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![Page 1: The Need for Sustainable, Integrative Long-Term Monitoring of the Gulf of Mexico Hypoxic Zone Summit on Long-Term Monitoring of the Gulf of Mexico Hypoxic.](https://reader036.fdocuments.net/reader036/viewer/2022062401/5a4d1b647f8b9ab0599aefbc/html5/thumbnails/1.jpg)
The Need for Sustainable, Integrative Long-Term Monitoring of the Gulf of
Mexico Hypoxic Zone
Summit on Long-Term Monitoring of the Gulf of Mexico Hypoxic ZoneJanuary 30-31, 2007
Alan Lewitus
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• Boesch & Rabalais begin monitoring (1985)
• NOAA’s Coastal Ocean Program study documented issue (NECOP 1990-96; supplemental research 1997-1999) – evidence for increasing hypoxic zone over time
History of Monitoring
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Areal Extent of Gulf of Mexico Hypoxic Zone: 1985-1999
Are
a (k
m )2
Rabalais et al.
30.0
Latit
ude
29.5
29.0
28.5
-93.0 -92.0 -91.0 -90.0 -89.0
Atchafalaya R.
Mississippi R.Louisiana
Gulf of Mexico
Bottom Water Hypoxia, July 23-29, 1997
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• Hypoxia has increased since the 1950’s
• River N load is main driver of hypoxia
• NO3 load is > 3X that of 1950’s:
90% of nitrate inputs from non-point sources;74% of nitrate load is from agricultural non-point sources.
CENR Conclusions
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85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05
Record = 22,000 km2 in 2002
Since mid 1990s, the 5-yr running average size of hypoxic zone has hovered around 15,000 km2
Rabalais et al.
Extension of Monitoring
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Gulf of Mexico
LOUISIANA
AtchafalayaR
.
Mississippi
R.
C61988
1993100 km
N
94o 93o 92o 91o 90o30o
28o
29o
Gulf of Mexico
LOUISIANA
AtchafalayaR
.
Mississippi
R.
C61988
1993100 km
N
94o 93o 92o 91o 90o30o
28o
29o
Justić et al. (2002)
Areal Extent of Hypoxic Zone – Coastal Goal Metric
Areal extent of the hypoxic zone at the peak time of hypoxia (July) has been well characterized and is a good indicator of the intensity of hypoxia in any given year
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0
5000
10000
15000
20000
25000
0 5000 10000 15000 20000 25000
Predicted Area of Hypoxia
Obs
erve
d Ar
ea o
f Hyp
oxia
Model: Hypoxia area (km2) = 0.0998 x May NOx flux + 672 x Year -13.4 x 105 (R2 = 0.82)
Turner et al 2006
Statistical models suggest that spring/early Summer nutrient fluxes (primarily nitrate) are good predictors of mid summer size of hypoxia
Areal Extent of Hypoxic Zone – Coastal Goal Metric
LOWERMISSISSIPPI
MISSOURI UPPERMISSISSIPPI
OHIO
GULF OFMEXICO
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Gulf of Mexico
LOUISIANA
AtchafalayaR
.
Mississippi
R.
C61988
1993100 km
N
94o 93o 92o 91o 90o30o
28o
29o
Gulf of Mexico
LOUISIANA
AtchafalayaR
.
Mississippi
R.
C61988
1993100 km
N
94o 93o 92o 91o 90o30o
28o
29o
Justić et al. (2002)
Hypoxic Zone Monitoring
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Need for Extension of Monitoring
• Action Plan (2001): “greatly expand the long-term monitoring program for the hypoxic zone, including greater temporal and spatial data collection, measurements of macro-nutrient and micronutrient concentrations, and hypoxia…”
• Monitoring, Modeling, and Research Workgroup Report (MMR, 2004): “(monitoring) efforts need to be increased in frequency, at a minimum monthly from May through September. To develop a more complete understanding of ecosystem dynamics, selected sites should be monitored year-round. The spatial boundaries of some of these existing monitoring efforts should be expanded to collect data for defining boundary conditions in modeling efforts."
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Atchafalaya River plume
Southwest Pass plume
Hypoxia 21-25 July 2004
Atchafalaya River plume
Southwest Pass plume
Hypoxia 21-25 July 2004
Causes of Hypoxia:
• Expansion of spatial boundaries
• Greater temporal resolution
Science Needs
DiMarco et al. (2006); image from N. Walker
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Causes of Hypoxia:
• Benthic processes
• Hypoxic volume
Science Needs
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Science Needs
• Need to trace effects of habitat loss through the food web to understand ecosystem-level effects
• Hypoxia effects in the Gulf are:
• Indirect
• Spatially-mediated responses to the environment
• Occur across multiple trophic levels
Impacts of Hypoxia:
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20 m
80 m
croaker
20 m
80 m
20 m
80 m
croaker
95%75%50%25%
20 m
80 m
croaker
95%75%50%25%
20 m
80 m
95%75%50%25%
95%75%50%25%
20 m
80 m
croaker
Moderate Hypoxia
Severe Hypoxia
(1983, 1987, 1988, 2000)
(1993, 1995, 1996, 1997)
Hypoxia Effects on Atlantic Croaker Distribution
0
5000
10000
15000
20000
1983
1986
1989
1992
1995
1998
2001
Year
Are
a H
ypox
ia (k
m2 )
~33-50% habitat loss
from K. Craig
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Science Needs
Support models used to:
• quantify the relationship between nutrient loading and hypoxia
• understand the causes of hypoxia
• understand the impacts of hypoxia
Hetland – ROMS model
Surface(0 - 10 m)
Pycnocline
Bottom(10 - 20 m)
Surface(0 - 10 m)
Pycnocline
Bottom(10 - 20 m) TR
FOt
NP
DO
A
A
Justic et al. (1996)
0
5000
10000
15000
20000
10 20 30 40 50 60N Load Reduction
Are
a (k
m)
2
Scavia et al 2003, 2004
10 20 30 50 70% Nitrogen Load Reduction
020406080
100%
Incr
ease
in O
xyge
nBierman et al 1994, 1999
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Science Needs