Geochemical and Microbial Community Attributes in Relation to Hyporheic Zone Geological Facies

Abstract

The hyporheic zone (HZ) is the active ecotone between the surface stream and groundwater, where exchanges of nutrients and organic carbon have been shown to stimulate microbial activity and transformations of carbon and nitrogen. To examine the relationship between sediment texture, biogeochemistry, and biological activity in the Columbia River HZ, the grain size distributions for sediment samples were characterized to define geological facies, and the relationships among physical properties of the facies, physicochemical attributes of the local environment, and the structure and activity of associated microbial communities were examined. Mud and sand content and the presence of microbial heterotrophic and nitrifying communities partially explained the variability in many biogeochemical attributes such as C:N ratio and %TOC. Microbial community analysis revealed a high relative abundance of putative ammonia-oxidizing Thaumarchaeota and nitrite-oxidizing Nitrospirae. Network analysis showed negative relationships between sets of co-varying organisms and sand and mud contents, and positive relationships with total organic carbon. Our results indicate grain size distribution is a good predictor of biogeochemical properties, and that subsets of the overall microbial community respond to different sediment texture. Relationships between facies and hydrobiogeochemical properties enable facies-based conditional simulation/mapping of these properties to inform multiscale modeling of hyporheic exchange and biogeochemical processes.

Influence of Hydrological Perturbations and Riverbed Sediment Characteristics on Hyporheic Zone Respiration of CO2 and N2

“…As pointed out by Harvey et al () and Lansdown et al (), studies on the role of streambed sediments on DN rates often provide inconsistent, often conflicting rates as a function of grain sizes. Conflicting results range from reports of higher overall respiration rates in coarse sediments (B. N. Harvey et al, ; Hou et al, ) and greater DN in coarse gravels in the top 10 cm along stream riffles (Lansdown et al, ) to reports of lower DN in coarse grain sizes (Garcia‐ruiz et al, ) and greater microbial activity in gravels paired with lower DN rates (Dodds et al, ). A variety of geomorphic, hydrodynamic, climatic, and sediment conditions have emerged as factors jointly controlling DN rates, yet the fundamental role of sediment structure in controlling respiration rates is missing (Findlay, ; J. W. Harvey et al, ; Ritz et al, ).…”

Identification and mapping of riverbed sediment facies in the Columbia River through integration of field observations and numerical simulations

“…Following the classification system of Folk (), the samples can be classified into four different geological classes: gravel (G), muddy gravel (MG), muddy sandy gravel (MSG), and gravelly mud (GM). Within this 320‐m reach, bio‐geochemical properties were shown to have good correspondence to the Folk grain size classes (Hou et al, ). The usefulness of the hydrodynamics‐based riverine facies identified in this study can be further evaluated by comparing the Folk classes with the riverine facies at the freeze core sample locations.…”

“…In Hou et al (), the relationships amongst biogeochemical and geological properties in the hyporheic zone along the Columbia River were investigated for the area of the Hanford Reach shown in Figure . GSD was determined for 55 freeze core samples taken just below the water line along 320 m of shoreline.…”

“…The alluvial layer is also known to be highly heterogeneous in both physical properties and biogeochemical processes. The spatial variations in local microbial activity are hypothesized to be strongly controlled by physical heterogeneity (Hou et al, ), and could give rise to biogeochemical microenvironments within the alluvium. However, direct observation is limited by physical inaccessibility and primarily consists of a small number of sediment cores collected by freeze‐coring (Hou et al, ; Moser et al, ) and local slug tests conducted in aquifer tubes screened within the alluvium (see (CH2M, ) Appendix C).…”

“…Conventional geologic facies classifications are linked to and used to interpret depositional environments and successional sequences (Reading, ). The facies concept has been extended to classifications based on a variety of sediment attributes with a range of specific practical applications, including hydrofacies (e.g., Klingbeil, Kleineidam, Asprion, Aigner, & Teutsch, ; Ritzi et al, ), geophysical facies (e.g., Šimíček & Bábek, ), reactive facies (e.g., Sassen et al, ), biogeochemical facies (e.g., Stegen et al, ), and microbial facies (Hou et al, ).…”