DOC Under-litter and Litter leachate
The mean UL DOC concentration was 44.26 (± 15.99)
mg.L-1 for the studied hillslope. The variation
between the events was significant. However, there was a large reduction
in the determination coefficients compared to that observed under-canopy
(TF and CL), with a total loss of model significances related to the
variables on antecedent humidity and characteristics of the rainfall
events (table 4). The 10-days AcR was the variable that most approached
the significance of the linear model for UL, maintaining the inverse
proportionality trend.
About UL data, there is an even bigger reduction in the coefficients of
determination for the variables of antecedent humidity and
characteristics of rainfall events. Such observation indicates no
influence of the dilution and pre-wash effects on DOC leaching from
litter.
The proximity to a significant correlation observed between UL data and
10-days AcR should be residual, reflecting part of the correlation
observed in TF, once the TF concentrations are start-values for the DOC
through-litter increase. However, it is noteworthy that litter is the
main DOC source in the forest leaching process and, thus, the UL field
values show less anterior compartment dependence (TF DOC) than was
observed in the BP-TF transition.
The comparison between different hillslope positions showed high
significance on DOC spatial variations. The VBT presented the lowest
mean DOC concentration for UL and LL for all events, except for LL at
EV7 (figure 7). The SMT tended to intermediate concentrations and both
mid-hillslope areas (UHS and LHS) achieved the highest concentrations.
The similarity in the spatial variation between the results obtained at
the different events reinforces the confidence in the average result
obtained.
Analyzing the DOC results in view of the spatial variability of litter
stocks, it is evident that both mid-hillslope areas (UHS and LHS), which
with the highest DOC concentrations, have similar litter stocks between
itself and intermediate litter mass compared to SMT and VBT. In VBT
rainwater percolates thin stocks with little accumulated organic matter,
resulting in lower DOC concentrations in the leachate. On the other
hand, the thicker litter stock at SMT did not materialize in higher DOC
concentrations, demonstrating some limiting factor to leaching compared
to what occurs in mid-hillslope areas.
Since the areas (hillslope positions) produce similar litterfall, the
difference between the litter stocks reflects differentiated
decomposition rates. Therefore, DOC concentrations are related to
decomposition rates analogously to that observed for litter stocks, with
more intense leaching in areas with intermediate decomposition rates.
This observation indicates the nonlinearity of the relationship between
DOC concentrations with litter stocks and their decomposition rates,
suggesting a curve trend (Second Degree Polynomial) that best
demonstrates an “optimal” condition for DOC leaching in this
environment under moderate stocks and decomposition rates (figure 8).
It’s important to state that we do not intend to expose a standard curve
representing a probabilistic model, as it would require a larger range
of positions to be significant. Our intention is only to emphasize the
nonlinearity trend under the conditions of the analyzed environment,
believing that such a general idea may contribute to analyzes in similar
environments. The high coefficient of determination value found for the
curve in DOC related to the litter stocks, besides being favored by the
low number of areas, reflects the fact that the stocks have similar
accumulated litter mass in UHS and LHS that produced similar DOC
concentrations, which was an interesting result.