71,662 research outputs found
The influence of coastal upwelling on the biodiversity of sandy beaches in South Africa
No full textSandy beaches are often highly allochthonous, depending on external subsidies of carbon and nutrients. Despite this, sandy beach macrofaunal assemblages have received little attention regarding their response to enhanced primary productivity generated from coastal upwelling. This thesis investigates the influence of upwelling on macrofaunal assemblages over a variety of spatial and temporal scales. Spatially, four regions were examined across two biogeographic provinces to remove temperature as a confounding factor, and limit biogeography-specific effects. A nested hierarchical design enabled both large and small scales to be examined and generalities about upwelling effects across multiple areas to be considered. Sampling was conducted in two seasons, and over two years, to test the persistence of any effects. Biogeography and region had the strongest influences on macrofaunal biodiversity. Upwelling influenced macrofaunal assemblages in every region when analyses were conducted at the species level. However, the particular effect, positive or negative, differed among regions depending on local factors, and between the response variables, abundance and biomass. Coarser scales of taxonomy, feeding guild and developmental mode were investigated; however, the influence of upwelling generally became weaker and more varied, and occasionally disappeared. Seasonality was greater on the South Coast but was still important in some analyses on the West Coast. At the small-scale, variation within-beaches was lower than between beaches, assemblage structure remained stable over time, and consistent zonation was not present. The influence of temperature on filtration rate and oxygen consumption of Donax serra was investigated to test a driving mechanism for assemblage responses to upwelling. Feeding ability was significantly reduced at colder temperatures indicating an important factor which may be involved in determining assemblage structure. These results suggest that alterations to upwelling regimes predicted under climate change scenarios will impact sandy beach macrofauna, however the specific outcome will depend on multiple contextual factors
Low faunal diversity on Maltese sandy beaches : fact or artefact?
No full textEight sandy beaches on Malta and two on Gozo were sampled for macrofauna to test the hypothesis that Maltese beaches have
an intrinsically low diversity. Stations distributed in the supralittoral (dry zone), mediolittoral (wet zone) and upper infralittoral
(submerged zone to 1m water depth) were sampled by sieving core samples and standardised searching during daytime, and pitfall
trapping and standardised sweeping of the water column using a hand-net at night, as appropriate. Physical parameters of the
sediment were measured and human occupancy of the beaches was estimated.
From the supralittoral and mediolittoral, 39 species represented by 1584 individuals were collected by the combined techniques of
pitfall trapping, sieving and standard searching. For Ramla beach, which had the highest diversity, 267 individuals representing 25
infaunal species were collected by sieving from a combined volume of 1.175m3 of sand, and 149 individuals representing 28
epifaunal species were collected by standardised searching from a combined area of 700m2 of sand during two winter and two
summer sampling sessions between 1992 and 1993. For nine other beaches sampled during the summer of 2000, only six
macrofaunal species were collected from core samples, with overall population densities ranging from 4.13 to 45.45 individualsm 2.
Only 92 individuals belonging to 12 species were collected by hand-net from the uppermost infralittoral of five beaches sampled
using this method during the summer of 2000. Taxa of gastropods, bivalves, decapods, mysids and staphylinid beetles generally
abundant on Mediterranean sandy beaches, were entirely absent from the beaches sampled.
Few correlations that could explain the impoverishment of Maltese sandy beaches were found between physical parameters and
faunal abundances, and other factors such as inadequate sampling effort, human disturbance and marine pollution were also
excluded; however, seasonally biased sampling may partly explain the results obtained. One factor that may explain why certain
species are missing could be lack of recruitment, due to Malta’s geographical isolation from the European and African mainlands.
2003 Elsevier Ltd. All rights reserved.peer-reviewe
Effect of clay amendments on nitrogen leaching and forms in a sandy soil
No full textNitrogen (N) leaching in sandy soil decreases fertiliser use efficiency and may depress plant production. Application of high cation exchange capacity (CEC) materials (e.g. high activity clay minerals) is hypothesized to reduce N leaching and increase plant N uptake in sandy soils. However, the mechanism of leaching in sands with clay amendment is not understood. A column experiment was conducted to determine N leaching and N concentration in soil solution in a sandy soil (1.4 % clay) with three soil amendments (nil, clay soil and bentonite clay) and three fertiliser rates (0, 28 N 17 P 22 K kg/ha and 56 N 34 P 44 K kg/ha). Soil amendments were applied at the rate of 50 Mg/ha. The soil columns were leached with de-ionised water equivalent to 50 mm rainfall every 4 days. Concentrations of soil solution extracted by Rhizon samplers indicated that NH4 leaching was decreased 38-43 % by bentonite addition but little of the soil solution N was in NO3 form and bentonite had no effect on mobility of this form of N. The application of bentonite was able to hold NH4 in soil solution of top soil. Leaching of NH4 was delayed to 15 day after fertiliser application in bentonite-amended sand
Measurement and Computation of Movement of Bromide Ions and Carbofuran in Ridged HUmic-Sandy Soil
No full textWater flow and pesticide transport in the soil of fields with ridges and furrows may be more complex than in the soil of more level fields. Prior to crop emergence, the tracer bromide ion and the insecticide carbofuran were sprayed on the humic-sandy soil of a potato field with ridges and furrows. Rainfall was supplemented by sprinkler irrigation. The distribution of the substances in the soil profile of the ridges and furrows was measured on three dates in the potato growing season. Separate ridge and furrow systems were simulated by using the pesticide emission assessment at regional and local scales (PEARL) model for pesticide behavior in soil–plant systems. The substances travelled deeper in the furrow soil than in the ridge soil, because of runoff from the ridges to the furrows. At 19 days after application, the peak of the bromide distribution was measured to be in the 0.1–0.2 m layer of the ridges, while it was in the 0.3–0.5 m layer of the furrows. After 65 days, the peak of the carbofuran distribution in the ridge soil was still in the 0.1 m top layer, while the pesticide was rather evenly distributed in the top 0.6 m of the furrow soil. The wide ranges in concentration measured with depth showed that preferential water flow and substance transport occurred in the sandy soil. Part of the bromide ion distribution was measured to move faster in soil than the computed wave. The runoff of water and pesticide from the ridges to the furrows, and the thinner root zone in the furrows, are expected to increase the risk of leaching to groundwater in ridged fields, in comparison with more level fields
Growth and yield responses in maize to split and delayed fertilizer applications on sandy soils under high rainfall regimes
No full textThe yield of maize (Zea mays L.) on sandy soils with high rainfall regimes is generally low due to poor nutrient use efficiency. Split and delayed basal fertilizer applications are possible strategies to improve the crop yield and reduce nutrient loss through leaching in sandy soils, but their effectiveness under high rainfall regimes to produce a maize growth response needs further investigation. The aim of the study was to determine the effect of fertilizer application methods on the growth, yield and agronomic characteristics of maize on a sandy soil with approximately 1,350 mm of rainfall during crop growth. Field experiments were conducted on Oxic Paleustults (Korat series) with a low cation exchange capacity (CEC) of 2–4 cmol kg–1. Three to four split applications of the fertilizer increased the grain yield from 2.7 to 3.3–4.5 Mg ha–1. There was a greater crop growth rate (CGR) and relative growth rate (RGR) with the split applications of fertilizer during 30–60 d after emergence (DAE). The highest agronomic efficiency (AE) resulted from a three-split application. However, application of fertilizer later than 45 DAE had only a low effective rate. Delaying the basal fertilizer application to 7–15 DAE increased the grain yield to 3.5–3.7 Mg ha–1, whereas a pre–planting application produced a yield of 2.7 Mg ha–1. Delaying the basal fertilizer application to 7–15 DAE improved the CGR, RGR and AE. These results indicated that fertilizer applications to minimize nutrient loss increased the growth and nutrient use efficiency of maize on sandy soil in a high rainfall regime
Grassland management, soil biota and ecosystem services in sandy soils
No full textRecent legislative restrictions on the use of fertilizers and irrigation, and a quest for sustainable farming systems have drawn renewed attention to the functioning of the soil and the ecosystem services it provides. Soil biota play an important role in the provision of these ecosystem services, which may be influenced by grassland management. The two objectives of this thesis were 1) to gain insight into the effect of different grassland management measures on soil biota in sandy soils; and 2) to explore the effect of grassland management on the ecosystem services provided by soil biota
Crushed rock and clay amelioration of a nutrient decifient, sandy soil of Maputaland
No full textBibliography: leaves 57-62.Various studies have suggested the possibility that food derived through subsistence agriculture in the Mseleni region of Maputaland contributes to malnutrition within the local community, particularfy within the high proportion of the population which suffers from a severe, disabling form of osteoarthritis. This study was conducted to determine if the application of local crushed rock or black clay to these nutrient deficient, sandy soils would increase available nutrient concentrations and improve the growth of plants in the ameliorated soil
Influence of drainage status on soil and water chemistry, litter decomposition and soil respiration in central Amazonian forests on sandy soils
No full textCentral Amazonian rainforest landscape supports a mosaic of tall terra firme rainforest and ecotone campinarana, riparian and campina forests, reflecting topography-induced variations in soil, nutrient and drainage conditions. Spatial and temporal variations in litter decomposition, soil and groundwater chemistry and soil CO2 respiration were studied in forests on sandy soils, whereas drought sensitivity of poorly-drained valley soils was investigated in an artificial drainage experiment. Slightly changes in litter decomposition or water chemistry were observed as a consequence of artificial drainage. Riparian plots did experience higher litter decomposition rates than campina forest. In response to a permanent lowering of the groundwater level from 0.1 m to 0.3 m depth in the drainage plot, topsoil carbon and nitrogen contents decreased substantially. Soil CO2 respiration decreased from 3.7±0.6 µmol m-2 s-1 before drainage to 2.5±0.2 and 0.8±0.1 µmol m-2 s-1 eight and 11 months after drainage, respectively. Soil respiration in the control plot remained constant at 3.7±0.6 µmol m-2 s-1. The above suggests that more frequent droughts may affect topsoil carbon and nitrogen content and soil respiration rates in the riparian ecosystem, and may induce a transition to less diverse campinarana or short-statured campina forest that covers areas with strongly-leached sandy soil
Non-discursive knowledge and the construction of identity. Potters, potting and performance at the bronze age tell of Százhalombatta, Hungary
No full textThis article explores the relationship between the making of things and the making of people at the Bronze Age tell at Százhalombatta, Hungary. Focusing on potters and potting, we explore how the performance of non-discursive knowledge was critical to the construction of social categories. Potters literally came into being as potters through repeated bodily enactment of potting skills. Potters also gained their identity in the social sphere through the connection between their potting performance and their audience. We trace degrees of skill in the ceramic record to reveal the material articulation of non-discursive knowledge and consider the ramifications of the differential acquisition of non-discursive knowledge for the expression of different kinds of potter's identities. The creation of potters as a social category was essential to the ongoing creation of specific forms of material culture. We examine the implications of altered potters' performances and the role of non-discursive knowledge in the construction of social models of the Bronze Ag
Efficient preservation of young terrestrial organic carbon in sandy turbidity-current deposits
No full text© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hage, S., Galy, V. V., Cartigny, M. J. B., Acikalin, S., Clare, M. A., Grocke, D. R., Hilton, R. G., Hunt, J. E., Lintern, D. G., McGhee, C. A., Parsons, D. R., Stacey, C. D., Sumner, E. J., & Talling, P. J. Efficient preservation of young terrestrial organic carbon in sandy turbidity-current deposits. Geology, 48(9), (2020): 882-887, doi:10.1130/G47320.1.Burial of terrestrial biospheric particulate organic carbon in marine sediments removes CO2 from the atmosphere, regulating climate over geologic time scales. Rivers deliver terrestrial organic carbon to the sea, while turbidity currents transport river sediment further offshore. Previous studies have suggested that most organic carbon resides in muddy marine sediment. However, turbidity currents can carry a significant component of coarser sediment, which is commonly assumed to be organic carbon poor. Here, using data from a Canadian fjord, we show that young woody debris can be rapidly buried in sandy layers of turbidity current deposits (turbidites). These layers have organic carbon contents 10× higher than the overlying mud layer, and overall, woody debris makes up >70% of the organic carbon preserved in the deposits. Burial of woody debris in sands overlain by mud caps reduces their exposure to oxygen, increasing organic carbon burial efficiency. Sandy turbidity current channels are common in fjords and the deep sea; hence we suggest that previous global organic carbon burial budgets may have been underestimated.We thank C. Johnson, M. Lardie, A. Gagnon, A. McNichol, and the NOSAMS (National Ocean Sciences Accelerator Mass Spectrometry) team (Woods Hole Oceanographic Institution [WHOI], Massachusetts, USA) for their help with ramped oxidation system and isotopes. We thank the captain and crew of CCGS Vector. Support was provided by UK Natural Environment Research Council (NERC) grants NE/M007138/1 (to Cartigny) and NE/L013142/1 (to Talling), NE/P005780/1 and NE/P009190/1 (to Clare); a Royal Society Research Fellowship (to Cartigny); an International Association of Sedimentologists Postgraduate Grant and National Oceanography Centre Southampton–WHOI exchange program funds (to Hage); an independent study award from WHOI (to Galy); the Climate Linked Atlantic Sector Science (CLASS) program (NERC grant NE/R015953/1); and the European Research Council under the European Union’s Horizon 2020 research and innovation program (Grant 725955, to Parsons). We thank François Baudin, Xingqian Cui, editor James Schmitt, and three anonymous reviewers
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