the relationship between taxonomic and functional …tracking environmental change using lake...
TRANSCRIPT
Study Location & Design:
Question: How will algae in phosphorus-rich
lakes respond to urea loading from moderate agricultural inputs to potent urban effluents?
Urea ([NH2]CO) pollution from fertilizer use, urban-, and agricultural-effluent
release is increasing globally, yet little is known of these effects on aquatic
ecosystems1. Previous studies suggest that differing N regimes in P-rich lakes
strongly influence algal community composition due to differences in N-
assimilation abilities across functional groups2,3,4. In particular, urea loading can
enhance colonial cyanobacterial growth (Microcystis, Planktothrix) and
production of the hepatotoxin microcystin2. Yet it is not known how this
response varies at different urea loads. In the summer of 2009, we conducted a
mesocosm experiment in hypereutrophic Wascana Lake to systematically
quantify the effects of different urea loading rates on the algal community.
Results:
Acknowledgements
We thank members of the Limnology Laboratory, Vincent Ignatiuk, Zoraida Quiñones-Rivera, Holly Kalyn Bogard, and the Kalyn
family for assistance with experiments and analyses. This work was supported by the Natural Sciences and Engineering Research
Council of Canada Discovery Grants, the Canada Research Chair Program, Canada Foundation for Innovation, the Province of
Saskatchewan, the University of Regina, and Nature Regina.
Conclusion: Moderate urea loading in hypereutrophic
lakes favors colonial cyanobacterial growth and enhanced microcystin toxicity, but these effects are minimized at higher loads due to the promotion of chlorophyte growth.
Works cited:
1. Glibert et al. 2006. Biogeochem. 77: 441-463.
2. Finlay et al. 2010. Limnol. Oceanogr. 55: 1213-1230.
3. Blomqvist et al. 1994. Arch. Hydrobiol. 132: 141-164
4. Zhu et al. 2010. J. Env. Sci. 22: 32-39.
5. Leavitt & Hodgson 2001. p.295-325 in J.P. Smol et al.
(eds.). Tracking environmental change using lake
sediments, v.3. Terrestrial, algal, and siliceous
indicators. Kluwer.
Regina, SK
Wascana Lake
Study Location
Mesocosms
0 5 10 15 20
Day 0 Day 7 Day 14 Day 21
0 5 10 15 20
0
40
60
80
100
20
0
40
60
80
100
20
0
40
60
80
100
20
Rela
tive c
om
mu
nity c
om
positio
n (
%)
Urea loading rate (mg N L-1 week-1)
0 5 10 15 20 0 5 10 15 20
July
A
ugust
Septe
mber
PCT_MYX
PCT_APH
PCT_CHLBPCT_ALX
PCT_DITX
0 5 10 15 20
UREA_MG_N_L
0
20
40
60
80
100
Va
lue
PCT_MYX
PCT_APH
PCT_CHLBPCT_ALX
PCT_DITX
0 5 10 15 20
UREA_MG_N_L
0
20
40
60
80
100
Va
lue
PCT_MYXPCT_APH
PCT_CHLBPCT_ALX
PCT_DITX
0 5 10 15 20
UREA_MG_N_L
0
20
40
60
80
100
Va
lue
PCT_MYXPCT_APH
PCT_CHLBPCT_ALX
PCT_DITX
0 5 10 15 20
UREA_MG_N_L
0
20
40
60
80
100
Va
lue
PCT_MYX
PCT_APH
PCT_CHLBPCT_ALX
PCT_DITX
0 5 10 15 20
UREA_MG_N_L
0
20
40
60
80
100
Va
lue
PCT_MYXPCT_APH
PCT_CHLBPCT_ALX
PCT_DITX
0 5 10 15 20
UREA_MG_N_L
0
20
40
60
80
100
Va
lue
PCT_MYXPCT_APH
PCT_CHLBPCT_ALX
PCT_DITX
0 5 10 15 20
UREA_MG_N_L
0
20
40
60
80
100
Va
lue
PCT_MYXPCT_APH
PCT_CHLBPCT_ALX
PCT_DITX
0 5 10 15 20
UREA_MG_N_L
0
20
40
60
80
100
Va
lue
PCT_MYX
PCT_APH
PCT_CHLBPCT_ALX
PCT_DITX
0 5 10 15 20
UREA_MG_N_L
0
20
40
60
80
100
Va
lue
PCT_MYXPCT_APH
PCT_CHLBPCT_ALX
PCT_DITX
0 5 10 15 20
UREA_MG_N_L
0
20
40
60
80
100
Va
lue
PCT_MYXPCT_APH
PCT_CHLBPCT_ALX
PCT_DITX
0 5 10 15 20
UREA_MG_N_L
0
20
40
60
80
100
Va
lue
PCT_MYX
PCT_APH
PCT_CHLBPCT_ALX
PCT_DITX
0 5 10 15 20
UREA_MG_N_L
0
20
40
60
80
100
Va
lue
Intermediate (1-8 mg N L-1) urea
additions caused rapid growth in
total algal abundance (Chl a),
while additions beyond ~8 mg N
L-1 had little additional effects on
total abundance.
For additional information, contact me at: [email protected]
Comparison of algal
groups across
experiments (i.e. July,
August, September)
revealed that
mesocosms receiving >
3 mg N L-1 week-1
tended toward greater
similarity by day 21,
while controls and
treatments of 1 mg N L-1
week-1 increasingly
differed in community
structure by the end of
each experiment.
18
8 3
1 0
Urea load
(mg N L-1 week-1)
0 5 10 15 20 25 Day
0.2
0.4
0.6
0.8
Bra
y-C
urt
is D
issim
ilari
ty
All urea additions
caused large initial (<1
week) shifts in the algal
community, favoring
chlorophyte (July) or
colonial cyanobacterial
(Microcystis,
Planktothrix) (August,
September). However,
by day 21, colonial
cyanobacteria
consistently dominated
at low to intermediate-
(1-8 mg N L-1), and
chlorophytes at high (>
8 mg N L-1) N loads.
• 15 mesocosms
• 3 Trials (July, August, September).
• 21 days each.
• Urea loads of 0,1,3,8,18 mg N L-1.
• Urea additions (Day 0,7,14).
• Monitoring (Day 0,4,7,14,21).
•Algal groups quantified using HPLC
pigment analysis5.
1 m 1 m
Volume = 3150 L
Urea loading rate (mg N L-1 week-1)
100
50
July
r2 = 0.98
p < 0.001
August
r2 = 0.98
p < 0.001
September
r2 = 0.91
p < 0.001
250
200
150
0
Chlo
rophyll
a (m
g L
-1)
0 5 10 15 20 0 5 10 15 20 0 5 10 15 20
1 2
Colonial Cyano. Chlorophytes Cryptophytes Diatoms N2-fixing Cyano.
Microcystin
concentrations
from days 4-21
were greatest at
intermediate urea
loads of 3 and 8
mg N L-1 week-1,
particularly in July
and August.
0.0
July
Urea Loading Rate
(mg N L-1 week-1)
0.5
1.0
1.5
2.0
2.5
Mic
rocystin (m
g L
-1)
August September
0 1 3 8 18