Solar parameters for modeling interplanetary background

The goal of the Fully Online Datacenter of Ultraviolet Emissions (FONDUE) Working Team of the International Space Science Institute in Bern, Switzerland, was to establish a common calibration of various UV and EUV heliospheric observations, both spectroscopic and photometric. Realization of this goal required an up-to-date model of spatial distribution of neutral interstellar hydrogen in the heliosphere, and to that end, a credible model of the radiation pressure and ionization processes was needed. This chapter describes the solar factors shaping the distribution of neutral interstellar H in the heliosphere. Presented are the solar Lyman-alpha flux and the solar Lyman-alpha resonant radiation pressure force acting on neutral H atoms in the heliosphere, solar EUV radiation and the photoionization of heliospheric hydrogen, and their evolution in time and the still hypothetical variation with heliolatitude. Further, solar wind and its evolution with solar activity is presented in the context of the charge exchange ionization of heliospheric hydrogen, and in the context of dynamic pressure variations. Also the electron ionization and its variation with time, heliolatitude, and solar distance is presented. After a review of all of those topics, we present an interim model of solar wind and the other solar factors based on up-to-date in situ and remote sensing observations of solar wind. Results of this effort will further be utilised to improve on the model of solar wind evolution, which will be an invaluable asset in all heliospheric measurements, including, among others, the observations of Energetic Neutral Atoms by the Interstellar Boundary Explorer (IBEX).Comment: Chapter 2 in the planned "Cross-Calibration of Past and Present Far UV Spectra of Solar System Objects and the Heliosphere", ISSI Scientific Report No 12, ed. R.M. Bonnet, E. Quemerais, M. Snow, Springe

Physiological responses of seagrasses used to identify anthropogenic nutrient inputs

Fertilization experiments have established that seagrass growth in Moreton Bay can be limited by the supply of both N and P. In the present study, morphological and physiological characteristics (canopy height, shoot density, biomass, growth, tissue nutrient content, amino acid concentrations and δN ratios) of Zostera capricorni Aschers, in Moreton Bay, close to and distant from nutrient sources, were compared. Z capricorni at the four sites close to nutrient sources (sewage, septic or prawn-farm effluent, or fiver discharge), had physiological characteristics representative of high nutrient availability and at the five sites distant from nutrient sources had physiological characteristics representative of low nutrient availability. Differences in sediment nutrient concentrations (NH and PO/), seagrass morphology and growth were not related to proximity to nutrient sources. However, the nutrient content of the seagrasses and their amino acid concentrations were consistently higher at sites close to a nutrient source. The amino acids glutamine and asparagine were the most responsive to elevated nutrient availability, and δN values of seagrasses reflected the source of N rather than the nutrient load. These results demonstrate that physiological characteristics of seagrasses can be used to identify the nutrient load and source affecting marine ecosystems

Growth and physiological responses of three seagrass species to elevated sediment nutrients in Moreton Bay, Australia

Seagrasses, marine angiosperms with high rates of primary productivity, are often limited by the supply of nutrients, particularly nitrogen (N) and phosphorus (P). We investigated growth and physiological responses of three seagrass species (Halodule uninervis (Forsk.), Zostera capricorni Aschers and Cymodocea serrulata (r. Br.) Aschers) to elevated sediment N (100 X control) and/or P (10 x control) in adjacent monospecific beds over a 3 month period from spring to early summer. Each species exhibited different growth and biomass responses to both N and P additions. Halodule uninervis growth and biomass increased in response to N and N + P additions, indicative of exclusive N limitation of growth. In contrast, growth and biomass of Z. capricorni increased in response to N + P additions only, indicative of balanced N and P limitation. Cymodocea serrulata growth and biomass were not affected by any of the nutrient additions. Physiological characteristics (amino acid composition, tissue nutrient content, δ N) of all three seagrass species responded to N additions (+ N and N + P). Total amino acid content of seagrass leaves increased by 2 to 4 fold in N additions compared with controls. Concentrations of the N-rich amino acids, glutamine and asparagine, increased by 10-1000 fold in N additions, suggesting that these amino acids may be a metabolic storage for N. Tissue N content of leaves, roots and rhizomes increased and δ N of the leaves decreased in response to N additions. Although seagrass growth and biomass responses to nutrient additions were species specific, metabolic responses were similar for all species. This suggests physiological characteristics of seagrasses are useful for identifying saturating nutrient supply to an environment, but should not be used to determine whether nutrient availability is limiting the seagrass growth rate

Photosynthetic responses of eelgrass (Zostera marina L.) to light and sediment sulfide in a shallow barrier island lagoon

Highly reducing sediments are prevalent in seagrass environments. Under anoxic conditions, hydrogen sulfide can accumulate as an end product of anaerobic respiration at levels which may be toxic to halophytes. The photosynthetic response of Zostera marina L. (eelgrass) to manipulations in sediment sulfide concentration and light regimes was examined in Chincoteague Bay in June 1991. Neutral density screens were used in a mesocosm experiment to decrease downwelling irradiance to 50 and 15% of insolation. Sediment sulfide levels were enriched using NaS and lowered using FeSO. Photosynthesis vs. irradiance (PI) relationships were determined experimentally at ten light levels throughout the 21 day experiment. Photoadaptation was detected in response to the previous 4 day light history of the plants, as maximum photosynthesis (P) decreased in response to lower daily light levels. Negative impacts of sulfide on eelgrass in this study were observed through reductions in P, increases in the light intensity at which gross photosynthesis equals respiration, and decreases in the initial slope of the PI curve. The effects of eutrophication through reduced light and increased sediment sulfide on P were additive. Elevated sediment sulfide levels may contribute to seagrass loss in stressed areas as the potential for utilization of available light is reduced

Light intensity and the interactions between physiology, morphology and stable isotope ratios in five species of seagrass

The effects of light intensity on stable isotope ratios, physiology and morphology of five seagrass species were investigated in an outdoor, light controlled experiment. Seagrasses were maintained in flowing seawater aquaria, with each seagrass species exposed to different light regimes (5, 15, 20, 30, 50, and 100% full sunlight) using shade screens. After 30 days exposure to the various light regimes the five species of seagrass showed markedly different δ13C signatures, with values ranging from −17.6 to −5.5%. Marked responses to light intensity were also shown by each species, with leaf δ13C values becoming at least 3 to 4%. less negative in full sunlight. Other common responses to light intensity were: higher productivities, higher C:N ratios, larger lacunal areas and more root biomass under full sunlight compared with lower light intensities. Less negative δ13C values at high light intensities could be primarily due to (a) increased uptake of 13C from the external C source or (b) increased internal recycling of CO2 in the lacunae due to the increased lacunal size. The increase in size of lacunae may be related to the need to supply more oxygen to the increased root biomass occurring in seagrasses under high light conditions. In contrast to δ13C, the δ15N values of seagrass leaf tissue appeared to be affected by the site of collection, rather than the species of seagrass or light intensity. Higher δ15N values were found at the more eutrophic site (western Moreton Bay = 8.6 to 8.8%.) than at the site further from anthropogenic influence (eastern Moreton Bay = 2.6 to 4.5%.)

Effects of light deprivation on the survival and recovery of the seagrass Halophila ovalis (R.Br.) Hook

Survival and recovery of the seagrass Halophila ovalis (R.Br.) Hook during and after light deprivation was investigated to assist in the interpretation of recent losses of Halophila spp. in Queensland, Australia. Light deprivation experiments were conducted in outdoor aquaria and in situ at two water depths. Halophila ovalis plants were deprived of light for a maximum of 30 days, and recovery processes were investigated for up to 18 days following 15 days of light deprivation. Measurements of H. ovalis biomass, storage carbohydrate concentrations, chlorophyll a + b concentrations, stable carbon isotopes ratios (δ13C) and chlorophyll a fluorescence parameters (F(o), F(m) and F(v)/F(m)) were made during and at the end of the light deprivation and recovery periods. Biomass declined after 3-6 days in the dark and complete plant death occurred after 30 days. During the recovery period, biomass continued to decline for a short duration of time before stabilising. Sugar concentrations declined rapidly for the first 2 days of light deprivation before stabilising, then increased rapidly during the recovery period. Chlorophyll a + b concentrations were sensitive to very small differences in light availability: concentration decreased in total darkness, remained unchanged at 0.1% of surface irradiance and increased at 0.5% of surface irradiance. Photochemical efficiency of photosystem II (F(v)/F(m)) remained unchanged during the light deprivation and recovery periods. The lack of response in δ13C during light deprivation indicated the cessation of carbon fixation. Decreased sugar utilisation after 2 days of light deprivation indicated a reduction in respiration and growth. Starch concentrations did not change during light deprivation, suggesting the inhibition of starch utilisation by anaerobic conditions within the plant. Plant death after 30 days was notably faster than previously reported for other species of seagrass. The rapid die-off may be due to a shortage of available carbohydrates or due to a build-up of the phytotoxic end products of anaerobic respiration. Overall, H. ovalis has a very limited tolerance to light deprivation when compared to larger species of seagrass. Consequently, the persistence of this species in coastal marine environments may be dependent upon the occurrence and duration of transient light deprivation events