Relative Influence of Environmental Variables on Macroinvertebrate Assemblages from an Iberian Basin

Abstract

The composition of macroinvertebrate assemblages was studied at 31 sites in the Sado basin, a lowland area with intermittent rivers located in southern Portugal. Riparian features of the sites, including bankfull width, composition, cover, shade, and relative amount of tree debris, were also measured, and local and basin abiotic variables were determined. Woody vegetation in the Sado basin was species poor and was dominated by the ash Fraxinus angustifolia, the alder Alnus glutinosa, and the willows Salix alba and S. salvifolia. The study sites included a broad range of cover and riparian longitudinal integrity. Macroinvertebrate assemblages revealed low levels of richness (4-29 taxa, average 17.6) and Shannon's diversity (0.65-2.87 bits, average 1.89), and were dominated by species or groups (especially chironomids) that tolerate organic pollution and habitat disturbance. Assemblages were composed of collector-gatherers (5.4-100%, average 58.1), and to a lesser extent collector-filterers (0-81.3%, average 14.1) and shredders (0-25.5%, average 10.6). Partial canonical correspondence analysis was used to relate the macroinvertebrate assemblages to the riparian characteristics of a site and to local and basin abiotic variables. Out of 8 riparian variables, overhanging tree shade, total tree cover, and abundance of F. angustifolia and A. glutinosa were significant predictors of assemblage variation. Of the 21 abiotic variables considered, only conductivity, distance from source, and the average number of flowless summer months were significant predictors of assemblage variation. Total macroinvertebrate variation was divided into portions that were: 1) explained solely by abiotic variables (ϳ14%); 2) explained solely by riparian variables (ϳ18%); 3) explained by both riparian and abiotic variables (ϳ2%); and 4) unexplained (ϳ66%). Riparian features had greater influence than other environmental characteristics on the composition of macroinvertebrate assemblages in the Sado basin, perhaps because riparian features are closely related to food types.

Benthic macroinvertebrate assemblages structure in two headwater streams, south-eastern Brazil

“…Forest clearance, silting, cattle raising and pasture formation, among others, favoured the homogenization of the bed of both water courses, reducing habitat and microhabitat diversity and thus affecting the biotic compartment of these ecosystems (DOBSON 1994, DUDGEON 1996, PRIMACK & RODRIGUES 2001, AGUIAR et al 2002, CALLISTO et al 2002a, BOYERO & BOSCH 2004, CASSATI et al 2006. The areas with the lowest scores in the characterization protocol also scored low values for the biological indexes of water quality (BMWP and ASPT), as well as low richness and equitability values for benthic organisms.…”

Combining Logistic Models with Multivariate Methods for the Rapid Biological Assessment of Rivers Using Macroinvertebrates

“…We think that the development of such metrics requires more laborious work, since they must be sensitive to human disturbances and must have well-understood unidirectional responses. But, the fluctuation of the flow regime of the Iberian river systems and environmental harshness is responsible for poorly predictable macroinvertebrate assemblages in this region (Gasith and Resh, 1999;Aguiar et al, 2002). Such a high temporal variability in community structure has also the potential to limit the sensitivity of other biomonitoring approaches, such as AUSRIVAS and RIVPACS systems, as is recognized by Bunn and Davies (2000), besides the mentioned huge effort to build those systems.…”

Relação entre uso do solo e composição de insetos aquáticos de quatro bacias hidrográficas do Estado de São Paulo

“…Porcentagem da área do terreno das sub-bacias ocupada por cada classe de declividade (Aagard et al, 2004;Ferrington Jr, 2008) e, muitas vezes, sua ocorrência é associada à degradação ambiental (Suriano e Fonseca-Guessner, 2004 (Foy et al, 2001;Karr, 1998 Alguns estudos que analisaram as interações de diferentes elementos do ecossistema em micro (variáveis da água) e macroescalas (usos e coberturas do solo) e os macroinvertebrados aquáticos apontaram resultados incongruentes e muitas vezes de difícil conclusão (Aguiar et al, 2002). A análise da influência de cada parte do sistema isoladamente sobre a biota apresenta resultados satisfatórios, porém o mesmo não pode ser dito quando se procura avaliar a interação desses fatores, devido à complexidade formada.…”

“…Dentre os benefícios, citam-se a estabilização das margens dos rios (Herlihy et al, 2005;Riley et al, 2003); o tamponamento e a filtragem de materiais alóctones, principalmente, pelo emaranhado das raízes; a participação na ciclagem de nutrientes, pela absorção de minerais do solo e pelo fornecimento de matéria orgânica; a interceptação e a absorção da radiação solar, com consequente estabilização térmica dos cursos d'água (Arango e Tank, 2008;Gillett e Schaffner, 2009;Yuan et al, 2009); a oferta de abrigo e alimento para animais intrínsecos e extrínsecos aos rios. Além disso, representam uma valiosa área de preservação e conservação de recursos naturais vegetais (Aguiar et al, 2002;Rodrigues et al, 1992). Há também a contribuição na manutenção do fluxo gênico entre populações de espécies animais que habitam as faixas ciliares ou fragmentos florestais interconectados (Bierregaard et al, 1992).…”