Pronounced Temporal Variability Research Articles

Spatial and Temporal Diversity Patterns of Planktonic Rotifer Assemblages in Water Bodies of the Floodplain Gemenc (Duna‐Dráva National Park, Hungary)

AbstractThe Gemenc floodplain of the Danube possesses numerous side arms and backwaters. The aim of my study was to explore connections between hydrological events and diversity patterns of the planktonic rotifer assemblages of these water bodies. During the study period (2002–2008) 75 taxa of rotifers were found. Generally, the water bodies of the floodplain had more diverse rotifer assemblages than the main arm. At low and medium water levels diversity was highest in the parapotamal water bodies. This result may be explained by the intermediate disturbance hypothesis. At high water levels the highest biodiversities shifted to the plesiopotamal. Biodiversity, dominance, and evenness correlated with water flow and temperature. Patterns of biodiversity seem to be determined by the water level of the main arm; therefore the water regime appears to provide pronounced temporal variability in the hydro‐ecology of the floodplain. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Hot spots and hot moments of planktonic nitrogen fixation in a eutrophic southern reservoir

Reservoirs have been identified as hot spots of biogeochemical activity, although they are known to exhibit pronounced temporal and spatial variability in planktonic community dynamics. Results from this 19-month study at 5 locations on a southern polymictic reservoir identify pronounced temporal (seasonal and interannual) and significant spatial variability in planktonic nitrogen fixation. Planktonic nitrogen fixation was found to be high during the warmest portion of the year and undetectable for most of the rest of the year. Interannual variability between 2 consecutive summer periods was high and likely due to differences in rainfall pattern and resulting differences in ambient nutrient concentrations and flushing rates. Rates during the dry summer exceeded those during the following summer when unexpected summer rains occurred. Spatial differences in areal and volumetric rates were also significant. Volumetric rates were highest in the inflow transition zone of a river draining a watershed impacted by dairy operations, with inflows exhibiting low N:P ratios. Areal rates were highest in the deeper and clearer portions of the reservoir. Areal rates of nitrogen fixation varied among the 5 stations by a factor of 4.4 in the dry summer and by a factor of 22 in the wetter summer.

Delivery, deposition and redistribution of fine sediments within macrotidal Fitzroy Estuary/Keppel Bay: Southern Great Barrier Reef, Australia

The Fitzroy catchment in central Queensland, Australia is the largest catchment discharging to the Great Barrier Reef (GBR) Lagoon. Sediments and nutrients (both particulate and dissolved) originating in the catchment, are discharged from the Fitzroy River, into the Fitzroy Estuary (FE) and ultimately into Keppel Bay (KB). The flow in the river is characterised by summertime high-flow events typically of several weeks duration followed by virtually no flow for the remainder of the year. In this manuscript, we describe the hydrodynamics and fine-sediment dynamics in the coupled FE–KB system. Particular emphasis is placed on describing the temporal and spatial variability of these dynamics and on how the interactions between the temporal scales have important implications for system function. The greater bulk of the fresh water, sediments and nutrients are discharged into the FE in a relatively short time, but these materials are then redistributed throughout the FE–KB system and beyond by vigorous macrotidal currents during the rest of the year. Pronounced temporal variability in concentrations of suspended sediments also occurs at semi-diurnal and fortnightly timescales arising from the variation in the strength of tidal currents. The fluxes of fine sediments from the system to the lagoon of the Great Barrier Reef demonstrate pronounced variability at interannual, seasonal, fortnightly, and semi-diurnal timescales. Suspended sediments in the river discharge have very small sinking rates, but flocculation that occurs when they encounter salty water greatly increases their sinking rate and is an important agent for trapping these sediments near the estuary mouth. The large temporal variability of the hydrodynamics and fine-sediment dynamics of the FE–KB system also has important consequences for the biogeochemical function of the system and poses major challenges for the interpretation of moored, shipboard, and remote sensing measurements.

High local and global diversity of Flavobacteria in marine plankton

Members of the phylum Bacteroidetes are among the most abundant microbes in coastal marine waters, but it is unclear to which extent the diversity within this phylum is covered by currently available 16S rRNA gene sequence information. We, thus, obtained a comprehensive collection of sequence types affiliated with Bacteroidetes in coastal North Sea surface waters and we compared this local diversity with the available sequences of marine planktonic and other aquatic Bacteroidetes. Approximately 15% of > 600 clones from two libraries (August 2000, June 2001) were related to Bacteroidetes, specifically to the Flavobacteria. Local diversity appeared to be almost exhaustively sampled. However, the diversity of the two libraries virtually did not overlap, indicating a pronounced temporal variability of the planktonic Flavobacteria assemblage. The majority of sequence types represented novel phylogenetic lineages, adding 6-7% to the currently known genera and species of Bacteroidetes in marine waters. Different diversity estimators suggested that so far only approximately half of the global diversity of planktonic marine Bacteroidetes has been described. The data set moreover indicated that cultivation-independent techniques and isolation approaches have recovered almost equally sized and virtually non-overlapping fractions of the currently known diversity within this phylum. Interestingly, only 15% of genera of Bacteroidetes from various aquatic environments appear to occur in more than one habitat type.

Long‐term sensitivity of a High Arctic wetland to Holocene climate change

Summary 1 The response of peat-rich permafrost soils to human-induced climate change may be especially important in modifying the global C-flux. We examined the Holocene developmental record of a High Arctic peat-forming wetland to investigate its sensitivity to past climate change and aid understanding of the likely effects of future climate warming on high-latitude ecosystems. 2 The microhabitat of mosses was quantified in the present-day polygon-complex at Bylot Island (73° N, 80° W) and used to interpret the radiocarbon-dated macrofossil record of three cores, comprising c. 3500 years of wetland development. Recurrent wet and dry phases in the reconstructed palaeohydrological record indicated pronounced temporal variability. Wet and dry phases were compared between cores and with palaeoclimatic proxy values, measured as percentage melt and δ18O in nearby ice cores. 3 Periodic wet and dry phases appear unrelated to past climate over c. 50% of the combined stratigraphic records, and are attributable instead to geomorphological mechanisms. At other times, association of wet and dry phases with significantly lower and higher values of percentage melt and δ18O indicate a possible effect of past climate change on polygon hydrology and vegetation, although inconsistencies between cores suggest that local geomorphological processes continued to modify a regional climatic effect. However, during a period incorporating the Little Ice Age (c. 305–530 cal. years bp), reconstructed moisture and vegetation change is pronounced and consistent among all three cores. 4 The results provide strong evidence for the sensitivity of a High Arctic terrestrial ecosystem to past climate change during the Holocene. The estimated magnitude of changes in soil moisture between wet and dry phases is sufficient to imply recurrent shifts in wetland function, periodically impacted upon by pronounced climatic variability, although controlled principally by autogenic processes. The structure and function of such wetlands may therefore be susceptible to predicted, human-induced climate warming.

New Silhouette Disks with Reflection Nebulae and Outflows in the Orion Nebula and M43

We report the detection of several new circumstellar disks seen in silhouette against background nebular light in the outskirts of the Orion Nebula and the neighboring H II region M43. These were detected as part of our Hα survey of Orion with the Advanced Camera for Surveys on board the Hubble Space Telescope. Several of the disks show bipolar reflection nebulae, microjets, or pronounced temporal variability of their central stars. The relatively large fraction of bipolar reflection nebulae and microjets in our sample may be a selection effect caused by the faint nebular background far from the Trapezium. Two disks in our sample are large and particularly noteworthy: A nearly edge-on disk, d216-0939, is located several arcminutes northwest of M43 and resembles the famous HH 30 disk/jet system in Taurus. It drives the 0.15 pc long bipolar outflow HH 667 and exhibits a remarkable asymmetric reflection nebula caused by the tilt of the flared disk. With a diameter of ∼26 (1200 AU), d216-0939 is as large as the giant edge-on silhouette disk d114-426 in the core of the Orion Nebula. The large disk d253-1536 is located in a binary system embedded within an externally ionized giant proplyd in M43. The disk exhibits distortions that we attribute to tidal interactions with the companion star. The bipolar jet HH 668 emerges from the proplyd ionization front in a direction orthogonal to the disk and can be traced to the young star embedded within it. A bow shock lies 54'' south of this binary system along the outflow axis. Proper motions over a 1.4 yr baseline confirm that these emission knots are indeed moving away from d253-1536 with speeds as high as ∼330 km s-1 in the HH 668 microjet and slower motion farther from the star.

Fractal dimensions of laser doppler flowmetry time series

Laser Doppler flowmetry (LDF) provides a non-invasive method of assessing cutaneous perfusion. As the microvasculature under the probe is not defined the measured flux cannot be given absolute units, but the technique has nevertheless proved valuable for assessing relative changes in perfusion in response to physiological stress. LDF signals normally show pronounced temporal variability, both as a consequence of the pulsatile nature of blood flow and local changes in dynamic vasomotor activity. The aim of the present study was to investigate the use of methods of nonlinear analysis in characterizing temporal fluctuations in LDF signals. Data were collected under standardised conditions from the forearm of 16 normal subjects at rest, during exercise and on recovery. Surrogate data was then generated from the original time series by phase randomization. Dispersional analysis demonstrated that the LDF data was fractal with two distinct scaling regions, thus allowing the calculation of a fractal dimension which decreased significantly from 1.23 ± 0.09 to 1.04 ± 0.02 during exercise. By contrast, dispersional analysis of the surrogate data showed no scaling region.

Hydrography, nutrients and plankton abundance in the hot spot of Abu Qir Bay, Alexandria, Egypt

The hydrography, nutrient levels and plankton abundance were investigated monthly for a complete annual cycle in the southwestern part of Abu Qir Bay, the most polluted and biologically productive area on the Egyptian Mediterranean coast. Intense temporal and spatial variability was observed in all measured parameters characteristic of the effects of several effluents discharged into the bay. Based on the present investigation, the southwestern Bay can be divided ecologically and biologically into two parts: one including the near shore strip, which is directly affected by the waste waters, and a second comprising the southwestern part of the coastal strip and the offshore stations, both of which are relatively far away from the land-based effluents.The Bay water was characterized by low transparency (monthly average: 64-280 cm), dissolved oxygen (monthly average 2.0-6.8 mg/l) and surface salinity (monthly average: 24.8-37.9 ppt), the highest limits usually being in the offshore section. Water fertility and plankton production were high in the Bay indicating an occasionally acute degree of eutrophication, particularly nearshore. Great variations occurred in the concentrations of nutrients throughout the year, with monthly averages of 0.8-50.88 mM for ammonia, 0.42-3.28 mM for nitrite, 1.29-17.36 mM for nitrate, 0.32-3.61 mM for reactive phosphate and 1.09-33.34 mM for reactive silicate. Similarly, the abundance of both phytoplankton and zooplankton showed pronounced temporal and spatial variability, whereas the monthly average chlorophyll-a fluctuated between 2.06 and 52.64 mg/l and zooplankton between 31x103 and 248.6x103 ind./m3. However, the absolute values of all parameters indicated remarkably wider ranges of variations.Significant correlation was found between chlorophyll-a and some ecological parameters like temperature, salinity, transparency, dissolved oxygen, nitrite and between zooplankton and temperature, while there was a significant correlation between nutrient concentrations and salinity changes.

Biogeochemical Cycling of Mn and Fe in an Area Affected by Eutrophication: The Adriatic Sea

Measurements of dissolved Mn and Fe and total particulate Mn, Fe and Al were made on seawater samples collected in the Northern Adriatic Sea in different seasons (May 1994, June–July 1994, September 1994 and February 1995), and in the Central Adriatic Sea in June–July 1994. Porewaters were also analysed for dissolved Mn and Fe in February 1994, June 1994, September 1994 and February 1995.Seasonal observations of dissolved Mn and Fe and particulate excess Mn and Fe in the Northern Adriatic Sea have demonstrated pronounced temporal and spatial variability of their distribution. This variability was mainly due to: (a) storm events which broke down stratification of the water column and enhanced resuspension and advective transport of particulate forms, and (b) fluctuations of oxygen concentrations in the water column and sediment–water interface, related to the biodegradation of the organic matter produced during bloom periods. Large inputs of dissolved Mn and Fe were attributed to reductive solubilization and diffusion from the sediment–water interface. Particulate excess Mn and Fe concentrations were also increased by oxidation in the presence of oxygen of dissolved Mn and Fe, which had diffused from the sediment–water interface.

Baseline contamination assessment for a new resource recovery facility in Germany part II: atmospheric concentrations of PCDD/F

The atmospheric levels of PCDD/Fs in both the gas and particle phases were measured continuously over 1 year at 7 sites in the outskirts of Augsburg, Germany, and at a rural site 15 km from the city. The homologue and congener patterns in the total air samples were similar among the different stations and stayed constant throughout the whole year. The PCDD/F levels were about two times higher at the sampling points on the edge of the city than at the remote location. There was a pronounced temporal variability of the total air concentrations, with levels in winter that were 9 times higher than the levels in summer. The gas/particle partitioning was characterised by higher gaseous fractions for more volatile compounds and higher ambient temperatures. It was concluded that the ambient air concentrations of the PCDD/Fs are determined by on-going local and regional emissions, with seasonal (winter) sources contributing the vast majority of the emissions fluxes.

Airborne infrared spectroscopy of Comet Wilson (1986l) and comparisons with Comet Halley

H2O and possibly CH4 have been detected in near-infrared spectra of Comet Wilson (1986l). The observed number and relative intensities of cometary H2O lines in the nu3 band at 2.65 microns were consistent with fluorescent excitation pumped by solar infrared photons. The H2O production rate in Comet Wilson was approximately 3 x 10 to the 29th/s at R = 1.2 AU; no pronounced temporal variability was observed. Lines in the nu3 band of CH4 at 3.3 microns were possibly detected at the 3 sigma confidence level. The CH4 abundance is in the range CH4/H2O = 0.014-0.045; the uncertainty is due primarily to the assumed effective excitation temperature of CH4. The CH4 abundance in this dynamically 'new' comet is similar to that observed in P/Halley. These values are low for equilibrium compositional models and very high for disequilibrium condensation in the solar nebula.

The dynamics of estuarine manganese cycling

Seasonal observations of dissolved managnese in the Tamar Estuary,south-west England have demonstrated pronounced temporal and spatial variability in the distribution of this component. Simultaneous observations of physical and physico-chemical properties of the estuarine system, together with kinetic measurements of dissolved managenese behaviour in isolated samples, have demonstrated that the observed distributions are the instantaneous product of dynamic interactions involving external sources and internal input and removal processes. Dissolved manganese is mobilized internally from reduced sedimentsduring advective resuspension of bed material so that this input is regulated by temporal and spatial variations in tidal stress. Manganese is returned to the sediments by continuous uptake on to suspended particles. The rate of this process is responsive to changes in suspended particulate load, ionic strength pH and temperature. The reaction changes from zero-order kinetics in freshwater to first-order kinetics characteristic of the saline medium, with marked deceleration in effective, removal rate, following small increases in salt concentration. Relative changes in the first-order removal rate throughout the estuary are consistent, but there are considerable temporal variations in the absolute rates. This is partially attributable to variations in the quality, as well as the quantity, of the suspended particles. These results indicate that changes in the relative effectiveness of both the input and removal mechanisms, which lead to internal cycling of manganese and to variable distributions of dissolved managanese within the estuary, are closely coupled to the internal behaviour of particles and hence to the tidally-induced oscillations in bed stress. This observation has been confirmed by sequential recordings of dissolved manganese distributions through a spring tide to neap tide period. Furthermore, climatic events producing enhanced disturbance of bed sediment have been shown to induce a similar sequence of events to that arising from tidally induced net mobilization of bed material.