Light Incubation Research Articles

Nutrient Fluxes in the Microalgal-dominated Intertidal Regions of the Lower Yaquina Estuary, Oregon (USA)

The effects of benthic microalgae on sediment nutrient fluxes were investigated at three sites across the intertidal zone of lower Yaquina Bay. Study sites were selected where microalage were present but where seagrass and mud shrimp were absent. Sediment columns were collected seasonally from one to three stations from September 1999 through August 2000 to determine the seasonal and spatial range in benthic fluxes. Collected sediments were carried to the nearby laboratory for light and dark incubation experiments. Nitrate fluxes ranged from −122 to −4 μmol N m−2 hr−1, whereas ammonia fluxes ranged from −52 to 101 μmol N m−2 hr−1. The ranges for orthophosphate and silicate were −7.4 to 12 μmol P m−2 hr−1 and −93 to 283 μmol Si m−2 hr−1. The sediments were always a net sink for nitrate. Nitrate uptake rates were highest during the warmest month (August) and lowest during the coldest months (November and January). Nitrate fluxes were not statistically different for light and dark conditions. Ammonium was ge...

Hypericin-loaded nanoparticles for the photodynamic treatment of ovarian cancer

A photodynamic approach has been suggested to improve diagnosis and therapy of ovarian cancer. As Hypericin (Hy), a natural photosensitizer (PS) extracted from Hypericum perforatum, has been shown to be efficient in vitro and in vivo for the detection or treatment of other cancers, Hy could also be a potent tool for the treatment and detection of ovarian cancer. Due to its hydrophobicity, systemic administration of Hy is problematic. Thus, polymeric nanoparticles (NPs) of polylactic acid (PLA) or polylactic-co-glycolic acid (PLGA) were used as a drug delivery system. Hy-loaded NPs were produced with the following characteristics: (i) size in the 200–300 nm range, (ii) negative zeta potential, (iii) low residual PVAL and (iv) drug loading from 0.03 to 0.15% (w/w). Their in vitro photoactivity was investigated on the NuTu-19 ovarian cancer cell model derived from Fischer 344 rats and compared to free drug. Hy-loaded PLA NPs exhibited a higher photoactivity than free drug. Increasing light dose or incubation time with cells induced an enhanced activity of Hy-loaded PLA NPs. Increased NP drug loading had a negative effect on their photoactivity on NuTu-19 cells: at the same Hy concentration, the higher was the drug loading, the lower was the phototoxic effect. The influence of NP drug loading on the Hy release from NPs was also investigated.

Observations on Some of the Mycelial Growth and Pigmentation Characteristics of Cordyceps militaris Isolates

Characteristic growth patterns of Cordyceps militaris isolates on various media, under varying light conditions and at varying incubation periods were examined. Light was found to be the most critical single factor in determining the density, texture, and pigmentation of the mycelial culture of the fungus. However, under the light condition, the degree of pigmentation and mycelial density were found to be affected by the incubation period and type of medium. Irrespective of the variations in medium type or incubation period, there was no pigmentation of the mycelium under dark condition. Radial growth of the mycelium was faster under dark incubation rather than under light incubation. Abundant mycelial density and darkest pigmentation of C. militaris isolates were produced in nutritionally rich media like SDAY, SMAY and CZYA, suggesting that these media may fulfill all the requirements for vegetative growth of the fungus. Growth characteristics of C. militaris isolates could be easily observed by the simple agar culture method, which would be useful to characterize the phenotypic characteristics of large number of pure cultures of the fungus under given conditions of growth factors such as medium, light and temperature.

Very strong UV-A light temporally separates the photoinhibition of photosystem II into light-induced inactivation and repair

When organisms that perform oxygenic photosynthesis are exposed to strong visible or UV light, inactivation of photosystem II (PSII) occurs. However, such organisms are able rapidly to repair the photoinactivated PSII. The phenomenon of photoinactivation and repair is known as photoinhibition. Under normal laboratory conditions, the rate of repair is similar to or faster than the rate of photoinactivation, preventing the detailed analysis of photoinactivation and repair as separate processes. We report here that, using strong UV-A light from a laser, we were able to analyze separately the photoinactivation and repair of photosystem II in the cyanobacterium Synechocystis sp. PCC 6803. Very strong UV-A light at 364 nm and a photon flux density of 2600 μmol photons m −2 s −1 inactivated the oxygen-evolving machinery and the photochemical reaction center of PSII within 1 or 2 min before the first step in the repair process, namely, the degradation of the D1 protein, occurred. During subsequent incubation of cells in weak visible light, the activity of PSII recovered fully within 30 min and this process depended on protein synthesis. During subsequent incubation of cells in darkness for 60 min, the D1 protein of the photoinactivated PSII was degraded. Further incubation in weak visible light resulted in the rapid restoration of the activity of PSII. These observations suggest that very strong UV-A light is a useful tool for the analysis of the repair of PSII after photoinactivation.

Morphophysiological dormancy in seeds of six endemic lobelioid shrubs (Campanulaceae) from the montane zone in Hawaii

The purpose of this study was to investigate seed dormancy breaking and germination requirements of six woody Hawaiian endemic lobelioids (Campanulaceae). Seeds of all species had underdeveloped, physiologically dormant embryos and thus morphophysiological dormancy. Fresh seeds of Clermontia pyrularia Hillebr. and Trematolobelia macrostachys (Hook. & Arnott) A. Zahlbr. did not germinate during 4 weeks of incubation in light at 15/6, 20/10, or 25/15 °C, whereas those of Clermontia fauriei H. Lev., Clermontia hawaiiensis (Hillebr.) Rock, Clermontia kakeana Meyen, and Cyanea angustifolia (Cham.) Hillebr. germinated to 61%–85% but only at 25/15 °C. Since seeds of the latter four species eventually germinated to 84%–100% when incubated for 12–36 weeks at the three temperature regimes, fresh seeds had conditional dormancy; the physiological component of morphophysiological dormancy was nondeep. Seeds of Trematolobelia macrostachys also came out of dormancy (and germinated to 90%) during 18 weeks of incubation at each of the three temperatures regimes, whereas those of Clermontia pyrularia did so only at 15/6 °C. Simulated seasonal temperature variations did not promote dormancy break and germination in any species except Clermontia pyrularia , in which a 12-week incubation period at 25/15 °C resulted in 90% germination after seeds were moved to 20/10 °C. Seeds of all species had an absolute light requirement for germination except those of Clermontia pyrularia, which germinated to 48% in darkness. Since seeds of the six species only require high temperatures for embryo growth and the breaking of physiological dormancy, they have nondeep simple morphophysiological dormancy.

Light-Dependent Incorporation of Adenine Nucleotide into Noncatalytic Sites of Chloroplast ATP Synthase

The binding of ADP and ATP to noncatalytic sites of dithiothreitol-modified chloroplast ATP synthase was studied. Selective binding of nucleotides to noncatalytic sites was provided by preliminary light incubation of thylakoid membranes with [14C]ADP followed by its dissociation from catalytic sites during dark ATP hydrolysis stimulated by bisulfite ions ("cold chase"). Incorporation of labeled nucleotides increased with increasing light intensity. Concentration-dependent equilibrium between free and bound nucleotides was achieved within 2-10 min with the following characteristic parameters: the maximal value of nucleotide incorporation was 1.5 nmol/mg of chlorophyll, and the dissociation constant was 1.5 microM. The dependence of nucleotide incorporation on Mg2+ concentration was slight and changed insignificantly upon substituting Ca2+ for Mg2+. Dissociation of nucleotide from noncatalytic sites was illumination-dependent. The dissociation kinetics suggested the existence of at least two nucleotide-binding sites with different dissociation rate constants.

High-level transient expression of recombinant protein in lettuce.

Transient expression following agroinfiltration of plant tissue was investigated as a system for producing recombinant protein. As a model system, Agrobacterium tumefaciens containing the beta-glucuronidase (GUS) gene was vacuum infiltrated into lettuce leaf disks. Infiltration with a suspension of 10(9) colony forming units/mL followed by incubation for 72 h at 22 degrees C in continuous darkness produced a maximum of 0.16% GUS protein based on dry tissue or 1.1% GUS protein based on total soluble protein. This compares favorably to expression levels for commercially manufactured GUS protein from transgenic corn seeds. A. tumefaciens culture medium pH between 5.6 and 7.0 and surfactant concentrations < or = 100 ppm in the vacuum infiltration did not affect GUS expression, while infiltration with an A. tumefaciens density of 10(7) and 10(8) colony forming units/mL, incubation at 29 degrees C, and a surfactant concentration of 1,000 ppm significantly reduced expression. Incubation in continuous light caused lettuce to produce GUS protein more rapidly, but final levels did not exceed the GUS production in leaves incubated in continuous darkness after 72 h at 22 degrees C. The kinetics of GUS expression during incubation in continuous light and dark were represented well using a logistic model, with rate constants of 0.30 and 0.29/h, respectively. To semi-quantitatively measure the GUS expression in large numbers of leaf disks, a photometric enhancement of the standard histochemical staining method was developed. A linear relationship with an R2 value of 0.90 was determined between log10 (% leaf darkness) versus log10 (GUS activity). Although variability in expression level was observed, agroinfiltration appears to be a promising technology that could potentially be scaled up to produce high-value recombinant proteins in planta.

Effects of light stimulation of embryos on the use of position-specific and object-specific cues in binocular and monocular domestic chicks ( Gallus gallus)

Chicks hatched from eggs incubated in the dark (D-chicks) or from eggs exposed to light during the last 3 days before hatching (L-chicks) were trained on day 4 to peck at small cones for food reinforcement. The cones had different patterns (checked or striped) and were located in different positions (either on the left or on the right of a rectangular arena) so as both object-specific (pattern) and position-specific cues could be used to discriminate cones that contained or that did not contain food. After learning, the position of the cones was reversed so that object- and position-specific cues provided contradictory information. No effect of light incubation was observed in binocular chicks that chose cones on the basis of object-specific cues. Monocular D-chicks also tended to approach and peck the cones with the correct pattern in the wrong position, whereas monocular L-chicks did not show any clear choice. Initial choices for one side or other of the arena were mostly determined by the first side visible through the non-occluded eye in D-chicks, particularly when using their left eye. These results suggest that light exposure of the embryo makes neural mechanisms that do not receive direct visual input (i.e., those of the occluded side) more available to be used in assessment of novelty.

Modulation of carbonic anhydrase activity in two nitrogen fixing cyanobacteria, Nostoc calcicola and Anabaena sp.

The activity of enzyme carbonic anhydrase (CA) was investigated in two diazotrophic cyanobacteria, Anabaena sp. (ARM 629) and Nostoc calcicola, in the presence of CO2/NaHCO3 and different inhibitors. The CA activity increased when the cells were pretreated with a high concentration of CO2/NaHCO3 and then transferred to ambient level CO2. Maximum activity of CA was observed after 8 h of incubation in light on transfer of cells from high Ci to ambient level CO2, and was low when incubated in dark. Addition of the photosynthetic inhibitor DCMU brought about a differential reduction in CA activity, depending on the carbon source (NaHCO3/CO2). CA inhibitors--ethoxyzolamide (EZ) and acetazolamide (AZ)--inhibited the enzyme activity in both the genera, but the extent of inhibition was greater in Anabaena sp. than in N. calcicola. Such a variation in extent of inhibition/stimulation of CA activity being different in the two genera reflects differences in their inherent potential and genetic background. The relevance of such cyanobacterial strains as CO2 sinks is also discussed.

Protocorm mycobionts of the Federally threatened eastern prairie fringed orchid, Platanthera leucophaea (Nutt.) Lindley, and a technique to prompt leaf elongation in seedlings

A yet unresolved question in orchid biology is whether mycorrhizal fungi (= mycobionts) utilized as a carbon source by young seedlings (= protocorms) are different from those utilized by adult plants. This is the first report documenting the protocorm mycobionts of the Federally threatened eastern prairie fringed orchid, Platanthera leucophaea, and the first report describing a technique to culture mycotrophic seedlings to the green leaf stage. Seeds of P. leucophaea placed in retrievable nylon mesh packets were sown at Hildy Prairie (Grundy Co.), Illinois in November, 2000 and recovered in August, 2002. All resulting protocorms yielded mycobionts assignable to Ceratorhiza goodyerae-repentis (Costantin & Dufour) Moore - the same anamorphic fungus recovered from mature P. leucophaea plants in previous studies. Protocorms cultivated in vitro with a Ceratorhiza mycobiont were placed on a substrate of sand, activated charcoal, and modified oats medium and subjected to chilling (6 oC) in darkness, followed by exposure to a 12 h photoperiod (L : D, 12 h : 12 h) at 24 oC. Leaf length accelerated after the second week of incubation in light. Green leaf color became evident during the photoperiod implying that seedlings were capable of photosynthesis. Seedlings also maintained a mycotrophic capability evidenced by the presence of fungal pelotons in root-like organs. This study has significant merit for conservation by providing a protocol for P. leucophaea's cultivation, and by underscoring the importance of C. goodyerae-repentis in the prairie ecosystem.

Development of Colletotrichum gloeosporioides isolated from green pepper in different culture media, temperatures, and light regimes

Control of anthracnose in green pepper involves the use of resistant varieties and/or fungicides. The selection of varieties and efficient products demands great amounts of conidia as inoculum. It is thus necessary to optimize the production of Colletotrichum gloeosporioides conidia in the laboratory, establishing the best conditions for fungus development. The present study aimed at determining the most favorable culture media, temperature, and light conditions for the production of fungus inoculum. The fungus was isolated from green pepper fruits (Capsicum annuum L.) and transferred to four culture media (PDA, oat, filtered pepper extract, and autoclaved pepper extract), under different temperatures (15, 20, 25, 30, and 35ºC) and light conditions (24h dark, and 24h light). Colony growth was evaluated after 7 and 12 days of incubation. No differences were found between the culture media. However, the greatest number of conidia was obtained from colonies grown in oat medium at 25ºC. Temperatures of 20 and 25ºC were the most favorable for colony growth and sporulation. Higher sporulation was obtained under incubation in constant light. Cultivation of C. gloeosporioides in oat medium, at 25ºC, and constant light is recommended.

Decrease in molecular weight of photosynthetic products of marine phytoplankton during early diagenesis

Changes in the size and neutral aldose (NAld) composition of phytoplankton photosynthetic products during the early diagenetic process were experimentally examined using 13C as a tracer. Most (94.7%) of the photosynthetically produced (P−) organic carbon (OC) was found to be particulate organic carbon (POC) after a 12‐h light incubation. An increase in the concentration of P‐dissolved organic carbon (DOC) was found after the shift to the dark incubation, probably due to a leakage of cellular constituents. An increase in the concentration of P‐DOC was mainly due to an increase in the high molecular weight (HMW: ≫10 kDa) fraction that reached its maximum concentration on day 3 and then declined at a relatively high rate. The change in the concentration of the low molecular weight (LMW: ≪10 kDa) DOC fraction was less marked than that in the HMW fraction, and the rate of decrease was much slower, indicating a more biorefractory nature of P‐LMW DOC. P‐dissolved carbohydrates (DCHO) accounted for 38% and 50% in P‐HMW DOC and P‐LMW DOC, respectively, after a 12‐h light incubation. The concentration of P‐LMW DCHO showed a rapid decrease in the early stage of the dark incubation, whereas the concomitant increase in the concentration of P‐LMW dissolved noncarbohydrate (DnonCHO) was noticed. The decrease in the contribution of CHO was noticed both in P‐POC and P‐HMW DOC fractions, but the decline rates were slower than that in P‐LMW DOC fraction. On day 60, the remaining P‐OC accounted for 4.6% of photosynthetic material originally produced. The distribution of the size fractions of the remaining P‐OC on day 60 (POC, 14%; HMW DOC, 22%; LMW DOC, 64%) indicates that phytoplankton photosynthetic products were rapidly degraded to the less bioreactive LMW DOM during early diagenesis. The present results indicate that the annual global ocean production rate of semilabile DOC with lifetimes exceeding 2 months is 1.91 PgC yr−1.

Germination and Survival of Fusarium graminearum Macroconidia as Affected by Environmental Factors

AbstractThe effects of temperature (4–20°C), relative humidity (RH, 0–100%), pH (3–7), availability of nutrients (0–5 g/l sucrose) and artificial light (0–494 μmol/m2/s) on macroconidial germination of Fusarium graminearum were studied. Germ tubes emerged between 2 and 6 h after inoculation at 100% RH and 20°C. Incubation in light (205 ± 14 μmol/m/s) retarded the germination for approximately 0.5 h in comparison with incubation in darkness. The times required for 50% of the macroconidia to germinate were 3.5 h at 20°C, 5.4 h at 14°C and 26.3 h at 4°C. No germination was observed after an incubation period of 18 h at 20°C in darkness at RH less than 80%. At RH greater than 80%, germination increased with humidity. Germination was observed when macroconidia were incubated in glucose (5 g/l) or sucrose (concentration range from 2.5 × 10−4 to 5 g/l) whereas no germination was observed when macroconidia were incubated in sterile deionized water up to 22 h. Macroconidia germinated quantitatively within 18 h at pH 3–7. Repeated freezing (−15°C) and thawing (20°C) water agar plates with either germinated or non‐germinated macroconidia for up to five times did not prevent fungal growth after thawing. However, the fungal growth rate of mycelium was negatively related to the number of freezing events the non‐germinated macroconidia experienced. The fungal growth rate of mycelium was not significantly affected by the number of freezing events the germinated spores experienced. Incubation of macroconidia at low humidity (0–53% RH) suppressed germination and decreased the viability of the spores.

Cyclic AMP levels in several macroalgae and their relation to light quantity and quality

Total cAMP levels were measured in the macroalgae Dictyota dichotoma, Gelidium sesquipedale and Ulva rigida under different light conditions in order to study its regulation either by phytochrome or photosynthesis. Incubation in red or far-red light did not promote a phytochrome-like response; instead, it showed a synergistic effect upon cAMP accumulation. cAMP levels seemed to depend on the amount of energy applied. The correlation between photosynthetic oxygen evolution and cAMP variations at sub-saturating white light irradiance pointed to photosynthetic electron transport as involved in the regulation of cAMP accumulation at least in G. sesquipedale and U. rigida. Inhibitors of thylakoidal and mitochondrial electron transport chains reduced cAMP levels in 70 to 99%. We conclude that cAMP accumulation could be regulated by photosynthetic activity rather than phytochrome in the macroalgae studied.

Effect of mixing patterns and light dose on growth of Anabaena circinalis in a turbid, lowland river

AbstractAnabaena circinalis is common in the lower Murray River, Australia, and may compromise water quality due to the release of toxins. The water is turbid and thermal structure may significantly affect light availability. An in situ experiment was designed to represent complete mixing, diurnal stratification and persistent stratification and test the effect on growth of A. circinalis. To represent the mixing treatments, cells were incubated in diffusion chambers that were adjusted to different positions in the water‐column throughout the day. Populations exposed to persistent stratification over six days grew significantly faster than the other treatments at a rate of 0.65 day−1. However, growth of the diurnally stratified populations was slower than (0.28 day−1), or similar to (0.40 day−1) the mixed population (0.40 day−1). Therefore, the growth of the subpopulations exposed to the euphotic zone was insufficient to counteract the slow growth of the majority that were confined to darkness during the stratified period. A relationship between growth rate (G) and average daily light dose (I) was constructed and growth rate at optimal light dose (Gmax), slope of linear section of G–I curve (α), and light dose where lines of Gmax and light‐limited portion of G–I curve intersect (Ik) were solved as 0.66 day−1, 0.12 day−1 (mol−1 m−2 day−1)−1 and 5.4 mol m−2 day−1, respectively. Using these parameters, a model was developed to predict possible differences in growth between diurnal and mixed populations under varying conditions of vertical light attenuation, mixed depth and incubation time. Copyright © 2003 John Wiley &amp; Sons, Ltd.

A growth regulatory loop that provides homeostasis to phytochrome a signaling.

Phytochrome kinase substrate1 (PKS1) is a cytoplasmic protein that interacts physically with, and is phosphorylated by, the plant photoreceptor phytochrome. Here, we show that light transiently increases PKS1 mRNA levels and concentrates its expression to the elongation zone of the hypocotyl and root. This response is mediated by phytochrome A (phyA) acting in the very low fluence response (VLFR) mode. In the hypocotyl, PKS1 RNA and protein accumulation are maintained only under prolonged incubation in far-red light, the wavelength that most effectively activates phyA. Null mutants of PKS1 and its closest homolog, PKS2, show enhanced phyA-mediated VLFR. Notably, a pks1 pks2 double mutant has no phenotype, whereas overexpression of either PKS1 or PKS2 results in the same phenotype as the pks1 or pks2 single null mutant. We propose that PKS1 and PKS2 are involved in a growth regulatory loop that provides homeostasis to phyA signaling in the VLFR. In accordance with this idea, PKS1 effects are larger in the pks2 background (and vice versa). Moreover, the two proteins can interact with each other, and PKS2 negatively regulates PKS1 protein levels specifically under VLFR conditions.

Changes in some enzymes of microbodies and plastid development in excised radish cotyledons: Effect of narciclasine

Narciclasine (NCS), isolated from mucilage of Narcissus bulb, showed inhibitory effects on growth and plastid development of excised radish cotyledons. NCS (0.1 mumol/L) started to show inhibitory effects on isocitrate lyase and hydroxypyruvate reductase activities after 24 h incubation in light. When NCS concentration was increased to 10 mumol/L, the activities of both enzymes are completely inhibited. From ultrastructural studies, NCS markedly prevented the degradation of protein bodies and lipid bodies, as well as chloroplast formation of excised radish cotyledons. There was only little degradation of protein and lipid bodies, and almost no chloroplast formation in the excised radish cotyledon treated with 1 mumol/L NCS. Therefore, our results provide clear evidence that NCS inhibited the transition of glyoxysomes and peroxisomes, and chloroplast development.

L-ascorbic acid metabolism in spinach (Spinacia oleracea L.) during postharvest storage in light and dark

Abstract l -ascorbic acid metabolism in spinach ( Spinacia oleracea L.) leaves during postharvest storage in low intensity white light (20–25 μmol m −2 s −1 ) and the dark was investigated. The endogenous pool of ascorbic acid (AsA) in both young and mature leaves showed higher values in the light than in the dark. The higher content of AsA in the light could not be explained by the activities of the different redox enzymes involved in AsA metabolism. The enzyme activities did not show marked differences between those stored under light and those in the dark. On the other hand, AsA catabolism as indicated by oxalic acid contents was not indicative of the effects of light and darkness since oxalic acid contents did not quantitatively relate well with AsA contents. Feeding of spinach leaf disks with l -galactono-1,4-lactone showed similar activities of l -galactono-1,4-lactone dehydrogenase during both light and dark incubation; however, production of AsA was higher in the light-incubated than in the dark-incubated leaf disks. Thus it is possible that light could enhance AsA synthesis in spinach leaves. The total soluble carbohydrates and glucose contents of leaves in the light were higher than those in leaves in the dark. These results suggest that continuous illumination of white light effectively supports the photosynthetic capacity of spinach leaves during postharvest storage thereby increasing the availability of soluble carbohydrates, especially glucose, enabling them to contribute to the control of the AsA pool size.

Contrasting seed germination patterns for intracontinental disjuncts of Heuchera (Saxifragaceae) in North America: the eastern temperate H. parviflora and western montane H. cylindrica

Heuchera parviflora var. parviflora grows primarily in southeastern North America and Heuchera cylindrica var. cylindrica in northwestern North America. Seeds of H. parviflora were collected in Kentucky in November 1995 and 1996 during the dispersal stage of the life cycle, and those of H. cylindrica were collected in Washington in August 1996. The purpose of the study was to compare the germination patterns of these two intracontinental disjunct species of Heuchera. During 2–12 weeks of incubation over a range of thermoperiods (15:6, 20:10, 25:15, 30:15, 35:20°C (12 h : 12 h)) that simulated habitat temperatures, fresh H. parviflora seeds germinated to 62–87% at 20:10 – 30:15°C in light. Cold stratification at 5°C effectively broke conditional dormancy in H. parviflora seeds: 76–96% germination took place during 2 weeks of incubation at 15:6 – 35:20°C in light following 12 weeks of cold stratification in light. In contrast, fresh H. cylindrica seeds germinated to 69–94% at 15:6 – 25:15°C in light during 2–12 weeks of incubation in light, but cold stratification at 5°C did not improve germination. Peak germination of H. parviflora seeds sown in November 1996 in an ambient-temperature greenhouse occurred in early March 1997, whereas that of H. cylindrica seeds sown in September 1996 occurred in late October 1996. Adaptive divergence of these species apparently has occurred with respect to their seed germination ecology. Their dormancy and germination characteristics are similar to the many other species growing in the same vegetation types.Key words: adaptive divergence, Heuchera cylindrica, Heuchera parviflora, physiological dormancy, Saxifragaceae, seed germination.

Temporal and spatial patterns of intertidal sediment-water nutrient and oxygen fluxes in the Douro River estuary, Portugal

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 233:55-71 (2002) - doi:10.3354/meps233055 Temporal and spatial patterns of intertidal sediment-water nutrient and oxygen fluxes in the Douro River estuary, Portugal Catarina M. Magalhães1,*, Adriano A. Bordalo1, William J. Wiebe2 1Laboratory of Hydrobiology, Institute of Biomedical Sciences, University of Porto, 4099-003 Porto, Portugal 2Department of Marine Sciences, University of Georgia, Athens, Georgia 30602, USA *Present address: Largo Abel Salazar 2, 4099-003 Porto, Portugal. E-mail: c_magalhaes@yahoo.com ABSTRACT: The Douro River watershed drains 17% of the Iberian Peninsula; the present average freshwater discharge into the estuary is 488 m3 s-1. The Douro River estuary receives largely untreated sewage from about 1 million inhabitants of Greater Porto. A major portion of the intertidal sediments is currently scheduled for removal by dredging. In order to assess their role in nutrient dynamics and productivity, sediment-water fluxes of ammonium, inorganic phosphorus, nitrate, nitrite, silicate and oxygen were determined quarterly in muddy and sandy intertidal sediments of the lower estuary. Fluxes were estimated with both light and dark incubations. The range of net nutrient uptake rates from all sites was as follows: ammonium 28 to 978 µmol m-2 h-1; nitrate 40 to 810 µmol m-2 h-1; nitrite 1 to 128 µmol m-2 h-1; dissolved orthophosphate 1 to 152 µmol m-2 h-1 and silicate 69 to 369 µmol m-2 h-1. Stepwise multiple regression analysis revealed strong coupling between the concentrations of most nutrients in the water column and the corresponding flux into the sediment. Mean net nutrient effluxes to the overlying water were observed in only 6 cases out of a total of 120, and only at the muddy sediment site. Net oxygen production (light incubation) ranged from 58 to 618 mgO2 m-2 h-1, while oxygen consumption (dark incubation) ranged from 11 to 64 mgO2 m-2 h-1. Primary production correlated significantly with chlorophyll a concentrations in the top (0.5 cm) sediment layer at the sandy sites, but showed no correlation at the muddy site. All sampling sites were net daily sources of oxygen to the water. The net productivity of the intertidal flats and their capacity for water-column inorganic nutrient removal assumes particular importance in the Douro River estuary, a eutrophic system with a permanently heterotrophic water column. KEY WORDS: Douro River estuary · Intertidal flat · Sediment-water interface · Nutrient uptake · Oxygen fluxes Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 233. Online publication date: May 21, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.