Geogenic sources and sinks of trace metals in the Larsemann Hills, East Antarctica: Natural processes and human impact

To evaluate the extent of human impact on a pristine Antarctic environment, natural baseline levels of trace metals have been established in the basement rocks of the Larsemann Hills, East Antarctica. From a mineralogical and geochemical point of view the Larsemann Hills basement is relatively homogeneous, and contains high levels of Pb, Th and U. These may become soluble during the relatively mild Antarctic summer and be transported to lake waters by surface and subsurface melt water. Melt waters may also be locally enriched in V, Cr, Co, Ni, Zn and Sri derived from weathering of metabasite pods. With a few notable exceptions, the trace metal concentrations measured in the Larsemann Hills lake waters can be entirely accounted for by natural processes such as sea spray and surface melt water input. Thus, the amount of trace metals released by weathering of basement lithologies and dispersed into the Larsemann Hills environment, and presumably in similar Antarctic environments, is, in general, not negligible, and may locally be substantial. The Larsemann Hills sediments are coarse-grained and contain minute amounts of clay-size particles, although human activities have contributed to the generation of fine-grained material at the most impacted sites. Irrespective of their origin, these small amounts of fine-grained clastic sediments have a relatively small surface area and charge, and are not as effective metal sinks as the abundant, thick cyanobacterial algal mats that cover the lake floors. Thus, the concentration of trace metals in the Larsemann Hills lake waters is regulated by biological activity and thawing-freezing cycles, rather than by the type and amount of clastic sediment supply. (c) 2005 Elsevier Ltd. All rights reserved.

Monitoring green turtles (Chelonia mydas) at a coastal foraging area in Baja California, Mexico: multiple indices to describe population status

From June 1995 to August 2002 we assessed green turtle (Chelonia mydas) population structure and survival, and identified human impact, at Bahia de los Angeles, a large bay that was once the site of the greatest sea turtle harvest rates in the Gulf of California, Mexico. Turtles were captured live with entanglement nets and mortality was quantified through stranding surveys and flipper tag recoveries. A total of 14,820 netting hours (617.5 d) resulted in 255 captures of 200 green turtles. Straight-carapace length and mass ranged from 46.0-100.0 cm (mean = 74.3 +/- 0.7 cm) and 14.5-145.0 kg (mean = 61.5 +/- 1.7 kg), respectively. The size-frequency distribution remained stable during all years and among all capture locations. Anthropogenic-derived injuries ranging from missing flippers to boat propeller scars were present in 4% of captured turtles. Remains of 18 turtles were found at dumpsites, nine stranded turtles were encountered in the study area, and flipper tags from seven turtles were recovered. Survival was estimated at 0.58 for juveniles and 0.97 for adults using a joint live-recapture and dead-recovery model (Burnham model). Low survival among juveniles, declining annual catch per unit effort, and the presence of butchered carcasses indicated human activities continue to impact green turtles at this foraging area.

Mass mortality following disturbance in Holocene coral reefs from Papua New Guinea

The frequency and intensity of disturbance on living coral reefs have been accelerating for the past few decades, resulting in a changed seascape. What is unclear but vital for management is whether this acceleration is natural or coincident only with recent human impact. We surveyed nine uplifted early to mid-Holocene (11,000-3700 calendar [cal] yr B.P.) fringing and barrier reefs along similar to 27 km at the Huon Peninsula, Papua New Guinea. We found evidence for several episodes of coral mass mortality, but frequency was < 1 in 1500 yr. The most striking mortality event extends > 16 km along the ancient coastline, occurred ca. 9100-9400 cal yr B.P., and is associated with a volcanic ash horizon. Recolonization of the reef surface and resumption of vertical reef accretion was rapid (< 100 yr), but the post-disturbance reef communities contrasted with their pre-disturbance counterparts. Assessing the frequency, nature, and long-term ecological consequences of mass-mortality events in fossil coral reefs may provide important insights to guide management of modern reefs in this time of environmental degradation and change.

Trace metals in Antarctic ecosystems: Results from the Larsemann Hills, East Antarctica

Sediments, mosses and algae, collected from lake catchments of the Larsemann Hills, East Antarctica, were analysed to establish baseline levels of trace metals (Ag, As, Cd, Co, Cr, Cu, Ni, Sb, Pb, Se, V and Zn), and to quantify the extent of trace metal pollution in the area. Both impacted and non-impacted sites were included in the study. Four different leaching solutions (1 M MgCl2, 1 M CH3COONH4, 1 M NH4NO3, and 0.3 N HCl) were tested on the fine fraction (< 63 mu m) of the sediments to extract the mobile fraction of trace metals derived from human impact and from weathering of basement lithologies. Results of these tests indicate that dilute HCl partly dissolves primary minerals present in the sediment, thus leading to an overestimate of the mobile trace metal fraction. Concentrations of trace metals released using the other 3 procedures indicate negligible levels of anthropogenic contribution to the trace metal budget. Data derived from this study and a thorough characterisation of the site allowed the authors to define natural baseline levels of trace metals in sediments, mosses and algae, and their spatial variability across the area. The results show that, with a few notable exceptions, human activities at the research stations have contributed negligible levels (lower than natural variability) of trace metals to the Larsemann Hills ecosystem. This study further demonstrates that anthropogenic sources of trace metals can be correctly identified and quantified only if natural baselines, their variability, and processes controlling the mobility of trace metals in the ecosystem, have been fully characterised. (c) 2006 Elsevier Ltd. All rights reserved.