Today… Hydrologic cycle Hydrologic cycle Reservoirs, fluxes, transient, steady state processes Reservoirs, fluxes, transient, steady state processes General.

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?

Ca Concentration

Sources of Ca other than marine aerosols

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

Other water sources

Dehydration of hydrated mineral phases Clays, amphiboles, zeolites Metamorphic water

Water from origin of earth – mantle water Juvenile water

Both small volumetrically; important geological consequences