History and Development of the NRCS Lag Time Equation1

Abstract: Many of the hydrologic methods that are used in engineering practice today resulted from the Spring Flood of 1936, which blanketed the Northeastern portion of the United States. Because of the flood damage that was caused by this rainfall‐snowmelt event, many federal agencies including the U.S. Army Corp of Engineers and the Soil Conservation Service (SCS) implemented the hydrologic theories that were available in the literature at this time and developed hydrologic procedures for design flow estimation. Sherman had recently published his unit hydrograph theory in 1932, and later in 1938 Snyder, who had been charged by the Water Resource Council to develop a synthetic unit hydrograph, published his famous paper. The SCS unit hydrograph theory was developed by Victor Mockus in the late 1950s. Most if not all of the theories at that time reported the rainfall‐runoff process for floods as a surface phenomenon, and as such those theories all required some type of a timing parameter to estimate watershed response time. This article documents the development of the SCS lag equation.     

Growth history and inshore migration of the tropical eel, Anguilla marmorata, in the Pacific

A comparative study of the otolith microstructure and microchemistry of Anguilla marmorata glass eels in the western North Pacific (Japan, Taiwan, the Philippines, Indonesia) determined the timing of metamorphosis and age at recruitment to freshwater habitats with a view to learning about the early life history and recruitment of this species of tropical anguillid eel, which has a wide range throughout much of the western Pacific and parts of the Indian Ocean. Three new samples (from Japan, Taiwan, Indonesia) were analyzed and statistically compared along with two other previously published samples that were analyzed using the same techniques. Ages at metamorphosis and recruitment, respectively, were 123ᆡ.4 days (mean-SD) and 154ᆥ.0 days in specimens from Japan, 116ᆢ.6 days and 145ᆣ.6 days in those from Taiwan, 120ᆡ.0 days and 154ᆡ.5 days in the Philippines stock and 132Nj.7 days and 159ᆟ.7 days, and 120ᆣ.6 days and 152ᆣ.2 days in the Indonesian stock. The average duration of the period of metamorphosis estimated from otolith microstructure was very similar (15-17 days) in the specimens from all locations. A close linear relationship was found between the ages at metamorphosis and recruitment at all locations, suggesting that individuals that metamorphosed earlier were recruited to freshwater habitats at a younger age. Back-calculated hatching dates ranged over about 6 months of the year, suggesting that this species may spawn throughout much of the year. It is hypothesized that specimens from all four sites are from the same spawning population originating in a spawning area in the North Equatorial Current of the western North Pacific.     

Acute toxicity and sublethal behavioral effects of copper on barnacle nauplii (Balanus improvisus)

This study documents the effects of short-term (24h) sublethal copper exposures on undirected swimming activity and photobehavior of Balanus improvisus stage II nauplii. All Cu treatments were static, with temperature and salinity conditions at 20°C and 15 or 30. The 24h LC 50 estimate for Cu is 88 ppb at 15 and >200 ppb at 30. Sub-lethal Cu concentrations cause reductions in swimming speed, which decrease progressively with increasing Cu dose. At 50 ppb Cu, this was significant primarily at light intensities below the phototactic threshold. At higher Cu concentrations, significant reductions in mean linear velocity occurred at most light intensities tested. At 30, 50 and 100 ppb Cu also reduce the positive phototactic response and 150 ppb Cu causes reversal of phototaxis at optimal intensities. Photokinesis is reduced at 100 ppb Cu and disappears at 150 ppb Cu. At 15, the behavioral effects of 50 ppb Cu resemble those occurring with 150 ppb Cu at 30. Swimming speed and photobehavior show promise as sensitive behavioral indicators of copper toxicity. Additional research is required to determine if these responses apply to a broad range of pollutants and to other planktonic organisms. There is also a need to further evaluate the significance of these behavioral effects ecologically.Contribution No. 181 from the EPA Environmental Research Laboratory, Narragansett, RI 02882, USA     

Reproduction of meso- and bathypelagic chaetognaths in the genus Eukrohnia

Reproduction of meso- and bathypelagic chaetognaths, a major group of zooplankton and hermaphroditic animals, became clear after the microscopic examination of samples collected from the Pacific Subarctic Water. Species of the genus Eukrohnia carry their developing eggs in two marsupial sacs, one on each side, and the young are retained in these marsupia for at least some period after hatching. This is in line with a general trend for low fecundity, as care of the young increases. Almost all individuals are protandric, the testes maturing sooner than ovaries. These facts suggest that the reproduction of these species depends upon cross-fertilization.     

Estimating bulk density in vertically exposed stoney alluvium using a modified excavation method

Despite many decades of education and refining land-use practices, accelerated stream bank erosion is still prevalent in the United States. Eroding stream banks produce a sediment load to the riverine system and can cause reduced water quality as a result of increased suspended sediment. As total maximum daily loads (TMDLs) for water bodies impaired by turbidity or suspended sediments become more numerous, a simple, in situ field technique will be needed to estimate the bulk density of readily erodible stream bank material so that reasonably accurate sediment loading rates can be estimated. In this study, the excavation/polyurethane-foam technique for estimating total bulk density was applied to vertically exposed alluvium with high coarse-fragment content. Though not previously attempted in vertically exposed alluvium with high coarse-fragment content, the excavation/polyurethane-foam technique appears to provide a reasonably accurate estimate of the total and soil (<2-mm size fraction) bulk density from vertically exposed, alluvial deposits with high coarse-fragment content (i.e., >70%) along eroding stream banks. Obtaining bulk density estimates using this method would facilitate calculation of sediment loading rates to riverine systems with actual field data.     

Plant and soil responses to biosolids application following forest fire

Soil stability and revegetation is a great concern following forest wildfires. Biosolids application might enhance revegetation efforts and enhance soil stability. In May 1997, we applied Metro Wastewater Reclamation District (Denver, CO, USA) composted biosolids at rates of 0, 5, 10, 20, 40, and 80 Mg ha(-1) to a severely burned, previously forested site near Buffalo Creek, CO to improve soil C and N levels and help establish eight native, seeded grasses. The soils on the site belong to the Sphinx series (sandy-skeletal, mixed, frigid, shallow Typic Ustorthents). Vegetation and soils data were collected for four years following treatment. During the four years following treatment, total plant biomass ranged from approximately 50 to 230 g m(-2) and generally increased with increasing biosolids application. The percentage of bare ground ranged from 4 to 58% and generally decreased with increasing biosolids rate. Higher rates of biosolids application were associated with increased concentrations of N, P, and Zn in tissue of the dominant plant species, streambank wheatgrass [Elymus lanceolatus (Scribn. & J.G. Sm) Gould subsp. lanceolatus], relative to the unamended, unfertilized control. At two months following biosolids application (1997), total soil C and N at soil depths of 0 to 7.5, 7.5 to 15, and 15 to 30 cm showed significant (P < 0.05) linear increases (r2 > 0.88) as biosolids rate increased. The surface soil layer also showed this effect one year after application (1998). For Years 2 through 4 (1999-2001) following treatment, soil C and N levels declined but did not show consistent trends. The increase in productivity and cover resulting from the use of biosolids can aid in the rehabilitation of wildfire sites and reduce soil erosion in ecosystems similar to the Buffalo Creek area.     

Using radiotracer techniques for coastal hydrodynamic model evaluation

A three-dimensional (3D) water circulation and contaminant transport model of Manila Bay has been developed with the aim of better understanding the formation and movement of harmful algal blooms. Radiotracer techniques were used to evaluate the model by recording the dispersion of a tracer at depths of 2 and 15 m near the injection point. The selected tracer was 99mTc eluted from a molybdenum/technetium medical generator. The rationale for the choice of the tracer and the location of the injection is discussed. At 2 m the transport was dominated by the prevailing winds, and at 15 m by tidally induced currents. The development of the hydrodynamic model and its experimental evaluation were iterative processes. The experimental study confirmed the need for full 3D modelling of Manila Bay; quantified the impact of the prevailing wind field on contaminant dispersion near the injection point; and allowed the calculation of transverse dispersivity to guide the selection of parameter values used in the overall model.     

Growth and yield responses of snap bean to mixtures of carbon dioxide and ozone

Elevated CO2 concentrations expected in the 21st century can stimulate plant growth and yield, whereas tropospheric O3 suppresses plant growth and yield in many areas of the world. Recent experiments showed that elevated CO2 often protects plants from O3 stress, but this has not been tested for many important crop species including snap bean (Phaseolus vulgaris L.). The objective of this study was to determine if elevated CO2 protects snap bean from O3 stress. An O3-tolerant cultivar (Tenderette) and an O3-sensitive selection (S156) were exposed from shortly after emergence to maturity to mixtures of CO2 and O3 in open-top field chambers. The two CO2 treatments were ambient and ambient with CO2 added for 24 h d(-1) resulting in seasonal 12 h d(-1) (0800-2000 h EST) mean concentrations of 366 and 697 microL L(-1), respectively. The two O3 treatments were charcoal-filtered air and nonfiltered air with O3 added for 12 h d(-1) to achieve seasonal 12 h d(-1) (0800-2000 h EST) mean concentrations of 23 and 72 nL L(-1), respectively. Elevated CO2 significantly stimulated growth and pod weight of Tenderette and S156, whereas elevated O3 significantly suppressed growth and pod weight of S156 but not of Tenderette. The suppressive effect of elevated O3 on pod dry weight of S156 was approximately 75% at ambient CO2 and approximately 60% at elevated CO2 (harvests combined). This amount of protection from O3 stress afforded by elevated CO2 was much less than reported for other crop species. Extreme sensitivity to O3 may be the reason elevated CO2 failed to significantly protect S156 from O3 stress.     

Brownfield redevelopment as a smart growth option in the United States

An evaluation is made of brownfields redevelopment as a smart growth policy compared to purchase of land, restrictive growth policies, changing transportation patterns, promoting compact development designs on the metropolitan fringe, and regional government. In the US brownfields redevelopment has clear advantages with regard to environmental protection, moral imperative, and government and special interest reactions. Its rank with regard to economic feasibility, ability to respond to changes in technology, and public reaction are not clear. A great deal more research is needed, especially about the costs of brownfield redevelopment and public preferences for housing type and location to be certain about brownfields redevelopment as a viable smart growth option.