Impact of extreme wet and dry years on Microcystisharmful algal blooms in San Francisco Estuary P. Lehman1, T. Kurobe2, S.J. Teh2

1California Department of Water Resources 2University of California at Davis

wet vs. dry years

• Reversal to wet conditions may not be sufficient to reverse CHAB species once established, as long as water temperature remains warm

species

This work is funded by the Interagency Ecological Program; California Department of Water Resources; California Department of Fish and Wildlife’ and the Infrastructure Improvement Act of 2014 (Proposition 1, CWC 79707, No. P1696041)

CONCLUSION

causal factors

San Francisco Estuary

QUESTION

Can record high streamflow years reverse CHAB formation?

Magnitude

Primary producer community

Spatial distribution

outflow and seawater intrusion

Seasonal pattern

Percent toxic and total cyanobacteria

Subsurface abundance cells/ml

Redundancy analysis – causal factors

-60 -40 -20 0 20 40dbRDA1 (94.4% of fitted, 67.3% of total variation)

-20

0

20

dbR

DA2

(5%

of f

itted

, 3.5

% o

f tot

al v

aria

tion)

Transform: Fourth rootResemblance: S17 Bray-Curtis similarity

qpcrTotMICI416

28

40

year20142017

fwtfph

nh4toc

X2km

pH

Water temperature

Seawater intrusion

• Microcystis blooms varied primarily with water temperature and the extent of seawater intrusion in 2014 and 2017

• the Microcystis bloom persisted in the severe wet year 2017, but differed in its spatial and temporal variation compared with the severe drought year 2014

Approach: compare Microcystis blooms during the severe wet year 2017 with the severe drought year 2014

• The lower seawater intrusion indicates residence time was much less for 2017 than 2014, but water temperature in 2017 remained sufficiently high to facilitate bloom development

• 2017 had a greater percentage of diatoms, green algae and cryptophytes compared with 2014

Lehman ORCID ID: orcid.org//0000-0001-9556-0542

• Peak Microcystis abundance shifted seaward into the central Delta in 2017 compared with 2014, when the bloom was in the south Delta

west southcentral west central south

record

2014 and 2017

• 2017 had a lower percentage of toxic cyanobacteria species than 2017

• Outflow was at least two times higher and saltwater intrusion was lower in the summer of 2017 than 2014

• 2017 and 2014 represent extreme wet and dry conditions over the period of record