Perspectives and predictions on the microbial ecology of the hyporheic zone

Abstract

1. Studies of hyporheic microbial ecology have suggested an important role for hyporheic microbial processes in stream ecosystem functioning. Using evidence from microbial communities in other aquatic habitats, some predictions are made concerning the diversity of microbial types and microbial processes likely to occur in the hyporheic zone, and the relative importance of these various types to the hyporheic ecosystem. 2. It is predicted that the biofilm growth form of interstitial micro‐organisms will create a variety of microniches, allowing coexistence of a great diversity of microbial types, and promoting the activity of some otherwise poor competitors. It is further predicted that the confluence of reduced groundwaters and aerobic surface waters will favour chemolithotrophic processes in the hyporheic zone, but that these will contribute significantly to hyporheic production only if surface water is very low in dissolved organic carbon, or the groundwater is extremely reduced, such as by the influence of riparian wetlands. A variety of anaerobic respiratory pathways, such as nitrate, ferric ion, sulphate and even methanogenic respiration will be employed in the hyporheic zone, with biofilm dynamics permitting these to occur even in aerobic sediments. Anaerobic pathways may account for a significant proportion of total hyporheic organic matter mineralization. 3. The role of fungi in hyporheic dynamics is, as yet, almost completely unstudied. However, it is expected that they will be important in breaking down buried particulate organic matter (POM), which may account for a large proportion of total stream POM. 4. Physicochemical conditions in hyporheic sediments appear to be highly heterogeneous, and this heterogeneity may be very important in the cycling of certain nutrients, especially nitrogen, which involves a series of steps requiring different conditions. 5. Various new techniques are now available by which biofilm dynamics and in situ microbial processes may be measured. Studies are recommended of intact microbial communities both at the microscale of the biofilm and at the scale of the heterogeneities occurring in hyporheic sediments. Studies are needed that measure actual rates of microbial processes under in situ conditions.

Methanogenic System of a Small Lowland Stream Sitka, Czech Republic

“…The river hyporheic zone, volume of saturated sediment beneath and beside streams containing some proportion of water from surface channel, plays a very important role in the processes of self-purification because the river bed sediments are metabolically active and are responsible for retention, storage and mineralization of organic matter transported by the surface water (Hendricks 1993;Jones & Holmes 1996, Baker et al 1999, Storey et al 1999, Fischer et al 2005. The seemingly well-oxygenated hyporheic zone contains anoxic and hypoxic pockets ("anaerobic microzones") associated with irregularities in sediment surfaces, small pore spaces or local deposits of organic matter, creating a 'mosaic' structure of various environments, where different microbial populations can live and different microbially mediated processes can occur simultaneously (Baker et al 1999, Morrice et al 2000, Fischer et al 2005.…”

Factors Controlling Sediment Denitrification Rates in Grassland and Forest Streams

“…The polyanionic polysaccharide matrix in the biofilm can capture OC and other nutrients from the stream water by ion exchange. Microbes use these resources as energy sources (Freeman and Lock 1995;Storey et al 1999). Denitrification rates can be higher in biofilms than in other sites such as stream water due to the supply of a highly-degradable OC and nutrients from biofilms (Howard-Williams et al 1989;Christensen et al 1990;Mariñelarena and Giorgi 2001;Bastviken et al 2003;Toet et al 2003;Venterink et al 2003).…”

Ecological effects on streams from forest fertilization; literature review and conceptual framework for future study in the western Cascades

“…Thus, if dissolved-N input during summer is through the riverbed as ground water is important, subsequent algal uptake and spiraling (Newbold et al, 1981) is likely to reduce the ability to measure the added nitrogen in the water column (Peterson et al, 2001), even though it may be transported downstream by recycling in benthic layers or as sloughed algae. Additionally, added N in a hyporheic zone could increase heterotrophic metabolism (Mullholand et al, 1997(Mullholand et al, , 1999Storey et al, 1999) while obscuring the increased N input in streams.…”

“…Extensive syntheses of various hyporheic processes and findings have been published by Cirmo and McDonnell (1997), Boulton et al (1998), Dahm et al (1998), and Storey et al (1999). Hyporheic function can be critical in determining hydrologic flow paths and nutrient exchange, as well as transformations of carbon and nitrogen.…”