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We evaluated the phenological response and litterfall production of Rhizophora mangle to changes in pore water chemistry over a five-year period (from 2009 to 2014 and 2010 to 2016) along the coast of Campeche, México. Severe drought conditions were recorded in 2009 with a Standardized Precipitation Index (SPI) of −1.5 and again in 2015 with a SPI of −1.16). A precipitation deficit of 22.1% was recorded between 2009 and 2016 ranging from 9.5% in Laguna de Terminos in the south to 64.4% in Los Petenes Biosphere Reserve in the north. Precipitation varied significantly per year (p < 0.001), seasonally (p < 0.001), and between years and seasons (p < 0.001). An interaction was observed in the salinity (p < 0.05), redox potential (p < 0.001), and precipitation (p < 0.001) of the Laguna de Terminos, Rio Champoton, and Los Petenes Biosphere Reserve regions. Significant differences were found between the years in the leaf and propagule production (p < 0.001), and between seasons in production of leaves, flowers, and propagules (p < 0.001). The determining factor in the production of flowers during both the rainy and dry seasons was the salinity, and the determining factors for the production of propagules were the redox potential and salinity. The results of this study suggest a low phenotypic plasticity in R. mangle.

Mangrove forests are conspicuous components of tropical wetlands that sustain continuous exposure to wastewater discharges commonly of municipal origins. Mangroves can remove nutrients from these waters to fulfill their nutrients demand, although the effects of continuous exposure are unknown. An experimental greenhouse imitating tidal regimes was built to measure the efficiency of mangrove seedlings to incorporate nutrients, growth and above biomass production when exposed to three periodic wastewater discharges. The experiment totaled 112 d. Nutrient removal by the exposed group, such as phosphates, ammonia, nitrites, nitrates and dissolved inorganic nitrogen (97%, 98.35%, 71.05%, 56.57% and 64.36%, respectively) was evident up to the second dumping. By the third dumping, all nutrient concentrations increased in the interstitial water, although significant evidence of removal by the plants was not obtained (p > 0.05). Nutrient concentrations in the control group did not change significantly throughout the experiment (p > 0.05). Treated plants increased twofold in stem girth when compared to the control (p < 0.05), although control plants averaged higher heights (p < 0.05). Biomass of treated group increased up to 45% against 37% of the control during the duration of the experiment (p < 0.05). We suggest that nutrient removal efficiency of mangroves is linked to the maintenance of oxic conditions in the pore-water because of oxygen transference from their aerial to their subterranean radicular system that facilitates the oxidation of reduced nitrogen compounds and plants uptake. Nevertheless, continuous inflows of wastewater would lead to eutrophication, establishment of anoxic conditions in water and soil, and lessening of nutrient absorption of mangroves.

Mangrove forests have proven to be resilient to most environmental change, surviving catastrophic climate events over time. Our study aimed to evaluate the chemical variability of pore water and its effect on phenological production in three mangrove species (Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa) along the coast of the state of Campeche during a year of severe drought (2009) and a year of average precipitation (2010). Pore water salinity and redox potential were measured monthly in a mangrove forest in 2009 and 2010. Litterfall production and reproductive phenology was measured monthly. We determined the relationships among litterfall production, reproductive phenology, pore water chemistry and precipitation of three species between years. Precipitation, pore water salinity and redox potential significantly differed among years, seasons and sites, and also showed significant interaction between years and seasons (p < 0.05). Significant variation was observed in litterfall production, propagules, flowers, and leaf litter among sites (p < 0.05). A significant change was observed in propagules and flowers among years, and in total litterfall and leaf litter between seasons and species (p < 0.05). Under severe drought, salinity had the strongest effect on total litterfall and propagules in R. mangle, while A. germinans, had the strongest effect on propagule/flower precipitation. Both A. germinans and L. racemosa showed higher resilience than R. mangle at all sites under severe drought conditions. These findings can support activity allocation for mangrove conservation and restoration by providing the tolerance thresholds of the three species that dominate in the regional area of Campeche state. Likewise, this research provides knowledge to the Intergovernmental Experts Group on climate change about drought intensity and its magnitude of impact on mangrove productivity, reproduction and integrity.