Tag Archive for 'estuaries'

Estuaries on the northwestern coast of Madagascar As Seen From Orbit

Estuaries on the northwestern coast of Madagascar are featured in this image photographed by an Expedition 28 crew member on the International Space Station. Photo retrieved from: www.spaceref.com

“This photograph highlights two estuaries located along the northwestern coastline of the island of Madagascar. The Mozambique Channel (top) separates Madagascar from the southeastern coast of Africa. Bombetoka Bay (upper left) is fed by the Betsiboka River and is a frequent subject of astronaut photography due to its striking red floodplain sediments. Mahajamba Bay (right) is fed by several rivers including the Mahajamba and Sofia Rivers; like the Betsiboka, the floodplains of these rivers also contain reddish sediments eroded from their basins upstream.

The brackish (mix of fresh and salty water) conditions found in most estuaries host unique plant and animal species adapted to live in such environments. Mangroves in particular are a common plant species found in and around Madagascar estuaries, and Bombetoka Bay contains some of the largest remaining stands. Estuaries also host abundant fish and shellfish species — many of which need access to freshwater for a portion of their life cycles — and these in turn support local and migratory bird species that prey on them.

However, human activities such as urban development, overfishing, and increased sediment loading from erosion of upriver highlands threaten the ecosystem health of the estuaries. In particular, the silt deposits in Bombetoka Bay at the mouth of the Betsiboka River have been filling in the bay.”

Read more: Spaceref

Cutting Edge Energy From Estuaries?

The Amazon River meets the sea - potential site for future non-dam salinity-based hydro? Photo retrieved from: www.internationalrivers.org

“Battery-operated electric vehicles are cutting CO2 emissions and raising awareness of our transportation carbon footprint. Recent cutting edge research now shows that batteries can also be harnessed in rivers and estuaries as a non-dam and hopefully low-impact form of electricity generation.

According to Stanford University, a team lead by Yi Cui (Associate Professor of Materials Science and Engineering), has developed a battery that takes advantage of the difference in salinity between freshwater and seawater to produce electricity.

The battery is simple, consisting of a positive and negative electrode immersed in water containing electrically charged particles, or ions – in this case, sodium and chlorine (i.e. table salt).

Battery in freshwater/saltwater cycle. Retrieved from: www.internationalrivers.org

  • Step 1: A small electric current charges the battery, pulling ions out of the electrodes and into the water.
  • Step 2: The fresh water is replaced with seawater, thereby increasing the amount of charged ions. Salty seawater contains 60 to 100 times more ions than freshwater.
  • Step 3: The salt water increases the electrical potential, or voltage, between the two electrodes, allowing the battery to generate far more electricity than the amount used to charge it. Electricity is then drawn from the battery for use, draining the battery of its stored energy.
  • Step 4: Seawater is discharged and replaced with river water, and the cycle starts again.

The impacts and limitations

According to the Stanford article, the potential environmental impact of the battery should be low. They recognize that river mouths and estuaries are environmentally sensitive areas. They chose manganese dioxide for the positive electrode, in part because it is environmentally benign. The discharge water would be a mixture of fresh and seawater, released into an area where the two waters are already mixing, at the natural temperature.”

Read more: International Rivers