Saturday, 15 July 2006

Chemical attributes of Ornithogenic Cryosols on volcanic rocks from Maritime Antartica.

Carlos E.G.R. Schaefer, Felipe N.B. Simas, Manoel R. Albuquerque, Liovando M. Costa, Luiz E. Dias, Victor V. Pereira, and Roberto F.M. Michel. Departamento do Solos-Universidade Federal de Viçosa, Campus da Universidade, Viçosa, Brazil

Ornithogenic soils are commonly observed on marine terraces of volcanic rock sediments across Admiralty Bay in King George Island. These cryogenic soils are strongly affected by sea-land transfer of nutrients by Penguins (Pygoscelidae), mostly Adélie, and skuas (Catharacta spp.) activity, through guano inputs in rookeries during their summer reproduction cycle. In these soils, a particular and complex process of deep soil phosphatization occurs. In order to investigate the relationship between soil formation, phosphatization and age of rookery occupation, a toposequence of ornithogenic and other associated soils were sampled and studied along levels of Marine Terraces and Moraines in Rakusa Point, Admiralty Bay; area 1 – soils in or around present day rookeries, soils of former rookery sites with abundant lichen and moss coverage and; area 2 - soils of highland areas without distinct ornithogenic influence. We analysed the availability of nutrients (P, Ca, Mg, K, Na, Fe, Mn, Cu) and selected heavy metals in order to assess the influence of seabird inputs, its biogeochemical cycle within the cryosols and to evaluate differences associated with topography and landscape development. The extraction procedures were based on standard international methodologies. Results from these two areas area discussed bellow. Non ornithogenic soils: In the uppermost soils (range 147 m a.s.l. to 87 m a.s.l.), a granular structured soil underlies a stony pavement of 10 cm, with some cobbles or with small gravels, in the case of A1. In one pedon, a shallow soil with some sparse Usnea/Colobanthus/Deschampsia vegetation cover, displayed evidence of former Skua activity (nesting) with small, scattered bone fragments. Levels of Na are high (range 1260-1440 mg/dm3), due to salt-spray sea inputs and little leaching due to local aridity. These soils are comparable to polar desert soils of Antartica inner dry valleys, where salinity is high. In the uppermost soils, levels of Ca, Mg and Na are greater, pH is high (6.6-7.0) and Al levels are lower than downslope soils. Vegetation is virtually absent, apart from a few crustose lichens. The granular structure in one pedon appears to be associated with fine particle flocculation due to salinity. Close to the scarpment, another pedon has less Ca, Mg and K levels, high available Al and P, due to increasing weathering and sea-birds droppings, rich in organic P. The landscape is very much like those described in the arid land area of continental Antarctica by Campbell & Claridge (1987).

Ornithogenic soils: Upland soils, developed on present-day or former Penguin rookeries, are readily distinguished from non-ornithogenic soils by several features, such as: low pH (range 3.8-5.8), very high P contents, high Al availability, and varying amounts of exchangeable Ca, Mg and K. The areas of former penguin rookeries present fossil soils with clear ornithogenic features. Here, P levels are greater near the present-day rookery (range 700-1800 mg/dm3), due to occasional dropping of Skuas guano, as in the case of well-drained soil positions. The P distribution is fairly regular with depth, being greater closer to the present Penguin colony. Exchangeable Al levels are higher in the uppermost ornithogenic soil, with decreasing levels downslope; hence, a greater part of P should be in the form of low cristallinity Al-P phases, corroborating the findings of Tatur and Myrcha (1985). Soils located on marine terraces further away form the present colony show much lower P values (range 60- 820 mg/dm3), and evidence of P transformation and leaching with depth, where exchangeable Al forms are abundant. In these soils, pH are higher, with much greater Ca and Mg values and less exchangeable K, due to limited input from sea-bird droppings (mainly Skuas) and greater soil development. Higher Ca can also be related to a till richer in basaltic rock fragments in this area, compared with present rookeries, where andesitic fragments are more commonly observed. In the soils localized near the Penguin rookery, the ornithogenic influence is much greater. At 50 m a.s.l., intense phosphatization was recorded and available P levels are exceedingly high, reaching 4150 mg/dm3 in subsurface. In the same area, a soil covered by stones and coarse gravel and less vegetation cover of lichen, mosses and Deschampsia, has also very high P levels, reaching 4270 mg/dm3 in the subsurface. At the lowest level of the toposequence, marine terraces are also phosphatized, but less pronounced. In the Marine Terrace soil, on gravels/cobbles, lateral percolates and outwash arise from Penguin rookeries upland, but P levels are considerably lower (300-600 mg/dm3) compared with the in situ ornithogenic areas upslope. The K and Al levels are high (500-780 mg/dm3 of K), indicating soluble leachetes containing Al, K and P dowslope, being dammed at the lowest level by the gravel beach terraces. However, most P is leached back to the sea, as indicated by the whitish tongues on rocks along the sequence down to the sea level. The high levels of available P in the soils studied may be related with the utilization of the Melich-1 acid solution, which extracts preferably P-Al forms. The use of the Olsen extractor is recommended, specially for the non ornithogenic soils in order to assess the availability of P-Ca forms.

Back to CR Soils of Northern, Southern Polar Region and Soils of High Elevations and Their Relationship to Global Climate Change - Poster
Back to WCSS

Back to The 18th World Congress of Soil Science (July 9-15, 2006)