Thesis (MSc)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Runoff is generally regarded as one of the most important routes of nonpoint source
pesticide pollution in agricultural surface waters. Of major concern is the fact that
low, sub-lethal levels of pesticide exposure are responsible for negative
ecotoxicological effects, stressing the need for methods capable of identifying
problem areas where populations could be at risk. Predicted average losses of three
pesticides in tributaries of nine sub-catchments of the Lourens River were calculated
through use of a GIS-based runoff model. There was a significant (p < 0.005) positive
correlation between the predicted average loss and mean measured concentrations of
the insecticides both in water and suspended sediments (R2 between 0.75 and 0.9),
indicating that the model could serve as a powerful tool for the risk assessment and
management of surface waters in South African orchard areas. Based on field relevant
exposure scenanos, the potential effects of azinphos-methyl on macroinvertebrate
communities were evaluated in a combined microcosm and field approach.
Microcosms were contaminated for 1 h with AZP (control, 0.2; 1,5and 20 ug/L;
three replicates each) and acute effects on survival were evaluated 6 days after
exposure. The sensitivity or tolerance of 12 core taxa was determined based on their
response to the exposure scenarios and compared to field tolerance/sensitivity as was
established by a field investigation at a control and contaminated site of the Lourens
River. The sensitivity/tolerance of ten of the 12 taxa corresponded to that which was
found in the field. Thus microcosm studies employing a field relevant design can be
successfully linked to field studies and indicate that transient pesticide contamination
affects the aquatic communities of the Lourens River. / AFRIKAANSE OPSOMMING
Afloop word oor die algemeen beskou as een van die belangrikste roetes van niepuntbron
pestisiedbesoedeling in landbou oppervlakwaters. Die feit dat lae, sub-letale
vlakke van pestisiedblootstelling negatiewe ektoksikologiese gevolge kan hê, is van
groot belang. Dit beklemtoon die behoefte aan metodes om probleemgebiede te kan
identifiseer waar bevolkings aan risiko onderhewig is. 'n GIS-gebaseerde
afloopmodel is gebruik om die gemidddelde verlies van drie pestisiede in die sytakke
van nege sub-opvangsgebiede van die Lourensrivier te voorspel. Daar was 'n
beduidende (p < 0.005) positiewe korrelasie tussen die voorspelde gemiddelde verlies
en gemete konsentrasies van insektisiede in beide die water en sediment (R2 between
0.75 and 0.9) fases, wat aandui dat die model as 'n kragtige hulpmiddel vir
risikobestuur van oppervlakwaters in Suid Afrikaanse boord-gebiede kan dien. Die
potensiële gevolge van azinfos-rnetiel (AZP) op makroinvertebraat gemeenskappe is
deur middel van 'n gekombineerde mikrokosmos (wat op veldrelevante blootstellings
gebaseer is) en veldbenadering bepaal. Mikrokosmosse is vir 1 h met AZP
gekontamineer (kontrole; 1; 0.2; 1; 5 en 20 ~g1L; drie replikate elk), en die akute
gevolge op oorlewing is ge-evalueer na ses dae van blootstelling. Die sensitiwiteit of
toleransie van 12 sleutel taksa is deur middel van hulle respons op die
blootstellingsreeks bepaal, en met hulle veldtoleransie/sensitiwiteit vergelyk wat in 'n
veldstudie by 'n kontrole- en gekontamineerde gebied in die Lourensrivier bepaal is.
Die sensitiwiteit/toleransie van 10 van die 12 taksa in die mikrokosmos eksperimente
het ooreengestem met die wat in die veld gevind is. Mikrokosmosstudies wat op 'n
veldrelevante ontwerp gebaseer is, kan dus suksesvol aan veldstudies gekoppel word,
en dui aan dat oorgedraagde pestisiedkontaminasie die akwatiese gemeenskap van die
Lourensrivier beinvloed.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52409 |
| Date | 12 1900 |
| Creators | Dabrowski, James Michael |
| Contributors | Schulz, R., Reinecke, A. J., Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 91 p. : ill. |
| Rights | Stellenbosch University |
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