http://vital.seals.ac.za:8080/vital/access/manager/Index ${session.getAttribute("locale")} 5 http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10708 Wed 12 May 2021 16:11:36 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:41596 Wed 12 May 2021 14:14:01 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:10623 6 mg l-1) were maintained throughout the water column mainly by wind and tidal action. However, stratification increased towards the deeper, channel-like middle and upper reaches of the estuary, followed by a significant reduction in bottom DO concentrations and development of hypoxia and anoxia. Bottom water hypoxia commonly occurs in microtidal estuaries due to the limited influence of mixing forces, mainly by wind and tidal action. The Goukamma Estuary is a channel-like microtidal estuary where stratification effectively limited oxygenation of the bottom water which resulted in frequent occurrence of bottom water hypoxia. During June 2010 when the highest local rainfall (75 mm) was recorded for the region, salinity and DO data showed that this amount of rainfall was insignificant as it did not replenish the water column of oxygen. Only the surface 0.5 m layer was fresh and oxygenated while below this, the water column was completely hypoxic. In an unimpacted state, the Goukamma Estuary is a blackwater system and is expected to be nutrient poor; however, farming activities in the catchment have resulted in elevated nutrient concentrations. This study showed that significantly higher nutrient concentrations were measured in the middle and upper reaches of the estuary, adjacent to cattle farms situated in the floodplain of these reaches. Nutrient concentrations represented mesotrophic (dissolved inorganic nitrogen [DIN] > 500 μg l-1) to eutrophic conditions (dissolved inorganic phosphorus [DIP] > 25 μg l-1). Nutrient input stimulated phytoplankton to attain a significantly high biomass, ranging between 0.3 – 112 μg l-1 (~ 7.7 ± 1.3 μg l-1; n = 128) and 0.8 – 289 μg l-1 (~ 21.1 ± 4.4 μg l-1; n = 80) during the open and closed states, respectively. High organic loads are associated with high oxygen demands which consequently result in hypoxia following decomposition. Exacerbated by natural salinity stratification which effectively limits oxygenation of the water column, unnaturally high nutrient concentrations and coinciding organic loads place the estuary at particular risk of degradation. This study captured key patterns and processes by quantifying salinity, oxygen and nutrient concentrations in addition to biological indicators (phytoplankton biomass and community composition). Considering possible budget constraints, it is recommended that monthly salinity and oxygen concentrations should be monitored as well as seasonal nutrient concentrations. It is also recommended that riparian buffer zones should be established in the middle and upper reaches of the estuary, as these vegetation buffers have been well documented to contribute to nutrient attenuation and improved water quality from agricultural run-off.]]> Thu 13 May 2021 01:05:57 SAST ]]> http://vital.seals.ac.za:8080/vital/access/manager/Repository/vital:62157 100 µm) dynamics within the dynamic coastal ecosystem of Algoa Bay, located within warmtemperate South Africa, in spring 2020 and summer 2021. This study revealed seasonal shifts in mesozooplankton taxa succession from spring herbivorous/omnivorous, dominated by copepods, to summer omnivorous/carnivorous mesozooplankton, dominated by copepods, Noctiluca sp., Cladocera, doliolids, salps and siphonophores. The mesozooplankton integrated abundance (mean ± standard error) increased from spring to summer, with 101 ± 26 (min. – max.: 18 – 200) x 103 ind m¯ 2 and 422 ± 80 (min. – max.: 37 – 1056) x 103 ind m¯ 2 , respectively. In summer, mesozooplankton composition was affected by the passage of a Natal Pulse, identified from satellite-derived sea level anomaly data. This study also provided the first vertical profiles of copepod distributions and suspended particles in Algoa Bay, with a peak of small particle (< 1 mm ESD) biomass close to the bottom and often, but not systematically, higher copepod abundances above the thermocline. The results presented herein are expected to contribute to the understanding of the coastal pelagic ecosystem in Algoa Bay in response to environmental perturbations]]> Mon 06 Mar 2023 09:45:34 SAST ]]>