Past and present land use influences on tropical riparian zones: an isotopic assessment with implications for riparian forest width determination

Abstract

In this article, by using carbon stable isotopes, we assessed the past and present land use influences that riparian areas are subject within agricultural landscapes. Emphasis is given to the understanding of the effects of the 2012 Brazilian Forest Act on such areas. We selected five riparian areas within a highly C4 dominated agricultural landscape. Three of them had 30 meters native riparian forest buffer (NRFB) and two of them had 8 meter and no NRFB. We used three 100 meter-transects located 5, 15 and 30 meters relative to stream channel to obtain soil samples (0 - 10 cm). All riparian areas presented soil carbon isotopic signatures that are not C3 (native forests) irrespective of having or not 30 meters NRFB. Two cases presenting less than 30 meters NRFB had higher C4 derived carbon contribution. All of the other three areas that followed the 30 meters NRFB presented, to some degree, C4 derived carbon, which was attributed to C4 organic matter deposition originated from cultivated areas and, in one case, to the persistence of former exotic grasses. With the 2012 Forest Act allowing narrower buffers (< 30 meters), we expect C4 contributions to soil organic matter to remain high in riparian areas and streams within agricultural landscapes dominated by C4 plants where 30 meter NRFB is no longer required. Such contributions will likely continue to have detrimental effects on stream water quality and biota.

Potential for Forest Restoration and Deficit Compensation in Itacaiúnas Watershed, Southeastern Brazilian Amazon

“…This change was reflected in the higher percentage of consolidated APPs found for this APP type (34% of the total consolidated APPs), as shown in Table 4. The reduced width of up to 5 m that need to be restored around rivers (in the case of properties up to 1 FM) was considered insufficient for maintaining ecosystem services [34][35][36].…”

Background and the use of isoscapes in the Brazilian context: essential tool for isotope data interpretation and natural resource management

“…Stable-isotope forensic studies have sporadically been used in Brazil. δ 15 N and δ 13 C helped to identify the origin of Brazilian marijuana seized , to trace origin and effect of illegal discharge of residues in streams and sediment (Barbieri et al, 2014;Roth et al, 2016), but also for an isotopic assessment to help understand the effects of the 2012 Brazilian Forest Act on tropical riparian zones (Salemi et al, 2016).…”

“…Very few studies using δ 13 C spatial patterns have been employed to measure land-use effects in aquatic (Sanaiotti et al, 2002;Augusto et al, 2015) and terrestrial ecosystems (Assad et al, 2013;Salemi et al, 2016;Figueira et al, 2016), which, therefore, might closely fit what has been applied in Brazil in terms of the isoscape approach in any published study led by Brazilian research groups.…”

Runoff, soil loss, and sources of particulate organic carbon delivered to streams by sugarcane and riparian areas: An isotopic approach

“…It is expected that these vegetation strips protect against stream bank erosion ( Martin and Church, 2000;McKergow et al, 2003;Zaimes et al, 2008;Zaimes and Schultz, 2015) and protect water bodies against pollution, by trapping a large fraction of the soil particles and runoff originating from arable land (Bussi et al, 2016;Dosskey et al, 2010;Zhang et al, 2010). However, recent studies have shown that trapping under field conditions is often considerably lower than anticipated from laboratory or experimental plots results due the formation of preferential pathways within the buffer strips that may reduce their buffering capacity (Knight et al, 2010;Salemi et al, 2016;Stehle et al, 2016;Wallace et al, 2018).…”