Impacts of hydrological changes on phytoplankton ... · Impacts of hydrological changes on phytoplankton succession in the Swan River, Western Australia Terence U. Chan, Barbara J.

Impacts of hydrological changes onImpacts of hydrological changes on

phytoplankton succession in the Swanphytoplankton succession in the Swan

River, Western AustraliaRiver, Western Australia

Terence U. Chan, Barbara J. Robson, David P. Hamilton, Chris DallimoreTerence U. Chan, Barbara J. Robson, David P. Hamilton, Chris Dallimore

Centre for Water Research, University of Western AustraliaCentre for Water Research, University of Western Australia

and Ben R. Hodges and Ben R. Hodges

Dept. of Civil Engineering, University of Texas at AustinDept. of Civil Engineering, University of Texas at Austin

Upper Swan River estuary phytoplankton succession

summer autumn winter spring summer

Objective: determine to what

extent this succession is the

result of anthropogenic changes

121,000 km2

Perth

The Swan-Avon Catchment

•• Extensive clearing for agriculture (~35% remains natural) Extensive clearing for agriculture (~35% remains natural)

•• Urbanization around estuary Urbanization around estuary

•• Construction of reservoirs Construction of reservoirs

•• River River ““trainingtraining”” to handle increased flows to handle increased flows

•• Removal of estuary sill Removal of estuary sill

HydrologicalHydrological

changeschanges

Agricultural clearingAgricultural clearing

with minimal retentionwith minimal retention

of riparian zoneof riparian zone

Perth

Urban drains and groundwater intrusion

dominate the summer inflows in the estuary

350

25

1.2

90% of

the

annual

inflow

Present

hydrology

Avon Avon ““RiverRiver””

during theduring the

summersummer

Catchment effects ofCatchment effects of

anthropogenic changesanthropogenic changes

Based onBased on

LASCAMLASCAM

model of model of VineyViney

and and SivapalanSivapalan

~ 5 fold~ 5 fold

~ 16 fold~ 16 fold

~ 40 fold~ 40 fold

Increased runoff due to clearing Increased runoff due to clearing

Increased nutrient loads from agriculture Increased nutrient loads from agriculture

Increased sediment yield Increased sediment yield

Salinity field data,

Sept 26, 1995

to

July 1, 1996

Salt-wedge

estuary during

summer in the

upper reaches

Sill at 2m

deepened

to 14 m

“Snapshot” comparison of field data

and 3D hydrodynamic model ELCOM

Computational Aquatic

Ecosystem Dynamics Model

CAEDYM

lines = CAEDYM/ELCOM model

points = field data

field vs base case simulationfield data

baseline

model results

Model scenariosModel scenarios

Reduced catchment flowsReduced catchment flows

Reduced nutrient loadsReduced nutrient loads

Removal of reservoirsRemoval of reservoirs

Restoration of Fremantle sillRestoration of Fremantle sill

ELCOM

model

salinity

results

baseline

reduced

catchment

flows

CAEDYM-

ELCOM

model

chlorophyte

results

baseline

reduced

catchment

flows and

nutrients

baseline

model results

reservoirs removed

model results

baseline

model results

reduced nutrient load

model results

baseline

model results

reduced nutrient load

and reduced flow

model results

reduced nutrient load

and reduced flow

model results

reduced nutrient load

model results

Work in progress – effect of the sill on salinity

ELCOM

model

results

baseline

sill

restored

Further WorkFurther Work

Apply longer run-up time to reduceApply longer run-up time to reduce

initialization artifactsinitialization artifacts

Model management targets for reducedModel management targets for reduced

nutrient loadsnutrient loads

Conclusions

Calibrated 3D model for water quality can capture

phytoplankton succession in the Swan River estuary

Anthropogenic nutrient loads have increased

phytoplankton biomass

Phytoplankton succession appears altered by changes in

flow and loads

Acknowledgements

• Western Australian Estuarine ResearchFoundation (WAERF)

• Water and Rivers Commission of WesternAustralia (W&RC);

• WA Department of Transport;

• WA Department of Environmental Protection;

• Dr. David Horn

For further info contact: [email protected]