PHYSICAL PROPERTIES OF WATER
(Disclaimer: these are lecture outlines with some figures; these are not
lecture notes)
MATTER IN WATER
* dissolved gases
* inorganic ions
* free organic molecules
* inorganic particles (clays, silts...)
* detritous
* living cells
Everything can not be measured easily as separate entities.
contributions of major fractions are easier to estimate.
But
Measurements used to characterize matter in water:
Total solids
-Total dissovled (filtrable) solids - solids that pass through a GFC
filter, 0.8 µm
-Total suspended (nonfiltrable) solids - solids that are retained on a
GFC filter
-Settable solids
-non-settable suspended solids
Clay
Silt
Sand
<2 µm
14 days to sink 5 cm water
2-20 µm
3.5 days
20-2000 µm 1.5 second
Overlap:
Both dissolved and suspended solids can be measured gravimetrically
Much of the fraction that is dissolved, can be estimated by conductivity.
Conductivity (specific conductance) - the capacity of a solution to
conduct electrical current. Estimates total dissolved
Much of the fraction that is suspended, can be estimated by measuring
light properties. Obviously then, suspended solids affect light and
temperature in natural waters.
LIGHT
Important in:
* primary production
* germination
* navigation and breeding in animals
* absorption produces heat
Fate of light in aquatic systems:
* Reflection - prevented from entering water by air-water surface
interface
* Angle of incidence
* Cloud conditions
* Surface waves
* Ice
* Scattering - suspended particles reflect light at a massive array of
angles
* Absorption - diminution of light by transformation into heat energy
Effects water and matter on wavelength transmission:
380
UV
400
460 520
580 620
violet
blue green
infrared-->thermal
680
820
yellow
1050 nm
orange red near IR
Light entering pure water:
* longer visable light (reds) absorbed shallower
Light entering lake water with other matter:
* organic cmpounds - often absorb blues and greens
* silts and clays - reds and oranges pentrate deeper, more likely to be
reflected/scattered
* phytoplankton chlorophyll - green not absorbed by Chl a
Turbidity - an expression of the optical properties that cause light to
be scattered and absorbed rather than transmitted in a straight line.
Turbidity is primarily caused by total suspended solids but a direct
relationship is varies from system to system. Why?
Nephlometer measures intensity of light scattered at 90°.
Vertical illumination (light penetration) - illumination at some depth as
measured by underwater photometer.
Light is absorbed exponentially with depth (a constant percentage of
light available is extingushed at each meter)
Iz = Io e-kz
where:
Io = intensity of light at surface
Iz = intensity of light at depth z in meters
k = vertical absorption coeficent
When plotted as depth vs log % incidence of light, line is straight in a
homogeneous solution.
What would a deflection in the line indicate?
Visibility - measure of the depth at which one can see into the water.
Measured by Secchi disc.
What factors affect this estimate?
Visibility can be used to estimate:
1. Compensation depth can be estimated from secchi depth if photometer
unavailable (secchi depth more constant thru day than photometer which is
dependent on angle of sun). Respiration exceeds photosynthesis within a
cell at about 1% of incident surface light (not absolute, some plants
shade apdapted, e.g. under ice). the region from the surface to where
99% of light has disappeared is the euphotic zone.
1% level = 2.7 (ZSD)
(3.0 use as rule-of-thumb)
(ZSD
is at 21%)
(2.1 for small piedmont impoundments)
?????
2. Carlson's Trophic State Index - 10 TSI units represents ~ 3X algae.
Based on empirical relationship between Chl a, SD, and phosphorus
TSI
= 60 - 14.41 ln SD
3. Non-algal turbidity (a) for SE lakes
a = 1/SD - 0.02 B
where B= chl a in mg/m3
???????
Observations:
-Light is absorbed
-Light transperency/scattering differs between inputs and output.
Hypotheses and predictions:
2) Visability dependent on particle concentration
Predictions:
-secchi depth versus surface turbidity, chl, residue
3) Low flow allows sedimentation, phytoplankton production (examine
longitudinal gradients).
Predictions:
-higher Chl values in lake than river
-change in spectral transmission with depth and distance
related to chlorophyll
-change nonfilterable residue?
-decrease turbidity with distance
-increase turbidity at depth that matches river
temperature
-decrease sedimentation rates with distance
TEMPERATURE
Properties of water
* density-temperature relationship
* high specific heat
* high specific gravity
Predominant sources of water movement:
* wind
* waves
* currents
* seiches
* lanagmuir spirals
* internal waves
Why is there a temperature difference between lake inputs and output?
Sources of heat
* direct absorption of solar radiation - DOMINANT
* transfer of heat from air
* inflows
Sinks of heat
* specific conduction of heat to air
* evaporation
* outflow
If light and air are major sources of heat, where should water initially
be the warmest?
Should temperature depth profile match light?
What forces breakdown this gradient?
Stratification dependent on
wind (conduction and convection minor in comparison)
currents (minor in many natural lakes, perhaps not in many reservoirs)
basin morphetry (shallower basins more easily mixed)
What should the vertical profile look like if surface waters are heated
more rapidly than heat is distributed by mixing?
Consider:
-change in density with temperature (esp. exponential at warmer temp.)
-wind mixing. Weak wind mixing will only affect upper layers.
-exponential decline in light (heat)
Observations:
1) Temperature difference between inputs and output.
Hypotheses and predictions:
1)Water stratifies, water stratification depends on lack of
physical forces
Predictions:
-warm layers overlay colder with layer of rapid change
(thermal
stratification profile does not exactly match light
extinction).
- metalimnion deeper in protected areas and is
independent of
depth (or river versus shallow cove)
4) Depth of thermocline is dependent on light.
-turbid areas have shallow thermoclines
TEMPERATURE
X
X
decline in wind
DEPTH
X
decline in light with depth, but also
mixing forces.
X
At some depth, stablizing forces
due to density differences over come
mixing forces.
X
X
X
X
Epilimnion - an upper stratum of less dense, more or less uniformly warm,
circulating, and fairly turbulent
Hypolimnion - lower stratum of more dencs, cooler, and relatively
quiescent water lying below the epilimnion.
Metalimnion (thermocline) - the transitional stratum of marked thermal
change between the epilimnion and hypolimnion (formerly, >1¡C/m). Two
metalimnion can develop->storm and calm.
Wind energy needed can be calculated based on density difference (which
depends not only on relative temp. diff., but also absolute because of
non-linear temp-dens rel.)
Seasonal temperture profiles (introduce isopleths).
Spring. discussed above. Smooth decline early disrupted by storm event
that mixes upper layers, establishing a thermocline. Sudden gradient
between water masses makes further mixing very difficult.
Summer - metalimnion slowly sinks as surface water transfers heat
(conduction, convection, animal migration, ...)
Fall - heat loss at surface exceeds transfer of heat from hypo- to
epilimn.
Cool water a surface becomes more dense, destabilizinng
stratification, making it easier for lake to mix. FALL OVERTURN.
Winter - prior to ice formation, reverse stratification possible when
lake < 4¡C.
Amictic
no appreciable mixing permanent ice cover
Holomictic
complete mixing, > time
Monomictic once
temperate lakes remain >4¡C
Dimictic
twice
temperate lakes < 4¡C
Polymictic more than twice
tropical lakes->rainfall
Meromictic Permanently stratified
saline subsurface inflows or
very deep lakes
What would be the difference between a windy spring and a calm spring?
Cooler hypolimnion if calm due to rapid stratification?
(test question: In many lakes, the photic zone is a deep as the
thermocline. Why? Would you expect the thermocline to be deeper or
shallower than (or the same as) the photic zone in a clear lake? Why?)
What other factors might affect density?
particles
Thermal stratification determines
stratification of gases
nutrient availability
seperation of food web
...........
dissolved and suspended
Major concepts
1. Light diminishes with depth, the rate at which is determined by matter
suspended and dissolved within the water
2. As a result, absorbed light and IR radiation cause upper layers to
heat more rapidly.
3. As densities of various layers become different, some point is reached
at which wind energy is incapable of mixing all water resulting in two
major zones (mixed and nonmixed layers)
CHEMICAL COMPOSITION OF NATURAL WATERS
DISSOVLED GASES
Soluability dependent on:
- >temperature --- <soluabilty
- >atmospheric concentration ---- >soluabilty
-(salinity)
Oxygen
Why important?
-product of photosynthesis
-needed for aerobic respiration
Much of an aquatic organisms energy budget devoted (15% rather than 1-2%
in terrestrial organisms)
1. Saturation pt. lower (at 21%, 300 mg/l in air, 15 mg/l or ppm in water
at 0 C¡) Means organisms can effect oxygen levels
2. Water much more viscous
3. Diffusion 300,000X slower
-determines chemical state of nutrients. Reduced nutrients more
soluable and available. Most metals and nitrogen (e.g. Ferric is
oxidize as rust, insoluable, Ferrous is reduced, soluable).
What are the sources?
-photosynthesis - review
-atmosphere - concentration in air high, but diffusion low. Greatly
aided by wind mixing. Excessive mixing can cause supersaturation (not in
eequilibrium when energy removed) as in waterfall (also caused by rapid
temperature increase).
What are the sinks?
-respiration - review
animial as well as DECOMPOSERS (dependent on organic matter
determined by primary production, i.e. a lot of photosynthesis means
alot of respiration somewhere. Flucuation in rates dangerous)
-atmosphere - diffusion back.
Temperature affects concentration of oxygen
-solubility (Figure 7-4)
-diffusion?
-metabolism
(how might supersaturation occur?)
What will oxygen vertical profiles look like?
-windy, unstatified? no change with depth
-stratified?
Epilimnion->high oxygen due to:
atm. diffusion
abundant light for photosynthesis
Hypolimnion-> low oxygen due to:
low diffusion rates of a gas thru water from atmossphere
low light reducing photosynthesis (1%)
high organic matter resulting from
HYPOTHESES AND PREDICTIONS FOR OXYGEN
What factors will affect profile:
-temperature -> thermal stratification will result in inflection in
oxygen profile at the thermocline rather than a profile matching a light
profile. (also metabolism and solubility affected).
-light penetration -> very clear lakes will have light well below mixing
(thermocline) depth.
-depth -> more water for organic matter to be diluted in deep lakes.
(also determines availability of nutrients to epilimnion for
photosynthesis at overturn).
-nutrients and organic matter.
-unusual concentrations of organisms (bacterial plates requiring reduced
cmpds, decrease sedimentation rates of organic matter at cooler layers,
low-light adapted algae near to available nutrients)
-inflows and outflows
-photo-inhibition (bust shape curves)
What should a typical profile in Allatoona look like?
Bust-shaped (thermally stratified, significant turbidity,
relatively shallow, nutrient loading)
Considering factors that affect profiles, what should profiles along
Allatoona look like?
Upper reservoir with shallower, steeper inflection -> lower light
penetration and shallower thermocline, shallower bottom, direct nutrient
input from basin
Oligotrophic - Little or no oxygen stratification: clear, deep, low
nutrients resulting in low productivity. (possibly higher oxygen in the
hypolimnion due to lower temperatures) - Orthograde
Eutrophic - Strong oxygen stratification: shallow, turbid, high nutrients
resulting in high productivity. - Clinograde
Nutrients/organic matter available either as
autochthonous - shallow basin
allochthonous - pollutants from basin
(Mesotrophic)
All lakes, being at the bottom of their drainage basin, will collect
organic matter and sediments.
Thus not only more nutrients, but lake
shallower.
Should lakes move from Oligotrophic to Eutrophic, or vice-a-versa?
Process known a EUTROPHICATION. Though the ultimate fate of most lakes,
rates greatly influenced by human activity (sediments, nutrients). Why
is high productivity undesirable? (human influences usually not regular
resulting in booms and bust that natural systems have difficulty in
recovering).
Hypolimnetic Oxygen Deficit = Saturation - actual oxygen
proportional to amount of organic matter available and can be used as an
estimate of productivity of the epilimnion (assumes in-out flow and no
allochth.)
(for Lanier, OxDef. = spring DO - summer DO)
Seasonal aspects and fish kills
Summer deficit restricted to hypolimnion, but may be critical for fish
the low tolerance to high temp.
Winter deficit - snow cover - wind speeds and time of freeze critical.
(annual variation in lakes may be largely attributed unpredictable
weather).
Tolerances of organisms:
General critical level - 4 mg/l for 24 h to maintain a diverse assemblage
<2 mg/l - most organism die or become dormant
1-2 mg/l - organism must be phisiologically adapted (modified gills,
specialized blood pigments)
O mg/l - bacteria that utilize oxidized compounds such as nitrate rather
than free oxygen as an electron acceptor
CARBON DIOXIDE
(high soluablity)
Importance:
- Direct source of carbon for organic matter. Capable of up to four
bonds, allowing for a diversity of carbon chain molecules. Usually not
limiting except in ????
- Act as a buffer
- Global carbon cycle to atmosphere, green house effect - fertilizing
southern ocean with iron as a possible solution.
Sources
- Respiration (including plants and bacteria)
- Diffusion
- Limestone Rock runoff
- Entering ground water (bacterial decomposition and limestone)
Sinks
- Photosynthesis
- Diffusion
- Precipation of insoluable CaC03
Most carbon in aquatic systems occurs as equilibrium products of carbonic
acid, and a smaller amount as organic (dissolved, particulate detritial,
and living)
CO2 affects pH and pH affects CO2 .
(ph review: pH is a measure of hydrogen ion activity and is the
logarithm of the reciprocal of the hygrogen ion concentration (or
negative log of H+?). Thus pH below 7 acidic.
Disassociation of Carbon dioxide
(similar to blood)
H20 + CO2 <----> (h2CO3) <----> HCO3-1 + H+ <----> CO3-2 + H+
carbonic acid
bicarbonate
carbonate
.
^
(think of chemical equilibria as a balance, if you dump something on one
side, the equilibrium will shift to the other to maintain balance)
(bicarbonate and carbonate disassociate to establish equilibrium into
hydroxyl ions that result in alkaline waters in lakes and streams)
e.g.
increase CO2 :
equilibrium, both
(i.e. respiration)
---->
more H+ (lower pH) (because it reaches
decrease CO2 :
(i.e. photosynthesis)
<----
less H+ (higher pH)
increase acid
(a substance that
disassoc. H+)
<----
more CO2
CO2 and bicarb increase)
Thus:
at low pH (high H+):......
H20 + CO2 <----> (H2CO3) favored
at pH 6-10:........................
HCO3-1 favored
at high ph:....................... CO3-2 favored
graph of concentrations and ph
But, if more bicarb. and carbonate present, a greater number of hydrogen
ions needed to shift pH; solution is buffered.
A source of bicarbonate
is CaC03
CaC03+ H+ <----> Ca(HC03)2
insoluable
soluable
calcium carbonate calcium bicarbonate
Dissolves in ground water which is low in pH (high H+) due to repiration
in dark.
^CaC03
H20 + CO2 <----> HCO3-1 + H+ <---------> Ca(HC03)2
if Ca(C03)2 high, than addition of acid will cause shift to H20 + CO2
rather than shift in pH.
if respiration high (inc CO2), then H= formed by Co2 disassociation will
bond with calcium bicarcarbonate rather than being free and decreasing pH
((alkalinity will also increase?))
if CO2 removed (i.e. photosynthesis),
<------ shift to insoluable form
(Marl)
Alkalinity - the capacity of water to except protons (H+) (bad term
because acidic water still has capacity to accept some protons, instead
"the buffer capacity" or "power to combine with acid")
Three kinds of alk. indicated: carbonate, bicarbonate, and hydroxide
(latter is rare in nature, usually the result of contamination). Express
as CaCO3 ((but high alk. could be the result of either high CaCO3 in
water shed or high pH or high CO2))
Determined by tritration with a standard strong acid until pH at
inflection points reached (8.3 for carbonate and 4.5 for bicarb.)
Carbon dioxide calculated (difficult to measure because low saturation
pt. means waters often supersaturated and thus is often lost in any
handling)
unkown
aklalinity and pH tell you this side
of scale
H20 + CO2 <----> (h2CO3) <----> HCO3-1 + H+ <----> CO3-2 + H+
use equation of nomograph
Hardness characteristic of water representing the total conc. of calcium
and magnesium ions expressed as grams of CaCo3 per liter
Hardness should be less than or equal to carbonate and bicarbonate
alkalinity (OH- , hydroxide produced aklinity rare in nature, usually the
result of contamination) if hardness due to Ca and Mg.
Hardness greater than alkalinity if ions other than Mg and Ca not minor
(Fe, Al, Mn)
0-60 mg/L CaCO3 Soft (hard rock, e.g. granites)
61-120
Moderately high
121-180
Hard
>181
Very hard
hardness orginally measured as the capacity to percipitate soap.
(total hardness calculated by titration complexing Mg and Ca with EDTA;
Calcium same way but pH made high so MgOH percipitates; Mg by subtracting
Ca from total).
Bottom line:
-waters are going to vary in their ability to resist change in pH due to
hardness of water.
Thus, soft water lakes susceptible to acid rain
(Allatoona should show very low pH at bottom). Acid rain affects
contraversial in U.S., but not in Europe.
RECENT DATA???
-if aklanity high, but pH is low, there must be alot of CO2
-if you assume hardness does not vary greatly within a system, lower pH
is a rough indication of areas of higher respiration relative to
photosynthesis.
Hypotheis and Predictions
What will pH, aklanity, and CO2 depth profiles look like?
NUTRIENTS
Liebergs law of the minimum: at any given instant, any metabolic process
is limited by only one factor at a time. i.e. Limiting Nutrient.
Extended to population regulation, but probably not accurate in all cases
(e.g. predation and limiting nutrient could both limited population
growth). Also, there are upper limits at which a nutrient can become a
toxin. In case of nutrients and primary productivity, it works
relatively well.
Carbon usually not limiting because abundant. Carbon dioxide generally
easier to assimulate, but carbonic anhydrase higher in algae and certain
macrophytes that utilize bicarbonate. (aquatic mosses can utilize only
CO2, restricted to low pH and High CO2 such as in springs).
Magnesium - needed in chlorophyll molecule.
Calcium - needed in exoskeletons of inverts, possibly limiting in some
cases.
Phosphate - often limiting because:
-no gaseous phase, thus no nitrogen fixing equivalent
-often geochemically scarce (apatite)
-binds with soils in watershed, thus often limiting
plants require a N:P of 7:1 (by weight), 16:1 (by element)
needed in DNA, RNA, ATP
Usually low 20 ug/l wordwide average. 200-700 very high
Sources:
Natural - phospahate bearing rock - Ca3(PO4)2 and Ca5(PO4)F
(aptite)
Human - fertilizers, detergents, sewage, deforestation (most
nutrient inc drastically with clearing of land)
Forms:
TOTAL SOLUABLE PHOSPHORUS
1. Dissolved Phosphate (orthophosphate PO4-3, and ions of phosphoric
acid, usually di- and monohydrogen ions HPO4-2 H2PO4-1at pH<9) inorganic
- only form used by algal cells.
(soluable reactive phosphorus -SRP- typically procedures overestimates
Dis. Phosphate because may hydrolyze some organic forms)
2. Inorganic polyphosphates (minor?)
3. Dissovled organic phosphorus (total soluable phosphorus) Bulk of total
sol. phos. Believed to be mostly nucleic acids.
Made available to algal cells by their release of AKLANINE
PHOSPHATASE that removes orthophosphate groups (luxury consumption and
storage as osmotically-safe polyphosphate granuales also a means of
competing in a low phosphate environment).
TOTAL SOLUABLE PHOSPHORUS most phosphorus in FW tied up and not
available.
1. Phosphorous in living matter (bacteria, plant, and animal).
2. Phosphorous adsorbed by clays and other minerals
Diagram of Phosphorus
--------------------------------------------------------->sediment
Particulate P
---------> Zooplankton------->
feces---->sediment
(bact, phyto, detritus..)
Á
!Á
!
!
SRP
DOP
SRP
DOP
Phosporous also moves to sediment as detritous and feces
50% of P excreted by zooplankton is ortho. Therefore zooplankton, though
grazing algae may enhance and maintain phytoplankton populations at a
constant level (rather than boom and bust
Zooplankton excretion and utilization of micropatches by algae through
rapid uptake. Production rates excluding grazers higher than can be
obtained in lab with same nutrient levels. Stirred (versus unstirred)
culture take up less P-33.
Macrophytes take most P up through roots and release P into water column.
Conflict on the benefit of macrophytes (nutrient avaible vs reduce
turbidity and erosion, habitat).
mesotrophic, open lake eutrophic.
Recent abstract: littoral zone
Phosphate in the presence of iron and oxygen will precipate as iron
phosphate (FePO4)
(other more complex processes believed also to remove P from water
column, such a sorption to clays). Also detritus sinks.
Free oxygen tends to make nutrients insoluable and unavailable
Well areated, oligotrophic lakes:
insoluable complexes with Fe
well areated water (>1-2 mg/l)
(>250 mv redox i.e low electron act.)
_________________________________________________________________
Oxidized microlayer (brown) - insoluable complexes
----------------------------------------------------------------------------Anoxic layer - soluable reduced compounds that must diffuse through ox.
microlayer to become available (anoxic due to respiration, w/o
photosyn.) many free e-, (up to -100 mv)
Depth of soluability depends on nutrient.
Low oxygen, eutrophic lakes:
soluable iron (FeII - ferous) can diffuse from sediment to hypolimnion.
precipation of phosphate into ferric complexes is prevent
low DO water (<1-2 mg/l)
(<250 mv redox i.e high electron act.)
as fertile lakes supply organic matter for decompostion (i.e. respiration
only
_________________________________________________________________
Anoxic layer at sed-water interface - soluable reduced compounds diffuse
directly (1000X faster),
many free e-, (up to -100 mv)
During a mixing event (spring, fall) nutrients circulate, some P is
available as complexes reform. THE RESULT IS SPRING AND FALL ALGAL
BLOOMS (some leakage to epilimn. may occur in summer)
Very fertile lakes: usually shallow, small - most loading internal,
little permanant loww to sediment.
Fe becomes tied up that (precipated by sulfide ions produced by sulphate)
that P not even precipated in presence of oxygen
very low DO water (<1-2 mg/l)
(<-100 mv redox i.e high electron
act.)
_________________________________________________________________
Anoxic layer - soluable reduced compounds that must diffuse through ox.
microlayer to become available (anoxic due to respiration, w/o
photosyn.) many free e-, (up to -100 mv)
Postive feedback. More nutrients mean more production which lowers
oxygen in the hypolimnion which means nutrients more available. Also
more production means less light, shallow photic zone)
(additional feedbacks as sediments build and nutrients in sediment are
more easily available to epilimnion)
Lakes may be oligotrophic for long periods, then rapidly eutrophify. Can
be accelarated by adding nutrients, making the basin shallower, adding
allochthonous matter.
Models to predict P reductions based on loading, retention time to
estimate changes in productivity.
Nitrogen
needed for protein...
Sources:
-nitrogen fixation
-nitrates moves through soils, amonium ions retained by soil particles
Sinks:
-Denitrification
-Outflow
-Sedimentation
Tends to be limiting in ocean waters.
Organic forms
In FW, typically 50% in organic form. Free organics tend to be soluable,
mostly short peptides chains, probably not directly availble until
modified by bacteria and fungi. particulate N sink to sediment, which
are major N sinks.
Inorganic forms
Nitrogen gas N2 fairly inert, though can form bubbles in blood of fish
under superstauration
Nitrate NO3- most oxidized
Nitrite NO2- rare except where organic pollutants high
Ammonia NH4+ preferred for plant growth, energetically more efficient.
Form excreted by zooplankton, thus explaining sign. productivity even
when nitrate is low. At elevated pH, ammonium ions become toxic (NH3
gaseous)
--------bact. denitrification---------> N2
---------------->
(oxygen obtained,
needed as e- acceptor)
NO3
--nitrogen fixation------(nitrogen obtained
<------------Bacterial nitrification (energy obtained)--------chemosynthesis
NH4+
<-----------leaky plants?---- assimulated N-----ammonification--->
(bacterial and fungal
decomposition
animal excretion. energy
obtained
through aerobic respiration)
---------------------------> assimulated N <-----------------------
animal
plant <-----------------------------------------Places in an oxygen stratified lake:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
N2-->Assim N
AssimN-->NH3
oxygen
(greater, light)
----------------------------------------NH4--->NO2 -------------------------------------N2-->Assim N
AssimN-->NH3
low O2
(greater, gravity)
____________________NO3-->N2
__________________________________________________
Nitrogen fixation Denitrification
Nitrification
Amonification
sediment
requires absence
of O2, but can occur
anywhere due to
thick wall heterocysts
Few genera of B-G algae
e.g. Nostoc & Anabaena
Sulfer also oxidized at metalimnion for energy and reduced in hypolimnion
for oxygen as an e- acceptor.
Silica(SiO2)
A major component of diatom frustules (stable so used by
paleoloimnologist)
Feldspar in granite a source, so probably not limiting in Allatoona
In many lakes though, silica depletion may favor less desirable algae
Sulfur
Involved in availablity of P.
DO.
Presence of H2S indiciative of very low
Other trace nutrients
Debated, see book
chelators (change ionic of metals making them available)
Hypothesis and predictions:
Available nutrients (NH4, NO3, PO4) will be processed differentially in a
lake depending on oxygen levels and biological demand.
Predictions:
1) Vertical profiles.
2) Longitudinal gradients. Where would be a good place to test if average
lake values at the lower level of detection?
-phosphate will decline more rapidly downlake than nitrates (because N
uptake is slow, P sediments out, and P is likely to be limiting).
-ammonia will decline more rapidly downlake than nitrates (because N
uptake is slow) but increase further downlake as NH3 regenerated through
excretion and ammonification.
-chl a concentration should be proportional to at least one
nutrient (indicating the one that is limiting, to be tested the following
week).