Multi-scale trend analysis of water quality using error propagation of generalized additive models.

Effective stewardship of ecosystems to sustain current ecological status or mitigate impacts requires nuanced understanding of how conditions have changed over time in response to anthropogenic pressures and natural variability. Detecting and appropriately characterizing changes requires accurate and flexible trend assessment methods that can be readily applied to environmental monitoring datasets. A key requirement is complete propagation of uncertainty through the analysis.

Four decades of water quality change in the upper San Francisco Estuary.

Quantitative descriptions of chemical, physical, and biological characteristics of estuaries are critical for developing an ecological understanding of drivers of change. Historical trends and relationships between key species of dissolved inorganic nitrogen (ammonium, nitrate/nitrite, total) from the Delta region of the San Francisco Estuary were modeled with an estuarine adaptation of the Weighted Regressions on Time, Discharge, and Season (WRTDS). Analysis of flow-normalized data revealed trends that were different from those in the observed time-series.

Blurred lines: Multiple freshwater and marine algal toxins at the land-sea interface of San Francisco Bay, California.

San Francisco Bay (SFB) is a eutrophic estuary that harbors both freshwater and marine toxigenic organisms that are responsible for harmful algal blooms. While there are few commercial fishery harvests within SFB, recreational and subsistence harvesting for shellfish is common. Coastal shellfish are monitored for domoic acid and paralytic shellfish toxins (PSTs), but within SFB there is no routine monitoring for either toxin.

Sources and fates of heavy metals in a mining-impacted stream: temporal variability and the role of iron oxides.

Heavy metal contamination of surface waters at mining sites often involves complex interactions of multiple sources and varying biogeochemical conditions. We compared surface and subsurface metal loading from mine waste pile runoff and mine drainage discharge and characterized the influence of iron oxides on metal fate along a 0.9-km stretch of Tar Creek (Oklahoma, USA), which drains an abandoned Zn/Pb mining area.

Prioritizing environmental risk of prescription pharmaceuticals.

Low levels of pharmaceutical compounds have been detected in aquatic environments worldwide, but their human and ecological health risks associated with low dose environmental exposure is largely unknown due to the large number of these compounds and a lack of information. Therefore prioritization and ranking methods are needed for screening target compounds for research and risk assessment. Previous efforts to rank pharmaceutical compounds have often focused on occurrence data and have paid less attention to removal mechanisms such as human metabolism.

Spatial heterogeneity of methane ebullition in a large tropical reservoir.

Tropical reservoirs have been identified as important methane (CH(4)) sources to the atmosphere, primarily through turbine and downstream degassing. However, the importance of ebullition (gas bubbling) remains unclear. We hypothesized that ebullition is a disproportionately large CH(4) source from reservoirs with dendritic littoral zones because of ebullition hot spots occurring where rivers supply allochthonous organic material.

Fish consumption and mercury exposure among Louisiana recreational anglers.

Background: Methylmercury (MeHg) exposure assessments among average fish consumers in the United States may underestimate exposures among U.S. subpopulations with high intakes of regionally specific fish.

Stable isotope (N, C, Hg) study of methylmercury sources and trophic transfer in the northern gulf of Mexico.

We combined N, C, and Hg stable isotope measurements to identify the most important factors that influence MeHg accumulation in fish from the northern Gulf of Mexico (nGOM), and to determine if coastal species residing in the Mississippi River (MR) plume and migratory oceanic species derive their MeHg from the same, or different, sources. In six coastal species and two oceanic species (blackfin and yellowfin tuna), trophic position as measured by delta(15)N explained most of the variance in log[MeHg] (r(2) approximately 0.8), but coastal species and tuna fell along distinct, nearly parallel lines with significantly different intercepts.

Relative importance of atmospheric and riverine mercury sources to the northern Gulf of Mexico.

A box model was developed to quantify the major sources and dominant fates of inorganic mercury (Hg) in the Mississippi River-influenced area of the northern Gulf of Mexico (nGOM). Riverine (75%) and direct atmospheric deposition (25%) deliver 9.7 t Hg y(-1) to this productive fishery; most (80%) accumulates in bottom sediments where it can be methylated and enter foodwebs.

Mercury bioaccumulation and trophic transfer in sympatric snapper species from the Gulf of Mexico.

Consumption of marine fish is a major route of toxic methyl mercury (MeHg) exposure to ocean apex predators and human populations. Here we explore the influence of trophic structure on total mercury (Hg) accumulation in red snapper (RS, Lutjanus campechanus) and gray snapper (GS, Lutjanus griseus) from the coastal Louisiana region of the Gulf of Mexico, west of the Mississippi River. The objectives of this investigation were to: (1) determine the effectiveness of the use of offshore recreational fishing charter boats and marinas as sources of fish samples and (2) compare species differences in Hg bioaccumulation, trophic position, and carbon sources.

Characterization of zinc, lead, and cadmium in mine waste: implications for transport, exposure, and bioavailability.

We characterized the lability and bioaccessibility of Zn, Pb, and Cd in size-fractionated mine waste at the Tar Creek Superfund Site (Oklahoma) to assess the potential for metal transport, exposure, and subsequent bioavailability. Bulk mine waste samples contained elevated Zn (9100 +/- 2500 ppm), Pb (650 +/- 360 ppm), and Cd (42 +/- 10 ppm), while particles with the greatest potential for windborne transport and inhalation (< 10 microm) contained substantially higher concentrations, up to 220 000 ppm Zn, 16 000 ppm Pb, and 530 ppm Cd in particles < 1 microm. Although the mined ore at Tar Creek primarily consisted of refractory metal sulfides with low bioavailability, sequential extractions and physiologically based extractions indicate that physical and chemical weathering have shifted metals into relatively labile and bioaccessible mineral phases.

Long-term fate of a pulse arsenic input to a eutrophic lake.

The long-term fate of a 30-year-old pulse arsenic input to a eutrophic lake was studied to determine if As has become effectively trapped in sediments or remains in active exchange with the water column. Legacy As was readily mobilized from sediments of Spy Pond (Arlington, MA), a eutrophic kettle-hole lake that was treated with 1000s kg As in the 1960s to manage excessive aquatic macrophyte growth. Arsenic was mobilized from hypolimnetic sediments during bottom-water anoxia in spring, summer, and fall, and As accumulated to maximum concentrations of 2100 nM.

Acceleration of amyloid beta-peptide aggregation by physiological concentrations of calcium.

Alzheimer disease is characterized by the accumulation of aggregated amyloid beta-peptide (Abeta) in the brain. The physiological mechanisms and factors that predispose to Abeta aggregation and deposition are not well understood. In this report, we show that calcium can predispose to Abeta aggregation and fibril formation.

Equilibrium-based sampler for determining Cu2+ concentrations in aquatic ecosystems.

The bioavailability of potentially toxic metals in aquatic systems is frequently related to the dissolved free metal ion (M2+) concentration. However, typical methods used to determine M2+ are labor intensive or require sophisticated equipment. We developed an inexpensive, in situ sampling device--the "gellyfish"--that simplifies Cu2+ determinations in seawater.

Particulate arsenic and iron during anoxia in a eutrophic, urban lake.

The bioavailability and transport of particle-reactive pollutants are influenced by their partitioning between dissolved and particulate phases. We explored the importance of particle complexation to the arsenic cycle in an urban lake (Upper Mystic Lake, eastern MA, USA) that experiences arsenic remobilization from contaminated sediments during seasonal hypolimnetic anoxia. Particle size distributions were measured using a new in situ serial filtration system that excludes oxygen and filters at low flow rates to minimize filtration artifacts.

Antimony: an unlikely confounder in the relationship between well water arsenic and health outcomes in Bangladesh.

Recent in vitro studies have suggested a potential role for antimony as a confounder in human health studies related to arsenic in drinking water. We measured tube-well water concentrations of antimony and arsenic in the Pabna region of Bangladesh, where arsenic concentrations are known to be elevated and the concentrations of antimony have not yet been thoroughly documented. Two hundred forty-five tube-well water samples were collected from various regions in Pabna, Bangladesh, as part of an ongoing case-control study.

Nitrate controls on iron and arsenic in an urban lake.

Aquatic ecosystems are often contaminated by multiple substances. Nitrate, a common aquatic pollutant, strongly influenced the cycling of arsenic (As) under anoxic conditions in urban Upper Mystic Lake (Massachusetts, USA) by oxidizing ferrous iron [Fe(II)] to produce As-sorbing particulate hydrous ferric oxides and causing the more oxidized As(V), which is more particle-reactive than As(III) under these conditions, to dominate. This process is likely to be important in many natural waters.