2.1. Study site
Macrophytes were collected from the Long Island Backwater in
Ornamental
Lake, Melbourne (37
◦
49
S, 144
◦
58
E) in January 2012.
Ornamental
Lake is the largest lake within the RBG, with a volume
of 62,000 m
3
, a surface area of 4.1 ha and average depth of
1.5
m (Symes, 2003). The lake was originally part of the nearby
Yarra
River. The waterbody was isolated over 100 years ago as
part
of a river-straightening programme to mitigate flooding of
the
city. Storm water, natural drainage and water from irrigation
runoff
within the gardens are now the main sources of water
to
the lake (Beckwith, 1997). Ornamental Lake was dredged in
1982
and 1983 to remove the invasive macrophyte Nuphar lutea
and
to increase its depth. The lake subsequently shifted to a
phytoplankton-dominated
state and regularly experienced algal
blooms
(in January
and
July) dominated by Anabaena and Microcystis
(Grace et al., 2010). Algal blooms declined in 2009 coincident
with
an
increase
in the % cover of P. crispus and C. australis.