Fine-scale spatiotemporal variations in bacterial community diversity in agricultural pond water.

Microbial communities in surface waters are affected by environmental conditions and can influence changes in water quality. To explore the hypothesis that the microbiome in agricultural waters associates with spatiotemporal variations in overall water quality and, in turn, has implications for resource monitoring and management, we characterized the relationships between the microbiota and physicochemical properties in a model irrigation pond as a factor of sampling time (i.e., 9:00, 12:00, 15:00) and location within the pond (i.e., bank vs. interior sites and cross-sectional depths at 0, 1, and 2 m). The microbial communities, which were defined by 16S rRNA gene sequencing analysis, significantly varied based on all sampling factors (PERMANOVA P < 0.05 for each). While the relative abundances of dominant phyla (e.g., Proteobacteria and Bacteroidetes) were relatively stable throughout the pond, subtle yet significant increases in α-diversity were observed as the day progressed (ANOVA P < 0.001). Key water quality properties that also increased between the morning and afternoon (i.e., pH, dissolved oxygen, and temperature) positively associated with relative abundances of Cyanobacteria, though were inversely proportional to Verrucomicrobia. These properties, among additional parameters such as bioavailable nutrients (e.g., NH3, NO3, PO4), chlorophyll, phycocyanin, conductivity, and colored dissolved organic matter, exhibited significant relationships with relative abundances of various bacterial genera as well. Further investigation of the microbiota in underlying sediments revealed significant differences between the bank and interior sites of the pond (P < 0.05 for α- and ß-diversity). Overall, our findings emphasize the importance of accounting for time of day and water sampling location and depth when surveying the microbiomes of irrigation ponds and other small freshwater sources.

Differential release of manure-borne bioactive phosphorus forms to runoff and leachate under simulated rain.

Limited information exists on the unhindered release of bioactive phosphorus (P) from a manure layer to model the partitioning and transport of component P forms before they reach an underlying soil. Rain simulations were conducted to quantify effects of intensity (30, 60, and 90 mm h-1) on P release from an application of 60 Mg ha-1 of dairy manure. Runoff contained water-extractable- (WEP), exchangeable and enzyme-labile bioactive P (TBIOP), in contrast to the operationally defined "dissolved-reactive P" form. The released P concentrations and flow-weighed mass loads were described by the log-normal probability density function. At a reference condition of 30 mm h-1 and maintaining the surface at a 5% incline, runoff was minimal, and WEP accounted for 20.9% of leached total P (TP) concentrations, with an additional 25-30% as exchangeable and enzyme-labile bioactive P over the 1-h simulation. On a 20% incline, increased intensity accelerated occurrence of concentrationmax and shifted the skewed P concentration distribution more to the left. Differences in trends of WEP, TBIOP, or net enzyme-labile P (PHPo) cumulative mass released per unit mass of manure between intensities were attributable to the higher frequency of raindrops striking the manure layer, thus increasing detachment and load of colloidal PHPo of the water phases. Thus, detailed knowledge of manure physical characteristics, bioactive P distribution in relation to rain intensity, and attainment of steady-state of water fluxes were critical factors in improved prediction of partitioning and movement of manure-borne P under rainfall.

Response of coliform populations in streambed sediment and water column to changes in nutrient concentrations in water.

As sediments increasingly become recognized as reservoirs of indicator and pathogen microorganisms, an understanding of the persistence of indicator organisms becomes important for assessment and predictions of microbial water quality. The objective of this work was to observe the response of water column and sediment coliform populations to the change in nutrient concentrations in the water column. Survival experiments were conducted in flow-through chambers containing sandy sediments. Bovine feces were collected fresh and introduced into sediment. Sixteen days later, the same fecal material was autoclaved and diluted to provide three levels - 1×, 0.5×, and 0.1× of nutrient concentrations - spike in water column. Total coliforms, Escherichia coli, and total aerobic heterotrophic bacterial concentrations were monitored in water and sediment. Bacteria responded to the nutrient spike with initial growth both in the water column and in sediment. The response of bacterial concentrations in water column was nonlinear, with no significant changes at 0.1 and .5× spikes, but a substantial change at 1× spike. Bacteria in sediment responded to the spikes at all added nutrient levels. Coliform inactivation rates both in sediment and in water after the initial growth occurred, were not significantly different from the inactivation rates before spike. These results indicate that introduction of nutrients into the water column results in nonlinear response of E. coli concentrations both in water and in sediments, followed by the inactivation with the same rate as before introduction of nutrients.

Comparing temperature effects on Escherichia coli, Salmonella, and Enterococcus survival in surface waters.

UNLABELLED: The objective of this study was to compare dependency of survival rates on temperature for indicator organisms Escherichia coli and Enterococcus and the pathogen Salmonella in surface waters. A database of 86 survival datasets from peer-reviewed papers on inactivation of E. coli, Salmonella and Enterococcus in marine waters and of E. coli and Salmonella in lake waters was assembled. The Q10 model was used to express temperature effect on survival rates obtained from linear sections of semi-logarithmic survival graphs. Available data were insufficient to establish differences in survival rates and temperature dependencies for marine waters where values of Q10  = 3 and a survival rate of 0·7 day(-1) could be applied. The Q10 values in lake waters were substantially lower in marine waters, and Salmonella inactivation in lake water was, on average, twice as fast as E. coli; data on E. coli substantially outnumber data on Enterococcus and Salmonella. The relative increase in inactivation with increase in temperature is higher in marine waters than lake water, and differences in inactivation between Salmonella and E. coli at a given temperature were significant in lake water but not in marine waters. SIGNIFICANCE AND IMPACT OF THE STUDY: Microbiological quality of surface waters is of paramount importance for public health. The novelty of this work is using a large compendium of published data to develop the first comparison of temperature effects on survival of the pathogen Salmonella and water quality indicator micro-organisms Escherichia coli and Enterococcus in natural waters. The existing relatively large body of knowledge on E. coli survival appears to be useful to assess the effect of temperature on survival of Salmonella. Moreover, results of this work constitute an essential input in models to support environmental management decisions on the use of surface water sources in agriculture, aquaculture and recreation.

Escherichia coli survival in waters: temperature dependence.

Knowing the survival rates of water-borne Escherichia coli is important in evaluating microbial contamination and making appropriate management decisions. E. coli survival rates are dependent on temperature, a dependency that is routinely expressed using an analogue of the Q10 model. This suggestion was made 34 years ago based on 20 survival curves taken from published literature, but has not been revisited since then. The objective of this study was to re-evaluate the accuracy of the Q10 equation, utilizing data accumulated since 1978. We assembled a database of 450 E. coli survival datasets from 70 peer-reviewed papers. We then focused on the 170 curves taken from experiments that were performed in the laboratory under dark conditions to exclude the effects of sunlight and other field factors that could cause additional variability in results. All datasets were tabulated dependencies "log concentration vs. time." There were three major patterns of inactivation: about half of the datasets had a section of fast log-linear inactivation followed by a section of slow log-linear inactivation; about a quarter of the datasets had a lag period followed by log-linear inactivation; and the remaining quarter were approximately linear throughout. First-order inactivation rate constants were calculated from the linear sections of all survival curves and the data grouped by water sources, including waters of agricultural origin, pristine water sources, groundwater and wells, lakes and reservoirs, rivers and streams, estuaries and seawater, and wastewater. Dependency of E. coli inactivation rates on temperature varied among the water sources. There was a significant difference in inactivation rate values at the reference temperature between rivers and agricultural waters, wastewaters and agricultural waters, rivers and lakes, and wastewater and lakes. At specific sites, the Q10 equation was more accurate in rivers and coastal waters than in lakes making the value of the Q10 coefficient appear to be site-specific. Results of this work indicate possible sources of uncertainty to be accounted for in watershed-scale microbial water quality modeling.