Tom Brikowski

Climate-related increase in the prevalence of urolithiasis in the United States

An unanticipated result of global warming is the likely northward expansion of the present-day southeastern U.S. kidney stone “belt.” The fraction of the U.S. population living in high-risk zones for nephrolithiasis will grow from 40% in 2000 to 56% by 2050, and to 70% by 2095. Predictions based on a climate model of intermediate severity warming (SRESa1b) indicate a climate-related increase of 1.6–2.2 million lifetime cases of nephrolithiasis by 2050, representing up to a 30% increase in some climate divisions. Nationwide, the cost increase associated with this rise in nephrolithiasis would be

Deep fluid circulation and isotopic alteration in The Geysers geothermal system: profile models

0.9–1.3 billion annually (year-2000 dollars), representing a 25% increase over current expenditures. The impact of these changes will be geographically concentrated, depending on the precise relationship between temperature and stone risk. Stone risk may abruptly increase at a threshold temperature (nonlinear model) or increase steadily with temperature change (linear model) or some combination thereof. The linear model predicts increases by 2050 that are concentrated in California, Texas, Florida, and the Eastern Seaboard; the nonlinear model predicts concentration in a geographic band stretching from Kansas to Kentucky and Northern California, immediately south of the threshold isotherm.

Geochemistry of a large impoundment – Part II: Fe and Mn cycling and metal transport

Abstract Rock alteration patterns related to the large felsic intrusive complex (felsite) beneath The Geysers steam field (California, USA) are important indicators of the origins of the modern geothermal system. Metagreywacke host rocks for the system show widespread moderate oxygen isotope alteration in the permeable steam reservoir above the felsite, with concentrated alteration low on the flanks of the intrusion. Numerical models of fluid, heat and oxygen isotope transport in the pre-development (natural state) Geysers system demonstrate that an unbroken caprock is required throughout the liquid-dominated lifetime of the system to produce this pattern. The widespread moderate alteration throughout the steam reservoir suggests a long-lived liquid system, and probably required upwardly increasing permeability in the steam reservoir. The models indicate that the maximum hydrothermal lifetime for the system is 0.5 million years (Myr), whereas the youngest dated large intrusive is 1.2 Myr. Combined, these factors indicate repeated igneous intrusions at The Geysers, up to at least 0.5–0.6 Myr ago, and development of a stable liquid-dominated system after that, the evolution of which was truncated by a relatively recent transition to vapor-dominated conditions. Observed chemical compartmentalization of fluids in The Geysers steam reservoir is inconsistent with the lateral extensiveness of alteration at depth, since the latter requires good horizontal connectivity of deep permeable zones to allow penetration of 18O-depleted fluids. This compartmentalization is probably recent, developing as a consequence of vapor-dominated conditions introducing relative permeability effects. Petrologic evidence for high paleo-fluid temperatures (300°C) within 1 km of the surface is difficult to reconcile with subdued 18O alteration beneath these locations. These peak paleotemperatures are likely to indicate small, short-lived penetrations of the caprock. Natural-state models allow the combined influence of these factors on the evolution of The Geysers to be analyzed quantitatively. Internet-accessible graphical animations of these results are available at http://www.utdallas.edu/∼brikowi/Research/Geysers .

Groundwater Arsenic in Nepal: Occurrence and Temporal Variation

Depletion of oxygen in lakes and reservoirs due to summer stratification has significant effects on many aspects of water chemistry, including lake productivity, elemental cycling and water quality. We have studied the redox conditions of Lake Texoma, a large impoundment lake on the border of Texas and Oklahoma, USA, formed from the confluence of the Red and Washita rivers, in order to understand the impact of summer anoxia on metal distribution. In summer, dissolved oxygen decreases with depth (from c. 7.0 to 0.1 mg/L), whereas dissolved (<0.45 µm) Fe (and Fe2+), Mn and HS− concentrations show complementary increases in the hypolimnion. Summer anoxia is, to a large degree, responsible for vertical variations in Fe and Mn concentrations, and Fe speciation is controlled by Fe-oxyhydroxide reduction and subsequent pyrite precipitation in sulphide-rich bottom waters. Summer anoxia is also responsible for vertical variations in the concentration of other metals including Ba, Pb and Ni in the deepest portion (main lake) of the lake. Lake Texoma and its two river arms show relatively minor variation in δ34SCDT (from +11.5 to +13.4‰), mirroring variation in Permian/Cretaceous marine gypsum and anhydrite deposits (δ34SCDT +10 to +15‰) in the headwater regions of the catchment. Increasing δ34SCDT with depth (>16 m) in the main lake is consistent with fractionation associated with sulphate reduction in anoxic bottom waters. δ13CPDB values of dissolved inorganic carbon (DIC) become more negative (from –2.5 to –8.2 ‰) with depth in summer, due to bacterial oxidation of organic matter linked to sulphate reduction. Summer anoxia may induce temporal degradation of water quality in the central three zones of the lake with elevated Fe and Mn concentrations owing to breakdown of oxyhydroxides and release of adsorbed heavy metals, such as Pb and Ni. However, complete turnover of the water column in the autumn lowers dissolved Fe, Mn and heavy metal concentrations by oxidation and formation of oxyhydroxides. The characterization of anoxia in Lake Texoma provides the background for further water quality research and management for the rapidly increasing population of North Texas and improves our understanding of redox cycling and metal mobility in reservoirs.

Doomed reservoirs in Kansas, USA? Climate change and groundwater mining on the Great Plains lead to unsustainable surface water storage

In Nepal, over two million people are exposed to excessive natural arsenic (10–1500 ppb) in groundwater. The majority of these people live in the agricultural Terai region, on the edge of Ganges floodplain at the base of the Himalayan foothills. The remainder are exposed via deep wells in the Kathmandu Valley in a primarily urban setting. Tube wells down to 50 m in the Terai commonly exhibit cyclical, temporally correlated variation in dissolved arsenic, iron, and other species. In Nawalparasi, the most arsenic-affected district, these wells tap thin (2 m) gray sand aquifers embedded in a thick (>50 m) sequence of organic clays. Monsoon recharge refreshes these aquifers, temporarily minimizing dissolved arsenic concentrations. Post-monsoon, average groundwater compositions exhibit increasing water–rock interaction with time (increasing TDS and cation exchange, forming increasingly Na-HCO– waters) and increasing dissolved arsenic and iron. Collectively these observations strongly support a model of reductive mobilization of arsenic from adjacent clays into aquifers in the Terai, tempered by repeated flushing during periods of heavy precipitation. In Kathmandu Valley, moderately elevated arsenic (up to 150 ppb) may be leached from overlying silts and clays, but concentrations remain constant throughout the year. In the Terai, effective mitigation is challenging, depending primarily on well-switching (marking contaminated wells) and installation of household point-of-use filters. Mitigation in the urban setting will emphasize blending with clean surface water from mountain reservoirs.