Microbial Transport Processes in the Environment: Cells and Solutes I
Presiding: K Searcy, Northwestern University; A Packman, Northwestern University; S Findlay, Institute of Ecosystem Studies
B23A-01 INVITED 13:30h
Hydrodynamics as multi-scale control on cells and solutes - an overview
The transport of cells and solutes has numerous important applications including movement of pathogens, introduction of organisms for bioremediation of aquifers, and controls on nutrient uptake and carbon processing in stream ecosystems. The transfer of microbial cells and solutes among aquatic habitats is mediated by the movement of water, and the growth of microbial communities reflects local habitat conditions. Conversely the nature of sediment biofilms and other biota can influence the hydraulic conductivity of sediments and the flux of water across the sediment-water interface. At the smallest scales, interaction of water-borne solutes and particles (including cells) with sediment grain surfaces depends on local flow conditions, surface-chemical characteristics such as charge, and removal processes (solute consumption, particle attachment) at the grain surface. At intermediate scales, flow through sediments is a function of the bed structure, which may be modified by micro-and macro-organisms. At the catchment scale, high flow events affect connections among landscape elements, which may be sources of solutes and cells, and perturb processes across a wide variety of scales. Various aquatic communities may be disturbed to different degrees by high flow events, and both the timing and magnitude of these disturbances influence the organization of the physical and biological systems. Feedback between flow, sediment structure, and biological growth ultimately yield diverse habitat conditions, biological communities and metabolic capacity. We propose a framework where large-scale factors such as geomorphology and climate are increasingly modified by biotic influences at smaller scales. Strong coupling across scales and between physical, chemical, and biological processes emphasizes the need to consider system behavior in an integrated fashion
B23A-02 13:45h
Transport of Cryptosporidium parvum in Surface Waters: Interplay of Hydrodynamic Processes, Sediments, and Biofilms
Understanding the movement of pathogens in the environment is necessary to ensure the safety and protection of municipal water supply systems. Cryptosporidium parvum is a human pathogen of particular concern as it is common in surface waters of the United States, it can survive for long periods of time in the environment, and it is difficult to disinfect in water treatment plants. The transport of oocysts through watersheds can be mediated by interactions with the stream channel and suspended particles in the water column. For example, the association of C. parvum oocysts with suspended particles can alter the effective physical properties of the oocysts and increase their settling velocity. The hydrodynamic coupling of the overlying water with the pore water of the sediment bed can carry oocysts from the surface water into the sediment bed. Surface-attached communities of microorganisms, called biofilms, are ubiquitous in surface water systems and can capture C. parvum oocysts. Laboratory experiments were conducted at multiple scales (flowcell, batch, and flume) to determine the association of oocysts with sediments and biofilm communities and to assess the impact of this association on C. parvum transport. The effects of flow conditions, water chemistry, sediment composition, biofilm composition, and biofilm structure on these associations were all evaluated. The experimental results demonstrate that oocyst-sediment-biofilm interactions have significant implications for the propagation of C. parvum oocysts through watersheds and should generally be considered when predicting the fate of pathogens in the environment.
B23A-03 14:00h
The Influence of Seasonally Changing Groundwater/Surface Water Interaction on the Composition of Sediment Fauna
Sediment fauna in both streams and groundwater are crucial to the functioning of sediment processes, and are known to be highly influenced by hydraulics. But how does the seasonal variation of groundwater/surface water interactions influence the faunal composition? This question was addressed in a small Western Australian catchment, where four stream sediment sites and 30 groundwater bores were sampled over the period of one year. Mixed fauna at those sites displaying groundwater/surface water interaction was expected. However, there were virtually no species common to groundwater bores and stream sediment tubes, although they were sampled using the same method. The missing species exchange was probably due to the small pore spaces. Since the hydrological and chemical variety within groundwater sites was surprising, going far beyond gradually changing interactions with surface water, we grouped the groundwater sites into four major hydrogeological classes and looked for patterns with which fauna reflected these groups. In two of these hydrogeological groups (Artesian and concentration zones) no fauna was found at all, while fauna was sampled regularly in discharging and recharging zones. Fauna in groundwater bores also reflected whether groundwater was recharged from precipitation alone or also at least seasonally from the stream.
B23A-04 INVITED 14:15h
Factors Influencing Biofilm Formation in Streams: Bacterial Colonization, Detachment and Transport
Surfaces in aquatic systems develop biofilms containing microorganisms embedded in complex extracellular matrices. Properties of the surface, water, and colonizing organisms impact biofilm formation. Biofilm features, physical disturbance, and interactions between macro- and microscopic organisms, in turn, influence detachment. In spite of the importance of biofilms, much remains unknown about factors controlling biofilms in streams and other natural environments. Experiments were conducted in the laboratory and field to examine factors influencing surface colonization, and subsequent biofilm formation, and detachment. Microscopy methods, fluorescent in situ hybridization and confocal laser microscopy, were used to examine responses, including abundance of different taxa and biofilm depth. From these experiments, we determined that different taxa differ in their colonization ability based on properties like extracellular polysaccharide production and surface features, like hydrophobicity and that water chemistry, such as magnesium concentration, plays an important role. Moreover, detachment varies among taxa and with environmental conditions and may be enhanced by activities of macrofauna. Variation in detachment, in turn, influences bacterial transport and subsequent re-attachment. Overall, examination of attachment, detachment, and interactions in biofilms allows us to begin to understand how environmental conditions may impact the function of these communities in aquatic systems.
B23A-05 14:30h
The Influence of Hyporheic-Surface Water Exchange on the Spatial Distribution of Benthic Algal Biomass and Community Composition in an Alluvial River.
We investigated the influence of hyporheic-surface water interactions on the spatial distribution of benthic algal biomass and community composition in the main-channel of the Middle Fork Flathead River in northwestern Montana. We examined hyporheic-surface water exchange at 120 randomly selected sites by measuring vertical hydraulic gradients (VHG) and hydraulic conductivities using metal piezometers. At each replicate site, we collected algae from a single cobble to analyze chlorophyll a concentration and estimate algal density and community composition. We used Non-metric Multidimensional Scaling (MDS) based on the Bray-Curtis Index of Similarity to evaluate the response of benthic algal communities to hyporheic-surface water exchange. Algal communities at upwelling (+VHG) and downwelling (-VHG) sites occupied discrete regions of ordination space created by the MDS. Algal communities at upwelling sites were dominated by the genus Stigeoclonium or Hydrurus, whereas communities at downwelling sites were dominated by the genus Achnanthidium. There was a statistically significant positive correlation between benthic algal biomass and hyporheic upwelling. The preliminary results of our study suggest that hyporheic-surface water exchange regimes influence the spatial distribution of benthic algal biomass and community composition in large alluvial rivers.
B23A-06 14:45h
Temporal Patterns of Periphyton Accumulation in a Temperate, Cold-Water Stream
Trophic state and producer abundance in streams are determined by many factors including climate, geology, watershed ecology, and anthropogenic influences. Spring Creek is a spring fed, limestone stream within the Chesapeake Bay watershed of central Pennsylvania. Variation in benthic algae was characterized at three-week intervals for one year, whereby collections were made at five sites to evaluate how biomass changed under seasonal fluctuations in ambient conditions. Biomass and taxonomic composition of the benthic algae on natural substrata were paired with physical data pertaining to flow, light, temperature, and other growth factors to determine which factors influence growth by the community. Preliminary data show varying degrees of seasonality at the sites, with some experiencing typical temperate fluctuations in the periphyton community and others showing little change over the year. Some sites on Spring Creek experienced limited temperature change annually and several appeared to be enriched with nutrients by development and agriculture within the local watershed. Additionally, scouring disturbances caused by floods during the sampling period clearly limited the accumulation of periphyton. Analysis of these observations combined with records of the physical conditions may identify the major factors in explaining the observed patterns in periphyton accumulation.