Miranda S. Fram

Bio: Miranda S. Fram is an academic researcher from United States Geological Survey. The author has contributed to research in topics: Groundwater & Aquifer. The author has an hindex of 17, co-authored 64 publications receiving 4163 citations. Previous affiliations of Miranda S. Fram include California State University.

Evaluation of specific ultraviolet absorbance as an indicator of the chemical composition and reactivity of dissolved organic carbon.

Abstract: Specific UV absorbance (SUVA) is defined as the UV absorbance of a water sample at a given wavelength normalized for dissolved organic carbon (DOC) concentration. Our data indicate that SUVA, determined at 254 nm, is strongly correlated with percent aromaticity as determined by 13C NMR for 13 organic matter isolates obtained from a variety of aquatic environments. SUVA, therefore, is shown to be a useful parameter for estimating the dissolved aromatic carbon content in aquatic systems. Experiments involving the reactivity of DOC with chlorine and tetra- methylammonium hydroxide (TMAH), however, show a wide range of reactivity for samples with similar SUVA values. These results indicate that, while SUVA measurements are good predictors of general chemical characteristics of DOC, they do not provide information about reactivity of DOC derived from different types of source materials. Sample pH, nitrate, and iron were found to influence SUVA measurements.

Effects of Groundwater Development on Uranium: Central Valley, California, USA

Abstract: Uranium (U) concentrations in groundwater in several parts of the eastern San Joaquin Valley, California, have exceeded federal and state drinking water standards during the last 20 years. The San Joaquin Valley is located within the Central Valley of California and is one of the most productive agricultural areas in the world. Increased irrigation and pumping associated with agricultural and urban development during the last 100 years have changed the chemistry and magnitude of groundwater recharge, and increased the rate of downward groundwater movement. Strong correlations between U and bicarbonate suggest that U is leached from shallow sediments by high bicarbonate water, consistent with findings of previous work in Modesto, California. Summer irrigation of crops in agricultural areas and, to lesser extent, of landscape plants and grasses in urban areas, has increased Pco(2) concentrations in the soil zone and caused higher temperature and salinity of groundwater recharge. Coupled with groundwater pumping, this process, as evidenced by increasing bicarbonate concentrations in groundwater over the last 100 years, has caused shallow, young groundwater with high U concentrations to migrate to deeper parts of the groundwater system that are tapped by public-supply wells. Continued downward migration of U-affected groundwater and expansion of urban centers into agricultural areas will likely be associated with increased U concentrations in public-supply wells. The results from this study illustrate the potential long-term effects of groundwater development and irrigation-supported agriculture on water quality in arid and semiarid regions around the world.

Subsidence Reversal in a Re-established Wetland in the Sacramento-San Joaquin Delta, California, USA

Abstract: The stability of levees in the Sacramento-San Joaquin Delta is threatened by continued subsidence of Delta peat islands. Up to 6 meters of land-surface elevation has been lost in the 150 years since Delta marshes were leveed and drained, primarily from oxidation of peat soils. Flooding subsided peat islands halts peat oxidation by creating anoxic soils, but net accumulation of new material in restored wetlands is required to recover land-surface elevations. We investigated the subsidence reversal potential of two 3 hectare, permanently flooded, impounded wetlands re-established on a deeply subsided field on Twitchell Island. The shallower wetland (design water depth 25 cm) was almost completely colonized by dense emergent marsh vegetation within two years; whereas, the deeper wetland (design water depth 55 cm) which developed spatially variable depths as a result of heterogeneous colonization by emergent vegetation, still had some areas remaining as open water after nine years. Changes in land-surface elevation were quantified using repeated sedimentation-erosion table measurements. New material accumulating in the wetlands was sampled by coring. Land-surface elevations increased by an average of 4 cm/yr in both wetlands from 1997 to 2006; however, the rates at different sites in the wetlands ranged from -0.5 to +9.2 cm/yr. Open water areas of the deeper wetland without emergent vegetation had the lowest rates of land-surface elevation gain. The greatest rates occurred in areas of the deeper wetland most isolated from the river water inlets, with dense stands of emergent marsh vegetation (tules and cattails). Vegetated areas of the deeper wetland in the transition zones between open water and mature emergent stands had intermediate rates of land-surface gain, as did the entire shallower wetland. These results suggest that the dominant component contributing to land-surface elevation gain in these wetlands was accumulation of organic matter, rather than mineral sediment, and that accumulation of organic matter in emergent marshes is strongly affected by hydrologic factors. Re-established, non-tidal wetlands with managed hydrology can produce significant increases in land-surface elevations, which can help to improve levee stability and protect subsided islands from future flooding.

Absorption spectral slopes and slope ratios as indicators of molecular weight, source, and photobleaching of chromophoric dissolved organic matter

Abstract: A new approach for parameterizing dissolved organic matter (DOM) ultraviolet-visible absorption spectra is presented. Two distinct spectral slope regions (275–295 nm and 350–400 nm) within log-transformed absorption spectra were used to compare DOM from contrasting water types, ranging from wetlands (Great Dismal Swamp and Suwannee River) to photobleached oceanic water (Atlantic Ocean). On the basis of DOM size-fractionation studies (ultrafiltration and gel filtration chromatography), the slope of the 275–295-nm region and the ratio of these slopes (SR; 275–295-nm slope : 350–400-nm slope) were related to DOM molecular weight (MW) and to photochemically induced shifts in MW. Dark aerobic microbial alteration of chromophoric DOM (CDOM) resulted in spectral slope changes opposite of those caused by photochemistry. Along an axial transect in the Delaware Estuary, large variations in SR were measured, probably due to mixing, photodegradation, and microbial alteration of CDOM as terrestrially derived DOM transited through the estuary. Further, SR varied by over a factor of 13 between DOM-rich wetland waters and Sargasso Sea surface waters. Currently, there is no consensus on a wavelength range for log-transformed absorption spectra. We propose that the 275–295-nm slope be routinely reported in future DOM studies, as it can be measured with high precision, it facilitates comparison among dissimilar water types including CDOM-rich wetland and CDOM-poor marine waters, and it appears to be a good proxy for DOM MW.

Microbiological effects of sublethal levels of antibiotics

Abstract: The widespread use of antibiotics results in the generation of antibiotic concentration gradients in humans, livestock and the environment. Thus, bacteria are frequently exposed to non-lethal (that is, subinhibitory) concentrations of drugs, and recent evidence suggests that this is likely to have an important role in the evolution of antibiotic resistance. In this Review, we discuss the ecology of antibiotics and the ability of subinhibitory concentrations to select for bacterial resistance. We also consider the effects of low-level drug exposure on bacterial physiology, including the generation of genetic and phenotypic variability, as well as the ability of antibiotics to function as signalling molecules. Together, these effects accelerate the emergence and spread of antibiotic-resistant bacteria among humans and animals.

Biogeochemistry of marine dissolved organic matter

Abstract: Marine dissolved organic matter (DOM) is a complex mixture of molecules found throughout the world's oceans. It plays a key role in the export, distribution, and sequestration of carbon in the oceanic water column, posited to be a source of atmospheric climate regulation. Biogeochemistry of Marine Dissolved Organic Matter, Second Edition, focuses on the chemical constituents of DOM and its biogeochemical, biological, and ecological significance in the global ocean, and provides a single, unique source for the references, information, and informed judgments of the community of marine biogeochemists. Presented by some of the world's leading scientists, this revised edition reports on the major advances in this area and includes new chapters covering the role of DOM in ancient ocean carbon cycles, the long term stability of marine DOM, the biophysical dynamics of DOM, fluvial DOM qualities and fate, and the Mediterranean Sea. Biogeochemistry of Marine Dissolved Organic Matter, Second Edition, is an extremely useful resource that helps people interested in the largest pool of active carbon on the planet (DOC) get a firm grounding on the general paradigms and many of the relevant references on this topic. * Features up-to-date knowledge of DOM, including five new chapters* The only published work to synthesize recent research on dissolved organic carbon in the Mediterranean Sea* Includes chapters that address inputs from freshwater terrestrial DOM