How the west was once: vegetation change in south-west Queensland from 1930 to 1995

Conflicting perceptions of past and present rangeland condition and limited historical data have led to debate regarding the management of vegetation in pastoral landscapes both internationally and in Australia. In light of this controversy we have sought to provide empirical evidence to determine the trajectory of vegetational change in a semi-arid rangeland for a significant portion of the 20th century using a suite of proxy measures. Ambathala Station, approximately 780 km west of Brisbane, in the semi-arid rangelands of south-western Queensland, Australia. We excavated stratified deposits of sheep manure which had accumulated beneath a shearing shed between the years 1930 and 1995. Multi-proxy data, including pollen and leaf cuticle analyses and analysis of historical aerial photography were coupled with a fine resolution radiocarbon chronology to generate a near annual history of vegetation on the property and local area. Aerial photography indicates that minor (< 5%) increases in the density of woody vegetation took place between 1951 and 1994 in two thirds of the study area not subjected to clearing. Areas that were selectively or entirely cleared prior to the 1950s (approximately 16% of the study area) had recovered to almost 60% of their original cover by the 1994 photo period. This slight thickening is only partially evident from pollen and leaf cuticle analyses of sheep faeces. Very little change in vegetation is revealed over the nearly 65 years based on the relative abundances of pollen taxonomic groups. Microhistological examination of sheep faeces provides evidence of dramatic changes in sheep diet. The majority of dietary changes are associated with climatic events of sustained above-average rainfall or persistent drought. Most notable in the dietary analysis is the absence of grass during the first two decades of the record. In contrast to prevailing perceptions and limited research into long-term vegetation change in the semi-arid areas of eastern Australia, the record of vegetation change at the Ambathala shearing shed indicates only a minor increase in woody vegetation cover and no decrease in grass cover on the property over the 65 years of pastoral activity covered by the study. However, there are marked changes in the abundance of grass cuticles in sheep faeces. The appearance and persistence of grass in sheep diets from the late 1940s can be attributed to the effects of periods of high rainfall and possibly some clearing and thinning of vegetation. Lower stock numbers may have allowed grass to persist through later drought years. The relative abundances of major groups of plant pollen have not changed significantly over the past 65 years

Stable isotope ratio as a tracer of mangrove carbon in Malaysian ecosystems

The ratio of stable carbon isotopes (δ13C) in plants and animals from Malaysian mangrove swamps, coastal inlets, and offshore waters was determined. Vascular plants of the swamps were isotopically distinct ( x±s.d.=-27.1±1.2‰) from plankton (-21.0±0.3‰) and other algae (-18.7±2.2‰). Animals from the swamps (-20.9±4.1‰) and inlets (-19.8±2.5‰) had a wide range of isotope ratios (-28.6 to-15.4‰), indicating consumption of both mangrove and algal carbon. Several commercially important species of bivalves, shrimp, crabs, and fish obtained carbon from mangrove trees. Mangrove carbon was carried offshore as detritus and was isotopically distinguishable in suspended particulate matter and sediments. Animals collected from 2 to 18 km offshore, however, showed no isotopic evidence of mangrove carbon assimilation, with ratios (-16.5±1.1‰, range-19.1 to-13.1‰) virtually identical to those reported for similar animals from other plankton-based ecosystems. Within groups of animals, isotope ratios reflected intergencric and interspecific differences in feeding and trophic position. In particular, there was a trend to less negative ratios with increasing trophic level

Amino acid biogeochemistry in the Laurentian Trough: vertical fluxes and individual reactivity during early diagenesis

The detailed composition of total hydrolysable (THAA), dissolved free (DFAA) and combined (DCAA) amino acids was studied in settling particles and the solid phase and porewaters of underlying sediments in the Laurentian Trough to evaluate their sources and individual reactivities during early diagenesis. Vertical fluxes of THAA measured at 150 m depth (234-980 [mu]mol/m2/day) represented 3.8% of the average daily primary production and 8-16% of total organic carbon (TOC) and 24-42% of total nitrogen (TN) fluxes. THAA concentrations decreased from 89±39 to 39±4.4 [mu]mol/g from settling particles to the top 3 cm sediments, with no significant change of the %THAA-C and %THAA-N. However, these parameters decreased with depth in the sediments (10-13 to 7-8% and 30-45 to 22-28%, respectively) indicating a selective THAA removal. THAA composition of settling particles and sediments was relatively uniform and showed a marked enrichment in serine, threonine and glycine relative to fresh plankton which is ascribed to the selective preservation of diatom cell-walls. Serine was the more specific diatom tracer; it covaried with diatom lipid biomarkers, was relatively more abundant at a seaward site and increased downcore reflecting the selective preservation of diatom cell-walls. An increasing trend with sediment depth was also observed for aspartic acid whereas glutamic acid and histidine decreased. Porewater DFAA and DCAA accounted for 3-25% of total DOC and showed low levels in the surface zone of most intense solid phase THAA decay. Both fractions showed clear compositional differences related to the prevailing source material: DCAA, as solid phase THAA, were dominated by serine and threonine+glycine, whereas DFAA were enriched in glutamic (Glu) and [beta]-aminoglutaric acids ([beta]Glu), probably originating from bacteria. These patterns changed with depth in the sediments: the proportion of serine and [beta]Glu increased in DCAA and DFAA, respectively, whereas that of glutamine, alanine and Glu decreased in the DFAA pool. The preferential downcore decay and conversion of Glu into [beta]Glu was reflected by a consistent increase of [beta]Glu/Glu ratios, particularly at a landward station where the higher rates of sedimentation and OM burial favor the continued metabolism of bacteria in deeper sediment layers