Springs and Nutrients
Are There Effects at the
Ecosystem Level?
January 29, 2008
Robert L. Knight, Ph.D.
Sky K. Notestein, M.S.
Wetland Solutions, Inc.
(www.wetlandsolutionsinc.com)
Ecosystem-Level Effects – Chapter Outline
• Chapter 1 - Springs as Ecosystems
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Springs Ecosystem Model
Environmental Forcing Functions
Energy Storages/Structure
Ecosystem-Level Processes
Human and Aesthetic Uses
• Chapter 6 - Effects of Nutrients on Spring Ecosystems
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–
–
–
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Primary Producers
Community Metabolism
Community Structure
Human and Aesthetic Effects
Additional Research Needs and Questions
1
Springs as Ecosystems
• Springs and spring runs represent a unique
class of aquatic ecosystems with distinct
structures and processes.
• Due to their complexity, a holistic approach to
spring studies is necessary to understand
anthropogenic effects on these ecosystems.
Silver Springs
Ecosystem Model
(Odum et al. 1998)
Springshed-Spring Linkages
• Development of a management strategy for
springs will be dependent upon a better
understanding of the relative importance and
synergism of direct stressors at the local level
and indirect stresses that occur at the regional
scale.
Springshed
Atmosphere (A)
N
Evapotranspiration
Groundwater
8
2,3
10
4,5
Goods & Services
Surface Water
(GW)
Economy (E)
$
Atmosphere (A)
(SW)
N
N
20
6,7
16,17
N
10
18,19
20
6,7
Natural Lands (NL)
Spring
Evapotranspiration
N
N
9
Economy (E)
Surface Water
Sun (S)
Outflows
16,17
$
(SS W)
N
N
Sun (S)
X
X
1
$
N
Silver Springs (SS)
18,19
27
N
11
22,23
$
12,13
26
Ground
Water (GW)
Downstream Export
1
22,23,24,25
$
21,28
Groundwater
Pumping
$
14,15
Surface Water
Outflows
Aquatic Plants &
Consumers (SS AB)
Outflows
24,25
Downstream Particulate
Export
N
N
Developed Lands
(DL)
Silver Springs Ecosystem
to 1,200-m Station
26
Silver Springs Springshed
2
The Study of Springs
Why study springs at the ecosystem level?
• Most springs’ studies:
– examined one or a few components of the
ecosystem, such as aquatic plants, invertebrates,
or water chemistry
– components are measured as amounts rather than
rates, for example, aquatic plant biomass vs.
aquatic plant productivity
– focused on the factors that are different between
springs rather than on their underlying similarities.
The Study of Springs
Why study ecosystem metabolism?
• Ecosystem metabolism is measured by techniques
that record the activity of the entire ecosystem through
its effects upon dissolved oxygen concentrations.
• Ecosystem metabolism is inclusive of all living
organisms that transform carbon through the biological
processes of primary productivity and respiratory
metabolism.
• Allows quantification and comparison of multiple
forcing functions, the trophic level structure,
ecosystem-level processes, and provides a more
holistic view of springs.
• Fortunately, there are some historical measures of
spring ecosystem metabolism for comparison to
current conditions.
3
Upstream-Downstream Ecosystem Metabolism Method
• Ecosystem-level metrics have
promise for providing a better
understanding of the properties that
many springs have in common.
• Specifically, the upstreamdownstream oxygen change method
for ecosystem metabolism
measurement pioneered in these
aquatic systems should be a
standard method to accompany all
new springs’ biological studies.
Effects of Nutrients on Spring Ecosystems
• There are consistent inverse
correlations between rising nutrient
concentrations (for both nitrogen and
phosphorus) and declining ecosystem
primary production and photosynthetic
efficiency.
4
Silver Springs: A 50-Year Retrospective Study (Munch et al. 2006)
Ecological Efficiency vs. Nitrate-N
GPP Efficiency (g O2/mol)
1.12
1.1
1.08
1.06
1.04
1.02
y = -0.2247x + 1.1892
R2 = 0.9619
1
0.98
0.96
0.94
0.92
0
0.2
0.4
0.6
0.8
1
1.2
NOx-N (mg/L)
* Phosphorus concentrations are relatively stable at this spring
Wekiva River and Rock Springs Run PLRG Analysis (Mattson et al. 2006)
Corroborative Ecosystem-Level Findings
(Wekiva, Rock, Alexander, Juniper Springs)
0.8
y = -0.2031x+ 0.355
2
R = 0.2882
GPP Efficiency
(g O2/mol)
0.7
0.6
WR-1
0.5
WR-2
RSR-1
0.4
RSR-2
0.3
ASC-1
0.2
JC-1
0.1
0.0
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
NOx-N(mg/L)
* A similar correlation between TP and GPP Efficiency was also observed.
5
Effects of Nutrients on Spring Ecosystems
• While this possible cause and effect
relationship appears counter-intuitive, it
may be explained based on the
subsidy-stress hypothesis.
Subsidy-Stress Hypothesis
Hypothetical example of two types of inputs and their resulting
ecosystem perturbations due to increasing input levels. Nutrients and
nitrate in particular could be viewed as an example of a usable input
(top curve), which have a subsidy effect on ecosystem productivity to
a point, beyond which stress is incurred (Figure from E. P. Odum et
al. 1979).
6
Effects of Nutrients on Spring Ecosystems
• Subsidy-Stress Hypothesis
– Low nitrate levels may be optimal for
ecosystem productivity while higher levels
may have the opposite effect of reducing
overall production.
– In their natural, low nutrient state, springs may
be adapted for optimal efficiency of light
utilization and maximum ecosystem
metabolism.
– Rising nutrient levels may result in the
competitive advantage of “weedy” plant
species that can capture light and spatial
resources through higher rates of net
productivity but lower gross productivity.
Effects of Nutrients on Spring Ecosystems
• Elevated nutrient levels in concert with
changes in other control mechanisms
(such as recreation, flow rates, or
grazing) may be linked to the
observed plant community shifts, from
adapted submerged aquatic plants
with sparse but productive periphyton
communities to systems dominated by
benthic and attached filamentous
algae.
7
Effects of Multiple Stressors on Spring
Ecosystems
• Other possible stresses affecting primary producers in
springs include:
– decreased dissolved oxygen in groundwater inflows
– altered grazer populations and introduction of exotic
species
– reductions in flow volume
– recreational disturbance
– increased stormwater runoff
– dams and other water management activities
– aquatic plant management
– invasion by exotic plant and animal species
• The diversity of anthropogenic stressors illustrates the
importance of an ecosystem-function level examination of
springs.
Recommendations for the Quantification of
Nutrient Effects on Spring Ecosystems
• The manner in which spring ecosystems can be
monitored for impacts resulting from nitrate or
other nutrient pollutants as well as other
stressors are presented as well as remaining
research needs.
• Three recommended approaches for springs’
ecosystem nutrient-effects research:
– Synoptic studies of multiple springs to provide
a better baseline for inter-spring comparisons
– Intra-spring comparisons
– In situ mesocosm studies
– Whole spring manipulation studies
8
Springs Research Recommendations
Synoptic Inter- and Intra-Spring Study
• State-wide spring ecosystem
metabolism baseline study over a
wide range of nutrient conditions,
flows, and conditions.
6.00
5.00
Spring Name
Alexander Springs
Chassahowitzka Springs Group
Fanning Springs
Gainer Springs Group
Homosassa Springs Group
Ichetucknee Springs Group
Jackson Blue Spring
Kings Bay Springs Group
Madison Blue Spring
Manatee Spring
Rainbow Springs Group
Silver Glen Springs Group
Silver Springs Group
Troy Spring
Volusia Blue Spring
Wacissa Springs Group
Wakulla Spring
Weeki Wachee Spring
Juniper Springs
Little River Spring
Ponce De Leon Springs
Rock Springs
Washington Blue Springs
Wekiwa Spring
3.00
2.00
1.00
ID
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
Spring
Fenney Spring
Hornsby Spring
Horn Spring
Cypress Spring
Starbuck Spring
Turtle Spring
Salt Spring (Hernando)
Hunter Spring
Ellaville Spring
Falmouth Spring
Alapaha River Rise
Wacissa Springs #2
Wakulla Tubing A/K-Tunnel
Black Spring (Jackson)
Wakulla Tubing K-Tunnel
Wakulla Tubing A/D-Tunnel
Holmes Blue Spring
Jackson Blue Hole Spring
Homosassa #1
Sanlando Springs
Suwanacoochee Spring
Gator Spring (Hernando)
Homosassa #2
Chassahowitzka Spring Main
Citrus Blue Spring
Levy Blue Spring
Mission Spring
Allen Mill Pond Spring
Chassahowitzka Spring #1
Magnolia Spring
Homosassa #3
Rock Bluff Springs
Bugg Spring
Blue Hole Spring (Columbia)
Springboard Spring
Volusia Blue Spring
Branford Spring
Siphon Creek Rise
Little Springs (Hernando)
Weeki Wachee Main Spring
Ichetucknee Head Spring (Suwannee)
Guaranto Spring
Wakulla Spring
Gadsen Spring
ID
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
Spring
Cedar Head Spring
Wakulla Tubing D-Tunnel
Gum Spring Main
Little River Spring
Wakulla Tubing C-Tunnel
Double Spring
Jackson Mill Pond Spring
Wakulla Tubing B-Tunnel
Rainbow Spring #6
Silver Spring Main
Hart Springs
Otter Spring
Bubbling Spring
Wekiwa Springs
Rainbow Spring #1
Deleon Spring (Volusia)
Ginnie Spring
Reception Hall Spring
Devils Ear Spring (Gilchrist)
Blue Grotto Spring
Madison Blue Spring
Rainbow Spring #4
Rock Springs
Mearson Spring
Gilchrist Blue Spring
Manatee Spring
Sun Springs
Telford Spring
Owens Spring
Troy Spring
Buckhorn Spring
Crystal Springs
Lafayette Blue Spring
Running Springs
Unknown 11365
Lithia Springs Major
Hays Spring (Jackson)
Jackson Blue Spring
Shangri-La Springs
Lafayette Ruth Spring
Fanning Springs
Apopka Spring
ID
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
Stats
Average
Min
Max
NOx-N
0.803
0.004
5.10
0.00
1
4
7
10
13
16
19
22
25
28
31
34
37
40
43
46
49
52
55
58
61
64
67
70
73
76
79
82
85
88
91
94
97
10
0
10
3
10
6
10
9
11
2
11
5
11
8
12
1
12
4
12
7
13
0
ID
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Average NOx-N (mg/L)
4.00
Spring
Beecher Spring
Copper Spring
Green Cove Spring
Holton Creek Rise
Orange Spring
Suwannee Springs
Newport Spring
Waldo Spring
Warm Mineral Spring
Santa Fe Spring (Columbia)
Nutall Rise
Alexander Springs
Silver Glen Springs
Washington Blue Spring (Choctawhatchee)
Steinhatchee River Rise
Santa Fe River Rise (Alachua)
Welaka Spring
Williford Spring
Juniper Springs
Columbia Spring
Fern Hammock Springs
Treehouse Spring
Salt Springs (Marion)
Crays Rise
Washington Blue Spring (Econfina)
Big Spring (Big Blue Spring) (Jefferson)
Morrison Spring
Spring Creek Rise #1
St. Marks River Rise (Leon)
Gainer Spring #1C
Spring Creek Rise #2
Tarpon Hole Spring
Gainer Spring #3
Poe Spring
Shepherd Spring
Brunson Landing Spring
Gainer Spring #2
Ponce De Leon Springs
Sulphur Spring (Hillsborough)
Rhodes Spring #1
Rhodes Spring #2
Rhodes Spring #4
Natural Bridge Spring
Beckton Springs
Spring ID
Springs Research Recommendations
Synoptic Inter-Spring Study
• Comparisons of Control and Affected Springs:
– Define the range of normal and altered ecosystem
metabolism in springs over a wide range of nutrient
conditions, including upstream/downstream studies
along nutrient gradients
– Implement controlled treatments in downstream
reaches for comparison to upstream “control”
reaches
– Define the trophic-level biomass pyramids and
energy flows in these reference spring systems
9
Springs Research Recommendations
In Situ Flow-Through Mesocosm
Studies
Springs Research Recommendations
In Situ Flow-Through Mesocosm
Studies
• Controlled Ecosystem-Level Studies:
– Mesocosm studies in situ to determine the
effects of nutrient levels on key primary
producers and effects of consumers on
various natural and “weedy” benthic and
periphytic algal assemblages
– Nutrient addition studies
– Single species macrophyte and
macroalgae productivity studies
– Consumer manipulation studies
10
Springs Research Recommendations
Whole-Spring Manipulation Studies
• Before-and-after recreation
reduction/elimination studies
• Exotic plant management studies
• Consumer control studies
Summary Effects of Nutrients on Spring
Ecosystems
• Evidence that the nutrients nitrogen and
phosphorus can have negative impacts on
springs (reduced ecosystem metabolism,
increased coverage/abundance of filamentous
algae and periphyton).
• Nutrients are not the entire story, declines in
springs appearance are also linked to recreation
impacts, the management of exotic plants and
animals, and reductions in spring discharge.
• Springs ecology studies can be improved by
measuring whole ecosystem metabolism.
11
Florida’s Springs
“…there exists a
marvelous opportunity
to study community
metabolism and
productivity…”
Howard T. Odum
(1957)
12