INTRODUCTION
Spatial flows of dissolved organic carbon (COD) are an important
component of the carbon (C) balance in ecosystems and the global cycle
of this element (Cole et al., 2007). Rainwater permeates terrestrial
environments, transporting considerable amounts of organic carbon (OC)
to waterbodies, which can affect limnic ecosystems and water resources
quality (Graeber et al., 2018).
The development of models that can synthesize the dynamics of DOC in
river basins, aimed to assist the management of water resources and meet
the growing demand for information about the C cycle, demands an
increasing knowledge about the production and migration dynamics of OC
in the terrestrial environment and the rainfall action on these process
(Neff & Asner, 2001). The watershed is the spatial matrix of
capitation, production, storage, decomposition, and export of OC.
In line with the relevance of this theme, some researchers have directed
their efforts towards the study of the balance of DOC in hydrographic
basins, as well as towards the flows between forest compartments and to
aquatic ecosystems (Hongve, 1999; Jiang et al., 2014; Meyer et al.,
1988). The modulation of DOC concentrations in streams has been
evaluated in their capacity to indicate the rates of surface runoff in
the basin area using the hydrogeochemical signature idea (Chaplot e
Ribolzi, 2014; Figueiredo et al., 2014).
In forest environments, litter above the ground is the main source of OC
for deep soil horizons and aquatic environments (Camino-Serrano et al.,
2014; Hafner, Groffman, & Mitchell, 2005; Moyer, Powell, Gordon, Long
& Bliss, 2015). In the soil, complex chemical interactions between
water, microorganisms and organic matter (OM) are manifested (Kaiser,
Peake, Willey, & Brooks, 1996; Singh et al., 2017;). Leaching of litter
and sorption to mineral particles are the main processes in the DOC
dynamics of terrestrial environments and their flow into aquatic
environments. These processes have equally important local features,
such as primary productivity, decomposition rates, pluviometric
dynamics, and soil water infiltration capacity.
The pluviometric dynamics given by the conditions of antecedent humidity
and characteristics of the rainfall events are variables that act
directly on the effects of DOC dilution and environments pre-washing (Li
et al., 2016; Michalzik, Kalbitz, Park, Solinger, & Matzner, 2001). In
addition, it acts in conjunction with the soil water infiltration
capacity to define the water flow pathways in terrestrial environments
and, consequently, regulate the sorption opportunities of DOC to soil
particles and arrival rates to waterbodies (Graeber et al., 2018).
Concentrated in temperate and boreal forests, studies on DOC leaching
has given attention to the control exercised by litter decomposition
rates. Several studies have compared coniferous and hardwood forests
about DOC flows including leaching of their leaves, discussing aspects
such as material lability (Fröberg, Hansson, Kleja, & Alavi, 2011; Lee
et al., 2018; Liu & Sheu, 2003). In tropical environments, DOC studies
that enter the universe of litter leachate and soil solution are still
scarce (e.g. Zhou et al., 2015), and studies on the balance of DOC in
hydrographic basins are a little more common, addressing DOC inputs by
rainfall (e.g. Godoy-Silva, Nogueira, & Campos, 2017) and/or outputs
through the drainage channel (e.g. Costa et al., 2017).
Our study area is a tropical rainforest environment with primary
productivity and litter decomposition rates different from temperate and
boreal forests. Previous studies confirmed that the rugged relief of the
area differentiated litter decomposition rates on the hillslope-scale
(Miranda & Avelar, 2019), a representative situation of the forested
mountains of the Brazilian coast and with a singular potential for
research about DOC litter leaching.
In this way, our work aimed to analyze and discuss the water DOC
concentrations from different forest compartments, in a hillslope-scale,
to contribute with a general panorama about the leaching and balance of
DOC in tropical rain forests, coupling an approach about the
decomposition rates influence for DOC leaching from litter provided by a
favorable laboratory-situation (decomposition rates heterogeneity).
Analysis of the rainfall characteristics allowed us to infer its
influence on the DOC concentrations in the different forest
compartments. Thus, the comparison between hillslope positions as
environmental spatial heterogeneity and the comparison between rainfall
events based on the potential control exercised by the precipitation
dynamics conform, respectively, the spatio-temporal scope of the present
paper.