Publications

This paper presents repeat field measurements of 222Rn and 223,224,226,228Ra, electromagnetic seepage meter-derived advective fluxes, and multi-electrode, stationary and continuous marine resistivity surveys collected between November 2005 and April 2007 to study coastal groundwater dynamics within a marine beach in Santa Barbara, California. The study provides insight into magnitude and...

We present details of a newly designed syringe pump apparatus for the retrieval and temporal analysis of helium (SPARTAH). The device is composed of a commercially available syringe pump connected to coils of Cu tubing, which interface the syringe and the groundwater or geothermal wellhead. Through test deployments at geothermal wells in Iceland and California, we show that well fluids...

In this paper, we show that the complex geological evolution of Valles Marineris, Mars, has been highly influenced by the manifestation of magmatism (e.g., possible plume activity). This is based on a diversity of evidence, reported here, for the central part, Melas Chasma, and nearby regions, including uplift, loss of huge volumes of material, flexure, volcanism, and possible...

Hindcasting decadal-timescale bathymetric change in estuaries is prone to error due to limited data for initial conditions, boundary forcing, and calibration; computational limitations further hinder efforts. We developed and calibrated a tidal-timescale model to bathymetric change in Suisun Bay, California, over the 1867–1887 period. A general, multiple-timescale calibration ensured...

Glen Canyon Dam, located on the Colorado River in northern Arizona, has affected the physical, biological and cultural resources of the river downstream in Grand Canyon. One of the impacts to the downstream physical environment that has important implications for the aquatic ecosystem is the transformation of the thermal regime from highly variable seasonally to relatively constant year...

The giant garter snake (GGS; Thamnophis gigas) is a federally listed threatened species endemic to wetlands of the Central Valley of California. Habitat destruction has been the main factor in the decline of GGS populations, but the effects of contaminants on this species are unknown. To contribute to the recovery of these snakes, the U.S. Geological Survey (USGS) began studies of the...

Distribution and characteristics of heavy metals enrichment in sediment were surveyed including the bio-available form analyzed for assessment of the Luan River source water quality. The approaches of sediment quality guidelines (SQG), risk assessment code and Hakanson potential ecological risk index were used for the ecological risk assessment. According to SQG, The results show that in...

1. We investigated diurnal nitrate (NO3−) concentration variability in the San Joaquin River using an in situ optical NO3− sensor and discrete sampling during a 5‐day summer period characterized by high algal productivity. Dual NO3− isotopes (δ15NNO3 and δ18ONO3) and dissolved oxygen isotopes (δ18ODO) were measured over 2 days to assess NO3− sources and biogeochemical controls over...

In order to estimate total mercury (HgT) loads entering San Francisco Bay, USA, via the Sacramento-San Joaquin River system, unfiltered water samples were collected between January 2002 and January 2006 during high flow events and analyzed for HgT. Unfiltered HgT concentrations ranged from 3.2 to 75 ng/L and showed a strong correlation (r2 = 0.8, p < 0.001, n = 78) to suspended sediment

Many national and regional groundwater studies have correlated land use "near" a well, often using a 500 m radius circle, with water quality. However, the use of a 500 m circle may seem counterintuitive given that contributing areas are expected to extend up-gradient from wells, and not be circular in shape. The objective of this study was to evaluate if a 500 m circle is adequate for...

Ground-water withdrawals in the San Joaquin Valley totaled 64 million m3 /day (19 million ac-ft) in 2000, supplying about 45% of agricultural irrigation demand and about 80% of municipal supply (Hutson et al., 2004). Most of the population and ground-water use are in the eastern San Joaquin Valley, where reliance on ground water is expected to increase as a result of rapid population...

A one-dimensional numerical model that simulates the effects of whitecapping waves was used to investigate the importance of whitecapping waves to vertical mixing at a 3-meter-deep site in Franks Tract in the Sacramento-San Joaquin Delta over an 11-day period. Locally-generated waves of mean period approximately 2 s were generated under strong wind conditions; significant wave heights...