Five groundwater samples taken from different hydrogeologic settings in Connecticut were analyzed for major cation chemistry and the concentration of U and Th decay series nuclides 238U, 234Th, 226Ra, 222Rn, 2•øpb, 2•øpo, 232Th, 228Ra, 228Th, and 224Ra. The concentration of 222Rn in the waters ranged between 103 and 104 dpm 1-• and was three to four orders of magnitude greater than that of the shortlived alpha daughters 224Ra, 228Ra, and 234Th, even though the rates of supply of these four nuclides to solution are expected to be similar. We infer that sorption removes radium and thorium from these groundwaters on a time scale of 3 minutes or less. The (224Ra/228Ra)•.and (234Th/228Th) activity ratios in these waters indicate that desorption of these nuclides occurs on a time scale of a week or less and that equilibrium between solution and surface phases is established. In situ retardation factors for radium, thorium, and lead may therefore be calculated directly from the isotopic data; values range from 4,500 to 200,000. Neither sorption time scales nor retardation factors are, strongly dependent on the nuclide or on hydrogeology of the aquifer. Since our study includes nuclides with diverse chemical properties, we suggest that other uncomplexed heavy metals and transuranic elements will also behave in a manner similar to those measured here. The approach presented here should therefore find application in developing site-specific models of the transport of radioactive or stable elemental waste through water-saturated media. 1. geochemical properties, their behaviors may serve as indica-1On leave from the Physical Research Laboratory, Ahmadabad, India. tors of the in situ chemical behavior of other nuclides injected into the system. With this aim we have analyzed several groundwaters from Connecticut for virtually every long-lived (half-life > 1 day) member of the 238U and 232Thseries in order to understand the processes controlling their concentration in solution and thereby to estimate the rates of those processes. The U and Th series nuclides are uniquely suited to this study because several isotopes of the same element are continuously introduced into groundwaters and because the supply rates of many of these nuclides can be estimated with adequate accuracy. Measurements of the distribution of these natural decay series nuclides yield site-specific empirical data on the in situ sorption processes. Parameters such as distribution coefficients or retardation factors derived from these measurements may be used in models of transport of both radioactive and stable nuclides that show analogous chemical behaviors. METHODSFive groundwater samples from the major aquifer types of Connecticut were collected for this study. The sampling locations, aquifer descriptions, and water chemistries are given in Table 1. Samples GW-3 and GW-7 were both taken from municipal water supply production wells in glacial drift aquifers. The large volumes of water pumped from these wells (Table 1) suggests that recharge is induced from n...

ABSTRACT/We quantified the stability of nine stream fish assemblages by calculating coefficients of variation of population size for assemblage members. Coefficients of variation were high and averaged over 96%; indicating that most assemblages were quite variable. Coefficient of variation (CV) estimates were not significantly affected by: (1) years of study, (2) mean abundance, (3) familial classification, or (4) mean interval between collections. We also detected minor regional differences in CVs. The high variability exhibited by many stream fish assemblages suggests that it may be difficult to detect the effects of anthropogenic disturbances using population data alone. Consequently, we urge managers to exercise caution in the evaluation of the effects of these disturbances. More long-term studies of the ecological characteristics of undisturbed stream fish assemblages are needed to provide a benchmark against which disturbed systems can be compared.We suggest that CVs are a better estimator of population/assemblage stability, than either Kendall's W or the standard deviation of the logarithms of numerical censuses. This conclusion is based on the following reasons. First, CVs scale population variation by the mean and, hence, more accurately measure population variability. Second, this scaling permits the comparison of populations with different mean abundances. Finally, the interpretation of CV values is less ambiguous than either of the aforementioned metrics.Annual and season variations in flow regimes (i.e., droughts and floods) can produce substantial fluctuations in the physical environment of many lotic ecosystems. Because droughts and floods occur with a relatively high frequency, especially when compared to many other natural disturbances (e.g., E1 Nifio, hurricanes), iotic environments are excellent systems for tests of equilibrium and nonequilibrium ecological theories. Implicit tests of such theories occurred as early as 1951, when William Starrett (1951) observed large variations in species abundances in an Iowa riverine fish assemblage and attributed these variations to unpredictable hydrologic events. Similar results were obtained by later researchers (Larimore 1954, Metcalf 1959, Paloumupis 1958, Larimore and others 1959, John 1964, Lowe and others 1967, Rinne 1975, Harrell and others 1967, Harrell 1978, Mills and Mann 1985, Moyle and Li 1979.Prompted by the general ecological debate regarding the importance of equilibrium and nonequilibrium processes to assemblage dynamics, Grossman and others (1982) reviewed the literature on stream systems. This review, coupled with a reanalysis of assemblage structure data from an Indiana stream, led them to reiterate Starrett's hypothesis and suggest that hydrologic variability may facilitate coexistence in assemblages of many stream organisms. The proposed

Abstract:A hydrological experiment was conducted in a small headwater catchment in southeast Dartmoor, UK, to monitor the temporal and spatial variations in soil moisture content at the hillslope scale in order to determine how the spatial organization affected runoff generation. Two distinctly different types of rainfall response were found. During the dry state the soil moisture pattern was very patchy and the increase in stream discharge was relatively small for most rainstorms. The catchment response was limited to about 10% of the area, a figure that is similar in extent to the saturated area identified in the valley bottom. During the wet state, however, modest to large storms resulted in significantly higher discharge rates. The area generating the runoff increased up to 65% of the area. The division between the two 'preferred' states occurred at a catchment wetness of about 0Ð60 cm 3 cm 3 . This figure was based firstly on the exceptional increase in range, as determined by geostatistical analyses, for the soil moisture content measured associated with very high stream discharges. Secondly, it was consistent with a steep rise in gradient noted for the soil moisture characteristic curves at about 0Ð60 cm 3 cm 3 . The greater catchment responses were therefore dependent on the pore size distribution plus other soil characteristics and the connectivity between the wet areas.

Land use and physiographic variability influence stream low flows, yet their interactions and relative influence remain unresolved. Our objective was to assess the influence of land use and watershed geomorphic characteristics on low‐flow variability in the southern Blue Ridge Mountains of North Carolina and Georgia. Ten minute interval discharge data for 35 streams (in watersheds from 3 to 146 km2) were measured for two late summer low‐flow seasons, coinciding with a severe drought period in the southeastern United States. Three low‐flow metrics were calculated (1 and 7 day minimum flows and 1st percentile flow) for each low‐flow season (5 August to 12 November 2007 and 1 August to 12 November 2008). A comprehensive suite of watershed characteristics, including factors of topography, channel network morphometry, soils, land use, and precipitation were used in multiple regression analysis of low‐flow variability among the 35 watersheds. Additionally, low flows in groups of lower‐ and higher‐forest cover watersheds were compared. Drainage density, areal coverage of colluvium, topographic variability (as slope standard deviation), and percent of the channel network as first order stream emerged as the most important variables for explaining low‐flow variability. Watershed forest cover demonstrated a consistent, significant positive relationship with low flows, despite the higher evapotranspiration rates associated with forest compared with other land covers and despite the relatively small range of disturbance in this study area. This highlights the importance of infiltration and recharge under undisturbed land cover in sustaining low flows, and it bears noteworthy implications for environmental flows and water resource sustainability.

breakthrough curves are often used to estimate model parameters, including effective porosity, finger width, Saprolite is a form of weathered bedrock that is commonly used as mobile zone porosity, and the retardation factor. Each the host material at waste disposal sites in the Southeastern Piedmont. However, estimating the unsaturated hydraulic and transport proper-approach provides valuable information about the beties of saprolite is difficult due to saprolite's low permeability. We havior of solute transport through unsaturated media. demonstrate the use of short-duration fluid irrigation pulses for main-Water potential responses are also used to estimate taining unsaturated conditions in intact saprolite columns. Concomihydraulic parameters (Inoue et al., 1998). In these cases, tant Cl Ϫ tracer experiments demonstrate that irrigated waters moved perturbations at the surface, from precipitation and irrithrough an effective volumetric porosity (0.038-0.108 cm 3 cm Ϫ3) subgation, and within the subsurface, from fluid injections stantially less than the ambient water-filled porosity (0.44 cm 3 cm Ϫ3). or removals, are monitored and used for parameter esti-We observed the unexpected result that irrigation-induced pressure mation. The unsaturated hydraulic conductivity, hywave velocities (1983-3670 cm d Ϫ1) were ≈ 1000 times faster than draulic diffusivity, or sorptivity are determined in these tracer velocities (2.04-6.00 cm d Ϫ1). The relationship between pressure wave velocities and fluid velocities is described using kinematic wave cases. Perturbations due to fluid injection or extraction, theory, presented for four parametric representations (Brooks-Corey, or the modification of the pressure head at a surface or van Genuchten-Mualem, Broadbridge-White, and the Galileo Numpoint, induce a step or spike change in fluid pressure ber), that predicts fluid pressure velocities to be from approximately that is transmitted through the unsaturated zone. The two to fifteen times faster than saprolite tracer velocities. None of pressure wave response, also called the kinematic the kinematic models was able to reproduce observed rapid pressure model, has been used to model subsurface stormflow wave velocities. A hydraulic form of the advection-diffusion equation (Beven, 1982), vertical flow through unsaturated soils based on Richards' equation is presented that favorably predicts the