The effects of irradiance and photoperiod on the growth rate of three freshwater green algae isolated from a eutrophic lake

In order to optimise algal growth in mass culture systems, the effect of irradiance and photoperiod on the growth rate of three freshwater green algae isolated from an eutrophic lake (Selenastrum minutum, Coelastrum microporum f. astroidea and Cosmarium subprotumidum) were studied in non axenic batch cultures, under non-nutrient limited conditions. Experiments were performed to determine a specific growth rate (μ max) and optimum light (Iopt) over a wide range of light intensities (30 to 456 μmol m2 s−1) at a temperature of 30◦ C, using a 15/9 (light/dark) photoperiod cycle. The maximum growth rates and optimum light intensities were 1.55 d−1 and 365 μmol m−2 s−1 for Selenastrum minutum, 1.59 d−1 and 390 μmol m−2 s−1 for Coelastrum microporum f. astroidea 0.88 d−1 and 360 μmol m−2 s−1 for Cosmarium subprotumidum. The photoperiod's effect was determined at 30◦ C and an incident light of 300 μmol m−2 s−1, under various light:dark cycles. The experimental values fitted by models of Belkoura et Dauta (1992) indicate an increase in the growth rate versus day length with a maximum at continuous light (1.84 d−1 for Selenastrum minutum, 1.72 d−1 for Coelastrum microporum f. astroidea, 0.88 d−1 for Cosmarium subprotumidum). However these experiments don't take into account the accumulated light intensities received by each culture (period of incubation: 24 hours). It was, therefore, not possible to independently appraise the real effect of the lengthened irradiance exposure. So more experiments were carried out, where all cultures under different (light/dark) photoperiod cycles at 30◦ C received the same cumulated irradiance (8.6 mol m−2 d−1). The results showed that the growth rate is not constant but increased with day length with a maximum at continuous light. These results confirm the real effect of photoperiod on the microalgae growth rate.Con objeto de optimizar el crecimiento algal en cultivos de producción masiva, se han estudiado, en cultivos no estériles y sin limitación de nutrientes, el efecto de la irradiancia y el fotoperiodo sobre la tasa de crecimiento en tres algas de agua dulce de un lago eutrófico (Selenastrum minutum, Coelastrum microporum f. astroidea and Cosmarium subprotumidum). Los experimentos fueron diseñados para determinar una tasa de crecimiento específica (μ max) y un óptimo de luz (Iopt) en un amplio rango de intensidades de luz (30 a 456 μmol m−2 s−1), a 30◦ C de temperatura y utilizando ciclo de fotoperiodo 15/9(luz/oscuridad). Las tasas máximas de crecimiento y las intensidades de luz óptimas fueron 1.55 día−1 y 365 μmol m−2 s−1 para Selenastrum minutum, 1.59 día−1 y 390 μmol m−2 s−1 para Coelastrum microporum f. astroidea y 0.88 día−1 y 360 μmol m−2 s−1 para Cosmarium subprotumidum. El efecto del fotoperiodo se determinó a 30◦ C y luz incidente de 300 μmol m−2 s−1, bajo varios ciclos luz:oscuridad. Los valores experimentales se ajustaron mediante modelos Belkoura y Dauta (1992) e indican un incremento en la tasa de crecimiento en relación con la duración del día, con un máximo a luz continua (1.84 día−1 for Selenastrum minutum, 1.72 día−1 for Coelastrum microporum f. astroidea, 0.88 día−1 for Cosmarium subprotumidum). No obstante, estos experimentos no tuvieron en cuenta las intensidades de luz acumulada recibidas por cada cultivo (periodo de incubación de 24 horas). Además, no fue posible apreciar de forma independiente el efecto real del tiempo de exposición de la irradiancia. Por ello se realizaron otros experimentos en los que todos los cultivos bajo diferentes ciclos de fotoperiodo (luz/oscuridad) y a 30◦ C, recibieron la misma irradiancia acumulada (8.6 mol m−2 d'ıa−1). Los resultados confirmaron el efecto real del fotoperiodo sobre la tasa de crecimiento de las microalgas

Water quality and water-use conflicts in Lake Taabo (Ivory Coast)

The Lake Taabo (Ivory Coast, Africa) results of the construction of the Taabo dam on the Ban- dama River. The changes in the water level of the 69-km² lake depend on 1) the rainfall linked to alternating dry/wet seasons; 2) the extraction of water for human uses; 3) the discharge of water from the upstream dam and the volumes tur- bined by the Kossou dam; 4) the various an- thropic effects (discharge of untreated waste water from towns and industries, and leaching from agricultural land). The average concentra- tions of nutrients (NH4-N: 1.1 mg/L, NO3-N: 1.62 mg/L, PO4-P: 10 mg/L, SiO2: 15 mg/L) and chlo- rophyll a (from 4.8 to 16.5 μg/L, average 11.4 μg/L) indicates some degree of eutrophication. The cumulated effects that threaten the ecosys- tem (degradation of water quality and eutrophi- cation) are such that they are likely to interfere with various water uses. In a context of growing health and environmental concerns in Africa, this study demonstrates conflicts between dif- ferent uses of this water resource and the urgent need for an appropriate policy including specific monitoring of lake water quality, wastewater control, and a programme to reduce agricultural fertilizers

Structure, fonctionnement et dynamique du phytoplancton dans le lac de Taabo (Côte d'Ivoire)

Cette étude effectuée sur le lac Taabo (Sud-Est de la Côte d Ivoire), porte sur l évaluation des paramètres de la qualité de l eau, le peuplement phytoplanctonique, et le suivi de la production primaire. Ce lac de 69 km se caractérise par une profondeur moyenne de 8 m, avec un temps de résidence moyen de 49,2 jours, une température moyenne de 29,5C, absence de stratification; il concerne une population environnante de 140 000 habitants. Les entrées d eaux dans le lac sont influencées par le barrage de Kossou situé en amont, la gestion hydroélectrique de Taabo, et le régime du fleuve Bandama qui est affecté par l alternance saison des pluies, saison sèche. L analyse des paramètres physico-chimiques a montré une homogénéité spatiale des eaux du lac de Taabo tandis qu au niveau temporel une saisonnalité marquée est observée entre les périodes des pluies et celle de saison sèche. Cette saisonnalité est principalement imputable aux importantes variations de paramètres tels que la conductivité, la turbidité, la transparence et les éléments nutritifs (valeurs moyennes en nitrate et orthophosphate, respectivement de 1,62 et 10 mg.l-1). Le lac de barrage hydroélectrique est gouverné par la combinaison de deux gradients, celui de l enrichissement en nutriments et celui de la minéralisation. L aval du lac présente toutefois quelques particularités : minéralisation et oxygénation plus élevées qu en amont, au niveau temporel. La chlorophylle a varie de 4,8 à 16,5 g/l. Au niveau de la composition spécifique algale, 118 taxons repartis en 5 grands groupes et 45 genres ont été identifiés. Le peuplement algal est dominé par les chlorophycées (30,5 %) suivi par des cyanobactéries (27,1 %). La productivité varie de 0,4 à 0,8 mg Oxygène produit par mg Chl a-1 heure -1 (soit +- 2,31 à 4,6 mg C. mg Chl a-1. heure -1). Extrapolées à l échelle annuelle, nos estimations de production primaire phytoplanctonique journalière se situent entre 1,5 à 2,66 g C m-2, avec une valeur annuelle de 167 à 306 g C m-2. Une étude théorique de la production des macrophytes implantés dans la zone amont et centrale, montre que ceux-ci représentent 77 % de la production primaire du lac. Ceux-ci affectent aussi les activités socio-économiques. Le lac Taabo est remarquable par les nombreux conflits d usages liés à l eau engendrées par la gestion hydraulique et les diverses activités humaines, aux quels se rajoutent des risques sanitaires (comme vecteurs de maladies humaines et des conflits d usages, etc.).This study of the Taabo Lake (South-East Coast Ivory) focuses on the evaluation of parameters of water quality, phytoplankton communities, and estimation of primary production. his lake of 69 km is characterized by an average depth of 8 m, a mean residence time of 49.2 days, a mean temperature of 29.5 C, no stratification; it concerns a population of about 140 000 inhabitants. The inputs of water in the lake are influenced by the dam upstream Kossou, the hydroelectric activity of Taabo plant, and the regime of the river Bandama which is affected by alternating rainy season, dry season. The analysis of physicochemical parameters showed a spatial homogeneity of the waters of Lake Taabo but a marked seasonality was observed between periods of rainfall and the dry season. This is mainly due to seasonal variations of parameters such as conductivity, turbidity, transparency and nutrients (average values in nitrate and orthophosphate, respectively 1.62 and 10 mg.l-1). The lake is governed by a combination of two gradients; a nutrient enrichment and the mineralization. The dowstream part of the lake has some peculiarities as mineralization and higher dissolved oxygen content, depending on season. Chlorophyll a varied from 4.8 to 16.5 g.l-1. In terms of algal species composition, 118 taxa divided into five major groups and 45 genera were identified. The algal population is dominated by Chlorophyceae (30.5%) followed by Cyanobacteria (27.1%). The productivity varies from 0.4 to 0.8 mg oxygen per mg Chl a producted hour -1 (or +- 2.31 to 4.6 mg C mg Chl a. Hour -1). Extrapolated on an annual cycle, our estimates of daily phytoplankton primary production ranged from 1.5 to 2.66 g C m-2, with an annual value of 167 to 306 g C m-2. A theoretical study of the production of macrophytes located in the upstream and central zone indicates that they represent 77% of primary production of the lake. They also affect the socio-economic activities. Taabo Lake is remarkable by the numerous conflicting uses related to water caused by the water management and the various human activities, which are in addition to health risks (such as vectors of human diseases and use conflicts, etc.. ).TOULOUSE-ENSAT-Documentation (315552324) / SudocSudocFranceF

Eutrophication and its effect on dissolved Si concentrations in the Garonne River (France)

Dissolved nutrient and chlorophyll-a concentrations were monitored on 17 occasions and at 16 sites in the Garonne River (France). Concentrations of dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) increased about threefold downstream of the urban area of Toulouse. Chlorophyll-a concentrations increased concomitantly with DIN and SRP downstream of Toulouse. Chlorophyll-a concentrations were maximal in late winter to early spring and in summer, in-between the snow-melt driven spring flood and rainfall-driven autumn flood. Dissolved silica (DSi) concentrations were negatively correlated with chlorophyll-a concentrations, suggesting uptake by algae. DSi depletion was more severe downstream of Toulouse, suggesting that eutrophication may affect DSi consumption in the Garonne River

Termes de gain et de perte relatifs à la dynamique du périphyton (étude expérimentale se référant au cas de la Garonne)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Développement des micro-organismes phytoplanctoniques et périphytiques en période d'étiage estival dans le fleuve Garonne

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Relation between algal available phosphate in the sediments of the River Garonne and chemically-determined phosphate fractions

International audienc

A systemic approach to mercury biomagnification in rivers affected by goldmining activities (French Guiana)

International audienc

温室条件下UV-B辐射对蓝藻结皮生长和超微结构的影响

UV-B辐射是野外蓝藻结皮经常面临的一种环境胁迫因子.报道了温室条件下UV-B辐射对蓝藻结皮形态、生理和超微结构特征的影响.在本研究中,首先通过接种具鞘微鞘藻和爪哇伪枝藻形成初始蓝藻结皮,接着以初始蓝藻结皮为材料进行3种辐射处理:光合有效辐射、UV-B辐射+光合有效辐射和N-乙酰半胱氨酸+UV-B辐射+光合有效辐射.在各种辐射处理的第0、1、3、6、9和20天分别测定蓝藻结皮的光合活性(Fv/Fm)、叶绿素a、伪枝藻素和胞外多糖含量.同时采用扫描电镜观察辐射处理下结皮的超微结构特征.此外,对结皮的表观形态如结皮颜色、厚度、干重等进行了测定.结果表明UV-B辐射对蓝藻结皮具有持续而明显的负面效应.与对照结皮相比,UV-B辐射下结皮的表观形态受到不利影响,结皮Fv/Fm被完全抑制,单位重量的叶绿素a含量和胞外多糖含量显著降低,而伪枝藻素含量并未受到UV-B辐射抑制,其含量则出现大量增加.电镜观察表明,UV-B辐射导致蓝藻结皮的超微结构遭到明显破坏,表现为藻丝体数量减少,缢缩成条索状,对沙粒的缠绕减弱等.研究还表明,N-乙酰半胱氨酸能够较好地保护UV-B辐射下结皮的光合活性,增加结皮的叶绿素a含量和胞外多糖含量,并有利于结皮表观形态的恢复.本研究探索了蓝藻结皮对UV-B辐射的响应,对于进一步理解蓝藻结皮对UV-B辐射的耐受限度以及应用蓝藻结皮进行荒漠化治理具有重要的理论与实际意义