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To promote the conservation of aquatic ecosystems, it is essential to delve into restoration techniques for selecting the most sustainable option for combating eutrophication. Hence, we study the effects of novel phosphorus (P) adsorbents (magnetic carbonyl iron particles, HQ, and two non-magnetic P adsorbents: CFH-12® and Phoslock®) on the growth and photosynthetic activity of Chlorella sp. More specifically, the intrinsic photochemical efficiency of PSII (ΦPSII) and the nonphotochemical quenching (NPQ) were measured in Chlorella sp. after different contact times with different concentrations of these adsorbents. Our initial hypothesis was that non-magnetic P adsorbents have more effects on the organisms than magnetic ones. However, our results did not show strong evidence of inhibitory effects caused by HQ nor CFH-12® (no significant effect size on ΦPSII), while Phoslock® showed inhibitory effects on the photosynthetic activity of Chlorella sp. for any of its concentrations (NPQ = 0). Lastly, we compared the effect of the studied P adsorbents in a real application scenery (Honda wetland, Spain). For this study case, it is likely that CFH-12® and HQ doses would not cause any negative effects on photosynthetic efficiency while Phoslock®, by limiting light availability, will drastically reduce it. [ABSTRACT FROM AUTHOR]

Loading, retention, and in-lake cycling of phosphorus (P), nitrogen, silica, and dissolved organic carbon (DOC) were studied 1 year before and 3 years after P-inactivation by aluminum (Al) hydroxide in Danish Lake Nordborg in 2006. Simultaneously, external P loading was reduced by 40% via establishment of precipitation ponds in two inlets. After Al treatment, the internal P loading (sediment P release) during summer declined 90%-94%, owing to adsorption to aluminum hydroxide. Also, silicate regeneration from the sediment was reduced by 69%-76%, and sediment oxygen uptake as well as ammonium release declined markedly. Consequently, lake water total P, dissolved inorganic P, silicate, and DOC decreased by 73%, 97%, 87%, and 46%, respectively. The Secchi depth increased in the summer period during the first post-treatment year, but declined afterwards to pre-treatment levels, even though the mean lake-water total P concentration during summer was reduced from ~240 µg x [L.sup.-1] before treatment to 26-65 µg x [L.sup.-1] in the first three post-treatment years. We conclude that a further reduction in external P loading is needed to obtain the full effect of the Al treatment in Lake Nordborg. Nous avons determine l'apport, la retention et le recyclage au sein meme du lac du phosphore (P), de l'azote, de la silice et du carbone organique dissous (DOC) un an avant et trois ans apres l'inactivation du P par l'hydroxyde d'aluminium (Al) dans le lac Norborg au Danemark en 2006. Au meme moment, la charge externe de P a ete reduite de 40% par l'etablissement d'etangs de sedimentation sur deux tributaires. Apres le traitement a Al, l'apport interne de P (liberation de P par les sediments) durant l'ete a decline de 90-94% a cause de l'adsorption a l'hydroxyde d'aluminium. De plus, la regeneration du silicate a partir des sediments a ete reduite de 69-76% et l'absorption d'oxygene par les sediments de meme que la liberation d'ammonium ont diminue de facon marquee. En consequence, le P total, le P inorganique dissous, le silicate et le DOC ont diminue dans l'eau du lac par respectivement 73%, 97%, 87% et 46%. La profondeur de Secchi s'est accrue durant la periode d'ete de la premiere annee apres le traitement, mais a decru ensuite pour atteindre les valeurs d'avant le traitement, meme si la concentration moyenne de P total a diminue de ~240 µg x [L.sup.-1] avant le traitement a 26-65 µg x [L.sup.-1] dans les trois premieres annees apres le traitement. Nous concluons qu'une reduction supplementaire de l'apport externe de P est necessaire afin d'obtenir le plein effet du traitement a l'Al dans le lac Norborg. [Traduit par la Redaction], Introduction Aluminum (Al) treatment has been widely used as a restoration tool in eutrophic lakes to precipitate phosphorus (P) in the lake water, and to reduce internal P release (e.g., [...]