LAKE ECOLOGY

1
LAKE ECOLOGY

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

2
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.

3
Modules 2/3 outline

1. Introduction
2. Major groups of organisms metabolism
3. Basins and morphometry
4. Spatial and temporal variability basic physical
   and chemical patchiness (habitats)
5. Major ions and nutrients
6. Management eutrophication and water quality

4
5. Water chemistry Gases, major ions nutrients
5
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)

6
Water chemistry gases

• What are the ecologically most important gases ?
• O2
• CO2
• N2
• H2S

7
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)

8
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)

9
O2 variability

• Diel (24 hr) variation due to ____________?
• Seasonal variation due to _____________ ?

10
Major sources of O2

• Sources
• Photosynthesis (phytoplankton, periphyton,
  macrophytes)
• Air from wind mixing
• Inflows
• tributaries may have higher or lower DO
• groundwater may have higher or lower DO
• Diffusion (epilimnion to hypolimnion and vice
  versa)

11
Major sinks of O2

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

12
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?

13
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?

14
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)

15
Gases N2

• 78 of air
• Concentrations in water usually saturated
  because it is nearly inert
• Supersaturation (gt100 ) 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

16
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 _at_ 1 atm (mg/L) Concentration _at_ 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?
17
CO2 reactions in water

• lt1 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

18
Inorganic - C equilibria
Note 100 CO2 for pHlt 4.5 100 bicarbonate
for pH 8 and 100 carbonate for pH gt 12
19
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

20
CO2 supersaturation killer Lake Nyos

• In 1986, a tremendous explosion of CO2 from Lake
  Nyos, in Cameroon, West Africa, killed gt1700
  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/resea
rch/nyos.html and http//perso.wanadoo.fr/mhalb/ny
os/index.htm for detailed information
21
Soda pop chemistry
22
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
  

23
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

24
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- 2CO32-
  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)

25
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 gt9, 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

26
CO2 chemistry Hardness

• Hardness - the total concentration of
  multi-valent (i.e. gt2) cations
• Ca2 Mg2 Fe 3 (when oxic) Mn2 (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

27
Water chemistry Major ions
Note plant nutrients such as nitrate, ammonium
and phosphate that can cause algae and weed
overgrowth usually occur at 10s or 100s of
parts-per-billion and along with other essential
micronutrients usually represent lt1 of the
actual amount of cations or anions present in the
water
28
Major ion concentrations - freshwater
Anions mg/L Cations mg/L
HCO3- 58.4 Ca2 15.0
SO4-2 11.2 Mg2 4.1
Cl- 7.8 Na 6.3
SiO2 13 K 2.3
NO3- 1.0 Fe3 0.7
Total 91.4 anions 28.4 cations 120 mg/L (TDS) Total 91.4 anions 28.4 cations 120 mg/L (TDS) Total 91.4 anions 28.4 cations 120 mg/L (TDS) Total 91.4 anions 28.4 cations 120 mg/L (TDS)
29
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

30
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

31
Phosphorus basic properties

• No redox or respiration reactions directly
  involved (organisms are not generating energy
  from P chemistry)
• PO43 highly adsorptive to cationic sites (Al3,
  Fe3, Ca2)
• Concentration strongly affected by iron redox
  reactions
• Ferric (3) insoluble floc
• Ferrous (2) soluble, unless it reacts with
  sulfide, causing FeS to precipitate

32
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

33
Where does phosphorus come from?
34
Phosphorus external sources

• Nonpoint sources
• Watershed discharge from tributaries
• Atmospheric deposition
• Point sources
• Wastewater
• Industrial discharges

35
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

36
Phosphorus point sources

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

37
Phosphorus internal sources

• Mixing from anoxic bottom waters with high
  phosphate levels is closely tied to iron redox
  reactions
• O2 gt 1 mg/L Insoluble ferric (3) salts form
  that precipitate and settle out, adsorbing PO4-3
• O2 lt 1 mg/L (anoxic) ferric ion reduced to
  soluble ferrous ion (Fe2) 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

38
Phosphorus Lake budget
39
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

40
Phosphorus cycling major sources

• Sewage
• Dissolved
• Tributaries and deposition
• Particulate
• Erosion
• Particulate
• Sediments
• Particulate and dissolved

41
Phosphorus cycling internal recycling

• Rapid PO4-3 recycling
• Bacterial uptake
• Algal uptake
• Adsorption to particles
• Detritus mineralization
• Zooplankton excretion
• Fish excretion

42
Phosphorus cycle major transformations

• The whole phosphorus cycle

43
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

44
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

45
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

46
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

47
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)

48
Nitrogen - toxicity

• Methemoglobinemia blue baby syndrome
• gt 10 mg/L NO3--N or gt 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

49
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-
50
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

51
Nutrients nitrogen cycle
Nutrients- The Nitrogen Cycle

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

52
Chemical forms of nitrogen in aquatic systems
organism-N detrital-N dissolved organic-N
Fixed or available-N
Dissolved inorganic-N (DIN)
Nitrate major runoff fraction
Ammonium basic unit for biosynthesis
Nitrite usually transient
N2 largest reservoir but cannot be used by most
organisms
53
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
• Nitratenitrite are usually measured together.
• Nitrite is usually negligible.

54
Main N-cycle transformations
Assimilation (algae bacteria) Assimilation
Denitrification
Mineralization
Denitrification (anoxic bacteria)
N2 - Fixation - Soil bacteria - Cyanobacteria -
Industrial activity - Sulfur bacteria
55
Whole lake N-budget
Tribs, GW, Precip DON, PON, NO3-, NH4
N2
Ammonia volatilization
N2-fixation
Assimilation
Outflow
Algae
NO3-
NH4
Denitrification
DIN PON DON
Mineralization
Mixing
Sedimentation
NO3-
oxic anoxic
Sedimentation
NO2-, N2O NO
Nitrification
NH4
Mineralization
diffusion
Burial
Burial
Surficial Sediments
Deep Sediments
56
Nutrients summer vertical profiles

• Oligotrophic

• Eutrophic

• 0

• anoxia

• anoxia

57
Sulfide and iron summer vertical profiles

• Eutrophic

• Oligotrophic

• anoxia

anoxia
58
(No Transcript)