1,721,065 research outputs found
Wasserman, Ryan J (Assoc Prof)
No full textDepartment of Zoology and Entomology (2014-present) Ryan Wasserman ORCID 0000-0002-4162-150
Organic matter dynamics in Nylsvley Wetland : Distribution and processes
Get PDFMENVSCDepartment of Ecology and Resource ManagementWetlands play a crucial role in nutrient and biogeochemical cycles and are among the most productive of ecosystems. Physical and biological processes are involved in the distribution and protection of organic matter in wetlands sediments. Productivity among wetlands therefore varies depending on the type of the wetland, climatic condition and vegetation communities. The application of biogeochemical techniques involving stable isotopes of carbon and nitrogen has been successfully used to determine sediment sources in aquatic ecosystems such as wetlands. The study investigated spatial and temporal changes in sources of organic matter in sediments and examined spatial and seasonal changes over two seasons within Nylsvley wetland. Samples of sediments were collected at each wetland site per season in order to determine amount of organic matter and to identify contributors to sediment organic matter. These samples were air dried and impurities removed, then put into the oven and dried at 60 °C to constant weight for 72 hours. Data was analyzed using a three–way ANOVA with Tukey’s HSD analysis ed to assess the differences in sediment organic matter (%) among wetland zones, sites and seasons. A Stable Isotope Analysis in R (SIAR) model was used to identify organic matter sources contributing to sediments in wetland zones per season. Results showed distribution was uneven throughout the wetlands; the seasonal zone had the highest sediment organic matter (27%) in the cool-dry season and the permanent zone had the highest (25%) sediment organic matter in the hot-wet season and the temporary zone had the lowest. Several studies have indicated that ∂13C and ∂15N can be used as indicators for environmental change. Carbon and Nitrogen stable isotope may be an alternative means to detect early environmental changes in aquatic ecosystems including wetlands.
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The seasonal zone had a high nutrient concentration (Calcium) in both hot-wet and cool-dry season ranging between 1000-1800 mg kg-1. Autochthonous plants were the main source of organic matter in sediments although allochthonous plants also contributed to the sediment organic matter content, autochthonous inputs was still dominant. In sediments the ∂13C mean values were higher than the ∂15N values in all sites and wetland zones. This study showed that sediment organic matter in wetlands is mainly derived from autochthonous sources. This study’s findings help to better understand the distribution of organic matter in wetland ecosystems. This is particularly important as wetlands play a vital role globally by their contribution to provisioning, regulating and cultural services. As such, future studies should continue to assess seasonal variations and identifying other sources of organic matter within the context of distribution and processes in wetland ecosystems not only in South Africa but globally.NR
Metacommunity structure and dynamics
No full textFreshwater biological communities are spatially distributed in relatively isolated patches over a terrestrial landscape matrix, but they may be connected through dispersal processes and can therefore be studied as a set of interrelated communities, constituting a metacommunity. In this chapter, we explore the different processes shaping metacommunity structure, and their relationship with diversity patterns. Besides evolution in the long term, there are three main ecological processes structuring metacommunities: environmental control, dispersal, and stochasticity. Environmental control (i.e., selection), also referred to as niche-control or species sorting, refers to the filtering effect of the environment by selecting species adapted to the abiotic and biotic conditions, working at local and regional scales. Another key process, whose role is highlighted by metacommunity theory, is dispersal, a scale-dependent process with a high influence on biodiversity. Finally, stochastic processes (e.g., ecological drift) can lead to unpredictable but important changes in community structure. Focusing on the influence of these mechanisms through different organisms and scales, we show how the relative roles of selection, dispersal, and drift are crucial in organizing tropical wetland metacommunities worldwide. We also illustrate how variation partitioning analysis, one of the most widely used methods for the study of empirical metacommunities, provides information about the major role of environmental, spatial, and neutral effects in tropical wetland metacommunity organization. Finally, we present some remarks on conservation biology under the lens of metacommunity theory, which assumes that not only local conditions but also the regional environment and connectivity are essential elements to be considered for successful management planning.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Assessing the effects of MACADAMIA ORCHARD pesticide inputs on recipient aquatic ecosystems
No full textPhDENVDepartment of Geography and Environmental SciencesAquatic environments, while not the target of many pesticide applications, often receive chemicals
through catchment runoff dynamics. In this regard, the use of pesticides in agricultural systems
may have deleterious effects on aquatic ecosystems within the same catchment area. Here using a
series of in–situ and ex–situ experiments, the study assessed (a) pesticide concentrations of
acetamiprid and chlorpyrifos across MACADAMIA ORCHARD and communal area reservoirs
using liquid chromatography tandem mass spectrometry (LC–MS/MS), (b) the behavioural
responses of Mozambique tilapia, Oreochromis mossambicus, following exposure to three
commonly used macadamia pesticides (i.e., Karate Zeon 10 CS, Mulan 20 SP, Pyrinex 250 CS at
different concentrations, (c) macadamia Macadamia integrifolia leaf litter decomposition and
mosquito colonisation following pesticide exposure, and (d) macroinvertebrate colonisation
associated with introduced stone substrates in cages within the MACADAMIA ORCHARD and
control reservoirs to explore whether macadamia pesticides affected on macroinvertebrate
colonisation dynamics.
Firstly, analysis of acetamiprid and chlorpyrifos associated with sediments in MACADAMIA
ORCHARD reservoirs revealed mean pesticide concentrations of 14.48 μg L–1 and 5.67 μg L–1,
respectively, whereas, in communal area reservoirs outside of agricultural catchments, both
pesticides were not detected. Acetamiprid was not detected across reservoir water, whereas the
mean pesticide concentration of chlorpyrifos of 6.51 μg L–1 (MACADAMIA ORCHARD) and
0.13 μg L–1 (communal area) were detected. Secondly, O. mossambicus demonstrated different
onset behavioural responses, i.e., swimming erratically, surfacing, vertical positioning, loss of
equilibrium, being motionless and mortality with high mortality at increased mortality. Thirdly,
macadamia leaf litter tended to decompose faster when exposed to pesticide treatments, whereas
chlorophyll–a were reduced. Furthermore, pesticide treatments seemed to promote mosquito (i.e.,
Culex spp.) and pupal abundances. Finally, a total of 644 macroinvertebrate individuals were
recorded across macadamia and communal reservoirs, mostly dominated by Chironominae (55.1
%), Ostracoda (14.4 %), Trithemis sp. (5.2 %), Anax sp. (5.2 %) and Radix natalensis (5.0 %).
The results indicate that MACADAMIA ORCHARD reservoirs are highly contaminated by
acetamiprid and chlorpyrifos and that these contaminants have implications for the ecological
functioning of aquatic ecosystems. Reduction of species diversity adjusted community structure
and altered energy flow and nutrient recycling were all demonstrated. The results of the study
collectively show how common pesticides used in the macadamia plantation may be exert pressure
on adjacent freshwater ecosystems. Future studies should examine effects on trophic interactions,
pesticide accumulation in faunal groups and allochthonous trophic transfer dynamics to terrestrial
environments. Such information would be useful for managers tasked with mitigation plans for the
region.National Research Foundation (NRF
Water and sediment chemistry quality, and biodiversity structure of floodplain pans in the Makuleke Wetlands, Kruger National Park, South Africa
No full textPhDENVDepartment of Geography and Environmental SciencesThe floodplain pans found in Makuleke wetlands are good representatives of floodplain ecosystems in the region. As such they provide a unique opportunity to investigate floodplain wetland ecological structure and functioning. The Makuleke wetlands are largely understudied despite their importance for provision of various ecosystem services such as flood protection, groundwater recharge and discharge, carbon storage, water quality and biodiversity maintenance, and nutrient cycling. Floodplain pans provide habitats for diverse flora and fauna, while also improving tourism which contribute to economic growth. The present study focused on assessing water quality, sediment quality, chlorophyll–a (chl–a) dynamics, trophic interactions and biodiversity structure within floodplain pans of the Makuleke wetlands, Kruger National Park. The study comprised of four data chapters (Chapters 3–6), each assessing a discrete and fundamental component of wetland ecology.
In Chapter 3, the study investigated the (1) spatial distributions of different metals (i.e., Zn, Mn, Cu, Fe, B, Na, Ca, K, Mg) in sediment cores (sediment depth), (2) identify relationships among sediment metals, and (3) determine the sediment contamination and toxic risks associated with the identified metals using pollution indices. This chapter demonstrated that the concentrations of metals in the assessed cores were higher in surface sediment than in deeper sediment. Furthermore, pans such as Mambvumbvanyi tended to be more polluted (at a depth of 0–20 cm) than Nyavadi and Jachacha pans. These results suggest that high surface sediment metal concentrations are likely to be due to plant debris in surface soils, plant cycling, pan drying as a subject of seasonal changes and soil deposition and through floodplain inundation waters arising from outside the park that contains metals. I further observed that
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pollution load by metals varied slightly across the studied floodplain pans and sediment depth due to catchment development upstream.
Chapter 4 of this thesis focused on assessment of benthic and pelagic chlorophyll‒a, water and sediment metal dynamics across hydroperiods among various pan systems in the Makuleke floodplain. This chapter aimed to assess the overall ecosystem health among pans and hydroperiod, and also assess chl–a concentrations in relation to various environmental variables across various floodplain pans in order to determine potential drivers of phytoplankton biomass and determine the spatio–temporal variation of chl–a based of hydroperiod (water level) and environmental variables. The result of this chapter revealed that the ecology of the floodplain pans was driven mainly by water quality (primarily total dissolve solids and chl–a), sediment chemistry (metal concentrations) and hydroperiod (low– and high– water period). Fluctuation of water levels within the pans resulted in changes of sediment chemistry within various pans. Generally, pelagic and benthic chl–a concentration increased with water and sediment chemistry variables.
In chapter 5, the study was conducted to identify different types of fish species and macroinverterbrates found in various pans in the Kruger National Park (Makuleke wetlands). The study further assessed the fish and macroinvertebrates diversity index with the use of ANalysis Of SIMilarities (ANOSIM) and SIMilatity PERcentage (SIMPER) and their relationship with environmental variables (i.e., sediment and water chemistry). Fish species (i.e., Tilapia sparminii, Gambusia affinis, Coptodon rendali, Oreochromis spp. hybrid, Oreochromis mossambicus, Enteromius palludinosus and Clarais gariepinus) and macroinvertebrates (i.e., Notonectidae, Libellulidae, Gerridae, Chironomidae larvae,
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Belostomatidae, Gomphidae, dytiscidae and Baetidae) were the dominant species across the different floodplain pans, indicating that the pans contain high biodiversity. Generally, fish and macroinvertebrates communities were high during high–water level as compared to low–water level, suggesting that hydroperiod play a significant role in structuring species community. In addition, pelagic chl–a was strongly positively associated with fish, in particular Gambusia affinis during high–water level period.
Lastly, chapter 6 of the thesis employed an experimental approach (an experiment called functional response) to understand predator and prey dynamics (multiple predator effects (MPEs)) within the pans using common fish species which are found in the wetlands (i.e., Oreochromis mossambicus and Enteromius paludinosus). During functional response (FR) experiments on multiple predator effects (MPEs), I used single predator species as well as intra– and interspecific paired species to contrast FRs under multiple predator scenarios. Attack rate and handling time estimates from single predator FRs were used to predict multiple predators feeding rates, which were compared to observed multiple predator feeding rates to quantify potential MPEs. From single fish trials, each species displayed a significant Type II FR, characterized by high feeding rates at low prey densities. Oreochromis mossambicus had a steeper (initial slope, i.e., higher attack rate) and higher (asymptote of curve, i.e., shorter handling time and higher maximum feeding rate) FR, whereas Enteromius paludinosus exhibited lower–magnitude FRs (i.e., lower attack rate, longer handling time and lower feeding rate). In multiple predator scenarios, feeding rates were well–predicted by those of single predators, both in conspecific and interspecific pairs, and thus I did not find evidence for antagonistic or synergistic MPEs. Predator–prey interactions in wetland systems can have significant consequences on the structure and dynamics of ecological communities. In turn, this could have destabilizing effects on resources in tropical wetlands. Although the results on
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this chapter on fish interactions and feeding habit were experimental, they help us understand how trophic interaction among conspecific or interspecific fish species in floodplain pan wetlands might have an effect on their aquatic prey species. Overall, this study shows that water, sediment and chl–a have significant impact on biodiversity structure and functioning of floodplain pans wetlands.NR
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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