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: bogard.matt@gmail.com

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