Ronald D. Jones

Phosphorus Biogeochemistry and the Impact of Phosphorus Enrichment: Why Is the Everglades so Unique?

The Florida Everglades is extremely oligotrophic and sensitive to small increases in phosphorus (P) concentrations. P enrichment is one of the dominant anthropogenic impacts on the ecosystem and is therefore a main focus of restoration efforts. In this review, we synthesize research on P biogeochemistry and the impact of P enrichment on ecosystem structure and function in the Florida Everglades. There are clear patterns of increased P concentrations and altered structure and processes along nutrient-enrichment gradients in the water, periphyton, soils, macrophytes, and consumers. Periphyton, an assemblage of algae, bacteria, and associated microfauna, is abundant and has a large influence on phosphorus cycling in the Everglades. The oligotrophic Everglades is P-starved, has lower P concentrations and higher nitrogen–phosphorus (N:P) ratios, and has oxidized to only slightly reduced soil profiles compared to other freshwater wetland ecosystems. Possible general causes and indications of P limitation in the Everglades and other wetlands include geology, hydrology, and dominance of oxidative microbial nutrient cycling. The Everglades may be unique with respect to P biogeochemistry because of the multiple causes of P limitation and the resulting high degree of limitation.

Spatial Characterization of Water Quality in Florida Bay and Whitewater Bay by Multivariate Analyses: Zones of Similar Influence

We apply an objective statistical analysis to a 6-yr, multiparameter dataset in an effort to describe the spatial dependence and inherent variation of water quality patterns in the Florida Bay-Whitewater Bay area. Principal component analysis of 16 water quality parameters collected monthly over a 6-yr period resulted in live principal components (PC) that explained 71.8% of the variance of the original variables. The “organic” component (PC1) was composed of TN, TON, APA, and TOC; the “inorganic N” component (PCII) contained NO2, NO3, and NH4+, the “phytoplankton” component (PCIII) was made up of turbidity, TP, and Chl a; DO and temperature were inversely related (PCIV); and salinity was the only parameter included in PCV. A cluster analysis of mean and SD of PG scores resulted in the spatial aggregation of 50 fixed monitoring stations in Florida Bay and Whitewater Bay into six zones of similar influence (ZSI) defined as Eastern Florida Bay. Core Florida Bay, Western Florida Bay, Coot Bay, the Inner Mangrove Fringe, and the Outer Mangrove Fringe. Marked differences in physical, chemical, and biological characteristics among ZSI were illustrated by this technique. Comparison of medians and variability of parameter values among ZSI allowed large-scale generalizations as to underlying differences in water quality in these regions. For example. Fastern Florida Bay had lower salinity, TON, TOC, TP, and Chl a than the Core Bay as a function of differences in freshwater inputs and water residence time. Comparison of medians and variability within ZSI resulted in new hypotheses as to the processes generating these internal patterns. For example, the Core Bay had very high TON, TOC, and NH4+ concentrations but very low NO3−, leading us to postulate the inhibition of nitrification via CO production by TOC photolysis. We believe that this simple, objective approach to spatial analysis of fixed-station monitoring datasets will aid scientists and managers in the interpretation of factors underlying the observed parameter distribution patterns. We also expect that this approach will be useful in focussing attention on specific spatial areas of concern and in generating new ideas for hypothesis testing.

Seasonal and long-term trends in the water quality of Florida Bay (1989–1997)

Analysis of 6 yr of monthly water quality data was performed on three distinct zones of Florida Bay: the eastern bay, central bay, and western bay. Each zone was analyzed for trends at intra-annual (seasonal), interannual (oscillation), and long-term (monotonic) scales. the variables TON, TOC, temperature, and TN∶TP ratio had seasonal maxima in the summer rainy season; APA and Chla, indicators of the size and activity of the microplankton tended to have maxima in the fall. In contrast, NO3−, NO2−, NH4+, turbidity, and DOsat, were highest in the winter dry season. There were large changes in some of the water quality variables of Florida Bay over the study period. Salinity and TP concentrations declined baywide while turbidity increased dramatically. Salinity declined in the eastern, central, and western Florida Bay by 13.6‰, 11.6‰, and 5.6‰, respectively. Some of the decrease in the eastern bay could be accounted for by increased freshwater flows from the Everglades. In contrast to most other estuarine systems, increased runoff may have been partially responsible for the decrease in TP concentrations as input concentrations were 0.3–0.5 μM. Turbidity in the eastern bay increased twofold from 1991 to 1996, while in the central and western bays it increased by factors of 20 and 4, respectively. Chla concentrations were particularly dynamic and spatially heterogeneous. In the eastern bay, which makes up roughly half of the surface area of Florida Bay, Chla declined by 0.9 μg l−1 (63%). The hydrographically isolated central bay zone underwent a fivefold increase in phytoplankton biomass from 1989 to 1994, then rapidly declined to previous levels by 1996. In western Florida Bay there was a significant increase in Chla, yet median concentrations of Chla in the water column remained modest (∼2 μg l−1) by most estuarine standards. Only in the central bay did the DIN pool increase substantially (threefold to sixfold). Notably, these changes in turbidity and phytoplankton biomass occurred after the poorly-understood seagrass die-off in 1987. It is likely the death and decomposition of large amounts of seagrass biomass can at least partially explain some of the changes in water quality of Florida Bay, but the connections are temporally disjoint and the process indirect and not well understood.

Determination of organomercury compounds in aqueous samples by capillary gas chromatography-atomic fluorescence spectrometry following solid-phase extraction

A new method based on capillary gas chromatography-atomic fluorescence spectrometry (GC/AFS) is described for the determination of methylmercury (MeHg) and ethylmercury (EtHg) in water samples. An improved sample preparation methodology was developed, which involves preconcentration of the alkylmercury species from water samples, drawn with a 12 channel peristaltic pump, onto sulfhydryl cotton fiber (SCF) adsorbent packed in a screening column, elution of MeHg and EtHg with a mixture of acidic potassium bromide and copper sulfate solution, and back-extraction using methylene chloride. Analysis was performed by capillary GC/AFS with a DB-1 column. Some important parameters, including sample pH, presence of anions and cations, concentration of dissolved organic carbon (DOC), eluent type, and eluent volume were evaluated. With AFS as a detector, the capillary gas Chromatographic technique provides high selectivity, high sensitivity, and a straightforward method for organomercury halide analysis. It eliminates possible spectral interferences to the detector from other sample components and from chemicals used in the sample preparation procedure. The detection limit was 0.01 ng l−1 in a 11 water sample for both MeHg and EtHg. The result for organomercury analysis in a number of natural water samples is shown to illustrate the applicability of this method to real environmental samples.

Nutrient limitations on microbial respiration in peat soils with different total phosphorus content

The effects of phosphate and ammonium additions on microbial respiration were determined using three peat soils with similar total N content (25–38 g kg−1) and different total P (TP) content: low (231 mg P kg−1), intermediate (385 mg P kg−1), and high (1.473 g P kg−1). These soils, obtained from Everglades National Park, Florida, had been formed predominantly from the partial decomposition of sawgrass (Cladium jamaicense). Soil respiration was measured by gas chromatography. Amendment of the soils with 0–100 mm PO4 or NH4 resulted in changes in the C-to-nutrient ratio that ranged from 4 to 2042 for C:P and 11.5 to 14.1 for C:N. Kinetic parameters for soil respiration were obtained by fitting the data to a kinetic model that describes soil C mineralization as the sum of an exponential decay function for readily mineralizable C and a zero-order decay function for stable C. Estimates of the zero-order rate constant for endogenous respiration in unamended soil samples increased with TP content of the soil (in mmol CO2 kg−1 d−1): low TP (36–40) < intermediate TP (49–52) < high TP (107–114). Addition of phosphate stimulated the respiration rate of the low and intermediate TP soil, but had no effect on the rate of soil respiration of the high TP soil. Ammonium additions inhibited soil respiration in the low and intermediate TP soils at most concentrations tested; the rate of respiration was inversely proportional to the amount of NH4 added. Addition of ammonium to the high TP soil stimulated respiration. Microbial respiration in the low and intermediate TP soils is limited by P availability, whereas N appears to limit respiration in the high TP soil. These results suggest that P pollution may have a marked, long-term effect on microbial respiration in organic soils with low TP content.

Carbon monoxide and methane distribution and consumption in the photic zone of the Sargasso Sea

Abstract Spatial and temporal distributions of carbon monoxide and methane along with microbial oxidations of these substances were examined on three cruises to the highly oligotrophic southeastern Sargasso Sea between June 1986 and May 1987. Dissolved CO profiles were similar to those reported by previous researchers, with the highest concentrations in the near-surface waters (0–20 m). CO concentrations ranged from 5.8 nM in the photic zone to 0.1 nM in the aphotic zone. CO concentrations decreased steadily throughout the rest of the water column. CH4 concentrations were more uniform in their distribution and typically decreased only slightly in the top 500 m of the water column. The microbial oxidation rates of both CO and CH4 were extremely slow when compared with more productive waters. Turnover times for CO ranged from 25 to 2922 h while those for CH4 ranged from 5 to > 100 years. These low oxidation rates may explain why no discernible diurnal variation in CO concentration was observed and why CH4, which is usually more conservative than CO, and CO distributions were similar during the June 1986 cruise. Ratios of CH4/CO oxidation indicate that the ammonium oxidizing bacteria could be responsible for much of the CO and CH4 oxidation in these waters. Due to the long turnover times for CO and CH4, the oxidation of these trace gases by bacteria is unlikely to represent a significant link within the carbon cycle in these highly oligotrophic waters.

Marsh vegetation patterns and soil phosphorus gradients in the Everglades ecosystem

In order to test the hypothesis that phosphorous enrichment is modifying Everglades marsh community composition, we sampled vegetation and soil phosphorus concentrations along four transects in areas representative of varying environmental conditions within the Everglades region. Each transect originated at or near a canal flow control structure and extended towards the center of the marsh because the canal flow structures were seen as potential nutrient input sources from ‘upstream’ agricultural areas. Cladium jamaicense, wet prairie communities and Typha spp. dominated sites were sampled along each transect. Correlations for between-species occurrences and between-species frequencies and phosphorus concentrations with distance from nutrient source were determined. Within-transect effects and between-transect effects from north to south across the Everglades region were compared. In all cases phosphorus concentrations and presence of Typha domingensis showed a negative relationship to distance from nutrient source, while the presence of Cladium and other natural communities showed a positive one. The pattern in marsh community composition and soil phosphorus content seen in the four marsh transects indicates that a strong relationship exists between Typha expansion, decline of Cladium marsh and wet prairie communities and rising phosphorus concentrations, and that these trends are correlated with nutrient input sources associated with agricultural runoff.

Evaluation of some Isolation Methods for Organomercury Determination in Soil and Fish Samples by Capillary Gas Chromatography—Atomic Fluorescence Spectrometry

Abstract Three extraction methods, acidic KBr/CuSO4 isolation-methylene chloride extraction. acidic KBr/CuSo4 isolation-methylene chloride extraction with an alkaline digestion pretreatment, and an extration method at a milder condition with citrate buffer and dithizone in chloroform, were studied for methylmercury and ethylmercury determination in soils, sediments and fish samples by the recently developed capillary gas chromatography—atomic fluorescence spectrometry system (GC-AFS). The acidic KBr/CuSO4-methylene chloride extraction and the acidic KBr/CuSO4-methylene chloride extraction with an alkaline digestion pretreatment were shown to be the effective methods for soils/sediments and fish samples analysis, respectively. The presence of ethylmercury species in soils of the Florida Everglades, observed with the acidic KBr/CuSO4 isolation and methylene chloride extraction procedure, was further confirmed with the dithizone complexation/extraction procedure. The GC-AFS analytical method offers high sens...

Photochemistry of natural dissolved organic matter in lake and wetland waters—production of carbon monoxide

Abstract The photochemical formation of carbon monoxide (CO) in various lake and wetland waters was found to be correlated with the concentration of dissolved organic carbon (DOC), as well as light absorbance and fluorescence of the waters, suggesting that dissolved organic matter is a major precursor for CO photoproduction. Rates of CO formation also increased nonlinearly with increasing concentration of dissolved iron. For the lake and wetland waters studied, CO production rates were between 13 and 910 nmol 1 −1 h −1 using June solar noon sunlight irradiations. Field experiments in a subtropical pond demonstrated that much of photochemically formed CO in the surface water was effluxed to the atmosphere. Considering the globally-averaged effective sunlight flux, we estimate that photoformation of CO leads to a turnover time of 2–10 yr for DOC in sunlit surface waters.

Gas chromatographic determination of organomercury following aqueous derivatization with sodium tetraethylborate and sodium tetraphenylborate. Comparative study of gas chromatography coupled with atomic fluorescence spectrometry, atomic emission spectrometry and mass spectrometry.

Several hyphenated analytical techniques, including gas chromatography (GC) coupled with atomic fluorescence spectrometry (AFS), microwave-induced plasma atomic emission spectrometry (AES), and mass spectrometry (MS), have been evaluated for methylmercury and ethylmercury analysis following aqueous derivatization with both sodium tetraethylborate and sodium tetraphenylborate. Both GC-AFS and GC-AES were shown to be excellent techniques with detection limits in the range of sub-picogram levels (0.02-0.04 pg as Hg). Both techniques have wide linear ranges, although setting of the AFS sensitivity has to be selected manually based on the concentration of mercury in the sample. Phenylation seems to be more favorable in this study because of its capability of distinguishing between ethylmercury and inorganic mercury, and low cost compared to ethylation. Although sensitivity of GC-MS is poor with detection limits ranging from 30 to 50 pg as Hg, it is an essential technique for confirmation of the derivatization products.