Effects of iron-ore mining and processing on metal bioavailability in a tropical coastal lagoon

In water systems, water quality and geochemical properties of sediments determine the speciation of trace metals, metal transport, and sediment-water exchange, influencing metal availability and its potential effects on biota. Studies from temperate climates have shown that iron-ore mining and tailing wastewaters, besides being a source of trace metals, usually show high levels of dissolved ions and particulate suspended matter, thus having the potential of indirectly changing metal bioavailability. For the first time in the tropics, we identified the effects of iron-ore mining and processing on metal bioavailability in a coastal lagoon. With an extensive sampling scheme, we investigated the potential sources of metals; the links among metal levels in water, sediments, and invertebrates; and the contrasting effects on metal speciation and bioavailability. The metals Fe, Mn, Al, Cr, Zn, Cu, Ni, Pb, Cd, Hg, and As were measured in water, sediments (surface and profiles), and invertebrates from Mãe-Bá Lagoon and in the sites directly influenced by the mining operations (tailing dams and nearby rivers). In addition, samples from two other lagoons, considered pristine, were analyzed. The study area is located in the southeast of Brazil (Iron Quadrangle Region and a coastal area of Espírito Santo State). General water characteristics included pH, dissolved organic carbon, alkalinity, and anion composition. Water metal speciation was assessed by a speciation model (Chemical Equilibria in Aquatic Systems). Grain-size distribution, organic carbon, carbonate, and acid volatile sulfide (AVS) were determined in sediments. Statistical methods included comparison of means by Mann-Whitney test, ordination and correlation analyses, and analysis of regression for geochemical normalization of metals with grain size. The dissolved metal concentrations, the total metal levels in sediments, and the normalization based on the fine sediment fraction showed that the mining operations constitute potential sources of Fe, Mn, Cr, Cu, Ni, Pb, As, and Hg to Mãe-Bá Lagoon. However, trace metal availability was reduced because of increased pH, hardness, and sulfide content (356 μmol/g) in the sites influenced by the mining. The lagoon showed similar water chemistry as in the mining sites, with metal bioavailability further decreased by the presence of dissolved organic carbon and chloride. Although AVS levels in the lagoon were low (0.48-56 μmol/g), metal bioavailability was reduced because of the presence of organic matter. Metal levels in invertebrates confirmed the predicted low metal bioavailability in Mãe-Bá Lagoon. The lagoon was considered moderately contaminated only by Hg and As. The iron-ore mining and processing studied here constitute potential sources of metal pollution into the tropical lagoon. Contrary to expectations, however, it also contributes to reducing the overall metal bioavailability in the lagoon. These findings are believed to be useful for evaluating metal exposure in a more integrated way, identifying not only the sources of pollution but also how they can affect the components involved in metal speciation and bioavailability in water systems, leading to new insights

Soil Response to Season and Interval of Prescribed Fire in a Ponderosa Pine Forest of the Blue Mountains, Oregon

Soil properties were examined at a season of burn and burn interval study located in the Malheur National for responses to prescribed burns used to reduce fuel loads and wildfire hazard. Prescribed burn comparisons included spring vs. fall burning, with either one 15-year interval burn or two 5-year interval burns of each season. Results showed that major change to soil organic matter was a reduction in the amount of O horizon. The percent bare ground increased with both spring and fall burning and was highest with multiple burns, indicating a loss of O horizon cover. There was also a decrease in O horizon thickness, particularly with two fall burns. Overall ecosystem C decreased by 21-31 percent with the prescribed burns. Extractable ammonium and phosphorus increased with the multiple burns relative to the single burn, but was similar to the controls. The flush of nutrients available following the burns may not persist more than 5 years. No burn effects were seen on soil cation exchange capacity or percent base saturation, possibly due to the high CEC and base cations in these soils. Soil temperatures were found to be highest with fall burns, particularly the 5-year interval burns. However, the soil moisture was also slightly higher with the 5-year interval burns, possibly due to decrease transpiration from reduced vegetation. Results to date suggest that the frequent fall burns may be harsher for soils than less frequent burns or spring burns, but could be used if needed, however they will reduce ecosystem C pools

Soil Organic Carbon Pools in Riparian Landscapes of Southern New England

Riparian zones are important catchment-scale depositional environments that receive episodic influx of sediment and C from watershed sources. The specific impacts of upland disturbances on riparian soil development and soil organic carbon (SOC) dynamics are still largely unknown. The goal of our study was to understand the role of riparian soils in retaining C at the landscape and catchment scales. We quantified SOC pools to a depth of 1 m at 29 headwater riparian sites in southern New England. Riparian SOC pools ranged from 117 to 495 Mg C ha-1, with a mean pool of 246 Mg C ha-1. On average, \u3e50% of the total SOC was stored below 30 cm. Riparian SOC pools differed significantly between soils formed in relatively fast accreting environments (those that contain buried surface horizons; 277 Mg C ha -1) and those in slow accreting environments where buried horizons were absent (188 Mg C ha-1). Catchment-scale analysis of SOC distribution indicated that riparian zones, on average, occupy 8% of the total watershed area yet store as much as 20% of the total catchment SOC. These results suggest that even though riparian zones occupy a small percentage of the overall watershed, these areas are an important component of the landscape for storage of SOC deposited as a result of catchment-scale disturbances