Managing eutrophication and harmful cyanobacterial blooms in shallow-waterManaging eutrophication and harmful cyanobacterial blooms in shallow-water ecosystems experiencing human- and climatically-induced environmental changeecosystems experiencing human- and climatically-induced environmental change

Hans Paerl1, Xu Hai2, Guangwei Xu2, Linghan Dong1, Benjamin Peierls1, Boqiang Qin2, J. Thad Scott3 & Karen Rossignol1

1Institute of Marine Sciences, UNC-Chapel Hill, Morehead City, NC, USA 2Nanjing Institute of Geography and Limnology, Nanjing, China

3Dept. of Crop, Soil, and Environmental Sciences, Univ. of Arkansas, Fayetteville, AR, USA

Shallow water systems nutrient issuesShallow water systems nutrient issues

Dogma: Primary production is controlled by Dogma: Primary production is controlled by PP availability. availability.

However: Accelerating anthropogenic However: Accelerating anthropogenic NN & & PP loading has loading has altered nutrient limitation and eutrophication dynamicsaltered nutrient limitation and eutrophication dynamics

Results: Human-impacted systems reveal a complex picture Results: Human-impacted systems reveal a complex picture and a challenge to nutrient management and a challenge to nutrient management

Problem Problem

Worldwide,in anthropogenically-impacted shallow water systems, Worldwide,in anthropogenically-impacted shallow water systems, harmful cyanobacterial blooms (CyanoHABs) have proliferated. harmful cyanobacterial blooms (CyanoHABs) have proliferated.

Both N and P loads have increased in these systems Both N and P loads have increased in these systems

Problem Problem

Worldwide,in anthropogenically-impacted shallow water systems, Worldwide,in anthropogenically-impacted shallow water systems, harmful cyanobacterial blooms (CyanoHABs) have proliferated. harmful cyanobacterial blooms (CyanoHABs) have proliferated.

Both N and P loads have increased in these systems Both N and P loads have increased in these systems

“Eutrophication of lakes cannot be controlled byreducing nitrogen input: Results of a 37-year

whole-ecosystem experiment”

Schindler et al. Proceedings of the National Academy of Science USA 105:11254-11258 (2008).

Recent controversy regarding nutrient limitation/controls

Conclusion by Schindler et al. (2008) (based on one lake: Lake 227) assumes that N2 fixation will supply ecosystem N needs

Therefore, why worry about N?

This assumption has been challenged (Lewis and Wurtsbaugh 2008; Conley et al., 2009;

Paerl 2009; Scott & McCarthy 2010: Lewis et al. 2011)

Lake Taihu Lake Taihu 33rdrd largest lake in China. largest lake in China. Nutrients (Lots!) Nutrients (Lots!) associated with unprecendented human development in the Taihu Basin associated with unprecendented human development in the Taihu Basin

(Jiangsu Province). Results:(Jiangsu Province). Results: Blooms have increased to Blooms have increased to ““pea souppea soup”” conditions within only a few decadesconditions within only a few decades

The water crises (2007- ?) in the Taihu Basin: Cessation drinking water use for >20 million (hepato- and neuro-toxins) Curtailed recreational use (contact dermatitis) Fisheries (commercial and recreational) Tourism???

To address Taihu’s WQ problems, mitigate CyanoHABs,

& ensure sustainability, we need to: Determine nutrient inputs, availability, and controls on CyanoHABs Develop nutrient-bloom thresholds Link eutrophication to algal toxicity and water use Formulate nutrient management recommendations Identify options for meeting them Engaging managers to develop long-term strategies for ensuring

sustainability of Taihu & other large lakes threatened by CyanoHABs

0102030405060708090

2006 2007 2008

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Nutrient (N&P) ratios in TaihuNutrient (N&P) ratios in Taihu

Redfield (balanced growth) Redfield (balanced growth) 15:1 (N:P)15:1 (N:P)

HYPOTHESISHYPOTHESISDual (N & P) reductions will be Dual (N & P) reductions will be needed to stem eutrophication needed to stem eutrophication

and CyanoHABsand CyanoHABs

Nutrient dynamics in Taihu Nutrient dynamics in Taihu N & P inputs exceed whatN & P inputs exceed what’’s needed for balanced algal growth. s needed for balanced algal growth.

Result: Result: ““RunawayRunaway”” eutrophication & toxic CyanoHABs eutrophication & toxic CyanoHABs

Xu et al., 2010

Effects of nutrient (N & P) additions on phytoplankton production (Chl Effects of nutrient (N & P) additions on phytoplankton production (Chl aa)) in Lake Taihu, China: in Lake Taihu, China: Both N & P inputs matter!!Both N & P inputs matter!!

Xu et al. 2010; Paerl et al. 2011Xu et al. 2010; Paerl et al. 2011

Is TaihuIs Taihu a a ““looking glasslooking glass”” for hypereutrophic for hypereutrophic

shallow ecosystems worldwide?shallow ecosystems worldwide?

Florida lakes : CFlorida lakes : Cylindrospermopsis raciborskiiylindrospermopsis raciborskii, rapidly-, rapidly-proliferating, proliferating, toxictoxic N N22 fixing cyanoHAB fixing cyanoHAB

High P uptake and storage capacityHigh P uptake and storage capacity

High NHHigh NH44++ uptake affinity uptake affinity (competes well for N)(competes well for N)

N additions (NON additions (NO33-- + NH + NH44

++) often significantly increase growth ) often significantly increase growth (chl (chl aa and cell counts) and productivity and cell counts) and productivity

NN22 fixer (can supply its own N needs) fixer (can supply its own N needs)

Tolerates low light intensities Tolerates low light intensities Eutrophication/decreased transparency favors Eutrophication/decreased transparency favors CylindroCylindro Often in water column with other cyanoHABsOften in water column with other cyanoHABs

control +N +P +N&P0

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St. Johns R. System, Florida: Nitrogen St. Johns R. System, Florida: Nitrogen and and Phosphorus Effects on CyanoHAB Growth and Phosphorus Effects on CyanoHAB Growth and

Bloom Potential (Bloom Potential (Cylindrospermopsis raciborskiiCylindrospermopsis raciborskii))

Take home message: Take home message: Cylindrospermopsis raciborskiiCylindrospermopsis raciborskii is opportunistic is opportunisticDual N & P input constraints will likely be needed to control itDual N & P input constraints will likely be needed to control it

Piehler et al, 2009

Lewis et al., ES&T 45:10300-10305 (2011)

N & P limitation in lakes worldwideN & P limitation in lakes worldwide

Lakes: N= 55

N2 Flux (g N m-2 yr-1)

LakeNitrogen Fixation Denitrification Net N2 Flux

Lake 227 (ELA*), Canada 0.5 5 – 7 -6.5 to -4.5

Lake Mendota, Wisconsin, USA 1.0 1.2 -0.2

Lake Okeechobee, Florida, USA 0.8 – 3.5 0.3 – 3.0 -2.2 to 0.5

Lake Erken, Sweden 0.5 1.2 -0.7

*Experimental Lakes Area

Does NDoes N22 Fixation meet N demands in lakes? Fixation meet N demands in lakes? NN2 2 flux from shallow eutrophic lakes indicates net loss (negative net Nflux from shallow eutrophic lakes indicates net loss (negative net N22 flux) flux)

of reactive N to the atmosphere.of reactive N to the atmosphere.

From: Paerl & Scott (2010) ES&T

Conclusions: 1. NConclusions: 1. N2 2 fixation does NOT meet ecosystem N demandsfixation does NOT meet ecosystem N demands

2. More N inputs will accelerate eutrophication2. More N inputs will accelerate eutrophication

Confounding Impacts of Climate Change: Its Getting WarmerConfounding Impacts of Climate Change: Its Getting Warmer

The link to CyanoHABs………Temperature affects growth rates

References: Kraweik 1982, Grzebyk & Berland 1996; Kudo et al., 2000, Litaker et al., 2002, Briand et al., 2004, Butterwick et al., 2005,

Yamamoto & Nakahara 2005, Reynolds 2006

Temperature increases and longer-lasting, more intense cyanobacterial blooms in Taihu. Is warming changing CyanoHAB

thresholds?

• N2 Fixation does not meet ecosystem N demands; hence new N inputs can control eutrophication.

• Both N and P controls are needed to counter CyanoHAB proliferation

• Developing nutrient input-bloom thresholds will need to take climate change (warming, changes in precip. patterns) into consideration

www.unc.edu/ims/paerllab/research/taihuwww.unc.edu/ims/paerllab/research/taihu//www.unc.edu/ims/paerllab/research/taihuwww.unc.edu/ims/paerllab/research/taihu//

82667701

Thanks to:Thanks to:

N. HallN. HallJ. HuismanJ. HuismanA. JoynerA. JoynerT. OttenT. OttenM. PiehlerM. PiehlerS. WilhelmS. WilhelmTLLER TLLER ““crewcrew””

Additional support: Nanjing Instit. of Geography and Limnology,Additional support: Nanjing Instit. of Geography and Limnology, Chinese Academy of Sciences NIGLASChinese Academy of Sciences NIGLAS

Relationships between presence of heterocystous N2 fixing cyanos (), non N2 fixingcyanos () and a mixture of both (), and total P and total N in 83 shallow European and S. American Lakes along a latitudinal gradient.

Adapted from Kosten et al. (2009) Ecol. Applic. 19:1791-1804.

Percentage of cyanobacterial biovolume in phytoplankton communities as a function of water temperature andnutrients in 143 lakes along a climatic gradient in Europe and South America. (a) Combined effects of temperature and nutrients as captured by a logistic regression model(b) Response surface obtained from interpolation of the raw data using inverse distance weighting.

From Kosten et al. (2011). Global Change Biology DOI: 10.1111/j.1365-2486.2011.02488.x

Cyanobacterial dominance along temperature & nutrient gradients in 143 lakes Cyanobacterial dominance along temperature & nutrient gradients in 143 lakes