Water Quantity & Quality in the Ichetucknee River:
What We Know and What We Need To Know
Matt Cohen
Forest Resources & Conservation
U i
University of Florida
i
f Fl id
Three Rivers Trust Research Road Map Meeting –
h
d
i
February 2011
b
20
Photo Credit ‐ L.V. Korhnak
A Systems View Springs Impairment
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•
•
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What are we managing for?
Which interactions matter?
How do stressors interact?
What can we restore?
What should we measure to evaluate what’s working?
Potential Modes of Impairment
Potential Modes of Impairment
• Nitrate
t ate eenrichment
c e t
– Effects on algal accumulation
– Effects on aquatic metabolism
• Flow variation
– Effects on dispersal, scour
– Effects on water chemistry (oxygen, hardness)
• Changes in internal ecosystem interactions
– Pulse (backwater floods) or press (recreation) stressors
– Complex interrelations between SAV and algae
Complex interrelations between SAV and algae
Nitrate
• Ubiquitous increases over the last 50 years
over the last 50 years
• Recent variability
– Declines
Declines in in ~ 35% of 35% of
springs
• Principally from p y
fertilizer based on isotopic evidence
– Isotopic enrichment due to denitrification is important
p
((Heffernan et al. in prep)
Longitudinal N Removal
• N
N removal is very
removal is very large large
(0.6 – 1.1 g N/m2/d)
• Most lost in “Grassy Flats”
M t l t i “G
Fl t ”
• Most (~ 80%) removed via (
)
denitrification (Heffernan and Cohen 2010)
• Isotopic evidence suggests denitrification is nitrate limited (Cohen et al. in prep)
limited (Cohen et al in prep)
Discharge and N Removal Dynamics
Heffernan et al. (2010) – Hydrologic and Biotic Influences on Nitrate Removal in a Subtropical Spring‐Fed River
The Ichetucknee Pulse – Diel Variance
Nutrient Limitation
Nutrient Limitation
• Leibig’s Law of the Minimum
• Effects are typically saturating
– As concentrations ↑, something else becomes limiting
• Odum (1957) suggested springs production is light limited
– Nitrate ~ 0.06 to 0.85 mg/L
g/
• Concentration is not a good predictor of eutrophication in rivers ((Borchardt 1996, Hilton 2007)
,
)
– Flux may be better (King et al. in prep)
– How much is available compared to how much the plants need?
(GPP)
Plant N Demand vs. Supply
GPP (g C/m
m2/d)
• Diel variation in nitrate gives us a new way to estimate plant + algae N demand
• GPP (springs to US27) is high (2‐6 g C/m2/d) but N demand vs. flux is small (0.05 – 0.15 vs. 2.4 g N/m2/d) 8.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
GPP = 34.7*Ua ‐ 0.2
R² = 0.77, p < 0.001
0
0.05
0.1
0.15
Assimilation (g N/m2/d)
0.2
Predicting Algal Response to Nutrient Limitation
SPRINGS
ESTUARIES
V. Smith, L&O 2006
V. Smith, L&O 2006
SHALLOW
LAKES
Fall 2002 (closed circles) and Spring 2003 (open triangles)
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 V. Smith, L&O 1982
Predicting Algal Cover
% CoverSpring = f[DO, Grazers] (r2 = 0.35, p< 0.001)
% CoverFall = f[DO, Grazers] (r2 = 0.17, p = 0.02)
Heffernan et al. (2010)
Data from Scott et al. 2004
Flow‐Induced Changes in Dissolved Oxygen
• “DO fluctuation in springs is largely related to O uctuat o
sp gs s a ge y e ated to
rainfall patterns and the Atlantic Multi‐decadal Oscillation. Rain was significantly higher in the 1950s to 1970s, meaning shorter underground h
d
d
residence time and higher DO. During the extended drought from 1980s to present (just
extended drought from 1980s to present (just ending), less rain meant longer residence time, lower springs flows, and lower DO, subsequently p g
q
y
affecting the grazers.”
– Russ Frydenbourg, FDEP (Feb 1, 2011)
NO3 = 0.75
NO3 = 0.65
0 65
NO3 = 0.45
= 0 45
Ichetucknee Algal Photo S
Survey
January 2009
(Joe Hand, FDEP)
NO3 = 0.55
Controls on Algal Accumulation
• Algae can accumulate from growing faster or being removed
more slowly
– Flow
– Grazing pressure
• Ob
Observational and preliminary ti
l d
li i
experimental evidence of STRONG top‐down control of accumulation (D. Liebowitz)
(
)
– Multivariate models [r2 = 0.67] pooled all variables except grazers, shade and DO
• Observational
Observational evidence of local evidence of local
control of flow velocity on algal accumulation (S. King)
Ln
n (Filamento
ous Algae
Biomaass)
8
6
4
2
0
-2
-4
-6
-5
-4
-3
-2
-1
0
1
2
3
Ln (Gastropod Biomass)
4
5
Overarching Research Questions
Overarching Research Questions
• What controls floral/faunal composition and productivity of the river ecosystem?
d ti it f th i
t ?
– Emphasis on what controls algal accumulation
– Space AND Time
S
AND Ti
• How are regional consumptive uses affecting flow, and how does declining flow affect the ecosystem?
dh d
d li i fl
ff t th
t ?
– Direct effects on discharge chemistry (e.g., DO)
– Indirect effects on river processes
I di t ff t
i
• Fate and effects of N load (500‐1000% background)?
– Where does it go and what does it do?
In the short term…
(some ongoing)
1. Quantify
1
Quantify discharge vs. chemistry relations
discharge vs chemistry relations
2. Fate of N (where does it go?)
3 Ecosystem metabolism (P, R) as a baseline for 3.
b li ( )
b li f
change detection
– Seasonality, Discharge, Tubing
4. Faunal controls on algal accumulation
5. Chemical controls on fauna
Longer Term Research/Monitoring
Longer Term Research/Monitoring
1. Robust monitoring of changes in and consequences of environmental drivers and ecosystem processes
Drivers
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•
Flows
•
•
Nutrients
Dissolved oxygen and other age proxies (vs. flow)
Ecosystem status and trends
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Vegetation
Fauna (snails, fish, crayfish, birds)
Ecosystem processes
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Metabolism, stoichiometry, phenology
2. Process specific studies
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–
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Detailed river hydrology
Sediment‐water interactions
Oxygenation (e.g., Mill Pond)
Questions?
[email protected] Mill Pond Spring