Managing eutrophication and harmful cyanobacterial blooms in shallow-water ecosystems experiencing human- and climatically-induced environmental change ecosystems experiencing human- and climatically-induced environmental change Hans Paerl 1, Xu Hai 2, Guangwei Xu 2, Linghan Dong 1, Benjamin Peierls 1, Boqiang Qin 2, J. Thad Scott 3 & Karen Rossignol 1 1 Institute of Marine Sciences, UNC-Chapel Hill, Morehead City, NC, USA 2 Nanjing Institute of Geography and Limnology, Nanjing, China 3 Dept. of Crop, Soil, and Environmental Sciences, Univ. of Arkansas, Fayetteville, AR, USA

Shallow water systems nutrient issues  Dogma: Primary production is controlled by P availability.  However: Accelerating anthropogenic N & P loading has altered nutrient limitation and eutrophication dynamics Results: Human-impacted systems reveal a complex picture and a challenge to nutrient management Shallow water systems nutrient issues  Dogma: Primary production is controlled by P availability.  However: Accelerating anthropogenic N & P loading has altered nutrient limitation and eutrophication dynamics Results: Human-impacted systems reveal a complex picture and a challenge to nutrient management

Problem Worldwide,in anthropogenically-impacted shallow water systems, harmful cyanobacterial blooms (CyanoHABs) have proliferated. Both N and P loads have increased in these systems Problem Worldwide,in anthropogenically-impacted shallow water systems, harmful cyanobacterial blooms (CyanoHABs) have proliferated. Both N and P loads have increased in these systems

“Eutrophication of lakes cannot be controlled by reducing nitrogen input: Results of a 37-year whole-ecosystem experiment” Schindler et al. Proceedings of the National Academy of Science USA 105: (2008). Recent controversy regarding nutrient limitation/controls Conclusion by Schindler et al. (2008) (based on one lake: Lake 227) assumes that N 2 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 3 rd largest lake in China. Nutrients (Lots!) associated with unprecendented human development in the Taihu Basin (Jiangsu Province). Results: Blooms have increased to “ pea soup ” conditions 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

AB C Nutrient (N&P) ratios in Taihu Redfield (balanced growth)  15:1 (N:P) HYPOTHESIS Dual (N & P) reductions will be needed to stem eutrophication and CyanoHABs Nutrient dynamics in Taihu N & P inputs exceed what’s needed for balanced algal growth. Result: “Runaway” eutrophication & toxic CyanoHABs Xu et al., 2010

Effects of nutrient (N & P) additions on phytoplankton production (Chl a) in Lake Taihu, China: Both N & P inputs matter!! in Lake Taihu, China: Both N & P inputs matter!! Xu et al. 2010; Paerl et al      

Is Taihu a “looking glass” for hypereutrophic shallow ecosystems worldwide?

Florida lakes : Cylindrospermopsis raciborskii, rapidly- proliferating, toxic N 2 fixing cyanoHAB  High P uptake and storage capacity  High NH 4 + uptake affinity (competes well for N)  N additions (NO NH 4 + ) often significantly increase growth (chl a and cell counts) and productivity  N 2 fixer (can supply its own N needs)  Tolerates low light intensities  Eutrophication/decreased transparency favors Cylindro  Often in water column with other cyanoHABs

St. Johns R. System, Florida: Nitrogen and Phosphorus Effects on CyanoHAB Growth and Bloom Potential (Cylindrospermopsis raciborskii) Take home message: Cylindrospermopsis raciborskii is opportunistic Dual N & P input constraints will likely be needed to control it Piehler et al, 2009

Lewis et al., ES&T 45: (2011) N & P limitation in lakes worldwide Lakes: N= 55

N 2 Flux (g N m -2 yr -1 ) Lake Nitrogen FixationDenitrificationNet N 2 Flux Lake 227 (ELA*), Canada0.55 – to -4.5 Lake Mendota, Wisconsin, USA Lake Okeechobee, Florida, USA0.8 – – to 0.5 Lake Erken, Sweden *Experimental Lakes Area Does N 2 Fixation meet N demands in lakes? N 2 flux from shallow eutrophic lakes indicates net loss (negative net N 2 flux) of reactive N to the atmosphere. From: Paerl & Scott (2010) ES&T Conclusions: 1. N 2 fixation does NOT meet ecosystem N demands 2. More N inputs will accelerate eutrophication

Confounding 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?

N 2 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

Thanks to: N. Hall J. Huisman A. Joyner T. Otten M. Piehler S. Wilhelm TLLER “crew” Additional support: Nanjing Instit. of Geography and Limnology, Chinese Academy of Sciences NIGLAS Chinese Academy of Sciences NIGLAS

Relationships between presence of heterocystous N 2 fixing cyanos ( ), non N2 fixing cyanos (  ) 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:

Percentage of cyanobacterial biovolume in phytoplankton communities as a function of water temperature and nutrients 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: /j x Cyanobacterial dominance along temperature & nutrient gradients in 143 lakes