Human nutrient over-enrichment in coastal watersheds There’s a long history There’s a long history Salomon van Ruysdael 1648

And more recent trends Mississippi R. Basin Taihu Basin Atmospheric N input Choptank R, Chesapeake Bay

Nutrient-eutrophication dynamics along the freshwater- marine continuum representing coastal watersheds  Dogma: Primary production controlled by P availability in freshwater, N in marine ecosystems.  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 Nutrient-eutrophication dynamics along the freshwater- marine continuum representing coastal watersheds  Dogma: Primary production controlled by P availability in freshwater, N in marine ecosystems.  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

Estuarine and coastal systems: What do the data tell us? DIN Loading vs. primary production in a range of N. American and European estuaries and European estuaries Nixon 1996

However: N +P enrichment is often most stimulatory: Nutrient stimulation of primary production in the brackish Baltic Sea Moisander et al. 1994; 2003

Nutrient limitation dynamics in the Chesapeake Bay  Chesapeake (Fisher et al. 1998) Fisher et al. 1998

Paerl et al., 1995; Gallo 2006 Chlorophyll (μg / L)  Neuse R. Estuary

  Effects of Upstream P reduction but no parallel N reduction on the Neuse River Estuary, NC phytoplankton biomass (Chl a)  P detergent ban, WWT improvements

Has Freshwater P Reduction w/o Parallel N Reduction Exacerbated Estuarine Eutrophication? What’s the mechanism?

May 2001 DIN:P RATIO DIN:P ratios on the shelf are very high, compared with Redfield values (16 N:1 P)

May 01 bioassay: Only treatments containing P led to increases in Chl a. Sylvan et al. 2006

Conclusions Excessive anthropogenic N loading has led to P limited conditions in spring. Spring bloom is controlled by P supplies. N limitation persisted in summer. Management option: Reduce BOTH N and P inputs to control eutrophication and hypoxia Sylvan et al. 2006; EPA SAB 2009

Nutrient load and phytoplankton growth response in Himmerfjärden, Sweden Courtesy: Ulf Larsson & Ragnar Elmgren Stockholm University

The Himmerfjärden case: Coastal area with large Sewage treatment plant, P removal since 1976, N removal started in 1993 (50%) & 2000 (80%). No N removal RESULTS ON PHYTOPLANKTON (Chl a)? B1 H4 Plant loads, tonnes/ year H4 =Eutrophicated station B1= Reference station

Conclusions: Chl a reductions responded to N reductions

Source: Ulf Larsson, pers.comm. Lowering nitrogen discharge below 400 tonnes/yr clearly reduced local phytoplankton biomass. Developing a N loading-bloom threshold

Chai et al., Sci. Total Environ  

Eutrophication of a Large Coastal Plain Lake: Taihu, China’s 3 rd largest Lake. Both N and P inputs increased dramatically in the past 3 decades

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      

Why doesn’t N 2 fixation support the N requirements in the marine to freshwater continuum? Examples: N limited lakes, estuarine, coastal and open ocean systems  W. Atlantic-Gulf Stream (oligotrophic)  Baltic Sea (mesotrophic)  Neuse River Estuary, NC (eutrophic)  Lake Taihu, China (hypereutrophic) Despite highly favorable N:P ratios (< 5:1)

There ’ s plenty of N2 fixing taxa to potentially supply N

Controls on N 2 fixation, it isn’t just P or N:P…Other controls Photosynthesis Heterotrophy Chemolithotrophy energy constraints Fe limitation O2O2 4 Fe S MW=60.5 KD 2 Fe Mo (V) MW=245 KD

The Baltic Sea: N 2 fixers, but rates don’t meet ecosystem N demands ~ 30% (Elmgren and Larsson 2001; Wulff et al. 2006)

Also, N 2 losses from shallow eutrophic systems exceed “new” N inputs via N 2 fixation Conclusions: 1. N 2 fixation does NOT meet ecosystem N demands 2.More N inputs will accelerate eutrophication 3.We Gotta get serious about controlling N!! Annual estimates of ecosystem N 2 fixation, denitrification, and net ecosystem N 2 flux in lakes. Location N 2 Fixation (g N m -2 yr -1 ) Denitrification (g N m -2 yr -1 ) Net N 2 Flux (g N m -2 yr -1 ) 1 Lake 227 (ELA) – -4.5 Lake Mendota Lake Okeechobee – – – 0.5 Lake Erken Lake Elmdale Lake Fayetteville Lake Wedington Net negative N 2 flux represents reactive N loss, positive represents gain; 2 Paerl and Scott (2010); 3 J.T. Scott (unpublished data); 4 Grantz et al. (2012)

 N limited or N/P co-limited Howarth et al. 1998; Capone et al. 2004; Paerl and Scott 2010

Conclusions/Implications  Primary production controlled by P availability in many freshwater systems. However, some are N & P co-limited or N limited.  In Estuarine/Coastal systems N limitation prevails. However, heavily N impacted systems can be P limited or N & P co-limited.  N 2 fixation does not meet ecosystem N requirements: External N inputs can enhance primary production/eutrophication  Expanding human water- and airshed activities have greatly increased N & P loading and altered nutrient limitation  Consider impacts of freshwater nutrient management on downstream marine nutrient limitation/eutrophication dynamics (along the freshwater-marine continuum). Conclusions/Implications  Primary production controlled by P availability in many freshwater systems. However, some are N & P co-limited or N limited.  In Estuarine/Coastal systems N limitation prevails. However, heavily N impacted systems can be P limited or N & P co-limited.  N 2 fixation does not meet ecosystem N requirements: External N inputs can enhance primary production/eutrophication  Expanding human water- and airshed activities have greatly increased N & P loading and altered nutrient limitation  Consider impacts of freshwater nutrient management on downstream marine nutrient limitation/eutrophication dynamics (along the freshwater-marine continuum).

Estuarine & Coastal Indicators of Nutrient Enrichment USDA, USDOD, Chinese Academy of Sciences Thanks to: J. Ammerman T. Fisher A. Joyner B. Peierls M. Piehler B. Qin K. Rossignol H. Xu G. Zhu