What is a coastal lagoon?
Coastal lagoons are bodies of water associated with the sea. They are usually separated from the sea by stretches of coast or islands of marine origin.
They are usually parallel to the shore and, in some cases, associated with estuaries and bays.
Sometimes, in addition to receiving the influence of the sea, coastal lagoons receive discharges of freshwater from rivers or streams. In these cases, the water column is usually mixed with salinities less than or equal to the sea.
What types of coastal lagoons are found in Puerto Rico?
Based on the hydrological pattern, average salinity, and dominant biota, coastal lagoons can be classified into three types: marine, hypersaline, or brackish.
Marine lagoons are characterized by having free exchange with the sea, and a substantial portion of its volume is renewed by the tide. Freshwater supply is limited. Chemical composition, temperature, and dissolved oxygen in the water are similar to that of the sea. The floor is sandy, the water is clear, and sometimes they are covered by phanerogams (seagrass prairies) and seaweed. Since the environmental conditions in these lagoons are similar to those of the sea, the organisms that live there are mostly marine and many times come from nearby coral reefs.
Hypersaline lagoons have poor communication with the sea. They have canals of little circulation and average salinities are higher than 40%. They are found in regions of high evaporation, with little rain and low runoff. Water temperature is usually higher than that of the sea. Fauna is scarce, consisting mainly of mollusks and some fish. High temperatures and salt concentration tend to limit or inhibit the reproduction and growth of many species.
When hypersaline lagoons are isolated from the sea or drastically reduce the renewal of its waters, salinity significantly increases as does the difficulty to maintain its natural biological populations. Under these extreme conditions, fauna is reduced to the few species adapted to survive in this environment.
Brackish lagoons are semi-closed bodies where seawater is measurably diluted with a supply of freshwater from the land. They are associated with streams or drainage canals; fluctuations in volume and saline composition of the water respond primarily to changes in the volume of runoff and freshwater intrusions. Under conditions of good drainage, the flow of freshwater displaces the saltwater towards the mouth of the lagoon and sometimes towards the open sea (if the exit is not blocked). This results in the formation of a salinity gradient towards the mouth of the lagoon.
Furthermore, the degree of the mix is also determined by winds and depth of the lagoon. The environmental conditions in those lagoons are unstable because changes in the chemical composition of water and parameters such as oxygen and temperature are broad.
Brackish lagoon floors are clayish with a high content of organic matter. These are mostly populated by estuarine species adapted to survive in unstable environmental conditions.
Which are the most important lagoons in Puerto Rico?
1 – Tortuguero
2 – Mata redonda
3 – Condado
4 – San José
5 – Torrecillas
6 – Piñones
7 – Aguas Prietas
8 – Laguna Grande
9 – Ceiba
10 – Pozuelo
11 – Mar Negro
12 – Puntas Arenas (Mar Negro)
13 – Salinas (Ponce)
14 – El Faro
15 – Salinas (Cabo Rojo)
16 – Boquerón (Rincón)
17 – Guaniquilla
18 – Joyuda
Why are coastal lagoons important?
Lagoons are one of the most important natural resources our island has because:
• Coastal lagoons have relatively shallow waters, which in some cases allow sunlight to penetrate the water column thus promoting the abundance of aquatic flora and fauna.
• In periods when water flow is higher than usual, coastal lagoons receive sediment and pollutants from streams or drainage currents, thus maintaining cleaner coastal waters.
• They serve as natural nurseries for some fish species and as habitat for copepods, mollusks, and other invertebrates.
• They serve as refuge for many species of native aquatic birds.
• A large number of marine species of human consumption migrate there to spawn.
• They can be used as natural laboratories where both citizens and scientists may develop their knowledge on the ecology of the system.
• They may be used for sports and recreational activities.
• They can retain large volumes of water, protecting the coast from possible floods.
How are coastal lagoons affected?
Coastal lagoons can be adversely affected by the following elements:
• Significant hydrological changes.
• Fast industrialization and population growth.
• Contamination of coastal lagoons by the discharge of domestic and industrial effluents, high water temperature, and other oil spills.
• Excessive sedimentation and salt fluctuations.
What are the most important protection measures for the area?
Coastal lagoons are characterized by their unique and peculiar resources as well as their role in the coastal zone. We must avoid activities that might cause irreparable harm such as cutting trees around them, extracting sand, allowing significant hydrological changes, and discharging liquid pollutants. The misuse of such an important resource could lead to the destruction of such an important ecosystem.
Author: Grupo Editorial EPRL
Published: August 27, 2014.
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