Around the first point, near New Orleans, the dominant
ecosystem is a swamp forest. This ecosystem is short-statured located where
upland forests meet swamps and are common in the Mississippi River delta and
the coast of Louisiana. This ecosystem is dominated by Fraxinus profunda
(Pumpkin Ash—tree) and other plant and tree species. It is usually a very wet
environment, which is why Pumpkin Ash and Little Duckweed thrive. (Nature Serve
Explorer, 2020, a)
Fraxinus profunda, or “pumpkin ash,” is a tree native to the
eastern U.S. and into Canada that can be found in wet ecosystems, especially
along the Mississippi and Ohio rivers (Missouri botanical garden, N.D.), like
Louisiana’s Swamp Forest. The pumpkin ash has no tolerance for dry soil, needs
space to grow, and prefers full sun to little shade. As they mature, they can
reach 60-80 feet in height (Missouri botanical garden, N.D.)! Ash trees are
susceptible to insect problems, most recently the invasive Emerald ash borer
(native to Asia). Because of its susceptibility to all and especially the
Emerald ash borer, the Pumpkin ash's future is of concern because it can kill
ash trees in as little as 3-5 years (Missouri Botanical Garden). It is a
threatened species in Michigan and endangered in New Jersey and Pennsylvania
(USDA, ND, a). Soil moisture is definitely a limiting factor in the pumpkin
Ash’s distribution. From the range map (below), we can see that temperature may
not be a huge issue, but it cannot tolerate dry soil (Missouri botanical
garden, N.D.).
Lemna obsura, most commonly known as “little duckweed,” is a floating aquatic plant found in much of the eastern and middle regions of the United States (USDA, ND, c). It thrives in the swamp forest ecosystem. In some places, it can be a pest, such as in Pennsylvania, where its status is currently ‘extirpated’ (USDA, ND, c). Because this is an aquatic plant, the availability of water bodies is a factor in dispersal and judging from the range map (below), temperature is as well.
Around point 2 (Pointe a La
Hache), the dominant ecosystem type is the Gulf Coast tidal freshwater marsh
dominated by Sagittaria lancifolia and Lythrum lineare. (NatureServe Explorer,
2020, c). It occurs in the marshlands of southern Louisiana as well as some
coastal areas in Texas and Alabama. This ecosystem is in very shallow water
with little water level variation, and the waters in these marshlands are tidal
fresh to oligohaline.
Sagittaria lancifolia L., or the
Bulltongue Arrowhead, is a member of the Water-Plantain family and grows in
areas with an abundance of slow-moving water because they are emergent aquatic
plants. (University of Texas, 2015). Limitations to the distribution of these
plants are due to their water and nutrient requirements. They prefer full sun,
so areas where that is not possible limit their distribution as well
(University of Texas, 2015).
Lythrum lineare, or the Narrow
loosestrife, is a grass native to brackish or salt marshes, flats, and
wetlands. The Narrow loosestrife is native to coastal regions along the gulf
and along the Atlantic. (University of Texas, 2009). The distribution of the
Narrow loosestrife would definitely be limited to water and nutrient availability,
even if temperature was not a factor.
At point 3, near Boothville- Venice, LA, one will find the Gulf Coast tidal salt marsh. This marsh is the major salt marsh type in coastal Louisiana, is "gulf-fringing" and is mainly found in the deltaic plain and large flanking bays. Biodiversity is generally low in the marsh itself and is dominated by smooth cordgrass, but Juncus roemerianus is may be present in the Deltaic Plain of Louisiana, specifically (Nature Serve Explorer, 2020, b). Lepidochelys kempii is also found here and all over the gulf (N.E.S.T., 2016).
Lepidochelys kempii, or the Ridley Sea turtle, is the
smallest sea turtle and is also critically endangered. They are native to the
northern Gulf of Mexico and favor Louisiana waters. Their preferred nesting
beaches are backed by swamps and have seasonal ocean channels (N.E.S.T., 2016).
Of course, temperature and availability of suitable habitat is a factor for the
distribution of the Kemp’s Ridley. Still, human activities and hunting/fishing
(eggs and the turtles themselves) have left this species critically endangered (N.E.S.T., 2016).
Juncus roemerianus, commonly known as the Black needlerush, is a grass native along the gulf and east coast from Texas to Maryland. It prefers medium-to-fine-textured soils, is tolerant of anaerobic conditions, and is adapted to live in a salt marsh (USDS, N.D., b). The usual distribution limitations are in play (temperature, water, and nutrient availability), but it can travel up to 10-15 miles inland from its range (USDS, N.D., b).
A natural disturbance regime present in all three locations is hurricanes. Hurricanes are a regular disturbance in the gulf and are necessary for many ecological functions. They are essential for the sustainability of wetlands (and marshes) because the precipitation associated with the storm introduces fresh water and nutrients to saline marshes to decrease the salinity, which increases productivity in the area (Day Jr. et al., 2007). They also deposit large amounts of sediment to the wetlands, which is an essential aid in the natural delta lobe cycle that contributes to the natural formation and loss of the wetlands (Day Jr. et al., 2007). This process experienced overall growth until the 20th centuries when human activities hindered the process (Day Jr. et al., 2007).
The mainland relies on the marshes that the three locations are and barrier islands to protect it from hurricane storm surges. In 2005 when hurricane Katrina made landfall, the storm surge exceeded 10m on the Mississippi coast, 6m southeast of New Orleans, and sent an extra 2m of run-up in the most exposed locations (Day Jr. et al., 2007). The disturbance of wetlands and buoyant low-salinity marshes with poor soil (like the tidal salt marsh) is common during hurricanes (Day Jr. et al., 2007).
Anthropogenic stressors in my study area are urbanization
(point 1), shipping channels and canals (point 2), and upriver damming (point
3). The urbanization of New Orleans and the surrounding area has caused a human
need to try to control the Mississippi river that they settled on through
levees and dams, which are one of the causes of wetland loss of which Louisiana
has lost over 2,000 square miles since the 1930s (Restore, 1). Without levees
and dams, the Mississippi river would be able to perform its natural source-sink
processes to rebuild wetlands from the destruction caused by oceanic forces
(Twilley, 2016). Located along a shipping channel, the anthropogenic stressor
at the second point (Point a La Hache) is shipping channels and canals of which over 15,000km have been dredged (Day et al., 2007). Increased submergence due to wetland loss, and increased salinity from canal
and oil infrastructure, could be detrimental to Sagittaria lancifolia L. All
three stressors adversely alter S. lancifolia L.'s ability to photosynthesize
and perform other gas exchange functions (Pezeshki et al., 1987). The building
of shipping channels and canals has been steadily contributing to the
destruction of freshwater ecosystems by an influx of saltwater from the ocean
(Restore, 1). At point 3, the Boothville location, the stressor is oil and gas
infrastructure; an example of this is the 2010 Deepwater Horizon Oil Spill (BP
Oil Disaster) that occurred approximately 40 miles off the coast of Louisiana.
This disaster contributed to the further decline of the Kemp Ridley Sea turtles
(a projected 20,000-60,000 deaths in 2010) and the deaths of birds, marine
mammals, fish, and other wildlife that numbers in the hundreds of thousands
(Restore, 2).
Using The Climate Explorer, under the RCP 8.5 scenario, the high-emission average daily maximum temperature projection raises the average temperature by 1 degree Fahrenheit every 5-10 years, especially after 2040 when the high emission projection makes a sharp break from what the maximum average would be in a low emission scenario. The temperature increase will also increase the intensity and frequency of hurricanes because the ocean will warm with the temperature. The Gulf of Mexico is one of the areas that have the highest frequency of hurricanes (Day et al., 2007). Increased hurricane intensity can further destroy wetlands through flooding, coastal erosion, subsidence, and damage oil and gas infrastructure, leading to more oil spills (Oceana, 2020). For example, Hurricanes Rita and Katrina (2005) destroyed over 100 platforms, and a mudslide from Hurricane Ivan (2004) sank an oil platform that buried numerous wells (Oceana, 2020). They leaked oil for fifteen years, and containment issues are still underway (Oceana, 2020).
Although Kemp’s Ridley sea turtle is a reptile and depends on heat to regulate its body temperature, coastal erosion and sea-level rise (another result of rising temperatures) threaten their nesting habitat in several ways (NOAA, N.D.). As temperature increases, the sand temperature will also increase, and that can be lethal to or alter eggs; coastal erosion (and sea walls) can decrease available habitat or make nests more susceptible to flooding (NOAA, N.D.). The increased threat to oil and gas infrastructure from increased hurricane intensity also threatens the endangered Kemp’s Ridley because, like OCEANA warns, with the high-intensity storms comes an increased risk (because offshore drilling already is). The next spill could be even more devastating than the Deepwater Horizon spill that killed 20,000-60,000 Kemp Ridley turtles alone.
So, to protect nesting sites and human settlements, Day et al. provides four approaches to restore the Mississippi deltaic plain and wetlands including, large scale reintroductions of the river to the deltaic plain through old distributaries, pumping dredged sediments over long distances (expensive), restoring barrier islands, and by restoring the natural hydrological processes (example: backfill canals, remove soil banks, close deep navigation channels, etc.) (Day et al., 2007). All three locations would benefit from wetland restoration because we would be restoring a natural buffer that can only benefit us. Hurricane Katrina inundated the communities (in the study area) at or below sea level and sent a 6m storm surge through New Orleans with an additional 2m wave run-up; needless to say, the levees were breached or destroyed (Day et al., 2007). Point 3 near Boothsville would benefit from the closing of offshore drilling. Not only would it make finding alternative power more urgent, but it would also promote independence from fossil fuels. Both of which would be one step closer to protecting the most valuable resource humans will ever have, the ocean.
References
Day Jr. John W., Donald F. Boesch, Ellis J. Clairain, G. Paul Kemp, Shirley B. Laska, William J. Mitsch, Kenneth Orth, Hassan Mashriqui, Denise J. Reed, Leonard Shabman, Charles A. Simenstad, Bill J. Streever, Robert R. Twilley, Chester C. Watson, John T. Wells and Dennis F. Whigham. 2007. Restoration of the Mississippi Delta: Lessons from Hurricanes Katrina and Rita. March 23. American Association for the Advancement of Science Vol 315, No. 5819, Pp. 1679-1684.
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b.
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c.
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d.
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