Lithium in drinking water and the incidences of crimes,suicides, and arrests related to drug addictions

Using data for 27 Texas counties from 1978-1987, it is shown that the incidence rates of suicide, homicide, and rape are significantly higher in counties whose drinking water supplies contain little or no lithium than in counties with water lithium levels ranging from 70-170 micrograms/L; the differences remain statistically significant (p less than 0.01) after corrections for population density. The corresponding associations with the incidence rates of robbery, burglary, and theft were statistically significant with p less than 0.05. These results suggest that lithium has moderating effects on suicidal and violent criminal behavior at levels that may be encountered in municipal water supplies. Comparisons of drinking water lithium levels, in the respective Texas counties, with the incidences of arrests for possession of opium, cocaine, and their derivatives (morphine, heroin, and codeine) from 1981-1986 also produced statistically significant inverse associations, whereas no significant or consistent associations were observed with the reported arrest rates for possession of marijuana, driving under the influence of alcohol, and drunkenness. These results suggest that lithium at low dosage levels has a generally beneficial effect on human behavior, which may be associated with the functions of lithium as a nutritionally-essential trace element. Subject to confirmation by controlled experiments with high-risk populations, increasing the human lithium intakes by supplementation, or the lithiation of drinking water is suggested as a possible means of crime, suicide, and drug-dependency reduction at the individual and community level.     

Lithium-Induced Hypothyroidism: Oxidative Stress and Osmotic Fragility Status in Rats

The present study was conducted to explore the possible effects of different doses of lithium carbonate on thyroid functions, erythrocyte oxidant–antioxidant status, and osmotic fragility. Twenty-four Wistar-type male rats were equally divided into three groups: groups I and II received 0.1 and0.2 % lithium carbonate in their drinking water, respectively, for 30 days. The rats in group III served as controls, drinking tap water without added lithium. At the end of the experimental period, the erythrocyte osmotic fragility and the levels of triiodothyronine (T₃), thyroxine (T₄), thyroid-stimulating hormone (TSH), malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione (GSH) were measured in blood samples. Compared to controls, there was a statistically significant increase of TSH but decreases of the T₃ and T₄ levels in group II. Both experimental groups showed a statistically significant increase of the maximum osmotic fragility limit. The minimum osmotic fragility values of the animals in group II were statistically higher than those of controls. The standard hemolytic increment curve of both experimental groups was shifted to the right when compared to the curve obtained from the controls. Also, relative to controls, the activities of MDA and SOD were significantly higher and the GSH level lower in group II, but not so in group I. The results of the present study show that treatment with lithium carbonate may result in thyroid function abnormalities, increased oxidative damage, and possible compromise of the erythrocyte membrane integrity resulting from increased osmotic fragility.     

No Benefit from Chronic Lithium Dosing in a Sibling-Matched,Gender Balanced,Investigator-Blinded Trial Using a Standard Mouse Model of Familial ALS

Background

In any animal model of human disease a positive control therapy that demonstrates efficacy in both the animal model and the human disease can validate the application of that animal model to the discovery of new therapeutics. Such a therapy has recently been reported by Fornai et al. using chronic lithium carbonate treatment and showing therapeutic efficacy in both the high-copy SOD1G93A mouse model of familial amyotrophic lateral sclerosis (ALS), and in human ALS patients.

Methodology/Principal Findings

Seeking to verify this positive control therapy, we tested chronic lithium dosing in a sibling-matched, gender balanced, investigator-blinded trial using the high-copy (average 23 copies) SOD1G93A mouse (n = 27–28/group). Lithium-treated mice received single daily 36.9 mg/kg i.p. injections from 50 days of age through death. This dose delivered 1 mEq/kg (6.94 mg/kg/day lithium ions). Neurological disease severity score and body weight were determined daily during the dosing period. Age at onset of definitive disease and survival duration were recorded. Summary measures from individual body weight changes and neurological score progression, age at disease onset, and age at death were compared using Kaplan-Meier and Cox proportional hazards analysis. Our study did not show lithium efficacy by any measure.

Conclusions/Significance

Rigorous survival study design that includes sibling matching, gender balancing, investigator blinding, and transgene copy number verification for each experimental subject minimized the likelihood of attaining a false positive therapeutic effect in this standard animal model of familial ALS. Results from this study do not support taking lithium carbonate into human clinical trials for ALS.     

Lithium and Other Elements in Scalp Hair of Residents of Tokyo Prefecture as Investigational Predictors of Suicide Risk

The high suicide rates in Japan and several reports of inverse associations of suicide rates with the levels of lithium (Li) in drinking water prompted determinations of Li along with other elements in samples of scalp hair of 100 male and 100 female residents of Tokyo Prefecture. In more than half of the samples of both genders, Li levels were below the instrumental detection limit or below or the lower limit of the laboratory reference ranges. Among other elements, the concentrations namely of cobalt were also frequently below the laboratory reference range, suggesting that low circulating levels of vitamin B(12) were common in this study population. As vitamin B(12) deficiency is associated with depression and other psychiatric conditions, and there is evidence of interactions between Li and vitamin B(12), Li deficiency as well as suboptimal vitamin B(12) status must be considered as potential suicide risk factors. In view of its established positive effects on mood and brain function, an adequate supply of selenium (Se) is important as well. Although the analytical results suggested that the Se status of the subjects was generally adequate, as seafood was a major dietary source of Se, much of it was actually sequestered by mercury and only a fraction was bio-available. In addition, the hair samples were found to contain not insignificant levels of As, Cd, Ni, and Pb, arising from the adventitious presence of these elements in foods and the environment. As these elements also interact with Se in vivo and are known to adversely affect mood and behavior, in investigational studies, subjects at risk need to be evaluated also with respect to these elements.     

Investigating lithium ion conductivity in amorphous solids containing [V10O28]6− clusters by computer simulation

Computer simulation method was applied to investigate the migration of lithium ion in three amorphous solid systems containing polyoxovanadate (POV) clusters [V₁₀O₂₈]^6 ? . The cluster was adopted from a recently synthesized crystalline poly[octa-μ-aqua-octaaqua-μ-decavanadato-hexalithium] (POAODH). The simulated POV systems correspond to amorphous solid half-dehydrated solid and completely dehydrated solid doped with LiCl salt. The simulation results show large diffusion constants of lithium ions in all systems in spite of highly negatively charged [V₁₀O₂₈]^6 ?  clusters presented in the system. The estimated ionic conductivity due to the migration of lithium ions reaches a magnitude of 10^? 4 S/m. The conductivity increases as the water content in the system decreases. The analysis of moving trajectories shows the lithium ion moves around the oxygen sites of POV clusters and hops between them. The estimated displacement of lithium ion is about 4～5 Å, which is much larger than the corresponding displacement of lithium ion in a polymer matrix. Rapidly rotating clusters shown by orientation correlation function analysis, in conjunction with the large separation between clusters in the system, provides favorable conditions for the large amplitude migration of lithium ions.     

Drinking water quality and arsenic health risk assessment in Sistan and Baluchestan,Southeastern Province,Iran

Access to drinking water is one of the most important indicators determined by the World Health Organization (WHO). This investigation surveyed the concentration of various pollutants in drinking water and its health risk attribute to Arsenic in Sistan and Baluchistan province, Iran. Water samples were collected from ground water and analyzed for physical parameters, anions, and heavy metals using the standard procedures. The concentrations of sulfate (269 ± 127 mg/l) in five sites exceeded the permissible limit (250 mg/l), while chlorine concentrations (223 ± 100 mg/l) in four sites exceeded the permissible limit (250 mg/l) set by WHO. Similarly, the concentrations of Mg (30 ± 11 mg/l) in four sites exceeded the permissible limit (30 mg/l), while Na concentrations (222 ± 99 mg/l) in five sites exceeded the permissible limit (200 mg/l) set by Institute of Standards and Industrial Research of Iran (ISIRI). In addition, arsenic was in acceptable levels recommended by WHO and local regulations. Based on the calculated indices of hazard qutient (HR) and excess lifetime cancer risk (ELCR), the in-use drinking water has no adverse effects on the consumer's health. Excessive use of fertilizers and pesticides, unsuitable sewerage systems, and inappropriate sludge and solid waste disposal in this province can lead to drinking water pollution. Also, excessive pumping of ground water should be managed as an effective method for supply of safe drinking water.     

Assessment of Trace Metals Contamination in the Suspended Matter and Sediments of a Semi-enclosed Mediterranean Gulf

This study investigates the distribution of heavy metals in the suspended particulate matter and the sediments of Kavala Gulf, located in Northern Greece. Particulate trace metals were determined in accordance to water column physicochemical parameters. Metals in sediments were related to the textural characteristics, the organic matter, and carbonate contents of surficial sediments. Results illustrated that the diverse human coastal activities influence the distribution of particulate and sediment metal concentrations, since lower trace metal levels were detected along the western (tourism) and eastern (aquaculture) coast, while increased values were observed at the central (urban and industrial). Overall, particulate metals show moderately low levels compared to other similar sites, with the exception of Ni and Cd depicting local peaks along the industrial coastal zone. Significantly increased levels for particulate lead (123.1 μg/g) and chromium (113.9 μg/g) were detected at the sites near the industrial zone. Direct effluents from a fertilizer plant appeared responsible for the increased Pb, Cr, and Cd levels, while the increased values in Zn, Cu, and Hg appear related to phosphogypsum leaching. Sediment contamination assessment indicated that the Kavala Gulf is characterized by clean to marginally polluted sediments, with moderately severe pollution levels along the urban coastline.     

Photosynthetic CO<Subscript>2</Subscript> uptake in seedlings of two tropical tree species exposed to oscillating elevated concentrations of CO<Subscript>2</Subscript>

Do short-term fluctuations in CO₂ concentrations at elevated CO₂ levels affect net CO₂ uptake rates of plants? When exposed to 600 μl CO₂ l^?1, net CO₂ uptake rates in shoots or leaves of seedlings of two tropical C₃ tree species, teak (Tectona grandis L. f.) and barrigon [Pseudobombax septenatum (Jacq.) Dug.], increased by 28 and 52% respectively. In the presence of oscillations with half-cycles of 20 s, amplitude of ca. 170 μl CO₂ l^?1 and mean of 600 μl CO₂ l^?1, the stimulation in net CO₂ uptake by the two species was reduced to 19 and 36%, respectively, i.e. the CO₂ stimulation in photosynthesis associated with a change in exposure from 370 to 600 μl CO₂ l^?1 was reduced by a third in both species. Similar reductions in CO₂-stimulated net CO₂ uptake were observed in T. grandis exposed to 40-s oscillations. Rates of CO₂ efflux in the dark by whole shoots of T. grandis decreased by 4.8% upon exposure of plants grown at 370 μl CO₂ l^?1 to 600 μl CO₂ l^?1. The potential implications of the observations on CO₂ oscillations and dark respiration are discussed in the context of free-air CO₂ enrichment (FACE) systems in which short-term fluctuations of CO₂ concentration are a common feature.     

Evaluation of Calcium and Magnesium in Scalp Hair Samples of Population Consuming Different Drinking Water: Risk of Kidney Stone

The objective of this study was to examine the relationship between calcium (Ca) and magnesium (Mg) in underground water (UGW), bottled mineral water (BMW), and domestic treated water (DTW) with related to risk of kidney stones. The water samples were collected from different areas of Sindh, Pakistan. The scalp hair samples of both genders, age ranged 30–60 years, consuming different types of water, have or have not kidney disorders, were selected. The Ca and Mg concentrations were determined in scalp hair of study subjects and water by flame atomic absorption spectroscopy. The Ca and Mg contents in different types of drinking water, UGW, DTW, and BMW, were found in the range of 79.1–466, 23.7–140, and 45–270 mg/L and 4.43–125, 5.23–39.6, and 7.16–51.3 mg/L, respectively. It was observed that Ca concentration in the scalp hair samples of kidney stone patients consuming different types of drinking water was found to be higher (2,895–4721 μg/g) while Mg level (84.3–101 μg/g) was lower as compare to referents subjects (2,490–2,730 μg/g for Ca, 107–128 μg/g for Mg) in both genders. The positive correlation was found between Ca and Mg levels in water with related to kidney stone formations in population, especially who consumed underground water. A relative risk and odd ratio were calculated; the relative risk had a strong positive association with incidence of kidney stone which depends on types of drinking water.     

Occurrence and risk assessment of organophosphorus pesticide residues in Chinese tea

Tea is the second widely consumed beverage next to water. Tea drinking is one of the important pathways for human exposure of organonphosphorus pesticide. Consequently, incidence of organonphosphorus pesticide residues and risk assessment should be clear. In this study, the level of organonphosphorus pesticide residues in 810 Chinese teas manufactured between 2010–2013 was investigated using gas chromatography coupled with tandem mass spectrometry and a flame photometric detector. Incidence of organonphosphorus pesticide residues occurred with a frequency of 29% and the average concentration of 93 μg kg^?1. The residue levels varied from tea types, sale spots, and production area. Chlorpyrifos, isocarbophos, and triazophos were the only three organonphosphorus pesticides with detectable residues, and the detectable rates were 13.0%, 13.6%, and 17.4%, respectively. The corresponding average daily intake of chlorpyrifos, isocarbophos, and triazophos by tea drinking was 0.000083 μg kg^?1 bw day^?1, 0.0036 μg kg^?1 bw day^?1, and 0.0022 μg kg^?1 bw day^?1. These results showed that the total hazard quotient of organonphosphorus pesticide pesticides from tea drinking was less than 0.02 and that the tea-drinking originated organonphosphorus pesticide exposure had a little adverse health effect for human being.     

Deep-water rhodolith productivity and growth in the southwestern Atlantic

Rhodolith beds are an important source of marine calcium carbonate worldwide. Dense aggregations are found in deep water in the tropical southwestern Atlantic. In order to understand the distribution of coralline algae that build rhodoliths, algae responses were measured in light levels over their depth range. Qualitative samples were obtained by dredging at 90–100 m depth 80 km offshore of Cabo Frio Island, southeastern Brazil. Histological sections indicate that Mesophyllum engelhartii (Foslie) Adey was the most frequent coralline algae in 22 sampling stations. Its lumpy and thin thallus is characterized by raised multiporate sporangial conceptacles, with cells of similar size and shape around the pore canal. Accretion growth rates were below detectable levels for two rhodolith species. Photosynthetic peak was reached at 0.5–1.5 % of the maximum surface irradiance (10–30 μmol photons m^?2 s^?1) showing an extremely narrow P–I curve of net primary production. Readings of primary production at irradiance close to saturation and lower light levels (5 μmol photons m^?2 s^?1) showed no significant difference, suggesting that rhodoliths are acclimated to restricted light ranges in deep water.     

Lithium Treatment Aggregates the Adverse Effects on Erythrocytes Subjected to Arsenic Exposure

The present study was designed to investigate the effects of lithium treatment on red blood cells which were given arsenic exposure. Long-term lithium therapy is being extensively used for the treatment of bipolar disorders. Arsenic is a group I carcinogen and a major toxic pollutant in drinking water that affects millions of people worldwide. Male SD rats were segregated into four groups, viz. normal control, lithium treated, arsenic treated, and lithium + arsenic treated. Lithium was supplemented as lithium carbonate at a dose level of 1.1 g/kg diet for a period of 8 weeks. Arsenic was given in the form of sodium arsenite at a dose level of 100 ppm in drinking water, ad libitum, for the same period. Lysates of red blood cells were used to investigate the effects of lithium and arsenic treatments on anti-oxidant enzymes, reduced glutathione (GSH), and lipid peroxidation (LPO) levels. Various hematological parameters, activities of Na⁺ K⁺ ATPase and delta-aminolevulinic acid dehydratase (δ-ALAD) were also assessed. A significant reduction was observed in the activities of antioxidant enzymes, GSH levels, total erythrocyte counts, Na⁺ K⁺ ATPase, and ALAD enzyme activities in lysates of red blood cells when exposed either to lithium or arsenic. In addition, a significant increase in the levels of malondialdehyde (MDA), lymphocytes, neutrophils, and total leukocytes was also observed following lithium as well as arsenic treatments. However, when arsenic-treated rats were subjected to lithium treatment, a pronounced alteration was noticed in all the above parameters. Therefore, we conclude that lithium supplementation to the arsenic-treated rats enhances the adverse effects on red blood cells and therefore use of lithium may not be medicated to patients who are vulnerable to arsenic exposure through drinking water. It can also be inferred that adverse effects of lithium therapy may get aggravated in patients thriving in the arsenic-contaminated area.

     

Tailoring the Field Distribution of ZnO by Polyaniline for SPR-Based Fiber Optic Detection of Hardness of the Drinking Water

Due to the industrial development, drinking water is getting polluted by disposing several waste products of the industries. Hardness is one of the prominent impurities in drinking water which is mainly due to the presence of carbonate and bicarbonate ions (CO₃ ^2? and HCO₃ ^?) in it. Here, we present the synthesis of the zinc oxide (ZnO) and polyaniline (PANI) nanocomposite for the detection and estimation of hardness of the drinking water. The chemical formula of such a nanocomposite is defined in terms of the fraction of polyaniline nanoparticles reinforced in ZnO matrix and is derived as ZnO_(1???x)PANI _x (0?≤?x?≤?0.9); x is the composition ratio. Silver and ZnO_(1???x)PANI _x layers are coated over the unclad core of the optical fiber so as to create the four layer system as that of Kretschmann configuration SPR structure. The working principle involves the change in dielectric constant of (ZnO_(1???x)PANI _x ) by CO₃ ^2? or HCO₃ ^? ions in aqueous atmosphere. Due to the strong interaction of the sensing surface to the CO₃ ^2? and HCO₃ ^? ions, a red shift in the SPR spectrum is observed in the concentration range 0–200 μg/l. The sensitivity of the sensor depends on the composition ratio of the nanocomposite and has been found to be maximum for the composition ratio lying in the range 0.45–0.60. This has been further confirmed in terms of the enhancement of the electric field density and found to be in agreement with the experimental value. The sensitivity of the sensor with optimum value of the composition ratio is 0.094 and 0.065 nm/(μg/l) for CO₃ ^2? and HCO₃ ^?, respectively. The sensor is highly selective to CO₃ ^2? and HCO₃ ^?. The sensor has advantages of online monitoring and remote sensing of water quality because the probe is fabricated over an optical fiber.     

Porcine bone grafts defatted by lipase: efficacy of defatting and assessment of cytocompatibility

Defatting is an important procedure for the preparation of bone grafts because lipids in bone grafts strongly influence the osteointegration. Lipases have been widely used in different fields. However, study on the application to defatting process for bone grafts preparation has never been found so far. In this study, bone samples were treated respectively by lipase, NaHCO₃/Na₂CO₃, acetone and deionized water. The lipids content of processed bone grafts was calculated in Soxhlet extractor method. Surface morphology of the bone grafts was observed under scanning electron microscope (SEM). DNA content of processed bone grafts was measured. Cytocompatibility was evaluated by co-culturing mouse preosteoblasts (MC3T3-E1) on defatted bone cubes. Proliferation rates of MC3T3-E1 were examined by cell counting kit-8 (CCK-8) assay. No statistically significant difference was found between lipids amount of bone processed by lipase (0.46 ± 0.16 %) and acetone (1.11 ± 0.13 %) (P > 0.05). Both of them were significantly lower than that in groups processed by Na₂CO₃/NaHCO₃ (3.46 ± 0.69 %) and deionized water (8.88 ± 0.18 %) (P = 0.000). Only cell debris were discovered over the surface of bone processed by lipase or acetone, while lipid droplets were observed on bone processed by Na₂CO₃/NaHCO₃ or water by SEM. The difference of DNA concentration between the bone processed by lipase (3.16 ± 0.81 ng/μl) and acetone (4.14 ± 0.40 ng/μl) is not statistically significant (P > 0.05). Both of them are significantly lower than that groups processed by Na₂CO₃/NaHCO₃ (5.22 ± 0.38 ng/μl) and water (7.88 ± 0.55 ng/μl) (P < 0.05). MC3T3-E1 cells maintained their characteristic spreading on the trabecular surfaces of bone processed by lipase. There were no statistically significant differences among absorbance of lipase, acetone groups in CCK-8 assay. The application of lipase to bone tissue defatting appears to be a very promising technique for bone grafts preparation.     

Lithium: Effect on [3H]spiperone binding,ionic content,and amino acid levels in the brain of rats

After prolonged treatment of rats with lithium (pellets, 0.21% lithium carbonate, or 0.5 mg/ml lithium chloride in drinking water) for three months, the level of lithium in plasma was 0.87 meq/liter; in several brain regions, between 1.06–1.39 eq/g wet weight. The content of sodium and potassium in the plasma was normal. The level of potassium in the brain regions tested increased by 13–30% and that of sodium by about 10%. Glycine levels increased significantly in all the regions (cerebral cortex, midbrain, cerebellum, and spinal cord). In the cerebellum GABA was also increased, while glutamine was decreased. In midbrain, apart from increases in glycine levels, alamine, valine, GABA and lysine were also increased. In the spinal cord, glutamic acid was also increased. Changes were largely in the putative neurotransmitters. Long-term treatment with lithium also influenced the high-affinity binding of [³H]spiperone in the cerebral cortex and corpus striatum. Two specific binding sites were found in both brain regions; the main change was the reduction in the lower affinity binding site (B _max2).     

Sub-equilibrium oxygen-18 and carbon-13 levels in biological carbonates: carbonate and kinetic models

Many biological carbonates contain less oxygen-18 and carbon-13 than expected for isotopic equilibrium with ambient waters. "Carbonate" explanations for the oxygen-18 deficiencies draw inspiration from McCrea's (1950) observation that dissolved inorganic carbonates (DIC), in isotopic equilibrium with water, lose oxygen-18 in proportion to the abundance of the carbonate ion. Spero et al. (1997) therefore suggested that high carbonate levels might cause foraminifera to produce isotopically lighter shells at elevated pH. Adkins et al. (2003) extended this idea to the (presumably) alkaline internal calcification sites of deep-sea corals, and related skeletal carbon-13 content to the use of molecular carbon dioxide in calcification. This review compares these "carbonate" ideas with an updated "kinetic" model, which attributes isotopic enlightenment (for carbon-13 and oxygen-18) to carbon-dioxide-based calcification, and incomplete isotopic equilibration between DIC and water.     

Health-risk assessment related to the fluoride,nitrate, and nitrite in the drinking water in the Sanandaj,Kurdistan County,Iran

The concentration of fluoride and nitrate in groundwater is usually higher than that of surface water. The main objective of this study was to estimate the health-risk assessment associated with fluoride, nitrate, and nitrite in drinking water in Sanandaj and its villages. The number of samples in the Sanandaj and its rural was 106. The average concentration of fluoride in urban and rural drinking water was 0.22 mg/l and 0.27 mg/l, respectively. Fluoride concentration was also close to urban and rural drinking water. The concentration of nitrate in urban and rural drinking water was in the range between 0.28–27.77 mg/l and 1.28–80 mg/l, respectively. The concentration of nitrate reported in rural samples was higher than that of urban samples. The maximum concentration of nitrate reported in this study was 80 mg/l. The mean CDI for nitrate in the men, women, and children was 0.4258, 0.5110, and 1.1454, respectively. The findings of this study indicated that all three groups studied were exposed to nitrate contact hazards (HQ > 1). Therefore, the HQ in each of the three groups was higher than 1, which should be carefully monitored and necessary measures should be performed.     

Effect of GABA Receptor Agonists or Antagonists Injected Spinally on the Blood Glucose Level in Mice

The possible roles of gamma-amino butyric acid (GABA) receptors located in the spinal cord for the regulation of the blood glucose level were studied in ICR mice. We found in the present study that intrathecal (i.t.) injection with baclofen (a GABA_B receptor agonist; 1–10 μg/5 μl) or bicuculline (a GABA_A receptor antagonist; 1–10 μg/5 μl) caused an elevation of the blood glucose level in a dose-dependent manner. The hyperglycemic effect induced by baclofen was more pronounced than that induced by bicuculline. However, muscimol (a GABA_A receptor agonist; 1–5 μg/5 μl) or phaclofen (a GABA_B receptor antagonist; 5–10 μg/5 μl) administered i.t. did not affect the blood glucose level. Baclofen–induced elevation of the blood glucose was dose-dependently attenuated by phaclofen. Furthermore, i.t. pretreatment with pertussis toxin (PTX; 0.05 or 0.1 μg/5 μl) for 6 days dose-dependently reduced the hyperglycemic effect induced by baclofen. Our results suggest that GABA_B receptors located in the spinal cord play important roles for the elevation of the blood glucose level. Spinally located PTX-sensitive G-proteins appear to be involved in hyperglycemic effect induced by baclofen. Furthermore, inactivation of GABA_A receptors located in the spinal cord appears to be responsible for tonic up-regulation of the blood glucose level.     

Net sediment N2 fluxes in a southern New England estuary: variations in space and time

Over the past three decades, Narragansett Bay has undergone various ecological changes, including significant decreases in water column chlorophyll a concentrations, benthic oxygen uptake, and benthic nutrient regeneration rates. To add to this portrait of change, we measured the net flux of N₂ across the sediment–water interface over an annual cycle using the N₂/Ar technique at seven sites in the bay for comparison with measurements made decades ago. Net denitrification rates ranged from about 10–90 μmol N₂–N m^?2 h^?1 over the year. Denitrification rates were not significantly different among sites and had no clear correlation with temperature. Net nitrogen fixation (?5 to ?650 μmol N₂–N m^?2 h^?1) was measured at three sites and only observed in summer (June–August). Neither denitrification nor nitrogen fixation exhibited a consistent relationship with sediment oxygen demand or with fluxes of nitrite, nitrate, ammonium, total dissolved inorganic nitrogen, or dissolved inorganic phosphate across all stations. In contrast to the mid-bay historical site where denitrification rates have declined, denitrification rates in the Providence River Estuary have not changed significantly over the past 30 years.