LAKE ECOLOGY
description
Transcript of 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.
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s3
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s4
5. Water chemistry: Gases, major ions & nutrients
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s5
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)
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s6
Water chemistry: gases
What are the ecologically most important gases ? O2
CO2
N2
H2S
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s7
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)
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s8
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)
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s9
O2 variability
Diel (24 hr) variation due to ____________?
Seasonal variation due to _____________ ?
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s10
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)
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s11
Major sinks of O2
Sinks Respiration
bacteria, plants, animals; water and sediments Diffusion to sediment respiration Outflow (tributary or groundwater)
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s12
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?
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s13
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?
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s14
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)
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s15
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s16
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?
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s17
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+
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s18
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s19
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s20
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s21
www.saddleback.cc.ca.us/faculty/thuntley/ms20/seawaterprops2/sld013.htm
Soda pop chemistry
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s22
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s23
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s24
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)
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s25
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s26
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s27
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s28
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)
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s29
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s30
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s31
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s32
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s33
Where does phosphorus come from?
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s34
Phosphorus – external sources
Nonpoint sources Watershed discharge from tributaries Atmospheric deposition
Point sources Wastewater Industrial discharges
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s35
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s36
Phosphorus – point sources
Wastewater Municipal treated wastewater Combined sewer overflows (CSOs) Sanitary sewer overflows (SSOs)
Industrial discharges
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s37
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s38
Phosphorus – Lake budget
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s39
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s40
Phosphorus cycling – major sources
Sewage Dissolved
Tributaries and deposition Particulate
Erosion Particulate
Sediments Particulate
and dissolved
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s41
Phosphorus cycling – internal recycling
Rapid PO4-3
recycling Bacterial uptake Algal uptake Adsorption to
particles Detritus
mineralization Zooplankton
excretion Fish excretion
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s42
Phosphorus cycle – major transformations
Modified from Horne and Goldman, 1994.
Limnology. McGraw Hill.
The whole phosphorus cycle
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s43
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s44
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s45
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s46
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s47
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
+)
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s48
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s49
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-
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s50
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s51
Nutrients- The Nitrogen Cycle
•modified from Horne and Goldman. 1994. Limnology. McGraw Hill.
Nutrients – nitrogen cycle
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s52
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s53
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.
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s54
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)
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s55
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
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s56
Nutrients – summer vertical profiles
•Oligotrophic •Eutrophic
TT
O2 O2
NO3
NO3
PO4
PO4 NH4
NH4
Depth
•0 •0
• anoxia
anoxia
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s57
Sulfide and iron – summer vertical profiles
TT
O2
O2
Soluble Fe
HH22SSHH22SS
Soluble Fe• anoxia
anoxia
•0 •0•Eutrophic•Oligotrophic
Dep
th
Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s58