LAKE ECOLOGY

LAKE ECOLOGY

Unit 1: Module 2/3 Part 5 - Major Ions and Nutrients January 2004

Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s2

Modules 2/3 overview

Goal – Provide a practical introduction to limnology

Time required – Two weeks of lecture (6 lectures) and 2 laboratories

Extensions – Additional material could be used to expand to 3 weeks. We realize that there are far more slides than can possibly be used in two weeks and some topics are covered in more depth than others. Teachers are expected to view them all and use what best suits their purposes.


Modules 2/3 outline

1. Introduction2. Major groups of organisms; metabolism3. Basins and morphometry4. Spatial and temporal variability – basic

physical and chemical patchiness (habitats)5. Major ions and nutrients 6. Management – eutrophication and water

quality


5. Water chemistry: Gases, major ions & nutrients


5. Water chemistry: Gases, major ions & nutrients

Gases Oxygen (O2) Carbon dioxide (CO2) Nitrogen (N2) Hydrogen sulfide (H2S)

Major ions (anions and cations) Nutrients (phosphorus and nitrogen)


Water chemistry: gases

What are the ecologically most important gases ? O2

CO2

N2

H2S


Gas solubility

The maximum amount of gas that can be dissolved in water (100% saturation) is determined by temperature, dissolved ion concentration, and elevation

solubility decreases with temperature“warm beer goes flat”

solubility decreases with higher dissolved ion content (TDS, EC25, salinity)

“DO saturation is lower in saltwater than freshwater (for the same temperature, solids “drive out” gases)


Water chemistry: O2

~ 21% of air Very soluble (DO) Highly reactive and concentration is dynamic Involved in metabolic energy transfers (PPr & Rn) Major regulator of metabolism (oxic-anoxic)

Aerobes (fish) vs anaerobes (no-fish, no zoops) Types of fish

Salmonids = high DO (also coldwater because of DO)

Sunfish, carp, catfish = low DO (also warmwater)


O2 variability

Diel (24 hr) variation due to ____________?

Seasonal variation due to _____________ ?


Major sources of O2

Sources Photosynthesis (phytoplankton, periphyton,

macrophytes) Air from wind mixing Inflows

tributaries may have higher or lower DOgroundwater may have higher or lower DO

Diffusion (epilimnion to hypolimnion and vice versa)


Major sinks of O2

Sinks Respiration

bacteria, plants, animals; water and sediments Diffusion to sediment respiration Outflow (tributary or groundwater)


Gases: wind mixing from storms

Oxygen from a storm – How many mixing “events” can you find for Halsteds Bay in Lake Minnetonka, MN in this 1 year record?


Gases: seasonal wind mixing

Oxygen varies seasonally and the entire water column lake may be fully saturated at certain times. How often did this happen in Ice Lake, MN in this 5+ year record?


O2: Human significance

Not a direct threat to humans Directly affects fish physiology and habitat Indirectly affects fish and other organisms via toxicants

associated with anoxia: H2S NH4

+ (converts to NH4OH and NH3 above ~pH 9) Indirectly affects domestic water supply

H2S (taste and odor) Solubilizes Fe (staining)

Indirectly affects reservoir turbines Via H2S corrosion and pitting (even stainless steel) Via regulation of P-release from sediments (mediated via

Fe(OH)3 adsorption)


Gases: N2

~ 78% of air Concentrations in water usually saturated

because it is nearly inert Supersaturation (>100 %) can occur in reservoir

tailwaters from high turbulence May be toxic to fish (they get “the bends)

N2 -fixing bacteria and cyanobacteria (blue-green “algae”) convert it to bio-available NH4

+

Denitrifying heterotrophic bacteria convert NO3-

to N2 and/or N2O under anoxic conditions


Gases: CO2

Only about 0.035% of air (~ 350 ppm) Concentration in H2O higher than expected based on low

atmospheric partial pressure because of its high solubility

Gas(at 10oC)

Concentration @ 1 atm (mg/L)

Concentration @ normal pressure (mg/L)

N2 23.3 18.2

O2 55.0 11.3

CO2 2319 0.81

How long does your soda pop fizz after shaking it?


CO2 reactions in water

<1% is hydrated to form carbonic acid:

CO2 + H2O H2CO3

Some of the carbonic acid dissociates into bicarbonate and hydrogen ions which lowers the pH:

H2CO3 HCO-3 + H +

As the pH rises, bicarbonate increases to 100% at a pH of 8.3. Above this, it declines by dissociating into carbonate:

HCO-3 CO3-2 + H+


Inorganic - C equilibria

Note – 100% CO2 for pH< ~ 4.5; 100% bicarbonate for pH ~ 8

and 100% carbonate for pH > ~12

H2CO3H2CO3 HCO3HCO3 CO3CO3

pH

Fra

ctio

n o

f c

arb

on

sp

ec

ies


Inorganic - C: Major sources and sinks

Sources: Atmospheric CO2 (invasion) Respiration and other aerobic and anaerobic

decomposition pathways in the water and sediments Groundwater from soil decomposition products Groundwater from volcanic seeps

Sinks: pH dependent conversions to bicarbonate and

carbonate Precipitation of CaCO3 and MgCO3 at high pH Photosynthesis


CO2 supersaturation – killer Lake Nyos

In 1986, a tremendous explosion of CO2 from Lake Nyos, in Cameroon, West Africa, killed >1700 people and livestock up to 25 km away.

Dissolved CO2 seeps from volcanic springs beneath the lake and is trapped in deep water by hydrostatic pressure. Nearby Lake Manoun is similar in nature

Although unconfirmed, a landslide probably triggered the gas release

Visit http://www.biology.lsa.umich.edu/~gwk/research/nyos.html and http://perso.wanadoo.fr/mhalb/nyos/index.htm for detailed information


www.saddleback.cc.ca.us/faculty/thuntley/ms20/seawaterprops2/sld013.htm

Soda pop chemistry


CO2 and the inorganic carbon system

• Carbon dioxide diffuses from the atmosphere into water bodies and can then be incorporated into plant and animal tissue

• It is also recycled within the water with some being tied up in sediments and some ultimately diffusing back into the atmosphere

• Fixed carbon also enter the water as “allocthonous” particulate and dissolved material


CO2 and the inorganic carbon system - 2

• Alkalinity, acid neutralizing capacity (ANC), acidity, carbon dioxide (CO2), pH, total inorganic carbon, and hardness are all related and are part of the inorganic carbon complex


CO2 chemistry: Alkalinity

Alkalinity – the ability of water to neutralize acid; a measure of buffering capacity or acid neutralizing capacity (ANC)

Total Alkalinity (AlkT) = [HCO3-] + 2[CO3

2-] +[OH-] - [H+]

Typically measured by titration with a strong acid. The units are in mg CaCO3/L for reasons relevant to drinking water treatment (details in Module 9)

Can be used to estimate the DIC (dissolved inorganic carbon) concentration if the [OH-]

Conversely, direct measurements of DIC by infrared analysis or gas chromatography, together with pH and the carbon fractionation schematic can be used to estimate alkalinity (* see slide notes)


Alkalinity and water treatment

Advanced wastewater treatment (domestic sewage) Phosphorus nutrient removal by adding lime (Ca(OH) 2)

or calcium carbonate (CaCO3)

As pH increases >9, marl precipitates adsorbed PO4-3

Settle and filter the effluent to obtain 90-95% removal Used for particle (TSS) removal also

Drinking water treatment For TSS removal prior to disinfection

Acid-rain mitigation to whole lakes Lime or limestone added as powdered slurry to increase

impacted lake pH Also broadcast aerially to alkalize entire watersheds


CO2 chemistry: Hardness

Hardness - the total concentration of multi-valent (i.e. >2) cations

Ca+2 + Mg+2 + Fe +3 (when oxic) + Mn+2 (when oxic); all other multivalent cations are typically considered to be negligible

Sources- Minerals such as limestone (Ca and Mg) and gypsum (Ca) Water softeners and other water treatment processes such as

reverse osmosis and ion exchange Evaporation can increase hardness concentration

Drinking water effects (no real health effects) Soap scums and water spots on glasses and tableware Deposits (scaling) can cause clogging problems in pipes,

boilers and cooling towers


Water chemistry – Major ions

SiO2 < 1

Note: plant nutrients such as nitrate, ammonium and phosphate that can cause algae and weed overgrowth usually occur at 10’s or 100’s of parts-per-billion and along with other essential micronutrients usually represent <1% of the actual amount of cations or anions present in the water


Major ion concentrations - freshwater

Anions mg/L Cations mg/L

HCO3- 58.4 Ca+2 15.0

SO4-2 11.2 Mg+2 4.1

Cl- 7.8 Na+ 6.3

SiO2 13 K+ 2.3

NO3- ~1.0 Fe+3 ~0.7

Total = ~91.4 anions + ~28.4 cations = ~ 120 mg/L (TDS)


Nutrients – phosphorus

Essential for plant growth Usually the most limiting nutrient in lakes Derives from phosphatic rock – abiotic, unlike

nitrogen No gas phase, but can come from atmosphere

as fugitive dust Adsorbs to soils

Naturally immobile unless soil is eroded or excess fertilizer is applied

Phosphorus moves with sediments


Nutrients – phosphorus

Not toxic Algae have physical adaptations to acquire

phosphorus High affinity (low k) APA Storage Luxury uptake

Single redox state Phosphorus cycle is closely linked to the iron

(Fe) cycle


Phosphorus – basic properties

No redox or respiration reactions directly involved (organisms are not generating energy from P chemistry)

PO4–3 highly adsorptive to cationic sites (Al+3,

Fe+3, Ca+2) Concentration strongly affected by iron redox

reactions Ferric (+3) – insoluble floc Ferrous (+2) – soluble, unless it reacts with

sulfide, causing FeS to precipitate


Phosphorus levels in the environment

Major factors affecting phosphorus levels, cycling, and impacts on water quality include: Soil properties Land use and disturbance Transport associated with runoff


Where does phosphorus come from?


Phosphorus – external sources

Nonpoint sources Watershed discharge from tributaries Atmospheric deposition

Point sources Wastewater Industrial discharges


Phosphorus – nonpoint sources

Watershed discharges from tributaries Strongly tied to erosion (land use management) Stormwater runoff (urban and rural) Agricultural and feedlot runoff On-site domestic sewage (failing septic systems) Sanitary sewer ex-filtration (leaky sewer lines)

Atmospheric deposition Often an issue in more pristine areas Arises from dust, soil particles, waterfowl


Phosphorus – point sources

Wastewater Municipal treated wastewater Combined sewer overflows (CSOs) Sanitary sewer overflows (SSOs)

Industrial discharges


Phosphorus – internal sources

Mixing from anoxic bottom waters with high phosphate levels is closely tied to iron redox reactions O2 > 1 mg/L – Insoluble ferric (+3) salts form that

precipitate and settle out, adsorbing PO4-3

O2 < 1 mg/L (anoxic) – ferric ion reduced to soluble ferrous ion (Fe+2) – allowing sediment phosphate to diffuse up into the water

Wind mixing (storms and fall de-stratification) can re-inject high P water to the surface, causing algal blooms


Phosphorus – Lake budget


Nutrients – phosphorus cycle

Major pools and sources of P in lakes “Natural” inputs are

mostly associated with particles

Wastewater is mostly dissolved phosphate

P is rapidly removed from solution by algal-bacterial uptake or by adsorption to sediments


Phosphorus cycling – major sources

Sewage Dissolved

Tributaries and deposition Particulate

Erosion Particulate

Sediments Particulate

and dissolved


Phosphorus cycling – internal recycling

Rapid PO4-3

recycling Bacterial uptake Algal uptake Adsorption to

particles Detritus

mineralization Zooplankton

excretion Fish excretion


Phosphorus cycle – major transformations

Modified from Horne and Goldman, 1994.

Limnology. McGraw Hill.

The whole phosphorus cycle


Nitrogen – basic properties

Nitrogen is relatively scarce in some watersheds and therefore can be a limiting nutrient in aquatic systems

Essential nutrient (e.g., amino acids, nucleic acids, proteins, chlorophyll)

Differences from phosphorus Not geological in origin Unlike phosphorus, there are many oxidation

states


Nitrogen – biologically available forms

N2 – major source, but usable by only a few species Blue green algae (cyanobacteria) and anaerobic

bacteria Nitrate (NO3

-) and ammonium (NH4+) – major

forms of “combined” nitrogen for plant uptake Also called dissolved inorganic nitrogen (DIN)

Total nitrogen (TN) – includes: DIN + dissolved organic nitrogen (DON) +

particulate nitrogen


Nitrogen – general properties

Essential for plant growth Not typically limiting but can be in:

Highly enriched lakes Pristine, unproductive lakes located in

watersheds with nitrogen-poor soils Estuaries, open ocean

Lots of input from the atmosphere Combustion NO2, fertilizer dust


Nitrogen – general properties

Mobile – in the form of nitrate (soluble), it goes wherever water flows Ammonium (NH4

+) adsorbs to soil particles Blue green algae can fix nitrogen (N2) from the

atmosphere Nitrogen has many redox states and is involved

in many bacterial transformations


Nitrogen – sources

Atmospheric deposition Wet and dry deposition (NO3

- and NH4+)

Combustion gases (power plants, vehicle exhaust, acid rain), dust, fertilizers

Streams and groundwater (mostly NO3-)

Sewage and feedlots (NO3- and NH4

+) Agricultural runoff (NO3

- and NH4+)

Regeneration from aquatic sediments and the hypoliminion (NH4

+)


Nitrogen - toxicity

Methemoglobinemia – “blue baby” syndrome > 10 mg/L NO3

--N or > 1 mg/L NO2--N in well

water Usually related to agricultural contamination of

groundwater NO3

- – possible cause of stomach/colon cancer Un-ionized NH4

+ can be toxic to coldwater fish NH4OH and NH3 at high pH

N2O and NOx – contribute to smog, haze, ozone layer depletion, acid rain


Nitrogen – many oxidation states

Unlike P there are many oxidation states Organisms have evolved to make use of these

oxidation-reduction states for energy metabolism and biosynthesis

-3 0 + 1 + 2 + 3 + 5

NH4+ N2 N2O NO2 NO2

- NO3-


Nitrogen – bacterial transformations

Organic N NH4+-N Heterotrophic ammonification or

mineralization. Associated with oxic or anoxic respiration.

NH4+-N NO3

- Involves oxygen (oxic). Autotrophic and chemosynthetic ("burn” NH4

+-N to fix CO2).

NO3- N2 (gas) Anoxic process. Heterotrophic.

("burn" organic matter and respire NO3

-, not O2).

N2 (gas) Organic N Some blue green algae are able to do this.

•Decomposition

•Nitrification

•Denitrification

•Nitrogen fixation


Nutrients- The Nitrogen Cycle

•modified from Horne and Goldman. 1994. Limnology. McGraw Hill.

Nutrients – nitrogen cycle


Org–N

N2 = largest reservoir

but cannot be used by most organisms

Fixed or available-N

organism-N + detrital-N+ dissolved organic-N

NH4 +

NO2-

NO3-

-3 +5+4+3+2+10-1-2Oxidation state

NO2N2ON2•gases

Chemical forms of nitrogen in aquatic systems

NH4 +

NO2-

NO3-

Dissolved inorganic-N (DIN)Ammonium:

basic unit for biosynthesis

Nitrite: usually

transient

Nitrate: major runoff fraction


Functionally in the lab using filters…

Total-N = particulate organic-N + dissolved organic-N

+ particulate inorganic-N + dissolved inorganic-N

TN = PN + DON + DIN

Dissolved inorganic-N = [Nitrate + Nitrite]-N + ammonium-N

DIN = NO3-N + NO2-N + NH4-N

Notes:

• Nitrate+nitrite are usually measured together.

• Nitrite is usually negligible.


Assimilation

(algae + bacteria)

Assimilation

-3 +5+4+3+2+10-1-2Oxidation state

AssimilationDenitrification

NO2N2ON2

NH4+

NO2-

Mineralization

Org-N

Main N-cycle transformations

N2 - Fixation- Soil bacteria- Cyanobacteria - Industrial activity- Sulfur bacteria

Denitrification(anoxic bacteria)

Nitrification 1(oxic bacteria)

Nitrification 2

NO3-

Ammonification

•gases

Anammox (anoxic bacteria)


Surficial Sediments

N2

AlgaeAlgae

oxic anoxic

NO3- NH4

+

Nitrification

Assimilation

Mineralization

NH4+

NitrificationNO2

-, N2ONO

Den

itri

fica

tio

n

Sed

imen

tati

on

DIN PON

DON

Sed

imen

tati

on

Deep SedimentsBurialBurial

Ammoniavolatilization

Tribs, GW, PrecipDON, PON, NO3

-, NH4+

NO3-

Outflow

diffusion

N2-fixation

Whole lake N-budget

Mixing

Mineralization


Nutrients – summer vertical profiles

•Oligotrophic •Eutrophic

TT

O2 O2

NO3

NO3

PO4

PO4 NH4

NH4

Depth

•0 •0

• anoxia

anoxia


Sulfide and iron – summer vertical profiles

TT

O2

O2

Soluble Fe

HH22SSHH22SS

Soluble Fe• anoxia

anoxia

•0 •0•Eutrophic•Oligotrophic

Dep

th


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