{"id":15335,"date":"2026-05-21T11:02:11","date_gmt":"2026-05-21T11:02:11","guid":{"rendered":"https:\/\/www.proefschriftmaken.nl\/portfolio\/yuxin-shi\/"},"modified":"2026-05-21T11:02:30","modified_gmt":"2026-05-21T11:02:30","slug":"yuxin-shi","status":"publish","type":"us_portfolio","link":"https:\/\/www.proefschriftmaken.nl\/en\/portfolio\/yuxin-shi\/","title":{"rendered":"Yuxin Shi"},"content":{"rendered":"","protected":true},"excerpt":{"rendered":"","protected":true},"author":7,"featured_media":15336,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"us_portfolio_category":[45],"class_list":["post-15335","us_portfolio","type-us_portfolio","status-publish","post-password-required","hentry","us_portfolio_category-new-template"],"acf":{"naam_van_het_proefschift":"Dual nitrogen and phosphorus control for mitigating eutrophication and cyanobacterial blooms","samenvatting":"Eutrofi\u00ebring, veroorzaakt door overmatige belasting met voedingsstoffen, blijft een grote uitdaging voor zoetwaterecosystemen wereldwijd. Zelfs met een vermindering van de externe aanvoer van nutri\u00ebnten, vereisen sommige meren nog steeds aandacht voor de interne beheersing van voedingsstoffen. Verschillende chemicali\u00ebn, zoals geo-engineering materialen, zijn gebruikt om fosfaat in de waterkolom te immobiliseren en het uit het sediment vrijkomende fosfaat te verminderen, met als doel de biologische beschikbaarheid van fosfaat voor cyanobacteri\u00ebn te beperken. Hun effectiviteit is ge\u00ebvalueerd op laboratorium-, mesocosm- en veldschaal. Dit proefschrift onderzocht de haalbaarheid van geo-engineering materialen bij het verzachten van eutrofi\u00ebring en cyanobacteri\u00eble bloei door zowel interne stikstof (N) als fosfor (P) te beheersen in gecontroleerde experimenten, en door de langetermijneffectiviteit van uitsluitend P-beheersing te monitoren in een interventie op het schaalniveau van een heel meer.\n\nHet onderzoek begon met de evaluatie van de bindingscapaciteiten voor opgelost reactief fosfaat (SRP) en ammonium (NH\u2084\u207a-N) van verschillende geo-engineering materialen, waaronder lanthaan-gemodificeerd bentoniet (LMB), commercieel bekend als Phoslock\u00ae, lanthaan-gemodificeerd zeoliet (LMZ), aluminium-gemodificeerd zeoliet (AMZ), commercieel bekend als Aqual-PTM, natuurlijk zeoliet (NZ) en hun combinaties. De resultaten (Hoofdstuk 2) lieten zien dat de combinatie van NZ en LMB (NZ+LMB), evenals AMZ alleen, effectief zowel SRP als NH4+-N kan binden en beide fluxen uit het sediment kan verminderen. In een opgeschaald experiment (Hoofdstuk 3) bleken NZ+LMB, NZ+PAC (NZ gecombineerd met poly-aluminiumchloride) en AMZ zeer effectief in het onderdrukken van sedimentfluxen. Op lanthaan gebaseerde producten zoals Zeofixer\u00ae zetten mobiel P om in stabielere vormen in de bovenste sedimentlaag.\n\nIn Hoofdstuk 4 werd de rol van de beschikbaarheid van nutri\u00ebnten bij de groei en toxiciteit van Microcystis aeruginosa bestudeerd. Het verminderen van de N-beschikbaarheid verminderde de biomassa van M. aeruginosa effectief. Het beperken van P-beschikbaarheid bleek echter niet effectief zodra de biomassa reeds aanwezig was, vanwege de interne opslagcapaciteit van de cellen (luxezuivering). Daarom wordt geadviseerd om P-binders zoals LMB en NZ v\u00f3\u00f3r het groeiseizoen toe te passen.\n\nTen slotte evalueerde Hoofdstuk 5 de veldtoepassing van de \"Floc & Lock\"-interventie in de De Kuil-plas (Nederland). De interventie verminderde de P-concentraties gedurende ten minste vier jaar effectief, maar de plas keerde uiteindelijk terug naar een eutrofe toestand door aanhoudende nutri\u00ebnteninvoer via het grondwater en interne belasting. Hoofdstuk 6 concludeert dat een systeemanalyse van individuele meren essentieel is voor succesvol herstel, aangezien elk meer uniek is en een op maat gemaakte aanpak vereist.","summary":"Eutrophication, driven by excessive nutrient loading, remains a major challenge for freshwater ecosystems worldwide. Even with reductions in external nutrient inputs, some lakes still require attention to internal nutrient control. Several chemicals, such as geo-engineering materials, have been used to immobilize phosphate in the water column and reduce phosphate released from sediment, with the aim of reducing phosphate bioavailability to cyanobacteria. Their effectiveness has been evaluated across laboratory, mesocosm, and field in-lake application scales. This thesis investigated the feasibility of geo-engineering materials in mitigating eutrophication and cyanobacterial blooms by controlling both internal N and P in controlled experiments, and by monitoring the long-term effectiveness of P-only control in a whole-lake intervention.\n\nThis thesis started by evaluating the soluble reactive phosphate (SRP) and ammonium (NH\u2084\u207a-N) binding capacities of several geo-engineering materials, including lanthanum-modified bentonite (LMB), commercially called Phoslock\u00ae, lanthanum-modified zeolite (LMZ), aluminium-modified zeolite (AMZ), commercially called Aqual-PTM, natural zeolite (NZ) and their combinations. The effectiveness of the best-performing materials and their combinations was subsequently tested in an up-scaled sediment core experiment to evaluate the N and P fluxes from the sediment. (Chapter 2). The results showed that the combination of NZ and LMB (NZ+LMB), as well as AMZ, can effectively bind both SRP and NH4+-N, and reduce both P and N fluxes from the sediment. Furthermore, the presence of co-existing cations reduced the NH\u2084\u207a-N binding capacity of NZ as a result of competitive interactions. Therefore, the effectiveness of NZ in reducing NH\u2084\u207a-N under natural environmental conditions should be further evaluated.\n\nIn the up-scaled experiment, several geo-engineering materials were applied to sediment corer to evaluate their effectiveness in controlling P and N release from sediment. The geo-engineering materials included the NZ+LMB, AMZ, poly-aluminium chloride (PAC) combined with NZ (NZ+PAC), and a novel lanthanum modified clay (LMC), which commercially known as LimnoPlus in Europe and named Zeofixer\u00ae by the manufacturer. Furthermore, sediment characteristics were analyzed after treatment to assess whether P and N were stably retained within the sediment (Chapter 3). We found that NZ+LMB, NZ+PAC and AMZ were all highly effective in reducing both SRP and NH4+-N sediment fluxes, while AMZ had a higher N reduction efficiency than NZ+LMB and NZ+PAC. In addition, applying La-based products can transform mobile P into more stable forms in the upper sediment layer, whereas NZ and AMZ effectively adsorbed NH\u2084\u207a-N from both overlying water and porewater.\n\nIn Chapter 4, the role of nutrient availability in regulating Microcystis aeruginosa growth and toxicity was studied by manually reducing SRP and NH\u2084\u207a-N concentrations and by applying NZ and\/or LMB. Decreasing N availability, either manually or through NZ application, effectively reduced M. aeruginosa biomass. While manually decreased N availability lowered the intracellular microcystin (MC) concentration, the decreasing trend with lower N availability was less distinct when NZ was applied. However, increasing N concentrations had a significantly negative impact on the intracellular MCs\/chlorophyll-a ratio under both N reduction approaches. Decreasing P availability, either manually or through the application of LMB, did not effectively reduce M. aeruginosa biomass and intracellular MC concentration when the biomass has present. Therefore, we recommended that LMB and NZ be applied before the growing season to improve cost efficiency. In addition, the results showed that M. aeruginosa preferentially utilizes NH\u2084\u207a-N, leading to a higher maximum chlorophyll-a concentration compared to treatments using NO\u2083\u207b-N as the N source. However, further studies are needed to determine whether targeting NH\u2084\u207a-N alone is sufficient to effectively achieve N limitation, and whether desorbed NH\u2084\u207a-N from NZ may support continued cyanobacterial growth.\n\nFinally, Chapter 5 evaluated the long-term field application of the \"Floc & Lock\" intervention combining PAC with LMB, in Lake De Kuil in the Netherlands. This intervention represented the second application in Lake de Kuil, as the lake returned to a eutrophic state eight years after the first intervention due to ongoing nutrient inputs. The second intervention effectively suppressed internal P release, reducing P and chlorophyll-a concentrations in the water column for at least four years. However, the treatment did not significantly influence internal N loading. Since 2020, the lake gradually returned to a eutrophic state due to continued nutrient inputs from groundwater on the eastern and southern sides and consistently internal nutrient load. Therefore, controlling external nutrient sources is essential before implementing repeated in-lake measures to address internal loading.\n\nIn Chapter 6, the findings contribute to optimizing nutrient management strategies for eutrophication control, highlighting the importance of material selection, dosing flexibility, and timing of application for long-term ecological restoration. Each lake is unique, and a system analysis of individual lakes is the initial step in managing eutrophication and cyanobacterial blooms. The system analysis will reveal what is best to do and will guide in choosing the most promising measures. Prior to implementing such measures in-situ, comprehensive experiments should be conducted to test their effectiveness, safety, dose needed and cost.","auteur":"Yuxin Shi","auteur_slug":"yuxin-shi","publicatiedatum":"15 juni 2026","taal":"EN","url_flipbook":"https:\/\/ebook.proefschriftmaken.nl\/ebook\/yuxinshi?iframe=true","url_download_pdf":"https:\/\/ebook.proefschriftmaken.nl\/download\/0d5f29c1-7065-48ca-87ef-d093ca32fb5f\/optimized","url_epub":"","ordernummer":"18806","isbn":"978-94-6534-409-6","doi_nummer":"","naam_universiteit":"Wageningen University","afbeeldingen":15337,"naam_student:":"","binnenwerk":"","universiteit":"Wageningen University","cover":"","afwerking":"","cover_afwerking":"","design":""},"_links":{"self":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/15335","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio"}],"about":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/types\/us_portfolio"}],"author":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/users\/7"}],"replies":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/comments?post=15335"}],"version-history":[{"count":1,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/15335\/revisions"}],"predecessor-version":[{"id":15338,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio\/15335\/revisions\/15338"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/media\/15336"}],"wp:attachment":[{"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/media?parent=15335"}],"wp:term":[{"taxonomy":"us_portfolio_category","embeddable":true,"href":"https:\/\/www.proefschriftmaken.nl\/en\/wp-json\/wp\/v2\/us_portfolio_category?post=15335"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}