The relative importance of chlorophyll and colored dissolved organic matter (CDOM) to the prediction of the diffuse attenuation coefficient in shallow estuaries

The availability of underwater light is a critical factor in the growth and abundance of primary producers in shallow embayments. The goal of this study was to examine the relative importance of factors influencing light availability in this type of water body. Many simulation models of aquatic ecosystems predict light attenuation from chlorophyll or phytoplankton stock. In the three southern New England sites studied here, no useful relationship was found to exist between chlorophyll and K_PAR (the diffuse attenuation coefficient of photosynthetically active radiation; Kirk 1994; Mobley 1994). In 40 of 53 cases, a regression of chlorophyll versus K_PAR was not statistically significant. Variation in K_PAR did demonstrate a correlation to salinity, implicating a freshwater source of light attenuating material. This was true even in a system with little freshwater inflow. Colored dissolved organic matter (CDOM) is one such terrestrial input that enters estuaries from their watersheds and can strongly influence the availability of light to aquatic primary producers. This study demonstrated that over 70% of the variability in the K_PAR coefficient can be attributed to CDOM in the shallow estuaries studied. This illustrates the need for improved model formulations that include CDOM in the prediction of light attenuation in shallow coastal systems. A new equation has been developed to predict K_PAR with CDOM.     

Iron and sulfide oxidation within the basaltic ocean crust: implications for chemolithoautotrophic microbial biomass production

Microbial processes within the ocean crust are of potential importance in controlling rates of chemical reactions and thereby affecting chemical exchange between the oceans and lithosphere. We here assess the oxidation state of altered ocean crust and estimate the magnitude of microbial biomass production that might be supported by oxidative and nonoxidative alteration. Compilations of Fe₂O₃, FeO, and S concentrations from DSDP/ODP drill core samples representing upper basaltic ocean crust suggest that Fe³⁺/ΣFe increases from 0.15 ± 0.05 to 0.45 ± 0.15 within the first 10-20 Myr of crustal evolution. Within the same time frame 70 ± 25% of primary sulfides in basalt are oxidized. With an annual production of 4.0 ± 1.8 × 10¹⁵ g of upper (500 ± 200 m) crust and average initial concentrations of 8.0 ± 1.3 wt% Fe and 0.125 ± 0.020 wt% S, we estimate annual oxidation rates of 1.7 ± 1.2 × 10¹² mol Fe and 1.1 ± 0.7 × 10¹¹ mol S. We estimate that 50% of Fe oxidation may be attributed to hydrolysis, producing 4.5 ± 3.0 × 10¹¹ mol H₂/yr.Thermodynamic and bioenergetic calculations were used to estimate the potential chemolithoautotrophic microbial biomass production within ridge flanks. Combined, aerobic and anaerobic Fe and S oxidation may support production of up to 48 ± 21 × 10¹⁰ g cellular carbon (C). Hydrogen-consuming reactions may support production of a similar or larger microbial biomass if iron reduction, nitrate reduction, or hydrogen oxidation by O₂(aq) are the prevailing metabolic reactions. If autotrophic sulfate reduction or methanogenesis prevail, the potential biomass production is 9 ± 7 × 10¹⁰ g C/yr and 3 ± 2 × 10¹⁰ g C/yr, respectively. Combined primary biomass production of up to ∼1 × 10¹² g C/yr may be similar to that fueled by anaerobic oxidation of organic matter in deep-seated heterotrophic systems. These estimates suggest that water-rock reactions may support significant microbial life within ridge flank hydrothermal systems, These estimates suggest that water-rock reactions may support significant microbial life within ridge flank hydrothermal systems.     

Urban and rural dewfall,surface moisture,and associated canopy-level air temperature and humidity measurements for vancouver,canada

Canopy-level humidity is often less at night during fine weather in a mid-latitude city, compared to its rural surroundings. This feature has been attributed, in part, to reduced urban dew, but links are largely unproven, because urban dew data are rare. In this study, surface moisture (i.e., dew + guttation by blotting) and dewfall (by mini-lysimeter) were measured at rural and urban residential sites in Vancouver, Canada, during the summer of 1996. Air temperature and humidity were measured at both sites, and on rural-to-urban vehicle traverses. Weather and location effects were evident. Humidity data suggested the small (< 1 g m^–3) urban moisture excess observed on fine nights was linked to reduced urban dew. For grass, the frequency of moisture events, and surface moisture amounts, were similar for both sites. However, on grass, rural dewfall (mean=0.10 mm per night) was more than urban dewfall (mean=0.07 mm per night). On the other hand, data for a roof lysimeter (mean dewfall=0.12 mm per night) showed that an urban roof could rival rural grass as a favoured location for dewfall in Vancouver.     

Evidence of temperature depression and hydrological variations in the eastern Sierra Nevada during the Younger Dryas stade

Sediment records from two lakes in the east-central Sierra Nevada, California, provide evidence of cooling and hydrological shifts during the Younger Dryas stade (YD; ~ 12,900-11,500 cal yr BP). A chironomid transfer function suggests that lake-water temperatures were depressed by 2°C to 4°C relative to maximum temperatures during the preceding Bølling-Allerød interstade (BA; ~ 14,500-12,900 cal yr BP). Diatom and stable isotope records suggest dry conditions during the latter part of the BA interstade and development of relatively moist conditions during the initiation of the YD stade, with a reversion to drier conditions later in the YD. These paleohydrological inferences correlate with similar timed changes detected in the adjacent Great Basin. Vegetation response during the YD stade includes the development of more open and xeric vegetation toward the end of the YD. The new records support linkages between the North Atlantic, the North Pacific, and widespread YD cooling in western North America, but they also suggest complex hydrological influences. Shifting hydrological conditions and relatively muted vegetation changes may explain the previous lack of evidence for the YD stade in the Sierra Nevada and the discordance in some paleohydrological and glacial records of the YD stade from the western United States.     

Preheat Issues in Hydrodynamic Hedla Experiments

Hydrodynamic experiments have become a very active area within High Energy Density Laboratory Astrophysics. In such experiments, preheat of an interior surface due to heating prior to shock arrival can alter the initial conditions for further evolution and can change the nature of the experiment (Olson et al., 2003). Unfortunately, preheat cannot typically be detected without undertaking dedicated experiments for this purpose. We have designed such experiments, relevant to hydrodynamic instability experiments using Omega Laser at intensities of ~10¹⁵ W/cm². Simulations using the HYADES code suggest that radiative preheat alone causes the interface to move approximately 2 μm before the blast wave reaches it. Hot-electron preheat could cause much larger motions. These experiments will use VISAR to examine the motion of an aluminum sample layer at the rear interface of a standard hydrodynamic target during the period before the shock reaches it (Allen and Burton, 1993).     

A clash of values and approaches: A case study of marine protected area planning in Mozambique

Many developing countries are expanding their network of Marine Protected Areas (MPAs) to meet ambitious marine conservation targets set globally and to develop tourism nationally. This study explores the human dimensions of MPA planning in Mozambique by engaging local resource users in a series of structured discussions about marine resource use, pressures on marine resources, ways to address such pressures, and the potential positive and negative impacts of MPAs on the management of marine resources and livelihoods, from a community perspective. Findings show that the groups and communities interviewed are at best ambivalent towards MPAs while at the same time supporting increased government regulation, including conventional fisheries management measures. The study suggests that without significant community involvement in the choice of marine conservation tools, the drive to establish MPAs to achieve biodiversity conservation and tourism development goals may be counterproductive, at least in terms of poverty alleviation and sustainable resource use. It argues that a wider range of marine conservation approaches and tools needs to be considered in addition to MPAs, taking into consideration local views and institutional capacities.     

Assessing Mix Layer Amplitude in 3D Decelerating Interface Experiments

We present data from recent high-energy-density laboratory experiments designed to explore the Rayleigh–Taylor instability under conditions relevant to supernovae. The Omega laser is used to create a blast wave structure that is similar to that of the explosion phase of a core-collapse supernova. An unstable interface is shocked and then decelerated by the planar blast wave, producing Rayleigh–Taylor growth. Recent experiments were performed using dual, side-on, x-ray radiography to observe a 3D “egg crate” mode and an imposed, longer-wavelength, sinusoidal mode as a seed perturbation. This paper explores the method of data analysis and accurately estimating the position of important features in the data.     

Recovery of Injected Freshwater from a Brackish Aquifer with a Multiwell System

Herein we propose a multiple injection and recovery well system strategically operated for freshwater storage in a brackish aquifer. With the system we call aquifer storage transfer and recovery (ASTR) by using four injection and two production wells, we are capable of achieving both high recovery efficiency of injected freshwater and attenuation of contaminants through adequately long residence times and travel distances within the aquifer. The usual aquifer storage and recovery (ASR) scheme, in which a single well is used for injection and recovery, does not warrant consistent treatment of injected water due to the shorter minimum residence times and travel distances. We tested the design and operation of the system over 3 years in a layered heterogeneous limestone aquifer in Salisbury, South Australia. We demonstrate how a combination of detailed aquifer characterization and solute transport modeling can be used to maintain acceptable salinity of recovered water for its intended use along with natural treatment of recharge water. ASTR can be used to reduce treatment costs and take advantage of aquifers with impaired water quality that might locally not be otherwise beneficially used.     

Potential climate change effects on warm-season livestock production in the Great Plains

Projected production responses were derived for confined swine and beef and for milk-producing dairy cattle based on climate change projections in daily ambient temperature. Milk production from dairy cattle and the number of days to grow swine and beef cattle were simulated. Values were obtained for three central United States transects and three climate scenarios which were based on projected mean daily ambient temperatures associated with a baseline, doubling, and tripling of atmospheric greenhouse gas (CO₂) levels for the period June 1 to October 31. For swine, a slight northwest to southeast gradient is evident. Transect 1 (west side) shows no losses under the doubling scenario and losses up to 22.4% under the tripling scenario. Transect 3 (east side) displays losses of over 70% under the tripling scenario. For beef, positive benefits were simulated in Transect 1 with increasing temperatures, although a northwest to southeast gradient was also evident. For dairy, no positive benefits in milk production were found due to climate effects. Projected production declines ranged from 1% to 7.2%, depending on location. However, ranges in predicted differences were less than those simulated for beef and swine. These simulations suggest regional differences in animal production due to climate change will be apparent. For small changes in climate conditions, animals will likely be able to adapt, while larger changes in climate conditions will likely dictate that management strategies be implemented. Exploration of the effects of climate changes on livestock should allow producers to adjust management strategies to reduce potential impact and economic losses due to environmental changes.