Eutrophication

Report
Eutrophication and Algal
Proliferation in Florida’s Springs
Forest Hydrology
Spring 2014
Water Quality and Aquatic Health
• Tenet #1: Contaminants from land end up in
the water
– Industrial, urban, agricultural chemicals
• Tenet #2: Aquatic systems may respond, often
in undesirable ways
• Habitat viability
• Aesthetics (color, aroma, clarity)
• Function (support C storage, N removal, flow)
• Human use potential (e.g., drinking or irrigation water)
Eutrophication
• Def: Excess C fixation
– Primary production is
stimulated. Can be a good
thing (e.g., more fish)
– Can induce changes in
dominant primary
producers (e.g., algae vs.
rooted plants)
– Can alter dissolved oxygen
dynamics (nighttime lows)
• Fish and invertebrate impacts
• Changes in color, clarity,
aroma
http://www.sjrwmd.com/publications/pdfs/fs_lapopka.pdf
Reduction in
Water Clarity =
Changes in Bottom
Habitats
Eutrophication may stimulate the growth of
algae that produce harmful toxins
Red Tide
Dead Zone in the Gulf of Mexico
http://serc.carleton.edu/microbelife/topics/deadzone/
Scope of the Problem in Florida
Source: USEPA (http://iaspub.epa.gov/waters10/state_rept.control?p_state=FL&p_cycle=2002)
What Causes Eutrophication?
• Leibig’s “Law of the
Minimum”
– Some element (or light
or water) limits
primary production
– Adding that thing will
increase yields (GPP)
– What is limiting in
forests? Crops?
Lakes? Pelagic ocean?
Justus von Liebig
What Limits Aquatic Production?
Typical Symptoms: Alleviation of
Nutrient Limitation
• Phosphorus limitation in
shallow temperate lakes
• Nitrogen limitation in
estuarine systems
(GPP)
V. Smith, L&O 2006
V. Smith, L&O 1982
Global Nitrogen Enrichment
• Humans have
massively amplified
global N cycle
– Terrestrial Inputs
• 1890: ~ 150 Tg N yr-1
• 2005: ~ 290+ Tg N yr-1
– River Outputs
• 1890: ~ 30 Tg N yr-1
• 2005: ~ 60+ Tg N yr-1
• N frequently limits
terrestrial and aquatic
primary production
– Eutrophication
Gruber and Galloway 2008
Local Nitrogen Enrichment
• The Floridan Aquifer (our
primary water source) is:
– Vulnerable to nitrate
contamination
– Locally enriched as much as
30,000% over background
(~ 50-100 ppb as N)
• Springs are sentinels of
aquifer pollution
– Florida has world’s highest
density of 1st magnitude
springs (> 100 cfs)
Arthur
et al.
2006
Mission Springs
Chassowitzka (T. Frazer)
Mill Pond
Spring
Weeki Wachee
1950’s
Weeki Wachee
2001
Core Question:
What Causes Algae to Reach Nuisance Levels?
GROW FASTER
LOST MORE SLOWLY
• Hnull: N loading alleviated GPP limitation, algae exploded
(conventional wisdom)
• Evidence generally runs counter to this hypothesis
– Springs were light limited even at low concentrations (Odum 1957)
– Algal cover/AFDM is uncorrelated with [NO3] (Stevenson et al. 2004)
– Flowing water mesocosms show algal growth saturation at ~ 110
ppb (Albertin et al. 2007)
– Nuisance algae exists principally near the spring vents, high
nitrate persists downstream (Stevenson et al. 2004)
N Enrichment in Springs
Fall 2002 (closed circles) and Spring 2003 (open triangles)
From Stevenson et al. 2004 Ecological condition of algae
and nutrients in Florida Springs DEP Contract #WM858
No correlation between algae and N
N Enrichment and Primary Production
[No Significant Association]
• More N does not
mean more GPP
(GPP)
Visualizing the Problem
Silver Springs (1,400 ppb NNO3)
Alexander Springs (50 ppb N-NO3)
Qualitative Insight: Comparing
Assimilatory Demand vs. Load
• Primary Production is very high
– 8-20 g O2/m2/d (ca. 1,500 g C/m2/yr)
• N demand is proportional
– 0.05 – 0.15 g N/m2/day
• N flux (over 5,000 m reach) is large
– Now: ca. 30 g N/m2/d (240 x Ua)
– Before: ca. 2.5 g N/m2/d (20 x Ua)
• In rivers, the salient measure of availability
may be flux (not concentration)
• Because of light limitation, this is best
indexed to demand
• When does flux:demand become critical?
Core Question:
What Causes Algae to Reach Nuisance Levels?
GROW FASTER
LOST MORE SLOWLY
Algal Loss Rates - Scouring
• Flow has widely
declined, in areas a lot
– Silver Springs
– White Springs
– Kissingen Spring
• Lower discharge
means lower scour
• Algal cover varies with
flow velocity (King 2014)
Algal Loss Rates - Grazing
• Algal cover is predicted by:
– Dissolved oxygen (DO)
– Grazer density
• DO is keystone variable for
aquatic animal health
– Proxy for groundwater age?
Observational Support:
Grazers and Algae are Correlated
Ln (Filamentous Algae
Biomass)
8
6
4
2
0
-2
-4
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
Ln (Gastropod Biomass)
Combined model (snails, flow, canopy)
explains over 70% of algae variation
Evidence of threshold effect?
Liebowitz et al. (in prep)
Experimental Confirmation:
Snails Control Algae
• Enclosed & excluded snails
What Kills Snails?
• Changes in DO
– Flow varying?
• Changes in salinity/[Ca]
• Human disturbance
Complex
Ecological
Causes
Questions?
[email protected]

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