lake plants speak out - niwa · lake plants speak out on lake condition introduction aquatic plants...
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Waikaremoana
Rotoma
Rotoiti1988
Rotoiti2003
Rotoehu1988 & 2003
Rotorua2003
Rotorua1988
Okareka1988
Okareka2003
Okaro1988
Okaro2003
This lineillustrates lakeecologicalcondition onthe decline!
Decline in lakeconditiontypicallypreceedspublicawareness -but thenconditionsare serious!
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Wakatipu
LA
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www.niwa.co.nzNational Institute of Water and Atmospheric Research Ltd PO Box 11-115, Hamilton, New Zealand
ph: +64-7-856 7026, fax: +64-7-856 0151 email [email protected]
Lake plants speak outon lake conditionIntroductionAquatic plants are valuable indicators of lake health, and for five
Rotorua lakes the submerged plants that inhabit them have been
given the chance to speak out on lake ecological condition.
LakeSPI or �Lake Submerged Plant Indicators� is a new
management tool that uses submerged plants from within lakes
to indicate lake ecological condition.
Lakes Rotoiti, Rotoehu, Rotorua, Okareka and Okaro were
chosen by Environment BOP for this assessment due to
widespread concern over their deteriorating condition.
LakeSPILakeSPI uses information based on aquatic plant measurements
taken from within lakes in order to generate three LakeSPI
indices:
�Invasive Condition Index�
This captures the invasive character of vegetation in a
lake based on the degree of impact by invasive weed
species.
�Native Condition Index�
This captures the native character of vegetation in a lake
based on diversity and quality of indigenous plant
communities.
�LakeSPI Index�
This is a synthesis of components from both the native
condition and invasive condition of a lake and provides an
overall indication of lake ecological condition.
Submerged plants are used as are they are easy to observe,
integrate long-term climatic and environmental influences and
bring a focus to the littoral margins of a lake where greatest
public interaction and perception occurs.
MethodFive sites were selected from within each of the five lakes and
LakeSPI surveys were carried out in September 2003.
LakeSPI indices were calculated and then compared with indices
generated for lakes from historic surveys.
Details of the LakeSPI method can be found in the LakeSPI
manuals or website shown below.
ResultsLake Rotoiti
l Overall lake condition � very poor!
l LakeSPI Index has decreased.
l Blue/green algae smothering plants.
l Invasive weed species close to maximum
impact.
l Worst rating weed (hornwort) dominant.
l Native condition at only 18% of its potential.
Lake Rotoehu
l Overall lake condition � Poor.
l LakeSPI Index has remained stable.
l Blue/green algae covering plants.
l Invasive weed species can still get worse.
Lake Rotorua
l Lake condition very poor.
l LakeSPI Index increased slightly due to declining
invasive species.
l Blue/green algae covering plants.
l Worst invasive weed (hornwort) present but having
little effect.
l Lake condition moderated by high exposure that
helps to minimise invasive weed impact and water
quality features.
Lake Okareka
l Lake condition � compromised and still declining.
l LakeSPI Index has decreased over 15 year period
(due to egeria spread + decline in meadows
attributable to deteriorating water clarity.
l Invasive weed species can get much worse (no
hornwort).
l Native charophyte meadows still present but
maximum depth is declining.
l Blue/green algae covering plants.
Lake Okarol Lake condition � very poor!
l LakeSPI Index largely unchanged from already
degraded state.
l Blue/green algae smothering plants.
l Invasive weed species can get much worse!
l Very few native species.
Conclusionsl Lake Rotoiti and Okareka have continued to decline in lake condition; while Lakes
Rotorua, Rotoehu and Okaro have remained in a stable yet degraded state since the
1980�s.
l All five lakes are now dominated by invasive weed species, native vegetation has
been largely displaced, former deep water charophyte communities have all but
disappeared, and the health of remaining aquatic vegetation is clearly compromised
by smothering growths of filamentous blue-green algae.
l LakeSPI will continue to provide meaningful baseline for assessing future management
initiatives on the Rotorua lakes.
www.niwa.co.nz/ncwr/lakespi
Tracey Edwards
John Clayton
Lake Okaro
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Acknowledgements
Environment BOP for their assistance.
FRST for funding under our Aquatic Plant Management programme that helped
support the development of the LakeSPI methodology.
Acknowledgements
Environment BOP for their assistance.
FRST for funding under our Aquatic Plant Management programme that helped
support the development of the LakeSPI methodology.
www.niwa.co.nzNational Institute of Water and Atmospheric Research Ltd PO Box 11-115, Hamilton, New Zealand
ph: +64-7-856 7026, fax: +64-7-856 0151 email [email protected]
Invasive Native LakeSPI
Lake plants speak outon lake condition
Lake Okareka
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Invasive Native LakeSPI
Lake Rotorua
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Invasive Native LakeSPI
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Lake Rotoehu
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Invasive Native LakeSPI
Lake Rotoiti
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Invasive Native LakeSPI
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