AN ASSESSMENT OF THE EFFECTIVENESS OF

VEGETATION HARVESTING AS A MEANS OF REMOVING

NUTRIENTS AND METALS FROM PONDS

Fiona Napier Urban Water Technology Centre

Dr Michael Barrett Center for Research in Water Resources

Prof Chris Jefferies Urban Water Technology Centre

Why the study?AQUATIC PLANTS

HARVESTING

INCREASED MAINTENANCE COSTS

Why the study?AQUATIC PLANTS

HARVESTING

INCREASED MAINTENANCE COSTS

POLLUTANT REMOVAL BENEFIT?

Key questions to answer

• What mass of each selected constituent is removed from the system when vegetation is harvested?

Key questions to answer

• What mass of each selected constituent is removed from the system when vegetation is harvested?

• How does this figure compare with mass of each constituent being removed by all processes within the system?

Methodology

• Desk study

Methodology

• Desk study

• Chemical mass balance for nutrients and metals in a pond treating urban/highway runoff, using data gathered from a number of published studies.

Data requirements

• In-situ pond with established vegetation and receiving urban/highway runoff

Data requirements

• In-situ pond with established vegetation and receiving urban/highway runoff

• Levels of selected constituents entering and leaving pond

Data requirements

• In-situ pond with established vegetation and receiving urban/highway runoff

• Levels of selected constituents entering and leaving pond

• Known weight of harvested vegetation

Data requirements

• In-situ pond with established vegetation and receiving urban/highway runoff

• Levels of selected constituents entering and leaving pond

• Known weight of harvested vegetation

• Chemical composition of removed plant material

La Costa pond

• Retention pond on Interstate 5, California

La Costa pond

• Retention pond on Interstate 5, California

• Recieves flow from 1.7ha catchment (48% impermeable cover), including northbound lanes of highway

La Costa pond

• Retention pond on Interstate 5, California

• Recieves flow from 1.7ha catchment (48% impermeable cover), including northbound lanes of highway

• 3 year water quality monitoring program

La Costa pond

• Retention pond on Interstate 5, California

• Recieves flow from 1.7ha catchment (48% impermeable cover), including northbound lanes of highway

• 3 year water quality monitoring program

• Established vegetation, including Typha

La Costa pond

• Retention pond on Interstate 5, California

• Recieves flow from 1.7ha catchment (48% impermeable cover), including northbound lanes of highway

• 3 year water quality monitoring program

• Established vegetation, including Typha

• Annual programme of Typha harvesting

La Costa Pond

Pre-harvest

Post-harvest

La Costa pondData available for pond

• Flow data

• Input/output concentrations for N, P, Cu, Pb, Zn

• Known weight of harvested vegetation

La Costa pondData available for pond

• Flow data

• Input/output concentrations for N, P, Cu, Pb, Zn

• Known weight of harvested vegetation

Data unavailable for pond

• Chemical composition of plant material

Additional data sources

Criteria for inclusion in study:-

• Plant studied must be Typha

Additional data sources

Criteria for inclusion in study:-

• Plant studied must be Typha

• Must be grown in environment containing levels of nutrients and metals similar to La Costa

Additional data sources

Criteria for inclusion in study:-

• Plant studied must be Typha

• Must be grown in environment containing levels of nutrients and metals similar to La Costa

• Must be harvested at same point in growing season

Results

% constituent removedN P Cu Pb Zn

All mechanisms

43.5 48.0 57.7 92.5 60.7

Harvested vegetation

5.0-7.0 2.9-8.5 0.3 0.2 1.8-2.0

Cost effective ?

0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

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Plant harvesting >70% total maintenance manhours = $14 000 (£7700)

• Aesthetics/amenity

• Safety

• Habitat

• Vector/algae control

• Pollutant removal

Why include vegetation in ponds?

Reducing costs?

Garver, E. G., Dubbe, D.R.. and Pratt, D.C.

Seasonal patterns in accumulation and partitioning of biomass and macronutrients in Typha spp

Aquatic Botany 32 pp115-127. 1988

Reducing costs?

• Study carried out over 2 growing seasons

• Identified July of second growing season as time for removing maximum amount of nutrients in minimum amount of biomass

Improving pollutant removal?

Fritioff, A. and Greger, M.

Aquatic and terrestrial plant species with potential to remove heavy metals from stormwater.

International Journal of Phytoremediation 5(3) pp 211-224 (2003)

Improving pollutant removal?

• Typha metal accumulation:

sediments»roots/rhizome»leaves/shoots

• Study showed that some submersed and free-floating aquatic plants have higher metal accumulation capacity in their shoots than emergent species