REMOCION DE NUTRIENTES EN UN HUMEDAL ARTIFICIAL UTILIZANDO PLANTULAS DE DOS ESPECIES DE MANGLE (Rhizophora mangle y Laguncularia racemosa)

Abstract

ABSTRACT During two cycles of shrimp farming we assessed the ability of nutrient removal in two species of mangrove (Laguncularia racemosa and Rhizophora mangle) in a constructed wetland in three experimental ponds of 10 m x 10 m with shrimp (Litopenaeus vannamei). In one of the ponds, platforms with seedlings of red mangrove (R. mangle) were placed, while in a second pond the platforms contained seedlings of white mangrove (L. racemosa) and the third pond represented the control system (without seedlings). On each pond 20 floating wooden platforms of one m2 each, with 36 hydroponic seedlings, were placed around the pond. Shrimps were stocked into each production pond at a density of 10 PL per m2. Filling water was pumped from the Urías Lagoon and 46% of the water was exchanged every 10 days and seawater samples were obtained to analyze the nutrients (nitrate NO3–, nitrite NO2–, ammonium NH4+ and orthophosphate PO4–3) within the pond with and without seedlings. Results obtained in the first shrimp culture cycle showed that L. racemosa pond showed removals of 84.4% of dissolved inorganic nitrogen (DIN) and 46.6% of orthophosphate, within R. mangle pond corresponding removals were 81.3% and 47.2%, and within the control 34% and 21% were removed. The fluxes of total nutrients from the inlet water to the ponds were 7269 g of N and 3095 g of P. In the ponds with mangroves, the nutrients were reduced to 1018-1071 g of N and 609-724 g of P. In the control pond the outlet water nutrient concentrations were up to 5564 g of N and 1583 g of P. The nutrients accumulated in the mangrove tissue was 18014-16711 g of N and 5976-5832 g of P. Volatilization of ammonium and adsorption by sediments of phosphorus varied from 17298-18570 g of N and 6249- 6268g of P. In the control pond it was 30022 g of N and 10922 g of P. In the second shrimp culture cycle L. racemosa showed a removal of 86.1% of DIN and 46.7% of orthophosphate, R. mangle removed 84.1% and 43.2%, and the control pond the removal was 29.6% and 24.1%. It was demonstrated that the removal percentages in ponds with seedlings were higher than to the control pond (without plants), also the ponds maintained a better water quality, reducing nutrient loading. For this reason, the nutrient outflow discharged from the wetland showed a low level of nutrients in the effluent water to the receiving system.