Forensic hydrology: what function tells about structure in complex settings

Abstract

Facing the challenges of the European Water Framework Directive and competing demands requires a sound knowledge of the hydrological system. This is a major challenge in regions like Northeast Germany. The landscape has been massively reshaped during repeated advances and retreats of glaciation during the Pleistocene. This resulted in a complex setting of unconsolidated sediments with high textural heterogeneity and with layered aquifer systems, partly confined, but usually of unknown number and extent of single aquifers. The Institute of Landscape Hydrology aims both at a better understanding of hydrological processes and at providing a basis for sustainable water resources management in this region. That would require sound information about the respective regions of interest that are rarely available at sufficient degree of detail. Thus, there is urgent need for alternative approaches. For example, time series of groundwater head, lake water level and stream runoff do not only depend on (unknown) geological structures, but in turn can reveal information about major geological features. To that end, different approaches have been developed and successfully applied at different scales, based both on advanced time series analysis and dimension reduction approaches and on well-known and rather simple methods. This approach has been coined ''forensic hydrology'': Like in a crime story, numerous pieces of evidence are combined in a systematic way to end up with a consistent conceptual model about the prevailing cause-effect relationships. An example is given for the Quillow catchment in Northeast Germany in a rather complex geological setting.

Interdisciplinary Geo‐ecological Research across Time Scales in the Northeast German Lowland Observatory (TERENO‐NE)

“…A patchwork of small drainless depressions, called (glacial) kettle holes, occurs. Within the Quillow River catchment, 1176 kettle holes have been identified (Lischeid et al, 2017). Many of them are at least occasionally filled with water, whereas the rest are filled with mineral soil and peat (Nitzsche et al, 2017).…”

Characterizing hydrological processes within kettle holes using stable water isotopes in the Uckermark of northern Brandenburg, Germany

“…To that respect, the initial studies conducted in the Uckermark region suggested that kettle holes are disconnected from groundwater domain and they should be treated as isolated water standings (Kalettka, Rudat, & Quast, ). Recent studies have suggested that the isolated kettle holes can be variably connected to each other as well as to the shallow groundwater and may show seasonally variable interactions (Gerke, Koszinski, Kalettka, & Sommer, ; Kalettka & Rudat, ; Lischeid et al, ; Nitzsche et al, ). This connection could potentially be related to the topographical position of a kettle hole with respect to the shallow groundwater system (Lischeid et al, ).…”

“…With respect to the major water suppliers of potholes, pond's permanence of the prairie pothole region is highly dependent on the direct rainfall on the potholes and upland run‐off generated form snow drift, snowmelt run‐off, and occasional summer run‐off during heavy rains (Brooks et al, ; Hayashi et al, ). By contrast, the pond's permanence of the kettle holes in the north‐east of Germany is heavily reliant upon the shallow groundwater inflows (Lischeid et al, ; Lischeid et al, ; Nitzsche et al, ) and is partially supplied with the direct rainfall on ponds and diffuse run‐off produced as a result of rainfall occurrence on the frozen soils (Gerke et al, ). Therefore, as there are a few studies in the north‐east of Germany (where the kettle holes are highly scatted) that have attempted to gain insights into the water storage suppliers of these kettle holes, the results of this study can be compared with an intensive and progressive research undertaken so far in the North of America.…”

Ephemeral kettle hole water and sediment temporal and spatial dynamics within an agricultural catchment

“…Glacial fluvial in origin, kettle holes are small ponds (<0.01 km 2 ) that form within landscape depressions. Evidence exists that shows kettle holes are not connected to groundwater (Gerke, Koszinski, Kalettka, & Sommer, ; Kalettka, Rudat, & Quast, ) or at a minimum, a hydrologic connection exists only during certain times in the growing season (Lischeid et al, ). The perimeter of kettle holes also changes rapidly with hydroperiod, and given that the area occupied by temporarily water‐filled kettle hole types (herein referred to as temporary kettle holes) is large, we might expect large spatial variation in organic matter (OM) turnover within the kettle hole vicinity.…”