https://commons.ufh.ac.za/vital/access/manager/Index ${session.getAttribute("locale")} 5 https://commons.ufh.ac.za/vital/access/manager/Repository/vital:41611 Wed 13 Mar 2024 14:10:26 SAST ]]> https://commons.ufh.ac.za/vital/access/manager/Repository/vital:5769 Wed 12 May 2021 20:34:10 SAST ]]> https://commons.ufh.ac.za/vital/access/manager/Repository/vital:20563 10 000 cells ml-1) of several different groups were recorded from the middle reaches of the estuary to the tidal limit. Diatoms were the dominant group during increased freshwater inflow (at mean daily flow rate of 2.14 m3 s-1) and low DIP levels, whereas flagellates were generally the dominant group during reduced flow and under higher nutrient levels. Although the different tidal stages had no effect on phytoplankton biomass per se, it did support co-existance between phytoplankton groups. This was noted during the spring ebb tide in September 2012 (i.e. flagellates, diatoms and dinoflagellate) and in February 2013 (i.e. dinoflagellates, diatoms and chlorophytes). Phytoplankton blooms have become persistent in the middle to upper reaches of the estuary where chlorophyll-a was > 20 µg l-1 and cell density exceeded 10 000 cells ml-1; a situation not reported in previous studies. The Motherwell Canal was and still is the main source of nitrogen (generally in the form of ammonium) to the estuary, whereas the Swartkops River is still the primary source of phosphorus to the estuary. Since the stormwater canal services the large residential area of Motherwell where leaks in the sewer system, the dumping of night soil buckets, and faulty pumps are often reported, polluted discharges from the Motherwell Canal can enter the canal at any given point. In contrast to the canal, DIP loading from the Swartkops River to the estuary generally occurred under conditions of low flow, whereas nitrogen showed no apparent relationship. Faecal bacteria originating from the Motherwell Canal had the most profound effect on the bacteriological status in the middle reaches of the estuary, whereas the Swartkops River had an intermediate effect due to bacteria die-offs occurring between the point of release from the WWTW to the riverine reaches and the tidal limit of the estuary. Nevertheless, Escherichia coli and enterococci levels are still high, especially in the summer months rendering the estuary unsafe for recreation during this season. Historical data on trace metals in the water column were limited and thus observations from the present study could not be concluded with much confidence. However, preliminary data suggest that levels of copper, zinc, iron and cadmium have increased by at least 90% in the estuary, at the tidal limit of the estuary and in the Markman and Motherwell canals. High inputs of nutrients, trace metals and faecal bacteria to the estuary from land-use activities indicate the necessity for remedial actions with the main objective being to conserve and protect the estuary’s recreational, ecological and economic functions.]]> Wed 12 May 2021 20:10:47 SAST ]]> https://commons.ufh.ac.za/vital/access/manager/Repository/vital:5742 0.05 in all other cases). There were two distinct spatial patterns in the distribution of the larger ichthyofauna (>50mm SL). These corresponded to a grouping associated with the mouth region and a grouping associated with the remaining regions of the estuary. Stable isotope analysis indicated that the primary source of carbon utilised by the ichthyofauna of the Kasouga estuary was derived from the channel, most likely microphytobenthic algae. The contributions of the riparian and salt marsh vegetation to the total carbon flow appear to be minimal.]]> Wed 12 May 2021 18:18:06 SAST ]]> https://commons.ufh.ac.za/vital/access/manager/Repository/vital:8990 Wed 12 May 2021 17:21:46 SAST ]]> https://commons.ufh.ac.za/vital/access/manager/Repository/vital:5666 Wed 12 May 2021 16:32:43 SAST ]]> https://commons.ufh.ac.za/vital/access/manager/Repository/vital:20751 Thu 13 May 2021 12:51:24 SAST ]]> https://commons.ufh.ac.za/vital/access/manager/Repository/vital:5700 Thu 13 May 2021 06:42:32 SAST ]]> https://commons.ufh.ac.za/vital/access/manager/Repository/vital:11073 Thu 13 May 2021 06:41:53 SAST ]]> https://commons.ufh.ac.za/vital/access/manager/Repository/vital:10631 Thu 13 May 2021 06:19:00 SAST ]]> https://commons.ufh.ac.za/vital/access/manager/Repository/vital:31640 Thu 13 May 2021 05:23:01 SAST ]]> https://commons.ufh.ac.za/vital/access/manager/Repository/vital:5321 Thu 13 May 2021 03:56:56 SAST ]]> https://commons.ufh.ac.za/vital/access/manager/Repository/vital:5583 0.05 in all cases). Numerical analyses failed to identify any effect of the sandprawn density on the macrofaunal community structure. The rate of bioturbation was, however, strongly correlated to the sand prawn density. Similarly, the microphytobenthic alga concentrations were significantly negatively correlated to the sand prawn densities ((P < 0.05). The absence of any distinct impact of the sandprawn on the macrobenthic community structure appeared to be related to their low densities in the lower reach of the estuary during the study. To better understand the role of the sandprawn as an ecosystem engineer, a caging experiment was conducted using inclusion and exclusion treatments (n= 5 for each treatment). Densities of the sandprawn in the inclusion treatments (80 ind m⁻²) were in the range of the natural densities within the estuary. The experiment was conducted over a period of 18 weeks in the lower reach of the estuary during summer. The presence of the sandprawn, C kraussi, contributed to a significant decrease in the microphytobenthic algal concentrations and the abundance and biomass of the macrofauna (P < 0.05 in all cases). The decrease in the microphytobenthic algal concentrations in the presence of the sandprawn appeared to be related to the res-suspension of the sediments (bioturbation) generated by the burrowing and feeding activities of the sandprawn. The observed decrease in macrofaunal abundances and biomass in the inclusion treatments appeared to be mediated by both the decreased food availability (mainly the microphytobenthic algae) and the burial of organisms within the sediments. Numerical analysis indicated that the sandprawn did, however, not contribute to a change in the species composition of the macrofauna. Results of the current study indicate that C.kraussi plays an important role in structuring the invertebrate community and energy flow within temporarily/open closed Kasouga Estuary.]]> Thu 13 May 2021 03:41:28 SAST ]]> https://commons.ufh.ac.za/vital/access/manager/Repository/vital:8998 Thu 13 May 2021 00:50:52 SAST ]]>