Structurally optimized modeling of non-linear effects of meteorological extreme events on water and solute dynamics
Final Report Abstract
Based on regional climate models increasing intensities of rainfall and drought events are anticipated for central Europe. Changes in the climatic and meteorological forcing will have impacts on the hydrologic dynamics and conditions in catchments, which are primary controls for biogeochemical processes and solute transformations. This will in turn affect the transport of solutes within and consequently their export from catchments. An improved understanding of the dominant hydrologic and biogeochemical processes that control the mobilization and transport of solutes in catchments is an important prerequisite to assess future water quality trends. We investigated the links between the hydrologic dynamics and biogeochemical patterns in the Lehstenbach catchment based on hydrologic and chemical field data as well as catchment and plot scale, explorative modelling. We identified two dominant hydrologic processes domains that contribute flow to the catchment outlet, deeper groundwater flows with residence times ranging from a few to more than 100 years and faster flow components from the riparian wetlands with residence times between hours and several days. The former are the main link between the upslope forested areas and the riparian wetlands and streams, whereas the latter control the event-based response of the system. Field data further suggest that deeper groundwater flow is the dominant export pathway for NO3 and SO4, whereas DOC is mainly derived from the riparian wetlands. We could show that the micro-topography of the hummocky wetland surface causes distinct shifts between surface and subsurface flow dominance and a non-linear, hysteretic relationship between the riparian water table and generated discharge, which is also evident in field data. Simulations of biogeochemical reactions along complex subsurface flow paths caused by the micro-topography show the formation of distinct biogeochemical patterns in the wetland with reactive hot spots for redox-sensitive species. Simulated vertical pore water profiles of the main solutes adequately match the range of observed profiles. Statistical analyses of water chemistry data revealed clear shifts in the chemical signature of stream water derived from a riparian wetland depending on the season and antecedent hydrologic conditions. Our findings to date strongly suggests that in the short term shifts in the meteorological forcing induced by climate change will primarily affect the hydrologic dynamics in the riparian wetlands with implications for the export of solutes derived from these areas.
Publications
- (2008), Mineralogical sources of the buffer capacity in a granite catchment determined by strontium isotopes, Appl Geochem, 23(10):2888-2905
Weyer, C. Lischeid, G., Aquilina L. and Pierson-Wickmann A.C.
- (2009), Effects of micro-topography on runoff generation and residence times in a riparian wetland, invited presentation at USGS, Menlo Park, USA
Fleckenstein, J.H. and Frei, S.
- (2010), Effects of micro-topography on surface-subsurface exchange and runoff generation in a virtual riparian wetland – a modeling study, Adv Water Resour, 33(11):1388-1401
Frei, S., Lischeid, G. and Fleckenstein J.H.
- (2011), Modelling interactions between hydrologic dynamics and biogeochemical processes in a riparian wetland of a low-order stream, IAHS Red Book 345:87- 92
Fleckenstein, J.H., Frei, S. and Knorr, K.H.
