Eutrophication Essay Example

(e. G. Rasa and Thornton (1996)). Natural transportation depends only on the local geology and natural features Of the catchments. Cultural transportation is associated with human activities which accelerate the transportation process beyond the rate associated with the natural process (e. .

By increasing nutrient loads into aquatic ecosystems). In South Africa where impoundments are man-made, the conceptual difference between 'natural' and 'cultural' seems less appropriate. Increased nutrient enrichment can arise from both point and non-point sources external to the impoundments as well as internal sources like the impoundments own sediments (that can release phosphate). The adjacent figure illustrates some of the factors that drive the transportation process in an impoundments.

Causes of transportation Increased loads of NH and KNOX in precipitation Atmospheric emissions Hypertrophied Atrophic Mesospheric Oligarchic Atrophic Status Increased nutrient loads in discharges from sewage treatment plants Increased nutrient loads in runoff (agricultural, urban, industrial)

Nutrient Enrichment

Nutrient leach inning from local geology and soils phosphate release from sediments Macrophage, algal and controversial growth Oxygen Light Temperature Retention time Phosphate uptake into sediments Figure 2. 1 .

Simplified schematic illustration of the most important factors driving the transportation process. Transportation 2-5 22. Atrophic status Transportation is a process and it is useful to be able to characterize the stage at which this process is at any given time in a particular water body. The 'atrophic status' of the water body is used as a description of the water body for this purpose. The following terms are used [Walleye, 2000]. Oligarchic - low in nutrients and not productive in terms of aquatic animal and plant life.

Mesospheric - intermediate levels of nutrients, fairly productive in

terms of aquatic animal and plant life and showing emerging signs of water quality problems. Atrophic - rich in nutrients, very productive in terms of aquatic animal and plant life and showing increasing signs of water quality problems. Hypertrophied - very high nutrient concentrations where plant growth is determined by physical factors. Water quality problems are serious and almost continuous.

It is convenient to associate the atrophic status in impoundments with total phosphorus and chlorophyll a measurements.

The following relations pips between atrophic status and these variables are used. These are essentially those of Van Ginkgo et al. 2000), which were based on the work of Walleye and Butts (1980) and Walleye (1984). These have been shown to be applicable to South African impoundments. Table 2.

Relationships between atrophic status and monitoring variables. Atrophic Status Variable unit Mean annual chlorophyll a Fig/R % of time chlorophyll a > 30 > 50 Total Phosphorus MGM/R x#o. 015 >0. 30 Atrophic status is therefore strictly related to one of the nutrients (namely phosphorus) and concentrations of platonic algae and contractible (as chlorophyll a).

(Note that it is not necessarily directly related to concentrations of macrophages or algae attached to rocks and other reface. ) It is also possible to have a relatively high nutrient concentration and yet low plant growth (I low chlorophyll a). For example, this can occur if light availability is reduced because of high levels of suspended solids or if high flushing rates occur. 2-6 Transportation IMPACTS 23.

Introduction Transportation is a concern because it has numerous negative impacts. The higher the nutrient loading in an ecosystem the greater the potential ecological impacts. Increased productivity in an aquatic

system can sometimes be beneficial. Fish and other desirable species may grow faster, roving a potential food source for humans and other animals (though this is not a common situation in South Africa). However, detrimental ecological impacts can in turn have other adverse impacts which vary from aesthetic and recreational to human health and economic impacts.

This is summarized in the following figure.

Potential general negative impacts of transportation Ecological impacts Human health impacts Recreational Aesthetic Economic Figure 2. 2. Summary of potential general negative impacts of a high atrophic status. The more detailed impacts of transportation are complex and interrelated. The excessive growth of aquatic plants and contractible has a multitude of impacts on an ecosystem. The specific impacts depend on what plants are stimulated to grow.

Transportation 2-7 Potential negative impacts Economic impacts Increased water treatment costs Decreased recreational use Decreased access to waterways Transportation Phosphate release water loss Domestic & wild animal deaths Macrophage invasions Algal & non-toxic controversial blooms toxic Decaying algae & non-toxic contractible Corrective action costs stock losses Loss of biodiversity Fish & invertebrate mortality Associations in raw water Low dissolved oxygen n bottom waters Decaying toxic contractible unsightly scum Morbidity & mortality (if water treatment inadequate) Human health impacts Dour & taste problems Figure 2. . Schematic illustration Of some specific impacts Of transportation. 2-8 Transportation 2.

Ecological Impacts

Macrophage invasions and algal and controversial (blue-green) blooms are themselves direct impacts on an ecosystem. However, their presence causes a number of other ecological impacts. Of critical concern is the impact of transportation on biodiversity.

Macrophage invasions impede or prevent the growth of other aquatic plants. Similarly, algal and controversial blooms consist of

species that have out-competed other species for the available nutrients and light.

Their impact on animal biodiversity is also of concern. By generally lowering the ecological integrity of an ecosystem, only the more tolerant animal species can survive. Contractible (also known as blue-green algae) and algae require water, carbon dioxide, inorganic substances and light for their life processes [Chorus and Bertram, 1999].

Contractible are found widely in nature and flourish in water that is salty, brackish or fresh, in cold and hot springs and in environments in which no other algae Can exist. The basic forms and structure include unicellular, colonial and multicultural filamentous forms.