Els resultats que es presenten en aquesta tesi estan centrats bàsicament en l'estudi de la biodiversitat de les diatomees epilítiques presents en els rius de la conca de l'Ebre i en la seva aplicació com a indicadores de l'estat ecològic de les masses d'aigua. Durant els mesos d'estiu del 2005 i 2006 es va realitzar el mostreig de la flora de diatomees epilítiques en un total de 197 i 211 estacions, respectivament, pertanyents a la Xarxa de Control de l'Estat de les Masses d'Aigües Superficials (CEMAS) de la Confederació Hidrogràfica de l'Ebre (CHE). Aquests mostrejos van ser impulsats per la CHE amb l'objectiu d'establir xarxes de control biològic, basades en bioindicadors del fitobentos per tal de conèixer l'estat ecològic de les aigües fluvials d'acord amb el que estableix la Directiva Marc de l'Aigua (DMA). La recollida de les mostres, el seu tractament químic i, la quantificació de les espècies per localitat, s'han basat en les normatives estandarditzades europees CEN/TC 230 EN 13946:2003, norma prEN 14407: 2004 i, en els protocols de la CHE per l'avaluació de la qualitat biològica en rius mitjançant diatomees. L'examen de les mostres recollides ha permès la identificació de 499 tàxons, repartits en 91 gèneres, dels quals 492 han estat a nivell específic o infra-específic. Dels tàxons identificats, 361 estan representats en 751 fotografies realitzades al microscopi òptic, agrupats en 25 làmines. Com a particularitats de la flora s'esmenta d'una banda la presència de 7 espècies al•lòctones segons les consideracions principalment de Coste & Ector 2000 Achnanthidium catenatum, A. druartii, Diadesmis confervacea, Didymosphenia geminata, Gomphoneis minuta, Navicula kotschyi y Reimeria uniseriata) i per l'altre, la presència en algunes localitats de diverses formes teratològiques que podrien indicar condicions adverses del medi (estrès químic o contaminació), encara que en alguns casos podrien ser originades simplement per causes naturals. Com a resultat de la determinació de l’estat ecològic de les masses d’aigua s'ha comprovat l'aplicació i funcionament òptim dels índexs de diatomees (Index de Pol•lució Específica IPS, Index Biològic de Diatomees IBD i Index Europeu CEE), sent l'IPS l'índex més convenient per la bioindicació de l'aigua a la conca de l'Ebre. No obstant, aquests índexs no reflecteixen prou bé les diferències entre algunes ecoregions de la conca de l'Ebre, com ara les capçaleres calcàries. Tenint en compte els resultats obtinguts amb l'IPS, la proporció de localitats estudiades que complirien amb la DMA en aquests 2 anys d'estudi són bastant similars, seria del <62% pel 2005 i del <64% pel 2006. Els resultats de l'índex de Shannon & Weaver indiquen que la diversitat i la riquesa específica s'ajusta a un model relacionat amb la qualitat del medi. Les correlacions d'aquests paràmetres respecte a variables ambientals (pH, conductivitat, clorurs, amoni, fosfats, nitrats, TSS, oxigen dissolt, altitud de la localitat, corrent, amplada i fondària del riu) i els resultats dels índexs de diatomees (IPS, IBD i CEE) mostren que la diversitat de les comunitats de diatomees en les localitats estudiades augmenta quan empitjora l'estat ecològic, seguint un gradient marcat principalment per l'altitud i la concentració de nutrients. L'estudi de l'ordenació de les comunitats de diatomees epilítiques en els rius de la conca de l'Ebre, tenint en compte les variables ambientals de les localitats estudiades, mostra que la seva distribució seguiria un gradient capçalera-desembocadura, marcat per l’increment progressiu de la mineralització en el que se superposen els efectes de les variables ambientals que es relacionen amb els impactes i els nutrients. Les anàlisis clúster dels inventaris seleccionats distingeixen 7 grups de localitats i 6 grups ecològics diferents de diatomees que responen a les pertorbacions observades i als gradients de mineralització i eutròfia que caracteritzen la conca de l'Ebre. / "Diatoms of the Ebro basin: Biodiversity and ecological state of water" TEXT: The aim of this PhD thesis is to contribute to the taxonomic knowledge of the epilithic diatom flora from the rivers of the Ebro basin and to determinate the water quality status in the studied area using benthic diatoms as indicators. The studied area is located inside the Water Quality Surveillance Network of the Ebro Water Agency, CHE (NE Spain). It includes the Ebro and Garona rivers and all the rivers and streams which run into them in the Spanish territory, mostly over a calcareous and sedimentary substrata. A total of 408 epilithic diatoms samples were collected from different environments and ecoregions within the limits of the network of the Ebro Water Agency, CHE (NE Spain) during the summers of 2005 (197 sites) and 2006 (211 sites). Epilithic diatom were sampled, and then treated to prepare permanent diatoms slides following the standard methods (European Committee for Standardization 2003, 2004). The number of taxa identified in the material studied amounted to 499 (492 a specific or infra specific level), belonging to 91 different genera. 361 taxa are presented in 751 light microscope micrographs regrouped in 25 plates. We noticed the presence of species considered rare or exotic for European freshwaters (Coste & Ector, 2000) such as Diadesmis confervacea; Achnanthidium catenatum, Reimeria uniseriata, Navicula kotschyi, Gomphoneis minuta and Didymosphenia geminata. A few diatoms species presented teratological forms have been detected in some localities. However, we could not find a direct relationship of these forms occurrence and any particular cause. In order to evaluate the water quality assessment, three diatoms indices were applied (Specific Pollution Index IPS, Biological Diatom Index BDI and European Index CEC). All of them correlated significantly with water physical and chemical variables, but SPI achieved better correlations, and is therefore to be the best diatom index to be applied in the Ebro basin, although in some cases it did not properly reflected special situations in this basin as calcareous headwaters. According to the cluster and canonical correspondence analyses, nutrient enrichment (from the headwaters to the mouth), environmental variables and impacts were to be the most important variables structuring diatom communities in the Ebro basin.

Pollution of aquatic resources in Uganda is on the increase and the trends are expected to increase with increase in population size and urbanisation. Assessment and mitigation of the environmental impacts on water quality and biodiversity have now become necessary. The aim of the study was to integrate invertebrate and fish as bioindicators and fish histopathology as a biomarker in the assessment of water quality deterioration in urban wetlands in Uganda. The integration harnesses the advantages and counteracts the shortcomings of each method and thus builds a more robust diagnostic tool that gives a better view of the impacts to the entire ecosystem. Four endpoints which included, physicochemical variables, benthic macroinvertebrate bioindicators, fish bioindicators and fish histopathology biomarkers were compared between varied effluent-impacted wetlands (Murchison Bay in Kampala, and Kirinya, Masese and Winday Bay in Jinja) and a non-impacted reference wetland (Lwanika in Mayuge). Results from the effluent-impacted sites differed from the less impacted reference site. The two sampling locations at Murchison Bay (inshore and offshore) and one sampling location at Kirinya (inshore), that were highly impacted with urban effluent, showed elevated nutrient levels, low pH, dissolved oxygen and secchi depth readings. This corresponded with low invertebrate taxa and fish species diversity and richness; and severe histopathological responses in liver, gonads and gills of O. niloticus. Sensitive taxa such as ephemeroptera and trichoptera were completely absent while pollution tolerant taxa Chironomus sp, Corbicula and Oligochaeta were present. Also notable was the absence of many native haplochromines and presence of mainly Brycinus sadleri, Oreochromis niloticus and leucostictus. The organs manifested high prevalence of severe inflammatory and regressive changes and higher organ indices that fell within the pathological category. These sites were consistently classified as highly polluted under the four endpoints. The reference site was classified as least polluted while Masese and Winday Bay were moderately polluted. Results suggested that the approach of using invertebrate and fish as bioindicators and the fish histopathology as a biomarker, in relation to water quality physicochemical variables was a useful tool in highlighting the spatial differences in environmental quality.

The Pacific Coastal ecoregion contains large tracts of economically important forest lands that also serve as critical stream habitat for endangered Salmonids. Excessive fine sediment deposition in streams of this region is a major environmental concern in the region but difficult to measure directly. The use of stream invertebrates to monitor fine sediment conditions in streams requires careful consideration of several important factors that complicate their use as bioindicators including high spatial and temporal variability and covariance with other environmental variables. To evaluate the use of stream invertebrates as bioindicators of excessive fine sediment, three hypotheses were tested. The first hypothesis was that invertebrates would be related to broad-scale climate variables (Chapter 2). The second hypothesis was that functional aspects of the invertebrate community would serve as useful indicators of excessive fine sediment condition (Chapter 3). The third hypothesis was that invertebrates in streams with naturally high levels of sediment would be tolerant to fine sediment (<2 mm, Chapter 4). Hypotheses were tested using a temporal data set at two streams in western Oregon, spatial data from 214 sites across the Oregon Coast Range, and in-situ experiment conducted in streams with erosive or resistant geologies. In the temporal study, both invertebrate density and functional traits were positively related to El Nino strength (R2 range = 0.22-0.36, ρ range = 0.008-0.04) and air temperature (R2 range = 0.32-0.49, ρ range = 0.002-0.01). The spatial study identified several environmental and hydrological factors that exhibited strong negative controls on both fine sediment (Mantel r range 0.14-0.25, ρ range = 0.001-0.01) and invertebrate Scrapers (R2 range = 0.11-0.14, ρ range = 0.001-0.04). The result of the experimental study provide evidence that invertebrates in streams with erosive geologies exhibit tolerance to sediment addition when compared to invertebrates in resistant geologies (mean loss=15%, ρ <0.01) and that invertebrate grazing traits were most strongly associated with fine sediment dosing frequency (ρ <0.05). The findings of this research demonstrate the role of geology in shaping invertebrate communities and their functional response to fine sediment addition and identify functional indicators that may be useful in different geologic settings. For environmental managers in the Pacific Coastal ecoregion, these findings are of potential value in assisting with the identification of biologically-relevant changes in stream fine sediment conditions and support efforts to balance economic needs in the region while protecting critical Salmonid habitat.

Thesis (MScConsEcol (Conservation Ecology and Entomology))--Stellenbosch University, 2008. / The great pressures on freshwaters require their conservationists and managers to develop methods to rapidly and accurately assess their condition. Dragonflies are excellent indicators of habitat integrity and are effective organisms for this purpose. However, assessment must be done at the correct spatial scale. My aim here is to optimize the spatial resolution at which species are mapped, using three different concepts and methods in freshwater invertebrate distribution mapping, with special emphasis on IUCN Red Listing. The first is the extent of occurrence (EOO) concept, using the minimum convex polygon, and the second, the area of occupancy (AOO) concept, using IUCN and quaternary catchments. The third approach uses a river layer to compare the suitability of grids as opposed to catchments in mapping. In this study I found that area estimation based on minimum convex polygons should not be encouraged for aquatic organisms. This study also suggests that the IUCN concept of area of occupancy (AOO) should be redefined simply as occurrence, referring to known point-locality presences only and, if future data allow, to known absences. The IUCN extent of occurrence (EOO), for aquatic species, should be defined as ‘the sum of the smallest hydrological units identified of presently known, inferred or projected occurrences of a taxon, excluding cases of vagrancy, that are used to estimate the threat to a taxon’. A single hydrological unit is also the conservation or management unit. Currently, that unit is the quaternary catchment. Dragonflies have excellent potential as indicators of habitat integrity. For this purpose, my aim was to develop the Dragonfly Biotic Index (DBI) for South Africa and compare the DBI to another index, the Average Taxonomic Distinctness Index (AvTD), which was believed to have potential in assessments. The DBI and AvTD are correlated, which suggests that they could be used on a complementary basis to prioritize sites. The DBI is a low-cost, easy-to-use method and is already used for measuring habitat recovery. It has great potential for environmental assessment and monitoring freshwater biodiversity, especially as a complement to freshwater quality assessments that use macroinvertebrate scores. I thus recommend its integration into freshwater management and conservation schemes.

Thesis (MScAgric (Conservation Ecology and Entomology)--University of Stellenbosch, 2005. / A semi-arid country, like South Africa, with unpredictable seasonal rainfall, is subject to great scarcity in water and an ever-increasing demand from the rising human population. Therefore, efficient reservoirs as well as monitoring methods are needed to manage the South African water supply. This study was undertaken on the Eerste River in the Western Cape, South Africa, focusing on the impact of the Klein Plaas dam system on the benthic macroinvertebrates. The study also examined the use of benthic macroinvertebrates as bioindicators of water quality with special reference to the South African Scoring System Version 5(SASS5) that is currently being used nationally. The impoundment of the water, as well as the inter-basin transfer programme and the experimental cage-culture trout farm, all play a significant role in the disturbance impact of the dam on the Eerste River system. The disturbance is manifested as a drop in water quality that can be seen in the distribution of keystone species, changes in the riparian vegetation, as well as in physical-, chemical-, and biomonitoring evaluations. The study also indicated that the SASS5 is effective, but needs some adjustments, such as inclusion of a prediction phase, finer spatial-scale methodologies and greater consideration of the rarity of species.

Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Soil is a fundamental, non-renewable resource in any ecosystem. To uphold food production for increasing global human populations, it is imperative to develop ways in which to sustain healthy biological productivity and sustainability of agricultural soils. Nematodes are one of the most abundant groups of Metazoa occurring in all soils, and form an integral part of the soil food web at several trophic levels. They respond rapidly to changes within their environments, and can easily be extracted from soil, identified and characterised into functional guilds. Nematodes thus have the potential to impart insight into the condition of the soil food web. This study aims to establish whether nematodes will be suitable bio-indicators of soil health for the deciduous fruit industry in the Western Cape. Three different objectives have been set to determine the practical use of nematode community structures as a tool for the measurement of soil health. The objectives include describing the nematode community structure, biodiversity and functionality within Fynbos soils; the characterization of organic and conventional orchards; and the differences in nematode soil communities in differently managed soils in an apple orchard. The number of nematodes in each soil sample was quantified and identified to family level. The nematode biodiversity and functionality for each site was determined by evaluating the nematode food webs for trophic group distribution, as enumerated by the Maturity Index (MI), the Enrichment Index (EI), the Structure Index (SI), the Basal Index (BI) and the Channel Index (CI), based on the weighted abundance of coloniser-persister guilds. The functional guild analysis of Fynbos samples indicated that the enrichment and the structure of any given sample were not bound to a certain area, but it was representative of each of the four quadrats within the faunal analysis. Different geographic areas were found to differ in nematode diversity and functionality, which was mainly associated with dominant plant families and species (such as strong associations between Fynbos families Fabaceae, Solanaceae and Celestraceae with the nematode family Pratylenchidae). The most abundant nematode families present in the Fynbos were Tylenchidae, which are plant-feeding nematodes, and Cephalobidae which are bacterial-feeding nematodes. Despite Tylenchidae and Cephalobidae both having coloniser-persister values (cp-values) of two, they are split up into different feeding types. Cp-2 nematodes are tolerant to disturbances, and occur in all environments. Only one omnivorous family, the Dorylaimida, was identified in Fynbos samples. The average MI value for Fynbos was found to be very low, with a mean value of 1.26. The value obtained indicated the presence of taxa with tolerance to disturbance, which, in turn, indicated the presence of a disturbed soil, in general. The number of plant-parasitic nematodes within the Fynbos soils was low, which was supported by the low plant-parasitic index (PPI) of 0.85. The diversity, richness and evenness values were low, indicating low nematode diversity, but a distribution of abundances amongst the families. The average Hill’s N0 index value was 8.0, indicating that, in general, eight nematode families would have been present in a Fynbos soil sample. A study was done to determine the biodiversity and the functionality of the nematodes associated with deciduous fruit orchards that were conventionally, or organically, managed. Herbivores were dominant in all the orchards. The organic apple orchard had the lowest numbers of herbivores and fungivores, with the highest number of carnivores. When comparing organic and conventional apricot orchards, higher numbers of plant-parasitic nematodes were found in the organic orchard. Criconematidae occurred in higher numbers in conventional apricot orchard soil. When comparing organic apricots and apples, higher numbers of Criconematidae occurred within the organic apple soil. Overall, higher levels of plant-parasitic nematodes occurred in the organic apricot orchard. The MI indicated that all orchard soils had values below 1.5, indicating disturbance. Conventionally managed apricot orchard soil had the highest MI value of 1.48. The PPI value was highest in organically managed apricot orchards. All orchard soils were located within Quadrat B of the faunal analysis, indicating enrichment and structure. Regarding the diversity, richness and evenness of the distribution, conventional apricot soil had the highest species richness, while organic apple soil had the most even family distribution. Different management practices did not show marked differences in community composition and structure. The species richness of Fynbos soils was comparable to those of deciduous fruit orchards. Soil samples from eight different soil surface treatments were collected from an apple orchard in the Grabouw area. Treatments were combined according to the soil surface treatments received (chemical control of cover crops and weeds, mulch and mulch + effective micro-organism spray). Bacterivores were dominant in all soil treatments, with the least number being present in the chemical control (of cover crops and weeds) treatment. Sites which received chemical control of cover crops and weeds had higher levels of fungivores, compared to the levels at the other sites. High numbers of Rhabditidae occurred within mulch and mulch + effective micro-organism (EM) treatment sites, while high numbers of Aphelenchidae occurred in chemical control sites. The carnivorous family Ironidae only occurred in mulch + EM sites. Strong associations were found between soil surface applications and nematode families present within the soil. Chemical control (of cover crops and weeds) applications had the highest MI value, while values were equal for the other soil applications. The faunal analysis indicated that the mulch and the chemical control fell within Quadrat A, indicating enriched, but unstructured, soil, while the mulch + EM treatment fell within Quadrat B, indicating enrichment and structure, as well as good overall soil conditions. All the systems were dominated by bacterial decomposition pathways. Controversially, sites that received chemical control of the cover crops and weeds had the highest species richness of all three applications, as well as the highest level of diversity, according to the Simpson Index. As only the cover crops and the weeds were chemically controlled, the soil can be regarded as undisturbed, which explains the results obtained in this study. Clear differences in nematode community structure and composition were observed between the different soil applications in the apple orchard. / AFRIKAANSE OPSOMMING: Grond is 'n fundamentele, nie-hernubare hulpbron binne enige ekosisteem. Ten einde voedselproduksie vir die toenemende globale menslike bevolking te handhaaf, is dit noodsaaklik om maniere te ontwikkel om gesonde biologiese produktiwiteit en volhoubaarheid van landbougrond in stand te hou. Nematodes is een van die volopste Metazoa in alle gronde en vorm 'n integrale deel van die grond voedsel-web op verskeie trofiese vlakke. Hulle reageer vinnig op veranderinge binne hul omgewings, kan maklik ekstraheer en identifiseer word; en ook maklik in funksionele gildes ingedeel word. Nematodes het ook die potensiaal om insig oor te dra ten opsigte van die toestand van die grond voedsel-web. Hierdie studie het ten doel om vas te stel of nematodes geskikte bio-indikatore van grond gesondheid kan wees spesifiek vir die sagtevrugte bedryf in die Wes-Kaap. Drie verskillende doelwitte is gestel om die praktiese gebruik van nematode populasie samestelling as 'n instrument vir die meting van grond gesondheid te gebruik. Die doelwitte sluit in die nematode populasie samestelling, biodiversiteit en funksionaliteit binne natuurlike Fynbos; organies verboude versus konvensionele boorde; en die verskil in nematode populasie samestelling tussen verskillend behandelde en bestuurde grondpersele binne ʼn appel boord. Die nematode biodiversiteit en funksionaliteit vir elke perseel was bepaal deur die evaluering van die nematode voedselweb vir trofiese groep verspreiding en enumerering deur die Maturity Index (MI) en die Enrichment Index (EI), Strukturele Indeks (SI), Basale Indeks (BI) en Channel Index (CI) wat gebaseer is op die geweegde oorvloed van koloniseerder-persister gildes. Die funksionele gilde vir Fynbos monsters het aangedui dat die verryking en struktuur van enige gegewe perseel nie gebonde is aan ʼn bepaalde gebied nie, aangesien dit verteenwoordig was in elk van die vier kwadrante van die Fauna Analiseerder. Daar is gevind dat verskillende areas verskil in nematode diversiteit en funksionaliteit, wat hoofsaaklik geassosieer was met die dominante plant families en spesies in die omgewing. Die volopste nematode familie wat teenwoordig was in die Fynbos was Tylenchidae, wat plant-voedende nematodes is, en Cephalobidae, wat bakterie-voedend is. Tylenchidae en Cephalobidae het beide ʼn cp-waarde van twee, maar is verdeel in verskillende VIII tipes voedingsgroepe. Die cp-2 nematodes is verdraagsaam vir versteurings en kom in alle omgewings voor. Slegs een omnivoor familie is geïdentifiseer in Fynbos monsters, nl. die Dorylaimidae. Die gemiddelde MI waarde vir Fynbos was laag, met 'n gemiddelde waarde van 1.26. Hierdie waarde is ʼn aanduiding van die teenwoordigheid van taxa met verdraagsaamheid tot versteuring, wat op sy beurt 'n versteurde grond in die algemeen aangedui het. Die aantal plant-parasitiese nematodes binne die Fynbos-gronde was laag, wat ondersteun word deur die lae PPI-waarde van 0.85. Die waardes vir die diversiteit, spesie-rykheid en egaligheid was laag, wat dui op 'n lae nematode diversiteit, maar 'n egalige verspreidings onder families. Die Hill’s N0 indeks waarde was gelyk aan 'n gemiddelde van 8.0 en dui daarop dat in die algemeen agt nematode families teenwoordig sal wees in 'n Fynbos grondmonster. 'n Studie is gedoen om die biodiversiteit en funksionaliteit van nematodes wat verband hou met vrugteboorde wat organies en konvensioneel bestuur is te bepaal. Herbivore was dominant in alle boorde. Organiese appels het die laagste aantal herbivore en fungivore gehad en die hoogste aantal karnivore. Wanneer organiese en konvensionele appelkoosboorde met mekaar vergelyk is, was hoër getalle van plant-parasitiese nematodes gevind in die organiese boord. Criconematidae was teen ʼn groter aantal in die grond van die konvensionele appelkoosboord gevind. Met die vergelyking van organiese appelkose en appels word, is ʼn hoër aantal Criconematidae binne die organiese appelgrond aangetref. In die algemeen was hoër vlakke van plant-parasitiese nematodes gevind in die organiese appelkoosboord. Die MI het getoon dat alle boord waardes laer as 1.5 gehad het, wat daarop dui dat die gronde versteurd is. Die konvensioneel bestuurde appelkoosboord het die hoogste MI waarde gehad met ʼn vlak van 1.48. Die waarde vir die PPI was die hoogste in organies bestuurde appelkoosboorde. Alle boord gronde is geleë binne kwadrant B van die Fauna Analiseerder, wat dui op verryking met struktuur. Met betrekking tot die diversiteit, spesie-rykheid en egaligheid van die verspreiding van families, het konvensionele appelkoos grond die hoogste spesierykheid, terwyl die gronde van die organiese appelboord die mees egalige familie verspreiding vertoon het. Verskillende bestuurspraktyke nie toon nie merkbare verskille in die gemeenskap samestelling en struktuur nie. Die spesie-rykheid van Fynbos gronde is vergelykbaar met dié van sagtevrugte-boorde. Monsters is geneem van agt verskillende grondeoppervlak-behandelings in ‘n appelboord in die Grabouw area. Die behandelings is gekombineer volgens die grond toediening wat dit ontvang het (chemiese beheer van dekgewasse en onkruid, deklaag en ‘n deklaag + effektiewe mikro- IX organismes). Bakterievoedende nematodes was dominant in elke grondoppervlak-behandeling, met die minste teenwoordig in die behandelings wat chemiese beheer van die dekgewasse en onkruid ontvang het. Behandelings wat chemiese beheer van die dekgewasse en onkruid ontvang het, het ook hoër vlakke van fungivore in vergelyking met die ander behandelings. ʼn Hoë aantal Rhabditidae het voorgekom in grondmonsters van die deklaag en die deklaag + EM (effektiewe mikro-organismes) behandeling persele, terwyl ʼn groot aantal Aphelenchidae voorgekom het in chemiese beheer persele. Die predatoriese familie, Ironidae, het slegs voorgekom in persele wat die deklaag + EM behandeling ontvang het. Sterk assosiasies bestaan tussen grond behandeling en nematode families wat in die grond teenwoordig was. Die chemiese beheer behandeling het die hoogste MI waarde getoon, terwyl waardes vir die ander behandelings laer en gelyk was. Die fauna analise het daarop gedui dat die deklaag en chemiese beheer binne kwadrant A is en dus verryk, maar ook ongestruktureerd is. Die deklaag + EM behandeling het binne kwadrant B geval wat aandui op toestande van verryking en struktuur wat 'n goeie algehele grondtoestand tot gevolg gehad het. Al die stelsels is oorbruggingsweë wat oorheers was deur bakteriële ontbinding. Kontroversieel, het persele wat chemiese beheer van die dekgewasse en onkruid ontvang het, die hoogste spesierykheid van al drie behandelings getoon asook die hoogste vlak van diversiteit volgens die Simpson-indeks. Slegs die dekgewasse en onkruid is chemies behandel, nie die grond nie, en dus kan die grond as onversteurd beskou word en die resultate wat verkry is in die studie verklaar. Duidelike verskille in die nematode gemeenskap struktuur en samestelling is waargeneem tussen die verskillende grond behandelings in appel boorde.

Predatory Ground beetles (Coleoptera: Carabidae) and Lady beetles (Coleoptera: Coccinellidae) are two of the most diverse groups found in wheat agroecosystems, globally. These groups are important from both an economic and ecological perspective due to their natural services provision. The effect of wheat agroecosystem management on species diversity, abundance, biomass and composition in South Africa is not yet documented, and there is no existing data indicating which predatory carabid and coccinellid species provides essential ecosystem services and bioindicator roles. Therefore, we examined the effects of organic, conventional and intercropped agroecosystems on ground beetle and lady beetle abundance, dried weight (biomass), composition and diversity. Sampling of wheat agroecosystems was conducted in three systems i.e. organic, conventional and organic intercropped. Post-hoc Tukey test indicated a statistically significant difference between species diversity, biomass and abundance in organic and intercropped systems compared to the conventional systems. Regression analysis indicated significant positive correlation between aphid’s density and predatory carabid and coccinellid beetles in the intercropped systems. Amongst the weather factors temperature influenced aphid density and carabid and coccinellid beetles’ abundance. PCA (Principal Component Analysis) revealed significant positive correlation between individual biomass and cropping system. Conventional system showed a negative correlations with carabid and coccinellid individual biomass. We found that some carabid and coccinellid species can be used to measure the quality of agroecosystems. This study provides a fundamental basis for identification and monitoring of carabid and coccinellid species and their role as bioindicators of ecological disturbance. The identified bioindicator species in this study can assist in developing conservation and biomonitoring strategies within agroecosystems. / Agriculture and  Animal Health / M. Sc. (Agriculture)