Saline Year-Gradients in the Lagoon “La Salina,” Tonameca, Oaxaca, Mexico: Effects on Growth of Mangrove Biotope

Abstract

In Mexico, the mangrove is distributed in 764,486 ha, comprising the Atlantic coast from the Laguna Madre in Tamaulipas to Chetumal Bay in the Caribbean and in the Pacific from Ensenada, Baja California to Chiapas. On the coast of Oaxaca, coexist four species: red mangrove (Rhizophora mangle), white mangrove (Laguncularia racemosa) button mangrove (Conocarpus erectus) and black mangrove (Aviccenia germinans). In the Laguna “Salina” Tonameca, grows and develops the white, button, and black mangroves, whose spatial distribution decreases by deforestation, land use change, and increased saline substrate. Salinity of soil and waters, its concentration, and tipogenesis associated with the growth of mangrove trees were determined. Three saline gradients were identified in rainy season (gradient I: 2.18 dS m−1; gradient II: 9.95 dS m−1 and gradient III: 36.14 dS m−1); while in drought season four gradients were detected (gradient I: 1.15 dS m−1; II: 17.83 dS m−1; III: 39.06 dS m−1 and IV: 57.75 dS m−1). The interannual saline variation is due to climatics, hydrologycal, and geomorpholigical conditions of the substrate. The lake salinity is hydrochloric, predominantly NaCl salt, of intense osmotic effect, which largely explains the mangrove halophytism. Moisture diluting brackish water, such that low salt conditions promotes growth and development of mangrove, but at concentrations > 35 g L−1 limits their growth. In drought, hypersaline (>70 g L−1) prevents the establishment and repopulation of this species.