Lagoon

Lagoon
Name	Lagoon
Caption	Coastal lagoon
Location	Various
Type	Shallow coastal or inland waterbody
Inflow	Rivers, tides, groundwater
Outflow	Sea, channels
Basin countries	Various
Area	Variable
Depth	Shallow

Lagoon is a shallow body of water separated from a larger body by a barrier such as a sandbar, coral reef, barrier island, or mangrove belt. Coastal examples occur along the coastlines of the Mediterranean Sea, Atlantic Ocean, Indian Ocean, and Pacific Ocean and inland equivalents form behind dunes, along rift basins, or within atoll structures like those in the Marshall Islands and Maldives. Lagoons are important in studies of geomorphology, coastal management, marine biology, wetland conservation, and climatology and often host economically significant fisheries and tourism infrastructure.

Definition and Types

A lagoon is generally defined as a shallow, often elongated waterbody separated from an adjacent larger water mass by a barrier such as a barrier island, sandspit, coral reef, or tombolo. Major types include coastal lagoons along the Gulf of Mexico and Bay of Bengal, atoll lagoons within chains like the Tuamotu Archipelago and Line Islands, and coastal lake analogs such as the Black Sea-adjacent estuarine basins. Other named variants are hypersaline lagoons like those on the Dead Sea margin, brackish lagoons along the Chesapeake Bay shoreline, and transient interdunal lagoons in regions like the Sahara fringe and Great Barrier Reef waters. Terminology overlaps with features such as estuary, sound, laguna de Mar Chiquita (Córdoba), Ria de Arousa, and fjard in local usage.

Formation and Geomorphology

Lagoons commonly form where sediment transport, sea-level change, and reef growth create barriers. Classic models invoke longshore drift along coasts like those of Louisiana and Bengal building spits and barrier islands, or coral reef accretion in regions such as the Great Barrier Reef and Red Sea creating lagoonal hollows. Tectonic basins such as the East African Rift and subsidence atolls in the Pacific Ocean produce depressions that become lagoons. Processes tied to the Holocene transgression, Younger Dryas fluctuations, and local storm events like Hurricane Katrina or the Bhola cyclone can breach, create, or close lagoon inlets. Sediment budgets involve sources from rivers like the Amazon River, Ganges, and Nile and sinks including tidal export to shelves such as the North Sea and East China Sea.

Hydrology and Water Chemistry

Hydrological regimes range from well-flushed tidal systems connected to seas like the Adriatic Sea to restricted inland basins resembling parts of the Caspian Sea or Aral Sea. Salinity gradients form via inputs from freshwater rivers such as the Po River and groundwater discharge from karst terrains like those in Yucatán Peninsula cenotes. Chemical processes include evaporative concentration observed in lagoons near the Dead Sea and Great Salt Lake, nutrient dynamics similar to those studied in Chesapeake Bay and Gulf of California, and hypoxia events resembling phenomena in the Baltic Sea and Gulf of Mexico hypoxic zone. Water column stratification, sediment oxygen demand, and metal cycling also mirror research in systems like the Black Sea euxinic layers and San Francisco Bay monitoring programs.

Ecology and Biodiversity

Lagoons support diverse assemblages including seagrass beds such as Posidonia oceanica meadows, mangrove forests as in Sri Lanka and Sumatra, and coral communities behind reef rims like those in Rarotonga. Faunal groups include benthic invertebrates comparable to those in Chesapeake Bay, fish nurseries used by species related to those in the Mediterranean Sea and Coral Triangle, migratory birds along flyways like the East Asian–Australasian Flyway and African-Eurasian Flyway, and endemic taxa seen in isolated atolls of the Line Islands and Hawaiian Islands. Primary productivity and trophic linkages connect to regional fisheries exploited by communities in Indonesia, Philippines, Brazil, and Spain. Lagoons can harbor threatened taxa protected under instruments like the Ramsar Convention and subject to conservation prioritization analogous to that for Galápagos Islands biodiversity.

Human Uses and Cultural Significance

Human societies have long used lagoons for subsistence, transport, and cultural practice: shell middens and fish traps dated back in regions such as Mesoamerica and Micronesia. Modern uses include aquaculture operations like shrimp farms seen in Vietnam and Ecuador, salt pans in Port Said and Aigues-Mortes, ports and marinas in cities like Venice and Monaco, and tourism concentrated around lagoonal beaches in Maldives resorts and Bali. Ritual and mythological associations appear in literature and art from Ancient Greece to Polynesia, and lagoons feature in place names such as Laguna Beach, Laguna Verde, and urban layouts of Venice and Rangiroa. Governance and resource rights are contested in coastal communities from Kerala to Louisiana.

Environmental Issues and Conservation

Lagoons face threats from pollution episodes like oil spills similar to Deepwater Horizon, eutrophication patterns observed in Baltic Sea and Chesapeake Bay, invasive species examples such as Caulerpa taxifolia spread in the Mediterranean Sea, and sea-level rise linked to IPCC projections threatening barrier stability in the Marshall Islands and Maldives. Restoration approaches draw on techniques used in Ecosystem-based management pilots, mangrove replanting programs in Bangladesh and Mozambique, seagrass transplantation projects near Seychelles, and protected area designations akin to Ramsar sites and Marine Protected Areas around the Galápagos Islands and Great Barrier Reef. Integrated responses involve stakeholders from institutions like UNESCO, World Wildlife Fund, The Nature Conservancy, national agencies in Australia and United States, and community groups in locales such as Nouméa and Zanzibar.

Category:Coastal landforms