Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Aquaculture has proven to be a viable operation in multi-used irrigation reservoirs (also referred to as farm
dams) in the Western Cape province (WCP) of South Africa. Many studies found that the fitness-for-use of
these reservoirs for both net cage culture of fish and irrigation of crops is feasible. However, practising
intensive fish farming in existing open water bodies can increase the nutrient levels of the water through
organic loading, originating from uneaten feeds and fish metabolic wastes. Under such conditions the
primary (irrigation) and secondary (drinking water and recreation) usage of the dam could be compromised
by deteriorating water quality. Rainbow trout (Oncorhynchus mykiss) farming is done in Mediterranean
climatic conditions of the WCP. This type of climate presents short production seasons with fluctuating water
quality and quantity. The study investigated the dynamics of water physico-chemical parameters and
assessed the long term impact of rainbow trout farming on irrigation reservoirs. Furthermore, associated
land-use in the catchment of such integrated aqua-agriculture systems is described, and mitigation to
minimise the impact of fish farming evaluated. The investigation concluded with assessing the contribution of
aquaculture to rural and peri-urban communities. The aim is to present an integrated, socio-ecologically
balanced farming system for irrigation reservoirs with associated aquaculture activities. A total of 35 reservoirs, including both fish farming and non-fish farming ones, were selected as research
sites. They were located in three geographical regions namely, Overberg (Grabouw/Caledon), Boland
(Stellenbosch/Franschhoek) and Breede River (Ceres/Worcester). Reservoirs were <20 ha in surface area
and the volume ranges from 300 000 to 1 500 000 m3. Water samples were collected monthly and
seasonally for the different investigations and analysed for a range of water quality parameters, including:
transparency (Secchi disc), temperature, dissolved oxygen (DO), pH, sodium (Na), potassium (K), calcium
(Ca), magnesium (Mg), iron (Fe), chloride (Cl), carbonate (CO3), bicarbonate (HCO3), manganese (Mn),
copper (Cu), zinc (Zn), boron (B), total phosphorous (TP), orthophosphate (PO4), total ammonia nitrogen
(TAN), nitrate-nitrogen (NO3-N), nitrite-nitrogen (NO2-N), aluminium (Al), total suspended solids (TSS), total
dissolved solids (TDS), alkalinity, hardness and sulphate. Phytoplankton samples were also collected,
genera identified and biomass calculated. The water quality data were analysed in terms of surface and
bottom strata in both fish farming and non-fish farming reservoirs based on repeated measurements at the
same site location at different times using the procedure General Linear Models of Stastical Analysis System
(SAS, 2012). Values p<0.05 were considered as statistically significant. A Principal Component Analysis
(PCA) biplot was used to graphically depict all the sites and measured water quality variables with the
purpose of trying to see whether the fish farming and non-fish farming ones showed any groupings and how
the sites were related to the measured variables. Structured questionnaires and informal discussions were
used to collect additional information on the water use, production data and socio-economic effects on fish
farmers. Categorical data gathered from the interviews (21 aquaculture projects) were analysed for
frequency of occurrence using the Statistical Product and Service Solutions (SPSS) computer programme
(SPSS Systems for Windows, Version 12.0). Results are presented in publication form with research
chapters focusing on the subject areas of water quality impact, catchment land-use, potential mitigation
measures and aquaculture contribution.
Results for the water quality analyses indicated that as a collective, the farm reservoirs’ overall minimum, mean and maximum values for the physico-chemical parameters were fit-for-use for trout farming. The depth
of the reservoirs ranged from 1.2 - 21.6 m with the low value taken during the summer season. Values lower
than 5.0 m can cause management problems for floating cages that require a minimum of 4.0 m for net
suspension and 1.0 m of free space below for adequate lateral flow. The Secchi disc reading of the
reservoirs ranged from 10 – 510 cm. Higher transparencies were recorded after the winter rains when sand,
silt and clay settled. Trout feeding is dependent on visibility and transparencies of more than 50 cm are
required for good feeding conditions. The dissolved oxygen (DO) ranged from 0.3 – 16.4 mg/L with values
below 5.00 mg/L recorded during summer when extraction and temperatures were high and provided
conditions unable to sustain trout farming. The situation reverses with the onset of winter when the dams fill
and DO rises above 5.00 mg/L as required for trout farming. The phosphorous (P) levels ranged from 0.001
– 0.735 mg/L. Higher concentrations were recorded during the winter turnover phase when bottom and
surface waters mixed. Concentration above 0.01 mg/L can cause eutrophication of the water bodies. Total
ammonia nitrogen (TAN) ranged from 0.015 - 6.480 mg/L. Higher concentrations were recorded during
summer when temperatures were high and depths were low. TAN can be toxic to fish when the pH and
temperature are high. The generally low least square means (LSM) for TAN were indicative of minor environmental impact of trout
farming operations conducted during the colder, winter rainfall months. Trout farming coincided with
conditions where the water temperatures were low, dam levels were high and dams were overflowing. The
difference in bottom and surface water quality of reservoirs and the site location were found to be more
important than the absence or presence of fish farming. The difference in bottom and surface water is
directly linked to the ecological status of the sediment, which serve as nutrient sinks. In monomictic dams
found in Mediterranean areas, mixing occurs during the winter turnover phase. Nutrients are released due to
surface and bottom water mixing, brought about by torrential rains and wind turbulence. The concentration of
organic material in the sediment and bottom waters is a function of the nutrient loading over time,
irrespective whether the non-point sources were fish farming or agricultural activities and therefore it is
difficult to partition causes and effects. In cases where reservoirs were already eutrophic due to past
agricultural practices, implementing aquaculture could exacerbate the poor water quality status of the
reservoir. There was a statistically significant difference between fish farming and non-fish farming for
phosphorous, Secchi disc, total suspended solids and nitrite-nitrogen (p<0.05) and no statistically significant
difference between fish farming and non-fish farming for dissolved oxygen, total ammonia nitrogen and
nitrate-nitrogen (p>0.05). There was a statistically significant difference between surface and bottom waters
for P and TAN (p<0.05). One reason for higher P and TAN concentrations in bottom waters is the
accumulation of both in the sediment and subsequent release in the water column when the water mixes. A
two-dimensional scatter plot was generated using the score for the first two principal components. The first
two principal components accounts for 40 and 17 % of the total variance respectively, and the two groups of
fish farming and non-fish farming did not separate well based on the first two principal components.
The occurrence and distribution of phytoplankton biomass fluctuated with dam water levels and nutrient
concentrations. The prevailing phytoplankton communities are important to fish farmers for two reasons: 1. It
leads to fluctuations in dissolved oxygen concentrations via users (respiration and decomposition) and
producers (photosynthesis). 2. It could lead to algal taint of fish flesh when geosmin-producing phytoplankton species are present. The frequency of occurrence indicated that the Group Chlorophyta (including genera,
Chlamydomonas, Closterium, Oocystis, Scenedesmus, Staurastrum, Tetraedron, etc) had the most
occurrences (n=371) with Chrysophyta (including genera, Dinobryon, Mallomonas, Synura, etc) the least
(n=34). There was a statistically significant difference between genera occurrence and season (p<0.05). The
geographical location of sites had no significance influence on the frequency of phytoplankton occurrence.
There was no direct link between water quality and production yield (p>0.05). The fish yield of farms were
linked mainly to the quality of fingerlings and the feed conversion ratio (FCR) achieved (p<0.05).
Land-use patterns in the catchment where fish farming dams were located have shown that the dams are
multiple-used systems. The ecological integrity of the farm dam ecosystem is dependent on the base
volume. The dam is primarily for irrigation and fish farming can be compromised when higher demand for
water is required during the dry season. The dams receive about 20 % of its water from rainfall and the rest
from runoffs. Farmers could not provide accurate extraction rates making it difficult to predict water levels for
future fish production.
Four potential mitigation measures to reduce nutrient loading were described namely, feed management
(quantity, frequency, type, etc.), feeding method (demand feeders, hand feeding), feed ingredients
(formulation) and floating gardens. Both feed management procedures and demand feeders were evaluated
as to the efficiency of reducing feed wastage and optimising FCR’s. The small-scale fish farmers were
producing approximately 6 tons and had an average FCR of 1.96:1 ± 1.15. If farmers could improve their
FCR’s by 0.1 (i.e. from 1.96 to 1.86), it would translate into a reduction of 100 kg feed for every ton of fish
produced and result in 5% decrease in nutrient loading. The results of the water analysis and visual
assessment of faecal length and colour showed no statistically significant difference between treatments for
the guar-gum based binder (p>0.05). In addition, the level of binder did not influence digestibility of the
experimental diets.
The floating garden study indicated that it was feasible to construct a low cost raft system that is easy to
manage and can produce plant crops as a hydroponic system in conjunction with fish farming cages. The
lettuces grown on farm dam water provided support for the premise that the water quality can be improved
via extraction of nutrients for crop production. For the production of 3.5 kg/m2 lettuce, a ratio of 1.09
plants/fish equal to 1.84 g feed/day/plant would reduce the accumulation of soluble nutrients around floating
net cage farming system. The socio-economic evaluation of the contribution of fish farming to the welfare of rural and peri-urban
farming communities supported the notion that aquaculture can lead to the upliftment of participating
communities. Seventy-one percent (71%) of the respondents indicated that their motivation for exploring
aquaculture is to supply fish to the wholesale market in order to generate income. Sixty-one percent (61%) of
the respondents conducted the sales themselves or co-opted family members to assist them. The
contribution of aquaculture provided direct benefits through improvement in household income, subsistence
food supply and skills development. Indirect benefits included providing an information hub for other
emerging farmers, elevation of the fish farmer’s status in the community through greater wealth and
knowledge creation and promoting sector diversification through new products and technology. The three main constraints to the promotion and growth of aquaculture were listed as lack of government support,
insufficient market intelligence and access, and limited choice in the availability of suitable candidate
aquaculture species.
Irrigation reservoirs in the WCP have a history of enrichment through external sources supplying water via
agricultural runoff (fertilisers and pesticides), catchment runoff (leaf litter and organic debris) and stormwater
effluent (grey and black water). The incorporation of aquaculture into such dams adds extra nutrients to the
water column and management is crucial to limit the nutrient loading and ensure environmental
sustainability. Such an approach will ensure that commercial land-based crop farmers’ irrigation regime and
water distribution operations would not be negatively affected. Therefore future research needs should focus
on; firstly the prevention and minimisation of pollution deriving from aquaculture through improved production
management and technology transfer, secondly the monitoring and evaluation of the catchment ecosystem
as a continuum with all the external factors affecting the ecology of farm dams and thirdly, evaluating the
sediment processes and dynamics as sinks for nutrient accumulation. / AFRIKAANSE OPSOMMING: Akwakultuur het getoon dat dit ‘n lewensvatbare inisiatief is vir meerdoelige-gebruik van besproeiingsdamme
(ook genoem plaasdamme) in die Wes-Kaap provinsie (WKP) van Suid-Afrika. Vele studies het bewys dat
die geskiktheid-vir-gebruik van die reservoirs haalbaar is vir beide visproduksie sowel as besproeiing van
landbougewasse. Nieteenstaande, die beoefening van intensiewe visboerdery in bestaande buitelug
watersisteme kan lei tot ‘n toename in nutriëntvlakke van die water as gevolg van organiese belading
afkomstig van ongevrete voere en metaboliese afvalstowwe van die vis. Onder sulke omstandigthede kan
die primêre- (besproeiing) en die sekondêre (drinkwater en rekreasie) gebruik van die dam in gedrang kom
weens ‘n afname in waterkwaliteit. Reënboogforel (Oncorhynchus mykiss) boerdery word beoefen in die
omliggende Mediterreense klimaat van die WKP. Die tipe klimaat verskaf kort produksie-seisoene met
wisselvallige water kwaliteit en kwantiteit. Die studie het die dinamika van water se fisies-chemiese
parameters ondersoek en het die impak van forelboerdery op besproeiingdamme oor die langtermyn beskryf.
Verder het die studie die geassosieerde landgebruik in die opvangsgebied met geïntegreerde akwa-landbou
sisteme beskryf, asook moontlike toetrede (mitigasie maatreëls) geëvalueer wat die impak moontlik kan
verlaag. Die ondersoek is afgesluit deur die bydrae wat akwakultuur lewer aan landelike en semi-stedelike
gebiede, te beskryf. Die hoofdoel is die daarstelling van ‘n geïntegreerde, sosio-ekologiese gebalanseerde
sisteem vir besproeiingdamme met gesamentlike akwakultuuraktiwiteite. ‘n Totaal van 35 besproeiingsdamme, insluitend die met visboerdery en nie-visboerdery, is gekies as
navorsingspersele. Dit is hoofsaaklik geleë in drie geografiese gebiede naamlik, Overberg
(Grabouw/Caledon), Boland (Stellenbosch/Franschhoek) en Breederivier (Ceres/Worcester). Die reservoirs
is almal < 20 ha in oppervlakarea en die volumes het gewissel van 300 000 – 1 500 000 m3. Watermonsters
is maandeliks sowel as seisoenaal versamel vir die onderskeie ondersoeke en ontleed vir ‘n reeks van
parameters, insluitend: sigbaarheid (Secchi disc), temperatuur, opgeloste suurstof (OS), pH, natrium (Na),
kalium (K), kalsium (Ca), magnesium (Mg), yster (Fe), chloor (Cl), karbonaat (CO3), bikarbonaat (HCO3),
mangaan (Mn), koper (Cu), sink (Zn), boor (B), totale fosfor (TP), ortofosfaat (PO4), totale ammoniak stikstof
(TAN), nitraat-stikstof (NO3-N), nitriet-stikstof (NO2-N), aluminium (Al), totale gesuspendeerde vaste stowwe
(TGV), totale opgeloste vaste stowwe (TOV), alkaliniteit, hardheid en sulfate. Phytoplanktonmonsters is ook
versamel, genera geïdentifiseer en die biomassa bepaal. Die waterkwaliteitsdata is ontleed in terme van
oppervlak- en bodemstrata vir beide visboerdery en nie-visboerdery reservoirs en was gebaseer op
herhaalde metings by dieselfde perseel op verskillende tye deur gebruik te maak van die Algemene Liniêre
Model van Statistiese Analitiese Sisteem (SAS, 2012). Waardes p<0.05 is oorweeg as statisties beduidend.
‘n Hoofkomponentanalise bi-stipping (HKA) is toegepas om die persele en veranderlikes grafies voor te stel
en te bepaal of die visboerdery en nie-visboerdery s’n enige groeperinge vorm asook hoe die persele
assosieer met die veranderlikes. Gestruktureerde vraelyste en informele besprekings is onderneem om
inligting in te samel op watergebruik, produksie-data, en die sosio-ekonomiese invloed wat akwakultuur bied
aan visboere. Kategoriese data wat deur die onderhoude (21 akwakultuurprojekte) ingesamel is, is ontleed
vir die frekwensie van aanwesigheid deur die gebruik van Statistiese Produk en Dienste-oplossings (SPDO)
rekenaarprogram (SPSS Systems for Windows, Version 12.0). Die resultate vir die verskeie ondersoeke is
beskryf en saamgestel in publikasie-vorm met die navorsingshoofstukke wat gefokus het op die areas van
waterkwaliteitsimpak, opvangsgebied landgebruik, toetrede-meganismes en die bydrae van akwakultuur. Die resultate vir die waterkwaliteitsanalises het getoon dat gesamentlik die reservoirs se oorhoofse
minimum, gemiddelde en maksimum waardes vir die verskillende fisies-chemiese parameters geskik is vir
forelboerdery. Die diepte van die reservoirs het gewissel van 1.2 - 21.6 m, met die laagste waarde
aangeteken gedurende die somermaande. Waardes laer as 5.0 m kan bestuursprobleme vir drywende
hokstelsels versoorsaak want ‘n minimum van tenminste 4.0 m vrye spasie onder die hokke word benodig vir
voldoende laterale vloei. Die Secchi-skyf lesing (sigbaarheid) van die reservoirs het gewissel van 10 – 510
cm. Hoër sigbaarheidswaardes is aangeteken na winterreëns wanneer sand-, slik- en klei deeltjies uitgesak
het. Forel voer op sig en sigbaarheid van > 50 cm word benodig om goeie voeding te handhaaf. Die OS het
gewissel van 0.3 – 16.4 mg/L met waardes onder 5 mg/L aangeteken gedurende somer wanneer
wateronttrekking en temperature hoog was. Dit het gelei tot ongunstige toestande vir forelboerdery. Die
situasie swaai om met die begin van winter wanneer die damme vol reën en die OS bo 5 mg/L styg soos
benodig vir forelboerdery. Die P-vlakke het gewissel van 0.001 – 0.735 mg/L. Hoër waardes is aangeteken
gedurende die winteromkeerfase wanneer die bodem en oppervlak se water meng. Konsentrasies bo 0.01
mg/L kan tot eutrofikasie van watersisteme lei. TAS het gewissel van 0-015 – 6.480 mg/L. Hoër
konsentrasies is aangeteken gedurende die somer wanneer temperature hoog is en damvlakke laag. By hoë
pH’s en temperature kan TAS toksies wees vir vis. The algemene lae kleinste kwadaat gemiddelde (KKG) waarde vir TAS het getoon dat daar ‘n klein impak op
die omgewing was wanneer forelboerdery bedryf word gedurende die koue, winter reënvalmaande.
Forelboerdery val saam met omstandigthede wanneer die watertemperature laag is, damvlakke hoog en die
reservoirs oorloop. Die verskil in die bodem- en oppervlak water in die besproeiingsdamme en die ligging
van die perseel is vasgestel om meer belangrik te wees as die teenwoordigheid of afwesigheid van
visboerdery. Die verskil in die bodem en oppervlak is toe te skryf aan die toestand van die sediment waar
nutriënte kan opgaar. In monomiktiese damme soos gevind in Mediterreende areas, vind vermenging plaas
gedurende die winteromkeerfase. Nutriënte word vrygestel a.g.v. die vermenging van die oppervlak en
bodem se water wat dan veroorsaak word deur harde reën en windturbulensie. Die konsentrasie van
organiese materiaal in die sediment en bodem water is ‘n funksie van die nutriëntlading met tyd, ongeag of
dit afkomstig was vanaf visboerdery of landbou-aktiwiteite. Dit is dus moelik om die spesifieke oorsaak van
besoedeling af te baken. In gevalle waar die reservoirs alreeds eutrofies is a.g.v. aangewese landbouaktiwiteite,
kan die toestand van die waterbron vererger indien akwakultuur toegepas word. Daar is ‘n
statistiese noemenswaardige verskil tussen visboerdery en nie-visboerdery vir P, Secchi-skyf, totale
gesuspendeerde vaste stowwe en nitrite-stikstof (p<0.05), en geen statistiese noemenswaardige verskil
tussen visboerdery en nie-visboerdery vir OS, TAS en nitraat-stikstof (p>0.05). Daar is ‘n statistiese
noemenswaardige verskil tussen oppervlak- en bodem water vir P en TAS (p<0.05). Een moontlike rede vir
hoër P en TAS konsentrasies in die bodemwater, is die akkumulasie van beide parameters in die sediment
en gevolglike vrystelling in die waterkolom wanneer die water gemeng word. ‘n Twee dimensionele
spreidingstipping is geprodueer deur die waardes te gebruik van die eerste twee hoofkomponente. Die
eerste twee hoofkomponente dra by 40 % en 17 % van die totale variansie onderskeidelik, en die twee
groepering van visboerdery en nie-visboerdery het nie duidelik getoon nie.
Die voorkoms en verspreiding van phytoplankton biomassa het gewissel met die verandering in damvlakke
en nutriëntkonsentrasies. Die aanwesige phytoplanktongemeenskappe is belangrik vir die visboer vir twee redes: 1. Dit kan wisselende OS-vlakke versoorsaak deur die verbruik (respirasie en dekomposisie) en
produksie (fotosintese) daarvan. 2. Dit kan lei tot alge na-smake van vis wanneer geosmin-produserende
phytoplankton spesies aanwesig is. The frekwensie van voorkoms het getoon dat die Groep Chlorophyta
(insluitend die genera, Chlamydomonas, Closterium, Oocystis, Scenedesmus, Staurastrum, Tetraedron,
ens.) die meeste voorkom (n=371), met Chrysophyta (insluitend die genera, Dinobryon, Mallomonas,
Synura, ens.) die minste (n=34). Daar is ‘n statistiese noemenswaardige verskil tussen genera voorkoms en
seisoen (p<0.05) vir phytoplankton. Die geografiese ligging van die perseel het geen noemenswaardige
invloed op die frekwensie van phytoplankton voorkoms nie. Daar is geen statistiese noemenswaardige
verbintenis tussen waterkwaliteit en visproduksieopbrengste nie (p>0.05). Die visopbrengste by plase is
hofsaaklik afhangende van die kwaliteit van die vingerlinge en die voeromsettingsverhouding (VOV) wat
bereik is (p<0.05).
Die landgebruikspatrone in die opvangsgebied waar visboere gesetel is, het aangedui dat die
besproeiingsdamme meeldoelige sisteme is. Die ekologiese integriteit van die plaasdam-ekosisteem is
afhanklik van die basisvolume. Die dam is hoofsaaklik daar vir die besproeiing en visboerdery kan in
gedrang kom wanneer daar ‘n hoër aanvraag vir water gedurende die droë seisoen is. Die damme het
omtrent 20 % van die water vanaf reënval ontvang en die res van aflope. Boere kon nie akkurate inligting
verskaf van waterontrekking nie wat dit moeilik gemaak het om te voorspel wat die beskikbare watervlakke in
die toekoms sou wees vir visproduksie.
Vier potensiële toetrede meganismes om die nutriëntlading te verminder, is beskryf naamlik
voedingsbestuur, (kwantiteit, frekwensie, tipe, ens.) voermetodes (aanvraagvoeder, handvoeding),
voerbestandele (formulasies) en drywende tuine. Beide voedingsbestuur prosedure en aanvraagvoeders is
geëvalueer as ‘n metode om die voervermorsing te verminder en die VOV te verbeter. Die kleinskaalse
visboere het ongeveer 6 ton produseer met ‘n gemiddelde VOV van 1.96:1 ± 1.15. Indien die visboere hul
VOV’s met 0.1 kan verbeter (bv. van 1.96 tot 1.86), sal dit beteken dat daar ‘n vermindering van 100 kg voer
bewerkstellig word vir elke ton vis geproduseer. Dit kan ook lei tot ‘n vermindering van 5 % in die
nutriëntlading. Die resultate van die wateranalises en die visuele waarneming van faeceslengte en kleur het
geen statistiese noemenswaardige verskil tussen die behandelinge vir die guar-gom binder getoon nie
(p>0.05). Verder, die hoeveelheid van die binder het nie die vertering van die eksperimentele diëte beïnvloed
nie. Die studie op die drywende tuine het getoon dat dit haalbaar is om ‘n lae-koste sisteem te bou wat maklik is
om te bestuur en gewasse kan produseer soos in ‘n hidroponiese sisteem tesame met visproduserende
hokstelsels. Die kropslaaie se groei het getoon dat die waterkwaliteit van besproeiingsdamme kan verbeter
word deur die opname van nutriënte wanneer plante verbou word. Vir die produksie van 3.5 kg/m2
kropslaaie, sal ‘n verhouding van 1.09 plante/vis of 1.84 g voer/dag/plant die akkumulasie van opgeloste
nutriënte rondom die hokstelsels verminder.
Die sosio-ekonomiese evaluasie van die bydrae van visboerdery tot die welvaart van die landelike en semistedelike
plaasgemeenskappe ondersteun die feit dat akwakultuur verbetering kan bewerkstellig, veral onder
deelnemende gemeenskappe. Een-en sewentig persent (71 %) van die respondente het getoon dat hul oorweging vir die bedryf van akwakultuur is om vis te voorsien aan die grootmark en daarvolgens geld te
maak. Een-en-sestig persent (61 %) van die respondente het aangedui dat hulself die vis verkoop of vir
familie-lede vra om met die verkope te help. Die bydrae van akwakultuur het direkte voordele aan die
deelmers voorsien deur ‘n verbetering in huishoudelike inkomste, voedselvoorsiening vir selfgebruik en die
ontwikkeling van vaardigthede. Indirekte voordele sluit in dat die deelmers ‘n bron van inligting geword het vir
opkomende boere, hul status in die gemeenskap het verbeter omdat hul kennis verbreed het en dit het
verder gelei tot diversifisering in die sektor a.g.v. die skepping van nuwe produkte en tegnologie. Die drie
hoof struikelblokke wat die groei en bevordering van akwakultuur belemmer is o.a., ‘n tekort aan
staatsondersteuning, onvoldoende markinligting en toegang en ‘n beperkte keuse in spesies vir boerdery.
Besproeiingsdamme in die WKP het ‘n geskiedenis van verryking deur eksterne bronne wat water voorsien
vanaf landbou-afloop (bemestingstowwe en pesbestrydingsmiddels), opvangsgebied-afloop (blare en ander
organiese debris) en stormwateruitlaat (gruis- en swart water). Die implementering van akwakultuur in sulke
damme voeg addisionele nutriënte tot die waterkolom en bestuur is krities om die lading te verminder en te
verseker dat omgewingsvolhoubaarheid behou word. Indien die regte praktyke en bestuur toegepas word,
sal dit beteken dat die kommersiële boer se besproeiing en waterverspreiding nie negatief beïnvloed word
nie.
Vervolgens moet toekomstige navosingsbehoeftes fokus op eerstens, die voorkoming en vemindering van
besoedeling afkomstig van akwakultuur deur verbeterde produksie-bestuur en tegnologie-oordrag,
tweedens, die monitoring en evaluering van die opvangs-ekosisteem as ‘n kontinuum met al die eksterne
faktore wat die ekologie van die plaasdam kan beïnvloed en laastens, die ondersoek en evaluering van die
sediment se prosesse en dinamika as ‘n sisteem wat nutriënte ophoop.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86432 |
| Date | 04 1900 |
| Creators | Salie, Khalid |
| Contributors | Rana, Krishen, Brink, Danie, Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xxvii, 162 p. : col. ill., col. maps. |
| Rights | Stellenbosch University |
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