Ana Maria Geraldes

Riparian ecotones and spatial variation of fish assemblages in Portuguese lowland streams

The first results of a long-term study on the role of riparian ecotones on the population and community dynamics of Iberian stream fish are presented and discussed. Riparian and macrophyte cover, bank slope and depth were among the most important variables affecting fish distribution. In general small fish favoured shallow areas with high macrophyte cover, whereas large fish dominated in deep areas with a high riparian cover. Slight spatial changes in terrestrial prey use were found suggesting a minor role for this resource during autumn. Finally, no significant spatial differences were found for linear growth, although some differences were obtained for the condition factor.

Distinct age and landscape influence on two reservoirs under the same climate

With the purpose of finding out whether different landscape occupation could affect water quality in two reservoirs of distinct age and subjected to the same climatic influence, several factors were investigated in a study lasting from January 2000 till December 2001. Total phosphorus, orthophosphate, chlorophyll a concentrations and water colour were determined monthly in winter and biweekly in summer, in two reservoirs located in the Portuguese part of River Douro catchment. Complementarily, variables such as nitrate, ammonium ion and ammonia gas, as well as water temperature, dissolved oxygen, conductivity, and transparency were measured. Trophic state of both reservoirs was assessed by computation of Carlsons Trophic State Index. The potential allochthonous sources of phosphorus and nitrogen to both reservoirs were identified and estimated. Differences between reservoirs were found for conductivity, water temperature, transparency and water colour. According to Carlsons Trophic State Index both reservoirs were classified as meso-eutrophic from winter to the beginning of summer, and as eutrophic from this period onwards. Intrinsic factors such as age of reservoir, organic matter inputs from decomposition of flooded terrestrial vegetation and exposure of littoral sediments to cycles of drying and wetting, as well as extrinsic factors such as grazing and frequent land fires, can explain the trophic state of S. Serrada Reservoir. Allochthonous sources of nutrients originated from agriculture and grazing in the catchment area, and recreational activities in the reservoir probably are the factors with greatest influence on Azibo Reservoir trophic state. Based upon the obtained data, management measures are suggested to prevent further eutrophication and water quality degradation in both reservoirs.

Limnological variations of a deep reservoir in periods with distinct rainfall patterns

OBJECTIVO: Com o presente estudo pretende-se obter informacao sobre os impactos da variacao da precipitacao nas concentracoes de fosforo total, de clorofila a, oxigenio dissolvido, condutividade e profundidade do disco de Secchi, bem como na abundância de Anabaena flos-aquae e das especies mais abundantes de crustaceos zooplactonicos. METODOS: As amostragens foram realizadas mensalmente de Outubro de 2000 a Setembro de 2002 e de Outubro de 2007 a Setembro de 2009 num unico ponto localizado na zona mais profunda do reservatorio. Todos os dados foram obtidos na zona eufotica. RESULTADOS: As concentracoes de fosforo total foram mais elevadas durante os periodos de maior precipitacao. Por seu turno, a condutividade decresceu durante os periodos mencionados. Anabaena so foi detetada entre Setembro e Dezembro de 2001. A abundância de Daphnia longispina sofreu grandes variacoes durante o decurso deste estudo. Diaphanosoma brachyurum e Ceriodaphnia pulchella apresentaram sempre um forte padrao sazonal. Ambas as especies sao termofilas e so comecam a ser detetadas a partir do inicio do verao quando a temperatura da agua atinge os 15 oC. Copidodiaptomus numidicus nao apresenta qualquer padrao sazonal. CONCLUSOES: Algumas das mudancas observadas nos parâmetros ambientais (condutividade, concentracoes de fosforo total e na abundância de Anabaena) sao induzidas pelas variacoes na precipitacao. Estas mudancas afetam a abundância do zooplâncton. As especies mais afetadas sao aquelas que nao apresentam padroes sazonais (C. numidicus) ou especies que ocorrem essencialmente entre o inverno e o inicio do verao. No entanto, uma grande variedade de interacoes de natureza fisica, quimica e biotica sao suscetiveis de afetar a abundância do zooplâncton. Assim, e necessario ter cautela quando se relacionam as alteracoes na comunidade zooplanctonica exclusivamente com variacoes na precipitacao. De facto, muitas das alteracoes observadas sao induzidas por outros fatores que variam de forma subtil sazonalmente ou inter-anualmente e independentemente da intensidade da precipitacao.

Searching for Algaecide or Algaestatic Effects of Several Plant Extracts on Phytoplankton: Preliminary Results

Aims: Evaluate the in vitro effects of essential oils and water extracts of Laurus nobilis , Rosmarinus officinalis , Mentha suaveolens and Fraxinus angustifolia on the growth of Anabaena cylindrica and Chlorella vulgaris.