In the uppermost millimeters of shallow submerged coastal sediments, photosynthesis by microalgae and cyanobacteria during daylight hours can cause oxygen supersaturation of sediment porewater, leading to bubble formation. In shallow water depths, the seabed is affected by the pressure maximum beneath the wave crest and pressure minimum beneath the wave trough. While the photosynthetically-generated gas bubbles persist within the surface layer highly permeable sand sediments, they may be exposed to pressure pulsations caused by tides and passing surface gravity waves, because pressure is not significantly attenuated in the upper few centimeters of permeable sediments. The question arises, whether the tens of thousands of millimeter-size bubbles that are produced on sunny days in each square meter of nearshore sands respond to these pressure oscillations and if so, what consequences these responses may have. The main goals of the research thus were the demonstration of the bubble pulsation within the sediment and the quantification of the pore water flow, associated interfacial solute flux, and sand grain movement caused by the pulsation. The central working hypotheses tested in this research were: 1) Millimeter-size photosynthetic gas bubbles buried in the surface layer of submerged permeable coastal sands respond to passing surface gravity waves by volume changes leading to bubble volume pulsation. 2) This bubble volume pulsation causes pore water flows and thereby exchange across the sediment-water interface and an increase of the net solute flux from the sediment. 3) The bubble volume pulsation causes sand grain movement and thereby local sediment compaction, alteration of sediment surface topography and vertical transport of substances attached to the sand grains. These three working hypotheses were addressed in Thesis chapters 1, 2 and 3, respectively. In-situ video observations with a buried camera showed that the bubbles (1-3 mm diameter) buried in the surface layer ([less than] 10 cm) of nearshore sand respond to passing waves by volume pulsation and allowed estimation of the oscillating volume change of the bubbles visible in the sediment-cross section. These observations revealed bubble volume oscillation with compressions of 7.4% caused by ~1 meter water waves producing a temporary 10 kPa pressure increase. Laboratory measurements in a custom-built pressure tank confirmed the in-situ observations: Bubbles with 1.24 mm to 2.12 mm diameter (1 mm3 to 5 mm3), embedded in transparent Nafion[TM] sand sediment, at 1 m water depth were compressed by 8.7 ± 1.3 % of their volume when exposed to the same pressure increase of 10 kPa as produced by a 1 meter water wave. With an observed abundance of 50,000 bubbles m-2 in sandy Gulf of Mexico sediments, the pulsation of bubbles with 2 mm diameter produced by the passing of thirty 1 m-waves per minute (8.3% compression) could pump 31.3 L m-2 h-1 (or 750 L m-2 d-1) of water across the sediment-water interface. Once it was established that surface layer bubbles pulsate due to pressure oscillations associated with passing surface gravity waves at a rate consistent with Boyle's Law, the effect of pulsating bubbles on pore water movement and grain movement was investigated. Fluorescein dye tracer experiments conducted at the same wave frequency (0.5 Hz) and wave height (75-100 cm) showed a linear correlation (R2 = 0.99) between interstitial gas bubble volume and interfacial tracer flux. The pulsation of 200 five-microliter bubbles embedded in the top 2 cm of a 10 cm (L) x 10 (W) x 45 cm (D) wet sediment core (bubbles occupied 0.5% of the volume of the 2 cm thick upper sediment layer) increased interfacial flux initially (first 7 min) by a factor of 17 compared to the control experiment, where tracer transport was limited to molecular diffusion and some tracer release caused by the setup of the experiment. The increase of flux caused by the bubbles is produced by the oscillating water flow across the sediment-water interface that pushes pore water out of the sediment that then is mixed into the overlying water through dispersion and turbulence. At an observed in-situ abundance of 50,000 bubbles m-2, bubble pulsation can be estimated to increase solute transport across the highly-active sediment-water interface by a factor of 30 when compared to molecular diffusion. Over time, the intermittent movement of sand grains driven by the pulsating bubbles resulted in a tighter packing of the sand, with a decrease in pore space, and an overall downward migration of grains above and around the buried bubbles. Particle Image Velocimetry showed that the cross-sectional area around the bubble, in which grains were moved by its pulsation, decayed exponentially over time. In the natural environment, decompaction of the sediment surface layer by bioturbation and sediment resuspension by bottom currents counteracts the compaction caused by the bubble pulsation, resulting in a continuous cycle of compaction/de-compaction that keeps a substantial fraction of the grains in the surface layer moving. With observed in-situ abundances of 50,000 bubbles m-2 and an average bubble volume of 5 mm3, approximately 5,000 cm3 m-2 or 50% of the grains in the top 1 cm of the sand bed are moved by the pulsation of buried gas bubbles every hour. The movement and net downward migration of surface layer sand grains towards pulsating bubbles has broad implications for sediment physical characteristics, sediment geochemistry and pore water flow. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Sciences in partial fulfillment of the Doctor of Philosophy. / Fall Semester 2015. / October 29, 2015. / Bubbles, Coastal, Pressure, Sand, Sediment, Waves / Includes bibliographical references. / Markus Huettel, Professor Directing Dissertation; Janie Wulff, University Representative; Ian MacDonald, Committee Member; Jeffrey Chanton, Committee Member; William Dewar, Committee Member.

After the Deepwater Horizon (DWH) blowout, MC252 crude oil was washed onto the shores of the northeastern Gulf of Mexico. Weathered oil was buried in sandy Florida beaches in the form of sands covered by oil films, small oil particles, large agglomerates and oiled sand layers. While oil films and oil particles were observed to degrade relatively quickly, larger buried sand and oil agglomerates (SOA) can persist in the dry beach sand, where they are protected from photodegradation and mechanical stress. To determine the degradation of such large agglomerates, a time series study was initiated that quantified the weight loss and compositional changes of MC252 standardized sand and oil agglomerates (sSOAs) buried at 5, 15, 25, 35, and 45 cm depths in dry beach sand at Pensacola Beach, Florida. Sets of 10 experimental, standardized SOAs were removed at 2 - 6 month intervals over a time period of 3 years. Analysis of the sSOAs revealed a total weight loss of 10.85% or 3.66 g per sSOA volume and a loss in petroleum hydrocarbons of 59% or 2.85 g per sSOA/ over the three-year burial period. Decay rate constants for saturated hydrocarbons (C15-C40) of the surface layer of the sSOAs averaged 0.0043 d-1 (SE = 0.0017) for initial 181-day period, and 0.0027 d-1 (SE = 0.0004) for the thee-year observation period (C15-C40). PAH initial decay was 0.022 d-1 (SE = 0.004) for the initial (181-day) decay and 0.005 d-1 (SE = 0.001) for three-year period for the compounds that could be detected in the sSOA surface layer (biphenyl, acenaphthylene, acenaphthene, fluorine, dibenzothiopene, phenanthrene, pyrene, benzo(c)phenanthrene, chrysene, 7,12-dimethylbenz(a)anthracene, benzo(b,j,k)fluoranthene, benzo(a)pyrene, and benzo(g,h,i)perylene) in the surface lay. The results indicate that buried larger SOAs persist in the dry beach sands for years despite access to oxygen in contrast to oil films on sand grains and buried small oil particles that at Pensacola Beach disappeared within a year. Causes for the slow degradation of larger SOAs in the beach include the lack of photodegradation, the protection from mechanical disintegration, as well as low nutrient and moisture concentrations in the sand. / A Thesis submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester 2018. / May 14, 2018. / BP Oil, degradation, oil decay, polycyclic aromatic hydrocarbons, saturated hydrocarbons, sediment / Includes bibliographical references. / Markus H. Huettel, Professor Directing Thesis; Ian R. MacDonald, Committee Member; Yang Wang, Committee Member; Olivia U. Mason, Committee Member.

Ephemeral macroalgal blooms are considered a symptom of eutrophication in shallow coastal lagoons, but their influence on nutrient cycling dynamics in these systems is not fully understood. From 2006-2008, I conducted a series of experiments to determine the influence of living and senescent macroalgae on sediment carbon (C) and nitrogen (N) cycling in coastal lagoons along the Delmarva Peninsula, USA. In particular, I focused on how macroalgae affect the microbial community at the sediment-water interface of shallow subtidal sediments because this complex consortium of autotrophic (e.g. benthic microalgae, BMA) and heterotrophic (e.g. bacteria) organisms plays a critical role in nutrient cycling within these systems. to more accurately address microbial uptake of nutrients and organic matter from porewater and surface water sources, I designed and tested the "perfusionator," an experimental apparatus which allowed for continuous and homogenous perfusion of sediment porewater with dissolved tracers. I used the perfusionator in an outdoor mesocosm study to investigate the influence of benthic micro- and macroalgae on sediment organic matter quantity and quality using bulk and molecular level (total hydrolyzable amino acids, THAA; phospholipid linked fatty acids, PLFA) analyses. In a companion study. I further quantified C and N cycling by explicitly tracking C and N uptake into the sediments in the presence and absence of macroalgae using a dual stable isotope (H13CO3-, 15NH4+) tracer approach in combination with isotope analyses of THAA and PLFA. Together, the studies demonstrated that BMA activity, which was dominated by diatoms according to PLFA biomarkers, increased storage of C and N in surface sediments, relative to dark treatments without BMA. BMA also increased the lability of sediment organic matter, which in turn resulted in observed increases in bacterial PLFA concentrations and isotopic incorporation. Efficient shuttling of C and N between BMA and bacteria in this system served as a mechanism for retention of C and N within the sediments. Macroalgae fundamentally altered sediment C and N cycling by decreasing sediment organic matter buildup. Macroalgae also sequestered C and N, but sediment C and N uptake decreased by ∼40% when macroalgae were present. This was likely due to shading of the sediment surface by macroalgae, which decreased BMA production, which in turn decreased bacterial production. Although macroalgae are capable of sequestering significant amounts of nutrients, storage of C and N as macroalgal biomass is only temporary, as these blooms often exhibit a bloom and die-off cycle. In the final portion of this project, I traced C and N from senescing macroalgae into relevant sediment pools. A macroalgal die-off was simulated by the addition of freeze-dried macroalgae, pre-labeled with 13C and 15N, to sediment mesocosms. Bulk sediments took up label immediately following the die-off, and macroalgal C and N were retained in the sediments for >2 weeks. Approximately 6 to 50% and 2 to 9% of macroalgal N and C, respectively, were incorporated into the sediments. Label from the macroalgae appeared first in bacterial and then BMA biomarkers, suggesting that shuttling of macroalgal C and N between these communities may serve as a mechanism for retention of some macroalgal nutrients within the sediments. Together, these experiments suggest that ephemeral macroalgae diminish C and N uptake by the sediment microbial community, which may substantially impact the response of coastal bays to increased nutrient loading.

Persistent organic pollutants (POPs) such as the organochlorine pesticide hexachlorocyclohexane (HCH) may undergo atmospheric transport and accumulate in regions remote from the source. It is important to develop techniques to help apportion source and identify transport or transformation processes to which HCHs and other mobile POPs may be subjected. Molecular tracers such as compound specific stable isotope and enantiomer ratios (ERs) may prove valuable in studying POP fate and transport. The objective of this study was to further develop the use of these two novel geochemical tools to evaluate the sources, transport and environmental fate of POPs, in the context of studying the fate and transport of HCH, a globally distributed POP. In the first part of my study, I evaluated the potential for using stable isotope ratios to track POP source and transport, using HCH in laboratory simulations of global distillation. I compared the relative fractionation of carbon versus deuterium isotopes during air-water gas exchange along a strong temperature gradient. The hypothesis, that perdeuterated, but not necessarily carbon-labeled compounds would show measurable and significant fractionation during air-water transfer, was validated within the confines of the experimental system. The results suggest that it may be possible to use a dual tracer approach on a larger scale, in which carbon isotopes could be used to track POP source, while fractionation of deuterium may be used to track POP transport distance. In the second part of the study, I evaluated the potential for use of ERs to evaluate HCH biodegradation. The rationale was that most enzymatic processes are stereoselective, enantiomers of pesticides may microbially degrade at significantly different rates, leading to increased environmental persistence of the non-degradable isomer. to bridge the gap between microbial and chemical information on enantioselective processes, I measured microbial activity, abundance, concentrations and enantiomer ratios of HCH in air and surface waters of the York River estuary. HCH concentrations and ERs were related with microbial activity but there were seasonal variations in enantioselectivity suggesting that seasonal as well as spatial differences in microbial communities may affect HCH ERs. The relationship between microbial parameters and enantioselective degradation appears to be complex and warrants further study before ERs can be used as effective tracers of chiral POP transport.

A numerical model of the global carbon cycle is presented which includes the effects of anthropogenic &CO\sb2& emissions &(CO\sb2& produced from fossil fuel combustion, biomass burning, and deforestation) on the global carbon cycle. The model is validated against measured atmospheric &CO\sb2& concentrations. Future levels of atmospheric &CO\sb2& are then predicted for the following scenarios: (1) Business as Usual (BaU) for the period 1990-2000; (2) Same as (1), but with no biomass burning; (3) Same as (1), but with no fossil fuel combustion; (4) Same as (1), but with a doubled atmospheric &CO\sb2& concentration and a 2 K warmer surface temperature associated with the doubled atmospheric &CO\sb2& concentration. The global model presented here consists of four different modules which are fully coupled with respect to &CO\sb2.& These modules represent carbon cycling by the terrestrial biosphere and the ocean, anthropogenic &CO\sb2& emissions, and atmospheric transport of &CO\sb2.&. The prognostic variable of interest is the atmospheric &CO\sb2& concentration field. The &CO\sb2& concentration field depends on both the sources and sinks of &CO\sb2& as well as the atmospheric circulation. In addition, the sources and sinks vary significantly as a function of both time and geographic location. The model output agrees well with measured data at the equatorial and mid latitudes, but this agreement weakens at higher latitudes. This is due to the less adequate representation of the terrestrial ecosystem models at these latitudes. In the first scenario, the predicted concentration of atmospheric &CO\sb2& is 362 parts per million by volume (ppmv) at the end of the 10 year model run. This establishes a baseline for the next three scenarios, which predict that biomass burning will contribute 3 ppmv of &CO\sb2& to the atmosphere by the year 2000, while fossil fuel combustion will contribute 5 ppmv. The net effect of a 2 K average global warming was to increase the atmospheric &CO\sb2& concentration by approximately 1 ppmv, due to enhanced respiration by the terrestrial biosphere.

A need exists for information on sedimentary microbes, expecially at the level of specific populations, and particularly with respect to their interactions with benthic macrofauna. Two examples were documented. / First, biochemical and conventional analyses were used to characterize the microbial food resources and digestive efficiency of Ptychodera bahamensis, an enteropneust hemichordate. Sediment was collected from freshly extruded fecal casts and adjacent feeding depressions. There were no significant differences between casts and depressions in granulometry, density of meiofauna, and concentrations of photopigments. Nematodes in casts were larger than those in depressions. Total phospholipid, ester-linked fatty acids (PLFA) were 30% lower and phospholipid phosphate was 49% lower in casts. Concentrations of 33 fatty acids were lower in casts, indicating that the hemichordate digests a wide variety of microorganisms. Only 18:1$\omega$7c, characteristic of Gram-negative organisms, was not lower in casts than in depressions. P. bahamensis either cannot digest this functional group of bacteria or contributes gut microbes containing 18:1$\omega$7c to sediment passing through its alimentary canal. / Second, the same methods were used to characterize the microbial populations within the burrow of Callianassa trilobata, a decapod crustacean. Sediment was collected from the burrow lining, burrow matrix, and ambient, subsurface sediment. The lining and matrix were composed of fine-grained material compared to sandy, ambient sediment. Meiofauna were most abundant in ambient sediment, not in the burrow as has been found for other species of macrofauna. Lipid analyses indicated that relative to the matrix and ambient sediment, the lining abounds with pro- and eukaryotic biomass. PLFA were assigned to functional groups of microorganisms to assess spatial variations in the absolute abundance and relative proportions of microbial populations. Dominance of prokaryotes was pronounced in all three areas, especially the matrix. The lining was the most aerobic location, but anaerobic microhabitats simultaneously harbored sulfate-reducing bacteria. The ratio of Gram-positive to Gram-negative bacteria increased from lining to matrix to ambient sediment. The Trans/cis ratio of 16:1$\omega$7 indicated that prokaryotes in the matrix were starved. / Source: Dissertation Abstracts International, Volume: 49-03, Section: B, page: 0601. / Major Professor: Paul A. LaRock. / Thesis (Ph.D.)--The Florida State University, 1987.

The purpose of this study is to investigate the evolution of the Arctic Ocean’s carbon uptake capacity and impacts on ocean acidification with the changing sea-ice scape. In particular, I study the influence on air-ice-sea fluxes of carbon with two major updates to commonly-used carbon cycle models I have included. One, incorporation of sea ice algae to the ecosystem, and two, modification of the sea-ice carbon pump, to transport brineassociated Dissolved Inorganic Carbon (DIC) and Total Alkalinity (TA) to the depth of the bottom of the mixed layer (as opposed to releasing it in the surface model layer). I developed the ice algal ecosystem model by adding a sympagic (ice-associated) ecosystem into a 1D coupled sea ice-ocean model. The 1D model was applied to Resolute Passage in the Canadian Arctic Archipelago and evaluated with observations from a field campaign during the spring of 2010. I then implemented an inorganic carbon system into the model. The carbon system includes effects on both DIC and TA due to the coupled ice-ocean ecosystem, ikaite precipitation and dissolution, ice-air and air-sea carbon exchange, and ice-sea DIC and TA exchange through a formulation for brine rejection to depth and freshwater dilution associated with ice growth and melt. The 1D simulated ecosystem was found to compare reasonably well with observations in terms of bloom onset and seasonal progression for both the sympagic and pelagic algae. In addition, the inorganic carbon system showed reasonable agreement between observations of upper water column DIC and TA content. The simulated average ocean carbon uptake during the period of open water was 10.2 mmol C m−2 day−1 ( 11 g C m−2 over the entire open-water season). Using the developments from the 1D model, a 3D biogeochemical model of the Arctic Ocean incorporating both sea ice and the water column was developed and tested, with a focus on the pan-Arctic oceanic uptake of carbon in the recent era of Arctic sea ice decline (1980 – 2015). The model suggests the total uptake of carbon for the Arctic Ocean (north of 66.5 N) increases from 110 Tg C yr−1 in the early eighties (1980 – 1985) to 140 Tg C yr−1 for 2010 – 2015, an increase of 30%. The rise in SST accounts for 10% of the increase in simulated pan-Arctic sea surface pCO2. A regional analysis indicated large variability between regions, with the Laptev Sea exhibiting low sea surface pH relative to the pan- Arctic domain mean and seasonal undersaturation of arag by the end of the standard run. Two sensitivity studies were performed to assess the effects of sea-ice algae and the sea-ice carbon pump in the pan-Arctic, with a focus on sea surface inorganic carbon properties. Excluding the sea ice-carbon-pump showed a marked decrease in seasonal variability of sea-surface DIC and TA averaged over the Arctic Ocean compared to the standard run, but only a small change in the net total carbon uptake (of 1% by the end of the no icecarbon-pump run). Neglecting the sea ice algae, on the other hand, exhibits only a small change in sea-surface DIC and TA averaged over the pan-Arctic Ocean, but a cumulative effect on the net total carbon uptake of the Arctic Ocean (reaching 5% less than that of the standard run by the end of the no-ice-algae run). / Graduate

No description available.

We investigate the silicon (Si) cycle in the Southern Ocean through two isotopic approaches: (1) 30Si-incubation experiments and (2) natural silicon isotopic composition (ä30Si). 30Si-spiked incubation allows to discriminate the short-term (~ 1 day) net Si-uptake flux in bSiO2 production and dissolution. ä30Si of both biogenic silica and dissolved silicon integrates at seasonal/annual scale bSiO2 production or dissolution and mixing. (1) A new mass spectrometer method (HR-SF-ICPMS) has been developed for 30Si-isotopic abundance measurements. This methodology is faster and easier than the previous available methodologies and has the same precision. A complete set of incubation was coupled with parallel 32Si-incubations and the two methodologies give not significantly different bSiO2 production rates. In the Southern Ocean, especially in the southern Antarctic Circumpolar Current, the large silicic acid concentration degrades the sensitivity of the method with Si dissolution fluxes staying generally below the detection limit. In contrast, the 28Si-isotopic dilution was sensitive enough to assess low biogenic silica dissolution rates in silicic acid poor waters of the northern ACC. We show that large accumulation of detrital dissolving biogenic silica after productive period implies really efficient silicon loop with integrated (euphotic layer) dissolution:production ratio equal or larger than 1. (2) We largely expand the silicic acid isotopic data in the open ocean. Relatively simple mass and isotopic balances have been performed in the Antarctic Zone and have allowed to apply for the first time ä30Si in a quantitative way to estimate regional net silica production and quantify source waters fueling bSiO2 productivity. We observe that at the end of the productive period as suggested with 30Si-incubation, large accumulation of detrital biogenic silica in the surface waters increase the D:P ratio and subsequently dampens the bSiO2 production mediated isotopic fractionation with residual biogenic silica carrying heavier ä30Si than expected. Seasonal isotopic evolution is simulated and seems in agreement with our observations. These simulations strongly suggest working with non-zero order equations to fully assess the seasonal expression of the different processes involved: mixing, uptake, dissolution. Si-isotopes are also tracking the origin and fates of the different ACC pools across the Southern Ocean meridional circulation. Moreover during the circumpolar eastward pathway, the bSiO2 dissolution in deep water decreases the corresponding ä30Si values and this imprint is further transmitted via the upper limb of the meridional circulation in the intermediate water masses.

Abstract The Tapong Bay and the Chiku Lagoon are major lagoons in the south of Taiwan and are ideal sites to study the influence of coastal environment change on the ecosystem. Therefore, this study aims to evaluate the influence of oyster culture racks removal on biochemical processes of carbon, nutrients and mercury in the Tapong Bay, as well as to compare the status of mercury and trace-metal pollution in Tapong Bay and Chiku Lagoon. Before the removal of the oyster culture racks from the Tapong Bay, the annual mean of water exchange time is about 10 days that is longer than that of the present condition (7.1 days). This suggests that the flushing condition of lagoon water is improved after the racks were removed. The annual mean of each nutrient concentration is also lower at present than before, probably due to the enhanced water exchange rate and biological utilization. The annual mean of ∆POC/∆PN is 8.1 that is larger than that of the previous condition (7.3), possibly resulting from the increase of inputs of organic detritus. The Tapong Bay is an autotrophic system (p-r>0) both before and after the removal of oyster culture racks. However, the net ecosystem production (p-r) at present is twice as large as before the removal of oyster racks. After the removal of racks, the annual nitrogen fixation still exceeds the annual denitrification in the Tapong Bay with a magnitude of 5.35 mole N m-2 yr-1. Mercury (Hg) is a highly toxic metal with high affinity to biota. As the lack of Hg distribution data around the coastal zone of Taiwan, the study also aims to develop the analytical methods of Hg species and apply to study Hg biogeochemistry in Tapong Bay and Chiku Lagoon. Distributions of Hg species in the Tapong Bay are spatio-temporally variable, ranging from 6.66 to 12.40 ng/l (ave., 10.01 ng/l) for total Hg (unfilt.), from 1.79 to 3.75 ng/l (ave., 2.56 ng/l) for total dissolved Hg (filt.), from 1.59 to 2.67 ng/l (ave., 1.90 ng/l) for reactive Hg and from 2.51 to 9.45 ng/l (ave., 5.60 ng/l) for particulate Hg. Distributions of Hg species in the Chiku Lagoon are also spatio-temporally variable, ranging from 4.47 to 9.20 ng/l (ave., 6.22 ng/l) for total Hg (unfilt.), from 2.03 to 5.69 ng/l (ave., 4.54 ng/l) for total dissolved Hg (filt.), from 1.70 to 2.87 ng/l (ave., 2.12 ng/l) for reactive Hg and from 2.50 to 7.65 ng/l (ave., 4.79 ng/l) for particulate Hg. The abundance of particulate Hg is positively correlated with chlorophyll a, and total dissolved Hg and reactive Hg are negatively correlated with chlorophyll a. Such relationships imply that distributions of Hg species are primarily controlled by biological uptake and/or adsorption/desorption. Reactive Hg (Hg2+) is also correlated positively with dissolved oxygen concentration suggesting the biological redox effect in modulating the distribution of Hg2+. Particulate Hg also shows positive relationships with total suspended matter and particulate organic carbon, primarily due to biological absorption and particle adsorption/desorption. Enrichment factor (EF) are employed to evaluate trace metal pollution in Tapong Bay and Chiku Lagoon. The results show that the magnitudes of EF are larger in Tapong Bay than in Chiku Lagoon for most metals, particularly for Hg, indicating an thropogenic influence on metal distributions in both lagoons. On the other hand, particulate Hg is poorly correlated with particulate Fe, Mn and Al, strongly indicating relatively little influence of terrestrial detritus in modulating the distributions of particulate Hg.