Stream periphyton response to grazing and changes in phosphorus concentration

Grazing by the large caddisfly larva, Dicosmoecus gilvipes (Trichoptera; Limnephilidae), drastically reduced periphyton biomass in laboratory channels at a current velocity of 20 cm s^–1. Reduction in biomass as chl a and AFDW ranged from 88 to 93% and 82 to 85%, respectively. On average, grazing rate increased with in-channel SRP (soluble reactive phosphorus) content from 6 to 10 µg 1^–1. Grazing rates averaged 25.9–29.3 µg chl a m^–2 d^–1 and 10.8–12.2 µg chl a mg^–1 d^–1 based on area and grazer biomass, respectively, with most variability among treatments being due to the grazing effect. Grazing tended to shift the algal community increasingly to filamentous blue-green algae regardless of enrichment. After three weeks, Phormidium comprised over 61% of the community in grazed treatments but only 35% in ungrazed treatments. The stalked diatom Gomphonema comprised only 4% of the grazed community, but 11% in the three ungrazed channels with similar values for Scenedesmus. A model that includes grazing was calibrated to the data and produced a reasonable expectation of periphyton biomass over a range in SRP concentrations. While the model with constant grazer abundance predicts a gradually increasing grazed biomass as SRP increases, grazer production in natural streams may actually increase to accommodate the increased food production.     

Primary production in Rattlesnake Springs,a cold desert spring-stream

Primary productivity and respiration were measured in Rattlesnake Springs, Washington, using the upstream-downstream diel pH-CO₂ curve and harvest methods.Daily P_g and P_n rates averaged 8.7 and 0.9, 0.6 and 0.3, and 9.3 and 1.2 g C m^–2 d^–1 for periphyton, watercress, and total community, respectively. Average photosynthetic efficiencies (%, P _n Lt^–1) were approximately 0.22 and 0.07 for periphyton and watercress, respectively. Annual community P_g was 2 700 g C m^–2 a^–1 and was highest for periphyton (2 526 g C m^–2 a^–1). Periphyton P_n (356 g C m^–2 a^–1) exceeded that of watercress (87 g C m^–2 a^–1). Community R was 2 257 g C m^–2 a^–1, and was highest for periphyton (2 170 g C m² a^–1).Desert streams appear to be enigmas in terms of their relationship between autotrophy and heterotrophy and their ability to be net importers or exporters of organic matter. The fact that they can be autotrophic and net importers of organic matter is probably related to the characteristic flash-flooding of desert streams, and emphasizes the necessity of examining these systems over more than a single annual cycle.     

Effects of nutrient (N, P, C) enrichment upon periphyton standing crop, species composition and primary production in an oligotrophic softwater lake

SUMMARY. 1. The effects of nutrient addition upon algal periphyton standing crop and benthic community metabolism were investigated in Lake Lacawac, Pennsylvania. Nutrient-diffusing flower pot substrates were filled with combinations of P (0.015 mol Na₂HPO₄), N (0.15molNaNO₃) and carbon as glucose (0.015mol (LG) or 0.15mol (HG)) or 0.58 mol NaHCO₃ (C). Fifty-two pots representing ten treatments were placed in the lake on 5 May 1985 and sampled after 32-38 days. 2. Maximum chlorophyll-a values of 23.82μgcm^?2 and 29.72μgcm^?2 were obtained on NPC and NPHG pots respectively, compared to 0.82μgcm^?2 on control pots. Algal growth was not enhanced unless N and either organic or inorganic carbon were supplied. Ash Free Dry Mass was especially high on NPHG pots. 3. Gross production, net production and community respiration were assessed with light-dark chambers affixed to the pots using microwinkler measurements of dissolved oxygen. Highest production rates were obtained on NC and NPC pots. Pots with NPLG and NPHG also showed significant increases in gross production compared to control levels (P < 0.01). Specific production (=gross production/chlorophyll-a) was significantly related to standing crop as chlorophylls (P < 0.001), alkalinity in the chambers (P < 0.00l) and light (P < 0. 05), but not to N or P supplied by the pots. 4. The periphyton community was dominated by Chlorophyta, which averaged 86.1% of total algal biovolume. Enrichment with NC and NPC significantly enhanced the growth of three Chlorophyceae (Stigeoclonium, Scenedesmus and an unidentified coccoid) and two Cryptophyceae (Cryptomonas. Rhodomonas) (all P < 0.05). In contrast, the filamentous green alga Mougeotia dominated other treatments, but declined significantly with NPC enrichment (P < 0.05). Addition of NPHG stimulated an 8-fold increase in total biovolume and significant increases in growth of Cryptomonas, Rhodomonas and Euglena (all P < 0.05).     

Field observations on nitrogen catch crops. III. Transfer of nitrogen to the succeeding main crop

In temperate climates with a precipitation surplus during autumn and winter, nitrogen (N) catch crops can help to reduce nitrogen losses from cropping systems by absorbing nitrogen from the soil and transfer it to a following main crop. In two field experiments the catch crop species winter rye (Secale cereale) and forage rape (Brassica napus ssp. oleifera (Metzg.) Sinsk) or oil radish (Raphanus sativus spp. oleiferus (DC.) Metzg.) were planted end of August and 3 weeks later with a non-limiting supply of N and zero-N controls. In the next spring catch crops were incorporated into the soil. In Expt 1, N transfer was measured as (i) the N uptake of a potato test crop, grown with zero and 12.5 g m^–2 N applied, and (ii) the increase in soil mineral N (0–30 cm) in uncropped soil covered with polythene film. In Expt 2, N transfer was measured as the increase in soil mineral N in covered cylinders placed in uncropped soil (in situ incubation). Subsidiary laboratory incubations were performed in Expt 2. In Expt 1, the apparent recovery in potato of fertilizer N (R _f) was 0.56. The recovery in potato of N mineralized from 'native' N pools other than catch crop material (R _n) ranged from 0.43 to 0.51, depending on the value assumed for the depth of N extraction by potato roots. The average recovery in potato of incorporated catch crop N (R _c) was 0.34. Expressed as `fertilizer N replacement factor' (F _r) the latter was 0.61 (i.e. 1 kg of N in catch crop material counts for 0.61 kg fertilizer N). Under the film in Expt 1 the fraction net mineralization of incorporated catch crop N (M _n) was 0.36 on August 11 and 0.43 on October 18. In Expt 2, the average value of M _n was 0.31, which was lower than in Expt 1 and probably associated with the drier soil in Expt 2. In the laboratory incubations (20°C) M _n showed values up to 0.54 after 84 days with the largest rates of change in mineralization occuring early after the start of the incubation. In conjunction with literature data it is concluded that cultivation of nitrogen catch crops shows promise as a means to reduce N input and N losses in temperate climates with wet winters.     

Comparative study of periphyton community structure in long and short-hydroperiod Everglades marshes

The Florida Everglades is a mosaic of short and long-hydroperiod marshes that differ in the depth, duration, and timing of inundation. Algae are important primary producers in widespread Everglades’ periphyton mats, but relationships of algal production and community structure to hydrologic variability are poorly understood. We quantified differences in algal biomass and community structure between periphyton mats in 5 short and 6 long-hydroperiod marshes in Everglades National Park (ENP) in October 2000. We related differences to water depth and total phosphorus (TP) concentration in the water, periphyton and soils. Long and short-hydroperiod marshes differed in water depth (73 cm vs. 13 cm), periphyton TP concentrations (172μg g⁻¹ vs. 107 μg g⁻¹, respectively) and soil TP (284 μg g⁻¹ vs. 145 μg g⁻¹). Periphyton was abundant in both marshes, with short-hydroperiod sites having greater biomass than long-hydroperiod sites (2936 vs. 575 grams ash-free dry mass m⁻²). A total of 156 algal taxa were identified and separated into diatom (68 species from 21 genera) and “soft algae” (88 non-diatom species from 47 genera) categories for further analyses. Although diatom total abundance was greater in long-hydroperiod mats, diatom species richness was significantly greater in short- hydroperiod periphyton mats (62 vs. 47 diatom taxa). Soft algal species richness was greater in long-hydroperiod sites (81 vs. 67 soft algae taxa). Relative abundances of individual taxa were significantly different among the two site types, with soft algal distributions being driven by water depth, and diatom distributions by water depth and TP concentration in the water and periphyton. Periphyton communities differ between short and long-hydroperiod marshes, but because they share many taxa, alterations in hydroperiod could rapidly promote the alternate community. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Denitrification in the periphyton associated with plant shoots and in the sediment of a wetland system supplied with sewage treatment plant effluent

Seasonal variation in denitrification and major factors controlling this process were determined in sediment, microbial communities attached to plant shoots (periphyton) and in the water of a Phragmites and an Elodea-dominated stand of a constructed wetland system between May 1997 and February 1998. The wetland was supplied with effluent from a sewage treatment plant. The denitrification rate in periphyton on plants shoots (expressed per shoot area) was always considerably higher than in the sediment and varied with the chlorophyll-a content of the periphyton in the course of the year. The algae in the periphyton provided attachment surfaces and probably also organic compounds to the denitrifying bacteria. Decreases in periphyton biomass and denitrification rate in the Phragmites and Elodea-dominated stands during the growing season were associated with enhanced shading by Phragmites shoots or a floating layer of macro-algae and Lemna spp., respectively. Light availability and the denitrification rate of periphyton increased again after the Phragmites shoots were cut in October. Nitrate appeared to limit the denitrification rate in the sediment. Periphyton denitrification rates were mostly lower on Elodea shoots than on Phragmites shoots, in spite of the higher living algal biomass on Elodea shoots. This difference was associated with lower nitrate concentrations in the Elodea-dominated stand. In the two stands, the daily denitrification rates in periphyton on shoots of Phragmites australis (44.4–121 mg N m^–2 stand area d^–1) and Elodea nuttallii (14.8–33.1 mg N m^–2 d^–1) were clearly more important than rates in the sediment (0.5–25.5 mg N m^–2 d^–1) or the water (0.4–3.9 mg N m^–2 d^–1). The presence of few bacteria attachment sites or low organic carbon availability possibly resulted in low denitrification rates in the water. Denitrification appeared to be a major process in nitrate removal from the through-flowing water in this wetland system.     

Phosphatase activity as an early warning indicator of wetland eutrophication: problems and prospects

A phosphorus (P) loading experiment conducted in the oligotrophic P-limited Everglades was used to assess the utility of phosphatase activity (PA) of periphyton as an early warning (EW) indicator of wetland eutrophication. Phosphorus loads of 0, 0.4, 0.8, 1.6, 3.2, 6.4 and 12.8 g P m^–2 yr^–1 were applied to mesocosms placed in a slough community consisting of Cladium jamaicense Crantz, Eleocharis spp. and calcareous periphyton mats. Phosphatase activity, expressed on a biomass-specific basis, was not a sensitive indicator of P enrichment for epiphytic periphyton growing on acrylic dowels or floating mat periphyton. However, surface-area-specific PA was a sensitive indicator of P enrichment, responding within 2–3 weeks of the initiation of dosing. Surface-area-specific PA of unenriched periphyton ranged from 0.42 to 0.7 nmol cm^–2 min^–1, while PA of periphyton growing in the highest load (12.8 g P m^–2 yr^–1), ranged from 0.11 to 0.29 nmol cm^–2 min^–1. Conclusions drawn from PA analyses were consistent with those obtained from periphyton primary productivity and P content. Phosphatase activity is a potentially valuable EW indicator when used in conjunction with other complementary indicators.     

Diel variations of certain physico-chemical parameters of water in selected aquatic systems

A field study was conducted during the months of October, January, May, and July (1979–80) to examine the diel variations in dissolved O₂ (DO), pH, dissolved CO₂, bicarbonate and carbonate alkalinity, NH₄-N, NO₃-N, and PO₄-P concentration, and conductivity (EC) of the water in six aquatic systems. Water in hyacinth (Eichhornia crassipes) ponds showed very little or no diel or seasonal variations in DO, pH, dissolved CO₂, and bicarbonate alkalinity. Dissolved O₂ concentration of the water under floating hyacinth cover was in the range of 0.2–3.0 µg/ml, while dissolved CO₂ levels were in the range of 10–35 µg/ml. In the aquatic systems with no floating vegetation, i.e., elodea (Egeria densa) pond, cattail (Typha sp.) pond, control pond (filamentous algae and Chara spp.), and eutrophic lake (algae in Lake Apopka), DO and pH of the water increased during mid-day and decreased during the night. Dissolved O₂ levels in these ponds were in the range of 5–20 µg/ml during mid-day and 2–8 µg/ml during the night, while pH of the water was in the range of 8–9.5 during mid-day and decreased to 7–8 during the night. An inverse relationship was observed between bicarbonate and carbonate alkalinity of the water in the aquatic systems with no floating vegetation while no carbonates were detected in the water with floating hyacinth plants. Ammonium N, NO₃-N and PO₄-P concentration of the water in these aquatic systems showed very little or no diel variations.Florida Agricultural Experiment Stations Journal Series No. 2788.     

Effect of bicarbonate,pH, methazolamide and stibenes on the intracellular potentials of cultured bovine corneal endothelial cells

Summary Micropuncture of cultured bovine corneal endothelial cells led to registrations stable for hours. Intracellular potentials were mainly in the range of –40 to –55 mV, average 46.3±0.6 mV (sem). Changes of extracellular [HCO ₃ ^– ] led to voltage transients, their amplitude depending logarithmically on [HCO ₃ ^– ] with a mean slope of 37.3±8.8 (sd) mV. After removal of bicarbonate/CO₂, a steady-state depolarization was seen. This steady-state depolarization, but not the voltage transients, could be reduced by 1mm Ba⁺⁺. After removal of bicarbonate, the voltage response to changes of extracellular potassium was reduced. Alteration of pH _i induced by permeable buffers (butyrate, glycodiazine and ammonium) also resulted in voltage transients, internal acidification being correlated with a hyperpolarization, and internal alkalinization with a depolarization. Also changes of external pH caused voltage responses, alkalinization causing a hyperpolarization, acidification a depolarization. Methazolamide, an inhibitor of carbonic anhydrase, as well as stilbenes (SITS or DIDS) caused a reduction of the voltage response to HCO ₃ ^– and pH. Their effects were additive. It is suggested that corneal endothelial cells possess one or two electrogenic transporters for HCO ₃ ^– or related species, one of which is inhibitable by stilbenes.     

Ammonium uptake by Chondrus crispus Stackhouse (Gigartinales,Rhodophyta) in culture

Cultivated Chondrus crispus was used in N-NH₄ uptake experiments in the laboratory. An elevation of temperature increased the apparent rate of uptake, especially up to 11 °C. Uptake in the dark was found to be 83 % of that in the light. The apparent uptake decreased with increasing internal N pool; rates were 26.5, 22.2 and 20.2 µg N g dry wt^–1 min^–1 for internal N pools of 2.7, 3.5 and 4.6%, respectively. Apparent uptake increased with the substrate N concentration. The resulting curve has two components: an active uptake and a diffusion component at high (> 5000 µg N L^–1) external N levels. Ks and V _max were calculated by deducting the diffusion component from the uptake curve: these were of 497 µg N L ^–1 and 14.4 µg N g dry wt^–1 min^–1. respectively, and reflect a low substrate affinity. This could be the result of 10 years of continuous culture of C. crispus. Uptake was similarly followed in the culture tanks and showed comparable results; nighttime would be the most appropriate time to supply nutrients.     

Phosphorus removal by the Ceratophyllum/periphyton complex in a south Florida (USA) freshwater marsh

Removal of phosphorus (P) by Ceratophyllum demersum L. and associated epiphytic periphyton was quantified by measuring the disappearance of soluble reactive P (SRP) from microcosms during 1-h in situ incubations conducted over a 1-year period. Initial P concentrations in these incubations ranged from 30 to >10,000 μg P L⁻¹. Phosphorus removal was proportional to initial P concentrations and was weakly correlated with solar irradiance and water temperature. Removal rates (0.6–32.8 mg P m⁻² d⁻¹) and k_v coefficients (0.68–1.93 h⁻¹) from experiments run at low initial P concentrations (up to 200 μg P L⁻¹) were comparable to results reported for other macrophytes. Removal rates from experiments run at the highest (>10,000 μg P L⁻¹) initial P concentrations (5300 and 11,100 mg P m⁻² d⁻¹) most likely represented luxury nutrient consumption and were not thought to be sustainable long term. We were unable to determine a V_max for P removal, suggesting that the nutrient-storage capability of the C. demersum/periphyton complex was not saturated during our short-term incubations. Based on N:P molar ratios, the marsh was P limited, while the C. demersum/periphyton complex was either N limited or in balance for N and P throughout this study. However, despite its tissue stoichiometry, the C. demersum/periphyton complex always exhibited an affinity for P. It appeared that the biochemical mechanisms, which mediate P removal, at least on a short-term basis, were more influenced by increases in ambient P levels than by tissue nutrient stoichiometry.     

Electrical effects of potassium and bicarbonate on proximal tubule cells ofNecturus

Summary The effects of stepwise concentration changes of K⁺ and HCO ₃ ^– in the basolateral solution on the basolateral membrane potential (V _bl) of proximal tubule cells of the doubly-perfusedNecturus kidney were examined using conventional microelectrodes. Apparent transference numbers were calculated from changes inV _bl after alterations in external K⁺ concentration from 1.0 to 2.5mm (t _{K, 1.0–2.5}), 2.5 to 10, and in external HCO ₃ ^– concentration (at constant pH) from 5 to 10mm (t _{HCO3, 5–10}), 10 to 20, or 10 to 50.t _{K, 2.5–10} was 0.38±0.02 under control conditions but was sharply reduced to 0.08±0.03 (P>0.001) by 4mm Ba⁺⁺. This concentration of Ba⁺⁺ reducedV _bl by 9±1 mV (at 2.5 external K⁺). Perfusion with SITS (5×10^–4 m) for 1 hr hyperpolarizedV _bl by 10±3 mV and increasedt _{K, 2.5–10} significantly to 0.52±0.01 (P<0.001). Ba⁺⁺ application in the presence of SITS depolarizedV _bl by 22±3 mV. In control conditionst _{HCO3, 10–50} was 0.63±0.05 and was increased to 0.89±0.07 (P<0.01) by Ba⁺⁺ but was decreased to 0.14±0.02 (P<0.001) by SITS. In the absence of apical and basolateral chloride, the response ofV _bl to bicarbonate was diminished but still present (t _{HCO3, 10–20} was 0.35±0.03). Intracellular pH, measured with liquid ion-exchange microelectrodes, increased from 7.42±0.19 to 7.57±0.17 (P<0.02) when basolateral bicarbonate was increased from 10 to 20mm at constant pH. These data show that the effects of bicarbonate onV _bl are largely independent of effects on the K⁺ conductance and that there is a significant current-carrying bicarbonate pathway in the basolateral membrane. Hence, both K⁺ and HCO ₃ ^– gradients are important in the generation ofV _bl, and their relative effects vary reciprocally.     

Transformation of thicket to savanna reduces soil quality in the Eastern Cape, South Africa

Xeric succulent thicket in the Eastern Cape, South Africa has been used for farming goats since the early 1900s. This habitat is characterised by a dense cover of the succulent bush Portulacaria afra and by a warm, semi-arid climate with evenly distributed annual rainfall of 250–400 mm. Heavy browsing by goats results in the loss of P. afra and transforms the thicket to an open savanna dominated by annual grasses. Eight fence-line comparisons between thicket and savanna were used to investigate differences in soil quality associated with the vegetation change. Composite soil samples were taken to a depth of 10 cm from 1 ha plots on either side of the fence-line. Associated with the change from thicket to savanna, a significant decrease (paired t-test, P < 0.05) was found in total C (respective means of 5.6 vs. 3.0%), total N (0.33 vs. 0.24%), labile C (2.8 vs. 1.5%), CO₂ flux (1.9 vs. 0.5 µmol m^–2 s^–1), soil respiration in the laboratory (144 vs. 79 ng C kg^–1 s^–1), (NH₄)OAc-extractable Mg (55 vs. 28 mmol_c kg^–1), and laboratory infiltration rate (51 vs. 19 mm h^–1). In the same direction there was a similarly significant increase in modulus of rupture (16 vs. 34 kPa), water-soluble Ca (2.3 vs. 3.4 mmol_c kg^–1) and pH (6.7 vs. 7.7). The soil C content of 5.6% in thicket is surprisingly high in this warm, semi-arid climate and suggests that the dense P. afra bush strongly regulates soil organic matter through microclimate, erosion control, litter quantity and perhaps chemistry. Savanna soils had a greater tendency to crust (as evident in a lower rate of laboratory infiltration and greater modulus of rupture) than thicket soils. This was attributed to their lower organic matter content, which probably reduced aggregate stability. Savannas are likely to be more prone to runoff and erosion not only because of sparser vegetation but also because of a decline in soil quality.     

The effects of reduced phosphorus and nitrogen loading on phytoplankton in Mondsee,Austria

Following restoration measures (ring canalization, treatment plant with phosphorus precipitation), phosphorus loading declined step-wise from 26.21 t year^–1 to 9.18 t year^–1 during the period 1979–1984 while P-retention increased from 48% to 78%. Phosphorus loading was poorely correlated with precipitation. Inorganic nitrogen load, largely NO₃– N, did not decline but was significantly correlated with precipitation (r = 0.95) throughout the investigation period (1978–1989).Total phosphorus loading reached acceptable levels in 1984 when compared to critical loading calculated according to Vollenweider (1976). Phosphorus input to the lake has remained at these levels in recent years.Average annual chlorophyll-a concentrations and biovolume of phytoplankton in the top 20 m layer of the lake decreased, in correspondence with the respective phosphorus concentrations, from eutrophic to mesotrophic levels. The decline was accompanied by a drastic reduction of blue-green algal populations, and especially of Oscillatoria rubescens D.C..     

Periphyton removal related to phosphorus and grazer biomass level

1. The proliferation of nuisance periphyton in enriched streams may be dependent on the biomass of the grazing macroinvertebrates present. In the present study, the effectiveness of grazer size and biomass in controlling periphyton and the extent to which grazing effectiveness was affected by enrichment level were determined. 2. Two sets of experiments with two caddisfly grazers were conducted in laboratory channels during spring and summer 1995 and 1996. The first set tested the combined effect of phosphorus enrichment and grazing, while the second set tested the effect of variable grazer biomass on periphyton biomass. 3. Grazing reduced periphyton biomass in excess of 80%, compared to ungrazed controls. Grazers were equally effective in controlling filamentous green algae, Stigeoclonium, diatoms and small colonial greens. Near complete removal of periphyton biomass by grazing occurred at even at the lowest grazer biomass level (750 mg m^??2, i.e. approximately one-third of natural levels). 4. Grazing controlled periphyton biomass more than did enrichment with soluble reactive phosphorus (SRP). 5. Grazing rates in the phosphorus-grazing interaction experiments averaged about 6 mg chl a g invertebrate^??1 day^??1, which was similar to past work in these channels and elsewhere, while rates were about five-fold higher in the variable grazer biomass experiments. 6. Simulating effects of SRP and grazing with a calibrated model suggests that higher SRP levels would be necessary to exceed a nuisance periphyton biomass level if grazers were present. However, if grazer biomass was more than 1500 mg m^??2, a nuisance level would probably not be exceeded at any SRP.     

The role of <Emphasis Type="Italic">Calamagrostis</Emphasis> communities in preventing soil acidification and base cation losses in a deforested mountain area affected by acid deposition

The effects of grass growth and N deposition on the leaching of nutrients from forest soil were studied in a lysimeter experiment performed in the Moravian-Silesian Beskydy Mts. (the Czech Republic). It was assumed that the grass sward formed on sites deforested due to forest decline would improve the soil environment. Lysimeters with growing acidophilous grasses (Calamagrostis arundinacea and C. villosa), common on clear-cut areas, and with unplanted bare forest soil were installed in the deforested area affected by air pollution. Wet bulk deposition of sulphur in SO₄^2– corresponded to 21.6–40.1 kg ha^–1 and nitrogen in NH₄⁺ and NO₃^– to 8.9–17.4 kg N ha^–1, with a rain water pH of 4.39–4.59 and conductivity of 18.6–36.4 S cm^–1 during the growing seasons 1997–1999. In addition, the lysimeters were treated with 50 kg N ha^–1 yr^–1 as ammonium nitrate during the 3 years of the experiment. Rapid growth of planted grasses resulted in a very fast formation of both above- and below-ground biomass and a large accumulation of nitrogen in the tissue of growing grasses. The greatest differences in N accumulation in aboveground biomass were observed at the end of the third growing season; in C. villosa and C. arundinacea, respectively, 2.66 and 3.44 g N m^–2 after addition of nitrogen and 1.34 and 2.39 g N m^–2 in control. Greater amounts of nitrogen were assessed in below-ground plant parts (9.93–12.97 g N m^–2 in C. villosa and 4.29–4.39 g N m^–2 in C. arundinacea). During the second and third year of experiment, the following effects were the most pronounced: the presence of growing grasses resulted in a decrease of both the acidity and conductivity of lysimetric water and in a lower amount of leached nitrogen, especially of nitrates. Leaching of base cations (Ca²⁺ and Mg²⁺) was two to three times lower than from bare soil without grasses. An excess of labile Al³⁺ was substantially eliminated in treatments with grasses. Enhanced N input increased significantly the acidity and losses of nutrients only in unplanted lysimeters. The leaching of N from treatments with grasses (3.9–5.6 kg N ha^–1) was 31–46% of the amount of N in wet deposition. However, the amount of leached N (4.2–6.0 kg N ha^–1) after N application was only 7.1–8.9% of total N input. After a short three year period, the features of soil with planted grasses indicated a slight improvement: higher pH values and Ca²⁺ and Mg²⁺ contents. The ability of these grass stands to reduce the excess nitrogen in soil is the principal mechanism modifying the negative impact on sites deforested by acid depositions. Thus it is suggested that grass sward formation partly eliminates negative processes associated with soil acidification and has a positive effect on the reduction of nutrient losses from the soil.     

Annual productivity of Spirulina (Arthrospira) and nutrient removal in a pig wastewater recycling process under tropical conditions

An evaluation was made of the annual productivity of Spirulina (Arthrospira) and its ability to remove nutrients in outdoor raceways treating anaerobic effluents from pig wastewater under tropical conditions. The study was based at a pilot plant at La Mancha beach, State of Veracruz, Mexico. Batch or semi-continuous cultures were established at different seasons during four consecutive years. The protein content of the harvested biomass and the N and P removal from the ponds were also evaluated. Anaerobic effluents from digested pig waste were added in a proportion of 2% (v/v) to untreated sea-water diluted 1:4 with fresh water supplemented with 2 g L^–1 sodium bicarbonate, at days 0, 3 and 5. A straight filament strain of Spirulina adapted to grow in this complex medium was utilized. A pH value 9.5 ± 0.2 was maintained. The productivity of batch cultures during summer 1998 was significantly more with a pond depth of 0.10 m than with a depth 0.065 m. The average productivity of semi-continuous cultures during summer 1999 was 14.4 g m^–2 d^–1 with a pond depth of 0.15 m and 15.1 g m^–2 d^–1 with a depth of 0.20 m. The average annual productivity for semi-continuous cultures operating with depths of 0.10 m for winter and 0.15 and 0.25 m for the rest of the year, was 11.8 g m^–2 d^–1. This is the highest value reported for a Spirulina cultivation system utilising sea-water. The average protein content of the semi-continuous cultures was 48.9% ash-free dry weight. NH₄-N removal was in the range 84–96% and P removal in the range of 72–87%, depending on the depth of the culture and the season.     

Methods of pH calibration of sedimentary diatom remains for reconstructing history of pH in lakes

The pH history of lakes can be inferred from diatom remains in dated sediment cores. To derive transfer functions for pH inference in acidic lakes, we counted diatoms in surface-sediment from 31 soft-water lakes in n. New England (NE) and 36 in Norway (N), covering pH 4.4–7.1. Cluster analysis of each data set indicates that pH 6 is an upper limit for a group of similar diatom assemblages. For each set, we developed multiple linear regressions to relate three versions of the diatom data to pH of surface-waters: (1) relative frequencies of selected diatom taxa, (2) the first principal component (1 PC) of these frequencies, and (3) the frequencies of Hustedt pH groups. Also, simple linear regressions were developed for two versions: (1) Index B and (2) Index Alpha, both based on pH groups. Regressions were run separately for lakes with pH 6; these are most relevant for pH inference in acidic lakes. The best regressions (N: taxa & 1 PC taxa) have r² 0.69–0.91 and S_e 0.24–0.31 pH units, the worst (NE: log alpha) have r² 0.27–0.57 and S_e 0.51. In all cases, errors for NE are greater than N, partly due to greater diversity of NE lakes. Regressions based on pH groups (directly & by indices) have smaller r² and larger S_e than those based on taxa and 1 taxa. The Index Alpha is least useful because its requirement for alkaline diatom units is unsatisfied at many acidic lakes. Regressions based on taxa may give erratic pH inferences due to sensitivity to unusual frequencies of individual taxa; this effect is reduced by using 1 PC taxa. Four regressions based on pH 6 lakes were used for inferring pH in a ²¹⁰Pb dated core from Nedre Målmesvatn, N (now pH 4.6). There is good agreement among three of the four (not for the regression based directly on taxa) that there has been a decrease of ca. 0.6 pH units starting in the late 1800's.     

Studies on the variables and kinetics of SCP production from nopal fruit juice

Summary Submerged batch cultivation under controlled environmental conditions of pH 3.8, temperature 30°C, and K_La200 h^–1 (above 180 mMO₂ l ^–1 h^–1 oxygen supply rate) produced a maximum (12.0 g·l ^–1) SCP (Candida utilis) yield on the deseeded nopal fruit juice medium containing C/N ratio of 7.0 (initial sugar concentration 25 g·l ^–1) with a yield coefficient of 0.52 g cells/g sugar. In continuous cultivation, 19.9 g·l ^–1 cell mass could be obtained at a dilution rate (D) of 0.36 h^–1 under identical environmental conditions, showing a productivity of 7.2 g·l ^–1·h^–1. This corresponded to a gain of 9.0 in productivity in continuous culture over batch culture. Starting with steady state values of state variables, cell mass (C_X–19.9 g·l ^–1), limiting nutrient concentration (C_ln–2.5 g·l ^–1) and sugar concentration (C_S–1.5 g·l ^–1) at control variable conditions of pH 3.8, 30°C, and K_La 200 h^–1 keeping D=0.36 h^–1 as reference, transient response studies by step changes of these control variables also showed that this pH, temperature and K_La conditions are most suitable for SCP cultivation on nopal fruit juice. Kinetic equations obtained from experimental data were analysed and kinetic parameters determined graphically. Results of SCP production from nopal fruit juice are described.Nomenclature C_ln concentration of ammonium sulfate (g·l ^–1) - C_S concentration of total sugar (g·l ^–1) - C_X cell concentration (g·l ^–1) - D dilution rate (h^–1) - K_ln Monod's constant (g·l ^–1) - m maintenance coefficient (g ammonium sulfate cell^–1 h^–1) - m_(S) maintenance coefficient (g sugar g cell^–1 h^–1) - t time, h - Y yield coefficient (g cells/g ammonium sulfate) - Y_m maximum of Y - Y_S yield coefficient based on sugar consumed (g cells · g sugar^–1) - Y_S(m) maximum value of Y_S - ^µm maximum specific growth rate constant (h^–1)     

The nitrogen cycle in lodgepole pine forests,southeastern Wyoming

Storage and flux of nitrogen were studied in several contrasting lodgepole pine (Pinus contorta spp.latifolia) forests in southeastern Wyoming. The mineral soil contained most of the N in these ecosystems (range of 315–860 g · m^–2), with aboveground detritus (37.5–48.8g · m^–2) and living biomass (19.5–24.0 g · m^–2) storing much smaller amounts. About 60–70% of the total N in vegetation was aboveground, and N concentrations in plant tissues were unusually low (foliage = 0.7% N), as were N input via wet precipitation (0.25 g · m^–2 · yr^–1), and biological fixation of atmospheric N (<0.03 g · m^–2 · yr^–1, except locally in some stands at low elevations where symbiotic fixation by the leguminous herbLupinus argenteus probably exceeded 0.1 g · m^–2 · yr^–1).Because of low concentrations in litterfall and limited opportunity for leaching, N accumulated in decaying leaves for 6–7 yr following leaf fall. This process represented an annual flux of about 0.5g · m^–2 to the 01 horizon. Only 20% of this flux was provided by throughfall, with the remaining 0.4g · m^–2 · yr^–1 apparently added from layers below. Low mineralization and small amounts of N uptake from the 02 are likely because of minimal rooting in the forest floor (as defined herein) and negligible mineral N (< 0.05 mg · L^–1) in 02 leachate. A critical transport process was solubilization of organic N, mostly fulvic acids. Most of the organic N from the forest floor was retained within the major tree rooting zone (0–40 cm), and mineralization of soil organic N provided NH₄ for tree uptake. Nitrate was at trace levels in soil solutions, and a long lag in nitrification was always observed under disturbed conditions. Total root nitrogen uptake was calculated to be 1.25 gN · m^–2 · yr^–1 with estimated root turnover of 0.37-gN · m^–2 · yr^–1, and the soil horizons appeared to be nearly in balance with respect to N. The high demand for mineralized N and the precipitation of fulvic acid in the mineral soil resulted in minimal deep leaching in most stands (< 0.02 g · m^–2 · yr^–1). These forests provide an extreme example of nitrogen behavior in dry, infertile forests.