@article{MohrCoppusIroumeetal.2013, author = {Mohr, Christian Heinrich and Coppus, Ruben and Iroume, Andres and Huber, Anton and Bronstert, Axel}, title = {Runoff generation and soil erosion processes after clear cutting}, series = {Journal of geophysical research : Earth surface}, volume = {118}, journal = {Journal of geophysical research : Earth surface}, number = {2}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-9003}, doi = {10.1002/jgrf.20047}, pages = {814 -- 831}, year = {2013}, abstract = {Timber harvesting by clear cutting is known to impose environmental impacts, including severe disturbance of the soil hydraulic properties which intensify the frequency and magnitude of surface runoff and soil erosion. However, it remains unanswered if harvest areas act as sources or sinks for runoff and soil erosion and whether such behavior operates in a steady state or evolves through time. For this purpose, 92 small-scale rainfall simulations of different intensities were carried out under pine plantation conditions and on two clear-cut harvest areas of different age. Nonparametrical Random Forest statistical models were set up to quantify the impact of environmental variables on the hydrological and erosion response. Regardless of the applied rainfall intensity, runoff always initiated first and yielded most under plantation cover. Counter to expectations, infiltration rates increased after logging activities. Once a threshold rainfall intensity of 20mm/h was exceeded, the younger harvest area started to act as a source for both runoff and erosion after connectivity was established, whereas it remained a sink under lower applied rainfall intensities. The results suggest that the impact of microtopography on surface runoff connectivity and water-repellent properties of the topsoil act as first-order controls for the hydrological and erosion processes in such environments. Fast rainfall-runoff response, sediment-discharge-hystereses, and enhanced postlogging groundwater recharge at catchment scale support our interpretation. At the end, we show the need to account for nonstationary hydrological and erosional behavior of harvest areas, a fact previously unappreciated in predictive models.}, language = {en} } @article{IroumeCareyBronstertetal.2011, author = {Iroume, Andres and Carey, Patricio and Bronstert, Axel and Huber, Anton and Palacios, Hardin}, title = {GIS application of USLE and MUSLE to estimate erosion and suspended sediment load in experimental catchments, Valdivia, Chile}, series = {Revista t{\´e}cnica de la Facultad de Ingenieria}, volume = {34}, journal = {Revista t{\´e}cnica de la Facultad de Ingenieria}, number = {2}, publisher = {Facultad de Ingenieria Universidad del Zulia}, address = {Maracaibo}, issn = {0254-0770}, pages = {119 -- 128}, year = {2011}, abstract = {This paper presents the results of a research aimed to quantify suspended sediment transport in three experimental catchments in southern Chile, to compare measured suspended sediment load with estimated erosion using the Universal Soil Loss Equation (USLE) applied in a GIS environment and to validate de Modified Universal Soil Loss Equation (MUSLE) used to estimate suspended sediment loads from forest catchments. The catchments are Los Pinos (94.2 ha), Los Ulmos 1 (12.6 ha) and Los Ulmos 2 (17.7 ha). Soil losses estimated with USLE for the three catchments are higher than those measured in runoff experimental lots under bare soil conditions, which could indicate an overestimation of the LS calculated in GIS and the fact that the USLE model does not compute sediment deposit and storage within the catchment. A statistical significant relation was found between measured and estimated (MUSLE) suspended sediment load, which would indicate that this model could be applied to estimate suspended sediment load from small catchments in southern Chile.}, language = {es} } @article{MohrMontgomeryHuberetal.2012, author = {Mohr, Christian Heinrich and Montgomery, David R. and Huber, Anton and Bronstert, Axel and Iroume, Andres}, title = {Streamflow response in small upland catchments in the Chilean coastal range to the M-W 8.8 Maule earthquake on 27 February 2010}, series = {Journal of geophysical research : Earth surface}, volume = {117}, journal = {Journal of geophysical research : Earth surface}, number = {23}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0148-0227}, doi = {10.1029/2011JF002138}, pages = {16}, year = {2012}, abstract = {Hydrological response to earthquakes has long been observed, yet the mechanisms responsible still remain unclear and likely vary in space and time. This study explores the base flow response in small upland catchments of the Coastal Range of south-central Chile after the M-W 8.8 Maule earthquake of 27 February 2010. An initial decline in streamflow followed by an increase of up to 400\% of the discharge measured immediately before the earthquake occurred, and diurnal streamflow oscillations intensified after the earthquake. Neither response time, nor time to maximum streamflow discharge showed any relationship with catchment topography or size, suggesting non-uniform release of water across the catchments. The fast response, unaffected stream water temperatures and a simple diffusion model point to the sandy saprolite as the source of the excess water. Base flow recession analysis reveals no evidence for substantial enhancement of lateral hydraulic conductivity in the saprolite after the earthquake. Seismic energy density reached similar to 170 J/m(3) for the main shock and similar to 0.9 J/m(3) for the aftershock, exceeding the threshold for liquefaction by undrained consolidation only during the main shock. Although increased hydraulic gradient due to ground acceleration-triggered, undrained consolidation is consistent with empirical magnitude-distance relationships for liquefaction, the lack of independent evidence for liquefaction means that enhanced vertical permeability (probably in combination with co-seismic near-surface dilatancy) cannot be excluded as a potential mechanism. Undrained consolidation may have released additional water from the saturated saprolite into the overlying soil, temporarily reducing water transfer to the creeks but enlarging the cross-section of the saturated zone, which in turn enhanced streamflow after establishment of a new hydraulic equilibrium. The enlarged saturated zone facilitated water uptake by roots and intensified evapotranspiration.}, language = {en} } @article{MohrKorupUlloaetal.2017, author = {Mohr, Christian Heinrich and Korup, Oliver and Ulloa, Hector and Iroume, Andres}, title = {Pyroclastic Eruption Boosts Organic Carbon Fluxes Into Patagonian Fjords}, series = {Global biogeochemical cycles}, volume = {31}, journal = {Global biogeochemical cycles}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0886-6236}, doi = {10.1002/2017GB005647}, pages = {1626 -- 1638}, year = {2017}, abstract = {Fjords and old-growth forests store large amounts of organic carbon. Yet the role of episodic disturbances, particularly volcanic eruptions, in mobilizing organic carbon in fjord landscapes covered by temperate rainforests remains poorly quantified. To this end, we estimated how much wood and soils were flushed to nearby fjords following the 2008 eruption of Chaiten volcano in south-central Chile, where pyroclastic sediments covered >12km(2) of pristine temperate rainforest. Field-based surveys of forest biomass, soil organic content, and dead wood transport reveal that the reworking of pyroclastic sediments delivered similar to 66,500+14,600/-14,500tC of large wood to two rivers entering the nearby Patagonian fjords in less than a decade. A similar volume of wood remains in dead tree stands and buried beneath pyroclastic deposits (similar to 79,900+21,100/-16,900tC) or stored in active river channels (5,900-10,600tC). We estimate that bank erosion mobilized similar to 132,300(+21,700)/(-30,600)tC of floodplain forest soil. Eroded and reworked forest soils have been accreting on coastal river deltas at >5mmyr(-1) since the eruption. While much of the large wood is transported out of the fjord by long-shore drift, the finer fraction from eroded forest soils is likely to be buried in the fjords. We conclude that the organic carbon fluxes boosted by rivers adjusting to high pyroclastic sediment loads may remain elevated for up to a decade and that Patagonian temperate rainforests disturbed by excessive loads of pyroclastic debris can be episodic short-lived carbon sources. Plain Language Summary Fjords and old-growth forests are important sinks of organic carbon. However, the role of volcanic eruptions in flushing organic carbon in fjord landscapes remains unexplored. Here we estimated how much forest vegetation and soils were lost to fjords following the 2008 eruption ofunknownChaiten volcano in south-central Chile. Pyroclastic sediments obliterated near-pristine temperateunknownrainforest, and the subsequent reworking of these sediments delivered in less than a decade similar to 66,000 tC of large wood to the mountain rivers, draining into the nearby Patagonian fjords. A similar volume of wood remains in dead tree stands and buried beneath pyroclastic deposits or stored in active riverunknownchannels. We estimate that similar to 130,000 tC of organic carbon-rich soil was lost to erosion, thus adding to the carbon loads. While much of the wood enters the long-shore drift in the fjord heads, the finerunknownfraction from eroded forest soils is likely to be buried in the fjords at rates that exceed regional estimates by an order of magnitude. We anticipate that these eruption-driven fluxes will remain elevated forunknownthe coming years and that Patagonian temperate rainforests episodically switch from carbon sinks to hitherto undocumented carbon sources if disturbed by explosive volcanic eruptions.}, language = {en} }