In the western United States vast acreages of land are exposed to low levels atmospheric nitrogen (N) deposition, with interspersed hotspots elevated N deposition downwind large, expanding metropolitan centers or large agricultural operations. Biological response studies in North America demonstrate that some aquatic and terrestrial plant microbial communities significantly altered by deposition. Greater productivity is counterbalanced biotic community changes deleterious effects on...

Abstract Nitrogen (N) deposition in the western United States ranges from 1 to 4 kilograms (kg) per hectare (ha) year over much of region as high 30 90 kg ha downwind major urban and agricultural areas. Primary N emissions sources are transportation, agriculture, industry. Emissions ammonia about 50% great nitrogen oxides. An unknown amount West Coast originates Asia. has increased because rapid increases urbanization, population, distance driven, large concentrated animal feeding...

To gain better understanding of the effects urbanization on organic matter transport in rivers, we quantified total carbon loading from point and non‐point urban sources within metropolitan area Sacramento compared these loads to amount carried downstream River. Median (TOC) concentrations River, runoff wastewater treatment plant effluent were 2.1, 8.9, 23 mg L −1 , respectively. Dissolved (DOC) river had similar specific UVA absorbance disinfection by‐product formation potential, but based...

Nitric oxide (NO) is an important trace gas and regulator of atmospheric photochemistry. Theory suggests moist soils optimize NO emissions, whereas wet or dry constrain them. In drylands, however, emissions can be greatest in when are rewet. To understand how aridity vegetation interact to generate this pattern, we measured fluxes a California grassland, where manipulated cover the length season [δ(15)-N]NO [δ(18)-O]NO following rewetting with (15)N-labeled substrates. Plant N uptake reduced...

In this study we quantified the sensitivity of snow to climate warming in selected mountain sites having a Mediterranean climate, including Pyrenees Spain and Andorra, Sierra Nevada California (USA), Atlas Morocco, Andes Chile. Meteorological observations from high elevations were used simulate energy mass balance (SEMB) calculate its climate. Very different sensitivities evident amongst various sites. For example, reductions 9%–19% 6–28 days mean water equivalent (SWE) duration,...

Long‐term measurements (1983–2001) of nutrients and seston in Emerald Lake (Sierra Nevada, California) have revealed ecologically significant patterns. Nitrate, both during spring runoff growing seasons, declined from 1983 through 1995. Declining snowmelt nitrate was caused primarily by changes snow regime induced the 1987–1992 drought: years with shallow, early melting snowpacks had lower concentrations owing to less labile N production catchment soils longer plant seasons. However,...

There is a pressing need for rapid and cost‐effective tools to estimate soil C across larger landscapes. Visible–near‐infrared diffuse reflectance spectroscopy (VNIRS) offers comparable levels of accuracy conventional laboratory methods estimating various properties. We used VNIRS total organic (TC) four fractions in 141 samples collected the Santa Fe River watershed Florida. The measured were (in order decreasing potential residence time soils): recalcitrant (RC), hydrolyzable (HC),...

Question: Although mangrove forests are generally regarded as highly threatened, some studies have shown that canopies in the Pacific coast of Mexico been increasing recent decades. We investigated possible causes driving this reported expansion. Location: The lagoons Magdalena Bay Baja California, Mexico. Methods: used 50-year-old aerial photographs and 24-year-old satellite images to compare long-term vegetation change, surveyed a coastal transect analyse flooding levels, compiled six...

The distribution of snow and the energy flux components snowmelt are intrinsic characteristics alpine water cycle controlling location source waters effect climate on streamflow. Interannual variability these is relevant to change hydrology. Our objective characterize interannual in spatial fluxes watersheds a maritime setting, Tokopah Basin (TOK) California's southern Sierra Nevada, continental Green Lake 4 Valley (GLV4) Colorado's Front Range, using 12 year database (1996–2007)...

During the ice-free period in Arctic, thermal structure and mixing dynamics of small lakes change with passing air masses. In Toolik Lake, Alaska, stable warm masses during season were associated lake warming, daily winds maximally 4–7 m s−1 for less than 12 h duration, numbers (LN) varied between 2 80, values coefficient vertical eddy diffusivity ranged from molecular to 10−6 m2 s−1. For 3-week warming following ice-off, mixing, which occurred primarily near lake's sloping boundaries,...

We used radiocarbon measurements of dissolved organic carbon (DOC) to resolve sources riverine within agriculturally dominated landscapes in California. During 2003 and 2004, average Δ14C for DOC was −254‰ agricultural drains the Sacramento–San Joaquin Delta, −218‰ San River, −175‰ California State Water Project −152‰ Sacramento River. The age bulk transiting rivers California's Central Valley is oldest reported large suggests wide-spread loss soil matter caused by agriculture urbanization....

Abstract Our objectives were to determine how temperatures in mountain lakes respond changes climate and characterize their responses are mediated by landscape or lake morphometric factors. analysis combines the use of high‐frequency temperature data from 1983 2016 a high‐elevation catchment Sierra Nevada California with summer water set 18 additional scattered throughout range. Average annual air warmed at 0.63°C decade −1 , but variation was driven primarily amount precipitation as snow....

Abstract Few coupled lake‐watershed studies examine long‐term effects of climate on the ecosystem function lakes in a hydrological context. We use 32 years and biogeochemical data from high‐elevation site Sierra Nevada California to characterize variation snowmelt relation variability explore impact factors affecting phytoplankton biomass. The magnitude accumulated winter snow, quantified through basinwide estimates snow water equivalent (SWE), was most important factor controlling timing...

Abstract Soil drying and wetting cycles can produce pulses of nitric oxide (NO) nitrous (N 2 O) emissions with substantial effects on both regional air quality Earth’s climate. While pulsed production N is ubiquitous across ecosystems, the processes governing pulse magnitude timing remain unclear. We studied producing NO O at two contrasting drylands, desert chaparral, where despite hot dry conditions known to limit biological processes, some highest flux rates have been measured. measured...

Abstract Two‐component hydrograph separations were performed for three, nested, snowmelt‐dominated catchments in Sequoia National Park. The purpose of the was to: (i) differentiate between old and new water contributions to discharge during snowmelt using δ 18 O signatures; (ii) identify fraction that travelled through subsurface (reactive) compartment period silica or sodium; (iii) investigate impact changing end‐member signatures on separations. ‘Old’ refers stored watershed previous year,...

Abstract Soils are an important source of NO , particularly in dry lands because trade‐offs that develop between biotic and abiotic ‐producing processes when soils out. Understanding how drier climates may offset the balance these as transition toward more arid states is, therefore, critical to estimating global budgets, especially drylands expected increase size. We measured emission pulses after wetting from similar lithologies along altitudinal gradient Sierra Nevada, CA where mean annual...

Abstract Transit times are hypothesized to influence catchment sensitivity atmospheric deposition of acidity and nitrogen (N) because they help determine the amount time available for infiltrating precipitation interact with soil biota. metrics, including fraction young water ( F yw ) mean transit (MTT), were calculated 11 headwater catchments in mountains western United States based on differences amplitude seasonal signal δ 18 O streamflow precipitation. Results statistically compared...

High surface water-groundwater connectivity characterizes watersheds underlain by karsts, increasing contaminant transport risks. However, karsts are highly complex, making research necessary to understand the of contaminants from surface, through aquifer, discharge areas. In Yucatan, lack waste water treatment raises risk groundwater contamination. We monitored stable isotopes (δ18 O-NO3 and δ15 N-NO3 ), cadmium, lead document contamination during rainy dry seasons, using samples collected...

Soils are the largest source of atmospheric nitrous oxide (N2O), a powerful greenhouse gas. Dry soils rarely harbor anoxic conditions to favor denitrification, predominant N2O-producing process, yet, among N2O emissions have been measured after wetting summer-dry desert soils, raising question: Can denitrifiers endure extreme drought and produce immediately rainfall? Using isotopic molecular approaches in California desert, we found that produced within 15 minutes dry (site preference = 12.8...