Large Woody Debris Input and Its Influence on Channel Structure in Agricultural Lands of Southeast Brazil

Abstract

Riparian forests are important for the structure and functioning of stream ecosystems, providing structural components such as large woody debris (LWD). Changes in these forests will cause modifications in the LWD input to streams, affecting their structure. In order to assess the influence of riparian forests changes in LWD supply, 15 catchments (third and fourth order) with riparian forests at different conservation levels were selected for sampling. In each catchment we quantified the abundance, volume and diameter of LWD in stream channels; the number, area and volume of pools formed by LWD and basal area and tree diameter of riparian forest. We found that riparian forests were at a secondary successional stage with predominantly young trees (diameter at breast height <10 cm) in all studied streams. Results showed that basal area and diameter of riparian forest differed between the stream groups (forested and non-forested), but tree density did not differ between groups. Differences were also observed in LWD abundance, volume, frequency of LWD pools with subunits and area and volume of LWD pools. LWD diameter, LWD that form pools diameter and frequency of LWD pools without subunits did not differ between stream groups. Regression analyses showed that LWD abundance and volume, and frequency of LWD pools (with and without subunits) were positively related with the proportion of riparian forest. LWD diameter was not correlated to riparian tree diameter. The frequency of LWD pools was correlated to the abundance and volume of LWD, but characteristics of these pools (area and volume) were not correlated to the diameter of LWD that formed the pools. These results show that alterations in riparian forest cause modifications in the LWD abundance and volume in the stream channel, affecting mainly the structural complexity of these ecosystems (reduction in the number and structural characteristics of LWD pools). Our results also demonstrate that riparian forest conservation actions must consider not only its extension, but also successional stage to guarantee the quantity and quality of LWD necessary to enable the structuring of stream channels.

Influence of landscape properties on stream water quality in agricultural catchments in Southeastern Brazil

“…This is not which occurs in the study area, where the landscape is degraded and remnant forests are highly fragmented (Valente and Vettorazzi, 2008;Paula et al, 2011). Neill et al (2001) found higher concentrations of nitrate in forested catchments than in pasture ones in Amazon streams, and also, the use of fertilizers in sugarcane plantations in Brazil is lower compared to other more developed countries (Martinelli and Filoso, 2008).…”

“…Maps of land use, hydrography and catchment limits were obtained from Paula et al (2011) using topographic maps (1:10 000, year 1979, Cartographic and Geographic Institute of the State of Sa˜o Paulo) and aerial photographs (scale 1:30 000, year 2000). Maps were derived using the software ArcGIS 9.2.…”

More of the Same: High Functional Redundancy in Stream Fish Assemblages from Tropical Agroecosystems

“…Conservation strategies for aquatic biodiversity in these systems should seek to restore and conserve riparian and landscape diversity (but see a context dependence evaluation by Nislow 2005). Through this way, it is possible to protect instream habitats from siltation (Sweeney and Newbold 2014), provide woody debris for instream habitat (Paula et al 2011(Paula et al , 2013, and mitigate the proliferation of grass on stream banks (Bunn et al 1997). This last goal is the main factor associated with functional redundancy in the studied region.…”

Ictiofauna de igarapes de pequenas bacias de drenagem em área agrícola do Nordeste Paraense, Amazonia Oriental

“…Indiretamente, esses efeitos determinam impactos negativos sobre a estrutura física e química do habitat dos peixes. Estes e outros aspectos foram estudados em trabalhos recentes, como Buss et al (2002), Allan (2004), Ferreira e Casatti (2006), Casatti (2010), De Paula et al (2011), Machado et al (2011.…”