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

Summary

By quantifying the current aquatic weed problems in peri-urban areas that are undergoing rapid development, and determining the extent to which both weed introduction and changed environmental factors influence aquatic weed spread, this project will assist in improving management practices to reduce weed impacts.

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: (1) quantifying the current aquatic weed problem in peri-urban environments (species, location, and abundance), (2) 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), and 3) identifying methods to manage landscapes in order to reduce aquatic weed spread and impact.

Outcomes

We quantified aquatic weed abundance according to land use through desktop and field-based surveys and classified 24 species in a ranked list based on distribution.  We note that 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 our studies.  Peri-urban land uses hosted an intermediate abundance of aquatic weed species in our field-based study, but evidence suggested weed species were better able to capitalize on peri-urban conditions than native aquatic species.  Our 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: 1.) land managers should focus their early-detection and control efforts on peri-urban and urban land use areas, and 2.) 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.
 

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