Rainfall and Human Impacts on Weathering Rates and Carbon-Nutrient Yields in the Watershed of a Small Mountainous River (Kaoping) in Southwestern Taiwan

Jia-Jang Hung,Yuan-Hui Li,Chun-Yi Yang,I-Jen Lai

doi:10.3390/su12187689

Jia-Jang Hung, Yuan-Hui Li + Show 2 more

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https://doi.org/10.3390/su12187689

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Abstract

This study presents the influence of rainfall and human perturbation on physical and chemical weathering rates, and carbon and nutrient yields in the basin of the Kaoping, a small mountainous river (SMR) in southwestern Taiwan. The study was derived principally from the spatial and temporal variability of aquatic geochemistry in the river during wet (1999–2000) and drought (2002) periods. The total, physical, and chemical weathering rates in the river basin ranged respectively from 4739, 3601, and 1138 g m−2 year−1 in the wet period to 1072, 656, and 416 g m−2 year−1 in the drought period, resulting mainly from a large difference in rainfall and river discharge between the two periods. The wet and drought periods were likely associated with La Niña and El Niño events, respectively. The weathering rates of the wet period were much higher than those reported from the world’s river basins, showing the unique characteristics of the SMR. The total carbon yield was derived mainly from dissolved inorganic carbon and was much higher in the wet period (140 g C m−2 year−1) than in the drought period (53.7 g C m−2 year−1). Taking silicate weathering (54.7 ± 10.2%) slightly over carbonate weathering (48.6 ± 9.5%) in determining dissolved ion loads, the Kaoping catchment may currently consume 0.155–0.298 MtC/year atmospheric CO2 without considering the CO2 released from chemical weathering. The nutrient yields were controlled mainly by human inputs but also enhanced by increased rainfall. Both regional and local climatic conditions and human impacts likely determined the weathering rates and total yields of carbon and nutrients. The SMRs may collectively contribute significantly to global fluxes of terrestrial sediments, geochemical matters, carbon, and nutrients to oceans.

Highlights

Physical and chemical weathering processes denude continents and produce suspended sediments and dissolved ions and matter in rivers [1,2,3,4]
The value (3600 g m−2 year−1) was exactly the same as our previous report of sediment yield in the same watershed in 2007 [19], which may imply the typical sediment yield in the wet condition in the small mountainous river (SMR) watershed. This sediment yield was much higher than the previous report of Taiwan’s average (1300 g m−2 year−1 [1]), partly because of a recent increase in denudation and possibly because most episodic events were missed in assessing the previous island-wide average
Physical and chemical weathering rates increased remarkably from the upper reach to the lower reach in this steep SMR watershed. They were apparently determined by the high-stand relief, young and weak geological conditions, land-use change, and river discharge, which, in turn, was determined by rainfall driven mainly by episodic events of heavy rain in May-yu and typhoon seasons

Summary

Introduction

Physical and chemical weathering processes denude continents and produce suspended sediments and dissolved ions and matter in rivers [1,2,3,4]. Many studies have focused largely on large river watersheds because such studies allow the erosion and denudation processes at a global scale to be addressed. Recent studies have demonstrated the importance of small watersheds, those in the high stand, in accounting for global sediment yields and chemical budgets [8,9,10]. The study of small watersheds in high-stand areas may provide valuable information to fill the gap of knowledge for the present state of global denudation

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