NUTRIENT EFFECTS ON INSHORE SEAGRASS BEDS EXPERIMENT
Postgraduate student Jane Mellors, working with QDPI, is currently conducting
research into the effects of artificially enhanced nutrients on the nearshore
seagrass (Halophila minor) at Picnic Bay and Bolger Bay, Magnetic
Island. The experiment aims to monitor seagrass response to increased
loadings of nitrogen (N) and phosphorus (P) under different sedimentary
regimes during the plants' slow and active growth seasons.
The island site has been prepared using `Osmocote', a common fertiliser,
to establish nutrient loadings for the experiment. The study supplied
underwater plots with a combination of N and P at loadings of 100g N m-2
and 32g P m-2 respectively. After 3 months the
porewater and extracted nutrients absorbed into sediment at each plot
increased ten fold compared to the control plots. Given there can be a
80-90% loss of fertilizer in the sea, Jane was able to calculate loadings
for each experimental treatment.
Using both nitrogen and phosphorus-only slow release Osmocote,
the first fertilisation experiment started on May 12 at Bolger Bay and
May 14 at Picnic Bay. High and low loadings, and various N and P combinations,
were placed under plugs of seagrass. Low experimental loadings represent
5x ambient, whilst the high are 15x ambient. Each treatment was assigned
one in three randomly positioned blocks. Experimental and field controls
were also assigned. A combination of these controls will test the response
of seagrass to this nutrient manipulation.
The experiment will run for 90 days, a time determined by several researchers
(Dr. W Dennison, James Udy & Greg Neighbour) and Jane as the longevity
of the slow release Osmocote in a marine environment. The cooler period
of this experiment coincides with the seagrasses dormant growth phase.
A second fertilisation experiment will commence in August 1995,
using the same loadings as the first experiment, and also run for 90 days.
This experiment will monitor the response of the seagrass to identical
manipulations during its active growth phase.
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