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Outline. Loading –concentrations littoral-open water interactions cyanobacteria and nutrients , N:P nitrogen-macrophytes temperature cyanobacteria diffuse loading problem focus on Lake Taihu…. P lake = P in /(1+  tw), tw = y -1. After 10 years. Chen et al, 2003. P-lake/P-in*100.

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outline
Outline
  • Loading –concentrations
  • littoral-open water interactions
  • cyanobacteria and nutrients , N:P
  • nitrogen-macrophytes
  • temperature cyanobacteria
  • diffuse loading problem
  • focus on Lake Taihu…
slide6

P-lake/P-in*100

P-lake=P-in/(1+retention time**0.5)

Lake Taihu

retetention estimated:

39% - ”measured”

35% (Qin, 2007)

Hydraulic retention time (years

slide7

Bioavailable P

Bioavailable P typically >

500-2000 in DK lakes

Zhu et al, 2006

slide8

Lake Arresø

Area 40 km2

% of country area 0.09

Mean depth 3.1 m

Max depth 5.9m

Tw 3.5 y

Lake Taihu

Area 2338 km2

% of country area

0.02!!!

Mean depth 1.9 m

Max depth 4.5m

tw 0.8 y

slide9

Hydraulic retention time:

3.5 years

Simple dilution

Three retention times (10.5 years) reduced by 95%

Jeppesen et al ,2007

resuspenion does not prevent improvements even in relatively large shallow lakes
Resuspenion does not prevent improvements-even in relatively large shallow lakes

Fraction of

suspended solids

made up by detritus

and inorganic SS

slide12

Seasonal changes in P concentration

Seasonal phosphorus concentrations (relative to winter values) in 265 shallow Danish lakes with different P levels.

phosphorus release mechanisms factors
Phosphorus release mechanisms/factors
  • Physical: temperature
  • Chemical
  • Biological
  • P release increases at rising temperatures due to increased mineralization and oxygen/nitrate consumption, thus diminishing the oxidised surface layer.

Cumulative P release from four lakes at 7, 14 and 21 oC.

Thickness of oxidised surface layer in four lakes at 7, 14 and 21 oC

Based on Jensen et al. (1992)

slide17

Model

dPV/dt = (Q/V)*[Pin]-SED+REL water

dPS/dt = SED-REL-IMM sediment

SED = bS*PV/Z

REL = bF*(tF^(TEMPV-20))*PS

IMM = bI*PS

parameters from the Danish model: bS=0.0695, bF=0.000468, tF=0.0867, bI=0.0000923. - 16 lakes-many years

PV og PS [g/m^2], rates [g/m^2/d].

Time step 1 month

slide18

Examples of the seasonal P-model

Borup

Useful for Lake Taihu?

Maybe if including the hydrodynamics

lake engelsholm
Lake Engelsholm

Before fish removal: 1989-1993

After fish removal : 1994-1999

Søndergaard et al,2003

p dynamics
P dynamics

Simple models useful?

Complex models taking hydrodynamics

into account better?

Sediment –water interactions – how to do realistic experiments

Spatial and temporal variability

Role of N for P release, role of macrophytes (bays), role of fish

slide22

lake intercept inlet mean depth retention time

Lake Taihu: 1.9 m mean depth, 5month retention time

prediction 56% loss - ”measured” 49%

slide25

Loading

N-lake

related to:

-Depth

-TW

-N-in

-Temp

Retention

Retention (%)

slide27

N-dynamics (chemical perspective)

Assimilation

PON

NO3-

NO2-

Excretion

N2

NH4+

Fixation

Sinking

DON

N2O

Water column

Sediment

NO3-

NO2-

NH4+

N2

DON

PON

DNRA

NO3-

N2O

DENITRIFICATION

Transformations within the nitrogen cycle in shallow aquatic systems

(Slide modified from version of Soonmo An)

UTMSI

slide28

Mark in Action

at Lake Taihu

China

n dynamics
N dynamics

Simple models useful?

Complex models taking hydrodynamics

into account better?

Sediment –water interactions – how to do realistic experiments

Spatial and temporal variability

Role of macrophytes (bays), role of fish

slide32

Physical: resuspension by wind/benthivorous fish

  • Resuspension increases turbidity and sediment-water interactions, particularly in very shallow lakes.
  • Submerged macrophytes and floating leaved plants may put a damper on the impact of resuspension. (Huang et al,2007)

Lake water changes during 10 days at changing wind speed (from 0-2 to 5-7 m/s to 2-3 m/s) in Western Stadil Fjord, Denmark (450 ha, mean depth: 0.8 m).

slide34

Pelagic- littoral zone interaction , Bay-main lake interactions

Huang et al, 2007 - resuspension 50% of open water

in Trapa beds.

Wang ,2007 - Higher concentration of nitrate in the reed

zone than 200 m away – indicating that trapped

nutrients are released from in here and trabsported to the

open water.

Littoral-open water interactions (trap-release) an important

research area . Redsistribution of sediment as well.

Local removal of sediment a relastic symptom treatment?

slide35

Diatoms

Silicate

Cyanobacteria

green algae

Lake Arresø

Jeppesen et al ,2007

slide39

Water clarity

increases not least

after zooplankton

biomass and body

size increases

slide40

Shallow Danish lakes

N-fixing Cyano

then

non-N fixing Cyano

then

Green algae

with increasing TP

Jensen et al, 1994

slide41

Green algae and not N fixing

cyanoes at the lowest

inorganic N

N fixers at intermediate TN:TP

not low TN:TP

Jensen et al, 1994

slide43

Deep

Shallow

slide46

High N input-- Enhances or reduces importance of

cyanobacteria?

or is P affinity the important factor ?

is N:P at all of importane in shallow lakes?

Should we focus on nutrient release /turnover instead

and on benthic pelagic coupling

changes in water temperature in danish survey lakes 1989 2005
Changes in water temperature in Danish survey lakes 1989-2005

simpel lineær regression

model log cyanobacteria biomass log tp log mean depth log wat temp
Model: log(cyanobacteria biomass) = log(TP), log (mean depth), log(wat. temp.)

Jeppesen et al, in prep.

model log cyanobacteria biomass log tp log mean depth log wat temp1
Model: log(cyanobacteria biomass) = log(TP), log (mean depth), log(wat. temp.)

Jeppesen et al, in prep.

slide50

Climate warming will likely enhance the risk of

cyanobacteria dominance and the duration of

blooming during the year

slide53

Mette Bramm

MSc, research assistant

National Environmental Research Institute, Silkeborg

Highlights from Master Thesis, 2002

biomass submerged plants
Biomass submerged plants

last day

one with plants

slide55

Perihyton and phytoplankton growth stimulated by N thereby out-shading the submerged macrophytesN threshold not a constant!!!various with fish density and probably climate

comparative studies
Comparative studies

Denmark (55°-57°N)

Uruguay (30°-35°S)

Meerhoff et al, in press,submitted

and on the road

slide58

High N may lead to losses of macrophytes in temperate lakes

at intermediate high TP

How about Lake Taihu plant communities?

Warmer winters than in DK , much warmer summers

Role of fish different or?.

slide67

Shallow

all seasons, but see spring

May, June ,autumn

slide68

Slope for log chla = x log TP + y log TN

FLORIDA - DENMARK

TP

Y

TN

TN

TP

X

month

month