ESR5: Effects of hydrogeomorphology and temperature on carbon cycling in stream gravel bars
Research Fellow: Kyle Boodoo, University of Vienna (Austria)
My main research interest is the development and application of ecohydrological concepts on the micro- to landscape scale. I am particularly interested in the application of interdisciplinary research techniques which utilize a unique combination of hydrology, ecology and biogeochemistry to determine the interaction among the physical (discharge, temperature, stream morphology), chemical (organic matter composition, dissolved oxygen/carbon dioxide), and biotic (micro-organisms, macroflora and fauna) components of stream ecosystems. I additionally have a keen interest and strong background in water resources management, in particular environmental flow assessment and the impact of anthropogenic changes to instream ecosystem structure and function.
My current research is focused on the elucidating the effects of changing discharge and temperature regimes on the hydrogeomorphological and temperature characteristics within the hyporheic zone of a coldwater alpine streams. My current worksite is located at the Oberer Seebach, Austria (Fig. 1). The main objectives of the study are to: i) Determine the presence and permanence of biogeochemical hotspots within gravel bars and the factors influencing these; ii) quantify and qualify the impacts of changing instream flow conditions on the physiochemical properties and biogeochemical processes in the hyporheic zone; iii) Elucidate the possible impacts of changing conditions on the stream scale Carbon cycle and metabolism.
Figure 1: The gravel bar at Oberer Seebach, Austria
The hyporheic zone (Fig. 2) is the saturated transition zone between surface water and groundwater bodies that derives its specific physical (e.g. water temperature) and biogeochemical (e.g. steep chemical gradients) characteristics from active mixing of surface and groundwater which provide a habitat and refugia for obligate and facultative species.” (Krause et al. 2009)
Figure 2: Hyporheic exchange in rivers, occurs in all 3-axial directions and is influenced by groundwater levels/forcing, in-stream structures (Gravel bars, log dams) , site specific and general river morphology (stream gradient and sinuosity) and river discharge levels (Source: Stonedahl (2013))
The hyporheic zone is a highly dynamic ecotone which undergoes constant changes in fluxes of streamwater and groundwater inputs and their associated chemical properties and nutrient/organic matter loads (Fig. 3). Thus the hyporheic surface-groundwater interface inherently plays a significant role in stream biogeochemistry. (Bardini et al. 2012)
Exchange fluxes between the hyporheic zone and the adjacent groundwater and stream (Source: Modified from USGS (2013))
Watch this short video of ESR5 Kyle Boodoo introducing himself and talking about his Interfaces project:
The hyporheic zone is the saturated transition zonebetween surface water and groundwater bodies, where the mixing of the two water bodies occurs. It is characterized by specific physical (e.g. water temperature) and biogeochemical (e.g. sharp changes in chemical composition) characteristics which provide a habitat and refugia for obligate and facultative species (Adapted from Krause et al. 2009).
The study of the transport and physiochemical changes of certain biologically important substances between a system (e.g a river and its basin) and the organisms within the system over a certain spatial area and time period.
The interdisciplinary science which investigates how the physical structure and composition of landforms determines the physical characteristics (e.g rate and direction of movement) of a water body and how in turn the water body alters the structure and composition of the landform over a certain spatial area and time period.
An interdisciplinary science that focuses on the interaction and linkage of hydrologic processes with landforms or earth materials and the interaction of geomorphic processes with surface and subsurface water in temporal and spatial dimensions (Sidle & Onda 2004).
A temporary or perennial instream structure which may or may not be attached to the bank of the river, consisting mainly of coarse material deposited by the river. The shape, size and composition of the gravel bar depends on the typical hydraulic conditions and physical features (e.g degree of meandering and geometry) of the river. Gravel bars facilitate movement of surface (river) and groundwater, in addition to dissolved and particulate matter through it at a rate dependant on its characteristic permeability and porosity. Gravel bars may or may not be vegetated, depending on their permanency.
The most common scale of study for rivers in which a relatively short, representative sub-section of a river’s length in the order of 10s -1000s of metres, which includes all main features found along the entire river’s length. Studies at this scale allow for the characterization of the physical, chemical and biological processes which occur within the river (thought to me a multiple of the study reach). Other scales of study : micro (centimetres) ; pool/riffle (10-100’s of meters); segment (100’s to 1000’s of metres) catchment (10’s to 1000’s of square kilometres) ; basin scale (100’s to 1000’s of square kilometres).
The sum of biochemical life sustaining processes occurring within the cells of organisms in which substances derived from the environment are physically and chemically transformed to provide energy for respiration and regulatory and growth processes of the organism, which results in the release of characteristic metabolic waste substances into the environment of the organism, indicating the form/degree of individual/community metabolism.
Warming of the surface layer of poorly mixed/slow moving water bodies by the sun’s energy can result in the occurrence of a separation of parcels of water based on temperature induced density differences, in which a stable warmer and less dense water layer occurs and is maintained above a cooler more dense water layer. Stratification can cause the reduction/prevention of upwelling of cooler water to the surface, increasing subsurface water residence time. The degree of stratification depends on the temperature difference resulting from the intensity and period of effective heating from the energy source.
Upwelling is movement of water and its associated particulate and dissolved substances upward toward the surface or across a transitional boundary (e.g movement of water/substances from the river bed sub-surface to the stream). Downwelling represents the process occurring in the opposite direction (movement of water/substances from the river downward from the bed sub-surface to the stream channel).
The movement of parcels of water through the water column due to temperature-density differences. Warm, lighter parcels of water move upward through the water column, while cooler, more dense water parcels sink downward.
Hydrodynamic hyporheic pathways
The movement of water through the hyporheic zone (flow path length, direction and velocity) is the result of several factors dependent on the scale of study. At the reach scale, river bed/bank topography and permeability are the major determinants of flow rate and direction.
The process by which the concentration of a chemical (eg. dyes, salts, and stable isotopes) added to a water body or some natural physical/chemical property (temperature/salinity) of the water body is utilized to determine one or more aspects of the system’s hydrology (e.g. water residence time, fractional mixing of water bodies, identification of water inflow/outflow areas and mixing pattern of water bodies) based on the measured concentrations of the added chemical/natural property at a downstream measuring point. Tracers may be conservative (do not change in chemical properties/decay over time) or non-conservative (are affected by factors other than dilution).
Mass spectrometry (MS)
MS is a chemical analytical technique which ionizes a sample and measures the resultant mass to charge ratio of different chemical fragments of the sample, each of which can be identified based upon its isotopic signature, thus allowing for the structural composition and thus identity of different chemicals within the analysed sample to be identified.
Dissolved Organic Carbon
Dissolved organic carbon is composed primarily of two categories of substances: (i) non-humic substances, a class of compounds that includes carbohydrates, proteins, peptides, fats, pigments and other low molecular weight compounds, and (ii) humic substances which form most of the organic matter in waters, and consist of coloured hydrophilic and acidic complexes ranging in molecular weight from the hundreds to thousands (Wetzel 1975)3. Non-humic substances are easily utilized and degraded by microorganisms (i.e., substances are labile) and exhibit rapid flux rates in aquatic systems. Their instantaneous concentrations are usually very low as a result, although they may play an important role in system metabolism. Humic substances are formed largely as a result of microbial activity on plant and animal material and are more persistent than non-humic substances. (Ministry of the Environment, Province of British Colombia 2013).
The processes in which the Carbon contained within source substances or reservoirs (e.g plant material from leaf litter or dissolved CO2) is altered via a series of biochemical reactions, being converted from one form/degree of complexity to another as it moves through the ecosystem from source to sink in a cyclical pattern.