level
More or less to scale…
including whale
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Steady state system:
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One that has invariant concentrations through
time
Fluxes: Input = output
Often can be described by equilibrium
conditions (thermodynamics)
Transient system:
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Abundances within reservoirs variable with
time
Fluxes variable with time
Transient systems
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Can be described by “Response time”
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The amount of time for mass to change to
certain value
Typically doubling or halving.
Sometimes considered “e-folding time”
Amount of time for exponentially growing quantity
to increase by a factor of e.
 Exponential decay = time to decrease by a factor
of 1/e
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Transient conditions
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Transient systems described by kinetics
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Much more complicated than equilibrium
chemistry
No real theoretical basis – largely empirical
Based on reaction rate reaction coefficients
Hydrologic cycle
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Hydrologic cycle = closed loop of the flux
of water
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E.g., all reservoirs and all fluxes
May be steady state or transient
Box models
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Convenient way to describe reservoirs and fluxes
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Three reservoir box
model
Fluxes and
abundances of water
Does this model
represent all
fluxes/reservoirs?
More descriptive box model
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Same as previous
model except finer
resolution
Provide
more/better info
on system
Harder to
parameterize
Example: Sea level rise since LGM
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At these space and time scales, global
hydrological cycle is transient
Smaller scale may be considered steady
state
Lambeck et al., 2014, PNAS
Projected Greenland contributions to SL
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Clearly not steady state
Surface mass balance and
outflow projected for 21st
century
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Red – mass loss; blue – mass
gain
Purple and green – equilibrium
lines at start and end of 21st
century
Insets – model estimates
contributions from outlet
glaciers & entire ice sheet
IPCC, 2013 5th AR
IPCC Global Carbon Cycle
Perturbation
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Perturbation
Black – fluxes and reservoirs - pre 1750
Red – Anthropogenic induced fluxes
Includes weathering – but limited to silicate minerals
Solomon et al., (eds) IPCC report 2007
Residence Time
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Average time that material is in reservoir
Only systems in steady state
Definition:
t= A/J
Where:
A = abundance (not concentration) of material
(units of mass)
J = flux (in or out of reservoir) of material
(units of mass/time)
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Example:
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What is t of students if 6 students/hr enter
room with 6 students?
t = 6 students/6 students/hr = 1 hour
Global hydrologic and solute
cycling
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Hydrologic cycle depends on processes
transferring water to and from reservoirs
Solute cycles depend on the compositions
of water
Thus… useful to think about what controls
concentrations within reservoirs of the
hydrologic cycle
Constant
composition?
Precipitation
Solutes?
Reaction
zones
Recirculated
seawater/MOR
Fluxes in hydrologic cycle – this figure is for water.
How would dissolved mass be included in this?
Water chemistry and the
hydrologic cycle
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Atmosphere
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Streams & Groundwater
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Rain + other depositional processes
Starting point – what controls composition?
Water/rock interactions – greatest amount of
alteration
Meteoric vs non-meteoric water
Oceans – constant salinity, constant
composition for some solutes
Composition of Water
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Chemical
composition
of water
Reaction: A = B
Langmuir, 1997
Begin to quantify
changes in
composition –
kinetics &
thermodynamics
A = # of moles
V = volume
dNA = fluxes of A in and out
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Importance
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Dissolution of gases (e.g., CO2)
Dissolution of solid phases – porosity
Precipitation of solid phases – cements
Coupled with hydrologic cycle - controls
flux of material
Controls on rainfall compositions, dNA
Rain water chemistry
Na+ concentrations
• What might be the most
likely source for Na and Cl?
Cl- concentrations
• How could you test to see
if this hypothesis is true?
• What are implications if this
is true, e.g. what and where
are other sources?
Ca Concentration
Sources of Ca
other than
marine aerosols
Relative concentrations, Rainfall
Note – total
concentrations differ
between samples
Pollution – H2SO4
Gypsum dust
Close to ocean
composition but still
modified
SO4 matches pH – H2SO4
SO4 matches Ca
SO4 marine influence –
dimethyl sulfide
Temporal variations
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During storm
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Rain starts salty, becomes fresher during
storm as moves from ocean – ultimate source
of water/aerosols
O and H isotopes also change during storm
Snow melt initially saltier & lower pH
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change in melting temperature
Fractionation factor, Fc
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Determine amount of dissolved mass from
sea spray and aerosols
Where:
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C
( ) sample
FC  Cl
C
( ) seawater
Cl
C is dissolved component, Cl is chloride
composition of sample or seawater
Similar idea (ratio of ratios) in isotopes
Other atmospheric sources
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Rainfall is not the only mechanism to deposit
material from atmosphere to land surface
Aerosol – suspension of fine solid or liquid in gas
(e.g. atmosphere)
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Examples – smoke, haze over oceans, air pollution, smog
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Dry deposition – aerosols
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Occult deposition
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Sedimentation of large aerosols by gravity
More general term - Dry deposition plus
deposition from fog
Dry and Occult deposition difficult to
measure
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Atmospheric deposition of material called
“Throughfall”
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Sum of solutes from precipitation, occult
deposition, and dry deposition
A working definition
Data Available
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National Atmospheric Deposition Program
http://nadp.sws.uiuc.edu/
Compositional changes resulting from
throughfall – NE US
• Open boxes –
throughfall
composition
• Shaded boxes –
incident
precipitation
composition
• Note – only H+
greater in
precipitation
Surface and Groundwater
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Atmospheric deposition leads to surface
and ground water
Variety of processes alter/move this
water:
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Gravity
Evaporation
Transpiration (vegetative induced
evaporation)
Evapotranspiration
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Movement across/through land surface
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Overland flow – heavy flow on land surface
Interflow – flow through soil zone
Percolate into ground water
Conceptualization of water flow
Important to consider how
each of these flow paths
alter chemical compositions
of water
Throughfall
Examples of changing chemistry
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Plants
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Soil/minerals
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Provide solutes, neutralize acidity, extract N
and P species
Dissolve providing solutes
Evaporation
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Increase overall solute concentrations
Elevated concentrations lead to precipitation
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Salts/cements
Stream Hydrology
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Baseflow
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Augmentations of baseflow
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Ground water source to streams
Allow streams to flow even in droughts
Interflow, overland flow, direct precipitation
Result in flooding
Chemical variations in time
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caused by variations in compositions of
sources
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Bank storage
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Flooding causes hydraulic head of stream to
be greater than hydraulic head of ground
water
Baseflow direction reversed
Water flows from stream to ground water
Hyporheic flow
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Exchange of water with stream bed and
stagnant areas of stream
Nutrient spiraling – chemical changes in
composition because changing reservoir
Stream compositions
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Generally little change downstream
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Changes usually biologically mediated
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Short residence time in stream
Little contact with solids
Nutrients (N, P, Si) uptake and release
(Nutrient spiraling)
Pollutants
Chemistry changes with discharge
Chemistry changes with exchange of GW
and SW
Diel stream
variations
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Example from
Ichetucknee River
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Clear water – high solar
radiation
Solar radiation changes
Nutrient and DO change
SpC, pH and Ca change
All sub-aqueous plant
mediated
De Montety et al., 2011, Chem. Geol.
Stream water composition
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USGS provide stream water quality data
across US
URL is
http://nwis.waterdata.usgs.gov/nwis
Ground water
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Unconfined example
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Porosity – fraction of total solid that is void
Porosity filled w/ water or water + gas
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Vadose zone – zone with gas plus water
(unsaturated – can be confusing term)
Phreatic zone – all water (saturated zone)
Water table – separates vadose and phreatic
zone
Groundwater flow
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Flow through rocks controlled by
permeability
Water flows from high areas to low areas
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Head gradients
Water table mimics land topography
Flow rate depends on gradient and
permeability
Confined aquifers
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Regions with (semi) impermeable rocks
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Confining unit
Confined aquifers have upper boundary in
contact with confining unit
Water above confining unit is perched
Level water will rise is pieziometric surface
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Hydrostatic head
Effects of confinement
Perched aquifers,
springs, water table
mimic topography
GW withdrawal
lowers head
Other types of water
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Meteoric water – rain, surface, ground
water
Water buried with sediments in lakes and
oceans
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Formation waters
Pore waters
Interstitial water/fluids
Typically old – greatly altered in composition
Other water sources
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Dehydration of hydrated mineral phases
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Water from origin of earth – mantle water
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Clays, amphiboles, zeolites
Metamorphic water
Juvenile water
Both small volumetrically; important
geological consequences