Seasonal Patterns in Microbial Community Composition in Denitrifying Bioreactors Treating Subsurface Agricultural Drainage.

Denitrifying bioreactors, consisting of water flow control structures and a woodchip-filled trench, are a promising approach for removing nitrate from agricultural subsurface or tile drainage systems. To better understand the seasonal dynamics and the ecological drivers of the microbial communities responsible for denitrification in these bioreactors, we employed microbial community "fingerprinting" techniques in a time-series examination of three denitrifying bioreactors over 2 years, looking at bacteria, fungi, and the denitrifier functional group responsible for the final step of complete denitrification. Our analysis revealed that microbial community composition responds to depth and seasonal variation in moisture content and inundation of the bioreactor media, as well as temperature. Using a geostatistical analysis approach, we observed recurring temporal patterns in bacterial and denitrifying bacterial community composition in these bioreactors, consistent with annual cycling. The fungal communities were more stable, having longer temporal autocorrelations, and did not show significant annual cycling. These results suggest a recurring seasonal cycle in the denitrifying bioreactor microbial community, likely due to seasonal variation in moisture content.

Spatial and temporal variation of algal assemblages in six Midwest agricultural streams having varying levels of atrazine and other physicochemical attributes.

Potential effects of pesticides on stream algae occur alongside complex environmental influences; in situ studies examining these effects together are few, and have not typically controlled for collinearity of variables. We monitored the dynamics of periphyton, phytoplankton, and environmental factors including atrazine, and other water chemistry variables at 6 agricultural streams in the Midwest US from spring to summer of 2011 and 2012, and used variation partitioning of community models to determine the community inertia that is explained uniquely and/or jointly by atrazine and other environmental factors or groups of factors. Periphyton and phytoplankton assemblages were significantly structured by year, day of year, and site, and exhibited dynamic synchrony both between site-years and between periphyton and phytoplankton in the same site-year. The majority of inertia in the models (55.4% for periphyton, 68.4% for phytoplankton) was unexplained. The explained inertia in the models was predominantly shared (confounded) between variables and variable groups (13.3, 30.9%); the magnitude of inertia that was explained uniquely by variable groups (15.1, 18.3%) was of the order hydroclimate>chemistry>geography>atrazine for periphyton, and chemistry>hydroclimate>geography>atrazine for phytoplankton. The variables most influential to the assemblage structure included flow and velocity variables, and time since pulses above certain thresholds of nitrate+nitrite, total phosphorus, total suspended solids, and atrazine. Time since a ≥30 µg/L atrazine pulse uniquely explained more inertia than time since pulses ≥ 10 µg/L or daily or historic atrazine concentrations; this result is consistent with studies concluding that the effects of atrazine on algae typically only occur at ≥30 µg/L and are recovered from.

Spatial variation in the bacterial and denitrifying bacterial community in a biofilter treating subsurface agricultural drainage.

Denitrifying biofilters can remove agricultural nitrates from subsurface drainage, reducing nitrate pollution that contributes to coastal hypoxic zones. The performance and reliability of natural and engineered systems dependent upon microbially mediated processes, such as the denitrifying biofilters, can be affected by the spatial structure of their microbial communities. Furthermore, our understanding of the relationship between microbial community composition and function is influenced by the spatial distribution of samples.In this study we characterized the spatial structure of bacterial communities in a denitrifying biofilter in central Illinois. Bacterial communities were assessed using automated ribosomal intergenic spacer analysis for bacteria and terminal restriction fragment length polymorphism of nosZ for denitrifying bacteria.Non-metric multidimensional scaling and analysis of similarity (ANOSIM) analyses indicated that bacteria showed statistically significant spatial structure by depth and transect,while denitrifying bacteria did not exhibit significant spatial structure. For determination of spatial patterns, we developed a package of automated functions for the R statistical environment that allows directional analysis of microbial community composition data using either ANOSIM or Mantel statistics.Applying this package to the biofilter data, the flow path correlation range for the bacterial community was 6.4 m at the shallower, periodically in undated depth and 10.7 m at the deeper, continually submerged depth. These spatial structures suggest a strong influence of hydrology on the microbial community composition in these denitrifying biofilters. Understanding such spatial structure can also guide optimal sample collection strategies for microbial community analyses.

Seasonal synchronicity of algal assemblages in three Midwestern agricultural streams having varying concentrations of atrazine, nutrients, and sediment.

Numerous studies characterizing the potential effects of atrazine on algal assemblages have been conducted using micro- or mesocosms; however, few evaluations focused on in situ lotic algal communities, potentially confounding risk assessment conclusions. This exploratory study, conducted at several sites in the midwestern United States where atrazine is commonly used, presents in situ observations of native algal communities relative to atrazine exposure and other parameters. Planktonic and periphytic algae from three streams in three Midwestern states, having historically differing atrazine levels, were sampled over a 16-week period in 2011 encompassing atrazine applications and the summer algal growth period at each site. Changes in abundance, diversity, and composition of algal communities were placed in the context of hydrological, climatic, and water quality parameters (including components sometimes present in agricultural runoff) also collected during the study. Diatoms dominated communities at each of the three sites and periphyton was much more abundant than phytoplankton. As expected, significant variations in algal community and environmental parameters were observed between sites. However, correspondence analysis plots revealed that patterns of temporal variation in algal communities at each site and in periphyton or phytoplankton were dominated by seasonal environmental gradients. Significant concordance in these seasonal patterns was detected among sites and between phytoplankton and periphyton communities (via procrustes Protest analysis), suggesting synchronicity of algal communities across a regional scale. While atrazine concentrations generally exhibited seasonal trends at the study watersheds; no effects on algal abundance, diversity or assemblage structure were observed as a result of atrazine pulses. This lack of response may be due to exposure events of insufficient concentration or duration (consistent with previously reported results) or the composition of the algal assemblages present. This was in contrast to the effects of elevated flow events, which were associated with significant changes in periphyton abundance, diversity and assemblage.