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\hypersetup{pdftitle={Effects of Rainforest Conversion to Cacao"=agroforestry on River Discharge and Nutrient Output in Central Sulawesi (Indonesia) },pdfauthor={Gerhard Gerold},pdfsubject={Tropentag 2010: Abstract},pdfkeywords={Cacao-agroforestry, nutrient output, rainforest, river discharge, water balance simulation  },pdfpagemode=None,colorlinks=true}
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\parbox[b]{13.4cm}{\centering \large{\textbf{Tropentag, September 14-16, 2010, Zurich}}\\[1ex] \Large{``World Food System  ---\\A Contribution from Europe''\\[2ex]}}
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\Large{\textbf{Effects of Rainforest Conversion to Cacao"=agroforestry on River Discharge and Nutrient Output in Central Sulawesi (Indonesia) \footnote{\textbf{Contact Address:} Gerhard Gerold, Georg-August-Universität Göttingen, Department of Landscape Ecology, Goldschmidtstraße 5, Göttingen, Germany, \mbox{e-mail}: \email{ggerold@gwdg.de}}\\[0.8ex]}}
\normalsize{\textsc{Gerhard Gerold}}
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\item[]{\small{\textit{Georg-August-Universität Göttingen, Department of Landscape Ecology, Germany}}}
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\textbf{Abstract}
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\normalsize{
Abstract: Forest conversion in the inner tropics play an important role for the water balance of tropical catchments. Distributed hydrological modelling that relate land cover changes and climate changes with river discharge changes for humid tropical catchment areas at the mesoscale level are rare. Sulawesi still has a forest cover of \mbox{48\,\%}, but as population has been growing by \mbox{66\,\%} over the past two decades massive land cover transformations are going on. After one to two years with slash\&burn (maize) smallholders are planting mainly cocoa as cash crop (cacao boom since 10 years). Since 2001 until 2009 we investigated the impact of forest conversion on the water balance, on nutrient loss and soil erosion of a small mesoscalic tropical catchment. Vertical water and nutrient fluxes are measured for natural rainforest, cacao agroforestry (7 and 18 years old) and slash\&burn (maize) plots. Components of the water balance are measured since 2001 for the sub"=catchments ``natural forest'' and ``forest conversion to cacao agroforestry''. We compared the changes in river discharge and nutrient output. For three scenarios (forest/cacao/slash\&burn) we applicate the water balance model WASIM-ETH with simulation results, which support the experimental results (increase of total discharge, higher peak discharges after forest conversion). Increase in overland flow leads to an increase in soil erosion with doubling of suspended sediment output from 2003 to 2005. Also higher soil nutrient leaching and increase in quick interflow cause an increase by ratios of 1.5 to 1.9 of the main cations (Ca, Mg, K) in the subcatchment partially deforested compared to the natural forest subcatchment. After 2005/2006 land degradation indicators of suspended sediment output and soluted nutrient output indicate a ``stabilising effect'' with decrease due to land use change to cacao agroforestry in the mid slopes of the catchment. Smallholder cacao agroforestry can reduce the risk of unbalanced river discharge (risk of flooding) and soil nutrient impoverishment with soil erosion and nutrient leaching. 



 







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\noindent \textbf{Keywords:} Cacao"=agroforestry, nutrient output, rainforest, river discharge, water balance simulation  
\index[key]{Cacao"=agroforestry}
\index[key]{Nutrient!output}
\index[key]{Rainforest}
\index[key]{River discharge}
\index[key]{Water!balance simulation  }
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