Historical failure to recognise the connection between surface water and groundwater and to manage river and groundwater systems conjunctively has led to over allocation of water resources. Examples of river systems that have been depleted by groundwater pumping, for example, are well documented.
Although conjunctive management of surface water and groundwater is preferred, it requires information on the magnitude of the interaction between the two reservoirs. While numerous different methods have been used to measure the exchange flux, the usefulness of many of these methods is limited by the very high spatial and temporal variability of the fluxes involved.
Methods that have been used successfully to estimate spatial variations in groundwater discharge to streams, over scales of interest to water managers, include water and solute mass balances. Groundwater discharge to streams can be determined from differences between river flow gaugings made at different points along the river, and from measurements of conservative ion concentrations. Sensitivity is greatest, however, when tracers are used whose concentration in the groundwater greatly exceeds that in surface water. This condition is often best met for the naturally occurring radioactive element radon (222Rn). Since radon in surface water is lost by exchange with the atmosphere (which is low in radon), a large contrast in concentration with the groundwater is maintained.
Measuring changes in groundwater discharge with time is more difficult, because the required frequency of measurements means that only parameters that can be measured remotely are suitable.
In this presentation, the earliest stages in the formation of a crystal will be discussed. For the example of stable prenucleation CaCO3 clusters, which can already be found prior to nucleation and even in undersaturated solution, it will be shown that an alternative crystallization pathway exists. Basic characterization of the clusters will be presented, and the driving forces for their formation will be discussed.
In arid and semiarid ecosystems, water availability is a primary driver of ecosystem processes. Water impacts on belowground processes result in large part from the interactions of indigenous microorganisms with soil water. Understanding and predicting how changing patterns of precipitation in California can be expected to impact carbon and nitrogen cycling processes requires integrating the understanding of the biophysics of water in soil, the physiological response mechanisms of soil microbes, and the dynamics of soil water, including the roles of plant evapotranspiration in soil-water dynamics. As soil dries, water film thickness begins to limit the diffusional supply of substrates, and microbes utilize a range of mechanisms to respond to and survive desiccation. Very dry soils experiencing rainfall events produce trace-gas pulses, and the response patterns of indigenous microbes delineate the trace gas dynamics as well as the nutrient cycling responses to wet up.
Author info: Professor Jerry Schnoor is the Allen S. Henry Chair in Engineering and the Co-Director of the Center for Global and Regional Environmental Research at the University of Iowa. Jerry is a member of the National Academy of Engineering (elected in 1999) for his research using mathematical models in science policy decisions. He chaired the U.S. Environmental Protection Agency’s ORD Board of Scientific Counselors, 2000-2004, and is a member of EPA’s Science Advisory Board and the National Institutes of Health (NIH) National Advisory Environmental Health Sciences (NAEHS) Council. Schnoor is considered one of the founding fathers of phytoremediation, using plants to help clean the environment. He serves as Editor-in-Chief of the leading international environmental journal, Environmental Science and Technology, and his other research interests include water quality modeling, environmental observatories, sustainability, and global change.
Abstract: The world is a dry place. Much of it is already arid or semi-arid, and drought is expected to become more frequent and intense. The effects of drought on biogeochemical processes are profound, but at times counter-intuitive. Current models assume that as soils dry, biogeochemical processes merely slow down and microbial populations decline; when soils rewet, processes just pick up again. All these assumptions are wrong. Rewetting a dry soil typically causes a huge burst of respiration, although it remains unclear where the carbon comes from—microbial C vs. C released from mineral surfaces or aggregrates. But surprisingly, when soils become extremely dry, the biomass of microorganisms in soil increases. Pools of extractable C and N increase. But, even very slight increases in moisture can switch biogeochemical patterns back to the “moist” conditions: biomass and pools of available resources decline. The causes of some of these dynamics remain obscure, but appear to result from the interactions of microbial stress physiology and the extent of hydraulic connectivity at the microscale in the soil.
About the Author: Josh Schimel did his Ph.D. in Soil Microbiology at UC Berkeley in 1987. After postdocs in Aberdeen, Scotland, and East Lansing, Michigan, he became an assistant professor at the University of Alaska, Fairbanks. He moved to UC Santa Barbara in 1995, where he is now a professor and Chair of the Environmental Studies Program. His research focuses on soil C and N cycles in Arctic and Mediterranean ecosystems: areas dominated by a stressful environment.
Distinguished Scientist Seminar Series
The ESD Distinguished Scientist Series is a monthly seminar featuring eminent individuals from various disciplines in the scientific community whose research is outstanding, interdisciplinary, and of broad interest to strategic interest initiatives in the earth sciences. Speakers normally spend a full day with researchers at Earth Sciences Division, LBNL, and the University of California, Berkeley.