Benthic fluxes of nutrients and some trace metals in the Tamar estuary,SW England

Pore water concentration gradients and fluxes of chemical components have been studied in sediments from six intertidal sites in the Tamar Estuary, SW England over the course of a year. Fluxes of nutrients (ammonia, nitrate, nitrite, phosphate and silicate) and trace metals (iron, manganese, zinc, copper and cadmium) were determined using a laboratory microcosm incorporatingin situ pore water samplers. Nutrients (except nitrate) were transported out of the sediment throughout the year, but nitrate fluxes were directed into the sediment in the summer (denitrification) and out of the sediment in the winter (nitrification). The activities of benthic macrofauna resulted in enhanced fluxes but these differed between sites depending on population structure and density and whether irrigation or sediment reworking predominated. Fluxes of trace metals were seasonally and spatially variable and specific differences were observed that could be attributed to both chemical and biological activity.     

Spatio-temporal variations of sea surface halocarbon concentrations and fluxes from southern Yellow Sea

Temporal and spatial distributions of five volatile halogenated organic compounds (VHOC), including chloroform (CHCl₃), trichloroethylene (C₂HCl₃), bromodichloromethane (CHBrCl₂), chlorodibromomethane (CHBr₂Cl), and bromoform (CHBr₃), were determined in the southern Yellow Sea (SYS) during four cruises from July 2008 to May 2009. The five VHOC distributed in the study area were affected by river inputs, anthropogenic activities, circulation system, and biological processes. In this study, CHCl₃, CHBrCl₂, CHBr₂Cl, and CHBr₃ concentrations showed significant differences between summer 2008 and spring 2009. The sea-to-air fluxes calculated using the equation of Liss and Merlivat (In: Buat-Menard P (ed) The role of air-sea exchange in geochemical cycling, 1986) indicated that the SYS was a source of CHCl₃ and C₂HCl₃ to the atmosphere during the investigation period.     

Short-term variations in the fluxes and composition of seston in near-bottom traps in the southern North Sea

In this study we attempted to measure the potential food availability for macrobenthic interface feeders using a new device (sediment recorder) which traps bed load particles at a height of 10 cm above the sea floor. The recorder is positioned flat on the seabed and alternately exposes a shallow collector mounted in a smooth surface mimicking the sediment surface. The samples were analyzed for their content of chlorophyll a (Chl) and dry weight (DM). We compared the sediment recorder data with the results obtained with a sediment trap suspended 3.2 m above the sea floor. Measurements were carried out in spring and fall at two stations in the southern North Sea with different sediment type, maximum current velocities and biomass (sand, station B vs silty sand, station F). The recorder deployments in November yielded higher Chl fluxes and a higher quality of particles (Chl:DM ratio) than the trap at both stations. Unlike the trap samples, in which Chl and DM were always positively and strongly correlated, maximum Chl and DM fluxes in the recorder samples were out of phase, particularly at station B, pointing to a highly variable quality during the tidal cycle. Unexpectedly, Chl fluxes and Chl:DM ratios in the recorder samples at station B were higher than at station F in both seasons, although the benthic biomass at the latter station was five times higher. The highest Chl fluxes and particle quality (Chl:DM) at station B were measured during slack tides when interface feeding would be least hampered by drag forces. Station B is nevertheless characterized by a low macrobenthic biomass and a scarcity of interface feeders, specifically of suspension-feeding bivalves. Possible reasons for this apparent discrepancy are discussed. Electronic Publication     

Dimethylsulfide and methane thiol in sediment porewater of a Danish estuary

Seasonal variation of dimethylsulfide (DMS) and methane thiol (MSH) concentrations in sediment porewater was determined in a Danish estuary. Dimethylsulfide (DMDS) was never found. Detectable DMS levels of up to 0.1 M were found only in the summer and only within the upper 5 cm of the sediment. The DMS accumulation was probably associated with decomposing fragments of macro-algae in the surface layer. Significant MSH accumulation of up to 1 M was found only in the deep, CH₄-rich sediment below the SO₄ ^2- zone. With depth, a detectable MSH level could thus be observed below the 1 mM SO₄ ^2--isopleth which also marked the SO₄ ^2--CH₄ transition. The transition zone was located deeper in the sediment in winter (20–25 cm depth) than in summer (5–10 cm depth). The absence of MSH in the SO₄ ^2- zone could be due to rapid utilization of the compound by SO₄ ^2--reducing bacteria. A possible involvement of MSH in anaerobic CH₄ oxidation at the transition zone is discussed; CH₄ and sulfide (HS^- form, pH 7) are proposed to form MSH and H₂ which in turn may be metabolized by, e.g. SO₄ ^2--reducing bacteria.     

Influence of Potamogeton pectinatus and microphytobenthos on benthic metabolism,nutrient fluxes and denitrification in a freshwater littoral sediment in an agricultural landscape: N assimilation versus N removal

The influence of Potamogeton pectinatus colonisation on benthic nitrogen dynamics was studied in the littoral zone of a lowland pit lake with high nitrate concentration (~200 μM). Our hypothesis was that in aquatic environments where nitrogen availability is not limiting, colonisation by rooted macrophytes changes the dynamics of the benthic nitrogen cycle, stimulating N assimilation and denitrification and increasing the system capacity to take up external nitrogen loads. To test this hypothesis, we quantified and compared seasonal variations of light and dark benthic metabolism, dissolved inorganic nitrogen (DIN) fluxes, denitrification and N assimilation rates in an area colonised by P. pectinatus and a reference site colonised by microphytobenthos. In both areas, the benthic system was net autotrophic and a sink for DIN (2,241–2,644 mmol m^?2 y^?1). Plant colonisation increased nitrogen losses via denitrification by 30% compared to the unvegetated area. In contrast to what is generally observed in coastal marine systems, where the presence of rooted macrophytes limits denitrification rates, under the very high nitrate concentrations in the studied lake, both denitrification (1,237–1,570 mmol m^?2 y^?1) and N assimilation (1,039–1,095 mmol m^?2 y^?1) played important and comparable roles in the removal of DIN from the water column.     

Genetic variations in time and space in massa carrara population (North West Tuscany-Italy)

The effect of population movement on the genetic structure was examined in Massa Carrara province by generation using blood group obtained from hospital donors. The sample was typed for ABO, Rh and Kell systems. The sample covers a temporal span of two generations (50 years) separated by the end of the last war. Spatial variation was statistical significant in both generations and was higher in the second generation, while temporal variation was significant only for the two principal towns of the province. Due to lack of migration from outside, the mountain subpopulations, which showed the highest contribution to spatial differentiation, has not changed since the last war. The comparison with a random sample shows that the results are not affected by the nature of the sample.     

Short-term variations in the physiological state of phytoplankton [2pt] in a shallow temperate estuary

Short-term changes in the photosynthetic carbon metabolism and physiological state of phytoplankton were studied over a summer fortnight-long period in the Urdaibai estuary (Bay of Biscay) and related to observed environmental patterns. Day-to-day variability in the hydrographical and biological features of the estuary during the study period was due to changes in meteorological and tidal conditions. Phytoplankton biomass and primary production increased with the improvement of weather, i.e., light conditions, during neap tides. Thus a mixed bloom of cryptophyceans, Euglena sp., and the dinoflagellate Peridinium foliaceum developed in the middle and upper estuary. Photosynthetic responses of phytoplankton were related to the time-scale of changes in light regime. Allocation of photosynthate to major macromolecular classes (LMWM, lipid, polysaccharide, and protein), like phytoplankton biomass and primary production, showed strong spatio-temporal variability. High carbon fixation into low molecular weight metabolites was associated with growth limitation by low light. The relative incorporation of photosynthetic carbon into proteins increased at the beginning of the phytoplankton bloom but overall, it was rather constant. However, carbon allocation into storage products such us lipid or polysaccharide increased when carbon and energy produced under optimal growth conditions exceeded what could be assimilated into protein. These patterns are explained by both spatio-temporal changes in the environmental conditions and species-specific differences. In general, daily variability appeared to be more important than diurnal periodicity in the physiological responses of phytoplankton. Results from this study show that phytoplankton photosynthesis and carbon metabolism are simultaneously affected by biotic and abiotic factors, although short-term light fluctuations may have a major influence on the physiological state of phytoplankton in the Urdaibai estuary.     

Modulation of dissolved oxygen levels in a hypertidal estuary by sediment resuspension

Hyperconcentrated benthic layers, which form during neap tides, recruit much of the fine sediment population of the turbidity maximum of a hypertidal estuary. Measurements of tidal amplitude and suspended solids concentration reveal that resuspension of the hyperconcentrated layers occurs between three and eight tides after neap tides rather than during spring tides (12 to 15 tides after neaps). During these resuspension events, dissolved oxygen levels are reduced but recover by spring tides. Peak solids concentrations and critically depressed dissolved oxygen levels are out of phase with tidal current amplitude. Thus observations close to neap and spring tides do not necessaraly capture the extremes of the envelope of water quality conditions.     

Mitotic exit control: a space and time odyssey

The mitotic exit network (MEN), a protein kinase cascade under the switch-like control of the small GTPase Tem1, triggers exit from mitosis in budding yeast. Now it emerges that signals from both Tem1 and the yeast Polo kinase Cdc5 converge onto the MEN kinase Cdc15 to accurately restrict MEN activation to late mitosis.     

Habitat-associated and temporal patterns of bat activity in a diverse forest landscape of southern New England, USA

The development and use of acoustic recording technology, surveys have revealed the composition, relative levels of activity, and preliminary habitat use of bat communities of various forest locations. However, detailed examinations of acoustic surveys results to investigate temporal patterns of bat activity are rare. Initial active acoustic surveys of bat activity on the Quabbin Reservoir watershed in central Massachusetts recorded high numbers of call sequences by five bat species. The results showed the importance of aquatic and open habitats for bats in this diverse forest landscape. Because the preliminary surveys were restricted in extent (habitats), number (replicates), and duration (active surveys only, limited number of repeated surveys), the authors strongly recommended more comprehensive and extensive surveys of bat activity on the area. This paper reports the results of active (manual) and passive (automated) acoustic bat activity surveys in three replicates of ten habitats, conducted three to four times per year over the course of the study between 2004 and 2006. Over the full study, 2,800 actively-recorded 37,632 passively-recorded call sequences were examined and identified to species when possible. General patterns in activity did not differ by habitat between the two survey methods. Call sequences were recorded more often in open, especially aquatic habitats than in cluttered habitats. The use of passive surveys allowed for the assessment of temporal patterns of activity and an analysis of the relationship between ambient temperature and activity.     

Winter production of CO2 and N2O from alpine tundra: environmental controls and relationship to inter-system C and N fluxes

Fluxes of CO₂ and N₂O were measured from both natural and experimentally augmented snowpacks during the winters of 1993 and 1994 on Niwot Ridge in the Colorado Front Range. Consistent snow cover insulated the soil surface from extreme air temperatures and allowed heterotrophic activity to continue through much of the winter. In contrast, soil remained frozen at sites with inconsistent snow cover and production did not begin until snowmelt. Fluxes were measured when soil temperatures under the snow ranged from –5°C to 0°C, but there was no significant relationship between flux for either gas and temperature within this range. While early developing snowpacks resulted in warmer minimum soil temperatures allowing production to continue for most of the winter, the highest CO₂ fluxes were recorded at sites which experienced a hard freeze before a consistent snowpack developed. Consequently, the seasonal flux of CO₂ –C from snow covered soils was related both to the severity of freeze and the duration of snow cover. Over-winter CO₂ –C loss ranged from 0.3 g C m⁻² season⁻¹ at sites characterized by inconsistent snow cover to 25.7 g C m⁻² season⁻¹ at sites that experienced a hard freeze followed by an extended period of snow cover. In contrast to the pattern observed with C loss, a hard freeze early in the winter did not result in greater N₂O–N loss. Both mean daily N₂O fluxes and the total over-winter N₂O–N loss were related to the length of time soils were covered by a consistent snowpack. Over-winter N₂O–N loss ranged from less 0.23 mg N m⁻² from the latest developing, short duration snowpacks to 16.90 mg N m⁻² from sites with early snow cover. These data suggest that over-winter heterotrophic activity in snow-covered soil has the potential to mineralize from less than 1% to greater than 25% of the carbon fixed in ANPP, while over-winter N₂O fluxes range from less than half to an order of magnitude higher than growing season fluxes. The variability in these fluxes suggests that small changes in climate which affect the timing of seasonal snow cover may have a large effect on C and N cycling in these environments. Received: 5 April 1996 / Accepted: 25 November 1996     

Vegetation dynamics: patterns in time and space

This paper introduces the collection of contributions in this special volume on temporal and spatial patterns of vegetation dynamics. First, it is pointed out that the dynamics of any piece of vegetation, large or small, is always dependent on the degree of isolation of that piece towards its environment. Then ten types of island situation are treated ranging from very much to very little isolated: remote species-rich oceanic islands, remote species-poor islands, young big islands near a continent, small off-shore islands, emerging islands, isolated hills, landscape islands, isolated patches of vegetation, and gaps in stands of vegetation.Also, eight forms of vegetation dynamics are treated, ranging from short-term to long-term changes and involving larger and larger units: individuals, patches, communities, landscapes and vegetation regions. The forms of dynamics are fluctuation, gap dynamics, patch dynamics, cyclic succession, regeneration succession, secondary succession, primary succession, and secular succession. Each form of dynamics may occur under varying degrees of isolation.The general conclusion is that processes and patterns of vegetation dynamics cannot be generalized in any simple manner. The 20 papers collected in this volume, divergent as they are, express the complexity of vegetation dynamics.     

Nutrient fluxes and microbial activity in sediment enriched with settled seston

The chemical and microbiological responses of profundal surface sediment were monitored in sediment enriched with natural settled material collected in May, July or August, and with diatom or cyanobacteria cultures. The activation of the sediment microbial community was clearest after the addition of settled seston collected in May which was richer in organic matter than those collected later in the summer. N was released when the sediment was enriched with settled seston which had been collected in July and August and had C:N ratios lower than 10:1. The diatom-rich May-material enhanced the release of P to the interstitial water, obviously because of chemical competition between P and diatom-derived Si at the sediment surface. The July- and August-materials did not release P, nor did the diatom and cyanobacteria cultures. The results thus indicate that the seasonal variations in the quality and quantity of the settling phytoplankton affect the P dynamics at the sediment surface, both chemically and biologically.     

Elephants in space and time

Autocorrelation in animal movements can be both a serious nuisance to analysis and a source of valuable information about the scale and patterns of animal behavior, depending on the question and the techniques employed. In this paper we present an approach to analyzing the patterns of autocorrelation in animal movements that provides a detailed picture of seasonal variability in the scale and patterns of movement. We used a combination of moving window Mantel correlograms, surface correlation and crosscorrelation analysis to investigate the scales and patterns of autocorrelation in the movements of three herds of elephants in northern Botswana. Patterns of autocorrelation of elephant movements were long‐range, temporally complicated, seasonally variable, and closely linked with the onset of rainfall events. Specifically, for the three elephant herds monitored there was often significant autocorrelation among locations up to lags of 30 days or more. During many seasonal periods there was no indication of decreasing autocorrelation with increasing time between locations. Over the course of the year, herds showed highly variable and complex patterns of autocorrelation, ranging from random use of temporary home ranges, periodic use of focal areas, and directional migration. Even though the patterns of autocorrelation were variable in time and quite complex, there were highly significant correlations among the autocorrelation patterns of the different herds, indicating that they exhibited similar patterns of movement through the year. These major patterns of autocorrelation seem to be related to patterns of rainfall. The strength of correlation in movement patterns of the different herds decreased markedly at the cessation of major rain events. Also, there was a strong crosscorrelation between strength of autocorrelation of movement and rainfall, peaking at time lags of between three and four weeks. Overall, these approaches provide a powerful way to explore the scales and patterns of autocorrelation of animal movements, and to explicitly link those patterns to temporally variable environmental attributes, such as rainfall or vegetation phenology.     

Net fluxes of ammonium and nitrate in association with H+ fluxes in fine roots of Populus popularis

Poplar plants are cultivated as woody crops, which are often fertilized by addition of ammonium (NH₄ ⁺) and/or nitrate (NO₃ ^?) to improve yields. However, little is known about net NH₄ ⁺/NO₃ ^? fluxes and their relation with H⁺ fluxes in poplar roots. In this study, net NH₄ ⁺/NO₃ ^? fluxes in association with H⁺ fluxes were measured non-invasively using scanning ion-selective electrode technique in fine roots of Populus popularis. Spatial variability of NH₄ ⁺ and NO₃ ^? fluxes was found along root tips of P. popularis. The maximal net uptake of NH₄ ⁺ and NO₃ ^? occurred, respectively, at 10 and 15 mm from poplar root tips. Net NH₄ ⁺ uptake was induced by ca. 48 % with provision of NO₃ ^? together, but net NO₃ ^? uptake was inhibited by ca. 39 % with the presence of NH₄ ⁺ in poplar roots. Furthermore, inactivation of plasma membrane (PM) H⁺-ATPases by orthovanadate markedly inhibited net NH₄ ⁺/NO₃ ^? uptake and even led to net NH₄ ⁺ release with NO₃ ^? co-provision. Linear correlations were observed between net NH₄ ⁺/NO₃ ^? and H⁺ fluxes in poplar roots except that no correlation was found between net NH₄ ⁺ and H⁺ fluxes in roots exposed to NH₄Cl and 0 mM vanadate. These results indicate that root tips play a key role in NH₄ ⁺/NO₃ ^? uptake and that net NH₄ ⁺/NO₃ ^? fluxes and the interaction of net fluxes of both ions are tightly associated with H⁺ fluxes in poplar roots.