[Show abstract][Hide abstract] ABSTRACT: Aims The field of ecohydrology is providing new theoretical frameworks and methodological approaches for understanding the complex interactions and feedbacks between vegetation and hydrologic flows at multiple scales. Here we review some of the major scientific and technological advances in ecohydrology as related to under-standing the mechanisms by which plant–water relations influence water fluxes at ecosystem, watershed and landscape scales. Important Findings We identify several cross-cutting themes related to the role of plant– water relations in the ecohydrological literature, including the con-trasting dynamics of water-limited and water-abundant ecosystems, transferring information about water fluxes across scales, under-standing spatiotemporal heterogeneity and complexity, ecohydro-logical triggers associated with threshold behavior and shifts between alternative stable states and the need for long-term data sets at multiple scales. We then show how these themes are embedded within three key research areas where improved understanding of the linkages between plant–water relations and the hydrologic cycle have led to important advances in the field of ecohydrology: upscal-ing water fluxes from the leaf to the watershed and landscape, effects of plant–soil interactions on soil moisture dynamics and controls exerted by plant water use patterns and mechanisms on streamflow regime. In particular, we highlight several pressing environmental challenges facing society today where ecohydrology can contribute to the scientific knowledge for developing sound management and policy solutions. We conclude by identifying key challenges and op-portunities for advancing contributions of plant–water relations re-search to ecohydrology in the future. Keywords: ecohydrology d plant water use d regime shift d thresholds d scaling d transpiration
[Show abstract][Hide abstract] ABSTRACT: Until recently, it has been challenging to couple hydrological and biogeochemical processes at the watershed scale. We have coupled two models, WTB and MEL, to simulate lateral water and nutrient fluxes and their influence on ecosystem functioning. WTB is a spatially explicit water balance model. Vertical flow was simulated using a capacitance model with lateral flow dependent on head development and the local slope of the confining layer. The Multiple Element Limitation (MEL) model is an ecosystem model, developed to examine limitation in vegetation acclimating to changes in the availability of two resources (carbon and nitrogen). MEL also incorporates the recycling of resources through the soil. In our coupled model, nutrients are treated as inert solutes and are transported vertically as well as laterally using a mixing model. Nutrients moving down the slope are repeatedly taken up, cycled through vegetation and soils, and released back into the soil solution. We are currently identifying the possibilities for incorporating flood dynamics into the model. We evaluated the impact of adding lateral nutrient fluxes to the original MEL model using a virtual experiment. The model (coupled and MEL only) was applied to a small, well defined catchment. After a simulation period of three years, we detect a redistribution of the stock of inorganic N. A larger amount of N is present near the river than at the top of the slopes of the catchment, largely due to lateral fluxes. Comparing the coupled model to the MEL model, we also find large losses of inorganic N in the coupled model due to large vertical fluxes out of the root zone. These vertical out-fluxes cause a smaller N uptake by plants. To detect if Carbon (C) uptake by plants is affected due to the changes in N distribution, the simulation period has to be increased due to a lag time in the optimization of the C:N ratio in plant biomass.
[Show abstract][Hide abstract] ABSTRACT: We studied three adjacent catchments located within the seasonal cloud forest belt in Central Veracruz, Mexico to understand the effects of land use change and climate change on discharge in these catchments. We gained such understanding from virtual experiments with a distributed hydrological model. Hydrological models would benefit from a more spatially distributed input for saturated hydraulic conductivity (Ksat) of the soil. We determined the spatial variability of (Ksat) in a pasture catchment and studied the relation between Ksat and penetration resistance of the soil, which is much easier to measure in the field, to enhance and facilitate a spatially distributed Ksat input in future hydrological modeling studies. Below 50 cm depth, Ksat curves are found to be similar along the slope in the pasture catchment. Comparing the Ksat curves between pasture and forest we also conclude that below 50 cm depth, hydraulic conductivities are similar for both land use types. Differences in the upper 10 cm of the soil are yet unknown but are expected to be large between pasture and forest. More measurements are needed in the pasture catchment to determine Ksat behavior in the upper 10 cm of the soil. Saturated hydraulic conductivity is negatively correlated with penetration resistance, with R2 values of 0.65 and 0.71. Our findings suggest that penetration resistance measurements can be used to determine Ksat behavior in the field. Conversion from pasture to a naturally regenerated secondary forest leads to a more fluctuating stream discharge and higher discharges during the wet season. Forest removal for pasture results in a total annual increase of discharge, where the bulk of the increase is observed in the dry season in the form of baseflow rather than an increasing response to rain events in the wet season. Climate change scenarios with rising temperatures cause small decreases in streamflow in the forest catchments, due to higher potential evaporation rates. As a result of more extreme rainevents we find total annual increases in streamflow in all three catchments. For the pasture catchment, this increase is found twice as high as for the two forest catchments, probably due to infiltration excess overland flow in the pasture catchment. Increases in streamflow occur during the wet season, when the mature forest and secondary forest more frequently experience saturation overland flow.