Ecological Impact of Nutrients
from Shrimp Farms
Mark O’Donohue, Adrian Jones, Simon Costanzo,
Michele Burford, Pat Glibert, Judy O’Neil, Cindy Heil
& William Dennison
Marine Botany
THE UNIVERSITY
OF QUEENSLAND
Assessing Ecological Health
Ecological health has been variously defined, including:
• Ecological health is the maintenance of biodiversity and
ecosystem integrity (Draft ANZECC Guidelines)
• Ecological health is represented by
a) a lack of ‘distress syndrome’
b) stability over time and
c) resilience to change
These definitions are appropriate for describing the
ecological health concept, but do not define ecological
health in terms of measurable quantities
Measuring Ecological Health
Ecological Health Indicators
• Habitat:
seagrass depth range, phytoplankton density (Chla)
• Anthropogenic Impact:
delta 15N, %N, amino acids, nutrient flux, water quality
• Key Processes:
denitrification, sediment N flux, phytoplankton bioassays
N Limitation in coastal waters
Phytoplankton bioassay responses
N (not P) additions stimulate
phytoplankton biomass
Treatment
Stimulation Factor
Control
DIN (NH4 + NO 3)
PO4
1
6
1
SiO3
All
1
11
DIBM 1998
Macroalgal tissue nutrient content*
%N correlates with dissolved inorganic [N]
r2 = 0.68
%P does not correlate with dissolved inorganic [P]
r2 = 0.08
*Horrocks et al. 94
N-Form influences biotic response
100
80
60
40
20
0
0
20 40 60 80 100
100
80
60
40
20
0
0
20 40 60 80 100
Macrophyteb
• NH4+/Urea/NO3- ratio affects
macrophyte amino acid content
a Glibert,
% Uptake of urea
% Uptake of
ammonium
Planktona
• N preference NH4+>Urea>>NO3• NH4+
Diatoms
• Urea
Dinoflagellates
• NO3Denitrifying bacteria
% Diatoms
% Dinoflagellates
O’Neil, Heil and O’Donohue b Jones, Horrocks, Udy and Dennison
The Problem
•Small fraction of nutrients added to aquaculture ponds is
absorbed by target species
Feed
2600
10400
Effluent
7000
NH4
15000
5400
Sediment
(g/ha/d)
Nitrogen budget (Burford et al. 99)
•Large fraction of nutrients added to aquaculture ponds is exported
•Nutrient enrichment of receiving waters could have potential
deleterious impact on ecological health
Key features of Shrimp Farm Effluent
•
•
•
•
•
Composition
seawater
clay particles
marine phytoplankton
particulate and dissolved nutrients
[NH4+]>[NO3-]>[PO43-]
By comparison, sewage effluent
• freshwater
• dissolved nutrients
• [NO3-]>[NH4+][PO43-]
Implications
High [nutrient] particularly
[NH4+]
 phytoplankton bloom
potential
Elevated turbidity
 potential for nutrient
sorption
Aims
• Develop & test ecological health indicators for
shrimp farm effluent
• Using appropriate indicators, assess influence
of shrimp farm effluent on ecological health of
receiving waters
• Formulate recommendations for aquaculture
effluent management
Vegetation Nutrient Content
Delta 15N
[Amino Acid]
Study Site: Moreton Bay (estuary)
Moreton
Bay
Delta 15N mangrove,
seagrass and
macroalgae
(passive indicators)
Amino acid
concentration
and composition
- seagrass
Amino Acid
Concentration
15 000
10 000
Amino Acid
Composition
Other
Glutamine
5 000
nmol g fresh -1
Proline
Phytoplankton
bioassays
Nutrient response
Study Site: Hinchinbrook Channel (tidal creek)
Hinchinbrook
Channel
0
5 10 15 20 25 30
Kilometers
Phytoplankton bioassays - Dry
Phytoplankton bioassay - Dry/Wet
Delta 15N - Macroalgae (4 day incubation)
Shrimp farm - Conceptual model
Dissolved N
Elevated
delta15N
Particulate N
Elevated
Elevated
phytoplankton [amino acid]
bloom potential
Low particulate and dissolved N
•Low delta15N
•Low [amino acid]
•Low phytoplankton bloom potential
Summary
• Coastal ecosystems N limited
• Shrimp farms contribute large proportion of
feed N to receiving waters
• Nutrients from aquaculture discharge stimulate
phytoplankton blooms (but effluent is not an ‘inoculum’
for receiving waters)
• N form can influence physiology and community
structure in receiving waters
• Ecological health indicators provide direct measures
of influence of aquaculture discharge
Implications
Recommend
• On-farm N removal to reduce downstream impacts
• Oxidation of N compounds to reduce potentially toxic
dinoflagellates and enhance denitrification
Ecological Health Indicators
• Can be used to assess potential influence of discharge on
intake waters
• Provide a mechanism for assessing downstream impacts
in a growing industry in relation to other N sources
Acknowledgments
•
•
•
•
Cooperative Research Centre for Aquaculture
Marine Botany, University of Queensland
CSIRO Marine Research
Horn Pt Labs, University of Maryland