Mobility, bioavailability and distribution of Fe and Cu in mangroves (Avicennia schaueriana and Rhizophora mangle) from a semiarid coast in NE Brazil.

Mangroves buffer metals transfer to coastal areas though strong accumulation in sediments making necessary to investigate metals' bioavailability to plants at the rhizosphere. This work evaluates the effect of mangrove root activity, through iron plaque formation, on the mobility of iron and copper its influence on metals' uptake, and translocation through simultaneous histochemical analysis. The Fe2+ and Fe3+ contents in porewaters ranged from 0.02 to 0.11 µM and 1.0 to 18.3 µg.l-1, respectively, whereas Cu concentrations were below the method's detection limit (<0.1 µM). In sediments, metal concentrations ranged from 12,800 to 39,500 µg.g-1 for total Fe and from 10 to 24 µg.g-1 for Cu. In iron plaques, Cu concentrations ranged from 1.0 to 160 µg.g-1, and from 19.4 to 316 µg.g-1 in roots. Fe concentrations were between 605 to 36,000 µg.g-1 in the iron plaques and from 2,100 to 62,400 µg.g-1 in roots. Histochemical characterization showed Fe3+ predominance at the tip of roots and Fe2+ in more internal tissues. A. schaueriana showed significant amounts of Fe in pneumatophores and evident translocation of this metal to leaves and excretion through salt glands. Iron plaques formation was essential to the Fe and Cu regulation and translocation in tissues of mangrove plants.

Phosphorus and suspended matter retention in mangroves affected by shrimp farm effluents in NE Brazil.

This study compares two mangroves with different land uses in the Jaguaribe River estuary, harboring large shrimp farms, and in the more pristine Pacotí River estuary. Normalized Difference Vegetation Index (NDVI) was used to compare the overall health of the forests. Measures of suspended matter (TSS), total (TP), particulate (PartP) and soluble reactive phosphorus (SRP) in the inflow and outflow waters of tidal channels draining the mangroves were performed during tidal cycles. NDVI varied from 0.65 in the Jaguaribe estuary to 0.85 in the Pacotí, suggesting the impact of shrimp farm effluents on mangrove canopy cover. The shrimp farm influenced site showed 10 times larger absolute ∑P (TP + PartP + SRP) = 1.2-5.2 kg.hr-1) flux than the pristine site (∑P = 0.22 kg.hr-1). Tidal balances showed smaller retentions of the total influx: 28-54%; 44-45%; 38-65% and 8-53% for TSS; TP; SRP; and PartP respectively, in the shrimp farm influenced site to over 93% of the total tidal input of TSS and all P fractions in the pristine mangrove. This suggests that mangrove phosphorus accumulation is decreased in the forest with lower NDVI and limits mangrove's potential as a natural barrier to the nutrient transport to adjacent estuarine and coastal waters.

Limnology of the largest multi-use artificial reservoir in NE Brazil: The Castanhão Reservoir, Ceará State.

This work reviews the limnology of the largest multi-use reservoir in NE Brazil, the Castanhão Reservoir in Ceará State, during 5 years of an extended drought when the reservoir's volume decreased from 88% to about 30%. Major physical and chemical parameters of the water column, phytoplankton community, trophic state and sediment geochemistry were monitored, as well as the impact from extensive aquaculture. Water quality of the full reservoir was maintained due to hydrodynamics, which transport nutrients to the hypolimnion of a stratified water column, rendering an oligotrophic state to the reservoir, notwithstanding the large nutrient inputs from aquaculture and irrigated agriculture. However, with the extension of the drought period, the reservoir volume reduced, decreasing water depth leading to breaking of the thermocline due to wind forcing, and mixing the entire water column. This increased turbidity, nutrient availability and primary productivity, also changed phytoplankton functional groups. As a result, at the end of the monitoring period, when the reservoir attained its lowest volume, its trophic state became eutrophic. Under a scenario of climate change, where annual precipitation is decreasing, human uses of reservoirs in the semiarid should be very restricted to maintain water quality proper for human use.

Mercury degassing from forested and open field soils in Rondônia, Western Amazon, Brazil.

A Teflon dynamic flux chamber was used to characterize Gaseous Elemental Mercury (GEM) flux from forested and open field soils in a highly changing environment in Rondônia State, western Amazon. We simultaneously analyzed meteorological parameters at the soil level relating GEM fluxes to soil temperature, air humidity, soil moisture, solar radiation, and speed and wind direction. We also examined variations of atmospheric GEM concentration. GEM fluxes during the day and night in the open field site were significantly different (17+/-14ngm(-2) h(-1) and 0.9+/-1.9ngm(-2)h(-1), for day and night, respectively), but were similar within the forest site (4.8+/-1.4ngm(-2)h(-1) and 4.4+/-1.8ngm(-2) h(-1) for day and night periods, respectively). A comparison between 24-h periods averages in the two sites showed much larger emission from the open field site. GEM fluxes at the open field site were positively correlated with soil moisture, solar irradiation and soil temperature and inversely correlated with air humidity. At the forest site GEM fluxes showed no correlation with meteorological variables. At the open field site GEM concentrations significantly correlated with GEM flux, at least during the day. At night in the open field site and during the day and night at the forest site no correlation was found between GEM fluxes and GEM concentrations in the ambient air. Higher emissions from the open field site support earlier studies showing larger Hg remobilization following forest conversion to pasture.

Mercury emissions into the Sepetiba Bay basin, SE Brazil

Mercury emissions to soil, waters, and the atmosphere in the Sepetiba Bay basin were estimated by means of emission factors and data base of major industrial and urban sources of Hg. This approach is the most effective in assessing pollutant loads from diffuse sources, as in the case of Hg in the Sepetiba Bay basin. Total Hg emission ranges from 20 to 364 kg yr(-1). A significant fraction of this input is to the atmosphere, ranging from 115 to 149 kg yr(-1) (41 to 58 per cent), mostly due to emissions from iron and steel production and an oil fired power plant. Inputs to soil range from 84 to 215 kg yr(-1) (42 to 59 per cent), mostly from an urban ladfill and from metal manufacturing. Direct inputs to surface water are small (<1.0 kg yr(-1). Estimated total and atmospheric emissions agree with measurements of atmospheric Hg deposition and with preliminary data on fluvial systems.