Invasive alien aquatic plant species management drives aquatic ecosystem community recovery: An exploration using stable isotope analysis
- Authors: Motitsoe, Samuel N , Hill, Jaclyn M , Coetzee, Julie A , Hill, Martin P
- Date: 2022
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/423527 , vital:72069 , xlink:href="https://doi.org/10.1016/j.biocontrol.2022.104995"
- Description: The socio-economic and ecological impacts of invasive alien aquatic plant (IAAP) species have been well studied globally. However less is known about ecosystem recovery following the management of IAAP species. This study employed a before-after study design to investigate ecological recovery following the management of Salvinia molesta D.S. Mitchell, at four field sites in South Africa. We hypothesized that the presence of S. molesta would have a negative impact on the ecosystem food web structure, and that following S. molesta control, the systems would show positive ecosystem recovery. Aquatic macroinvertebrate and macrophyte samples collected before and after mechanical or biological control of S. molesta, were analysed for δ13C and δ15N stable isotopes. Salvinia molesta infestations negatively impacted the food web structure, indicated by reduced food chain length, trophic diversity and basal resources. This represented an altered aquatic food web structure, that in some cases, led to the collapse of the aquatic community. In contrast, after either mechanical or biological control, there were increases in food chain length, trophic diversity and abundance of energy resources accessed by consumers, indicating improved food web structure. Although the study showed positive ecosystem recovery following control, we noted that each control method followed a different recovery trajectory. We conclude that S. molesta invasions reduce aquatic biodiversity and alter ecosystem trophic dynamics and related ecosystem processes, necessitating control.
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- Date Issued: 2022
A new approach to the biological monitoring of freshwater systems: Mapping nutrient loading in two South African rivers, a case study
- Authors: Motitsoe, Samuel N , Hill, Martin P , Avery, Trevor S , Hill, Jaclyn M
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/444480 , vital:74244 , https://doi.org/10.1016/j.watres.2019.115391
- Description: Excessive addition of nitrogen (N) has threatened aquatic ecosystems for decades. Traditional water quality and biological monitoring assessment tools are widely used for monitoring nutrient loads and ecosystem health, but most of these methods cannot distinguish between different types and sources of pollution. This is a challenge, particularly when dealing with non-point sources of anthropogenic nitrogen inputs into freshwater systems. Recent laboratory studies using stable isotopic ratios (δ15N and C/N) of aquatic macrophytes (duckweed: Spirodela spp.) have shown successful differentiation and mapping between different N-sources and further, showed abilities to act as early warning indicators for environmental N-loading. Therefore, the aim of this study was to field test the potential of stable isotopic values of transplanted Spirodela spp. to map temporal and spatial N-loading variation and determine the main sources of N-loading in two river systems in the Eastern Cape Province of South Africa, using previously grown, isotopically calibrated and transplanted Spirodela plants, collected over a 13-month sampling period.
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- Date Issued: 2020
Biological control of Salvinia molesta (DS Mitchell) drives aquatic ecosystem recovery
- Authors: Motitsoe, Samuel N , Coetzee, Julie A , Hill, Jaclyn M , Hill, Martin P
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/444515 , vital:74247 , https://doi.org/10.3390/d12050204
- Description: Salvinia molesta D.S. Mitchell (Salviniaceae) is a damaging free-floating invasive alien macrophyte native to South America. The biological control programme against S. molesta by the weevil Cyrtobagous salviniae Calder and Sands (Erirhinidae) has been successful in controlling S. molesta infestations in the introduced range, however, there is some debate as to how biological control success is measured. This study measured the response of epilithic algae and aquatic macroinvertebrate communities in a S. molesta-dominated state and subsequently where the weed had been cleared by biological control, as a proxy for ecosystem recovery in a before–after control–impact mesocosm experiment.
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- Date Issued: 2020
Pollution Mapping In Freshwater Systems: Using Aquatic Plants To Trace N-Loading
- Authors: Hill, Jaclyn M , Motitsoe, Samuel N , Hill, Martin P
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/444527 , vital:74248 , https://www.wrc.org.za/wp-content/uploads/mdocs/2262-1-15.pdf
- Description: The global degradation of both marine and freshwater ecosystems is primarily driven by the excessive addition of anthropogenic nutrients to watersheds. Increased nitrogen loading, for example, can result in widespread ecosystem deterioration and may include harmful algal blooms, large scale fish kills, hypoxia, the loss of aquatic vegetation and habitat, loss of biodiversity, disruption of ecosystem functioning and the establishment of invasive species. Reactive nitrogen inputs (N) stem from intensive agricultural land use, resulting in the increased use of N-containing organic and inorganic fertilizers and/or animal manure and their consequent run-off and the discharge of human sewage. In recent years, aquatic ecosystem health has been monitored using a number of techniques, of which the most widely applied in South Africa is the South African Scoring System (SASS5; Dickens and Graham, 2002). Bio-monitoring, however, typically identifies eutrophication prob-lems only after ecosystem-level impacts have already occurred and where ecosystem health has been disrupted, it is often not possible to link biotic changes to identifiable causes (especially in the case of non-point source pollution). Any methods that would allow for the detection of emerging eutrophication which can also trace and identify nutrient sources would greatly improve our ability to effectively manage our aquatic resources.
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- Date Issued: 2015