Geographical Patterns of Hydrologic Flow in Tropical Rainforests

Luiselli Mauro^*
*Correspondence: Luiselli Mauro, Department of Cultural Heritage, University of Bologna, Via degli Ariani, Ravenna, Italy, Email:

Introduction

A qualitative picture of anticipated hydrologic processes had already formed, albeit implicitly, in the literature on tropical geomorphology long before the first quantitative field research of runoff generation in a tropical jungle. Implicitly, since the only supporting data for these processes were observations or, more frequently, conclusions drawn from the correlations between certain processes and landforms. Tropical geomorphologists have previously, perhaps somewhat accidentally, anticipated the range of runoff generating mechanisms as characterised much later by hydrologists, leaving aside this restriction and a few terminology issues specific to the field. It is unfortunate that this corpus of information has been largely disregarded by the hydrological community, as this illustrates a dearth of inter-disciplinary collaboration. The upside of this is a refreshing absence of attempts to form opinions about the world.

About the Study

The stormflow hydrograph of a stream is created when a precipitation event activates flowpaths. The fundamental tenet of the proposed paradigm is that which flowpaths are specifically triggered in response to a given event depends on the interaction between soil physical properties and rainfall characteristics. Because most soils are anisotropic, vertical water movement often predominates between precipitation events, albeit there may be a modest horizontal component. However, during rainfall episodes, this horizontal component may become dominant, resulting in lateral flow. With the exception of saturation-excess overland flow, soil anisotropy—which is best described as the variation in soil hydraulic conductivity with depth—plays a critical role in activating flowpaths in practically all stormflow generation modes. The biological activity of the soil is correlated with how a subsurface stormflow transforms into a return flow. There are several advantages to using microbiological characteristics as markers of soil contamination in theory. In many respects, microbes are the perfect soil pollution monitors due to their bulk, activity, and close proximity to the soil microenvironment. The results of stressors that naturally arise on microbial communities in soil and their actions, such as temperature changes, extremes in pH and water potential, physical soil disturbances, a reduction in gas exchange, a shortage of nutrients, and an increase in antagonists and competitors. Individually or together, any of these occurrences can significantly impact both the measure of the microbial community's size and activity.

Overland flow monitoring is made difficult by the existence of return flow and more so by the present inability to predict it everywhere but where it is coupled with channels. Almost all overland flow studies rely on a very small number of runoff plots, whose placement in the field is typically determined more by intuitive, topography, or practical factors than anything else. These methods are likely to overlook the "proper" locations for runoff plots, which are those that are downslope from pipe exits as point sources of overland flow, in return flow-prone environments. A record of very little or no overland flow may therefore merely represent a site selection issue and not necessarily the lack of this flowpath in an environment that is conducive to near-surface flowpaths. With the probable exception of Horton overland flow, all hillslope hydrologic response modes actually do or can be reasonably anticipated to occur in tropical rainforests. This result is presented as a discrete, idealised spectrum with the end-members of the "Acrisol"- and "Ferralsol"-types. To emphasise the previously noted caution that, at least for Acrisols, the association with a specific pattern of runoff formation is not unique and unambiguous, particularly not at this taxonomic level, the taxonomic names are placed in quotation marks. All sites with a dominant lateral, nearsurface flow component, however, are on acrisols, which is quite unexpected. This significant relationship supports the notion of an end-member of the type "Acrisol." The prototypical "Ferralsol"- type end-member, which contains the functionally equivalent, is defined at the Reserva Duke site.

This review led to the notion that overland flow is a potentially significant mechanism of runoff generation in wooded Acrisol but not in ferralsol settings. This hypothesis needs to be tested in the field. This task is not nearly as insurmountable as it may initially seem, thanks to the numerous field studies to examine the effects of land use and land cover change that always include a control site in primary rainforest as a benchmark for comparisons and at least temporary, if not year-round, personnel presence. A pilot study using runoff detectors, similar to that of Elsenbeer and Lack, is sufficient to test this hypothesis with little material investment, with the added bonus of offering a sound rationale for choosing the location for the installation of runoff. The above example highlights the difficulties in field monitoring and understanding changes in soil microbial respiration, which is ostensibly an easy trait to assess. If a pollutant is also injected into the system, it will likely be very difficult to assess its impacts unless it has extremely dramatic consequences, such as the near complete death generated by an effective fumigant like chloroform or methyl bromide. It is intriguing that in this field experiment, sample variation increased when there was significant rain. The peak of microbiological activity would occur about then, making it extremely challenging to identify the impacts of pollution. These comprised the soil's physical and chemical characteristics, temperature, and meteorological information [1-5].

Conclusion

Additional field research is necessary to confirm the review's conclusion that overland flow is a potentially significant mechanism of runoff generation in forested Acrisol landscapes but not in ferralsol environments. Due to the numerous field studies that have been conducted to look into the effects of land use and land cover change, which always include a control site in primary rainforest as a standard for comparisons and at least temporary, if not yearround personnel presence, this task is not nearly as insurmountable as it may initially appear to be. This hypothesis can be tested with little to no material effort with the help of a pilot study using runoff detectors along the lines of Elsenbeer and Lack, with the added bonus of offering a sound rationale for choosing the location for the installation of runoff.

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