Elevated levels of mercury in aquatic environments remote from industrial sources have been broadly attributed to long-range atmospheric transport and deposition anthropogenic Hg. Evidence support this prevailing scientific viewglobal biogeochemical Hg models, sedimentary archives historic fluxes, geographic trends soil Hghave challenged as being insuf ficiently rigorous rule out the alternative explanation that natural geologic are principal contributors locations. In review, we examine...

Mercury contamination of remote lakes has been attributed to increasing deposition atmospheric mercury, yet historic rates and inputs from terrestrial sources are essentially unknown. Sediments seven headwater in Minnesota Wisconsin were used reconstruct regional modern preindustrial mercury. Whole-basin mercury fluxes, determined lake-wide arrays dated cores, indicate that the annual increased 3.7 12.5 micrograms per square meter since 1850 25 percent catchment is exported lake. The...

We determined the densities of diapausing eggs copepod Diaptomus Sanguieneus in sediments from two small freshwater lakes Rhode Island. Sediment cores, sliced at 1—cm intervals, showed that egg ranged between 4 x 10 and 8 eggs/m 2 near sediment surface declined to very low values depths 10—15 cm both lakes, although were found as deep 30 one lake. Between 50% these hatched short—term laboratory experiments, actual viability is probably higher. 210 Pb—dating revealed relatively constant...

Lakes have a disproportionate effect on the global carbon (C) cycle relative to their area, mediating C transfer from land atmosphere, and burying organic-C in sediments. The magnitude temporal variability of burial is, however, poorly constrained, degree which humans influenced lake cycling through landscape alteration has not been systematically assessed. Here, we report biome specific trajectories sequestration based 516 lakes show that some rates (i.e., those tropical forest grassland...

The distribution among Labrador (Canada) lakes of remains from 21 chironomid taxa was analysed by means canonical correspondence analysis (CCA). Tests with partial CCA three hypotheses revealed that the distributions were significantly correlated summer surface-water temperature and maximum lake depth, but not sediment organic content. In addition, an exploratory possible relationships fauna residual longitude Fe concentration. A weighted-averaging-regression/calibration model...

Historic increases in atmospheric mercury deposition caused by anthropogenic emissions have been well documented from sediment cores lakes and peatlands North America Europe. Few previous studies addressed the question of whether has increased continuously to present or it declined recent decades. We stratigraphic data a suite Minnesota that indicate peaked 1960s 1970s, at least for upper Midwest. Recent declines, which appear both rural urban lakes, are not evident remote coastal...

Using two different natural archiving media from remote locations, we have reconstructed the atmospheric deposition of mercury (Hg) over last 800–1000 years in both hemispheres. This effort was designed (1) to quantify historical variation and distributional patterns Hg fluxes midlatitudes North America at Nova Scotia (N.S.) a comparable midlatitude region Southern Hemisphere New Zealand (N.S.), (2) identify influence anthropogenic contributions fluxes, (3) further investigate suitability...

Atmospheric mercury is the dominant Hg source to fish in northern Minnesota and elsewhere. However, atmospherically derived must be methylated prior accumulating fish. Sulfate-reducing bacteria are thought primary methylators of environment. Previous laboratory field mesocosm studies have demonstrated an increase methylmercury (MeHg) levels sediment peatland porewaters following additions sulfate. In current ecosystem-scale study, sulfate was added half experimental wetland at Marcell...

We reconstruct from lake-sediment archives atmospheric Hg deposition to Arctic Alaska over the last several centuries and constrain a contemporary lake/watershed mass-balance with real-time measurement of fluxes in rainfall, runoff, evasion. Results indicate that (a) anthropogenic impact is similar magnitude at temperate latitudes; (b) whole-lake sedimentation determined 55 210Pb-dated cores five small lakes demonstrates 3-fold increase since advent Industrial Revolution; (c) because high...

Concentrations of methylmercury in game fish from many interior lakes Voyageurs National Park (MN, U.S.A.) substantially exceed criteria for the protection human health. We assessed importance atmospheric and geologic sources mercury to watersheds within identified ecosystem factors associated with variation contamination lacustrine food webs. Geologic were small, based on analyses underlying bedrock C-horizon soils, nearly all O- A-horizon soils was derived deposition. Analyses dated...

SUMMARY Stratigraphic analyses of inorganic geochemistry, pigments and fossil diatoms in a 0.7 m core profundal sediments are used to reconstruct the limnological history Harvey's Lake, Vermont, over last 1000 years. The lake is moderately productive, deep (44 m) clear, phytoplankton today dominated by blue‐green alga, Oscillatoria rubescens. Sedimentary unique algae, oscillaxanthin myxoxanthophyll, provide detailed changes O. rubescens population. Accurate sediment chronology derived from...

Although sediment is a natural constituent of rivers, excess loading to rivers and streams leading cause impairment biodiversity loss. Remedial actions require identification the sources mechanisms supply. This task complicated by scale complexity large watersheds as well changes in climate land use that alter drivers Previous studies Lake Pepin, lake on Mississippi River, indicate supply has increased 10-fold over past 150 years. Herein we combine geochemical fingerprinting suite geomorphic...

Abstract Northern forests are important ecosystems for carbon (C) cycling and lakes within them process bury large amounts of organic-C. Current burial estimates poorly constrained may discount other shifts in organic-C driven by global change. Here we analyse a suite northern to determine trends throughout the Anthropocene. We found rates increased significantly over last century up five times greater than previous estimates. Despite correlation with temperature, warming alone did not...

Abstract Rivers in watersheds dominated by agriculture throughout the US are impaired excess sediment, a significant portion of which comes from non‐field, near‐channel sources. Both land‐use and climate have been implicated altering river flows thereby increasing stream‐channel erosion sediment loading. In wetland‐rich landscapes upper Mississippi basin, 20th century crop conversions led to an intensification artificial drainage, is now critical component modern agriculture. At same time,...

Over the 20th century, surface water temperatures have increased in many lake ecosystems around world, but long-term trends vertical thermal structure of lakes remain unclear, despite strong control that stratification exerts on biological response to climate change. Here we used both neo- and paleoecological approaches develop a fossil-based inference model for mixing depths thereby refine understanding We focused three common planktonic diatom taxa, distributions which previous research...

Lakes are a central component of the carbon cycle, both mineralizing terrestrially derived organic matter and storing substantial amounts (OC) in their sediments. However, rates controls on OC burial by lakes remain uncertain, as do possible effects future global change processes. To address these issues, we 210 Pb-dated sediment cores from 116 small Minnesota that cover major climate land-use gradients. Rates for individual presently range 7 to 127 g C m –2 yr –1 have increased up factor 8...

Human activities over the last several centuries have transferred vast quantities of mercury (Hg) from deep geologic stores to actively cycling earth-surface reservoirs, increasing atmospheric Hg deposition worldwide. Understanding magnitude and fate these releases is critical predicting how rates will respond future emission reductions. The most recently compiled global inventories integrated (all-time) anthropogenic are dominated by emissions preindustrial gold/silver mining in Americas....

Both cinnabar (HgS) and metallic mercury (Hg0) were important resources throughout Andean prehistory. Cinnabar was used for millennia to make vermillion, a red pigment that highly valued in pre-Hispanic Peru; Hg0 has been since the mid-16th century conduct amalgamation, an efficient process of extracting precious metals from ores. However, little is known about which deposits exploited by cultures, environmental consequences Hg mining amalgamation remain enigmatic. Here we use isotopes...

Eutrophication can initiate sudden ecosystem state change either by slowly pushing lakes toward a catastrophic tipping point beyond which self-reinforcing mechanisms establish an alternate stable state, or through rapid but persistent changes in external forcing mechanisms. In principle, these processes be distinguished determining whether historical focal parameters (phytoplankton) exhibit transient (rising then declining) continuously-elevated variability characteristic of states "paradox...