Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s1 Rich Axler, NRRI-UMD Senior Research Associate Grad Faculty: Water

Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s1

Rich Axler, NRRI-UMDSenior Research Associate

Grad Faculty: Water Resources Science Grad Faculty: Integrated Biosystems

[email protected] 218-788-2716

Wetland Biogeochemistry: Major ions, nutrients = NBiology 5870 Sep 24, 2015


I. Wetland biogeochemistry (mostly about nutrients (N,P)

Biogeochem is about the transport and transformations of chemicals

Can talk about input-output mass balances the wetland is a box (sources & sinks)

What goes on inside the box determines how it functions

•WETLAND/LAKE PHOSPHORUS BUDGET•WETLAND/LAKE PHOSPHORUS BUDGET


Anaerobic

Aerobic

Source, Sink, or Transformer?

Rates (mass/area/time, mass/volume/time, or mass/time) = Dynamic

versus

Pools (mass, or concentration [mass/volume or mass/area) = Static


Water chemistry (biogeochemistry): Gases, major ions & nutrients

Gases

Oxygen (O2)

Carbon dioxide (CO2) – dissolves in water to form carbonic

acid H2CO3 , then fractionates to HCO3- + CO3

-2 + CO2

according to pH of the water

Nitrogen (N2)

Hydrogen sulfide (H2S)

Major ions: anions HCO3- , SO4

-2, Cl- ; cations Ca+2, Mg+2, Na+, K+

Nutrients (nitrogen and phosphorus)

Trace (micronutrient) metals, vitamins, etc


Additional nomenclature

Dissolved (soluble) versus particulate

What type of filter, net, or screen to use

And organic versus inorganic


Gas solubility

Maximum amount of gas that can be dissolved in water (“~” 100% saturation) 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)

Why does elevation affect the concentration of dissolved gases?


O2 variability

Diel (24 hr) variation due to ____________?

Seasonal variation due to _____________ ?


Short-term variability- Hypereutrophic Halsteds Bay, L. Minnetonka, MN

Productive Bay

Temp Red = warm O2 Black = anoxic

This is a month of 6hr data from an 8m deep bay. Similar patterns have been found in algal mats (millimeters), shallow wetlands and ponds (centimeters), tidal flats, etc.

What factors control the DO depth and time pattern?


Seasonal DO variability (Apr-Oct) SKIP

Black = anoxia Green = high DO

or depth into sediments in cmsor depth into sediments in cms


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)

Types of invertebrates • Types of plants- Stoneflies = high DO - cattails, bulrushes, reeds, rice- Tubificids = low DO vs alders, cedars, and upland

plants


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 between layers (surface to bottom and vice versa)

Diffusion from plant roots (and stems?)


Emergent plant adaptations

Cattail roots from subsurface flow gravel bed constructed wetland – 3 ys old (domestic septic tank effluent [NERCC Cell 1])

Even dead, cattails passO2 the wet substrate -directly, and by venturi- induced (wind) convection.

Other adaptations to low O2 ??


Major sinks of O2

Sinks Respiration

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


O2: Human significance SKIP for lecture

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

neither N2 fixation nor denitrification typically affects overall N2 levels


Gases: CO2 SKIP 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?


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 are <1% of the actual amount of cations or anions present in the water which are at levels of 10’s of thousands of parts-per-billion


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)

Major ion concentrations – freshwater SKIP


Why the focus on N and P?Limiting nutrients – demand versus supply

Nitrogen and phosphorus are typically in extremely short supply in water relative to plant demand

The “Redfield ratio” is the average composition of elements in phytoplankton algae

Ratio – 100DW:40C:7N:1P


Electron Acceptors in Oxidation of Organic Carbon

Everyone understands this – right ??


RESPIRATION

What’s reduced?- O2 ,NO3-, Mn4+ ,Fe2+ ,S4

2-, and CO2

[aerobic respiration; anaerobic denitrification, sulfate

reduction, methanogenisis etc.] What’s oxidized? Organic carbon (“food”)

Who does it? Auto- & Heterotrophs (plants, animals, bacteria)

Why? To get energy for cellular metabolism

Other important biotic energy producing redox reactions

What’s oxidized?- NH4+, S2- oxidation, Fe3+ , …

[nitrification, sulfide and iron oxidization, …)Who does it?- Chemoautotrophs (chemosynthesizers) Why? To get energy for CO2 fixation (to make organic-C)

Microbial metabolism


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)

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

states

II. Nitrogen – basic properties


Nitrogen – biologically available forms

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

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 (PON ~ PN)


Nitrogen – general properties

Essential for plant growth (amino acids/proteins; nucleic

acids, chlorophyll, …)

Always important to plant growth and can be “limiting”: phosphorus enriched lakes, ponds, wetlands

Pristine, unproductive lakes, streams and wetlands located in

watersheds with nitrogen-poor soils (Know places like this?)

Estuaries, open ocean (major cause of Gulf “hypoxia” +HABS)

Wetlands with high rates of N-loss relative to inputs

Lots of input from the atmosphere in many regions

Combustion NOx , fertilizer dust, fertilizer aerosols (NH3)


Nitrogen – general properties

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

+) tends to adsorb to soil particles (usually electronegative but be careful here)

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 bottom water (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 higher pHs ( > ~ 9)

N2O and NOx – contribute to smog, haze, ozone layer depletion, acid rain, climate change, global dimming


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

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

+-N to fix CO2).

NO3- -N N2 (gas) Anoxic process. Heterotrophic.

("burn" organic matter and respire NO3

-, not O2). Also creates N2O

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

Algae/PlantsAlgae/Plants

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/wetland N-budget

Mixing

Mineralization


Wetland plants: importance to N- cycling

• Supply O2 to root rhizosphere

• Aerobic vs anaerobic interface• Enhanced nitrification (with O2)

• Enhanced denitrification • (without O2 via nitrate production)

• Assimilate nitrate and ammonium (temporary storage)• Source of DOC to microbial communities in root zone

• Enhanced O2 depletion and bacterial activity in general• Stabilize sediments (reduce N-loss via flushing and erosion)

• Plants and plant litter may affect temperature ( + or - ??)

Documents

Developed by: R.Axler and C. Hagley Draft Updated: January 13, 2004 U1-m2/3Part 5-s1 Rich Axler, NRRI-UMD Senior Research Associate Grad Faculty: Water