Abstract
The addition of nutrients to accelerate biodegradation of oil is an adequate strategy to clean up polluted mangrove soils which pollutes mangrove soils. However, the hydrology of these ecosystems might interfere with such strategy. The effect of flooding frequency and nutrient addition on hydrocarbon removal in mangrove sediments was investigated in this study. Microcosms consisted of pots with 5 kg of fresh mangrove sediments and one seedling of Avicennia germinans. Treatments included: planted microcosms with fertilizer and crude oil (PNC), planted microcosms with oil (PC), non-planted microcosms with oil and fertilizer (NC), planted microcosms with fertilizer (PN) and planted microcosms without oil or fertilizer (P). Mexican Maya crude oil and inorganic nutrients were added in a single dose of approximately 5.0 g DW·kg-1, 0.33 g of N DW·kg-1 and 0.06 g P DW·kg-1. Microcosms were either permanently flooded (PF) or intermittently flooded (IF: 14 hours drained and 10 hours flooded), and kept in a glasshouse in Xalapa, Veracruz, Mexico. In both flooding conditions, oil decreased the relative growth rate of A. germinans by 56% in (PC) treatments and 40% in (PNC) treatments. Redox potential in the oiled treatments (-44.73 to +75.34 mV) was lower than non-oiled treatments (-1.31 to +163.43 mV). Total Petroleum Hydrocarbons (TPHs) removal in PC treatments was low in both permanent (2.99% ± 3.51%) and intermittently flooding conditions (11.75% ± 1.46%). The highest TPHs removal was observed in (PNC) and (NC) under IF conditions (47% ± 3.86% and 50.32% ± 7.15% after 4 months, respectively). It was concluded that nutrient addition increased TPHs removal but only under IF conditions and helped mangrove plants to deal with TPHs toxicity.
Highlights
Mangrove forests are ecotones between marine and terrestrial ecosystems, commonly found along low wave energy shorelines in tropical and subtropical regions [1]
The objective of this study is to investigate the effect of flooding frequency and nutrient addition on plant growth, redox potential, and Total Petroleum Hydrocarbons (TPHs) removal in mangrove microcosms
Nutrient addition stimulated aerial biomass production even when oil was present; higher aerial biomass in Planted Microcosms with Nutrients and Crude Oil (PNC) was observed compared to treatments with oil only (PC)
Summary
Mangrove forests are ecotones between marine and terrestrial ecosystems, commonly found along low wave energy shorelines in tropical and subtropical regions [1]. In the last 30 years, several oil spill accidents have occurred in marine systems affecting mangrove habitats around the world [5]-[9]. Recurrent oil spills in these areas have polluted Mexican mangrove ecosystems [13] [14]. Protocols utilized for oil clean up involve the use of dispersants, cleaners, and soil oxidizers as well as mechanical techniques that involve collection and skimming, cutting and removal of contaminated vegetation, and gentle flushing with clean water. Bioremediation is an ecological alternative for detoxification of oiled mangrove sediments which is highly efficient for the removal of hydrocarbons even at low concentrations [16][18]. Oil bioremediation in Mexican mangrove soils has received little attention [16]. There are two strategies for oil bioremediation in soils: bioaugmentation, which involves the addition of external (indigenous or exogenous) microbial populations to contaminated soil and biostimulation, which involves the addition of appropriate microbial nutrients to a polluted soil or water to stimulate biodegradation of pollutants by endogenous microorganism [19]
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