Swan grazing on seagrass: abundance but not grazing pressure varies over an annual cycle in a temperate estuary

2014 ◽  
Vol 65 (8) ◽  
pp. 738 ◽  
Author(s):  
Gary E. Choney ◽  
Kathryn McMahon ◽  
Paul S. Lavery ◽  
Neil Collier
Keyword(s):  
Annual Cycle ◽  
River Estuary ◽  
Grazing Pressure ◽  
Food Sources ◽  
Spatial And Temporal Variation ◽  
Human Disturbances ◽  
Black Swans ◽  
New Findings ◽  
Cycle Maximum ◽  
Negative Effect

Herbivorous waterfowl such as black swans are significant grazers in temperate waterbodies; their abundance, distribution and grazing rates vary over seasonal cycles. The present study examined spatial and temporal variation in the abundance and grazing rates of black swans in the Lower Swan River estuary, Western Australia, using visual surveys over 1 year (2009), and potential drivers of this variation, food sources and disturbance factors were assessed. We predicted that swan abundance and grazing pressure would be greater in summer and autumn when seasonal wetlands dry and the abundance of food sources would positively influence their distribution, whereas the level of disturbance would have a negative effect. Plant–grazer interactions are dynamic and complex; the present study revealed new findings on the seasonality of this relationship, where swan abundance but not grazing pressure varied over an annual cycle. Maximum swan abundance occurred in autumn (185) with minima in spring (53) but the swan grazing pressure did not vary between seasons, ranging from 6% to 25% of seagrass production consumed. Swan abundance was a function of season and the cover of seagrass. Key hot spots for swan abundance were identified where management efforts could be targeted by minimising human disturbances and protecting seagrass.

scholarly journals Patterns of Feeding by Householders Affect Activity of Hedgehogs (Erinaceus europaeus) during the Hibernation Period

Animals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1344 ◽  
Author(s):  
Abigail Gazzard ◽  
Philip J. Baker
Keyword(s):  
Food Sources ◽  
Energy Deficit ◽  
Net Energy ◽  
Survey Period ◽  
Erinaceus Europaeus ◽  
Ecological Features ◽  
Hibernation Period ◽  
Negative Effect ◽  
Anthropogenic Food Sources ◽  
The Town

West European hedgehogs (Erinaceus europaeus) are likely to encounter unusual ecological features in urban habitats, such as anthropogenic food sources and artificial refugia. Quantifying how these affect hedgehog behaviour is vital for informing conservation guidelines for householders. We monitored hedgehog presence/absence in gardens in the town of Reading, UK, over the winter of 2017–2018 using a volunteer-based footprint tunnel survey, and collected data on garden characteristics, supplementary feeding (SF) habits, and local environmental conditions. Over a 20-week survey period, hedgehog presence was lowest between January and March. Occupancy analysis indicated that SF significantly affected hedgehog presence/absence before, during, and after hibernation. The number of nesting opportunities available in gardens, average temperatures, and daylength were also supported as important factors at different stages. In particular, our results suggest that SF could act to increase levels of activity during the winter when hedgehogs should be hibernating. Stimulating increased activity at this sensitive time could push hedgehogs into a net energy deficit or, conversely, help some individuals survive which might not otherwise do so. Therefore, further research is necessary to determine whether patterns of feeding by householders have a positive or negative effect on hedgehog populations during the hibernation period.

Spatial and temporal variation of picophytoplankton in the Pearl River Estuary

2013 ◽  
Vol 33 (7) ◽  
pp. 2200-2211 ◽  
Author(s):  
张霞 ZHANG Xia ◽  
黄小平 HUANG Xiaoping ◽  
施震 SHI Zhen ◽  
叶丰 YE Feng ◽  
刘庆霞 LIU Qingxia
Keyword(s):  
Temporal Variation ◽  
River Estuary ◽  
Pearl River Estuary ◽  
Spatial And Temporal Variation ◽  
Pearl River ◽  
The Pearl River Estuary ◽  
The Pearl River

Climatological annual cycle of Benguela upwelling system using different upwelling indices

2020 ◽  
Author(s):  
Mohammad Hadi Bordbar ◽  
Volker Mohrholz ◽  
Martin Schmidt
Keyword(s):  
Chlorophyll A ◽  
Vertical Velocity ◽  
Annual Cycle ◽  
Ekman Transport ◽  
Spatial And Temporal Variation ◽  
Clear Correlation ◽  
Ekman Pumping ◽  
Chlorophyll A Concentration ◽  
Upwelling System ◽  
Benguela Upwelling

<p>Several long-established upwelling indices derived from the observed wind fields, Chlorophyll-a concentration, sea surface temperature (SST) are used to investigate the climatology annual cycle of Benguela Upwelling System (BUS). Chlorophyll-a concentration is taken as an indicator of ocean primary production. In addition, we analyze a multi-decadal simulation of a state-of-the-art eddy resolving ocean model which was forced by observed atmospheric heat and momentum fluxes. We take the vertically averaged of simulated vertical velocity in water column as a direct measure of upwelling strength.</p><p>The Ekman offshore transport tends to have two distinctive upwelling cells near the coast of Lüderitz (26.3°S) and Cape Frio (17°S) with large seasonal cycles. The former peaks between September and December. The latter features a biannual cycle with two peaks over April-June and September-December, which is concurrent with meridional migration of Angola-Benguela SST front. The offshore (30-200 km) vertical velocity, primarily induced by Ekman transport divergence, depicts a similar annual cycle, but with smaller magnitude. It becomes broader from south to north with four distinctive upwelling cells located near the coast of Cape Columbine (33°S), Orange River (28°S), Walvis Bay (23°S) and northern part of Cape Frio (16°S). The spatial and temporal variation of Ekman pumping and Chlorophyll-a, as measures of upwelling, show a clear correlation. However, such a correlation is not evident when Ekman coastal transport is taken. SST-based index depicts a very similar spatial pattern. However, the seasonal cycle does not match with other observational and simulated indices. Our finding suggests that the local SST anomalies are strongly influenced by horizontal heat advection and surface heat flux anomaly which can dominate over the anomalies associated with the upwelling; meaning that SST-index alone may not give a realistic estimate of upwelling strength over the region.</p>

Annual cycle of hypoxia off the Changjiang (Yangtze River) Estuary

2012 ◽  
Vol 77 ◽  
pp. 1-5 ◽  
Author(s):  
Baodong Wang ◽  
Qinsheng Wei ◽  
Jianfang Chen ◽  
Linping Xie
Keyword(s):  
Annual Cycle ◽  
Yangtze River ◽  
River Estuary ◽  
Yangtze River Estuary

Grazing pressure impacts on two Aristida/Bothriochloa native pasture communities of central Queensland

2017 ◽  
Vol 39 (3) ◽  
pp. 227 ◽  
Author(s):  
Trevor J. Hall ◽  
Paul Jones ◽  
Richard G. Silcock ◽  
Piet G. Filet
Keyword(s):  
Ground Cover ◽  
Predictive Modelling ◽  
Grazing Pressure ◽  
Total Contribution ◽  
Themeda Triandra ◽  
Crown Cover ◽  
Economic Production ◽  
Eastern Australia ◽  
Negative Effect ◽  
Native Pastures

Managing native pastures for sustainable and economic production requires a good understanding of grazing effects on pasture dynamics. The Aristida/Bothriochloa pastures of north-eastern Australia are important for cattle production but little data on grazing pressure impacts on pastures are available to guide management decisions of producers, for land management education programs, or for predictive modelling. To address this deficiency, four different continuous grazing intensities were imposed on woodland communities over 7 or 8 years at two sites: a Eucalyptus populnea (poplar box) and a E. melanophloia (silver-leaved ironbark) community. Both sites had replicated paddocks grazed at a low, medium or high grazing pressure by +/− tree killing using herbicide (12 paddocks), and 12 ungrazed (nil grazing pressure) 1-ha plots subjected to the same tree-killing contrasts. Grazed paddock areas were fixed and varied between 3.5 and 21.5 ha. Differential grazing pressures were reset each autumn, by adjusting cattle numbers to consume over the next year the equivalent of 0%, 25%, 50% or 75% of the standing pasture mass available. Pasture grasses suitable as indicators of grazing pressure were identified for both communities. Under low grazing pressure, Themeda triandra (kangaroo grass) was the only desirable grass to show a significant increase in total contribution over time at both sites, although Dichanthium sericeum (Queensland bluegrass) also increased its contribution at the poplar box site. Chloris species increased their contribution as grazing pressure increased. The proportion of less palatable Aristida spp. (wiregrasses) in the pasture was not affected by high grazing pressure, although they increased at low grazing pressure in the poplar box community. There were no consistent changes in native legumes or weedy forb species to any treatment. Increasing grazing pressure had a greater negative effect on pasture mass, ground cover and pasture crown cover area than on changing species composition. Most changes in composition due to grazing pressure were smaller than those associated with variable seasonal rainfall, and were greater in the poplar box community. In above-average rainfall years grazing up to 50% of autumn standing pasture mass had no detrimental effect on composition in treeless poplar box country in the short term. The pastures remained stable or improved in both communities when grazing pressure was set annually to utilise 25% of the standing autumn forage.

scholarly journals Transport Processes in the Gulf of Mexico Along the River-Estuary-Shelf-Ocean Continuum: a Review of Research from the Gulf of Mexico Research Initiative

2021 ◽  
Author(s):  
Dubravko Justić ◽  
Villy Kourafalou ◽  
Giulio Mariotti ◽  
Songjie He ◽  
Robert Weisberg ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Harmful Algal Blooms ◽  
Algal Blooms ◽  
River Estuary ◽  
Deep Ocean ◽  
Open Ocean ◽  
Transport Processes ◽  
Spatial And Temporal Scales ◽  
Research Initiative ◽  
New Findings

AbstractEstuarine and coastal geomorphology, biogeochemistry, water quality, and coastal food webs in river-dominated shelves of the Gulf of Mexico (GoM) are modulated by transport processes associated with river inputs, winds, waves, tides, and deep-ocean/continental shelf interactions. For instance, transport processes control the fate of river-borne sediments, which in turn affect coastal land loss. Similarly, transport of freshwater, nutrients, and carbon control the dynamics of eutrophication, hypoxia, harmful algal blooms, and coastal acidification. Further, freshwater inflow transports pesticides, herbicides, heavy metals, and oil into receiving estuaries and coastal systems. Lastly, transport processes along the continuum from the rivers and estuaries to coastal and shelf areas and adjacent open ocean (abbreviated herein as “river-estuary-shelf-ocean”) regulate the movements of organisms, including the spatial distributions of individuals and the exchange of genetic information between distinct subpopulations. The Gulf of Mexico Research Initiative (GoMRI) provided unprecedented opportunities to study transport processes along the river-estuary-shelf-ocean continuum in the GoM. The understanding of transport at multiple spatial and temporal scales in this topographically and dynamically complex marginal sea was improved, allowing for more accurate forecasting of the fate of oil and other constituents. For this review, we focus on five specific transport themes: (i) wetland, estuary, and shelf exchanges; (ii) river-estuary coupling; (iii) nearshore and inlet processes; (iv) open ocean transport processes; and (v) river-induced fronts and cross-basin transport. We then discuss the relevancy of GoMRI findings on the transport processes for ecological connectivity and oil transport and fate. We also examine the implications of new findings for informing the response to future oil spills, and the management of coastal resources and ecosystems. Lastly, we summarize the research gaps identified in the many studies and offer recommendations for continuing the momentum of the research provided by the GoMRI effort. A number of uncertainties were identified that occurred in multiple settings. These include the quantification of sediment, carbon, dissolved gasses and nutrient fluxes during storms, consistent specification of the various external forcings used in analyses, methods for smooth integration of multiscale advection mechanisms across different flow regimes, dynamic coupling of the atmosphere with sub-mesoscale and mesoscale phenomena, and methods for simulating finer-scale dynamics over long time periods. Addressing these uncertainties would allow the scientific community to be better prepared to predict the fate of hydrocarbons and their impacts to the coastal ocean, rivers, and marshes in the event of another spill in the GoM.

Factors influencing concentrations of polychlorinated biphenyls in organisms from an estuarine ecosystem

1982 ◽  
Vol 33 (6) ◽  
pp. 1057 ◽  
Author(s):  
GR Shaw ◽  
DW Connell
Keyword(s):  
Polychlorinated Biphenyls ◽  
Direct Relationship ◽  
Steric Effect ◽  
Laboratory Data ◽  
River Estuary ◽  
Sediment Concentration ◽  
Food Sources ◽  
Major Influence ◽  
Log P ◽  
Estuarine Ecosystem

Polychlorinated biphenyls (PCB's) were detected in both the abiotic and biotic components of the Brisbane River estuary. Maximum average concentrations were detected in the muscle tissue of pelican (8.2 mg kg-1), gull (2.6 mg kg-1) and catfish (2.1 mg kg-1). Biomagnification was shown not to be a significant factor controlling PCB concentrations in the organisms investigated except in pelicans and gulls. In these cases, estimates of uptake from food sources indicated that biomagnification could be the major process involved. Metabolism or excretion was also found to influence the observed PCB composition of these organisms. Field and laboratory data indicated that, with some benthic organisms, sediment concentrations were the major influence on body concentrations of PCB's and a direct relationship between body concentration and the log of sediment concentration was established. Further laboratory experiments indicated that the uptake of individual PCB's was influenced primarily by two factors: the partition coefficient of n-octanol to water (p) and stereochemical effects. A direct relationship between uptake and the product of log p and the steric effect coefficient was demonstrated. Thus, maximum uptake was found with penta- and hexachlorobiphenyls, predominant in Arochlor 1254. Comparatively less uptake was found with di-, tri- and tetrachlorobiphenyls (Arochlor 1242), which have lower values for log p, and hepta- and octachlorobiphenyls, predominant in Arochlor 1260, which have lower steric effect coefficients.

Biconcentration of Chlorophenols by Leeches and Their Use as In Situ Biological Monitors

1988 ◽  
Vol 23 (1) ◽  
pp. 69-87 ◽  
Author(s):  
K. J. Hall ◽  
C. Jacob
Keyword(s):  
Laboratory Experiments ◽  
River Estuary ◽  
Assessment Method ◽  
Spatial And Temporal Variation ◽  
Equilibration Time ◽  
Degree Of Contamination ◽  
The North ◽  
Integrative Assessment ◽  
Depuration Rate

Abstract Leeches were used as in situ monitors of the biological availability of Chlorophenols to estimate the degree of contamination in the North Arm of the Fraser River Estuary, British Columbia, where several forest industry operations use Chlorophenols as wood preservatives. A large spatial and temporal variation was observed in the concentration of 2,3,4,6-tetrachlorophenol (<0.01-15.20 μg·lࢤ1) and pentachlorophenol (<0.01-2.80 μg·lࢤ1) in a series of grab and composite water samples. This demonstrated the sporadic nature of releases and the need for an integrative assessment method. Leeches readily concentrated the Chlorophenols and had a slow depuration rate. In seven days leeches bioconcentrated Chlorophenols to μg·gࢤ1 levels (28-2946 μg TTCP·fgࢤ1 wet wt and 29-846 μg PCP·gࢤ1 wet wt). Based on laboratory bioconcentration studies, leeches provided an estimate of average exposure concentrations from <0.1 to 10 μg·lࢤ1 in the river over the bioassay periods. Laboratory experiments demonstrated a higher bioconcentration potential and a longer equilibration time at higher temperatures. At lower pH there was higher bioconcentration of Chlorophenols indicating that the un-ionized molecule was adsorbed more readily. Uptake of the un-ionized chlorophenol correlated well with the partition coefficient (Ko/W) of the compound.

Physical Simulation Study on Transverse Effect of Bolted Discontinuous Rock Mass

2014 ◽  
Vol 1008-1009 ◽  
pp. 1292-1296
Author(s):  
Ying Xuan Jia ◽  
Hong Wei Song ◽  
Gui Zhang ◽  
Xing Kuang
Keyword(s):  
Rock Mass ◽  
3D Model ◽  
Physical Simulation ◽  
Shear Loading ◽  
New Findings ◽  
Bolt Stress ◽  
Negative Effect ◽  
Transverse Effect ◽  
Discontinuous Rock ◽  
Bolt Diameter

In order to illustrate the mechanism of supporting, maintain the safety and keep the stable of underground projects, it is of great significance to study the transverse effect of bolted discontinuous rock mass. With a 3D model and corresponding physical simulation, analyzing the testing results of the bolt stress, rock stress and displacement discovers some new findings. Besides its reinforcing effect to the rock mass, the bolt has a negative effect on the discontinuous rock mass by its so-called ‘railway effect’ under shear loading. The finding of this bolt function will help to further understand of bolting mechanism and it is very important to raise the safety of bolt supporting design. Furthermore the effect grade is a positive correlativity with the bolt diameter, and the shear displacement is one of its necessary conditions.

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