Predicting anoxia in low-nutrient temperate lakes.

Absence of dissolved oxygen (anoxia) in the hypolimnion of lakes can eliminate habitat for sensitive species and may induce the release of sediment-bound phosphorus. Lake anoxia generally results from decomposition of organic matter, which is exacerbated by high nutrient loads. Total phosphorus (TP) in lakes is regulated by static aspects of the lake's watershed, but lake TP can be readily increased by human activities. In some low-nutrient lakes, basin morphometry may induce naturally occurring anoxia. The occurrence of natural anoxia is especially important to consider in lake water quality assessments that compare observed conditions to expected reference conditions. To investigate the occurrence of natural vs. anthropogenically influenced anoxia, we constructed a logistic regression model to calculate the probability of low-nutrient lakes (TP < 15 µg/L) developing aerial anoxic extent ≥10% by testing the predictive potential of variables related to basin morphometry, depths of lake thermal strata, epilimnetic TP, and dissolved organic carbon (DOC). Maximum lake depth and the proportion of lake area under the top of the metalimnion were the most important variables to predict the likelihood of hypolimnetic anoxia, which correctly predicted anoxic condition in 84% of lakes (Model 1). Adding TP as a third variable to Model 1 produced a significantly improved model (Model 2) but the prediction success rate was comparable (86%). We also present a model for lakes with limited bathymetric data, which predicts anoxia with 81% accuracy based on maximum lake depth and mean thermocline depth at peak stratification. DOC was relatively low (4.3 ± 1.5 mg/L [mean ± SD]) in the study lakes and its inclusion did not improve model performance. In Model 1, lakes with an anoxic extent ≥10% of lake area had significantly higher epilimnetic TP than lakes with oxic hypolimnia, regardless of prediction category or success. Our results indicate that including TP as a variable helps refine models based on morphometry alone, but lake morphometry and stratification dynamics are the most important factors in the development of anoxic extent in low-nutrient temperate lakes. Our approach informs studies concerned with identifying key factors that influence regime shifts in a variety of ecosystems.

Solar Radiation as the Likely Cause of Acid-Soluble Rare-Earth Elements in Sediments of Fresh Water Humic Lakes.

We studied photochemically induced precipitation of rare-earth elements (REEs) in water from a tributary to Plesné Lake and a tributary to Jirická Pond, Czech Republic. Both tributaries had high concentrations of dissolved organic matter (∼1.8 mmol C L-1). Filtered (0.2 µm) samples were exposed to artificial solar radiation of 350 W m-2 for 48 to 96 h, corresponding to 3 to 6 days of natural solar radiation in summer at the sampling locations. Experiments were performed with altered and unaltered pH ranging from 3.8 to 6.0. The formation of particulate REEs occurred in all exposed samples with the fastest formation observed at the original pH. The formation of particulate metals continued in irradiated samples after the end of irradiation, suggesting that photochemically induced reactions and/or continuing precipitation continue in darkness or in deeper water due to mixing. Results were compared with paleolimnological records in the Plesné Lake sediment. At pH 5.0, the photochemically induced sediment flux was 3509 nmol m-2 y-1 for Ce, corresponding to 42% of the REEs' annual sediment flux in recent sediment layers. Combining the formation rates obtained in the laboratory irradiation experiments and known 1 day incident solar radiation enabled the estimation of a possible REE sediment flux. For Plesné Lake, the photochemically induced formation of particulate REEs explained 10-44% of the REE concentrations in the upper sediment layers. Observed photochemically induced sequestration of REEs into sediments can explain a significant part of the REEs' history in the Holocene sediment.

Chemical Force Spectroscopy Evidence Supporting the Layer-by-Layer Model of Organic Matter Binding to Iron (oxy)Hydroxide Mineral Surfaces.

The adsorption of dissolved organic matter (DOM) to metal (oxy)hydroxide mineral surfaces is a critical step for C sequestration in soils. Although equilibrium studies have described some of the factors controlling this process, the molecular-scale description of the adsorption process has been more limited. Chemical force spectroscopy revealed differing adhesion strengths of DOM extracted from three soils and a reference peat soil material to an iron (oxy)hydroxide mineral surface. The DOM was characterized using ultrahigh-resolution negative ion mode electrospray ionization Fourier Transform ion cyclotron resonance mass spectrometry. The results indicate that carboxyl-rich aromatic and N-containing aliphatic molecules of DOM are correlated with high adhesion forces. Increasing molecular mass was shown to decrease the adhesion force between the mineral surface and the DOM. Kendrick mass defect analysis suggests that mechanisms involving two carboxyl groups result in the most stable bond to the mineral surface. We conceptualize these results using a layer-by-layer "onion" model of organic matter stabilization on soil mineral surfaces.

The effect of sediment mixing on mercury dynamics in two intertidal mudflats at Great Bay Estuary, New Hampshire, USA.

Estuarine sediments store particulate contaminants including mercury (Hg). We studied Hg sediment dynamics in two intertidal mudflats at Great Bay estuary, NH, over multiple years. Sediments at both mudflats were physically mixed down to ~10 cm, as determined by 7Be measurements, albeit via different mechanisms. Portsmouth mudflat (PT) sediments were subject to bioturbation by infaunal organisms and Squamscott mudflat (SQ) sediments were subject to erosion and redeposition. The presence of higher concentrations of fresh Fe(III) hydroxide at PT suggested bioirrigation by the polychaetes (Nereis virens). At depths where infaunal bioirrigation was observed, pore-water inorganic Hg (Hgi) and methylmercury (MeHg) were lower potentially due to their interaction with Fe(III) hydroxide. Methylmercury concentrations increased immediately below this zone in some samples, suggesting that the observed increase in material flux in bioirrigated sediments may initiate from lower depths. Pore water in sediment at PT also had higher fractions of more protein-like and labile DOC than those at SQ that can lead to increased MeHg production in PT, especially at depths where Hgi is not removed from solution by Fe(III) hydroxide. Where sediment erosion and redeposition were observed at SQ, Hg species distribution was extended deeper into the sediment column. Moreover, methyl coenzyme M reductase (MCR) and mercury reductase (mer-A) genes were higher at SQ than PT suggesting differences in conditions for Hg cycling. Results showed that the near-surface region of high MeHg concentrations commonly observed in unmixed sediments does not exist in physically mixed sediments that are common in many estuarine environments.

Kinetics of homogeneous and surface-catalyzed mercury(II) reduction by iron(II).

Production of elemental mercury, Hg(0), via Hg(II) reduction is an important pathway that should be considered when studying Hg fate in environment. We conducted a kinetic study of abiotic homogeneous and surface-catalyzed Hg(0) production by Fe(II) under dark anoxic conditions. Hg(0) production rate, from initial 50 pM Hg(II) concentration, increased with increasing pH (5.5-8.1) and aqueous Fe(II) concentration (0.1-1 mM). The homogeneous rate was best described by the expression, r(hom) = k(hom) [FeOH(+)] [Hg(OH)2]; k(hom) = 7.19 × 10(+3) L (mol min)(-1). Compared to the homogeneous case, goethite (α-FeOOH) and hematite (α-Fe2O3) increased and γ-alumina (γ-Al2O3) decreased the Hg(0) production rate. Heterogeneous Hg(0) production rates were well described by a model incorporating equilibrium Fe(II) adsorption, rate-limited Hg(II) reduction by dissolved and adsorbed Fe(II), and rate-limited Hg(II) adsorption. Equilibrium Fe(II) adsorption was described using a surface complexation model calibrated with previously published experimental data. The Hg(0) production rate was well described by the expression r(het) = k(het) [>SOFe((II))] [Hg(OH)2], where >SOFe((II)) is the total adsorbed Fe(II) concentration; k(het) values were 5.36 × 10(+3), 4.69 × 10(+3), and 1.08 × 10(+2) L (mol min)(-1) for hematite, goethite, and γ-alumina, respectively. Hg(0) production coupled to reduction by Fe(II) may be an important process to consider in ecosystem Hg studies.

Assessment Indices of Littoral Habitat Condition for Lakes in Maine and New England, USA.

Littoral habitat is critical for lake biota but is adversely affected by residential shoreland development through the loss and reduced structural complexity of lakeshore vegetation. There currently exists no assessment methodology for evaluating littoral habitat condition of individual lakes in northeastern US. We addressed this assessment need by creating multi-metric indices of littoral habitat condition that focus on lakeshore residential development as the primary stressor. We did this by using habitat metrics derived primarily from National Lake Assessment (NLA) Physical Habitat (PHAB) survey field observations to create Linear Discriminant Analysis (LDA) models that assign lakeshore stations into littoral habitat condition categories. Lake PHAB survey data were used from New England NLA surveys as well as state-level surveys completed in Maine, New Hampshire, and Vermont. Prediction success rates in New England models averaged 83%. The Maine LDA models, which used finer scale survey methods, had an average prediction success rate of 89%. We used 95% bootstrapped confidence intervals to make assessment designations of natural (meeting reference quality), diminished (not meeting reference quality), or intermediate (existing between natural and diminished) littoral habitat condition for each lake. Our results show that efficacious single-lake littoral habitat assessments may be completed within the framework of NLA PHAB methodology, but confidence in assessment results, and therefore better-informed management decisions, can be improved with finer-scale observation data.

Mercury sources and fate in the Gulf of Maine.

Most human exposure to mercury (Hg) in the United States is from consuming marine fish and shellfish. The Gulf of Maine is a complex marine ecosystem comprising twelve physioregions, including the Bay of Fundy, coastal shelf areas and deeper basins that contain highly productive fishing grounds. Here we review available data on spatial and temporal Hg trends to better understand the drivers of human and biological exposures. Atmospheric Hg deposition from U.S. and Canadian sources has declined since the mid-1990s in concert with emissions reductions and deposition from global sources has increased. Oceanographic circulation is the dominant source of total Hg inputs to the entire Gulf of Maine region (59%), followed by atmospheric deposition (28%), wastewater/industrial sources (8%) and rivers (5%). Resuspension of sediments increases MeHg inputs to overlying waters, raising concerns about benthic trawling activities in shelf regions. In the near coastal areas, elevated sediment and mussel Hg levels are co-located in urban embayments and near large historical point sources. Temporal patterns in sentinel species (mussels and birds) have in some cases declined in response to localized point source mercury reductions but overall Hg trends do not show consistent declines. For example, levels of Hg have either declined or remained stable in eggs from four seabird species collected in the Bay of Fundy since 1972. Quantitatively linking Hg exposures from fish harvested from the Gulf of Maine to human health risks is challenging at this time because no data are available on the geographic origin of seafood consumed by coastal residents. In addition, there is virtually no information on Hg levels in commercial species for offshore regions of the Gulf of Maine where some of the most productive fisheries are located. Both of these data gaps should be priorities for future research.

Controls on the epilimnetic phosphorus concentration in small temperate lakes.

Phosphorus (P) is one of the key limiting nutrients for algal growth in most fresh surface waters. Understanding the determinants of P accumulation in the water column of lakes of interest, and the prediction of its concentration is important to water quality managers and other stakeholders. We hypothesized that lake physicochemical, climate, and watershed land-use attributes control lake P concentration. We collected relevant data from 126 lakes in Maine, USA, to determine the major drivers for summer total epilimnetic P concentrations. Predictive regression-based models featured lake external and internal drivers. The most important land-use driver was the extent of agriculture in the watershed. Lake average depth was the most important physical driver, with shallow lakes being most susceptible to high P concentrations; shallow lakes often stratify weakly and are most subject to internal mixing. The sediment NaOH-extracted aluminum (Al) to bicarbonate/dithionite-extracted P molar ratio was the most important sediment chemical driver; lakes with a high hypolimnetic P release have low ratios. The dissolved organic carbon (DOC) concentration was an important water column chemical driver; lakes having a high DOC concentration generally had higher epilimnetic P concentrations. Precipitation and temperature, two important climate/weather variables, were not significant drivers of epilimnetic P in the predictive models. Because lake depth and sediment quality are fixed in the short-term, the modeling framework serves as a quantitative lake management tool for stakeholders to assess the vulnerability of individual lakes to watershed development, particularly agriculture. The model also enables decisions for sustainable development in the watershed and lake remediation if sediment quality is conducive to internal P release. The findings of this study may be applied to bloom metrics more directly to support lake and watershed management actions.

Highly Efficient Iron Oxide Nanoparticles Immobilized on Cellulose Nanofibril Aerogels for Arsenic Removal from Water.

The application and optimal operation of nanoparticle adsorbents in fixed-bed columns or industrial-scale water treatment applications are limited. This limitation is generally due to the tendency of nanoparticles to aggregate, the use of non-sustainable and inefficient polymeric resins as supporting materials in fixed-bed columns, or low adsorption capacity. In this study, magnesium-doped amorphous iron oxide nanoparticles (IONPs) were synthesized and immobilized on the surface of cellulose nanofibrils (CNFs) within a lightweight porous aerogel for arsenic removal from water. The IONPs had a specific surface area of 165 m2 g-1. The IONP-containing CNF aerogels were stable in water and under constant agitation due to the induced crosslinking using an epichlorohydrin crosslinker. The adsorption kinetics showed that both As(III) and As(V) adsorption followed a pseudo second-order kinetic model, and the equilibrium adsorption isotherm was best fitted using the Langmuir model. The maximum adsorption capacities of CNF-IONP aerogel for As(III) and As(V) were 48 and 91 mg As g-IONP-1, respectively. The optimum IONP concentration in the aerogel was 12.5 wt.%, which resulted in a maximum arsenic removal, minimal mass loss, and negligible leaching of iron into water.

Experimental photochemical release of organically bound aluminum and iron in three streams in Maine, USA.

Laboratory photochemical experiments with stream water were done to characterize the photodegradation of dissolved organic carbon (DOC) and photochemical release of organically bound metals. The samples were collected from Bear Brook Watershed, Hadlock Brook, and Mud Pond Stream in Maine, USA, during January and April 2006. Filtered samples were irradiated in a reactor equipped with 350 nm irradiation lamps. Aliquots of irradiated samples were analyzed for DOC, dissolved aluminum (Al(d)) and iron (Fe(d)), pH, and UV-Vis spectra. Organically bound metals (Fe(o) and Al(o)) were measured after passing the sample through a column filled with a strong cation exchange resin (Dowex HCR-W2). UV radiation resulted in a decrease in DOC concentration and structural changes in DOC composition. UV-Vis spectra showed a decrease in aromaticity and molecular weight of DOC during irradiation. The DOC ranged from 0.1 to 0.35 mmol L(-1) at the beginning of experiments and decreased 5% to 37% after irradiation. Oxidation and structural changes in DOC resulted in the release of organically bound metals. Initial Fe(o) concentrations ranged from 0.16 to 0.79 µmol L(-1) and decreased 56% to 81% during the irradiation. The concentration of Al(o) ranged from 1.0 to 3.85 µmol L(-1) and declined steadily throughout the irradiation, resulting in 8% to 76% decline. Degradation of a small percentage of organically bound Al and Fe occurs rapidly enough so as to be an important process in first- and second-order streams. Irradiation energy absorbed by samples during hours of laboratory experiments equates to days in stream environment. Degradation of more refractory complexes occurs on a time scale that requires longer residence times, such as in lakes. This study demonstrated a strong impact of photochemical degradation of DOC on its metal-complexing ability and capacity. The results also suggest different binding properties of Fe and Al in their organic complexes.

Mobilization of metals and phosphorus from intact forest soil cores by dissolved inorganic carbon.

Increased dissolved inorganic carbon (DIC) enhances the mobilization of metals and nutrients in soil solutions. Our objective was to investigate the mobilization of Al, Ca, Fe, and P in forest soils due to fluctuating DIC concentrations. Intact soil cores were taken from the O and B horizons at the Bear Brook Watershed in Maine (BBWM) to conduct soil column transport experiments. Solutions with DIC concentrations (∼20-600 ppm) were introduced into the columns. DIC was reversibly sorbed and its migration was retarded by a factor of 1.2 to 2.1 compared to the conservative sodium bromide tracer, corresponding to a log K (D) = -0.82 to -0.07. Elevated DIC significantly enhanced the mobilization of all Al, Fe, Ca, and P. Particulate (>0.4 µm) Al and Fe were mobilized during chemical and flow transitions, such as increasing DIC and dissolved organic carbon (DOC), and resumption of flow after draining the columns. Calcium and P were primarily in dissolved forms. Mechanisms such as ion exchange (Al, Fe, Ca), ligand- and proton-promoted dissolution (Al and Fe), and ligand exchange (P) were the likely chemical mechanisms for the mobilization of these species. One column was packed with dried and sieved B-horizon soil. The effluent from this column had DOC, Al, and Fe concentrations considerably higher than those in the intact columns, suggesting that these species were mobilized from soil's microporous structure that was otherwise not exposed to the advective flow. Calcium and P concentrations, however, were similar to those in the intact columns, suggesting that these elements were less occluded in soil particles.

Modeling response of water quality parameters to land-use and climate change in a temperate, mesotrophic lake.

Lake Auburn, Maine, USA, is a historically unproductive lake that has experienced multiple algal blooms since 2011. The lake is the water supply source for a population of ~60,000. We modeled past temperature, and concentrations of dissolved oxygen (DO) and phosphorus (P) in Lake Auburn by considering the catchment and internal contributions of P as well as atmospheric factors, and predicted the change in lake water quality in response to future climate and land-use changes. A stream hydrology and P-loading model (SimplyP) was used to generate input from two major tributaries into a lake model (MyLake-Sediment) to simulate physical mixing, chemical dynamics, and sediment geochemistry in Lake Auburn from 2013 to 2017. Simulations of future lake water quality were conducted using meteorological boundary conditions derived from recent historical data and climate model projections for high greenhouse-gas emission cases. The effects of future land development on lake water quality for the 2046 to 2055 time period under different land-use and climate change scenarios were also simulated. Our results indicate that lake P enrichment is more responsive to extreme storm events than increasing air temperatures, mean precipitation, or windstorms; loss of fish habitat is driven by windstorms, and to a lesser extent an increasing water temperature; and catchment development further leads to water quality decline. All simulations also show that the lake is susceptible to both internal and external P loadings. Simulation of temperature, DO, and P proved to be an effective means for predicting the loss of water quality under changing land-use and climate scenarios.

Photochemical release of humic and fulvic acid-bound metals from simulated soil and streamwater.

This study demonstrates the strong impact of photochemical degradation of soil dissolved organic matter (DOM) on its metal complexing capacity. The role of light in the fate of organically-bound metals transported from soils to surface waters was studied in laboratory experiments. We studied four humic and one fulvic acid isolates from different soil horizons in the Bohemian Forest (Czech Republic). Different concentrations of aluminium (Al) and iron (Fe) salts were added to the solutions of organic acids (initial dissolved organic carbon (DOC) concentration 0.5 mmol L(-1)), and the samples were irradiated in a reactor equipped with 350 nm irradiation lamps for 0 to 120 min. Aliquots of irradiated samples and dark controls were analyzed for DOC, ionic and organically-bound Al and Fe (Al(i), Fe(i), and Al(o), Fe(o), respectively), pH, and UV-VIS spectra. The initial Fe(o) concentrations in the samples (2.09 to 5.66 micromol L(-1)) decreased from 21 to 52% during irradiation, while the initial Al(o) concentrations (2.28 to 5.37 micromol L(-1)) decreased from 7 to 41%. The greatest decrease in the organically-bound metal concentrations occurred for the fulvic acid, and the smallest decrease occurred for the humic acid from the deepest soil horizon. The extrapolation of laboratory experiments to in situ conditions suggested that the DOM's ability to bind metals changes greatly within the first few hours after groundwater enters the stream. The rapid degradation of organically-bound Al and Fe can be an important process in first and second-order streams, and lake epilimnia.

Chemical controls on dissolved phosphorus mobilization in a calcareous agricultural stream during base flow.

This study explores the sources and mechanisms of dissolved phosphorus (P) mobilization under base flow conditions in a headwater stream. We characterized the relevant chemical species and processes within the watershed to investigate connections between stream sediment, surface water, and groundwater with respect to P dynamics. Waters were monitored monthly during the 2017 snow-free period for temperature, pH, dissolved oxygen, conductivity, soluble reactive P (SRP), total P, strong acid anions, strong base cations, dissolved organic carbon (DOC), Al, Fe, and Mn. Phosphorus speciation within sediment samples was determined by sequential chemical extractions. The emerging groundwater was under-saturated by up to 40% with respect to O2, with pH = 7.24, T = 7.0 °C, and SRP = 3.0 µg L-1. Groundwater PCO2 was up to ~35× the ambient PCO2 (410 ppm). Degassing of CO2 from the emerging groundwater resulted in a significant increase in pH downstream, and an increase in the SRP concentration from 3.0 to a maximum of 40.6 µg L-1. Laboratory experiments, using homogenized stream sediment, identified a reduction in the P adsorption capacity, and an increase in desorption of native P with increasing pH from ~7.25 (emerging groundwater) to ~8.50 (air-equilibrated surface water). These data allow us to identify the pH-dependent desorption from P-laden sediment as the most significant source of dissolved P in the headwater stream under base flow conditions.

Sediment geochemistry of Al, Fe, and P for two historically acidic, oligotrophic Maine lakes.

Phosphorus (P) may be liberated from lake sediments by reductive dissolution of Fe(OH)(3(S)) during periods of hypolimnetic anoxia. P, however, remains adsorbed to Al(OH)(3(S)) regardless of redox conditions. During chronic or episodic acidification of a catchment, ionic Al is mobilized from soils to receiving waters. A fraction of the mobilized Al may precipitate as a consequence of higher pH of the receiving waters. We hypothesized that phosphorus retention in lake sediments is directly related to the magnitude of Al loading in response to low pH in the watershed. We studied cores representing over 200 years of sediment accumulation in historically acidic Mud Pond and Little Long Pond in eastern Maine, USA. Sequential chemical extractions of sediment were used to assess the history of Al, Fe, and P interactions. Mud Pond is a first-order pond with a pH of approximately 4.7, having acidified slightly in response to anthropogenic acidification from approximately 1930. The inlet stream to Mud Pond has dissolved Al concentrations often exceeding 500 microg/L, of which more than half is organically-bound. Mud Pond drains into Little Long Pond, a second-order pond with a historical pH of <6, and which has shown little pH or alkalinity response to increases or decreases in atmospheric SO(4)(2-) input. Sequential extractions show that Al and P are predominantly in the 0.1 M NaOH-extractable fraction in the sediments from both ponds throughout the cores. The concentration of the likely biogenic and non-reactive P within the NaOH fraction increases up core from <30% to approximately 60%. Extractable Fe (<20% of extractable Al) is mainly in the 0.1 M NaOH-extractable fraction, except for the top few cm, which are predominantly in the bicarbonate-dithionite reducible fraction. Accumulation rates of sediment, Al, Fe, and P in both ponds have increased in the last 50-60 yr, but fractions remain in the same proportion. Throughout both sediment cores the molar ratio of specific Al:P fractions greatly exceeds 25, and molar ratio of specific Al:Fe fractions greatly exceeds 3, the thresholds proposed by Kopácek et al. [Kopácek J, Borovec J, Hejzlar J, Ulrich K-U, Norton SA, Amirbahman A. Aluminum control of phosphorus sorption by lake sediments. Environ Sci Technol 2005; 39: 8784-89.] for P release during anoxia. The data illustrate a continuous association of P with Al in both ponds during the last two centuries, likely due to the persistent natural acidity of the catchments.

Speciation of Al, Fe, and P in recent sediment from three lakes in Maine, USA.

Sequential extraction of sediments [Psenner R, Pucsko R. Die Fraktionierung organischer und anorganischer Phosphorverbindungen von Sedimenten. Arch Hydrobiol/Suppl 1988. 70(1): 111-155.] from short, (210)Pb-dated cores from three lakes in Maine USA demonstrates that sediment P is dominantly associated with the NaOH-extractable fraction (P-NaOH(25)) and less with the bicarbonate-dithionite extractable fraction (P-BD). The ratios (Al-NaOH(25))/(Fe-BD) and (Al-NaOH(25))/(P-NH(4)Cl+P-BD) for upper sediment for two oligo-mesotrophic lakes exceeded 3 and 25, the thresholds for preventing substantial release of P from sediments during hypolimnetic anoxia [Kopácek J, Borovec J, Hejzlar J, Ulrich K-U, Norton SA, Amirbahman A. Aluminum control of phosphorus sorption by lake sediments. Environ Sci Technol 2005a;39:8784-8789.]. Hypolimnetic water chemistry verifies this effect. The third lake, currently eutrophic, has values for the ratios that are below the thresholds and this lake has substantial release of P from recent sediment. The sediment characteristics remain relatively constant over the last 150+ years, indicating that the processes responsible for P retention have operated long before atmospheric acidification of watersheds might have influenced the flux of Al and Fe to the lake. In 2002, the pH of inlets and the lakes was generally between 6 and 8. Input to the lakes had high concentrations of acid-soluble particulate and dissolved Al, Fe, and P, and dissolved Al and Fe complexed with dissolved organic carbon (DOC). Lake water column and outlet Al, Fe, and P were typically 90-95% lower than inlet concentrations over a 12 month period. Photo-oxidation of Al-DOC and Fe-DOC in the lake, liberation of inorganic Al and Fe, precipitation of Al(OH)(3) and Fe(OH)(3), adsorption of P by the hydroxides, and sedimentation are responsible for the changes in water quality and long-term sediment characteristics.

Semipermeable membrane device (SPMD) for monitoring PCDD and PCDF levels from a paper mill effluent in the Androscoggin River, Maine, USA.

Paper mill effluents may contain polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) that are normally generated due to chlorinated bleaching of pulp and paper. We used the semipermeable membrane device (SPMD) to monitor PCDD/F levels upstream and downstream of a paper mill on the Androscoggin River, in Jay (ME). Following the 36 day deployment, SPMD dialysis and cleanup, the samples were analyzed by HRGC/HRMS. Total concentrations of PCDD/Fs in SPMDs (sum of all tetra-through octachlorinated congeners) ranged from 4.71 pg g(-1) to 26.26 pg g(-1). Five out of the targeted 17 toxic congeners were detected, including: 2,3,7,8-TCDF; 1,2,3,7,8-PeCDF; 2,3,4,7,8-PeCDF; 1,2,3,4,6,7,8-HpCDD and OCDD. Permeability reference compounds (PRCs) were used for in situ calibration of the SPMD sampling rate (Rs). In all sites, water concentrations were the highest for OCDD (0.081-0.103 pg l(-1)), and the lowest for 1,2,3,7,8-PeCDF (0.005-0.009 pg l(-1)). There was not a consistent pattern of upstream-downstream gradient in the PCDD/F levels. This suggested that processes other than the mill in Jay (multiple sources, river dynamics) governed the flux of PCDD/Fs in the sampling locations. The SPMD results were validated by comparison to other studies on the Androscoggin River and elsewhere, confirming the potential of the device as a useful monitoring technique for PCDD/Fs in large river systems.

Photodegradation of taste and odor compounds in water in the presence of immobilized TiO2-SiO2 photocatalysts.

Disinfection by ultraviolet (UV) radiation is a growing trend in public water treatment systems because of its effectiveness with respect to inactivation of protozoa and other pathogenic microorganisms. However, removal of different classes of organic compounds, including taste and odor compounds in water is not effective with UV irradiation. In this study, a novel TiO2-based immobilized photocatalyst is developed to enhance the UV photodegradation of two of the major taste and odor compounds, 2-methylisoborneol (MIB) and Geosmin (GSM) in water. Evonik (formerly Degussa) P-25 powder-modified TiO2 was immobilized on glass slides using TiO2-SiO2 sol-gel mixture as the binder and calcined at 500 °C. Several catalyst films with different Si amounts were synthesized and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL) and scanning electron microscopy (SEM). Photocatalytic degradation of MIB and GSM was investigated by irradiating aqueous solutions under UV-A light (350 nm). Generation of hydroxyl radicals (OH) was also assessed to evaluate the activity of the photocatalyst films. Catalyst films with surface ratios of Ti:Si ≈6 showed similar degradations rates but better robustness compared to immobilized P25 films.

Factors contributing to the internal loading of phosphorus from anoxic sediments in six Maine, USA, lakes.

Phosphorus (P) is the limiting macronutrient for primary production in most lakes. Seasonal anoxia in the hypolimnion of lakes has been strongly correlated with internal P loading to the water column. Gravimetric sediment cores were collected before and after the onset of anoxia in six Maine (USA) lakes during the summer of 2003. This study investigates the relative importance of P sequestration by aluminum hydroxide (Al(OH)3(s)), and ferric (oxy)hydroxide (Fe(OH)3(S)) dissolution with subsequent P release in lakes with varying trophic status. Two lakes, Pennesseewassee and Highland, are oligotrophic. The remaining lakes, China, Cobbosseecontee, Webber and Salmon, have varying levels of productivity. Sediment P, Al and Fe in the top 10 cm were extracted sequentially using ammonium chloride (NH4Cl), bicarbonate-dithionite (BD), and sodium hydroxide (NaOH) at 25 degrees C. The results suggest that a sediment [NH4Cl-Al+BD-Al+NaOH25-Al]:[NH4Cl-Fe+BD-Fe] molar ratio >3 and a sediment [NaOH25-Al]:[NH4Cl-P+BD-P] molar ratio >25 predict low P flux from sediments during the development of anoxia, as proposed by Kopácek et al. [Kopácek J, Borovec J, Hejzlar J, Ulrich K, Norton S, Amirbahman A. Aluminum control of Phosphorus Sorption in Lake Sediments. Environ Sci Technol 2005; 39: 8784-8789.], despite the development of anoxia in and the release of Fe(II) from the hypolimnia of the two study lakes. However, when these molar ratios are not exceeded the model does not adequately describe sedimentary P flux. The application of the model proposed by Kopácek et al. to Cobbosseecontee Lake suggests that its sediment may be a source of P to the water column. However, water column data indicate little to no sedimentary P flux. Therefore, the lack of P flux may be attributed to the absence of Fe(III) reduction in the Cobbosseecontee Lake sediment or perhaps to the slow diagenesis of organically-bound P.

Mercury bioaccumulation in green frog (Rana clamitans) and bullfrog (Rana catesbeiana) tadpoles from Acadia National Park, Maine, USA.

Mercury contamination in the northeastern United States, including Acadia National Park (ANP; ME, USA), is well documented and continues to be a public health issue of concern. Mercury contamination of wild amphibians has received little attention, however, despite reports of worldwide population declines. Here, we report total Hg and methyl Hg (MeHg) concentrations for water, sediment, and green frog (Rana clamitans) and bullfrog (Rana catesbeiana) tadpoles (age, approximately one year) from ANP. Total Hg concentrations (mean+/-standard error) in green frog and bullfrog tadpoles were 25.1+/-1.5 and 19.1+/-0.8 ng/g wet weight, respectively. Mean total Hg was highest for green frog tadpoles sampled from the Schooner Head site (ANP, Bar Harbor, ME, USA), a small, semipermanent beaver pond where Ranavirus was detected during the summer of 2003 sampling period. Methyl Hg comprised 7.6 to 40% of the total Hg in tadpole tissue (wet-wt basis), and mean total Hg levels in tadpoles were significantly different among pond sites (n = 9). Total Hg in pond water was a significant predictor of tadpole total Hg levels. Dissolved organic carbon was a significant predictor of both total Hg and MeHg in water, and total Hg in water also was strongly correlated with MeHg in water. Of the nine pond ecosystems sampled at ANP 44% had a methylation efficiency (water MeHg to total Hg ratio) of greater than 10%, and 33% had total Hg levels in sediment that were approximately equal to or greater than the established threshold level effect concentration for freshwater sediments (0.174 mg/kg dry wt). Our data indicate that wetland food webs in ANP likely are susceptible to high levels of total Hg bioaccumulation and that methylation dynamics appear to be influenced by local abiotic and biotic factors, including disturbances by beavers and in situ water chemistry patterns. These findings may be important to National Park Service resource managers, especially considering the class I airshed status of ANP and the strong potential for negative effects to aquatic ecosystem structure and function from Hg pollution.