Project Details
Projekt
Overlooked bed shift? Modulation of the stream microbial food web and metabolism by patches of migrating sand ripples
Subject Area
Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
Term
from 2018 to 2023
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 400895888
The overall objective of the project is to understand the significance of sediment disturbance in migrating sand ripples for the structure of the microbial food web and the metabolism in streams and rivers. The common concept of sediment disturbance in stream ecology focusses on 'catastrophic' singular big flood events that cause deep scour and far downstream relocation of sediments. However, low discharges can already relocate fine sediments. Streams with a large proportion of sandy sediments experience movement of sand in patches of migrating ripples (MRPs). MRPs occur over a wide range of flows and can cover the entire stream bed in the extreme. Given the increased input of sand in most cultivated catchments around the world, MRPs are a predominant feature in many, if not the majority of streams. Despite the phenomenon’s ubiquity, implications of migrating ripples on the microbial food web and metabolism have been largely neglected. Data from the few existing observational studies on the significance of shifting sands report contradicting findings. The aim of the proposed project is to clarify the significance of sediment disturbance by periodically shifting sands in MRPs for the microbial food web (community structure and functional feeding mode), carbon flow towards invertebrates (13C incorporation into PLFA of microorganisms and invertebrates) and stream bed metabolism (community respiration and gross primary production). Derived from previous studies we assume MRPs to change local (within ripple patch) and linked microbial food webs in stable bed sediment patches (SBPs) due to group or species-specific responses, and in turn affect the overall metabolism and trophic state of the streams. We propose i) sediment disturbance in MRPs to shift metabolism, microbial food web and carbon flow towards heterotrophy disregarding light intensity and nutrient concentrations, ii) that whole stream metabolism changes non-linearly in relation to MRP coverage due to increased overall vertical water flux to hyporheic stable sediments by MRPs and iii) that return of metabolism and microbial community structure after periodic sediment disturbance by ripple migration depends on duration in MRPs and light availability. The project approaches its objectives in a series of experiments in a laboratory microcosm device simulating the micro-environment in migrating ripples and in 16 outdoor experimental streams with variable proportion of MRPs and SBPs. The experiments will be completed and verified by field work measuring in situ metabolism and vertical water flux and observing the microbial food web and carbon flow in migrating ripples of streams and rivers. We want to achieve a mechanistic understanding for the whole stream metabolic effects of migrating ripple patches (MRPs). The project findings will significantly contribute to better valuate migrating sand in streams and rivers with implications for the management of ecosystem functions and services.
DFG Programme
Research Grants
