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www.marine.unc.edu/Paerllab
Nutrient over-enrichment: “The most rapidly-expanding threat to water quality and ecological condition”. “Scales of sources and impacts are increasing“ (UNESCO-IHP 2014; US National Academy of Sciences 2010, 2016)
Choptank R,
Mississippi R. Chesapeake Bay
Basin
Neuse R. Estuary, NC
Flow corrected N concentrations, Trent R. at Trenton, NC: From Lebo 2016
Trends in watershed/airshed nutrient inputs
Nutrient-eutrophication dynamics along the freshwater-
marine continuum
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 hence
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
Nixon 1996
However: N +P enrichment is
often most stimulatory: Nutrient
stimulation of primary production in the
brackish Baltic Sea
Baltic Sea 2000, Bioassay A Baltic Sea 2000, Bioassay A
Primary Productiv ity Chlorophyll
700 0.13
Legend
Day 1 0.12
600 Day 2
Day 3 0.11
Chlorophyll a ( g/l)
500 0.1
0.09
DPM/ml
400 0.08
0.07
300
0.06
0.05
200
0.04
100 0.03
l l Fe e e l ol
tro nito N P A
DT N+F P+F N+
P
t ro it N P Fe DTA +Fe +Fe N+
P
n E on nn N P
Co Ma n + +E
Fe C Ma Fe
Moisander et al. 1994; 2003
Nutrient limitation dynamics in the Chesapeake Bay, USA
Chesapeake Fisher et al. 1998
(Fisher et al. 1998)
Chlorophyll (μg / L)
Neuse R. Estuary
Paerl et al., 1995; Gallo 2006
Clarifying impacts of nutrient loading on
eutrophication of the Neuse R. Estuary
1. How did we get there?
2. Evaluating management actions
3. The rationale for N and P input controls
Some history
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
Chlorophyll a
Neuse River Estuary
Distance Downstream (km)
70 70
60 60
60
50 50
40 40 45
30 30
20 20 30
10 10
1986 15
0 0
-10 -10
0
Apr
Apr
Jul
Apr
Jan
Oct
Oct
Oct
Apr
Jul
Jul
Apr
Jul
Jan
Oct
Oct
Oct
Apr
Jan
Jan
Jul
Jul
Jan
Jan
1986 1987 1988 1994 1995 1996
P detergent ban,
WWT improvementsFreshwater P Reduction w/o Parallel N Reduction
Exacerbated Estuarine Eutrophication
What’s the mechanism?Need: Reduce Estuarine Primary Production (Chl a) by
Establishing an N Input Threshold
Recommendation: 30% N Input Reduction
Proof: Using dilution bioassays to evaluate
mandated 30% N input reduction = TMDL)
Seasonal Effect of 30% Reduction in N Concentration
84 Hour Incubation
1.4
(proportion of control)
Legend
Assimilation Number
1.3 M15
SFB
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
st er ry ri l y ne st er ry
ugu t ob nua Ap Ma Ju ugu t ob r ua
A c Ja A c b
O
1997 1998
O Fe 1999
Assimilation No. is an indicator of growth potential = Productivity / Chl aNutrient load and
phytoplankton growth
response in Himmerfjärden,
Sweden
Courtesy: Ulf Larsson & Ragnar Elmgren
Stockholm UniversityThe Himmerfjärden case:
Coastal area with large Sewage
treatment plant,
P removal since 1976, N removal started in 1993
(50%) & 2000 (80%). No N removal 2004-2008
RESULTS ON PHYTOPLANKTON (Chl a)?
Plant loads , tonnes/ year H4
B1
H4 =Eutrophicated station
B1= Reference stationThe results: Reducing DIN inputs reduced Chl a and controlled CyanoHABs
Inorganic Nitrogen (DIN), annual mean
180
160 B1
140 H4
DIN µgL-1
120
100
80
60
40
20
0
1975 1980 1985 1990 1995 2000 2005 2010
Surface Chlorophyll, annual mean
8
B1
7
H4
6
Klorofyll a µgL -1
5
4
3
2
1
0
1975 1980 1985 1990 1995 2000 2005 2010
Larsson and Elmgren, In Prep.Developing a N loading-bloom threshold
Himmerfjärden Chlorophyll a Lowering nitrogen
vs tot-N from sewage plant discharge below 400
9 tonnes/yr clearly
reduced local
8
phytoplankton biomass.
Chlorophyll mg/m3 0-14m
7
6
5
4
3
2 y = 0.0068x + 2.44
1 r2 = 0.71
0
0 200 400 600 800 1000
Total nitrogen, tonnes/yr Source:
Ulf Larsson, pers.comm.Florida FW-marine continua : Cylindrospermopsis raciborskii,
rapidly-proliferating, toxic N2 fixing cyanoHAB
High P uptake and storage capacity
High NH4+ uptake affinity (competes well for N)
N additions (NO3- + NH4+) often significantly increase growth (chl a
and cell counts) and productivity
N2 fixer (can supply its own N needs)
Tolerates low light intensities
Eutrophication/decreased transparency favors Cylindro
Often in water column with other cyanoHABsSt. Johns R. System, FLorida: Nitrogen and Phosphorus
Effects on CyanoHAB Growth and Bloom Potential
(Cylindrospermopsis raciborskii)
mg C m -3 h-1
300
250 1 day
4 days
200
150
100
50
0
control +N +P +N&P
14000
C. raciborskii
12000
units/ml
10000
8000
6000
4000
2000
0
control +N +P +N&P
Take home message: Cylindrospermopsis raciborskii is opportunistic
Dual N & P input constraints will likely be needed to control it
Piehler et al, 2009Eutrophication dynamics in lakes in coastal watersheds: Lake Taihu, China. Nutrients (Lots!) associated with unprecedented human development in the Taihu Basin (Jiangsu Province). Results: Cyano blooms have increased to “pea soup” conditions within few decades
Qin et al., 2010 Xu et al., 2015
The “nutrient problem” in Taihu in a nutshell
N & P inputs exceed what’s needed for balanced algal growth.
Result: “Runaway” eutrophication
A
& toxic CyanoHABs B
90 station-1 station-2 350 station-1 station-2
80 300
70
60 250
DTN/DTP
TN/TP
50 200
40 150
30 100
20
10 50
0 0
J F MAMJ J AS ONDJ F MAMJ J AS ONDJ F MAMJ J ASOND J F MAMJ J AS ONDJ F MAMJ J ASONDJ FMAMJ J AS OND
2006 2007 2008 2006 2007 2008
Nutrient (N&P) ratios in Taihu
25 station-1 station-2 C
20 Redfield (balanced growth)
15:1 (N:P)
15
PN/PP
10 HYPOTHESIS
5 Dual (N & P) reductions will be
0 needed to stem eutrophication
J F MAMJ J AS ONDJ F MAMJ J AS ONDJ F MAMJ J ASOND and CyanoHABs
2006 2007 2008 Xu et al., 2010Effects of nutrient (N & P) additions on phytoplankton production (Chl a)
in Lake Taihu, China: Both N & P inputs matter!!
Xu et al. 2010; Paerl et al. 2011; 2016What about large lakes (Erie)? J. Chaffin et al., (2013) “Nitrogen Constrains the Growth of Late Summer Cyanobacterial Blooms in Lake Erie” Advances in Microbiology 3, 16-26.
Lets ask the lakes? Whole-Lake Fertilization Experiments
(ELA, Quebec, NWT, Sweden)
Co-Limitation Dominant Wurtsbaugh et al., 2012; Paerl et al., 2016Large lakes and reservoirs in which algal blooms (mostly cyanobacteria)
have been shown to be N & P stimulated
Lake Erken Lake Peipsi
Lake District (UK) Lakes (N. Germany)
Lake 227
Klamath Lake Lake Balaton
Great Salt Lake Lake Erie
Rocky Mtn. Lakes Midwest Lakes
Lake Taihu
Lake Okeechobee
Lake Dianchi
Lake Atitlán Lake Valencia
Orinoco Floodplain
Lakes Lake Victoria
Lake Titicaca
Coastal Lagoons
(Brazil) Murray-Darling System
Lake Taupo/
Lake Okaro
Sources: Havens et al., 2003; Elser et al. 2007; North et al., 2007; Lewis & Wurtsbaugh 2008; Conley et al., 2009;
Moisander et al., 2009; Lewis et al. 2011; Abell et al., 2011; Özkundakci et al., 2011; Paerl et al., 2014; and many others.Why does N limitation persist in eutrophic systems? N2 losses from
shallow eutrophic systems exceed “new” N inputs via N2 fixation
Annual estimates of ecosystem N2 fixation, denitrification, and net ecosystem N2 flux
in lakes.
Location N2 Fixation Denitrification Net N2 Flux
(g N m-2 yr-1) (g N m-2 yr-1) (g N m-2 yr-1)1
Lake 227 (ELA)2 0.5 5-7 -6.5 – -4.5
Lake Mendota2 1.0 1.2 -0.2
Lake Okeechobee2 0.8 – 3.5 0.3 – 3.0 -2.2 – 0.5
Lake Erken2 0.5 1.2 -0.7
Lake Elmdale 10.43 184 -7.6
Lake Fayetteville 10.63 234 -12.4
Lake Wedington 7.03 124 -5.0
1Net negative N flux represents reactive N loss, positive represents gain; 2Paerl and
2
Scott (2010); J.T. Scott (unpublished data); 4Grantz et al. (2012)
3
Conclusions: 1. N2 fixation does NOT meet ecosystem N
demands
2. More N inputs will accelerate eutrophication
3. We Gotta get serious about controlling N (as well as P) !!Conclusion: N limitation persists in aquatic ecosystems,
even ones receiving anthropogenic N enrichment
Bottom line: Need to reduce N along with P to control eutrophication and
bloom formationConclusions & Management Recommendations
• Freshwaterestuarinecoastal continuum N & P co-limited. Strongly
influenced by human activity.
• In most ecosystems, N2 fixation does not meet ecosystem N
demands, perpetuating N limitation (i.e. more N inputs lead to
accelerated eutrophication).
• Recommendation: Continue P reductions, but parallel N reductions
are needed to control eutrophication along the continuum.
• Continuous water quality monitoring critical for gauging long-term
success and needs to adjust N&P loadings.Thanks!!
www.unc.edu/ims/paerllab/research/
Thanks to:
A. Joyner
T. Otten
B. Peierls
B. Qin
M. Piehler
K. Rossignol
S. Wilhelm
H. Xu
G. Zhu
TLLER “crew”
82667701
Additional support: Nanjing Instit. of Geography and Limnology,
Chinese Academy of Sciences & Ministry of Science & TechnologyYou can also read
