Eutrophication in California’s “Bar‐Built Estuaries:”
Connecting Science to Management
Martha Sutula and Karen McLaughlin
Biogeochemistry Department
Southern California Coastal Water Research Project (SCCWRP)
Headwaters to Oceans Conference May 2011 San Diego
Eutrophication Is Among Top Three Impairments to Aquatic Ecosystems (EPA 2001)
• Accelerated accumulation of organic matter within an aquatic ecosystem
• Nutrient overenrichment is major driver
• Adverse effects include hypoxia, reduced biodiversity, altered food webs, etc.
• Symptoms vary by habitat type
Coastal Ocean
Estuaries
Streams
Lakes
Diversity of California Estuaries
Geoform
Tidal Regime
Perennially Tidal Enclosed Bay
No. Enclosed Bay
Perennial
30
Lagoon
Perennial
Intermittent
Ephemeral
15
33
46
River mouth
Perennial
11
Intermittent
270
_________________________________
Total
405
Intermittently Tidal Lagoon
Ephemerally Tidal Lagoon
Intermittently Tidal River Mouth
Overview of Talk
•
Defining characteristics of bar‐built estuaries
–
•
Factors that influence eutrophication
Comparison of susceptibility to eutrophication in four estuaries (part of SD Lagoon TMDL studies)
–
Santa Margarita River Estuary
–
Loma Alta Slough
–
Buena Vista Lagoon
–
San Elijo Lagoon
Bar‐Built Estuaries– Important Processes
Coastal Lagoon
River Mouth Estuary
• Two dominant physical processes:
– Energetic wave climate builds up sand bar
– Magnitude and seasonality of terrestrial inputs
• Defines geomorphology, habitat type distribution, inlet dynamics
1000
800
-1
Closed Inlet
600
400
200
0
Jan-08
Sp. Conductivity (mS cm ) Water Depth (m, NADV 88)
Open Inlet
Mar-08
May-08
Jul-08
Sep-08
Mar-08
May-08
Jul-08
Sep-08
Mar-08
May-08
Jul-08
Sep-08
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
Jan-08
60
50
40
30
20
10
0
Jan-08
Time
Loma Alta Slough, San Diego County
Freshwater Flow (cfs)
Inlet Closure as A Function of Freshwater Flow
Inlet Status Controls Dominant Primary Producers
Benthic diatoms and macroalgae on intertidal flat in “open” state
Marsh
3
Intertidal Flats
2
Shallow Subtidal
1
Deepwater or Turbid Subtidal
Floating macroalgae, submerged aquatic vegetation & phytoplankton in “closed” state
Primary Producer Biomass
-2
(g C m )
-1
Sp. Conductivity (mS cm )
Open Inlet
Closed Inlet
60
50
40
30
20
10
0
Jan-08
Mar-08
May-08
Jul-08
Sep-08
1000
100
10
1
0.1
0.01
0.001
Jan-08
Mar-08
May-08
Jul-08
Inlet Status Controls Hydraulic Residence Time
Sep-08
Time
Longer Residence Time Increases That Nutrients Are Available for Primary Production
-1
Dissolved Oxygen (mg L ) Sp. Conductivity (mS cm-1)
Inlet Closure Controls Dissolved Oxygen
60
50
40
Open Inlet
Closed Inlet
30
20
10
0
Jan-08
Mar-08
May-08
Jul-08
Sep-08
Mar-08
May-08
Jul-08
Sep-08
20
15
10
5
0
Jan-08
Inlet Closure Can Cause “Salt Trap”
Ocean
Ocean
Inlet Closure
Slough
Fresher Water
Dense Salty Water
Four Estuaries Representing Gradients in Inlet Status and Geoform
Ephemerally Tidal
Loma Alta Slough
INLET STATUS
Perennially Tidal
Santa Margarita River Estuary
Fluvial
GEOFORM
Buena Vista Lagoon
San Elijo Lagoon
Lagoonal
Study of Susceptibility to Eutrophication in Four San Diego Estuaries
•
Sources – watershed TN and TP loads (MacTech 2009, CDM 2009)
•
Indicators of eutrophication
–
Primary producer biomass and cover
–
Continuous dissolved oxygen, WSE, conductivity, turbidity et al.
–
Water column, sediment pore water nutrients
•
Sediment grain size, bulk characteristics, seasonal and long‐term annual sediment deposition (Be‐7 and Pb‐210)
•
O2, TCO2, nitrogen and phosphorus fluxes using in situ benthic chambers (e.g. Berelson et al. 1999)
•
Denitrification, benthic nitrogen fixation rates via acetylene reduction (Chan and Knowles 1979)
Macroalgae Dominates, with 10X Higher Biomass When Inlet Closed
2
+
e
1
1
+
e
8
1
+
e
4
1
+
e
2
33
e
e
4
︶
︵
Phytoplankton
MPB
Macroalgae
SAV
1
+
e
6
2
m
C
t
w
y
r
d
g
20
s
r
e
c
u
d
o
r
p
y
r
a
m
i
r
p
f
o
s
s
a
m
o
i
b
Primary Producer Biomass‐ July 2008 y
h
Santa Margarita Loma Alta r
g
a
uSlough
S
River Estuary
u
o
t
n
n
Buena Vista San Elijo o
o
oLagoon
o
Lagoon
g
g
0
Net Benthic Oxygen Fluxes ‐ July 2008 -50
-100
-150
-200
-250
-300
goon
goon
ough
Santa Margarita Loma Alta Buena Vista San Elijo River Estuary
Slough
Lagoon
Lagoon
uary
‐2 ‐1
O2 Flux (mmol m d ) O m‐2 d‐1)
July 2008 Oxygen Flux (mmol
2
Lagoons Have Higher Sediment Oxygen Demand Relative to River Mouth Estuaries
Lagoons Sediments Provide More Consistently A Source of Nitrogen To Surface Waters
25
20
15
10
5
goon
goon
ough
0
tuary
NH4+ N03 Flux (mmol m‐2 d‐1)
30
Net Benthic Dissolved Inorganic Nitrogen Fluxes ‐ July 2008 Santa Margarita Loma Alta Buena Vista San Elijo River Estuary
Slough
Lagoon
Lagoon
Relative Importance of Internal Recycling to Total Summer Areal N Loading Rates: Geoform Matters
Estuary
Freshwater Summer Summer Benthic % Benthic Flux of Mean Sediment Areal N Loading3
N Flux (g m‐2 d‐1) Total N Loads % Fines (0‐8 cm)
(g m‐2 d‐1)
Snta. Margarita River Estuary
0.04
0.007
17%
10%
Loma Alta Slough
0.07
0.02
20%
19%
0.03
0.03
49%
60%
0.01
0.05
79%
90%
San Elijo Lagoon
0.02
0.17
87%
58%
Famosa Slough
0.01
0.04
80%
93%
Upper Newport Bay1
Buena Vista Lagoon
1
Berelson et al., unpublished data
2 Additional N source suspected, but unaccounted for in this estimate.
3 CDM (2009) and MacTech Inc (2009)
River Mouth Estuaries Are Less Susceptible to Eutrophication Than Lagoons
Fluvial
Higher water velocity
Sandy sediments
Low sediment OC & oxygen demand, low algal biomass
Lagoonal
Lower water velocities
Fine grained sediments
High sediment OC & oxygen demand, high algal biomass
Options for Management Force Tradeoff Between “Natural Habitat” and Water Quality
• Easiest option is to maintain inlet open, but eliminates brackishwater habitat
• Other option involves reducing/eliminating dry weathers flows before inlet closes, but expensive
What is the right choice?
Acknowledgements:
•Study funded by Prop 50 Coastal NPS grant • Thanks to MacTech Inc. and CDM Inc. (watershed loads, estuary continuous water quality data)
Thank You!
Marthas@sccwrp.org; 714‐755‐3222