Survival and energy metabolism in an oxygen deficient environment. Field and laboratory studies on the bottom fauna from the profundal zone of Lake Esrom,Denmark

The three macroinvertebrate taxa, Potamothrix hammoniensis, Chironomus anthracinus and Pisidium spp. are permanent inhabitants of the regularly microxic/anoxic profundal zone in Lake Esrom. In situ and laboratory studies (10 °C) of metabolism (aerobic and anaerobic) and anaerobic survival in P. hammoniensis and Pisidium spp. are compared with previous results from C. anthracinus. The late summer microxic conditions in the lake lasts 2–2 months, during which the three taxa display metabolic and behavioral strategies in order to survive. All three are respiratory oxy-regulators with critical oxygen levels at 1 mg O₂ l^–1 (P. hammoniensis and Pisidium spp.) or 2–3 mg O₂ l^–1 (C. anthracinus). The lethal time (LD₅₀) in experimental anoxia follows a similar trend, with 150–170 days of survival in P. hammoniensis and Pisidium spp., compared to 2–5 weeks in C. anthracinus. The glycogen stores are almost (C. anthracinus) or fully exploited (P. hammoniensis and Pisidium spp.) during anaerobis and the animals finally enter a state of quiescence or dormancy. During the late phase of anoxia, their metabolism is down at (C. anthracinus) or below (P. hammoniensis and Pisidium spp.) 1% of normoxic metabolism. The populations in the lake behave rather similar in so far that the energy gain from anaerobic degradation of glycogen maximizes 1% of normoxic conditions regardless of species. Also, in Pisidium this appears to be the only energy source during dormancy. However, as previously presented in case of C. anthracinus, P. hammoniensis maintain a partly aerobic metabolism constituting 44% of normoxia during the microxic period, compared to the 12–19% obtained by C. anthracinus. It is thus demonstrated that P. hammoniensis and Pisidium spp. possess a remarkable ability to survive in situ severe oxygen depletion. P. hammoniensis can benefit from the presence of merely traces of oxygen, whereas C. anthracinus with poorer anaerobic survival is strongly dependent on minute oxygen supplies.     

Secondary production of Rhyacophila minora,Ameletus sp., and Isonychia bicolor from streams of low and circumneutral pH in the Appalachian Mountains of West Virginia

We estimated the secondary production of Rhyacophila minora, Ameletus sp., and Isonychia bicolor in three acidic streams and one circumneutral stream in Randolph County, West Virginia. Quantitative benthic samples were collected monthly from these second-order streams from November 1990 to October 1991. Mean pH values in the acidic streams were 4.5, 4.8, and 4.8, and mean pH in the circumneutral stream was 6.7. Production estimates for Rhyacophia minora in the acidic streams were 49.6, 19.2, and 15.8 mg m^–2 y^–1. Production of R. minora in the circumneutral stream was 1.0 mg m^–2 y^–1. Ameletus sp. production estimates for the acidic streams were 144.8, 176.8, and 208.3 mg m^–2 y^–1. Ameletus sp. production in the circumneutral stream was 7.4 mg m^–2 y^–1. Secondary production of I. bicolor in the circumneutral stream was 116.6 mg m^–2 y^–1. No Isonychia were collected from the acidic streams. The higher production of R. minora and Ameletus sp. in the acidic streams may be associated with differences in macroinvertebrate community structure.     

Iron accumulation on the cell wall of the aquatic moss Drepanocladus fluitans in an acid lake at pH 3.4–3.8

Iron accumulation was studied in shoots of the aquatic moss Drepanocladus fluitans (Hedw.) Warnst collected from an acid lake and stream. The concentration of iron in the shoots of the moss from Lake Usoriko (pH 3.4–3.8) increased from the tip toward the base and ranged from 0.07 to 10% on a dry weight basis. The iron concentration in the lake water was 0.15 mg 1^–1. In contrast, iron concentration in the shoots of D. fluitans from Kashiranashigawa stream (pH 4.2–4.7), one of the streams flowing into Lake Usoriko, was only 0.02 mg g^–1 at the shoot tip and 0.3% at the shoot base, while that in the stream water was <0.02 mg 1^–1. Transmission electron microscopy using a X-ray microanalyzer (TEM-XMA) study revealed accumulation of needle-like iron crystals on the cell wall and decomposed cell components. In addition, many rod-type bacteria were found in the accumulated iron deposits.The accumulation of iron in the shoots of D. fluitans is due to two processes: biological accumulation of essential iron dissolved in acid water, and abiological crystal growth on the surface of organic particulate material including the cell wall.     

Uptake of lead,cadmium and zinc by the fairy shrimp,Branchinecta longiantenna (Crustacea: Anostraca)

Individuals of the fairy shrimp, Branchinecta longiantenna, were subjected to 5 concentrations (0.1 to 15 mg l^–1) of Pb in diluted habitat water at 13 °C. Lead concentrations (mg kg^–1 wet weight) in the animals were determined at 2-day intervals by digestion in nitric acid followed by atomic absorption analysis. The shrimp were also subjected to 0.1 mg l^–1 media of Cd and Zn, separately.Uptake rates by the fairy shrimp for the three metal ions at 0.1 mg l^–1 were: 0.111, 0.0885, and 0.0460 mg kg^–1 day^–1 for Zn, Pb, and Cd, respectively. After 2 days in 1.0 mg l^–1 Cd or Zn, the animals expired; but they surviced for 8 days in a 10 mg l^–1 Pb medium and for 2 days in 25 mg l^–1 Pb. Lead uptake demonstrated a linear dependence on the Pb concentration in the media.Shrimp survived at much higher tissue accumulations of Pb compared to Zn and Cd. Estimated lethal doses were 20, 1.2–2.4, and 0.4–1.4 mg kg^–1 wet weight for Pb, Zn, and Cd, respectively. Pb was found to be at much lower concentration than Cd or Zn in the natural pond water but between Cd and Zn levels in the sediment. Thus Cd and Zn probably present a greater threat to B. longiantenna than Pb, although Pb may be in higher concentration in the environment.Contribution 47, Laboratory of Ecology, The Claremont Colleges, Claremont, CA 91711, USA. Send reprint requests to Clyde Eriksen.     

Environmental effects on growth and biochemical composition ofNitzschia inconspicua Grunow

The effects of nitrate and silicate levels, and carbon source on growth, biochemical composition and fatty acid composition ofNitzschia inconspicua were investigated using batch cultures. Within the range of silicate levels supplied (8.8–176 M), no marked variations in growth trend, biochemical composition or fatty acid composition were shown. Biomass at stationary phase, ranging from 64–66 mg ash-free dry weight (AFDW) L^–1, and specific growth rate () based on chlorophylla (0.41–0.50 d^–1) of the cultures grown within 0.3–3.0 mM NaNO₃ were not significantly different. Cultures supplemented with glucose (0.1 % w/v), acetate (0.1 % w/v) or 5% CO₂ attained higher biomass (85, 85, 97 mg AFDW L^–1) than the control which was grown in synthetic seawater and agitated by magnetic stirring. Cells grown at <3.0 mM NaNO₃ contained higher carbohydrate contents (14.8–21.5% AFDW) than those grown at 3.0 mM (4.0% AFDW). Lipid content increased at the expense of proteins in cells aerated with 5% CO₂. The dominant fatty acids, 16:0 and 16:1, ranged from 35.7–45.0% and 36.4–45.4% total fatty acids (TFA), respectively, while the relative proportions of 20:4 (n-6) and 20:5 (n-3) ranged from 1.7–5.4% and 3.4–5.9% TFA respectively. Cultures aerated with 5% CO₂ attained the highest biomass (97 mg AFDW L^–1) and yield of 20:5 (n-3) (0.34 mg L^–1).     

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.     

Long-term effects of metals in sewage sludge on soils,microorganisms and plants

Summary This paper reviews the evidence for impacts of metals on the growth of selected plants and on the effects of metals on soil microbial activity and soil fertility in the long-term. Less is known about adverse long-term effects of metals on soil microorganisms than on crop yields and metal uptake. This is not surprising, since the effects of metals added to soils in sewage sludge are difficult to assess, and few long-term experiments exist. Controlled field experiments with sewage sludges exist in the UK, Sweden, Germany and the USA and the data presented here are from these long-term field experiments only. Microbial activity and populations of cyanobacteria,Rhizobium leguminosarum bv.trifolii, mycorrhizae and the total microbial biomass have been adversely affected by metal concentrations which, in some cases, are below the European Community's maximum allowable concentration limits for metals in sludge-treated soils. For example, N₂-fixation by free living heterotrophic bacteria was found to be inhibited at soil metal concentrations of (mg kg^–1): 127 Zn, 37 Cu, 21 Ni, 3.4 Cd, 52 Cr and 71 Pb. N₂-fixation by free-living cyanobacteria was reduced by 50% at metal concentrations of (mg kg^–1): 114 Zn, 33 Cu, 17 Ni, 2.9 Cd, 80 Cr and 40 Pb.Rhizobium leguminosarum bv.trifolii numbers decreased by several orders of magnitude at soil metal concentrations of (mg kg^–1): 130–200 Zn, 27–48 Cu, 11–15 Ni, and 0.8–1.0 Cd. Soil texture and pH were found to influence the concentrations at which toxicity occurred to both microorganisms and plants. Higher pH, and increased contents of clay and organic carbon reduced metal toxicity considerably. The evidence suggests that adverse effects on soil microbial parameters were generally found at surpringly modest concentrations of metals in soils. It is concluded that prevention of adverse effects on soil microbial processes and ultimately soil fertility, should be a factor which influences soil protection legislation.     

Seasonal changes in composition and biomass of epilithic algal floras of a chalk stream and a soft water stream with estimates of production

Microscopic epilithic algae in the River Itchen at Otterbourne near Southampton and in the Ober Water in the New Forest were studied during 1984 and 1985. The River Itchen rises from chalk springs and has a steady pH near 8.2 and a mean alkalinity of 236 mg HCO₃ 1^–1; at the study site the river is about 16 m wide and 20 cm deep, with a mean flow rate of 0.33 m s^–1 and a discharge ranging through the year between 0.34 and 2.46 m³ s^–1. The Ober Water, which drains sands and gravels, has a pH between 6.9 and 7.2 and a mean alkalinity of about 50 mg HCO₃ 1^–1; at the study site it is about 6 m wide, with a mean flow rate of 0.27 m s^–1 and a discharge ranging through the year between 0.08 and 1.0 m³ s^–1.Epilithic algae removed from the pebbles that form the major part of the beds of both streams show seasonal changes in abundance and composition. Diatoms peaked in April/May and dominate the epilithic flora in both streams, comprising 70–95% of all algal cells; highest numbers of chlorophytes occurred in summer and cyanophytes increased in autumn. The species composition of the epilithic flora in the two streams was different, as was the population density; algal cell numbers ranged between 500 and 7000 cells mm^–2 of stream floor in the River Itchen and between 8 and 320 cells mm^–2 of stream floor in the Ober Water. The chlorophyll a content of epilithic algae in the River Itchen ranged between 115 and 415 mg m^–2 of stream floor, representing an annual mean biomass of about 8 g m^–2, whereas in the Ober Water a chlorophyll a content of 2.2 to 44 mg m^–2 of stream floor was found, representing an annual mean biomass of about 1 g m^–2. Cautious estimates of the annual production of epilithic algae in these streams suggest a value of about 600 g organic dry weight m^–2 in the River Itchen and about 75 g m^–2 in the Ober Water.     

In situ phosphorus release experiments in the Warnow River (Mecklenburg,northern Germany)

Results are presented of in situ benthic phosphorus release experiments in an undercut bank of an impounded river. Due to high sedimentation of phytoplankton biomass high oxygen consumption rates between 259.4 and 947.0 mg O₂ m^–2 d^–1 developed, leading to almost anaerobic conditions and phosphorus releases between 175.2 and 236.3 mgP m^–2 d^–1 over a period of 18 days.In a second series of experiments the water column overlying the sediment was aerated, resulting in much lower P release rates (1.1 to 32.9 mgP m^–2 d^–1) over a period of 30 days. The influence of pH and nitrate was studied by adjusting pH and adding NO₃ ^– to the overlying water. Increasing pH positively affected P release rates and enhanced NO₃ ^– levels led to an increase of benthic P release, too.     

Joint and single toxicity of Cd and Fe related to metal uptake in the mayfly Leptophlebia marginata (L.) (Insecta)

The toxic effects of Cd and Fe on the mayfly Leptophlebia marginata were tested during single and joint exposure to the metals. Data on uptake and localization of the metals were related to the following biological parameters: survival, food consumption (% gut contents) and activity (escape from prodding).The uptake of Cd by L. marginata was significantly reduced by the presence of Fe (p<0.0005).Fe²⁺- and Fe³⁺-crusts on the gills, body surface and on the gut membrane precipitated when the mayflies were exposed to either Fe alone or to Fe and Cd. This caused decreased food consumption by the mayflies.In the pigments of the eyes and the cuticle Fe²⁺ was found.Exposure to Cd led to disturbances in Cl^– and K⁺ ion balance, which were ameliorated by additional Fe-exposure due to co-precipitation processes.Exposure to Cd caused an increase in the concentrations of S and P in the mayflies.Whereas Fe caused sublethal effects (food consumption) without being taken up into the organism. Cd caused lethal effects (inactivity, death) due to disturbances of the ion balance at the membranes.     

Dynamics of phosphorus fractions during fallow with natural vegetation and planted Pueraria phaseoloides in south-western Nigeria

A study was conducted in 1998 and 1999 on a long-term fallow management trial, established in 1989 at the International Institute of Tropical Agriculture (IITA), Ibadan, in the derived savanna of southwestern Nigeria, to quantify P fractions under natural fallow (NF) and a Pueraria cover crop fallow. Plots with previous 1:1, 1:2, and 1:3 crop/fallow ratios before reverting to fallow in either 1998 or 1999 were considered. Biomass accumulation under the two fallow types was comparable and increased linearly with fallow age, reaching slightly above 7 t dry matter ha^–1 after 8 months of fallow. Phosphorus accumulation in the fallow vegetation ranged from 2.1 – 9.1 kg ha^–1 for natural fallow (NF) and from 1.5 – 6.6 kg ha^–1 for Pueraria. Magnesium was also higher under NF (9.1 – 21 kg ha^–1) than under Pueraria (4.4 – 13 kg ha^–1), whereas N, Ca, and K contents were higher in Pueraria biomass than under NF at 1 year after fallow. Pueraria fallow tended to lower soil pH compared with NF. However, plots with less frequent cropping (1:3 crop/fallow ratio) did not have significantly different pH irrespective of the fallow vegetation type. Olsen extractable soil P increased as fallow length increased irrespective of the fallow system and previous crop/fallow ratio. For example, under NF (0–5 cm depth, 1:1 crop/fallow ratio in1998) Olsen P increased from 12 mg kg^–1 to 17 mg kg^–1 after 1 year of fallow and under Pueraria, it increased from 8 mg kg^–1 to 15 mg kg^–1. Fallow type and previous crop/fallow ratio had no significant and consistent effects on soil P fractions. However, NaOH- and concentrated HCl- extractable organic P fractions increased with fallow length. In 1998, under NF, NaOH- extractable organic P increased from 12 to 21 mg kg^–1 (1:1 crop/fallow ratio) and from 10 to 19 mg kg^–1 for both 1:2 and 1:3 crop/fallow ratio. HCl- extractable organic P increased from 11 to 30 mg kg^–1 (1:1 crop/fallow ratio), from 13 to 27 mg kg^–1 (1:2 crop/fallow ratio) and from 18 to 35 mg kg^–1 (1:3 crop/fallow ratio). Similar trend was observed under Pueraria fallow. These results suggest that P was reallocated to non-readily available organic P fractions irrespective of fallow type and previous land use. These organic P fractions, which are usually more stable, reflect the overall change in soil organic P levels when the soil was stressed by cultivation and then reverted to fallow. These pools may thus represent an active reservoir (source and sink) of P in shifting cultivation under tropical conditions without inorganic fertilizer application.     

Experimental and mathematical simulation of plant growth promoting rhizobacteria and plant interaction under cadmium stress

Bacterial inoculants of the commercially available plant growth promoting rhizobacteria (PGPR) Arthrobacter mysorens 7, Flavobacterium sp. L30, and Klebsiella mobilis CIAM 880 were selected to obtain ecologically safe barley crop production on cadmium (Cd) polluted soils. All the PGPR immobilized 24–68% soluble cadmium from soil suspension. A. mysorens 7 and K. mobilis CIAM 880 were highly resistant to Cd and grew in up to 1 and 3 mmol CdCl₂ on DAS medium respectively. All PGPR were able to fix nitrogen (276–1014 nmol mg^–1 bacterial DW) and to produce indole acetic acid (IAA) (126–330 nmol mg^–1 bacterial DW) or ethylene (4.6–13.5 nmol bacterial DW). All the PGPR actively colonized barley root system and rhizosphere and significantly stimulated root elongation of barley seedlings (up to 25%), growing on soil containing 5 or 15 mg Cd kg^–1 of soil. Created in the simulation mathematical model confirms our hypothesis that PGPR beneficial effect on barley growing under Cd-stress is a complex process. One of mechanisms underlying this effect might be increase of bacterial migration from rhizoplane to rhizosphere, where PGPR bind soluble free Cd ions in biologically unavailable complex forms. Among the studied PGPR K. mobilis CIAM 880 was the most effective inoculant. Inoculation with K. mobilis CIAM 880 of barley plants growing on Cd contaminated soil (5 mg Cd kg^–1 of soil) under field conditions increased by 120% grain yield and 2-fold decreased Cd content in barley grain. The results suggest that the using K. mobilis CIAM 880 is an effective way to increase the plant yield on poor and polluted areas.     

<Emphasis Type="Italic">Cannabis sativa</Emphasis> L. growing on heavy metal contaminated soil: growth,cadmium uptake and photosynthesis

The effects of different cadmium concentrations [17 mg(Cd) kg⁻¹(soil) and 72 mg(Cd) kg^{− 1}(soil)] on Cannabis sativa L. growth and photosynthesis were examined. Hemp roots showed a high tolerance to Cd, i.e. more than 800 mg(Cd) kg⁻¹(d.m.) in roots had no major effect on hemp growth, whereas in leaves and stems concentrations of 50 – 100 mg(Cd) kg⁻¹(d.m.) had a strong effect on plant viability and vitality. For control of heavy metal uptake and xylem loading in hemp roots, the soil pH plays a central role. Photosynthetic performance and regulation of light energy consumption were analysed using chlorophyll fluorescence analysis. Seasonal changes in photosynthetic performance were visible in control plants and plants growing on soil with 17 mg(Cd) kg⁻¹(soil). Energy distribution in photosystem 2 is regulated in low and high energy phases that allow optimal use of light and protect photosystem 2 from overexcitation, respectively. Photosynthesis and energy dissipation were negatively influenced by 72 mg(Cd) kg⁻¹(soil). Cd had detrimental effects on chlorophyll synthesis, water splitting apparatus, reaction centre, antenna and energy distribution of PS 2. Under moderate cadmium concentrations, i.e. 17 mg(Cd) kg⁻¹(soil), hemp could preserve growth as well as the photosynthesis apparatus, and long-term acclimation to chronically Cd stress occurred.     

Studies on the aquatic hyphomycetes of a sulfur spring in the Western Ghats, India

Studies on the occurrence of aquatic hyphomycetes were carried out in Panekal sulfur spring in the Western Ghats, India by incubation of leaf litter and analysis of natural foam and of induced foam. Sampling was done once every three months over a period of two years from September 1989 to June 1991. The temperature, pH, dissolved oxygen, and sulfide content of water were also measured. No fungi were observed within the spring, whereas 16 species belonging to 13 genera were isolated from two outflow sites of the stream. The percent frequency of Triscelophorus monosporus was high (24.0%). The temperature of water in the spring ranged between 30.0 and 38.5°C and the sulfide content between 3.2 and 4.3 mg 1^–1. Studies showed that sulfide water (4.0 mg 1^–1). from the spring inhibited the growth of the colonies of Dactylella aquatica, Phalangispora constricta, Tetracladium setigerum, Vermispora cauveriana, and Wiesneriomyces laurinus. When the leaves colonized by aquatic hyphomycetes were incubated at different temperatures in sulfur-spring water and stream water separately, sporulation was not observed in any of the fungi at and above 35°C except Phalangispora constricta, which could sporulate at 35°C. At lower temperatures (15–30°C) relatively fewer species were found to sporulate in sulfur-spring water than in stream water. Correspondence to: K.M. Kaveriappa     

Growth and betacyanin production by hairy roots of Beta vulgaris in airlift bioreactors

Hairy roots of red beet (Beta vulgaris L.) were cultivated in different types of airlift bioreactors (cone, balloon, bulb, drum and column bioreactors of 5 l capacity and containing 3 l of half strength Murashige & Skoog medium). The cone type of airlift bioreactor gave the highest biomass of hairy roots and betacyanin accumulation. Betacyanin accumulation was 27 mg g^–1 dry wt in cultures aerated at 0.3 vvm. Light irradiation of 20 mol m^–2 s^–1 promoted hairy root growth but optimum betacyanin (34 mg g^–1 dry wt) accumulation was with the cultures grown under 60 mol m^–2 s^–1.     

The relative exclusion of zinc and iron from rice grain in relation to rice grain cadmium as compared to soybean: Implications for human health

During 2000–2002, diagnostic rice and soybean plant samples and concurrent soil samples were collected from cultivated fields within a geo-physically unique Zn/Cd co-contaminated location in Thailand. For the fields sampled, aqua regia-digested Zn and Cd concentrations ranged from 2.91–284 and 254–8036 mg kg^–1, respectively. In comparison, rice and soybean Cd concentrations ranged from 0.02–5.00 and 1.08–1.71 mg kg^–1, respectively. Further, the results indicate that grain Cd, Zn and Fe concentrations are in the order rice^Gr=soybean^Gr, soybean^Gr>rice^Gr, soybean^Gr>rice^Gr, respectively. However, and critically from a human health perspective, Cd:Zn and Cd:Fe ratios are in the order rice^Gr>soybean^Gr. In addition, the rice^Gr Cd:Fe ratio is an order of magnitude higher than that determined for soybean^Gr. The results of this study, clearly demonstrate that compared to rice stalk (rice^St) and rice leaf (rice^L), rice^Gr accumulates comparatively higher Cd than Zn and Fe thus resulting in the high rice^Gr Cd:Zn and Cd:Fe ratios. This is in direct contrast to the results observed for soybean.     

Growth of the toxic dinoflagellate Alexandrium minutum (Dinophyceae) using high biomass culture systems

Toxic dinoflagellates are important in natural ecosystems and are ofglobal economic significance because of the impact of toxic blooms onaquaculture and human health. Both the organisms and the toxins they producehave potential for biotechnology applications. We investigated autotrophicgrowth of a toxic dinoflagellate, Alexandrium minutum, inthree different high biomass culture systems, assessing growth, productivityandtoxin production. The systems used were: aerated and non-aerated2-L Erlenmeyer flasks; 0.5-L glass aerated tubes; anda 4-L laboratory scale alveolar panel photobioreactor. A range ofindicators was used to assess growth in these systems. Alexandriumminutum grew well in all culture conditions investigated, with amarked increase in both biomass and productivity in response to aeration. Thehighest cell concentration (4.9 × 10⁵ cellsmL^–1) and productivity (2.6 ×10⁴cells mL^–1d^–1) was achieved inthe aerated glass culture tubes. Stable growth of A.minutum in the laboratory scale alveolar panel photobioreactor wasmaintained over a period of five months, with a maximum cell concentration of3.3 × 10⁵ cells mL^–1, a meanproductivity of 1.4 × 10⁴ cells mL^–1d^–1, and toxin production of approximately 20g L^–1 d^–1 with weeklyharvesting.     

Hydrolysis of settleable substrate in domestic sewage

The hydrolysis of settleable substrate in domestic sewage was evaluated using its O₂ utilization rate profile generated in an aerated batch reactor. The hydrolysis rate coefficient was 1.2 d^–1, significantly lower than 3.8 d^–1 and 1.9 d^–1 characterizing soluble and suspended slowly biodegradable fractions. The settled portion of the sewage incorporated an active biomass fraction of 1560 mg COD l^–1 that needed to be accounted for in the hydrolysis kinetics. The texture of the biomass/settled substrate mixture and the gradual hydrolysis of the particulate substrate within the floc structure were examined by microscopic analysis.     

Effects of soil cadmium on Pinus sylvestris L. seedlings

The effects of Cd on the growth and distribution of Cd and mineral nutrients within plant tissues were investigated for Pinus sylvestris L. seedlings grown in mineral forest soil with increasing levels of Cd addition (0–100 mg kg^–1). Approximately 20% of added Cd was found to be extractable from sandy loam forest soil. Root growth was less affected by Cd than shoot growth, which showed a significant reduction in the 100 mg Cd kg^–1 treatment. Cadmium accumulated in roots up to 325 mg kg^–1. Decreased concentrations of K in needles and Ca in stems with increasing Cd levels suggest a disturbance of mineral nutrition as a result of Cd addition.     

Cadmium-Induced Changes in Chloroplast Lipids and Photosystem Activities in Barley Plants

Fatty acid content and composition of chloroplast membranes, ethylene production associated with thylakoid lipids degradation as well as photosynthetic electron transport involving photosystems 1 and 2 were used to determine the effects of increasing Cd concentrations in the growth medium [0, 14, 28, and 42 mg (Cd) kg^–1(sand)] on the photosynthetic performance of barley plants (H. vulgare L., cv. CE9704). High concentrations of Cd triggered serious disturbances of the chloroplast membranes. Ethylene production increased whereas a drop of 18:3 fatty acid content occurred, indicating that Cd mediates lipid peroxidation in the thylakoids. The enhanced ethylene production could be used as an early indicator of Cd-induced membrane degradation, yet at very high concentration (42 mg kg^–1) Cd decreased ethylene production.