capturing-flow-weighted-water-suspended-particulates-from

Capturing Flow-weighted Water and Suspended Particulates from Agricultural Canals During Drainage Events

The purpose of this study is to describe the methods used to capture flow-weighted water and suspended particulates from farm canals during drainage ...

University of Florida

Flow adsorption calorimetry was used to investigate the energetics of arsenate sorption on amorphous aluminum hydroxide (AHO) and its effect on surface charge and ion exchange. Arsenate sorption at pH 5.7 was exothermic and the molar heats of adsorption were quite variable, ranging from -3.0 to -66 kJ/mol. Repetitive exposure of the same sample to arsenate in the calorimeter showed that the AHO was able to regenerate a considerable amount of reactive surface over time periods as short as 15 to 20 min. The large variability in heats of arsenate adsorption and the ability to regenerate reactive surface is believed to result from the amorphous nature of the AHO used. Heats of Cl/NO3 exchange were much smaller and more consistent, ranging from about 3.0 to 6.0 kJ/mol. The molar ratio of exchangeable Cl:Al was about 6:1 for the AHO, indicating a highly porous material. At pH 5.7, arsenate sorption neutralized surface positive charge as measured by Cl/NO3 exchange. Only at the two highest loadings (>60,000 mg/kg) did arsenate sorption result in any negative surface charge as measured by Na/K exchange. These results showed that most of the arsenate was adsorbed by a mechanism that involved no increase in surface negative charge. The PZNC of the AHO decreased by about 1 pH unit when exposed to arsenate in the flow calorimeter. Exposure to arsenate in a batch system decreased the PZNC about 4 pH units. This difference in behavior between batch and flow systems was related to differences in the amount of arsenate adsorbed.

Energetics of arsenate sorption on amorphous aluminum hydroxides studied using flow adsorption calorimetry.

Specific conductance in farm canals of the Everglades Agricultural Area (EAA) in south Florida is an important water quality parameter that was categorized as a parameter of concern according to an observed frequency of >5% excursions over the Class III water quality criterion and needed to be addressed as a part of the Everglades Regulatory Program. This study was conducted to evaluate specific conductance in farm canals of the EAA. Specific conductance was monitored at 10 representative farms (a total of 12 pump stations) in the EAA using multi-parameter water quality data loggers, for periods ranging from 24 to 83 mo. Cation and anion concentrations were also determined. Nonparametric Mann-Kendall trend analyses and Sen's slope analysis of specific conductance were conducted to determine specific conductance trends. Mean specific conductance ranged from 0.74 to 1.68 dS m(-1) and only 2 of the 10 farms were above the State Class III water quality criterion of 1.275 dS m(-1). Statistically significant downward trends were observed at 3 of the 10 farms. Determination of ion compositions in grab samples at 8 of the 10 farms indicated that the major ions contributing to the increase in specific conductance in the EAA were Cl-, HCO3-, and Na+. Mean Na/Cl ratios in most of the EAA canals ranged from 0.57 to 0.78, whereas those of SO4/Cl ranged from 0.46 to 0.98. Investigation of historical data and literature indicates that elevated specific conductance in parts of the EAA is a natural phenomenon due to entrapment of connate seawater in the Everglades formation. Sulfur contributes minor increases in specific conductance in the EAA with probable sources from organic soil mineralization, ground water, Lake Okeechobee, and S fertilizers.

Specific conductance and ionic characteristics of farm canals in the everglades agricultural area.

Estimates of the number of species of bacteria per gram of soil vary between 2000 and 8.3 million (Gans et al., 2005; Schloss and Handelsman, 2006). The highest estimate suggests that the number may be so large as to be impractical to test by amplification and sequencing of the highly conserved 16S rRNA gene from soil DNA (Gans et al., 2005). Here we present the use of high throughput DNA pyrosequencing and statistical inference to assess bacterial diversity in four soils across a large transect of the western hemisphere. The number of bacterial 16S rRNA sequences obtained from each site varied from 26,140 to 53,533. The most abundant bacterial groups in all four soils were the Bacteroidetes, Betaproteobacteria and Alphaproteobacteria. Using three estimators of diversity, the maximum number of unique sequences (operational taxonomic units roughly corresponding to the species level) never exceeded 52,000 in these soils at the lowest level of dissimilarity. Furthermore, the bacterial diversity of the forest soil was phylum rich compared to the agricultural soils, which are species rich but phylum poor. The forest site also showed far less diversity of the Archaea with only 0.009% of all sequences from that site being from this group as opposed to 4%-12% of the sequences from the three agricultural sites. This work is the most comprehensive examination to date of bacterial diversity in soil and suggests that agricultural management of soil may significantly influence the diversity of bacteria and archaea.

Pyrosequencing enumerates and contrasts soil microbial diversity.

A mandatory best management practices (BMP) program was implemented in the Everglades Agricultural Area (EAA) farms basin-wide in 1995 as required by the Everglades Forever Act to reduce P loads in drainage water reaching the Everglades ecosystem. All farms in the EAA basin implement similar BMPs, and basin wide P load reductions have exceeded the 25% reduction required by law; however, differences remain in water quality between subbasins. Our objective was to determine long-term trends in P loads in discharge water in the EAA after implementing BMPs for 7 to10 yr and to explore reasons for differences in the performance of the subbasins. Two monitoring datasets were used, one from 10 research farms and the second from the EAA basin inflow and outflow locations. Mann-Kendall trend analysis was used to determine the degree of change in water quality trends. A decreasing trend in P loads was observed in general on sugarcane (Saccharum officinarum L.) farms, while mixed crop farms showed either decreasing or insignificant trends. The insignificant trends are probably related to management practices of mixed crop systems. Decreasing trends in P loads were observed in the outflow of the EAA basin, S5A, and S8 subbasins from 1992 to 2002. Inflow water from Lake Okeechobee had increasing P concentration from 1992 to 2006 with the highest trend in the east side of the lake. This analysis indicated there may be other factors impacting the success of BMPs in individual farms including cropping rotations and flooding of organic soils. Elevated P concentrations in Lake Okeechobee water used for irrigation may pose a future risk to degrade water quality on farms in the EAA, especially in the S5A subbasin.

Long-term water quality trends after implementing best management practices in South Florida.

Agricultural land management, such as fertilization, liming, and tillage affects soil properties, including pH, organic matter content, nitrification rates, and the microbial community. Three different study sites were used to identify microorganisms that correlate with agricultural land use and to determine which factors regulate the relative abundance of the microbial signatures of the agricultural land-use. The three sites included in this study are the Broadbalk Experiment at Rothamsted Research, UK, the Everglades Agricultural Area, Florida, USA, and the Kellogg Biological Station, Michigan, USA. The effects of agricultural management on the abundance and diversity of bacteria and archaea were determined using high throughput, barcoded 16S rRNA sequencing. In addition, the relative abundance of these organisms was correlated with soil features. Two groups of microorganisms involved in nitrogen cycle were highly correlated with land use at all three sites. The ammonia oxidizing-archaea, dominated by Ca. Nitrososphaera, were positively correlated with agriculture while a ubiquitous group of soil bacteria closely related to the diazotrophic symbiont, Bradyrhizobium, was negatively correlated with agricultural management. Analysis of successional plots showed that the abundance of ammonia oxidizing-archaea declined and the abundance of bradyrhizobia increased with time away from agriculture. This observation suggests that the effect of agriculture on the relative abundance of these genera is reversible. Soil pH and NH3 concentrations were positively correlated with archaeal abundance but negatively correlated with the abundance of Bradyrhizobium. The high correlations of Ca. Nitrososphaera and Bradyrhizobium abundances with agricultural management at three long-term experiments with different edaphoclimatic conditions allowed us to suggest these two genera as signature microorganisms for agricultural land use.

Ca. Nitrososphaera and Bradyrhizobium are inversely correlated and related to agricultural practices in long-term field experiments.

The activity of ammonia-oxidizing archaea (AOA) leads to the loss of nitrogen from soil, pollution of water sources and elevated emissions of greenhouse gas. To date, eight AOA genomes are available in the public databases, seven are from the group I.1a of the Thaumarchaeota and only one is from the group I.1b, isolated from hot springs. Many soils are dominated by AOA from the group I.1b, but the genomes of soil representatives of this group have not been sequenced and functionally characterized. The lack of knowledge of metabolic pathways of soil AOA presents a critical gap in understanding their role in biogeochemical cycles. Here, we describe the first complete genome of soil archaeon Candidatus Nitrososphaera evergladensis, which has been reconstructed from metagenomic sequencing of a highly enriched culture obtained from an agricultural soil. The AOA enrichment was sequenced with the high throughput next generation sequencing platforms from Pacific Biosciences and Ion Torrent. The de novo assembly of sequences resulted in one 2.95 Mb contig. Annotation of the reconstructed genome revealed many similarities of the basic metabolism with the rest of sequenced AOA. Ca. N. evergladensis belongs to the group I.1b and shares only 40% of whole-genome homology with the closest sequenced relative Ca. N. gargensis. Detailed analysis of the genome revealed coding sequences that were completely absent from the group I.1a. These unique sequences code for proteins involved in control of DNA integrity, transporters, two-component systems and versatile CRISPR defense system. Notably, genomes from the group I.1b have more gene duplications compared to the genomes from the group I.1a. We suggest that the presence of these unique genes and gene duplications may be associated with the environmental versatility of this group.

Genome sequence of Candidatus Nitrososphaera evergladensis from group I.1b enriched from Everglades soil reveals novel genomic features of the ammonia-oxidizing archaea.

Samira H. Daroub

Soil and Water Sciences Department

University of Florida

Capturing Flow-weighted Water and Suspended Particulates from Agricultural Canals During Drainage Events