The application of synthetic algaecides for the control of algae produces by-products that are sometimes toxic to the environment. There is a need for natural and cheap alternatives to synthetic algaecides. In the present study, we investigated the potential of aqueous crude extract of Azadirachta indica to inhibit the growth of Scenedesmus quadricauda. Phytochemical screening of the extract revealed the presence of groups of bioactive compounds that are capable of inhibiting microalgal growth. Chlorophyll a concentration, dry weight production and cell density of microalga decreased with increasing crude extract concentration. After three days of exposure, the 1000 mg/L extract concentration resulted in complete growth inhibition and cell lysis. Furthermore, the ability of S. quadricauda to form multi-celled coenobial structures was compromised in a concentration dependent manner. In general, catalase and peroxidase activities of the microalga were upregulated with increasing extract concentration. These results imply that aqueous neem extract may provide a cheap and ecofriendly alternative for the control of microalgae in aquatic ecosystems.

As espécies de algas verdes e sua associação com parâmetros físico-químicos em lagoas artificiais de Zaria, Nigéria foram estudados entre novembro de 2005 e agosto de 2006. As amostras de fitoplâncton e de água foram coletadas, preservadas e analisadas usando métodos padrões. Foram registradas um total de 27 espécies de algas verdes divididas em 16 famílias. Os indices de diversidade de Shannon variaram de 1,75 a 2,39 em todas as lagoas; índice de dominância de 0,14 a 0,23 e a eqüidade de espécies de 0,56 a 0,64. Closterium sp. e Rhizoclonium hookeri Kuetz. foram associados positivamente com a concentração de Fe, porém eles foram correlacionados negativamente (sensíveis) à alcalinidade, condutividade elétrica e sólidos totais dissolvidos. As espécies Stichococcus bacillaris Naegeli, Staurastrum rotula Nordst. e Sphaeroplea sp. tiveram relação positiva e significativa com a demanda bioquímica de oxigênio, e com os níveis de Mn e Mo na água. Pseudouvella americana (Snow) Wille. e Scenedesmus quadricauda (Turp.) de Bréb. mostraram estreita associação positiva com a alcalinidade, mas foram sensíveis ao Fe, DBO, Mn e Mo. As espécies relatadas aqui apresentaram associação próxima com fatores físico-químicos nessas lagoas.

Green algal species and their association with physicochemical parameters in some manmade ponds in Zaria, Nigeria were studied from November 2005 to August 2006. Phytoplankton and water samples were collected, preserved and analyzed using standard methods. A total of 27 green algal species divided into 16 families were recorded. Shannon diversity indices ranged from 1.75 to 2.39 in all ponds, dominance index from 0.14 to 0.23 and species evenness 0.56 to 0.64. Closterium sp. and Rhizoclonium hookeri Kuetz. were positively associated with the concentration of Fe, however they were negatively correlated (sensitive) to alkalinity, total dissolved solids and electrical conductivity. Stichococcus bacillaris Naegeli, Staurastrum rotula Nordst. and Sphaeroplea sp. had significant positive relationship with biochemical oxygen demand (BOD), Mn, and Mo levels in the water. Pseudouvella americana (Snow) Wille. and Scenedesmus quadricauda (Turp.) de Bréb. showed a close positive association with alkalinity but were sensitive to Fe, BOD, Mn and Mo. The species reported here showed closed association with physicochemical factors in these ponds.