Permeability of riparian forest strips in agricultural, small subtropical watersheds in south-eastern Brazil

Abstract

If riparian buffer zones are ineffective in preventing C4 plant carbon from upland areas reaching the stream sediment, the composition of stream fauna can be significantly altered. The permeability of riparian forest strips in agricultural, small subtropical watersheds in south-eastern Brazil was measured in nine watersheds categorised according to the predominant land cover of the legally required 30-m buffer riparian zone. Four watersheds with well preserved riparian forest along the 30-m buffer zone were designated as FOREST watersheds; three watersheds, with a predominance of C4 grasses from sugarcane to pasture, mixed with preserved riparian forests, were designated MIXED watersheds; and two watersheds were termed PASTURE-SUGAR because their entire 30-m buffer zone was covered by C4 plants. Stable carbon (δ13C) isotopes were used as tracers of upland C4 carbon in sediments, suspended particulate organic carbon, terrestrial and aquatic invertebrates and two species of neotropical fish. Although the intact 30-m buffer zone of riparian forests did not entirely prevent the input of C4 to the river environment and food web, there was a significant increase in C4 carbon in those watersheds where the buffer zone was not covered by riparian forests. These findings emphasise the importance of riparian forests in mitigating disturbance in streams and support efforts to preserve such riparian corridors.

Isotopic variation in five species of stream fishes under the influence of different land uses

“…In the areas with sugar cane cultivation and pasture, plants are C4. Despite their disadvantages (because they are less nutritious and difficult to digest), recent studies have suggested that the contribution of C4 plants can be substantial for aquatic communities (Hoeinghaus et al , ; Ferreira et al , ). Of the species assessed here, A .…”

“…Thus, the resources present in each land use category were considered separately in all analyses performed in this work. The fractionation values used were 1‰ for carbon (Oliveira et al , ) and 3‰ for nitrogen (Ferreira et al , ). The assumed significance level was P < 0·05.…”

“…This substitution can also significantly alter the incidence of solar energy and the exchange of organic and inorganic material between aquatic and terrestrial ecosystems (Pusey & Arthington, 2003). Changes in riparian vegetation cover interfere with nutrient supply, allochthonous material, autochthonous production and the quality and quantity of available food resources, which may alter the trophic webs of affected environments and have an effect on aquatic biodiversity (Pusey & Arthington, 2003;Thomas et al, 2004;Meynendonckx et al, 2006;Ferreira et al, 2012). Thus, one way to observe the effects of anthropogenic changes on aquatic communities is to assess how fish respond to changes in the sources of available resources.…”

“…The 15 N isotope, in turn, is consistently fractionated throughout the trophic web, allowing inferences about the trophic relationships of consumers with their diet ( Vander Zanden et al, 1997;Post, 2002;Vanderklift & Ponsard, 2003). Therefore, these two isotopes are useful to trace the transfer of carbon and nitrogen from plants and detritus to primary and secondary consumers (Peterson & Fry, 1987;Ferreira et al, 2012;Jardine, 2014).…”

The effect of agriculture on the seasonal dynamics and functional diversity of benthic biofilm in tropical headwater streams

“…The regional climate is classified as "Cwa" (humid subtropical climate) in the Köppen classification, with dry winters and wet summers (Cetra & Petrere, 2006). The average temperature in winter is 17ºC and exceeds 22ºC in summer (Ferreira, Cyrino, Duarte-Neto, & Martinelli, 2012).…”