Potential effects of climate change on DOC release from three different soil types on the Northern Pennines UK: examination using field manipulation experiments

Three field manipulation experiments were carried out during 1993–1995 on the Northern Pennines to investigate the influences of temperature, solar radiation and rainfall on the release of dissolved organic carbon (DOC) from vegetated soil cores using zero‐tension lysimeters. The cores were manipulated by being translocated to four sites down a climatic gradient, by artificial soil heating or being exposed to double normal rainfall. In each experiment three soil types, a brown earth, a micropodzol and a peaty gley, with differing organic matter content and distribution within the profile, were studied. DOC data, expressed as mg C m^?2 day^?1, were analysed following log₁₀ transformation, by a repeated measures analysis of variance procedure, using climatic variables measured concurrently with sampling, and 1 and 2 months before sampling. DOC release was dominated by rainfall but was also associated with solar radiation and temperature. With each of the three climatic variables, rainfall, solar radiation and temperature, both positive and negative effects on DOC release have been found significant, indicating that the concurrent and delayed effects of the same variable may be different. DOC release was positively related with all three soils to concurrent rainfall, indicating rainfall's primary leaching action. DOC release was also negatively related to rainfall of the previous month indicating that its action depletes the leachable pool of DOC in the soil. DOC release was positively associated with solar radiation 2 months earlier, indicating that DOC's main source is that of primary production; DOC peaks closely followed peaks of annual primary production. DOC release was linked with temperature, the strongest association being with temperature 2 months earlier, indicating that temperature effects both primary production and DOC regeneration via organic matter decomposition. A conceptual model, relating our findings to those processes known to govern DOC release from soils, has been presented.     

Seasonal and within-event dynamics of rainfall and throughfall chemistry in an open tropical rainforest in Rondônia,Brazil

Prolonged dry periods, and increasingly the generation of smoke and dust in partially-deforested regions, can influence the chemistry of rainfall and throughfall in moist tropical forests. We investigated rainfall and throughfall chemistry in a palm-rich open tropical rainforest in the southwestern Brazilian Amazon state of Rondônia, where precipitation averages 2300 mm year^?1 with a marked seasonal pattern, and where the fragmentation of remaining forest is severe. Covering the transition from dry to wet season (TDWS) and the wet season (WS) of 2004–2005, we sampled 42 rainfall events on event basis as well as 35 events on a within-event basis, and measured concentrations of DOC, Na⁺, K⁺, Ca²⁺, Mg²⁺, NH ₄ ⁺ , Cl^?, SO ₄ ^2? , NO ₃ ^? and pH in rainfall and throughfall. We found strong evidence of both seasonal and within-event solute rainfall concentration dynamics. Seasonal volume-weighted mean (VWM_S) concentrations in rainfall of DOC, K⁺, Ca²⁺, Mg²⁺, NH ₄ ⁺ , SO ₄ ^2? and NO ₃ ^? were significantly higher in the TDWS than the WS, while VWM_S concentrations in throughfall were significantly higher for all solutes except DOC. Patterns were generally similar within rain events, with solute concentrations declining sharply during the first few millimeters of rainfall. Rainfall and throughfall chemistry dynamics appeared to be strongly influenced by forest and pasture burning and a regional atmosphere rich in aerosols at the end of the dry season. These seasonal and within-event patterns of rainfall and throughfall chemistry were stronger than those recorded in central Amazônia, where the dry season is less pronounced and where regional deforestation is less severe. Fragmentation and fire in Rondônia now appear to be altering the patterns in which solutes are delivered to remaining moist tropical forests.     

Modeling Allochthonous Dissolved Organic Carbon Mineralization Under Variable Hydrologic Regimes in Boreal Lakes

Here, we explore the interaction between hydrology and the reactivity of allochthonous dissolved organic carbon (DOC_alloch) in determining the potential of DOC_alloch to generate CO₂ through biological and photo-chemical mineralization in boreal lakes. We developed a mechanistic model that integrates the reactivity continuum (RC) concept to reconstruct in-lake mineralization of DOC_alloch under variable hydrologic conditions using empirical measurements of DOC_alloch concentrations and reactivity as model inputs. The model predicts lake DOC_alloch concentration (L-DOC_alloch) and its average overall reactivity \( \left( {\bar{K}_{\text{alloch}} } \right) \), which integrates the distribution of DOC_alloch ages within the lake as a function of the DOC loading (DOC_in), the initial reactivity of this DOC_in (k ₀), and the lake water residence time (WRT). The modeled DOC_alloch mineralization rates and concentrations were in agreement with expectations based on observed and published values of ambient lake DOC concentrations and reactivity. Results from this modeling exercise reveal that the interaction between WRT and k ₀ is a key determinant of the ambient concentration and reactivity of lake DOC_alloch, which represents the bulk of DOC in most of these lakes. The steady-state \( \left( {\bar{K}_{\text{alloch}} } \right) \) also represents the proportion of CO₂ that can be extracted from DOC_alloch during its transit through lakes, and partly explains the patterns in surface water pCO₂ oversaturation that have been observed across gradients of lake size and volume. We estimate that in-lake DOC_alloch mineralization could potentially contribute on average 30–40% of the observed surface carbon dioxide partial pressure (pCO₂) across northern lakes. Applying the RC framework to in-lake DOC_alloch dynamics improves our understanding of DOC_alloch transformation and fate along the aquatic network, and results in a predictable mosaic of DOC reactivity and potential CO₂ emissions across lakes within a landscape.     

Vertical pattern and its driving factors in soil extracellular enzyme activity and stoichiometry along mountain grassland belts

Headwater streams are foci for nutrient and energy loading from terrestrial landscapes, in situ nutrient transformations, and downstream transport. Despite the prominent role that headwater streams can have in regulating downstream water quality, the relative importance of processes that can influence nutrient uptake have not been fully compared in heterotrophic aquatic systems. To address this research need, we assessed the seasonality of dissolved organic carbon (DOC) and nitrate (NO₃^?) uptake, compared the relative influence of hydrologic and biogeochemical drivers on observed seasonal trends in nutrient uptake, and estimated the influence of these biological transformations on watershed scale nutrient retention and export. We determined that seasonal reductions in DOC and NO₃^? concentrations led to decreases in the potential for the biotic community to take up nutrients, and that seasonality of DOC and NO₃^? uptake was consistent with the seasonal dynamics of ecosystem metabolism. We calculated that that during the post-snowmelt period (June to August), biotic retention of both dissolved organic carbon and nitrate exceeded export fluxes from this headwater catchment, highlighting the potential for biological processes to regulate downstream water quality.     

Photoadaptation of an ice algal community in thin sea ice,Saroma-Ko Lagoon,Hokkaido, Japan

We investigated the shade adaptation of a seasonally well-developed ice algal community in thin sea ice at Saroma-Ko Lagoon, Hokkaido, Japan on 3–4 March 2006 and 4–5 March 2007, by examining photosynthetic pigment concentrations, the chlorophyll a-specific light-absorption coefficient (a _ph *), and the light-saturation index (E _k ). The high proportions of photosynthetic pigments, including chlorophyll a, fucoxanthin, and chlorophyll c, and the low values of a _ph *₍₄₄₀₎ and a _ph *₍₆₇₅₎ suggested that the lagoon’s ice algal community was shade-adapted. The high ratio of E _k to total photosynthetically active radiation (PAR) in the ice algal habitat suggested that the degree of shade adaptation is weak. Scaling of E _k to total PAR could be extended to studies of the degree of photoadaptive succession of ice algal communities in the Northern Hemisphere. The degree of shade adaptation of ice algal communities in the Northern Hemisphere might be related to ice thickness, regardless of latitude.     

Modeled Effects of Dissolved Organic Carbon and Solar Spectra on Photobleaching in Lake Ecosystems

Dissolved organic matter (DOM) contains molecules that absorb light at various wavelengths. This chromophoric DOM (CDOM) influences the transmission of both visible and ultraviolet energy through water. The absorption of light by CDOM often causes structural changes that reduce its capacity to further absorb light, a process termed ‘photobleaching‘. A model was designed to assess photobleaching through the entire water column of lake ecosystems. The model uses lake morphometry and dissolved organic carbon (DOC) concentration in conjunction with a defined solar spectrum and experimentally measured photobleaching rates to compute the total water columm photobleaching. The model was initially applied to a theoretical ‘average‘ lake using solar spectra for both the north (N) and south (S) temperate western hemispheres and variable DOC from 0.3 to 30 mg L⁻¹. The consequences of varying waveband-specific photobleaching coefficients and lake morphometry were explored in a second set of simulations. Finally, the model was also applied to four temperate northern lakes for which we had prior measurements of CDOM photobleaching rates. The model demonstrates that all three wavebands of solar radiation (UVB, UVA, and PAR) contribute significantly to total water column photobleaching, with UVA being most important. The relative contributions of the three wavebands were invariant for DOC more than 3 mg L⁻¹. Total water column photobleaching at 440 nm was three to five times faster under the UV-enriched solar spectrum of the southern hemisphere. Increasing the lake’s mean depth (from 0.37 to 9.39 m) resulted in five- or 15-fold slower rates of total water column photobleaching for DOC concentrations of 1 or 10 mg L⁻¹, respectively. Varying the waveband-specific photobleaching coefficients by 10-fold resulted in a similar change in total water column photobleaching rates. Applying the model to four specific lakes revealed that photobleaching for the entire water column would reduce CDOM light absorption by 50% in 18–44 days under summer conditions. Received 17 November 1998; accepted 27 June 2000.     

Deep-water aquatic plant communities in an oligotrophic lake: physiological responses to variable light

1. Oligotrophic Lake Waikaremoana, New Zealand, is used for hydroelectric power generation and the lake levels are manipulated within an operating range of 3 m. There was concern that rapidly changing water levels adversely affected the littoral zone by decreasing light availability in two ways: local turbidity caused by shoreline erosion at low water levels; and decreased light penetration to the deep littoral zone caused by high water levels in summer. 2. The littoral zone was dominated by native aquatic plants with vascular species to 6 m and a characean meadow below this to 16 m. The biomass and heights of the communities in the depth zone 0–6 m were reduced at a site exposed to wave action relative to those at a sheltered site. However, the community structure below 6 m was similar at exposed and sheltered sites. The lower boundary of the littoral zone was sharply delimited at 16 m and this bottom boundary remained constant throughout the year despite large seasonal changes in solar radiation and the 3 m variation in lake level. 3. There was evidence that the deep-water community consisting of Chara corallina had adapted physiologically to low-light conditions. Net light saturated photosynthesis (CO₂ exchange) per unit chlorophyll a (Chl a) was reduced to 1.7 μg C (μg Chl a)^?1 h^?1 at the lower boundary, half of that recorded at 5 m. The concentration of Chi a per gram of biomass (dry weight), was considerably greater at the lower boundary than higher in the profile [c. 7 mg Chl a (g dry wt)^?1 at 16 m vs. 4 mg Chl a (g dry wt)^?1 at 5 m]. Chl b also increased with depth and there was no change in the ratio of Chl a and Chl b with increasing depth. The saturation light intensity (I_k) of the community at the lower boundary was only 78 μmol photons m^?2 s^?1. Photosynthetic parameters (I_k and α) as well as the Chl a content remained relatively constant throughout the seasonal and short-term changes in radiation. 4. The photosynthetic characteristics of the littoral community were therefore not greatly affected by the lake level change caused by the present hydroelectric operations. However, the sharpness of the lower boundary and its extreme shade characteristics imply that the deep-water community would be sensitive to any further changes in underwater light availability.     

Body temperature variation of South African antelopes in two climatically contrasting environments

To understand the adaptive capacity of a species in response to rapid habitat destruction and climate change, we investigated variation in body temperature (T_b) of three species of antelope, namely eland, blue wildebeest and impala, using abdominally-implanted temperature data loggers. The study was conducted at two climatically contrasting environments in South Africa, one with a less seasonal and mild winter (Mapungubwe National Park) and the other with a more seasonal, long and cold winter (Asante Sana Game Reserve). Since the habitat with long and cold winters would be suboptimal for these African antelopes, which evolved in less seasonal and hot environments, antelopes in Asante Sana were expected to exhibit a larger amplitude in T_b and a lower minimum body temperature (Min T_b) during winter to reduce T_b and the ambient temperature (T_b−T_a) gradient to save energy. In both eland and impala, 24-h body temperature amplitude did not differ between the study sites, regardless of season. Conversely, wildebeest in Mapungubwe showed a higher variability in the 24-h amplitude of body temperature and also a lower Min T_b during winter and spring than the wildebeest in Asante Sana. This variation in T_b among Mapungubwe wildebeest was influenced by both the amplitude of ambient temperature (positive) and cumulative rainfall (negative), which was not the case for wildebeest in Asante Sana. We propose that the low Min T_b of wildebeest in Mapungubwe was the result of nutritional stress during winter and spring; an evident response even during a year of average rainfall. Therefore, these wildebeest apparently live in a physiologically stressful environment. With the predicted increase in the frequency and intensity of drought periods in southern Africa, wildebeest and other grazers, will likely experience greater nutritional stress in the future.     

Examination of the potential relationship between droughts, sulphate and dissolved organic carbon at a wetland-draining stream

Rising dissolved organic carbon (DOC) concentrations observed at a number of sites in the northern hemisphere over recent decades are the subject of much debate, and recent reports suggest a link between DOC patterns in surface waters and changes in sulphate (SO₄) related to droughts or deposition. In order to investigate the potential influence of changes in SO₄ concentration on DOC patterns in south‐central Ontario, we used long‐term (1980–2001) stream monitoring data from a wetland‐dominated catchment (Plastic Lake‐1 subcatchment, PC1) that has been the focus of intensive investigations of both SO₄ and DOC dynamics. Annual average volume‐weighted DOC concentration increased significantly between 1980 and 2001, whereas SO₄ concentration declined, but the decrease was not significant due to large increases in SO₄ that occurred during drought years. There was no relationship between SO₄ and DOC in annual data series; however, seasonal analyses indicated significant negative correlations between SO₄ and DOC concentrations in spring (March–April–May), summer (June–July–August) and fall (September–October–November). In spring, DOC concentration was negatively correlated with flow whereas SO₄ concentrations increased with flow, and their opposing relationships with discharge explain the negative correlation between SO₄ and DOC in this season. In summer and fall, low SO₄ concentrations occur during periods of low flow as a result of microbial SO₄ reduction, whereas correspondingly high DOC concentrations in the summer and fall can be attributed to optimal conditions (i.e. stagnant flow, warm temperatures) for DOC production in the wetland. Increases in SO₄ (and acidity) following droughts were not associated with declines in DOC; instead the primary impact of droughts on DOC was to limit DOC export due to diminished stream flow. Rather than an acidification effect, we suggest that negative relationships between SO₄ and DOC were either directly (spring) or indirectly (summer/fall) caused by underlying relationships with hydrology.     

Predominance of phytoplankton-derived dissolved and particulate organic carbon in a highly eutrophic tropical coastal embayment (Guanabara Bay,Rio de Janeiro,Brazil)

We investigate the carbon dynamics in Guanabara Bay, an eutrophic tropical coastal embayment surrounded by the megacity of Rio de Janeiro (southeast coast of Brazil). Nine sampling campaigns were conducted for dissolved, particulate and total organic carbon (DOC, POC and TOC), dissolved inorganic carbon (DIC), partial pressure of CO₂ (pCO₂), chlorophyll a (Chl a), pheo-pigments and ancillary parameters. Highest DOC, POC and Chl a concentrations were found in confined-shallow regions of the bay during the summer period with strong pCO₂ undersaturation, and DOC reached 82 mg L^?1, POC 152 mg L^?1, and Chl a 800 μg L^?1. Spatially and temporally, POC and DOC concentrations varied positively with total pigments, and negatively with DIC. Strong linear correlations between these parameters indicate that the production of TOC translates to an equivalent uptake in DIC, with 85% of the POC and about 50% of the DOC being of phytoplanktonic origin. Despite the shallow depths of the bay, surface waters were enriched in POC and DOC relative to bottom waters in periods of high thermohaline stratification. The seasonal accumulation of phytoplankton-derived TOC in the surface waters reached about 105 g C m^?2 year^?1, representing between 8 and 40% of the net primary production. The calculated turnover time of organic carbon was 117 and 34 days during winter and summer, respectively. Our results indicate that eutrophication of coastal bays in the tropics can generate large stocks of planktonic biomass and detrital organic carbon which are permanently being produced and partially degraded and buried in sediments.     

Relationship of trophic and chemical conditions to photobleaching of dissolved organic matter in lake ecosystems

Dissolved organic matter (DOM) is a major light-absorbing substance, responsible for much of the color in water bodies. When sunlight energy is absorbed by DOM, some color can be lost by the process of photobleaching. We measured rates of DOM photobleaching in thirty lakes that varied greatly in color, trophic status and ionic composition. Loss of color (measured as absorbance at 440 nm and expressed as absorption coefficients) was a first order function of sunlight dose, and rates were nearly identical for 0.2m- and GF/F-filtered samples suggesting that the process was predominantly abiotic. Photobleaching rates were rapid (color loss of 1–19% d^–1) and varied about seven-fold among lakes. Our method under-estimated the actual rate by 15–20% based on comparisons between the glass bottles we used in the survey and quartz containers. The large variation in photobleaching rates was examined in relation to lake trophy and chemical conditions. The best predictor of this variability was acid-neutralizing capacity (ANC) (r ²=0.94;p<0.001) such that photobleaching was most rapid in the most alkaline lakes. The relationship between ANC and photobleaching suggests that differences in ionic conditions among lakes may influence the solubility and configuration of humic and fulvic acids and hence their susceptibility to photobleaching.     

Flux of organic carbon in a riverine mangrove wetland in the Florida Coastal Everglades

Short-term (daily) and seasonal variations in concentration and flux of dissolved organic carbon (DOC) were examined over 15 tidal cycles in a riverine mangrove wetland along Shark River, Florida in 2003. Due to the influence of seasonal rainfall and wind patterns on Shark River’s hydrology, samplings were made to include wet, dry and transitional (Norte) seasons. We used a flume extending from a tidal creek to a basin forest to measure vertical (vegetated soil/water column) and horizontal (mangrove forest/tidal creek) flux of DOC. We found significant (p < 0.05) variations in surface water temperature, salinity, conductivity, pH and mean concentration of DOC with season. Water temperature and salinity followed seasonal patterns of air temperature and rainfall, while mean DOC concentration was highest during the dry season (May), followed by the wet (October) and ‘Norte’ (December) seasons. This pattern of DOC concentration may be due to a combination of litter production and inundation pattern of the wetland. In contrast to daily (between tides) variation in DOC flux between the mangrove forest and tidal creek, daily variations of mean water quality were not significant. However, within-tide variation of DOC flux, dissolved oxygen content and salinity was observed. This indicated that the length of inundation and water source (freshwater vs. saltwater) variation across tidal cycles influenced water quality and DOC flux in the water column. Net DOC export was measured in October and December, suggesting the mangrove forest was a source of DOC to the adjacent tidal creek during these periods. Net annual export of DOC from the fringe mangrove to both the tidal creek and basin mangrove forest was 56 g C m⁻² year⁻¹. The seasonal pattern in our flux results indicates that DOC flux from this mangrove forest may be governed by both freshwater discharge and tidal range.     

Penetration of solar ultraviolet radiation into New Zealand lakes: influence of dissolved organic carbon and catchment vegetation

Eleven lakes in the South Island of New Zealand were sampled in summer 1996. Water column profiles of ultraviolet radiation (UVR) at four wavelengths and photosynthetically available radiation (PAR) were obtained, along with analyses of dissolved organic carbon (DOC) concentration, total suspended solids (TSS), and catchment vegetation, including forest and natural grassland. Downward attenuation coefficients (K _d) and lake water transparency (1/K _d) for UVR were examined in relation to these variables. Consistent with other regions of the world, DOC concentration and variables related to DOC were the best predictors of UVR penetration. With our data set, we calculated ratios of water column integrals (RI) of UVR/PAR irradiance, using equations from the literature. At DOC concentrations below 4 g m⁻³, a progressive increase in RI shows that lakes become increasingly transparent to UVR. We also normalized chromophoric dissolved organic matter (CDOM) absorption of UVR at 380 nm (a ₃₈₀) to DOC concentration and found that the UVR-absorbing capacity per unit DOC increases with increasing percentage of forest in the catchment area. This indicates that not only DOC concentration but also DOC type or composition is important in determining the transparency of lake water to UVR, and that qualitative differences in DOC are dictated by the type and amount of vegetation present in the lake's catchment area. Received: September 18, 2000 / Accepted: December 14, 2000     

Kinetic analysis of biphasic protein modification reactions cooperative effects

A mathematical treatment of protein modification reactions is presented, and it is shown thai in these cases protein modification is described by a summation of exponential functions of reaction time, the number of exponentials being equal to the number of modified protein species. It is shown that in cases of protein modification cooperativity, there is a strict dependence of the coefficients of the multiexponential modification equation on the constants of the same equation. The conditions necessary for a reduction of a multiexponential protein modification equation to one of a summation of two exponentials only are examined. The possible formulae for the coefficients of a two-exponential-summation equation, used to describe the modification of protein models with two, three or four modifiable residues (as well as some aspects of models with five and six modifiable residues) per protein molecule are derived. It is seen that the number of such coefficients is severely limited. The most frequently obtained formula for the lower stoichiomelric coefficient of a 'wo-exponential-summation equation is Ak_a/(k_a-k_b). where k_b and k_b are the constants of the two exponentials of the equation, and A is a constant. The value most frequently arrived at for A is (n?1)/n, where n is the number of modifiable residues per protein molecule, while values such as 1/n, or a/n (where a is an integer, and also where a < n) are also possible. In most of the cooperative protein modification models worked out, k_a is identical with k_n, viz., k_a is identical with the rate constant for the first stoichiometric protein modification.     

The size distribution of insertions and deletions in human and rodent pseudogenes suggests the logarithmic gap penalty for sequence alignment

The size distributions of deletions, insertions, and indels (i.e., insertions or deletions) were studied, using 78 human processed pseudogenes and other published data sets. The following results were obtained: (1) Deletions occur more frequently than do insertions in sequence evolution; none of the pseudogenes studied shows significantly more insertions than deletions. (2) Empirically, the size distributions of deletions, insertions, and indels can be described well by a power law, i.e., f _k = Ck ^–b , where f _k is the frequency of deletion, insertion, or indel with gap length k, b is the power parameter, and C is the normalization factor. (3) The estimates of b for deletions and insertions from the same data set are approximately equal to each other, indicating that the size distributions for deletions and insertions are approximately identical. (4) The variation in the estimates of b among various data sets is small, indicating that the effect of local structure exists but only plays a secondary role in the size distribution of deletions and insertions. (5) The linear gap penalty, which is most commonly used in sequence alignment, is not supported by our analysis; rather, the power law for the size distribution of indels suggests that an appropriate gap penalty is w _k = a + b ln k, where a is the gap creation cost and blnk is the gap extension cost. (6) The higher frequency of deletion over insertion suggests that the gap creation cost of insertion (a _i ) should be larger than that of deletion (a _d ); that is, a _i – a _d = In R, where R is the frequency ratio of deletions to insertions. Correspondence to: W.-H. Li     

The further investigation of physical and photochemical properties of quasimetacyclophane derived from thymine

The thymine derived quasimetacyclophane exist in two conformers $\text{a}$ and $\text{b}$. The absorption spectra of $\text{a}$ and $\text{b}$ were evaluated and the conformational equilibrium in different solvents /H₂O : EtOH/ were examined. The rate constant k_?1 for reaction $\text{b}\text{→}\text{a}$ was established as well as E_a.     

Structure and Dynamics of a Two‐Helix SNARE Complex in Live Cells

SNAREs are clustered membrane proteins essential for intracellular fusion steps. During fusion, three to four SNAREs with a Q_a‐, Q_b‐, Q_c‐ and R‐SNARE‐motif form a complex. The core complex represents a Q_aQ_bQ_cR‐SNARE‐motif bundle, most certainly assembling in steps. However, to date it is unknown which intermediate SNARE complex observed in vitro also exists in vivo. Here we have applied comparative fluorescence recovery after photobleaching (FRAP)‐studies as a novel approach for studying in intact cells a SNARE interaction involved in synaptic vesicle fusion [catalyzed by syntaxin 1A (Q_a), SNAP25 (Q_b/Q_c) and synaptobrevin 2 (R)]. We find that the Q_b‐SNARE‐motif of SNAP25 interacts reversibly with clustered syntaxin. The interaction requires most of the alpha helical Q_b‐SNARE‐motif and depends on its position within the molecule. We conclude that a zippered Q_aQ_b‐SNARE complex represents a short‐lived SNARE intermediate in intact cells, most likely providing an initial molecular platform toward membrane fusion.     

Venturi aeration and thermophilic aerobic sewage sludge digestion in small-scale reactors

Summary The aeration performance of two venturi aeration reactors (operating volumes 381 and 251) was studied for an air-water system. It was found that the mass transfer coefficient (k _la) could be described in terms of the superficial gas velocity (V _s) alone by the simple expressionk _La=aV _infb ^supS with constantsa=0.313,b=0.579 for the 38-1 reactor anda=0.214,b=0.534 for the 25-1 reactor. A similar relationship was obeyed when the 38-1 reactor was aerated with a diffuser tile (a=17.0,b=1.52). A linear relationship betweenk _La and gas hold-up was observed for the 38-1 reactor with both venturi and diffuser aeration. The 25-1 reactor was used successfully for the thermophilic aerobic digestion of sewage sludge. A mean sludge temperature rise of 30°C was observed. Chemical oxygen demand, pH, and total solids content of the digested sludge differed significantly from the feed sludge and were similar to values obtained for full-scale thermophilic aerobic digestion. No significant differences between inorganic solids content, dissolved oxygen concentration, or redox potential were observed between feed and digested sludge.     

Seasonal Variation in Aboveground Production and Radiation-use Efficiency of Temperate rangelands Estimated through Remote Sensing

Aboveground net primary production (ANPP) of grasslands varies spatially and temporally. Spectral information provided by remote sensors is a promising new tool that may be able to estimate ANPP in real time and at low cost. The objectives of this study were (a) to evaluate at a seasonal scale the relationship between ANPP and the normalized difference vegetation index (NDVI), (b) to estimate seasonal variations in the coefficient of conversion of absorbed radiation into aboveground biomass (ε_a), and (c) to identify the environmental controls on such temporal changes. We used biomass-based field determinations of ANPP for two grassland sites in the Flooding Pampa, Argentina, and related them with NDVI data derived from the NOAA Advanced Very High Resolution Radiometer (AVHRR) satellites using three different models. Results were compared with data obtained from the new Moderate Resolution Imaging Spectroradiometer (MODIS) sensor at an additional site. The first model was based solely on NDVI; the second was based on the amount of photosynthetically active radiation absorbed by the green vegetation (APAR_g), which was derived from NDVI and incoming photosynthetically active radiation (PAR); the third was based on APAR_g and ε_a, which was in turn estimated from climatic variables. NDVI explained between 63 and 93% of ANPP variation, depending on the site considered. Estimates of ANPP were not improved by considering the variation in incoming PAR. At both sites, ε_a varied seasonally (from 0.2 to 1.2 g DM/MJ) and was significantly associated with combinations of precipitation and temperature. Combining ε_a variations with APAR_g increased our ability to account for seasonal ANPP variations at both sites. Our results indicate that NDVI produces good, direct estimates of ANPP only if NDVI, PAR, and ε_a are correlated throughout the seasons. Thus, in most cases, seasonal variations of ε_a associated with temperature and precipitation must be taken into account to generate seasonal ANPP estimates with acceptable accuracy.     

Seasonal changes in daily metabolic patterns of Lacerta viridis

Summary Lacerta viridis maintained under natural photoperiodic conditions show daily and seasonal changes in metabolic rates and body temperature (T _b) as well as seasonal differences in sensitivity to temperature change. At all times of the year lizards have a daily fluctuation in oxygen consumption, with higher metabolic rates during the light phase of the day when tested at a constant ambient temperature (T _a) of 30°C. Rhythmicity of metabolic rate persists under constant darkness, but there is a decrease in the amplitude of the rhythm.Oxygen consumption measured at various T_as shows significant seasonal differences at T _as above 20°C. Expressed as the Arrhenius activation energy, metabolic sensitivity of Lacerta viridis shows temperature dependence in autumn, which changes to metabolic temperature independence in spring at T _as above 20°C. The results indicate a synergic relationship between changing photoperiod and body temperature selection, resulting in seasonal metabolic adjustment and seasonal adaptation.Abbreviations ANOVA analysis of variance - LD long day (16 h light) - SD short day (8 h light) - T _a ambient temperature - T _b body temperature