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Today…
Hydrologic cycle Reservoirs, fluxes, transient, steady
state processes General origins of solutes
Atmospheric deposition, surface water, groundwater
Other types of water…
Terminology - hydrologic cycle
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
Major H2O reservoirs
Three phases (gas, liquid, solid) Free H2O only (not hydrated
minerals) 97% in oceans 2% in ice (solid)
Melting would raise sealevel by 2% (about 80 m)
Greenland alone would raise sealevel ~7 m 1% in ground water 0.01% in streams and lakes 0.001% in atmosphere (vapor)
East AAIS (52 m)
Gainesville (your house) elevation ~20-30 masl West AAIS
(5 m)
Greenland IS(7m)
Modern Sea level
Continental ice sheets and sea level
More or less to scale… including whale
Steady state system: One that has invariant concentrations
through time Fluxes: Input = output Often can be described by equilibrium
conditions (thermodynamics) Transient system:
Abundances within reservoirs variable with time
Fluxes variable with time
Transient systems
Can be described by “Response time” 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
Transient conditions
Transient systems described by kinetics Much more complicated than
equilibrium chemistry No real theoretical basis – largely
empirical Based on reaction rate reaction
coefficients
Hydrologic cycle
Hydrologic cycle = closed loop of the flux of water E.g., all reservoirs and all fluxes May be steady state or transient
Box models
Three reservoir box model
Fluxes and abundances of water
Does this model represent all fluxes/reservoirs?
Convenient way to describe reservoirs and fluxes
More descriptive box model
Same as previous model except finer resolution
Provide more/better info on system
Harder to parameterize
Example: Sea level rise since LGM
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 Clearly not steady state Surface mass balance and
outflow projected for 21st century 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
Solomon et al., (eds) IPCC report 2007
Black – fluxes and reservoirs - pre 1750 Red – Anthropogenic induced fluxes Includes weathering – but limited to silicate minerals
PerturbationPerturbation
Residence Time 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)
Example: 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
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
Fluxes in hydrologic cycle – this figure is for water.How would dissolved mass be included in this?
Pre
cipit
ati
on
Recirculated seawater/MOR
Sublimation
Solutes?
Constantcomposition?
Reaction
zones
Water chemistry and the hydrologic cycle
Atmosphere Rain + other depositional processes Starting point – what controls
composition? Streams & Groundwater
Water/rock interactions – greatest amount of alteration
Meteoric vs non-meteoric water Oceans – constant salinity, constant
composition for some solutes
Composition of Water Begin to quantify
changes in composition – kinetics & thermodynamics
Langmuir, 1997
Chemical composition of water
A = # of molesV = volumedNA = fluxes of A in and out
Reaction: A = B
Importance 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 chemistryNa+ concentrations
Cl- concentrations
• What might be the most likely source for Na and Cl?
• 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?
Relative concentrations, Rainfall
Pollution – H2SO4
Gypsum dust
SO4 matches Ca
SO4 matches pH – H2SO4
SO4 marine influence – dimethyl sulfide
Close to ocean composition but still modified
Note – total concentrations differ between samples
Temporal variations
During storm 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 change in melting temperature
Fractionation factor, Fc
Determine amount of dissolved mass from sea spray and aerosols
Where: C is dissolved component, Cl is chloride
composition of sample or seawater Similar idea (ratio of ratios) in
isotopes
seawater
sample
C
)Cl
C(
)Cl
C(
F
Other atmospheric sources
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) Examples – smoke, haze over oceans, air pollution,
smog
Dry deposition – aerosols Sedimentation of large aerosols by
gravity Occult deposition
More general term - Dry deposition plus deposition from fog
Dry and Occult deposition difficult to measure
Atmospheric deposition of material called “Throughfall” Sum of solutes from precipitation, occult
deposition, and dry deposition A working definition
Data Available 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
Atmospheric deposition leads to surface and ground water
Variety of processes alter/move this water: Gravity Evaporation Transpiration (vegetative induced
evaporation) Evapotranspiration
Movement across/through land surface Overland flow – heavy flow on land
surface Interflow – flow through soil zone Percolate into ground water
Conceptualization of water flow
Through-fall
Important to consider how each of these flow paths alter chemical compositions of water
Examples of changing chemistry
Plants Provide solutes, neutralize acidity,
extract N and P species Soil/minerals
Dissolve providing solutes Evaporation
Increase overall solute concentrations Elevated concentrations lead to
precipitation Salts/cements
Stream Hydrology Baseflow
Ground water source to streams Allow streams to flow even in droughts
Augmentations of baseflow Interflow, overland flow, direct
precipitation Result in flooding
Chemical variations in time caused by variations in compositions of
sources
Bank storage 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
Exchange of water with stream bed and stagnant areas of stream
Nutrient spiraling – chemical changes in composition because changing reservoir
Stream compositions Generally little change downstream
Short residence time in stream Little contact with solids
Changes usually biologically mediated 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
Example from Ichetucknee River 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
USGS provide stream water quality data across US
URL is http://nwis.waterdata.usgs.gov/nwis
Ground water
Unconfined example Porosity – fraction of total solid that is
void Porosity filled w/ water or water +
gas 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
Flow through rocks controlled by permeability
Water flows from high areas to low areas Head gradients
Water table mimics land topography Flow rate depends on gradient and
permeability
Confined aquifers
Regions with (semi) impermeable rocks 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 Hydrostatic head
Effects of confinement
GW withdrawal lowers head
Perched aquifers, springs, water table mimic topography
Other types of water
Meteoric water – rain, surface, ground water
Water buried with sediments in lakes and oceans Formation waters Pore waters Interstitial water/fluids Typically old – greatly altered in
composition