Abstract:
In former studies, a linkage between stream water element exports and stream discharge was observed at the 8.6 ha microcatchment in the montane forest of Ecuador, which was attributed to different water flow paths and the accessibility of different element sources in soil. Climate models predict an increase in temperature and precipitation. This climate change will have an impact on the water flow paths in soil and therefore alter element exports. To estimate current and future element exports, the hydrological model WaSiM was applied to the study site in daily resolution and discharge was modelled for the period 1998 - 2013. Furthermore, weekly measurements of total organic carbon (TOC), NO3-N, NH4-N, dissolved organic nitrogen (DON), PO4-P, total dissolved phosphorus (TDP), S, Cl, K, Ca, Mg, Na, Zn, Al and Mn concentrations in stream water 1998-2012 were grouped into three flow classes (baseflow, intermediate and storm) representing the rate of modelled discharge at the time of stream water sampling. By multiplying the mean concentrations of elements per flow class by the average of the yearly discharge sums per flow class and subsequently summing up per element, fluxes for current element exports were calculated. To derive estimations for future element exports in stream water, discharge was modelled under the emission scenarios A1B and B1 for the decades 2050 - 2059 and 2090 - 2099 and grouped into the three flow classes (as per above). To derive the future element exports for each scenario, yearly sums of the predicted volumes of stream water per flow class were multiplied by the mean element concentrations per flow class and finally summed up per element. For the 1998 – 2013 period the resulting mean annual exports of TOC (57.56), NO3-N (1.21), NH4-N (1.82), DON (1.8), PO4-P (0.47), TDP (0.68), S (2.56), Cl (8.15), K (4.92), Ca (7.61), Mg (4.95), Na (37.41), Zn (0.12), Al (0.18), and Mn (0.01) in kilograms per hectare per year in 1998 - 2013 were in the same range as values from the literature, except for P compounds with higher export rates and Al with lower export rates. The number of days with high discharge rates (storm) was predicted to increase and low flow days (baseflow) to occur less often under both climate scenarios and decades. Furthermore, mean discharge rates were predicted to increase by between 7.5 and 21 % until the end of the 21st century. Whereas exports of TOC (+10-25 %), NO3-N (+11-27 %), NH4-N (+6-18 %), S (+4-13 %), Cl (+10-26 %), K (+6-16 %), Ca (+7-19 %), Mg (+7-20 %), Na (+4-15 %), Zn (+12-29 %), Al (+24-53 %), Mn (+10-28 %) were predicted to increase until 2090-2099, PO4-P (+4 to -1 %) and TDP (+3 to -2 %) exports were predicted to remain relatively constant. My results demonstrate, that alterations of the water flow paths through soil due to climate change could have a considerable influence on future element exports.
