dc.description.abstract | All forms of life are dependent on water for survival. South Africa is a water scare country, due
to seasonal rainfall and high temperatures, thus it is important to manage water resources in
such a way that it benefits the needs of humans and maintains the integrity of aquatic
ecosystems. Agriculture activities, industrial activities and poor sanitation are some of the
threats to water resources. Biomonitoring is one of several methods used to evaluate changes
within aquatic ecosystems and makes use of the organisms found within the ecosystem to
monitor the ecological integrity of that ecosystem — terrestrial or aquatic. As the aquatic
organisms are continuously exposed to the environmental conditions within the ecosystem
they are constantly exposed to the effects of pollution in the ecosystem which in turn modifies
community structure. Biomonitoring could potentially be applied to all aquatic ecosystems
including rivers, lakes, oceans, estuaries and wetlands.
Wetlands are important ecosystems as they are areas with a large variety of biota and provide
numerous resources and ecological services for humans. However, wetlands are susceptible
to nutrient enrichment and pollution as materials are brought into the ecosystem by water,
wind and humans in the catchment area. As wetlands acts as ‘sinks’ sediment and pollutants,
including nutrients, accumulate in wetland ecosystems. These pollutants enter the ecosystem
through runoff, seepage, direct application or are wind driven. As humans make use wetlands
as a source of food and water and wetlands support an abundance of biota it is important to
monitor the health of these aquatic ecosystems.
Monitoring of wetland biota can be problematic at times as the variability in depth and
inundation time does not allow some systems to support fish and/or macroinvertebrates. For
this reason, diatoms are useful as biological indicators to monitor wetlands as they are
microorganisms. Furthermore, diatom communities are species rich, respond rapidly to
changes in the environment, are easy to collect, abundant and are the most diverse algae
group. There is a paucity of aquatic biodiversity information on South Africa’s Ramsar
wetlands and specifically the diatom communities.
The present study focused on two Ramsar wetlands in South Africa namely Lake Sibaya and
the Makuleke Wetlands. The aims of the study were to determine the distribution and
occurrence of diatoms in the Makuleke Wetlands and Lake Sibaya in relations to water quality
and secondly, to determine if European diatom-based indices for indicating wetland water
quality conditions. Water and diatom samples were collected from the Makuleke Wetlands during a wet (April
2015) and dry season (September 2015). Lake Sibaya was sampled during a winter (July
2015) and two summer seasons (November 2015 and February 2016). The nutrient
concentrations present in the water column were measured. Diatom taxa from both wetlands
were identified and indicator species were used to determine the trophic level and ecosystem
quality of these wetlands.
Measured phosphate and inorganic nitrogen concentrations indicated both Lake Sibaya and
the Makuleke Wetlands as nutrient enriched. The diatom community and indices (Specific
Pollution sensitivity Index (SPI) and Generic Diatom Index (GDI)) correlated with the measured
water quality and indicated both sites as nutrient enriched. The measured water quality
variables indicated the wetlands to be either mesotrophic, eutrophic or hypertrophic. Diatom
indices indicated that the study sites were in a bad/poor quality state with dominant diatom
species occurring in polluted and nutrient enriched ecosystems. Thus, both wetlands are
undoubtedly enriched with nutrients, however, it is unsure if these levels can be considered
natural for these systems as nutrient accumulation is a key feature of wetlands.
Diatom taxa identified in the Makuleke Wetlands ranged from 12 – 20 species between the
pans with a total of 70 species identified in the wetland as a whole. A total of 59 species were
identified in Lake Sibaya with a ranging from 20 – 35 species identified at the sampling sites.
Dominant diatom species in the Makuleke Wetlands included Aulacoseira granulata,
Gomphonema parvulum, Navicula sp. and Nitzschia sp. Dominant species at Lake Sibaya
included Cocconeis placentula, Epithemia adnata and Gomphonema sp. Dominant species
for both wetlands were indicators of nutrient enriched ecosystems and tolerant of generally
polluted conditions.
The diatom community (dominant species and diatom indices) and water quality indicated
increased nutrients in the studies wetlands, suggesting a declining ecosystem quality. It is
concluded that methods for diatom community analysis and water quality analysis were
successfully applied and indicated both wetland ecosystems as nutrient enriched, however
there are doubts as to whether this can in turn be viewed as indicating poor ecosystem health
in general. Thus it is recommended that further in-depth studies be completed on diatom
community structure and water quality of wetland ecosystems to determine how to define
natural conditions. This will enable better understanding of the nutrient levels within wetlands
as well as the use of diatoms as bio-indicators for wetland ecosystems | en_US |