A Unified Assessment of Hydrologic and Biogeochemical Responses in Research Watersheds in Eastern Puerto Rico Using Runoff–Concentration Relations

An examination of the relation between runoff rate, R, and concentration, C, of twelve major constituents in four small watersheds in eastern Puerto Rico demonstrates a consistent pattern of responses. For solutes that are not substantially bioactive (alkalinity, silica, calcium, magnesium, sodium, and chloride), the log(R)–log(C) relation is almost linear and can be described as a weighted average of two sources, bedrock weathering and atmospheric deposition. The slope of the relation for each solute depends on the respective source contributions to the total river load. If a solute were strictly derived from bedrock weathering, the slope would be ?0.3 to ?0.4, whereas if strictly derived from atmospheric deposition, the slope would be approximately ?0.1. The bioactive constituents (dissolved organic carbon, nitrate, sulfate, and potassium), which are recycled by plants and concentrated in shallow soil, demonstrate nearly flat or downward-arched log(R)–log(C) relations. The peak of the arch represents a transition from dominantly soil-matrix flow to near-surface macropore flow, and finally to overland flow. At highest observed R (80 to >90 mm/h), essentially all reactive surfaces have become wetted, and the input rate of C becomes independent of R (log(R)–log(C) slope of –1). The highest R are tenfold greater than any previous study. Slight clockwise hysteresis for many solutes in the rivers with riparian zones or substantial hyporheic flows indicates that these settings may act as mixing end-members. Particulate constituents (suspended sediment and particulate organic carbon) show slight clockwise hysteresis, indicating mobilization of stored sediment during rising stage.     

Late Devensian evolution of the marine offshore environment of western Scotland

Offshore boreholes from the outer Firth of Clyde and from the Sea of the Hebrides passed through marine deposits of Holocene, Loch Lomond Stadial (LLS) and Windermere Interstadial (WI) age, but it is likely that older, probably Dimlington Stadial (DS) strata, now removed by erosion, were formerly present at the entrance to the Firth of Clyde. The late-glacial environment was one of very rapid deposition punctuated by erosive episodes. Reworking and redeposition led to the mixing of otherwise incompatible warm, shallow-water and cold, offshore faunas, particularly during a ‘warm’ event towards the end of the WI. The latter is correlated with Greenland Interstadial GI1a, but no evidence has been found for climatic ameliorations corresponding to GI1c and GI1e earlier in the Wl. A less cold interval at the end of the LLS may be coeval with climatic changes in Norway and the Shetland–Faroe Channel. Glacier ice disappeared from the outer Firth of Clyde before the close of the DS, and the Glasgow area was deglaciated across the DS/WI transition. The borehole evidence for the timing of deglaciation in the Sea of the Hebrides is inconclusive.     

Ecology of Diloma nov Aezelandiae at Portobello,New Zealand

Some aspects of the biology of Diloma (Fractarmilla) novaezelandiae (Anton) (= Zediloma subrostrata), a soft‐shore trochid gastropod, were investigated in Latham Bay, Portobello, South Island, New Zealand (45° 50’ 25” S, 170° 38’ 30” E). The distribution of D. novaezelandiae during September 1973 to June 1974 was recorded along three transects; pebble distribution, macroalgal cover, grain‐size distribution and organic carbon content in the sediment, range of water salinity, and length of time of exposure to air were also recorded along the transects.

The greatest population density of D. novaezelandiae occurred between 0.8 m and 1.4 m above Chart Datum. The trochid was found to prefer a hard substratum to a soft substratum, and there was a positive correlation of organic content of the sediment with density of D. novaezelandiae. As the population density decreased towards low water the individual shell size increased. Size: weight relationships were calculated and the results showed that dry flesh weight and dry shell weight were both proportional to the cube of the shell diameter.     

Historical and paleolimnological evidence for expansion of Lake Athabasca (Canada) during the Little Ice Age

A multi-proxy paleolimnological record obtained from a small, lowland closed-drainage basin located in the Peace-Athabasca Delta (Alberta, Canada), 10 km northwest of the present-day shore of Lake Athabasca, captures evidence of pronounced hydroecological changes over the past ~400 years. Consistent with historical maps produced by early European explorers of western Canada, paleolimnological data support the existence of a Lake Athabasca highstand during the Little Ice Age (LIA), c. 1600–1900 Common Era (CE). This contrasts with interpretations from previous analyses on sediment cores from an upland closed-drainage basin located centrally within the Peace sector of the delta that indicate low water levels during this interval. The different paleohydrological records at these two basins reflect the relative influence of different controls on the lake water balances. During the LIA, the lowland site was influenced by high levels in Lake Athabasca, whereas the elevated basin was outside the range of water-level rise in the lake and its distributaries, and was instead controlled by dry atmospheric conditions that led to evaporative drawdown. Integration of paleolimnological records and historical sources demonstrates that the ecosystem has undergone marked climate-driven hydroecological change over the past century, which is important information for effective management.     

Multilevel samplers as microcosms to assess microbial response to biostimulation

Passive multilevel samplers (MLS) containing a solid matrix for microbial colonization were used as in situ microcosms in conjunction with a push-pull biostimulation experiment designed to promote biological U(VI) and Tc(VII) reduction. MLS were deployed at 24 elevations in the injection well and two downgradient wells to investigate the spatial variability in microbial community composition and growth prior to and following biostimulation. The microbial community was characterized by real-time quantitative polymerase chain reaction (Q-PCR) quantification of bacteria, NO(3)(-)-reducing bacteria (nirS and nirK), delta-proteobacteria, Geobacter sp., and methanogens (mcrA). Pretest cell densities were low overall but varied substantially with significantly greater bacterial populations detected at circumneutral pH (t-test, alpha= 0.05), suggesting carbon substrate and low pH limitations of microbial activity. Although pretest cell densities were low, denitrifying bacteria were dominant members of the microbial community. Biostimulation with an ethanol-amended ground water resulted in concurrent NO(3)(-) and Tc(VII) reduction, followed by U(VI) reduction. Q-PCR analysis of MLS revealed significant (1 to 2 orders of magnitude, Mann-Whitney U-test, alpha= 0.05) increases in cell densities of bacteria, denitrifiers, delta-proteobacteria, Geobacter sp., and methanogens in response to biostimulation. Traditionally, characterization of sediment samples has been used to investigate the microbial community response to biostimulation; however, collection of sediment samples is expensive and not conducive to deep aquifers or temporal studies. The results presented demonstrate that push-pull tests with passive MLS provide an inexpensive approach to determine the effect of biostimulation on contaminant concentrations, geochemical conditions, and the microbial community composition and function.     

The spectrum of multiply ionized iron between 10 and 17 Å

Valency and inner shell transitions in multiply ionized iron have been excited in the transient pinch of a Plasma Focus discharge. Hartree-Fock calculations have been made to identify the levels involved and a comparison is made with observations of solar flares.