No abstract

in stream flow discharge, including changes in hydrological processes (with network waterproofing), are common characteristics of human-modified streams, resulting in a decrease in soil percolation and an increase in superficial discharge (Dunne and Leopold 1978). As a consequence, changes in channel stability and morphology and increases in wastewater discharge are expected, which are reflected in ecological aspects, such as changes in species distributions (Maloney and Weller 2010; Alexandre et al. 2010; Cunico et al. 2012), decreases in species richness, and dominance of tolerant species to environmental degradation (Paul and Meyer 2001; Meyer et al. 2005). Although in recent years there has been a significant increase in the studies of the ichthyofauna in tropical streams the knowledge is less extensive than that of temperate areas (Winemiller et al. 2008). In Brazilian inland waters, especially in urban stream, the estimates of the fish diversity are still imprecise due to the lack of complete inventories (Agostinho et al. 2008). First-order streams are abundant and unique components of a river network, they showing high biological diversity and are important for maintenance of the biological integrity of entire ecosystem (Meyer et al. 2007). List of species contributes to build a database on species distribution patterns in altered environments, and to set the ground for future actions of biodiversity management and conservation In the present study, we sampled ichthtyofauna in three first-order streams affected by urban activities, aiming at inventorying the fish species that occur in these particular environments.

Stable isotopes of carbon (δ 13 C) and nitrogen (δ 15 N) were used to describe sources of energy and trophic position for adult Leporinus friderici in the area of the Corumbá Reservoir, Brazil. Samples were collected from April 1999 to March 2000. Spatial variations were not identifi ed in the isotopic composition. The maximum and minimum contribution of C 4 plants calculated integrating the variation of plants and fi sh were 47.7% and 2.4%, respectively. Among C 3 plants, periphyton presented closer isotopic values to those observed for fi shes, corresponding to an important carbon source. The proportion of ingested plant item is larger in rivers upstream from the reservoir (42.7%), which justifi es the smaller trophic level among there. However, in the reservoir, the ingestion of fi sh was 81.4%, while ingested plants contributed with 18.6%. Downstream from the dam, participation of plant item was even smaller (14.4%). Although the trophic position calculated with diet data was proportional to the one calculated with δ 15 N values, the former elevated the trophic level of L. friderici in the food web, because estimated trophic positions were based on fi sh items belonging to the 2 nd (a) and to the 3 rd (b) trophic levels.

SynopsisIn this paper we analysed autotrophic sources of the carbon (d 13 C) and the trophic position (d 15 N) of Leporinus friderici in the influence area of Corumba´Reservoir, Brazil. We collected samples of muscles of fish from different sizes riparian vegetation, C 4 grasses, zooplankton, periphyton and particulate organic carbon (POC). There were significant differences for the carbon isotope proportion found in muscles of L. friderici in the different size groups analysed. The highest values of d 13 C recorded for middle sized individuals is attributed to the large contribution of C 4 plants in their diet. Small individuals sampled upstream also receive similar contribution from C 4 plants. In contrast the same size group sampled downstream from the reservoir, has a much smaller of C 4 plants. The d 13 C negative character of small individuals from downstream is due to the larger contribution of C 3 plants (except periphyton). At larger sizes we found intermediate d 13 C values. The d 15 N proportions we found for each size group were not significantly different, however we found decreasing mean values with increasing size. The trophic level calculated from the dietary data was higher than that found with the d 13 C concentration in the muscle, except for small individuals, when the values were equal.

Terrestrial invertebrates link terrestrial systems to aquatic ones, making vegetal material produced in the watershed available to aquatic food webs. In this study, using carbon and nitrogen stable isotopes, we evaluated the importance of introduced C4 grasses as a source of carbon in aquatic food webs of headwater streams of the coastal Atlantic Forest located on the north coast of the State of São Paulo, in the southeastern region of Brazil. Terrestrial invertebrates were collected in two streams: one where the main land cover was pristine montane Atlantic Forest (forest stream) and another where the main land cover was introduced C4 forage grasses for livestock (pasture stream). The average δ13C of terrestrial invertebrates collected in the forest stream (−26.3±2.1‰) was significantly (p<0.01) smaller than the average δ13C of terrestrial invertebrates collected in the pasture stream (−15.7±4.7‰), denoting a larger contribution of C4grasses to terrestrial invertebrates of the pasture stream. The average δ15N of terrestrial invertebrates of the forest stream (4.1±2.4‰) was significantly (p<0.01) lower than the average δ15N of terrestrial invertebrates of the pasture stream (9.5±2.7‰). The relative contribution of C3 and C4 plants to terrestrial invertebrates was estimated using SIAR. In the forest stream, the C3 contribution was on average 0.75 (0.72 minimum to 0.79 maximum), and the C4 contribution was on average 0.25 (0.21 minimum to 0.28 maximum). In the pasture stream, the C3contribution decreased to 0.20 (0.14 minimum to 0.26 maximum), and the C4 contribution increased to 0.80 (0.74 minimum to 0.86 maximum). These results have several implications for the ecosystem functioning as well as for recent changes in environmental policies of Brazil. The lower nutritional value of C4 grasses may not only decrease invertebrate performance, but also alter the stoichiometry of several components of the aquatic food webs with potential consequence for the whole ecosystem functioning. On the public policy side, recent changes in the Brazilian Forest Act, a series of laws that regulate land cover at the property level, reduced the width of the forested riparian area with potentially dangerous consequences for aquatic ecosystems.