Wetlands,
Biodiversity and Salt
Macrophytes
August 2006
Macrophytes are aquatic plants. They include charophytes, algae that resemble flowering plants in
form, but exclude other types of algae. They take many growth forms – emergent, submerged,
floating leaved and free floating.
Macrophytes are generally conspicuous and defining features of wetlands, and the presence and
type will have profound effects on the wetland system. They underpin many wetland processes and
dictate the presence of other biota.
Photos: Keely Ough and Michele Kohout
Our aims
If we are to avoid detrimental levels of wetland salinity, it’s important we know what those salinity levels are.
We need to know the relative sensitivities of species and the overall response of macrophyte communities to
salinity.
In this project we aim to
•
better understand how macrophyte communities vary with salinity
•
determine the impact of increased salinity/secondary salinisation
•
determine whether species’ responses are similar, and
•
explore critical salinity limits
using complementary field survey and experimental approaches.
Field study
Experimental program
The macrophytes of 58 wetlands in the Wimmera
were sampled to gain an understanding of the
distribution of macrophyte species relative to
salinity, and changes in community structure and
composition caused by secondary salinisation.
Soil cores were collected from wetlands during
their dry phase and in glasshouses subjected to
inundation at a range of salinities. After a typical
inundation period, macrophyte emergence, growth
and reproduction were assessed. In a similar
experiment we also simulated wetlands being
flushed with fresh water after several months of
saline inundation to investigate the resilience of
wetland seedbanks.
Photo: Keely Ough
Photo: Keely Ough
A Victorian
Government
initiative
Our results so far
Both field and experimental data indicate that increased salinity leads to a
•
reduction in the abundance of macrophytes
•
decline in species richness, and
•
change in community structure.
This will have flow-on effects to wetland function such as primary production, nutrient cycling and habitat
provision.
Critical levels of salinity
No. of individuals
Individual taxa show a range of responses to an increase in salinity, rather than all taxa declining at the same
level of salinity.
Increasing salinity
Species response to salinity varied, from unaffected to very sensitive.
For example we might wish to compute the salinity at
which the number of emergents is reduced to say 50%
of the optimum – Salinity Level 50 for emergence
(SL50e). Or we could use any desired proportional
response. These figures would allow comparisons
between species, and between life history stages, and
could represent critical levels of salinity that lead to
response of a particular magnitude – somewhat
analogous to LD50 figures used by toxicologists. We
will do this over the coming months.
Optimal
No. of emergents
We propose a useful procedure is to compute the
salinity that decreases the number of plants (or
biomass or reproductive capacity) to a given proportion
of the modelled number at the salinity of optimal
response.
SL70e
SL50e
Increasing salinity
Proposed critical salinity levels, which will allow
comparison between species and life history stages,
and could allow us to set wetland salinity maxima.
Potential uses of relative sensitivity data
This variation in species response could be used as a management tool, both in terms of determining how much
salt is too much, and being better able to monitor the outcomes of increased levels of salinity.
For example, to protect a particular wetland, the salinity could be kept below the critical level for a suite of the
most sensitive taxa. These taxa then provide the basis for a targeted monitoring program, which would simplify
measuring of the performance of programs designed to avoid or alleviate salinity. For rehabilitation programs,
species would best be chosen from the least sensitive end of the spectrum, potentially saving money on the
planting of salt sensitive taxa whose critical salinity levels have been exceeded.
As more of our analyses are completed, we are building up a picture of the range of critical salinity levels
important to the long-term maintenance of freshwater macrophyte communities.
Published by the Victorian Government Department of Sustainability and EnvironmentMelbourne, August 2006
© The State of Victoria Department of Sustainability and Environment 2006
This publication is copyright. No part may be reproduced by any process except in accordance with the provisions of the Copyright Act 1968.
Authorised by the Victorian Government, 8 Nicholson Street, East Melbourne.
ISBN 1 74152 603 5
For more information contact the DSE Customer Service Centre 136 186 or Dr Michael Smith on (03) 9450 8612 or michael.smith@dse.vic.gov.au, Arthur Rylah Institute,
Department of Sustainability and Environment, PO Box 137, Heidelberg 3084.
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the Wetlands, Biodiversity and Salt project can be found by following ‘Research Themes’ to
‘Salinity and Climate change’