Abstracts
Land-use change, i.e., the transformation of natural land into agricultural and urban area is among the most important human impacts on habitat quality and species diversity. In this study, we investigated the effects of land use on river habitat quality and sediment granulometry in a larger tropical river, affected by urbanization and agricultural land use. We selected 15 representative sampling reaches in the Rio das Mortes basin, 12 of them along the main river from its headwater to its mouth, and 3 in major tributaries. A habitat survey was conducted in these reaches in the dry season 2010 and sediment samples were taken for granulometry analyses. Sub-basin land cover of reaches was dominated by natural vegetation (41.6 to 60.2% of total land cover), followed by agricultural land cover (38.4% to 56.9%) and urban land cover (1.4% to 5.6%). Sediments were dominated by poorly to moderately sorted silts to sands, little conducive to diverse biological communities. According to the river habitat survey, all investigated river reaches exhibited moderately to totally disturbed habitat integrity, due to diverse and often co-occurring human impacts, such as riparian deforestation, water abstraction, sand and gravel extraction, and margin erosion. Only one of the investigated sampling reaches exhibited the minimum riparian forest corridor width demanded by the Brazilian Forest Code. Our results indicated that river habitat and sediment quality mainly depended on conditions in the direct vicinity of river reaches. Accordingly, initial cost-effective restoration of aquatic habitats could be achieved by relatively simple channel restoration measures and the protection of the riparian corridor in the investigated tropical river.
Neotropical rivers; urbanization; agriculture; structural integrity
Mudanças no uso e ocupação do solo representam um importante impacto antrópico sobre a qualidade de habitats e a diversidade biológica. Os efeitos do uso do solo sobre a qualidade de habitats e a granulometria do sedimento em um rio tropical impactado por urbanização e agricultura fora m investigados. Foram selecionados 15 trechos de amostragem representativos da bacia do Rio das Mortes, sendo 12 localizados no leito principal, desde a cabeceira até a foz, e os restantes em três dos principais tributários. Um levantamento de habitat foi realizado nestes trechos durante a estação seca de 2010 e amostras de sedimento foram coletadas para análise granulométrica. A cobertura da bacia nos trechos estudados foi dominada por vegetação natural (41.6 a 60.2%), seguida por agricultura (38.4 a 56.9%) e urbanização (1.4 a 5.6%). Os sedimentos foram dominados por silte e areia, pouco favoráveis à diversidade biológica. De acordo com o levantamento de habitat, todos os trechos apresentaram integridade moderada ou totalmente perturbada, devido a diversos impactos frequentes, tais como remoção de mata ciliar, captação de água, extração de areia e cascalho e erosão. Apenas um dos trechos estudados apresentou largura de corredor ripário em concordância com o exigido pelo Código Florestal Brasileiro. Os resultados indicam que a integridade de habitat e a qualidade do sedimento riverinos dependem principalmente das condições presentes na vizinhança imediata dos trechos estudados. Assim, a restauração custo-efetiva dos habitats aquáticos poderia ser alcançada por medidas simples de restauração do canal e a proteção da vegetação ripária neste rio tropical.
Rios neotropicais; urbanização; agricultura; integridade estrutural
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Publication Dates
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Publication in this collection
22 Jan 2014 -
Date of issue
Dec 2013
History
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Received
28 Oct 2013 -
Accepted
19 Nov 2013