Sea level history in Beringia during the past 250,000 years

This paper attempts to relate current knowledge of sea-level history in Beringia to the Broecker-van Donk “Termination” concept of climatic and sea-level history. The Einahnuhtan transgression is thought to represent Termination III, which according to Broecker and van Donk, took place about 225,000 y.a. The Kotzebuan transgression is thought to represent a positive fluctuation that modulated the generally falling sea level during the ensuing 100,000 yr. Sea level probably fell to about ?135 m in the Bering Sea area during the maximum phase of the penultimate glaciation. The two Pelukian shorelines probably represent Termination II (about 125,000 yr BP in the Broecker-van Donk chronology) and one of the two positive fluctuations that modulated the generally falling sea level of early Wisconsinan time, about 105,000 and 80,000 y.a. according to Broecker and van Donk. Another positive modulation brought sea level to at least ?20 m, about 30,000 y.a. Sea level evidently fell to between ?90 and ?100 m during the late Wisconsinan regression, but a substantial part of the outer Bering shelf remained submerged. Submerged shoreline features at ?38m, ?30 m, ?24 to ?20 m, and ?12 to ?10 m represent stillstands or slight regressions that modulated Termination I, the late Wisconsinan, and early Holocene recovery of sea level.     

The effect of low-rate sand filtration and modified feed management on effluent quality,pond water quality and production of intensive shrimp ponds

Pond water in intensive shrimp ponds is typically high in nutrients, solids, and BOD and may have an adverse environmental impact when discharged to natural waters. As part of ongoing research to develop intensive production technologies that minimize the potential for environmental impact, a study investigated the effect of lowrate, coarse-grain sand filtration on the quality of effluent being discharged from an intensive shrimp pond receiving 5% d^?1 water exchange. The effect of sand filtration on a recirculating no-exchange pond was also examined. For comparison, a third pond received no water exchange and no filtration. Sand filtration removed some particulate matter, but levels of dissolved and particulate organic and inorganic nutrients were changed little and were sometimes higher as the result of in situ decomposition. Low-rate sand filtration is not seen as a cost-effective method of increasing the carrying capacity of no-exchange shrimp ponds or drastically improving the effluent quality of ponds with water exchange. Compared to previous studies with decreased or no water exchange, the application of feed in these ponds was more stable with small portions fed at frequent intervals with a constant rate of 80 kg ha^?1 d^?1. These ponds, stocked with 40 m^?2 juvenilePenaeus vannamei, had excellent survival and normal growth, resulting in productions levels approaching 7,000 kg ha^?1 crop^?1 without water exchange. This indicates that intensive shrimp farming may be possible in static no-exchange systems, thereby minimizing the potential impact of effluent as long as feed inputs do not overwhelm the assimilative capacity of the pond ecosystem. *** DIRECT SUPPORT *** A01BY069 00011     

Comparative evaluation of GIS-based best–worst method (BWM) for emergency facility planning: perspectives from two decision-maker groups

Natural Hazards - Nowadays, organizational decisions are made collectively in decision groups to achieve more meaningful and impactful outcomes, ranging from product design, policy and strategy...     

Changes in event-based streamflow magnitude and timing after suburban development with infiltration-based stormwater management

Green stormwater infrastructure implementation in urban watersheds has outpaced our understanding of practice effectiveness on streamflow response to precipitation events. Long-term monitoring of experimental suburban watersheds in Clarksburg, Maryland, USA, provided an opportunity to examine changes in event-based streamflow metrics in two treatment watersheds that transitioned from agriculture to suburban development with a high density of infiltration-focused stormwater control measures (SCMs). Urban Treatment 1 has predominantly single family detached housing with 33% impervious cover and 126 SCMs. Urban Treatment 2 has a mix of single family detached and attached housing with 44% impervious cover and 219 SCMs. Differences in streamflow-event magnitude and timing were assessed using a before-after-control-reference-impact design to compare urban treatment watersheds with a forested control and an urban control with detention-focused SCMs. Streamflow and precipitation events were identified from 14 years of sub-daily monitoring data with an automated approach to characterize peak streamflow, runoff yield, runoff ratio, streamflow duration, time to peak, rise rate, and precipitation depth for each event. Results indicated that streamflow magnitude and timing were altered by urbanization in the urban treatment watersheds, even with SCMs treating 100% of the impervious area. The largest hydrologic changes were observed in streamflow magnitude metrics, with greater hydrologic change in Urban Treatment 2 compared with Urban Treatment 1. Although streamflow changes were observed in both urban treatment watersheds, SCMs were able to mitigate peak flows and runoff volumes compared with the urban control. The urban control had similar impervious cover to Urban Treatment 2, but Urban Treatment 2 had more than twice the precipitation depth needed to initiate a flow response and lower median peak flow and runoff yield for events less than 20 mm. Differences in impervious cover between the Urban Treatment watersheds appeared to be a large driver of differences in streamflow response, rather than SCM density. Overall, use of infiltration-focused SCMs implemented at a watershed-scale did provide enhanced attenuation of peak flow and runoff volumes compared to centralized-detention SCMs.     

Detecting a salinity plume in an unconfined sandy aquifer and assessing secondary soil salinization using electromagnetic induction techniques, North Dakota, USA

 Land-use changes on the Sheyenne Delta in southeastern North Dakota, USA, have prompted research on impacts to the unconfined Sheyenne Delta aquifer (SDA). This study examines effects of the saline discharge of a flowing artesian well that taps the Dakota aquifer (DAK) on SDA groundwater chemistry and soil salinity. Objectives were to map the saline plume in the SDA using induction techniques, to assess chloride migration in the SDA, and to evaluate induction sensitivity to moderately saline sands. Induction data, collected in a 2.9-ha grid, were compared to 31 soil profiles analyzed for gravimetric moisture, electrical conductivity, and chloride. Soil salinization is widespread, but only 7% of the area meets the 4-dS/m threshold for saline soils. SDA chloride distribution was determined on transects oriented with and perpendicular to the flow path determined from induction readings. Chloride was detected in the aquifer 550 m from the source, indicating a transport rate of 21 m/yr. Complex recharge and discharge patterns and hummocky relief contribute to a wide chloride plume at this site. A mass balance based on soil-water content and chloride concentration shows that only 4% of the chloride from the DAK well remains in the grid volume. Received, January 1998 · Revised, January 1999 · Accepted, March 1999     

An anisotropy of magnetic susceptibility (AMS) fabric record of till kinematics within a Late Weichselian low Baltic till,southern Sweden

Herein we report on the results of an anisotropy of magnetic susceptibility (AMS) fabric case‐study of two Late Weichselian tills exposed in a bedrock quarry in Dalby, Skåne, southern Sweden. The region possesses a complex glacial history, reflecting alternating and interacting advances of the main body of the Scandinavian Ice Sheet (SIS) and its ice lobes from the Baltic basin, perhaps driven by streaming ice. AMS till fabrics are robust indicators of ice‐flow history and till kinematics, and provide a unique tool to investigate till kinematics within and amongst till units. The till section investigated here contains ~8 m of the Dalby Till – a dark grey silt‐clay rich till deposited during one or more Baltic advance – overlain by ~1.5 m of the regional surface diamicton. AMS fabrics within the lower part of the Dalby Till conform to the regional surface fluting, and reflect sustained flow from the ENE with progressive increases in basal strain. A boulder‐rich horizon approximately 3 m from the base of the till marks a restricted excursion in till fabric direction, fabric strength and style of strain. Ice flow is from the SW and W in the upper section. We interpret these fabrics to record shifting ice flow and bed conditions at the margins of the Young Baltic Advance ice lobe in southern Sweden, prior to a short‐lived re‐advance of the main body of the SIS over mainland Sweden recorded by the surface diamicton.     

Itrax μ-XRF core scanning for rapid tephrostratigraphic analysis: a case study from the Auckland Volcanic Field maar lakes

Itrax micro X-ray fluorescence (μ-XRF) core scanning is a non-destructive, rapid approach to measuring elemental concentrations and their variability in sediment cores. As such, it records elemental signatures of tephra layers, which serve as correlation tie points and chronological markers for these sedimentary archives of past climatic changes. The traditional tephra identification approach using electron microprobe-based geochemical fingerprinting of glass shards is a slow and invasive process, whilst μ-XRF scanning of rhyolite tephra in sediment cores from Auckland (New Zealand) could provide a faster, non-invasive approach to aid the recognition of tephra layers. This study highlights the potential and pitfalls in this novel approach: changes in most scanning parameters, and the use of two different Itrax core scanners, still led to similar chemical characterizations of the tephra layers. Changes in other scanning parameters have a biasing influence on the chemical characterization of the tephra, which would lead to misidentification of unknown layers. We demonstrate that μ-XRF core scanning provides a faster and non-invasive approach to correlation of sediment sequences using chemically distinct, visually pure tephra layers if a strict scanning protocol is followed. Nevertheless, an extensive database of μ-XRF-scanned rhyolite tephra is required for recognition of unknown tephra units using this approach.     

Production of fish in two small streams in the north island of New Zealand

Data are presented on biomass, mortality, growth, and production of fish populations inhabiting two small streams in the Wairarapa district of the North Island of New Zealand. The main water of both streams contained a mixed population of bullies (Philypnodon breviceps Stokell), brown trout (Salmo trutta Linn.), and eels (Anguilla dieffenbachii Gray, and A. australis schmidtii Phillipps). The headwater tributaries of one of the streams contained a large population of Galaxias divergens Stokell and a few eels, but other fish species were absent. All species of fish appeared to be using the same food supply of small benthic invertebrates, mainly ephemeropteran and dipteran larvae. Biomass of benthos per unit area was appreciably higher in the headwater tributary examined than in the main waters downstream. Mean annual stock of benthos in the tributary (Hinau north branch) was 19.75 g/m², in the Hinau main water 10.71 g/m² and in the Hinaki main water 13.47 g/m² Nevertheless, production per unit area from the nearly monospecific fish population in the Hinau north branch (14.28 g/m²) was less than that of the mixed populations in the main waters (24.17 g/m² in the Hinau, 73.54 g/m² in the Hinaki). Possibly fish production in the headwaters might be greater if the species composition of fish was more diverse.