Effect of land use and peri-urban development on aquatic weeds

Summary

We are interested in understanding the individual growth responses and competitive dynamics of native and invasive aquatic macrophytes in various environmental conditions.  Before initiating a more complex study, we propose to evaluate the effects of a single factor, shading, on the growth of non-native aquatic macrophytes.  This factor is relevant to the larger scope of our research, in which we are investigating the effects of peri-urban development on aquatic plant populations.  Riparian clearing is common in urban and agricultural landscapes, and the resulting increase in light (and water temperature) may contribute to the proliferation of aquatic invaders.  Indeed, other researchers have demonstrated the efficacy of shading in reducing populations of these species.  We are interested in applying this question to three previously untested species and establishing the critical level of shading that limits their growth.

Aims

The purpose of this project is to understand the impacts of peri-urban development on the invasiveness of aquatic weeds in Australia. This will be achieved by:

• Quantifying the current aquatic weed problem in peri-urban environments (species, location, and abundance)
• Determining to what extent aquatic weed problems are the consequence of introduction events (propagule pressure) and/or modified environmental factors (i.e. nutrient inputs, stream hydrodynamics, and riparian canopy structure)
• Identifying methods to manage landscapes in order to reduce aquatic weed spread and impact.

Outcomes

Aquatic weed abundance was quantified according to land use through desktop and field-based surveys and classified 24 species in a ranked list based on distribution.  Management efforts should be tailored to the relative distribution of these species, with recommendations for biocontrol of widespread species and focused early-detection programs for those currently classified as rare.

The land use types that hosted the greatest numbers of aquatic weed species were those that were classified as “urban” or “intensive” in this studies.  Peri-urban land uses hosted an intermediate abundance of aquatic weed species in the field-based study, but evidence suggested weed species were better able to capitalise on peri-urban conditions than native aquatic species.  Field-based and experimental work revealed that aquatic weed growth was inversely related to canopy cover and shade.

Two recommendations follow from the results of this project:

• Land managers should focus their early-detection and control efforts on peri-urban and urban land use areas
• Riparian forests should be restored  to reduce light availability and buffer nutrient inputs, resulting in sustained reduction of aquatic weed populations.

Background

Peri-urban areas are expanding rapidly in Australia, and due to landscape modifications such as disturbance, increased nutrients and changes in hydrology and increased introduction of weed species, they are experiencing severe weed problems.

Weeds in waterways (aquatic weeds) are both a problem in their own right and as a source of introduction of weeds into previously pristine environments.  Effective management of such species will require holistic management strategies across local landscapes.

This project will identify the environmental conditions and plant characteristics that drive weed invasion of aquatic systems, to assist in better managing introduced plants with potential to adversely affect our waterways in the future.

Publications and Resources

None listed

Citation

Land & Water Australia. 2008. Effect of land use and peri-urban development on aquatic weeds. [Online] (Updated April 28th, 2009)
Available at: http://lwa.gov.au/node/2576 [Accessed Monday 22nd of March 2010 02:37:09 AM ].