Salt Water Intrusion

When it comes to Louisiana, there is no one reason for coastal land loss. Causes are both natural and man-made, but when those forces combine, they are detrimental to Louisiana’s coast. One example contributing to these synergistic forces is known as salt water intrusion.

Facts about Salt Water Intrusion: [4]

  • May occur in freshwater systems like aquifers or coastal marshes.
  • Is the movement of saltwater into interior areas or underground sources such as aquifers of freshwater marsh.
  • Most common in coastal regions, where freshwater is displaced by the inland movement of saltwater from the ocean.
  • Can also occur inland, far away from an ocean, as freshwater is pumped out from underground reservoirs and the salt-laden water from surrounding salty layers of the earth flow in.
  • Most common cause of saltwater intrusion is the pumping of freshwater from wells near coasts.
  • Climate change can increase saltwater encroachment along coastal regions as sea level rises.
  • Increased salinity of coastal freshwater can threaten the plant life and wildlife of coastal areas, destroy habitats such as marshes, and force the abandonment of drinking-water supplies.

swi_22

Coastal Louisiana is currently experiencing higher than expected salinity in traditionally freshwater marshes, waterways, and reservoirs [1]. It is possible for wildlife to adapt to locally saline conditions, but that is a process that requires time. A study by two professors at the University of Louisiana at Lafayette concluded:

  • Resident marsh fishes have genetic adaptations for localized salinity conditions [1].
  • Continued adaptation will be most successful if salinity increases gradually [1].
  • The existence of adaptation to salinity tolerance will be most important in aiding survival during surges of high salinity, such as those associated with hurricanes [1].

At the same time that sea level is rising, man-made actions are intensifying salt water intrusion through [4]:

  • Canal dredging, including oil and gas access canals
  • Channelization or straightening of natural waterways
  • Construction of levees for flood control
  • General development activities in the coastal zone

CWPPRA hydrologic restoration projects help reduce the inland march of salt water. Culverts and pumps restore the flow of freshwater into marshes, while locks and weirs create “one-way” channels out of the marsh that salt water can’t access.

Help Prevent Salt Water Intrusion
Coastal Zone Management Solutions for Salt Water Intrusion
[5] Educational Video (3minutes and 42 sec):   Testing the limits of salt water intrusion 
[6] Educational Video (13minutes 50 sec): A Video Presentation of Saltwater Intrusion from a student of the University of Idaho.
[7] Educational Video (1minute 49sec): Saltwater intrusion threatens rice acres
[8] Educational Video: 12min 05sec): Rosemary Knight, “Sentinel Geophysics: Imaging Saltwater Intrusion from Monterey to Santa Cruz”.

Source:

[1] Leberg, P. and Klerks, P. 2004. Final Report: Saltwater Intrusion On The Gulf Coast: An Assessment Of The Interactions Of Salinity Stress, Genetic Diversity And Population Characteristics Of Fish Inhabiting Coastal Marshes. University of Louisiana at Lafayette (ULL). Available: https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.highlight/abstract/5385 [May 22, 2018].

[2] Spatafora, James. 2008. Saltwater Intrusion of Coastal Aquifers in the U.S. Available: http://kanat.jsc.vsc.edu/student/spatafora/default.htm#homepage  [May 22, 2018].

[3] Encyclopedia.com. 2018. Available: https://www.encyclopedia.com/environment/energy-government-and-defense-magazines/saltwater-intrusion [May 22, 2018].

[4] Southern Regional Water Program. 2018. Louisiana Environmental Restoration. Available: http://srwqis.tamu.edu/louisiana/program-information/louisiana-target-themes/watershed-restoration/ [May 22, 2018].

[5] Fowler, Kristen. “Saltwater Intrusion – EnvS 546 Univ of Idaho”. ” 23 April 2016. Online video clip. YouTube. Accessed on 24 May 2018. <http://www.youtube.com/watch?v=puSkP3uym5k>

[6] PBS Newshour. “Testing the limits of saltwater intrusion”. 17 September 2015. Online video clip. Youtube. Accessed on 24 May 2018. https://www.youtube.com/watch?v=75CoHNQVbY8

[7] LSU AgCenter Video Archive. “Saltwater intrusion threatens rice acres”. 8 Jan 2016. Online video clip. Youtube. Accessed on 24 May 2018. https://www.youtube.com/watch?v=Z4TGPtq4bD0

[8] Stanford Alumni. Rosemary Knight, “Sentinel Geophysics: Imaging Saltwater Intrusion from Monterey to Santa Cruz”. 2 April 2014. Online video clip. Youtube. Accessed on 24 May 2018. https://www.youtube.com/watch?v=k4XcBx7OT3Y

 

 

 

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Decomposing in the salt marsh

Throughout the year salt marshes exhibit cycles of birth, growth, and death. That may be most obvious when looking at the plants, but it also applies to animals, bacteria, and fungi, sometimes on longer and sometimes on shorter time scales. Since marshes are such productive ecosystems, what happens to all of that organic matter when something dies, be it a leaf, single-celled organism, or alligator? Detrivores are an important part of the marsh ecosystem, breaking down organic matter and cycling nutrients; in fact, in salt marshes, detrivores are the dominant consumers.

 

Fiddler-Crab-688
Fiddler crabs separate decaying matter from sand and mud. Photo from NPS (https://www.nps.gov/foma/learn/nature/crustaceans.htm)

Most decaying plant matter in a salt marsh is consumed by bacteria and fungi, which are then food for larger creatures, but a host of species in the salt marsh are detrivores: snails, crabs, amphipods, nematodes, fish, and many others. Some of these, like fiddler crabs, feed by finding pieces of detritus on grains of sand and soil, while others specialize on a particular species’ remains. Gammarus palustris is an amphipod which consumes the dead leaves from salt marsh cordgrass (Spartina alterniflora). Zimmer et al. (2004) suggested a variety of detrivores were needed in any habitat type for efficient decomposition and that you couldn’t substitute one species for another- the different species contribute in different ways. Whether big or small, detrivores keep nutrients moving within the system and prevent dead organic matter from building up, and that helps salt marshes continue to be so productive.

Works Cited:

Zimmer, M, Pennings, SC, Buck, TL and TH Carefoot. 2004. Salt marsh litter and detrivores: a closer look at redundancy. Estuaries 27: 753-769.

Mangroves in Winter

The recent cold weather in Louisiana may have been the end of the road for some plants as temperatures dipped into the teens and stayed below freezing for full days. The hibiscus in your garden may have survived because you gave it extra insulation, but what about marsh plants? Louisiana salt marshes are home to black mangroves (Avicennia germinans), but this represents the very northernmost part of their range. Of the three mangrove species found in the continental United States [red (Rhizophora mangle), black, and white (Laguncularia racemosa)], black mangroves are the most cold-hardy, but they are still sensitive to winter weather- they generally cannot establish above 28° N and S latitude because winters are too cold (a sliver of the Birdsfoot Delta is below 29° N, so we really are at their limit).

The three mangrove species are also different in their tolerances for other environmental conditions: red mangroves establish in the intertidal zone, while black and white mangroves are found at higher elevations, and white mangroves can colonize areas with little to no soil. In Florida where all three species occur, mangrove zones can be defined from the water extending inland and up in elevation .

ZONATION1
Red mangroves are found in the intertidal zone, while black and white mangroves establish at higher elevations. Graphic from the Florida Museum of Natural History at the University of Florida (https://www.floridamuseum.ufl.edu/southflorida/habitats/mangroves/zonation/)

Black mangroves are an important component of Louisiana salt marshes, providing habitat to a variety of species. The complex root systems trap and collect sediment, limiting erosion and maintaining land. Juvenile invertebrates and fish find shelter among the roots, while seabird chicks, such as brown pelicans and roseate spoonbills, are protected from high water events and predators up in the branches.

CWPPRA projects that nourish barrier islands and create new marsh habitat help maintain black mangrove populations by providing new land for the plants to colonize; in turn, the mangroves help the new land persist in the face of wind and wave energy.

Wetland Marshes

Marsh is a type of wetland that is continuously flooded with water. Emergent-soft stemmed vegetation is present in marsh due to the saturated soil conditions. In Louisiana, there are four types of wetland marsh: freshwater, intermediate, brackish, and salt. Marshes are classified according to the salinity of the water. The location of Louisiana marshes in relation to the Gulf of Mexico often directly correlates to the level of salt content in the water. Salinity also changes based upon rainfall, drainage, soil texture, vegetation, depth of water table, and freshwater inflow.

The salinity range for each marsh type is as follows:

  • Freshwater – 0 ppt (parts per thousand)
  • Intermediate – 0-5 ppt
  • Brackish – 5-15 ppt
  • Salt – 15 or greater ppt

marsh_salinity

A wide variety of animals such as nutria, turtles, and many bird species can be spotted in the freshwater and intermediate marshes of Louisiana, as well as species of special concern like Louisiana black bears and Calcasieu painted crawfish. The exchange between freshwater and salt water is frequent in the state of Louisiana due to its close proximity to the Gulf of Mexico. An estuary is characterized by this mixture of freshwater and salt forming brackish water where many wetland species spend their juvenile lives. The estuaries of coastal Louisiana support economically important fisheries and provide important wildlife habitat. Crabs, fish, and shrimp are a few of the animals found in Louisiana’s salt marsh, and birds like brown pelicans and reddish egrets often nest in the shrubby vegetation bordering salt marshes. Each of these marsh types play a significant role. It is vital to keep these marshes healthy for them to maintain their value and support the people, plants, and animals of Louisiana.

 

 

Wetland Vegetation

Wetland ecologists often refer to wetland vegetation as the foundation of coastal restoration. Native plants and vegetative plantings both provide significant benefits to wetlands. Wetland plants build and stabilize soil, create habitat, purify water, and shield infrastructure. These plants tend to accumulate the thick mud of marshes which prevents the soil from washing away. Animals that live in wetlands depend on plants or plant-eating animals for their food supply. Without wetland vegetation, the supply chain would self-destruct. By absorbing nutrients and chemicals from the water and sediment, plants reduce toxins and groundwater contamination. Wetland vegetation is key to preventing shoreline erosion and reducing storm surge which affects the coastal infrastructure.

The Coastal Wetlands Planning, Protection and Restoration Act funds a variety of wetland enhancement projects, such as vegetative planting. Vegetative planting is the process of planting by hand or aerial seeding to shore up eroding banks and jump-start plant colonization.

You can read more about CWPPRA Projects that use the vegetative planting restoration technique by clicking here.

Louisiana’s State Reptile – The American Alligator

The American alligator (Alligator mississippiensis), the largest reptile in North America, is also known as the state reptile of Louisiana. Ancestors of the American alligator appeared nearly 160 million years ago. Alligators are cold-blooded, and their body temperature is regulated by the environment around them. There are approximately 2 million wild alligators in the state of Louisiana. Alligators can be spotted in ponds, lakes, bayous, rivers, swamps, and even occasionally swimming pools near these coastal areas in the dry months. The highest populations of alligators within Louisiana are found in coastal marshes. Coastal marshes account for about 3 million acres of alligator habitat in Louisiana.

Alligators are predators in the wetland ecosystem. Young alligators typically feed on small animals such as crawfish, insects, small fish, and frogs. An adult alligator’s diet consists of crabs, turtles, nutria, large birds, and sometimes deer. Alligators assist in population control and support diversity in the environment.  During nest construction, alligators dig burrows with their tails in peat, a boggy type of soil, which often facilitates plant growth. The burrows become “alligator holes”, or wetland depressions, which serve as a breeding area to many species other than alligators during dry periods. Alligators are key contributors to the diversity and productivity of coastal wetlands.

American-Alligator-Photos

Giant Salvinia

Giant Salvinia, or Salvinia adnata, often referred to as the green monster, poses a serious threat to wetland ecosystems. This highly invasive, aquatic plant species is native to Brazil. The floating aquatic fern has leaves covered with small hairs on the upper surface that become compressed into chains forming a dense, compiled mat-like structure. In the United States, it’s difficult to control Giant Salvinia due to the lack of legal herbicides that work efficiently to stop it from spreading. Giant Salvinia was first spotted in Chenier Plain Marshes in 2009; since then it has spread throughout.

This non-native plant species has an exceedingly rapid growth rate, and under the right conditions it can potentially take over a waterway causing catastrophic results. The mat blocks sunlight from penetrating into the water, ultimately killing phytoplankton and other aquatic plant species, as well as exhausting oxygen levels, which alters the area as a waterfowl habitat and degrades the water quality for fish. Giant Salvinia is unintentionally spread to new water bodies on boats and fishing gear. One way to prevent the expansion of Giant Salvinia is to properly clean boating equipment and vessels of any plant fragments. These plant fragments, garden, and aquarium plants should all be discarded properly in the trash and kept out of water bodies. It is important to properly control and dispose of the plant material in order to keep lakes, rivers, ponds and other freshwater wetlands functioning properly without the disturbance caused by Giant Salvinia.

Cyrtobagous salviniae, a species of weevil, is often referred to as the salvinia weevil due to being a biological pest control against the highly invasive Giant Salvinia. For more information on Giant Salvinia and CWPPRA’s efforts to control this invasive plant species visit the Coastwide Salvinia Weevil Propagation Facility (LA-284) Fact Sheet.