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1.
The elevated levels of primary productivity associated with eastern boundary currents are driven by nutrient- rich waters upwelled from depth, such that these regions are typically characterised by high rates of nitrate-fuelled phytoplankton growth. Production studies from the southern Benguela upwelling system (SBUS) tend to be biased towards the summer upwelling season, yet winter data are required to compute annual budgets and understand seasonal variability. Net primary production (NPP) and nitrate and ammonium uptake were measured concurrently at six stations in the SBUS in early winter. While euphotic zone NPP was highest at the stations nearest to the coast and declined with distance from the shore, a greater proportion was potentially exportable from open-ocean surface waters, as indicated by the higher specific nitrate uptake rates and f-ratios (ratio of nitrate uptake to total nitrogen consumption) at the stations located off the continental shelf. Near the coast, phytoplankton growth was predominantly supported by ammonium despite the high ambient nitrate concentrations. Along with ammonium concentrations as high as 3.6 µmol l–1, this strongly suggests that nitrate uptake in the inshore SBUS, and by extension carbon drawdown, is inhibited by ammonium, at least in winter, although this has also been hypothesised for the summer. 相似文献
2.
The physico‐chemical characteristics and microbial composition of the final effluents of two municipal wastewater treatment plants in South Africa were assessed between July and September 2009. The impact of the treated final effluents on the receiving water bodies was also evaluated. The temperature across all sampling points ranged between 14 and 22°C, while pH varied from 6.9 to 7.6. High levels of turbidity, chemical oxygen demand (COD), ammonia, nitrate, nitrite and orthophosphate (PO4) were observed in many cases. Turbidity of the samples was in the range of 2.2–288.6 NTU. The concentrations (mg/L) of other physico‐chemical parameters are as follows: COD (9.33–289); ammonia (0.000340–45.4); nitrate (0.062–539); nitrite (0.021–22.6); PO4 (5.3–33.2). The microbial quality of the effluents discharged from the plants did not comply with the limits set by the South African guidelines with respect to pathogens such as Salmonella, Shigella, Escherichia coli, total coliform, faecal coliform, enterococci, faecal streptococci, and viral particles for effluents intended for discharge into receiving watersheds. This study revealed an undesirable impact on the physico‐chemical and microbial qualities of the receiving water bodies as a result of the discharge of inadequately treated effluents from the wastewater treatment facilities. This poses a health risk to several rural communities which rely on the receiving water bodies primarily as their sources of domestic water and recreational purposes. There is therefore a need for the intervention of appropriate regulatory agencies in South Africa to ensure compliance of treatment facilities with wastewater effluent quality standards. 相似文献
3.
A geochemical assessment of the middle and lower Mvoti river system,KwaZulu-Natal,South Africa 总被引：1，自引：1，他引：0
This paper presents one of the first investigations into the geochemical enrichment of the middle and lower Mvoti river system.
Chemical elements are naturally present in aquatic sediments, but their concentrations tend to rise to potentially toxic levels
via both natural and anthropogenic processes. This study evaluated the concentrations of aluminum, arsenic, boron, barium,
cadmium, calcium, cobalt, chromium, copper, iron, lead, magnesium, manganese, molybdenum, nickel, phosphorous, selenium, silicon,
strontium, titanium, vanadium and zinc, using inductively coupled plasma optical emission spectroscopy. The levels of elements
present were used to assess their spatial distribution within the river and to determine the contamination factors and enrichment
factors for each element. The pollution load index (PLi) is another contributing parameter that was calculated to determine
the degree of pollution at each site. The results indicate that the sediments of the Mvoti are low to moderately polluted
and deteriorating with time (average PLi value of 5.19), and that a major contributing factor to this contamination is natural
sources. 相似文献
4.
Estuaries, the interface of interaction of fluvial discharge and marine action serve as temporary repositories of materials (solid and dissolved) before finally exporting them to sea. This interchange of material is dependant on a range of factors such as those due to tidal variation, fluvial flows and estuarine morphodynamics. The efficacy of transfer of materials to the marine environment is important for estuarine health particularly in estuaries located in highly developed areas such as the major coastal metropolitan areas of many countries. This study assesses this efficacy for three estuaries of the eThekwini Municipality (TM) of the city of Durban, South Africa which maintains an open mouth status, ensuring tidal exchange through the year. The net flux of nitrates was measured for these estuaries on a seasonal basis for both spring and neap tides. Results indicate that although there is a net export of nitrates to the nearshore, there were instances, particularly on the spring tide, when a net import of nitrates into the estuary occurred. Data analysis reveal summer and neap tide flux dominance for the Tongati and Mgeni estuaries whilst the Isipingo Estuary exhibited larger flux variance for spring tides and the spring season. The origin of the latter is likely derived from unusually high biotic decomposition at sea and/or the longshore transport of decomposing sewage outfall. This creates an added dimension for consideration in estuarine management plans. Taking all three estuaries studied into consideration, a net export of nitrates for all seasons for the TM was measured with a clear seasonal influence detected where high rainfall seasons led to greater export as a consequence of greater fluvial flows, erosion and leaching of agricultural lands and, longer ebb duration and flows. 相似文献
5.
Ecosystem engineering by plants and animals significantly influences community structure and the physico-chemical characteristics of marine habitats. In this paper we document the contrasting effects of ecosystem engineering by the cordgrass Spartina maritima and the burrowing sandprawn Callianassa kraussi on physico-chemical characteristics, microflora, macrofaunal community structure and morphological attributes in the high shore intertidal sandflats of Langebaan Lagoon, a marine-dominated system on the west coast of South Africa. Comparisons were made at six sites in the lagoon within Spartina and Callianassa beds, and in a “bare zone” of sandflat between these two habitats that lacks both sandprawns and cordgrass. Sediments in Spartina habitats were consolidated by the root-shoot systems of the cordgrass, leading to low sediment penetrability, while sediments in beds of C. kraussi were more penetrable, primarily due to the destabilising effects of sandprawn bioturbation. Sediments in the “bare zone” had intermediate to low values of penetrability. Sediment organic content was lowest in bare zones and greatest in Spartina beds, while sediment chl-a levels were greatest on bare sand, but were progressively reduced in the Spartina and Callianassa beds. These differences among habitats induced by ecosystem engineering in turn affected the macrofauna. Community structure was different between all three habitats sampled, with species richness being surprisingly greater in Callianassa beds than either the bare zone or Spartina beds. In general, the binding of surface sediments by the root systems of Spartina favoured rigid-bodied, surface-dwelling and tube-building species, while the destabilising effect of bioturbation by C. kraussi favoured burrowing species. The contrasting effects of these ecosystem engineers suggest that they play important roles in increasing habitat heterogeneity. Importantly, the role of bioturbation by C. kraussi in enhancing macrofaunal richness was unexpected. By loosening sediments, reducing anoxia and enhancing organic content, C. kraussi may engineer these high shore habitats to ameliorate environmental stresses or increase food availability. 相似文献
6.
The St. Lucia Estuary is the largest estuarine system in Africa. The estuary is part of the Greater St. Lucia Wetland Park, which has been declared a World Heritage Site. This ecosystem has been subjected to severe drought conditions over the last four to five years, resulting in its mouth being closed off from the ocean in June 2002 for a period of over four years. The main aim of this study was to document the effects of the prevailing drought on the macrofauna of the system, since the last work on this benthic component had been undertaken over a decade ago, during a normal-to-wet phase. Macrofauna samples together with physico-chemical data were collected at representative sites in the Narrows, and the South and North lakes in February, April, August and October 2005. The drought exerted a strong influence on the system, leading to hypersaline conditions developing in its northern regions (maximum of 126 at Hell's Gate), and to the loss of aquatic habitat. Ordinations and clustering indicated that the macrofauna of the system could generally be separated into three clusters viz. (1) the Narrows and the southern portion of South Lake, (2) the northern half of South Lake, and (3) the North Lake–False Bay complex. Multivariate correlations indicated weak relationships between macrofaunal community structure and physico-chemical parameters. The distinction in macrofaunal assemblages between these clusters was probably caused by these habitats being physically separated at the peak of the drought, with no water flow between them, thereby preventing exchange of planktonic larvae and retarding colonisation of habitats. There was a northward decline in taxonomic richness and diversity of macrofauna in the system, which correlated positively with water depth and negatively with the biomass of microphytobenthos. It is evident that the drought structured macrofauna communities primarily through its effects on water depth and habitat fragmentation. The results of this investigation provide valuable information regarding the effects of droughts on estuarine–lake systems and the possible mechanisms by which they occur. 相似文献
7.
The St. Lucia Estuary is Africa's largest estuarine system. It is a major component of the iSimangaliso (formerly Greater St. Lucia) Wetland Park, which was declared a World Heritage Site in 1999. The system has been severely affected by drought conditions which have culminated in the mouth of the system being cut off from the Indian Ocean since June 2002, for a period of almost five years. This study aimed to document the dynamics of meiofauna of the system during a drought phase, since (1) the effects of droughts on estuaries are poorly documented and understood and (2) because studies of meiofauna have never been undertaken in this system before. Meiofauna samples as well as physico-chemical data were collected at representative sites in February, April, August and October 2005. The drought had a major effect on the estuary, resulting in the development of hypersaline conditions (maximum 126 at Hells Gate), and to the complete evaporation of pelagic habitats, especially in the northern regions. The meiofauna of the St. Lucia Estuary was statistically separated into two distinct spatial clusters under drought conditions. The first cluster comprised sites in the Narrows and the southern region of South Lake, while the second comprised sites in the northern regions of South Lake and False Bay. Meiofauna of cluster 1, which was least affected by the drought, comprised nematodes, polychaetes, copepods, amphipods and ostracods, all of which accounted for 97% of meiofauna in this cluster. Cluster 2 on the other hand, which was more severely affected by the drought, was dominated by nematodes and copepods, which cumulatively contributed 97% to meiofauna in this group. Taxonomic richness and diversity of meiofauna were positively correlated with water depth, while abundance was inversely correlated with water temperature. The major effects of low water levels on the meiofauna of the system occurred through a negative impact on diversity and taxonomic richness, resulting in assemblages dominated by taxa most physiologically suited to such conditions. Secondly, at the peak of the drought, there was discontinuous water flow in the St. Lucia Estuary, resulting in parts of the northern and southern regions of the system being fragmented. This could have prevented the spread of meiofaunal taxa between the different basins of the system, and also explains the spatial separation of meiofauna into distinct clusters within the estuary. 相似文献
8.
Large amplitude solitons are investigated in an electron-positron plasma consisting of a hot and cold component for each charged species. The existence (and amplitudes) of the solitons are studied as a function of plasma parameters such as particle number densities and temperatures. Both compressive and rarefactive solitons are found to occur. Possible applications to pulsar magnetospheres are discussed.Also attached to Plasma Physics Research Institute, University of Natal, Durban, South Africa. 相似文献
9.
Samantha Naidoo Srinivasan Pillay Ajay Bissessur Hari Ballabh Delon Naicker 《Journal of Earth System Science》2018,127(3):39
This study describes the geochemical and physico-chemical characterization of contaminant status of six wetlands of the lower uMngeni River floodplain, KwaZulu-Natal Province, South Africa. At all sites, organic matter content, calcium carbonate and metal concentrations were highest within the fine-sediment dominated surface laminae, decreasing with depth. Exceptions were displayed by arsenic (As), nickel (Ni) and vanadium (V), presumed to be derived from normal geochemical processes. Geochemical indicies indicated high contamination factors for lead (Pb) and V, pointing to moderate anthropogenic metal pollution contribution. Most conspicuous are the contamination high factors for Pb across most sites. Fe and Pb contamination is ubiquitous in all surface laminae, with contamination factors being either border-line, moderate or of high contamination. Enrichment factors for As, Mn and P at site S6 indicate possible anthropogenic sources. The data also shows a possibility of anthropogenic input of P and Zn at site S3. Apart from the enrichment factors established for Ni across all sites, all other metals indicate some degree of enrichment. A range of variable results for the mid to deeper laminae are indicative of natural processes with some human influence. Results of ANOVA confirm the above. Principal component analysis reveals a 46.4% variance from component 1 elements (Al, Ca, Cr, Cu, Fe, Mg, Mn and Zn) and a 17.8% variance from component 2 (Al, Cu and Fe). Given the rapid rate of development in this region, the protection of these floodplain wetlands must receive high conservation priority from the local municipality. 相似文献
10.