Effect of Flooding Frequency and Nutrient Addition on Plant Growth and Total Petroleum Hydrocarbons Removal in Mangrove Microcosms

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.