AbstractsBiology & Animal Science

Determination of biotic and abiotic factors influencing soil structure development in a riparian system based on observational and experimental approaches

by Ulfah Mardhiah

Institution: Freie Universität Berlin
Department: FB Biologie, Chemie, Pharmazie
Degree: PhD
Year: 2015
Record ID: 1112011
Full text PDF: http://edocs.fu-berlin.de/diss/receive/FUDISS_thesis_000000098889


Flagogna reach endures various disturbances, mainly due to the natural dynamics of the river system. As described in Bertoldi et al., (2009), river flow with water levels of approximately 200 cm (as measured in the local Villuzza gauge), will cause an interaction between the river flow and the various vegetated patches within the reach. Further increase of water level (above 300 cm) will cause severe vegetation disturbance, most importantly erosion on fluvial island margins and the uprooting of mature trees which will later disperse within the reach serving as fluvial island nucleation points. We used both field measurements (dendrochronology) and historical sources (river stage records, oblique photographs, and aerial image analysis) to construct the historical changes of different age patches within the reach. We found that both approaches sufficiently support each other and help us to specifically identify the time of uprooted trees establishment and how they developed or eroded through certain temporal sequence. We also found that the aerial image analysis is a valuable tool and statistically correct in supporting our current analysis. We managed to use the various tools to understand the phases of island development within the reach. Our oldest sampling area, for example, showed the evolution of fluvial islands before the dispersal of uprooted trees, right after the establishment of uprooted trees, and then followed the evolution from pioneer, building and finally established island as its current state. We also found that historically, the dispersal of uprooted trees does not guarantee that these pioneer islands develop into established islands. Our data showed (Chapter 2) that various island age groups can take different rates of development constrained by the particular dynamics experienced within each of the different age groups. The permanence of fluvial islands in such dynamic system has been known to be relatively unstable, with islands usually incapable of sustaining more than a decadal temporal range (Wyrick and Klingeman, 2011). This study showed how at least in our period of study (~40 years) uprooted trees can be deposited and developed into established island and how the development of younger islands (building and pioneer islands) will mainly be constrained by the coming flood pulses and their magnitude. We understood from our system that the aggrading process and relative distance of vegetated island patches to the water table is an important factor which ensures a gradual evolution of fluvial islands. We also understood that disturbances like flood and flow pulses will be able to reset the development of fluvial islands. We found that as fluvial islands develop through time, so does the surface soil structure (Chapter 3). In fact our system reaches ~80% macroaggregate content within 40 years. We found that the rate of growth was constrained differently; such that in the short to medium term it was highly varied and mostly depended on the organic carbon content, fungal variables and also…