Samenvatting Ecohydrology
Afkortingen:
GPP: Gross Primary Productivity. GPP is the rate at which ecosystems use energy
(from photosynthesis), either for respiration or the creation of biomass. If you
subtract the respiration from the whole, you get the NPP.
NPP: Net Primary Productivity. NPP is the rate at which biomass is created
TER: Total Ecosystem Respiration
NEP: Net Ecosystem Productivity
NEE: Net Ecosystem Exchange (Net CO2 gas exchange). NEE = GPP - TER
LAI: Leaf Area Index = m 2 leaf m 2 soil
WUE: Water Use Efficiency = mmol O2 fixed / mol H2O lost
LUE: Light Use Efficiency
NUE: Nutrient Use Efficiency

ET: Evapotranspiratie
Week 36:
Hydro-ecology: The landscape ecological study of ecosystems dependent on
groundwater and surface water (Wassen 1994). (Ecologie centraal)
Eco-hydrology: The interdisciplinary study of groundwater hydrology as a
component of ecosystems and as a determining factor for the pattern,
distribution and development of vegetation (Pedroli1994). (Hydrologie centraal)
Ecohydrology started in the Netherlands in the 1970s.
Photosynthesis:
6CO2 + 6H2O + energy → C6H12O6 + 602
 Produces sugars and O2
 Solar energy needed
 Radiation energy in visible spectrum absorbed by pigments
 Takes place in green leaves (chloroplasts)
Nitrogen: Important in photosynthesis: linear correlation between N in leaves
(in Rubisco, chlorophyll) and photosynthesis rates.
Photosynthetic Pathways:
 C3  Rubisco in leaves (Less maintainance)
 C4  Rubisco in bundle sheath cell (More CO2 efficient)
 CAM 
o
Separated in time: CO2 exchange at night, photosynthesis during
day
o
Stomata stay close during the day
o
Very water efficient, but slow growth
o
Mainly succulents (cacti)
Respiration: C6H12O6 + 602 → 6CO2 + 6H2O + energy
o
Autotrophic respiration: ‘burns’ organic matter (sugars) to
provide energy for plant functions (for example transport across
membranes)
Heterotrophic respiration: The conversion of organic matter to CO2 by
organisms other than plants (decomposers, animals). Is dependent on:
- Temperature (increase respiration exponentially to max, then decrease to
zero (enzymatic activity interrupted)).
- Moisture
- Level of oxygen (low in dry conditions, increases to maximum at
intermediate moisture levels, decrease when moisture content excludes
oxygen).
- Nutrient content (Poor quality more difficult to convert)
Water & Plants:
 70%-90% of fresh weight of non-woody biomass is water!
 Involved in chemical reactions (photosynthesis, respiration)
 Solvent
 Turgidity (water in vacuoles within protoplasts): Hydrostatic pressure in
plant cells.
 Transport medium
Water Movement
 Bulk flow: water flows from high to low potential
 Diffusion: from a high to a low concentration
 Osmosis: water flow through a semi-permeable membrane from a solution
with a high water potential (low solute concentration) to a solution with a
low water potential (high solute concentration)
Water flows from roots to leaves because of the very large negative potential in
the canopy due to transpiration.
Soil Definitions:
 Saturation: Maximum water drainage
 Field Capacity: The maximum possible amount of water remaining in the
soil after excess water has drained away. Water cannot drain freely. Water
can be taken up by plants
 Permanent wilting point: Water cannot drain freely. Water cannot be taken
up by plants due to the turgor limit of plants. It is defined as the minimal
point of soil moisture the plant requires not to wilt.
Water Use Efficiency (WUE)
 WUE = mmol CO2 fixed / mol H2O lost
 Water Use Efficiency: CAM > C4 > C3
 Low stomatal conductance (depressed ET) → high WUE
Week 37
Biogeochemistry: Interactions between chemistry of water, soil and biosphere.
Hydrochemistry
• Three main types of water
• Distinct chemical composition:
• Amount of dissolved ions (EC)
• Relative amounts of Ca and Cl
Rainwater chemistry
• Fractionation factor: use of chloride as a stable marker
X Cl rain

FCl 
X Cl seawater
• Calculate contributions of sources other than seawater

Adsorption
• Adherence of ions to the surface of soil particles
• Based on electrochemical load (soils often negative load)
• Adsorption capacity (CEC) depends on total surface area of soil particles
 soils with small particles (e.g. clay) and/or high organic matter
content (e.g. peat) have high adsorption capacity
• Also dependent on chemical composition of the soil particle (load!)
Ion exchange
• Exchange of adsorbed or absorbed ions and ions in groundwater
• Specific sequence of adsorption based on electrochemical charge:
Al3+  H+  Ca2+  Mg2+  K+  NH4+  Na+
Main differences aerobic-anaerobic C-cycle
• Rates of processes (fast-slow)
• End products (CO2 – CH4)
• Soil organisms (aerobic – anaerobic; fungi - bacteria)
• Mechanisms (OM decomposition – ‘chemical’ oxidation)
• Influence of water quality
Aerobic N-transformation


Nitrogen mineralization:
NH2·CO·NH2 + H2O  2NH3 + CO2
NH3 + H20  NH4+
Nitrification (actually ammonium oxidation):
NH4+ + O2

NO2- + 4H+ + 2e- (by Nitrosomonas spp.)
NO2-+H2O

NO3- + 2H+ + 2e- (by Nitrobacter spp.)
Anaerobic N-transformation
 Denitrification (actually nitrate reduction):
C6H12O6 + 4NO3-  6CO2 + 6H2O + 2N2
 Nitrification not possible
NH4+ + O2  NO2- + 4H+ + 2e Significant denitrification only possible when:
1) There is a nitrate stock (e.g. after flooding)
2) At the aerobic – anaerobic interface
3) Rewetting and drying alternate
4) There is an external nitrate source (e.g. nitrogen deposition,
fertilizer application or inflow)
Phosphorus cycling: Anaerobic conditions
 P-availability mainly chemically regulated
 Chemical binding susceptible to redox and pH
 Low pH: binding to Fe and Al, high pH: binding to Ca
 Redox effects: increased solubility of reduced metals (dissolution of
insoluble metal-phosphate complexes)
Plant adaptations to drought
 Strategies to minimize water loss:
- Leaf structure (grootte, vorm en waslaagje op blad)
- Type of photosynthesis (C3, C4, CAM)
- Timing of activity
 Strategies to maximize water uptake:
- Extensive root systems
 Water storage
Plant growth under wet conditions
 Stress from being waterlogged
- Lack of oxygen for root activity
- Toxicity of reduced compounds in the soil
- Lowering of nutrient availability
- Physical stress from water flow
Plant adaptations to being waterlogged
 Physiological response: anaerobic metabolism
 Physical responses:
- Aerenchyma formation (and Radial Oxygen Loss)
- Adventitious root formation
- Petiole (bladsteel) elongation and hyponastic growth (bladeren
gaan rechtop staan)
During short periods of being waterlogged plants can metabolize anaerobe
Salt stress
 Toxicity (inhibition of physiological processes)
 Physical damage (crystal formation)
 Osmotic stress
Als een plant in zout water staat kan water bij droogte door osmotische stress uit
de plant diffunderen.
Stress from acidity/alkalinity
 Toxicity (inhibition of physiological processes)
 Mobilization of heavy metals (often Al)
 Access to nutrients blocked
Acidity:
 Organic soils
 Rainwater accumulation/infiltration
Alkalinity (or neutral conditions):
 Calcium rich soils,
 Exfiltration of groundwater
The nutrient that gives the biggest growth is limiting.
Species interactions:
 Competition
o Nutrients:
 Better access: Root architecture, Symbiosis
 More efficient use (NUE): More biomass produced per unit
of nutrients
o Light/Space:
 Growth form
 Active eradication of other species: secondary metabolites
 Facilitation
o Species modify environment, other species also profit
Week 38
Definitions:
 Evapotranspiration = Evaporation + Transpiration
 Interception = water intercepted by vegetation
 Interception evaporation




Througfall = precipitation - interception evaporation
Percolation = drainage to groundwater
1 mm rain = 1 liter / m2
Watercontent of soil: fraction or % of total volume
Darcy’s Law:
q  k







q
k
H
z
h
H
z
= water flux in (m/d)
= Hydraulic conductivity in (m/d)
= Hydraulic Head = stijghoofte (m)
= Elevation Head = hoogte van de water kolom (m)
= Pressure Head = H-z (m)
o ∂H= -0.2m
o ∂z= 0.4m
o We measured a flux of 5 m/d
o So: q=5=-k · -0.2/0.4
o k=10 m/d
 k (depends on grain sizes)
o Gravel = 100 - 1000 m/d
o Sand = 1 - 100 m/d
o Clay = 1e-6 - 0.2 m/d
Water flows from high to low Hydraulic head
Waterflow in pores:
v avg


q


vavg

Isohypsen:
waterflow in pores
Porosity: 0.35 - 0.5, peat: 0.7
Points with equal Hydraulic head.
No flow: ∂H = 0
Large densities of Isolines  large water flow
(also called equipotential lines)
Zuigspanning (soil water pressure)
 pF = log (-Pressure head (in cm))
 pF = log (-h)
Natter dan de veldcapaciteit kunnen de meeste planten geen water opnemen.
Transpiratie van planten is de grootste flux.
Why does a plant transpire?
1. Meteorological: cooling optimal T on leaves
2. Plant physiological: Photosynthesis stomata open for CO2 losing H2O
3. Soil Science: Root water uptake of nutrients
Modellen
Components
1. State variables: amounts, number
2. Rate variables: interactions (per time)
3. Model parameters: system properties
N in soil:
Initial amount: N(t=0) = 100 kg/ha
Rate constant: a = 0.02 d-1
N(t)  N(t 1)  aN(t 1)dt
N(t)  N(t 1)
 aN(t 1)
dt
If t is very small:
dN
 aN(t 1)
dt
Leaf
cooling model:
Warming up: solar radiation
Cooling down: ambientair (H)
Latent heat (Transpiration)
Test on leaf: with gas-chambers
Test on canopy level: with for instance sapflow
Test on ecosystem: with eddy covariance
Week 39:
Excursie: The Horstermeerpolder is one of the deeper polders in the area,
located between 2.5 and 3.5 m below mean sea level. Its low position in the
landscape is problematic, because the polder now attracts water from adjacent
areas, including valuable nature reserves such as the Ankeveense – and
Kortenhoefse Plassen. Furthermore, it diverts the deeper groundwater flows as
well. Water extraction to keep the polder dry is so intense that it not only
attracts water from adjacent areas, but also attracts salt water from deeper
aquifers. The ditches in the central part of the polder are therefore brackish, and
you can find several salt tolerant species there.
Water depletion in the adjacent nature reserves used to be solved by the
inlet of river water from the Vecht, inlet of water from the Spiegelplas and inlet
of water from the ‘boezem’ (which drains the superfluous water from polders).
This caused problems because of the different chemical composition of the water
and because of pollution of the river water.
More recently, another strategy is being tried. In the southern part of the
polder, buffer zones are being created to counteract seepage from the adjacent
nature reserves. These bufferzones consist of former agricultural land, which is
isolated from the hydrological system of the polder, allowing the groundwater
level (or actually, the pressure head) to rise. Predicted by Darcy’s law, this
should reduce water flow from the adjacent areas. In the literature assignments,
you have read about research that was performed here on the ecological impact
of these measures.
Week 40
SVAT modeling
SVAT: Soil-Vegetation-Atmosphere-Transfer
Solar radiation is dependent on the location on the earth.
Saturation: Maximum water drainage
Field Capacity: Water cannot drain freely. Water can be taken up by plants
Permanent wilting point: Water cannot drain freely. Water cannot be taken up
by plants.
Evapotranspiration
1)
Energie Budget:
Rn  E  H  G  0
Rn = net radiation
E = latent heat = evapotranspiration
H = sensible heat
G = storage heat in ground (= 0 (versimpeling))

2)
Vapor Transport (Fick’s Law):
E  

3)

'va  va
rs  ra
 = latent heat of vaporization (J/kg)
’vs = vapor density at the surface (kg/m3) (‘ = verzadigd in
’vs)
3
va = vapor density at the atmosphere (kg/m )
rs = surface resistance = stomatal resistance (s/m)
ra = boundary layer or aerodynamic resistance (s/m)
Heat Transport (Fouriers Law)
Ts  Ta
H  c
ra
H = Sensible heat loss (W/m2)
Ts = Surface temperature (K)
Ta = Air temperature (K)
ra = boundary layer or aerodynamic resistance (s/m)
c = Volume specific heat capacity (J  m-3K-1)
The temperature at the surface is very hard to measure!
4)
’vs - va = ’va - va + s(Ts – Ta)
----> Combine 2 & 4
5)

6a)

6b)
E  
'va  va  s(Ts  Ta )
rs  ra
H
 ra
c
Rearrange 1: H  Rn G  E
T  Ta 
Rearrange 3: s
----> Combine
c
T T 
 ra
Rn  E
7) 

s
a
----> Combine 5 & 7
 ( 'va  va  s
8)

E 
rs  ra
Rn  E
 ra
c
Al deze vergelijkingen moet je doen, omdat je Ts (temperatuur blad) moeilijk
kunt meten.
Penman – Monteith equation:
s Rn  c  (  'va va) ra
E 
s   (1 rs ra )
 = psychometric constant = c  = 0.495 g  m-3  K-1
Hoef je niet uit je hoofd te leren!
Relative humidity = va 'va = (Vapor density atmosphere / Saturation density

atmosphere)  ’va is afhankelijk van temperatuur

Aerodynamic component (ac) of Penman – Monteith equation:

---->
a
c('va  va) r
'va  va  0
Priestly Tailor equation:
If air is saturated  ac = 0 

E 

s(Rn  G)
s
Replace aerodynamic component (ac) with constant :
E   
s
 (Rn  G) ( = 1.26 for well watered grass)
s  
Coupling: degree to which a plants responds to its environment (CO2, vapor,
etc.)

If: leaf/canopy completely coupled:
E imp 
( 'va  va)
rs
assume --> ra very small
--> Ts = Ta
rs = surface resistance  is belangrijk,
dus beter Penman - Monteith gebruiken.
If: leaf/canopy completely decoupled:

E dec 
s
 Rn
s
dus beter Priestly Taylor gebruiken.

assume --> ra very large
--> aerodyn. comp. richting 0
E   E dec  (1  ) E coupling
 = degree coupling
0 = perfect coupling
1 = perfect decoupling
rs most effective when  = 0

Veg factor = 1  e
( LAI )
Soil – Vegetation:
Darcy’s Law:

Jw  k
<-- naar transpiratie
d
dz
k = hydraulic conducivity
Saturated zone
ksat ~ pore size
kunsat ~ soil water content

Richard’s
equation:

    
Jw  

 k
 k g U

 t z  z

 = density water
 = volume water content
 = soil water potential
t = time
k = hydraulic conductivity
z = soil depth
g = acceleration of gravity
U = source–sink term (root water uptake)
Simplification: Tipping-Bucket approach
Week 41
In het Kruger National Park in Zuid-Afrika vind je ook venen. Ook al is er weinig
neerslag en hoge verdamping. Er is heel warm grondwater.
Isohypsen: Lijnen met grondwaterstand van gelijke hoogte.
IJzer duidt op een kwelzone
Ab Grootjans: Wanneer er een probleem is, analyseer dan mogelijke oorzaken
eerst. Als je het systeem niet begrijpt is de kans groot dat je door
‘herstelmaatregelen’ het probleem vergroot. Do not jump to restoration!
Kalk slaat neer als CO2 uit water aan de lucht ontsnapt. Dit kun je meten aan de
hand van EC-metingen in de beekjes. Stroomafwaarts worden de waarden
steeds lager, omdat er steeds minder kalk in het water zit.
Our expedition has shown that Peninsula Mitre holds a wide variety of mire
types over two exciting gradients:
–
local geology induced gradients from extremely carbonate rich to
extremely acid.
–
a regional climate induced west – east gradient from Sphagnum
magellanicum- in the West, via Caltha dioneaefolia-, to Astelia pumiladominated mires in the East of the Peninsula.
This wide variety makes the Peninsula to a globally important mire region that
deserves full protection.
Overgrazing stimulates surface water erosion.
Surface water erosion lowers groundwater tables in the peat.
Thufur: lifted peat due to frost.
Low water tables promote the disruption of thufurs. Frost upheaving is adding
to the problem.
Week 42
Stomata: exchange of CO2 and water vapor. But the diffusion rate of water
vapour is 1.6 times greater than CO2.
Guard cells regulate diffusive conductance of the leaf (gs) between 0 (stomata
closed) and maximal (gsmax) (fully open)
High CO2  Species develop Low gsmax
Low CO2  Species develop High gsmax
High gsmax can only reached with high stomatal density (D)
Miljoenen jaren geleden was er meer CO2, dus planten hadden lage stomatale
conductance. Als er meer CO2 is, gaat de plant efficiënter om met water.
Phenotipic plasticity: aanpassing binnen de genetische grenzen.
CO2 gaat via diffusie de plant in (dus door concentratie gradiënt).
Stomatal adaptation at 3 timescales:
Relevant for anthropogenic climate change!
•
Dynamic adaptation (seconds ~ hours)  plants open/close stomata
•
Structural adaptation (> years ~ decades)  plants grow leaves
different number and size stomata within phenotypic plasticity
•
Genetic adaptation (> ~centuries)  natural selection alters ranges of
phenotypic plasticity
Canopy transpiration decrease at double CO2
College Max Rietkerk
(Semi-)arid ecosystems
•
Yearly potential evaporation exceeds yearly rainfall
•
Plant growth water limited
•
40% land surface
•
Main land-use is grazing
Infiltration rate increases with vegetation cover
Run-off and soil
loss decrease with
vegetation cover
Catastrophic shifts:
 Are sudden, abrupt, as compared to gradual environmental change
 Show hysteretic loops (difficult to reverse)
 Have different threshold values associated with this
 There are no early warning signals
 Result from positive feedback
 In mathematical terms: Spacial bifurcation
Self-organized patchiness!
 Outcome of internal dynamics only, starting from random initialization
 As a result of plant-soil characteristics
 Concentration of soil water under vegetated patches
 This is due to the fact that higher biomass leads to higher infiltration rates
outbalancing higher transpiration rates
Stefan Dekker
Positive feedbacks:
 Transpiration – precipitation feedbacks
 Albedo feedbacks
Stability analysis doe je door een systeem te verstoren (pertubations) en kijken
wat er gebeurt.
Multiple equilibria are possible due to: different strengths, history and
interplay of feedbacks at disparate scales
Week 43
Op kleine schaal: cm*s-1
Op grote schaal: 104 km*103yr-1
Het is dus inefficiënt om deze samen te modelleren.
What are the major drivers of photosynthesis?
 Energy
o Light
 Water availability
 Plant N content (chloroplasts)
Photosynthesis is highly related to transpiration
Ways to model transpiration:  decrease complexity
 Penman – Monteith
 Priestly – Taylor
 Function of radiation alone
 Function of min and max temperature.
Transpiration cools the leaf due to evaporative cooling.
Soil moisture is ook beperkende factor bij evapotranspiratie en dus ook bij
photosynthese (zit bij WUE inbegrepen).
Nitrogen
 Taken up from the atmosphere through symbiosis by nitrogen fixating
bacteria.
 Ammonification: Bacteria convert dead matter into NH4+. Kan alleen
onder aërobe omstandigheden.

Nitrification: Bacteria convert other N-forms into NO3-. Kan alleen onder
aërobe omstandigheden.
Elke plant heeft een bepaalde C:N-ratio.
Detritus = Litterfall (canopy) + Root Turnover
 Micro-organisms (small animals, bacteria and fungi) decompose detritus,
releasing CO2, water, nutrients and more resistant organic matter
(humus).
Decomposition depends on:
 Temperature (exponential because of enzymes)
 Soil moisture (slow in dry soils)
 Soil acidity (slower in acid soils)
 Litter composition (nitrogen rich leaves decompose fast, lignins (wood)
and polyphenols slow)
 Oxygen availability (aerobic vs anaerobic decomposition)
Autocorrelatie: Memory soil moisture (regenbui)
Flip Witte
Een overschot aan regenwater zorgt voor verzuring.
Three feedbacks of vegetation to drought:
1)
Closing of stomata
2)
CO2  transpiration T
3)
Reduction of vegetation cover
Tact = function of soil water suction (Feddes, 1978)
Soil water suction depends on:
 P and ETref
 vegetation type (Tpot)
 exposure to the sun
 soil texture (k(Θ) and h(Θ))
 groundwater depth
Versterking van de verschillen:
Wat droog is, wordt droger
Wat nat is, wordt natter
Shortcommings of ecological models: Verkeerd gebruik van data.
Output GIGO: Garbage in  Garbage out.
Als je input waarden slecht zijn, krijg je ook slechte waarden eruit. Er is vaak
geen random sampling.
Je moet altijd kijken of de output van je model realistisch is.