Leafy elodea (Egeria densa) growth and decay
About Egeria densa
Leafy elodea is a perennial plant which grows beneath the water’s surface. It is usually rooted in the mud, however it may also be free floating within the water. Leafy elodea forms dense mats beneath the water surface that:
- restrict water flows
- increase silting
- outcompete native plants
- reduce food and shelter for fish and other native aquatic animals
- can block irrigation equipment, domestic pumps and hydroelectric systems.
- make swimming, boating and fishing difficult.
Leafy elodea grows in warm temperate, subtropical and tropical regions though it is more cold tolerant than many other aquatic weeds. It has been found in slow-moving or still water up to 7 m deep including ponds, lakes and slow moving streams and rivers. It grows best in nutrient-rich conditions, though it tolerates a wide range of nutrient levels. It prefers areas where the sediment has been disturbed. Leafy elodea can tolerate very low light levels caused by either shade or sediment in the water.
Water requirements
This model, describing the growth and decay of Egeria densa was developed to support water planning in the Hawkesbury-Nepean River system. The model uses a ‘rating curve’ approach, whereby the rate of growth is defined by a relationship between growth and temperature. There is a maximum growth rate from 30-35 degrees Celsius. The decay component of the model is also a rating curve style, whereby the removal of (decay) Egeria desna is defined by high flow conditions.
Model purpose
This model has been constructed to help predict periods of high Egeria densa growth. The purpose of the model is test the likely effectiveness of alternative water management scenarios at controlling Egeria densa growth.
Development context
This model, describing the growth and decay of Egeria densa was developed to support water planning in the Hawkesbury-Nepean River system.
Spatial application
This model, describing the growth and decay of Egeria densa was developed to support water planning in the Hawkesbury-Nepean River system. However, the model parameters could be set for other locations.
Model description
Ecohydrological rules
The model has two components.
1) Decay: this is removal of macrophyte biomass and is to represent the removal of Egeria Densa during periods of high discharge.
2) Growth: the growth component of the model represents the rate of growth which is limited by temperature (nutrient and light are assumed to not be limiting).
There is no predation included in the model.
The model generates a daily biomass score which is simply the addition of the daily growth values. The accumulated growth is only reduced via the decay function.
Assessment method
This model produces continuous yearly results (Egeria densa biomass growth). The biomass values are not intended to represent an accurate biomas, but rather to allow the comparison of trajectories of growth and weed removal under alternative water use scenarios.
These results are then aggregated to a binary yearly result and then further to a binary temporal result based on the defined assessment parameters.
The temporal results are then analysed across locations to report an overall landscape risk by considering the simultaneous occurrence of failures across the system.
Inputs
Data
- Daily flow data
Parameter Sections
- Data – define the component type and function. Set the type as growth or decay, and create the magnitude curve to map flow to growth/decay.
Outputs
- Daily time series of biomass change
- Yearly time series of total biomass
- Yearly time series of assessment results
- Temporal time series of assessment results
- Spatial time series of assessment results
User interface
Underlying code
This plugin is written in Python and its underlying code is publicly available from the Eco Risk Projector computation repository.
Marting F. Goman & Dianne J.Bray. Maccullochella mariensis in Fishes of Australia, accessed 20 Dec 2022, https://fishesofaustralia.net.au/home/species/3000
Barriers and instream structures. Source: Berghuis, A,. Queensland Government, 2021. https://wetlandinfo.des.qld.gov.au/wetlands/resources/publications/latest-news/2021-04-30.html 
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