Variation in hydrologic connectivity as a result of microtopography explained by discharge to catchment size relationship

Oosterwoud, Marieke; van der Ploeg, Martine; van der Schaaf, Sake; van der Zee, Sjoerd


In hydrological terms, raised bogs are often approximated by simple models as in the acrotelm-catotelm concept. However, raised bogs are often characterized by a pronounced surface topography, causing large changes in connectivity of contributing areas on the bog. In this study, daily regression of measured discharges versus catchment areas is used to quantify the impact of surface topography on catchment connectivity within a raised bog. The resulting coefficient of determination shows the strength of the relationship between the discharge and catchment area over time under different hydrological conditions. Monitoring of discharge, water table, transmissivity, and basic weather data on a raised bog (1.9 km2) in eastern central Estonia took place from May 2008 to June 2010. Contributing areas, calculated based on the outlet's discharge volume (VQ) divided by the net precipitation volume ( VPnet), of the outlet containing the central pool-ridge system varied between 1×10-3 and 0.7 km2, suggesting significant differences in connectivity between hydrological events. Correlation between discharge and theoretical catchment size was high (R2>0.75) when the water table was close to the surface (less than 5 cm below peat surface), and consequently, transmissivities were also high (up to 1,030m2d-1), which led to connectivity of local storage elements, such as pools and hollows. However, a water table below this threshold resulted in large parts of the catchment being disconnected. The importance of water table depths on catchment connectivity suggests the need to reconsider the hydrological concept of raised bogs; to incorporate these shallow flow components and better understand residence time and consequently transport of solutes, such as DOC, from patterned peatlands.