Nitrogen and phosphorus uptake by the Brazilian kelp Laminaria abyssalis (Phaeophyta) in culture

The uptake of ammonium, nitrate and phosphate by laboratory-grown young sporophytes of Laminaria abyssalis was measured in a perturbed system (batch mode) at 18 °C and 35 ± 5 µE m^–2 s^–1 photon flux density. Uptake of all appeared to follow saturation-type nutrient uptake kinetics. The NO _inf3 ^sup– (K _s = 14.0 µM, V _max = 5.0 µmol h^–1 g^–1 dry wt) and NH _inf4 ^sup+ (K _s = 4.6 µM, V _max= 2.0 µmol h^–1 g^–1 dry wt) were taken up simultaneously, although NH _inf4 ^sup+ was taken up more rapidly. Values of K ₃ and V _max for phosphate were, respectively, 2.21 µM and 0.83 µmol h^–1 g^–1 dry wt. Nitrate and phosphate were both consumed in similar rates (V _max /Ks 0.37) at low concentrations. NH _inf4 ^sup+ , thus, might be a more efficient form of N fertilizer if artificial enrichment of seawater is used.     

Ammonium uptake in alpine streams in the High Tatra Mountains (Slovakia)

Uptake of NH _inf4 ^sup+ -N by streambed biota of mountain brooks was studied in the alpine zone of the High Tatra Mountains. Experiments were performed involving in situ dosing of ammonium directly to the acidified stream and incubations of ammonium and streambed bryophytes in enclosures within a range of pH from 4.45 to 8.10.NH _inf4 ^sup+ -N uptake length decreased with decreasing stream discharge, while comparable values of discharge-normalized uptake lengths were found during two in situ experiments.Maximum uptake rates of NH _inf4 ^sup+ -N obtained during the incubation of bryophytes (6 to 11 mg m^–2 h^–1) were comparable with results of two in situ experiments (8 and 12 mg m^–2 h^–1). The average NH _inf4 ^sup+ -N uptake rates observed during incubations lasting 3 to 5 hours (4.3 mg m^–2 h^–1) were not related to the pH of stream water. Nitrification of about 50% of the NH _inf4 ^sup+ -N added was observed in non-acidified streams, but was negligible in acidified streams. Significant photoinhibition of nitrification was observed in non-acidified streams during enclosure experiments.     

Sels minéraux et cycles de marées dans un estuaire de Bretagne nord (Dourduff,France)

Short-term variations in nutrient concentrations of water-masses have been studied in a Brittany estuary over several tidal cycles, during winter and summer. NH _inf4 ^sup+ , NO _inf2 ^su– , NO _inf3 ^sup– , SiO₂ and PO _inf4 ^su3– have been measured at a fixed station. The Dourduff estuary is characterized by a very low river discharge (80 l · s^–1 during the minimum water runoff and 1 000 l · s^–1 during the maximum) and an important tidal range (9 m at spring tides). SiO₂ and NO _inf3 ^sup+ concentrations are directly related to freshwater flow whereas PO _inf4 ^su3– is partially adsorbed by seston in the turbid ebb waters. NH _inf4 ^sup+ concentration seems to be, in part, dependent upon sediment resuspension: late ebb and onset of flood periods liberate NH _inf4 ^sup+ into the overlying water column. Nutrient concentrations are also related to seasons. Nutrient fluxes are insignificant or negative during summer periods, so the estuary imports nutrients for its own regulation whereas during winter periods it exports NO _inf3 ^sup– and SiO₂ (ca 50 kg NO _inf3 ^sup– and ca 200 g SiO₂ during a single spring tide). The NO₃: PO₄ ratio is always above 15:1 and can reach 300:1; moreover this ratio fluctuates during the tidal cycle. This imbalance originates in terrestrial discharges of nitrogen compounds.

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Sels minéraux et cycles de marées dans un estuaire de Bretagne nord (Dourduff, France)

     

Effect of nutrient deficiency on accumulation and relative molecular weight of poly-β-hydroxybutyric acid by methylotrophic bacterium,Pseudomonas 135

Summary Pseudomonas 135, a facultative methylotroph, was cultivated on methanol as a sole carbon and energy source for the accumulation of poly--hydroxybutyric acid (PHB). The cells grew fairly well on minimal synthetic medium containing 0.5% (v/v) of methanol at pH 7.0 and 30° C. The maximum specific growth rate was determined to be 0.26–0.28 h^–1 with a growth yield of 0.38 in the optimized growth medium. For stimulation of PHB accumulation in the cells, deficiency of nutrients such as NH _inf4 ^sup+ , Mg²⁺ and PO _inf4 ^sup3– was crucial even though cell growth was significantly suppressed. The PHB content of a 40-h culture was determined to be 37% of the total cell mass in NH _inf4 ^sup+ -limited medium, 42.5% on Mg²⁺-deficient medium, and 34.5% on PO _inf4 ^sup3– -deficient medium. The maximum content of PHB in the cells could reach 55% in NH _inf4 ^sup+ -limited fed-batch culture. The average relative molecular eight determined by gel permeation chromatography was 3.7 × 10⁵ in NH _inf4 ^sup+ -limited culture, 2.5 × 10⁵ in Mg²⁺-deficientmedium, and 3.1 × 10⁵ in PO _inf4 ^sup3– -deficient medium. Polydispersity determined in each culture was relatively high (about 10–11). The solid PHB had a melting temperature of 173° C. Correspondence to: J. M. Lebeault     

Zooplankton induced decrease in inorganic phosphorus uptake by plankton in an oligotrophic lake

Experiments conducted on samples collected from a large oligotrophic lake revealed the following: (1) excretion rates of PO _inf4 ^sup3– by single Daphnia thorata were below detection (5 pmol animal^–1 min^–1) in 20 ml of oligotrophic lake water over a period of 10 min, (2) experimental addition of D. thorata to 20 ml aliquots of lake water decreased community-wide microbial uptake of PO _inf4 ^sup3– on two occasions (as measured by ³²PO _inf4 ^sup3– incorporation), and (3) the presence of D. thorata increased uptake by organisms smaller than 1µm, and decreased uptake by large phytoplankton. The specific mechanism for these responses remains unclear, but the results imply that when phytoplankton larger than 1µm encounter cm scale patches of water recently occupied by Daphnia they may experience decreased PO _inf4 ^sup3– availability rather than elevated concentrations of PO _inf4 ^sup3– caused by excretion. We show that ³²P uptake experiments using natural plankton assemblages can be influenced by the presence or absence of large zooplankton, and that neither grazing, turbulence, nor PO _inf4 ^sup3– excretion can account for this influence.     

The Shatt al-Arab River: A nutrient salt and organic matter source to the Arabian Gulf

The distribution of dissolved reactive phosphate, nitrate and nitrite in the waters as well as total organic carbon, total phosphorus and Kjeldahl nitrogen in the sediments of the Shatt al-Arab Estuary and the NW Arabian Gulf were studied from November 1979 to April 1980. The Shatt al-Arab waters contain 0.18 to 0.70 µg-at P-PO _inf4 ^sup3– l^–1, 26.12 to 52.39 µg-at N-N0 _inf3 ^sup– l^–1 and 0.53 to 0.70 µg-at N-NO _inf2 ^sup– l^–1, indicating that this river should be considered a source of nutrients to the Arabian Gulf. It is concluded that most of the nitrate is supplied in dissolved form, while an appreciable amount of phosphate is absorbed to fine suspended particles and released at higher salinities. Total organic carbon in surficial sediments was found to vary between 0.14% and 0.96%. These rather low values are attributed to dilution by dust fallout, which is a major cource of sediments in this area.     

Hydrochemical response during storm events in a South African mountain catchment: the influence of antecedent conditions

The influence of different antecedent conditions on hydrochemical response during storm events was investigated in a small, south-western Cape mountain catchment. Winter and summer storms (four in total) were sampled both before and after the catchment was deliberately burnt. During winter storms, discharge responded rapidly to rainfall, and direct runoff represented the major component of streamflow. Marked lags were observed between rainfall and discharge peaks during the summer storms, and streamflow was dominated by delayed interflow. Chloride, PO _inf4 ^sup3– -P and NO _inf3 ^sup– -N exhibited variable response to discharge according to seasonal variations in soil-moisture levels, whereas the response of HCO _inf3 ^sup– , H⁺ and NH _inf4 ^sup+ -N was not influenced by season. The movement of ions appears to be affected more by geochemical processes operating within the soil than by plant-uptake dynamics, as the prescribed burn appeared to have little effect on relationships between ionic concentration and discharge. The findings of the study highlight the complexity of relationships between solute concentration and discharge.     

Effects of aflatoxin B1 on in vitro cultures ofNicotiana tabacum var. Samsun

Calli ofNicotiana tabacum (tobacco) were treated with two dose ranges of aflatoxin B₁ (0.1–2.0 µg ml^–1 - low does; 5–25 µg ml^–1 aflatoxin B₁). The ability of calli to recover following 3 weeks of toxin exposure was also investigated. The I₅₀ (50% inhibition) value for fresh mass accumulation was approximately 2 µg ml^–1 AFB₁. Fresh mass accumulation was significantly lower than the control value from 0.5 µg ml^–1 AFB₁. Following 3 weeks growth without a toxin source, the growth of calli up to and including 10 µg ml^–1 AFB₁, was significantly greater than control calli, indicating reversibility of the toxic effects. With increasing toxin concentration, chlorophyll content of callus was inhibited from 0.5 µg ml^–1. Transfer to a toxin-free medium resulted in a degree of recovery (up to 0.5 µg ml^–1). In the dose range 5–25 µg ml^–1, the levels of chlorophyll were drastically reduced, with no recovery following AFB₁ removal. Electron microscopy revealed a disruption of chloroplast structure as an early deteriorative event in AFB₁ exposure of callus cells. Protein levels were less sensitive, with inhibition manifested only in the high dose range. Shoot development occurred at all concentrations, but was significantly inhibited from 5 µg ml^–1 AFB₁. Recovery following toxin removal was minimal at these higher AFB₁ concentrations. The number of necrotic calli increased progressively from 5 µg ml^–1 as toxin levels increased.     

Non-mycorrhizal uptake of amino acids by roots of the alpine sedge Kobresia myosuroides: implications for the alpine nitrogen cycle

Non-mycorrhizal plants of the alpine sedge, Kobresia myosuroides, take up the amino acid glycine from nutrient solutions at greater rates than NO _inf3 ^sup- or NH _inf4 ^sup+ . The amino acids glutamate and proline were also taken up at high rates. Total plant biomass was twice as high after 4 months of growth on glycine, compared to NH₄NO₃, with significant increases in both root and leaf biomass. By taking advantage of differences in the ¹³C signature of air in the growth chamber and the glycine used for growth, a two-member mixing model was used to estimate that a significant amount of the glycine was taken up as intact molecules, enough to contribute 16% of the total carbon assimilation over a 4-month growing period. Glycine uptake was inhibited when roots were exposed to N₂ in place of air, and when the protonophore carbonyl cyanide m-chlorophenylhydrazone (CCCP) was added to the root solution. From these results it is concluded that glycine uptake occurs through active transport. Glycine uptake exhibited a Q₁₀ of 2.0 over the temperature range 5–15° C, with relatively high rates maintained at the lowest temperature measured (5° C). Roots of Kobreasia were not capable of taking up NH _inf4 ^sup+ at measureable rates. To our knowledge, this is the first report of a plant whose non-mycorrhizal roots cannot take up NH _inf4 ^sup+ . Measurements of three N fractions (NO _inf3 ^sup- , NH _inf4 ^sup+ , and total amino acids) in the soil pore water were made over two growing seasons in two Kobresia dry meadows using microlysimeters. At the West Knoll site, which is characterized by soils with average amounts of organic matter, the dominant forms of N in the soil pore water were NO _inf3 ^sup- and NH _inf4 ^sup+ (0–450 mol L^-1). Amino acid concentrations were generally less than 20 mol L^-1 at this site. At the East Knoll site, which is characterized by soils with higher than average amounts of organic matter, amino acids were generally present at higher concentrations (17–100 mol L^-1), compared to NO _inf3 ^sup- and NH _inf4 ^sup+ . The most abundant amino acids were glycine (10–100 mol L^-1), glutamate (5–70 mol L^-1), and late in the season cystein (5–15 mol L^-1). The results demonstrate that this sedge, which dominates dry meadow communities in many alpine ecosystems, is capable of taking up intact amino acids as a principal N source, and has access to high amino acid concentrations in certain alpine soils. Such uptake of organic N may accommodate plant N demands in the face of slow alpine N mineralization rates due to cold soil temperatures.     

Nitrogen cycling in lake sediments bioturbated by Chironomus plumosus larvae, under different degrees of oxygenation

Sediment cores containing different densities of Chironomus plumosus, ranging from 0 to 12 000 ind. m^–2, were incubated in the laboratory, with 100 and 39% O₂ saturation in the overlying water. Rates of O₂ uptake, and fluxes of the various inorganic N species were measured after addition of ¹⁵NO _inf3 ^su– to the overlying water. The animals enhanced O₂ and NO _inf3 ^su– uptake, due to irrigation. Denitrification of NO _inf3 ^su– coming from the overlying water (Dw) and dissimilatory NO _inf3 ^su– reduction to NH _inf4 ^sup+ (DNRA) represented 20–30 and 4–10% of the NO _inf3 ^su– uptake, respectively. Only 20–40% of the measured NH _inf4 ^sup+ effluxes corresponded to DNRA, the rest was probably due to animal excretion. Nitrite production, mostly from dissimilatory NO _inf3 ^sup– reduction, was detected at both 39 and 100% oxygen saturation. Higher rates of NO _inf2 ^su– production at the lower oxygen concentrations, were probably due to a thinner oxic layer, compared to fully oxygenated waters. The presence of Chironomus plumosus increased nitrification rates, relative to non-inhabited microcosms. However, nitrification rates were low compared to Dw, probably due to low numbers of nitrifiers in the sediment. At 39% oxygen saturation, rates of nitrification and denitrification of NO _inf3 ^su– generated within the sediment were not measurable.     

The influence of salinity on the kinetics of NH inf4 sup+ uptake in Spartina alterniflora

Summary The effects of short- and long-term exposure to a range in concentration of sea salts on the kinetics of NH _inf4 ^sup+ uptake by Spartina alterniflora were examined in a laboratory culture experiment. Long-term exposure to increasing salinity up to 50 g/L resulted in a progressive increase in the apparent K_m but did not significantly affect V_max (mean V_max=4.23±1.97 mole·g^–1·h^–1). The apparent K_m increased in a nonlinear fashion from a mean of 2.66±1.10 mole/L at a salinity of 5 g/L to a mean of 17.56±4.10 mole/L at a salinity of 50 g/L. These results suggest that the long-term effect of exposure to total salt concentrations within the range 5–50 g/L was a competitive inhibition of NH _inf4 ^sup+ uptake in S. alterniflora. No significant NH _inf4 ^sup+ uptake was observed in S. alterniflora exposed to 65 g/L sea salts. Short-term exposure to rapid changes in salinity significantly affected both V_max and K_m. Reduction of solution salinity from 35 to 5 g/L did not change V_max but reduced K_m by 71%. However, exposing plants grown at 5 g/L salinity to 35 resulted in an decrease in V_max of approximately 50%. Exposure of plants grown at 35 g/L to a total sea salt concentration of 50 g/L for 48h completely inhibited uptake of NH _inf4 ^sup+ . For both experiments, increasing salinity led to an increase in the apparent K_m similar to that found in response to long-term exposure. Our data are consistent with a conceptual model of changes in the productivity of S. alterniflora in the salt marsh as a function of environmental modification of NH _inf4 ^sup+ uptake kinetics.     

Impact of trichloroethylene and toluene on nitrogen cycling in soil.

The effects of trichloroethylene (TCE) and toluene on soil nitrogen-cycling activities were examined. Ammonium oxidation potential (AOP) was reduced after incubation with as little as 1 microgram of TCE ml-1, and the effects were generally greater when toluene was present and increased with longer exposure. Arginine ammonification potential and denitrification enzyme activity were constant regardless of TCE concentration or the presence of toluene, while nitrite oxidation potential (NOP) exhibited variable sensitivity. KCl-extractable ammonium levels increased dramatically after exposure to 30 and 60 micrograms of TCE ml-1 in the presence of toluene, whereas gamma-irradiated or sodium azide-treated soil incubated with the same concentrations of TCE and toluene showed no increase. Alfalfa-amended soils showed similar decreases in AOP and increases in extractable ammonium during incubation with 60 micrograms of TCE ml-1 and 20 micrograms of toluene ml-1, although most probable number estimates of the ammonium oxidizer population showed no difference between exposed and unexposed soil. AOP and extractable ammonium returned slowly to control levels after 28 days of incubation in the presence of TCE and toluene. Activity assays to which various TCE and toluene concentrations were added indicated that AOP and NOP were relatively more sensitive to these compounds than was arginine ammonification potential. These results indicate that the soil microbial populations responsible for nitrogen cycling exhibit different sensitivities to TCE and toluene and that they may be more susceptible to adverse effects than previously thought.     

The phytotoxicity of selected mycotoxins on mature,germinatingZea mays embryos

Mature maize (Zea mays) embryos were exposed to 5, 10 and 25 µg ml^–1 of deoxynivalenol (DON), zearalenone (ZEA), ochratoxin A (OA) and a mixture of zearalenone and deoxynivalenol (ZEA/DON) for 9 days. DON and the ZEA/DON combination were consistently more inhibitory of the measured parameters than either ZEA or OA. Based on the predicted additive values, it would appear that, in combination, ZEA and DON act synergistically to inhibit root and shoot growth. For ZEA alone, a concentration of 5 µg ml^–1 ZEA was generally inhibitory of root and shoot elongation and fresh mass accumulation, while at 10 and 25 µg ml^–1, this toxin had a stimulatory effect on these parameters. For OA, the measured effects on root and shoot growth at 5 and 25 µg ml^–1 were stimulatory, while at 10 µg ml^–1 OA, an inhibitory effect was observed. For all toxins, inhibitory/stimulatory effects were generally more marked for root parameters than for shoot elongation or mass.Abbreviations ADON acetyldeoxynivalenol - AFB₁ aflatoxin B₁ - DAS diacetyoxyscirpenol - DON deoxynivalenol - FB₁ fumonisin B₁ - FHB Fusaium head blight - MON moniliformin - NIV nivalenol - OA ochratoxin A - ZEA zearalenone     

Ammonium and nitrate as nitrogen sources in two Eriophorum species

Summary We compared ammonium and nitrate nutrition in Eriophorum scheuchzeri and E. vaginatum, two Alaskan sedges that are native to high- and low-fertility sites, respectively. When grown in solution culture, the two species were similar in their kinetics of NH _inf4 ^sup+ NO _inf3 ^sup- absorption: at nitrogen concentrations below 50 M, net NH _inf4 ^sup+ and NO _inf3 ^sup- were absorbed at similar rates, but at higher concentrations, net uptake of NO _inf3 ^sup- was significantly faster than that of NH _inf4 ^sup+ . The two species also showed similar abilities to assimilate NO _inf3 ^sup- . Growth of E. vaginatum under NO _inf3 ^sup- nutrition was only slightly less than that under NH _inf4 ^sup+ . The observed similarities between these species from contrasting edaphic habitats indicate that factors other than tissue-specific rates of nitrogen acquisition and assimilation may underlie local adaptation to soil N fertility. Moreover, the capacity of these species to exploit NO _inf3 ^sup- as a N source supports the view that NO _inf3 ^sup- availability may be significant even in wet, acidic, arctic soils.     

Effects of oxygen partial pressure and combined nitrogen on N2-fixation (C2H2) associated withZea mays and other gramineous species

Summary The objectives of this investigation were to determine the effects of oxygen partial pressure (pO₂) and combined nitrogen (NH ₄ ⁺ ) on rates of acetylene reduction (AR) associated with roots of intact corn, sorghum, and pearl millet plants. Soil-grown plants were carefully removed from soil and incubated hydroponically with the root system enclosed in a plastic cylinder; the tops were left exposed to ambient conditions. Oxygen concentrations around the root systems were controlled by sparging the nutrient solution with known quantities of O₂ in N₂. Ammonium nitrogen was added to the nutrient solution following establishment of AR rates to determine its effect on rates of N₂-fixation (AR). Substantial AR rates (0.1–1.5 mol C₂H₄ g dry wt^–1 h^–1) were associated with roots exposed to 0–2% O₂ (v/v) (0.0–2.02 kPa) in N₂ following at 12–24 h period of exposure to the reduced oxygen tension. Root systems exposed to air failed to demonstrate AR while those exposed to 100% N₂ showed lower activity than those at reduced pO₂ values. Addition of NH ₄ ⁺ (10–20 g N ml^–1 of nutrient solution) reduced AR by 75–90% within 24 h after addition. Oxygen uptake by roots exposed to low pO₂ was substantially reduced.     

A method for removal of toxic chromium using dialysis-sac cultures of a chromate-reducing strain of Enterobacter cloacae

Summary A method for removal of toxic hexavalent chromium (chlomate: CrO _inf4 ^sup2– ) was developed by use of dialysis-sac cultures of a chromate-reducing strain of Enterobacter cloacae (HO1). E. cloacae strain HO1 cells were put in dialysis (semipermeable membrane) sacs, and the sacs were submerged in water containing toxic CrO _inf4 ^sup2– . The dialysis sacs allowed CrO _inf4 ^sup2– to diffuse into the culture, and CrO _inf4 ^sup2– was reduced anaerobically in the dialysis sacs by the E. cloacae cells. Because reduced chromium readily formed insoluble chromium hydroxides in the dialysis sacs, the greater part of reduced chromium was unable to diffuse out through the semipermeable membrane. Thus the dialysis culture of E. cloacae strain HO1 could successfully remove toxic chromium from the surrounding water. If the initial concentration of CrO _inf4 ^sup2– was less than 4mM (208 ppm as chromium), about 90% of the total chromium could be removed from water by the described method. Offprint requests to: H. Ohtake     

Adaptive significance of nitrogen storage in Bistorta bistortoides,an alpine herb

Summary Studies were conducted to examine the importance of nitrogen storage to seasonal aboveground growth in the alpine herb Bistorta bistortoides. Stored reserves accounted for 60% of the total nitrogen allocated to the shoot during the growing season. The stored nitrogen was equally partitioned between preformed buds of the shoot and the roots/rhizome. Reliance on stored N was similar in populations of a 105-day growing season site and of a 75-day growing season site. Contrary to our initial hypothesis, stored nitrogen reserves were not used to extend the growing season of this species into the late-spring when soils are still cold, and saturated with snow-melt water. The time at which stored nitrogen was used to initiate shoot growth coincided with the time of root initiation, rapid soil warming, and near maximum soil concentrations of NO _inf3 ^sup– and NH _inf4 ^sup+ . Thus, nitrogen demand and soil nitrogen supply were both high at the same time. The importance of nitrogen storage in this species appeared to be in satisfying the high demand of simultaneous vegetative and reproductive growth during the early-growing season after soils thawed. The initiation of rapid leaf and inflorescence growth occurred in mid-June in both sites. The maximum pool size of shoot nitrogen (maximum nitrogen demand) occurred only 12 days later in the long season site, and 28 days later in the short season site. The early-season utilization of nitrogen stores allows plants of this species to initiate reproductive allocation at the same time vegetative tissues are exhibiting maximal growth rates. By releasing vegetative and reproductive growth from competition for nitrogen, seeds could mature early in the alpine growing season, before the frost probability sharply increases in mid-August.     

The Ethiopian Rift Valley lakes: chemical characteristics of a salinity-alkalinity series

The study on 10 lakes within the Ethiopian Rift Valley during March–May 1991 covered a range of conductivity (K₂₅) between 286 and 49100 µS cm^–1. HCO₃ ^– — CO _inf3 ^sup2– and Na⁺ were the dominant ions in all the lakes. Concentrations of K⁺, Cl^– and SO _inf4 ^sup2– increased with increasing salinity and alkalinity, whereas Ca²⁺ and Mg²⁺ decreased. Comparison of these data with previous records showed that a ten-fold dilution of total ionic concentration occurred over 30 years in Lake Metahara and about three-fold increase occurred over 65 years in Lake Abijata. Concentrations of soluble silica were generally high (12–222 mg SiO₂ 1^–1) and increased with increasing salinity, except for Lake Chamo which showed SiO₂ depletion (to < 1 mg SiO₂ 1 ^–1) over the past three decades.The relationship between ionic concentration and phosphorus was irregular although high phosphorus concentrations generally corresponded with increasing salinity. Fitting data to the Dillon & Rigler (1974) chlorophyll a — total phosphorus relationship suggested that lakes Zwai, Awassa and Chamo are phosphorus-limited, whereas others have surplus phosphorus.     

Ulva rigida (Ulvales,Chlorophyta) tank culture as biofilters for dissolved inorganic nitrogen from fishpond effluents

Ulva rigida was cultivated in 7501 tanks at different densities with direct and continuous inflow (at 2, 4, 8 and 12 volumes d^–1) of the effluents from a commercial marine fishpond (40 metric tonnes, Tm, of Sparus aurata, water exchange rate of 16 m³ Tm^–1) in order to assess the maximum and optimum dissolved inorganic nitrogen (DIN) uptake rate and the annual stability of the Ulva tank biofiltering system. Maximum yields (40 g DW m^–2 d^–1) were obtained at a density of 2.5 g FW 1^–1 and at a DIN inflow rate of 1.7 g DIN m^–2 d^–1. Maximum DIN uptake rates were obtained during summer (2.2 g DIN M^–2 d^–1), and minimum in winter (1.1 g DIN m^–2 d^–1) with a yearly average DIN uptake rate of 1.77 g DIN m^–2 d^–1 At yearly average DIN removal efficiency (2.0 g DIN m^–2 d^–1, if winter period is excluded), 153 m² of Ulva tank surface would be needed to recover 100% of the DIN produced by 1 Tm of fish.Abbreviations DIN= dissolved inorganic nitrogen (NH _inf4 ^sup+ + NO _inf3 ^sup– + NO _inf2 ^sup– ); - FW= fresh weight; - DW= dry weight; - PFD= photon flux density; - V= DIN uptake rate     

Diurnal variation in physical-chemical properties and primary production in the interconnected marine,mangrove and freshwater biotopes of Kakinada coast,Andhra Pradesh,India

Diurnal variation in hydrological variables and dissolved inorganic nutrients such as PO _inf4 ^sup3– -P, N O _inf2 ^sup– -N, NO _inf3 ^sup– -N and NH _inf4 ^sup+ -N were studied in three interconnected biotopes including freshwater, marine and mangrove brackish water of the Kakinada coastal zone, Andhra Pradesh. Samples were collected at intervals of 3 hours, for a period of 24 hours. In the marine environment salinity varied from 26 to 32 whereas in the mangrove waters it fluctuated from 12 to 20 and in both biotopes salinity showed bimodal type of oscillation. Dissolved oxygen content was high in the mangrove waters during day time but decreased rapidly during the night hours. In the marine environment PO_f4 ^p3–-P concentration varied from 0.345 to 1.195 g at l^–1, NO _inf3 ^sup– -N from 1.03 to 6.62 g at l^–1 and NO _inf2 ^sup– -N from 0.086 to 0.506 g at l^–1. The highest and the lowest concentrations of PO _inf4 ^sup3– -P, NO _inf3 ^sup– -N, NO _inf2 ^sup– -N recorded in the mangrove waters were 0.790 and 0.325 g at l^–1, 7.10 and 1.60 g at l^–1 and 0.278 and 0.060 g at l^–1, respectively. The concentration of PO _inf4 ^sup3– -P, NO _inf3 ^sup– -N and NO _inf2 ^sup– -N were high in the freshwater canal, the maximum and minimum values being 1.110 and 0.730 g at l^–1, 26.40 and 9.98 g at l^–1 and 0.520 and 0.252 g at l^–1 respectively. The concentration of ammonia was relatively high in the mangrove water. Gross and net primary production in the mangrove water was 4 times higher than in the marine biotope. There was no export of dissolved nutrients from the mangrove environment to the adjacent marine waters.