Upload
rita-domingues
View
787
Download
0
Tags:
Embed Size (px)
Citation preview
Phytoplankton nutrient limitation in the Ria Formosa:
implications for eutrophication assessment
Rita B. Domingues1,2, Cátia C. Guerra1, Ana B. Barbosa1, Helena M. Galvão1
1 Centro de Investigação Marinha e Ambiental, Universidade do Algarve2 Centro de Oceanografia, Faculdade de Ciências, Universidade de Lisboa
What is phytoplankton?
unicellular, photosynthetic prokaryotic and eukaryotic organisms whose powers of locomotion are such that they drift freely in the water column
diatoms, dinoflagellates, coccolithophores, cyanobacteria, …
Why is phytoplankton so important?
phytoplankton is the main primary producer in most aquatic ecosystems
phytoplankton is a fundamental player in many ecosystem processes
phytoplankton is a gauge of ecological condition and change
phytoplankton can be used to predict the functioning of aquatic ecosystems and ecosystem responses to natural and anthropogenic perturbations
Studying phytoplankton is not straightforward…
the ecological role played by different phytoplankton groups and species varies significantly
phytoplankton in coastal ecosystems is undergoing marked changes (biomass, composition, phenology) – linked to local anthropogenic influences and climate change
links between environmental and phytoplankton changes are difficult to establish
Importance of nutrients
Nutrient availability is a key driver of phytoplankton dynamics
Nutrient limitation is a central question for eutrophication control
How do nutrients affect phytoplankton growth, diversity and
production?
Assessment of the impact of nutrient enrichment
(eutrophication) and subsequent nutrient reduction strategies
Why the Ria Formosa coastal lagoon?
multiple anthropogenic influences very vulnerable to climate change
phytoplankton regulation is a critical aspect in a fast-changing ecosystem
lack of information on phytoplankton regulation in the Ria Formosa studies are mostly descriptive
Goals• to determine the limiting nutrients for phytoplankton growth and their seasonal variation in the Ria Formosa coastal lagoon
• to understand the effects of potential anthropogenic nutrient enrichment on phytoplankton structure in the Ria Formosa
Project PHYTORIA – Environmental Regulation of Phytoplankton in the Ria Formosa coastal lagoon (PTDC/MAR/114380/2009)
Approaches
nutrient addition experiments in 2 L microcosms containing natural phytoplankton assemblages from the Ria Formosa coastal lagoon
autumn, winter, spring, summer
addition of dissolved inorganic macronutrients, alone and in combinations, in a single, saturating pulse
control+NO3
- +NH4
+ +P +Si +NP +SiN +SiP +NPSi
in situ incubation (under in situ T and light) phytoplankton growth (epifluorescence and inverted microscopy) nutrient consumption
higher N uptake in N-enriched treatments in relation to the control indicate N limitation phytoplankton in the Ria Formosa is N-limited throughout the year
NO3- concentrations up to 12 µM were limiting to phytoplankton
growth
control
Nit Amm P Si NP SiN SiP NPSi-5
0
5
10
15
20
25
30
N u
ptak
e (µ
M d
-1)
control
Nit Amm P Si NP SiN SiP NPSi-5
0
5
10
15
20
25
N u
ptak
e (µ
M d
-1)
control
Nit Amm P Si NP SiN SiP NPSi-2.5
-0.5
1.5
3.5
5.5
7.5
9.5
11.5
13.5
N u
ptak
e (µ
M d
-1)
control
Nit Amm P Si NP SiN SiP NPSi-5
0
5
10
15
20
25
30
35
N u
ptak
e (µ
M d
-1)
Results – N consumption
Autumn
Winter
Spring
Summer
Application of nutrient limitation criteria based on Ks – problems…
Ks obtained for unialgal cultures under equilibrium conditions
Ks vary temporally, spatially, inter- and intraspecifically
Establishment of nutrient criteria
- should consider the seasonal variation of phytoplankton community (different spp. are limited in different ways by different nutrients)
- should consider that limiting concentrations don’t have to be necessarily low concentrations (e.g., in the Guadiana estuary N is limiting up to 20 µM: Domingues et al., 2011)
Results – Establishing nutrient criteria
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0,5
control N P Si NP SiN SiP NPSi
Co
mm
un
ity
net
gro
wth
rat
e (d
-1)
**
**
**
**
B
spring Initial N = 22 µM
control
Nit Amm P Si NP SiN SiP NPSi-0.5
-0.3
-0.1
0.1
0.3
0.5
0.7
0.9
1.1
Com
mun
ity
net
grow
th r
ate
(d-1
)
Results – Phytoplankton net growth
Increased nutrient uptake
phytoplankton growth
control
Nit Amm P Si NP SiN SiP NPSi0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45N
et g
row
th r
ate
(d-1
)luxury consumption
Summer
Winter
Effects of ultraviolet radiation and CO2 increase on winter
phytoplankton assemblages in a temperate coastal lagoon (Ria
Formosa)
Rita B. Domingues, Ana B. Barbosa, Vanda Brotas
18h15
Bottle effects on microcosm experiments
Effects of nutrient enrichment on bacterioplankton in the RF
Phytoplankton mortality in the Ria Formosa
Acknowledgements
FCT project Phytoria – Environmental regulation of phytoplankton in the Ria Formosa coastal lagoon (PTDC/MAR/114380/2009)
Postdoctoral fellowship awarded to RBD (SFRH/BPD/68688/2010)
Thank You for Your Attention!