1,720,985 research outputs found
Modelling energy fluxes in remote wetland ecosystems with help of remote sensing
No full textThe study of the material and energy fluxes that characterise an ecosystem is fundamental to understanding the
behaviour of that system and its resiliency in the face of changing local and global conditions. In the present research,
an extended energy balance model was used to examine the fluxes that characterise the energy exchange between a
large wetland area and its environment. For each flux term, a number of modelling approaches was compared.
Modelling was complemented through the use of irradiance measurements from satellite data. The model output
shows the daily and season variations in each energy term, as well as a comparison of the modelling approaches. The
final output of the model is validated with the measured hourly variation in the enthalpy (water temperature) of the
lagoon. A comparison is made of the relative importance of each energy term in the overall balance of the system.
This physical based model is being used to examine possible modifications of local and global environments to the
wetland energy balance. The model is also being combined with fauna models to examine the relation between climate
and population characteristics (habitat). The present work is directed towards the study of a subtropical lagoon in the
internationally important wetland, the Esteros del Ibera in Argentin
On the presence of Pseudo-nitzschia calliantha Lundholm, Moestrup et Hasle and Pseudo-nitzschia delicatissima (Cleve) Heiden in the Southern Adriatic Sea (Mediterranean Sea, Italy)
No full textThis investigation included a 2-year monitoring program aimed at assessing the abundance and distribution of harmful marine phytoplankton along the Southern Adriatic coast of Italy. Monthly sampling was conducted from April 1995 to March 1997 at four sampling stations along four transects, to determine the temporal and spatial presence/abundance of the potentially toxic Pseudo-nitzschia species. The study focussed on the most abundant taxa Pseudo-nitzschia calliantha and Pseudo-nitzschia delicatissima, the identities of which were confirmed by TEM on cleaned net material. The distribution patterns of these potential Amnesic Shellfish Poisoning (ASP) toxin producers were statistically analysed by Generalised Linear Model ANalysis Of VAriance, Principal Component Analysis (GLM ANOVA, PCA) and Spearman's correlation analysis in order to address relationships between environmental variable and population dynamics. Abundances displayed horizontal and vertical structure in the study area. Inter-annual variability was also observed for both species that appeared to respond differently to the environmental factors investigated. Distributions of P. calliantha showed a stronger seasonality and was more correlated with winter water conditions than P. delicatissima, which in turn exhibited a broader temporal distribution and appeared independent from major environmental constraints. This is the first report of the occurrence and dynamics of P. calliantha and P. delicatissima populations in Southern Adriatic coastal waters
Light limitations to algal growth in tropical ecosystems
No full text1. Spatial and temporal variations in algal concentrations are controlled in many aquatic ecosystems by the availability of solar irradiance, rather that nutrients or grazing. In such light limiting conditions, changes in the optical or hydrological characteristics of the water column will directly impact biomass concentrations. Here we develop and test an approach based on the relationship between available solar irradiance within the mixed layer and algal biomass concentrations.
2. As with most nutrient/biomass relationships, an increase in available solar energy favours an increase in biomass when light limitation prevails. The ratio between light/biomass is then used to determine a critical light requirement that can be used to estimate critical depth and compensation irradiance and open the way to exploring how changes in mixing depth and vertical attenuation may influence algal biomass concentrations.
3. This approach is used to describe real conditions in two disparate algal communities; the phytoplankton community in Lake Victoria, East Africa and the microphytobenthos community in the lacustrine system of Esteros del Iberá (South America).
4. Differences in the critical light requirement were used to examine the relative efficiency of the algal communities in their use of available solar energy. The tropical phytoplankton community showed similar energetic requirements to theoretical estimates and were found to be less efficient when compared with the phytobenthos community
Examining the dynamics of phytoplankton biomass in Lake Tanganyika using Empirical Orthogonal Functions
No full textThe spatial and seasonal variations in phytoplankton concentrations can be pronounced in
large tropical lakes and can have a direct impact on the regional communities in developing
nations. Given the complex hydrodynamics and ecology of the African Great Lakes, there
is a clear need for spatial databases to address their inter-annual and seasonal variability.
In the past, phytoplankton studies in these extensive ecosystems focused mostly on point
stations or lake transects repeated over several years. In the present work, satellite based
reflectanceswere used to determine anomalies in chlorophyll related reflectance bands over
a 7-year period for the whole of Lake Tanganyika. Empirical Orthogonal Function analysis
was used to define regions with similar temporal co-variation of phytoplankton biomass.
Using AutoRegressive Integrated Moving Average modelling techniques, it was possible to
determine differences in phytoplankton dynamics and link these to climate and lake basin
characteristics. An important shift in the phytoplankton seasonalitywas observed at the end
of 2000, in concomitance to changes in wind and air temperatures which favoured entrainment
of nutrients present in the deeper lake waters. This shift confirms the high sensitivity
of the lake to climate change. The combination of extensive satellite based measurements
with modelling approaches that consider both spatial and temporal dynamics is an important
contribution to the understanding of long term changes in this important freshwater
ecosystem
Spatial and temporal characterisations of dissolved humic substances in freshwater lake
No full textDissolved organic matter (DOM) is a key component in freshwater ecosystems, strongly influencing the optical, chemical
and biological environment. The influence of the organic material on lake water depends on the molecular characteristics of the
compounds. In the present study, the spatial distribution of dissolved organic matter and humic concentrations was determined
together with the indices for optical colour (a440) and the degradation of high molecular weight organic molecules. By considering
these spatial and temporal variations, it was possible to determine the role of hydrological conditions of the lake basin on the
lake water quality.
The spatially explicit data obtained in a shallow wetland lake were used to determine a series of algorithms that estimate the
time dependant relationship between the water optical properties and the residence time in the lake, in particular in relation to
the degradation of dissolved organic matter and to the progressive loss of colour and spectrophotometric absorbance
The analysis of the seasonal, spatial and compositional distribution of humic substances in a subtropical shallow lake
No full textThe spatial and temporal distribution of humic substances in aquatic ecosystems can have
important effects on ecosystem productivity, negatively impacting primary productivity
while positively impacting secondary productivity. In the present investigation, a large shallow lake ecosystem was studied to determine the spatial and seasonal variation of the
Hydrobiology, composition and concentration of humic substances. Concentrations of total dissolved orMinister
of Agriculture, ganic matter, humic acid, and fulvic acid were found to display significant spatial distributions (1.3...13.5 mg/L, DOM; 0.1...5.4 mg/L, HA). The distribution is described by using
mapping techniques and the analysis of the spatial distribution of the lake. An analysis of
the seasonal variations also indicated the dependence of the occurrence of these compounds
on meteorological and hydrological conditions.
To identify the potential sources of these organic materials, an analysis was made of the
ratio of humic and fulvic acid fractions and total DOM. It was found that areas of high DOM
concentration coincided with the areas of highest HA percentage of total DOM. Furthermore
using the ratio of the normalised concentrations of HA, FA, and residual DOM
(< 5000 g/mol) it was found that areas dominated by each are spatially distinct. This
confirms the hypothesis that in these shallow lakes, photodegradation and bacterioplankton
activity will create a residence time dependent zonation of each component of the
total DOM
Relationships between wetland ecotones and inshore water quality in the Ugandan coast of Lake Victoria
No full textMuch of the lake shore in Lake Victoria is covered by extensive wetlands, often dominated by dense papyrus stands that extend out over the lake waters. These wetlands, their extension and management play a role in the physical, chemical and biological conditions of the inshore waters. Continuous transects along 180 km of shoreline together with spatial grids of sampling sites in eight bays were performed in the Ugandan inshore waters in order to analyze the relationships between the wetland characteristics and water quality. Measurements of extension of the wetland ecotones, water temperature (T), pH, Secchi disk depth (SD), dissolved oxygen (DO), total nitrogen (TN), total phosphorous (TP), dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP) and chlorophyll-a (CHL) were made in each sampling area. Data of T, pH and DO collected during the transects showed that the water characteristics of the bays differ from the open shoreline. Moreover, the magnitude of these physical–chemical differences is strongly conditioned by the dimension of the bordering wetlands. Bays with extensive wetlands ecotones were characterized by cooler, more acidic and poorly oxygenated waters. TN : TP ratios and especially DIN : SRP ratios decreased with the wetland presence along the coastline, showing a higher probability of N limitation in the inshore waters where large wetlands are present. Results point to denitrification processes in the wetland ecotones as the cause of this trend. The distribution of CHL was found to be highest in the presence of two significant point loading sources: a river (in Katonga Bay) and a major population centre (Kampala, in Murchison Bay). The reduction of external P loading is shown as an important step in the management of the eutrophication process of Lake Victoria inshore waters
The spatial distribution of the optical properties in the UV and Visible in an aquatic ecosystem.
No full textIn aquatic ecosystems, the UV and visible radiation environment
is strongly influenced by variation in the chemical and
physical parameters of the ecosystems. In shallow lakes, highly
heterogeneous water characteristics produce a wide variety of
optical environments. Such ecosystems require analysis approaches
that consider a potential variability. In this study, 77
stations were used to characterize the optical properties of a
shallow lake (open water surface 54 km2). The vertical
attenuation of solar radiation at 305,313,320 and 340 nm and
at photosynthetically active radiation was measured during the
seasonal cycle. Dissolved organic matter (DOM), turbidity,
fluorescence, pH, temperature, conductance and dissolved oxygen
were simultaneously measured. The spatial variation of the
extinction spectra of the dissolved fraction at each sampling
station was also measured and analyzed between 270 and
400 nm. The spatial heterogeneity of the lake was examined by
determining the distributions of the attenuation coeff~cientsa nd
biooptical parameters at high spatial resolution and describing
the distributions in a series of maps. The methodology permitted
a quantitative description of the interaction between solar radiation
and aquatic ecosystems as well as a spatial classification of
the dominating processes within the lake. This included the
determination of the role played by DOM loading and changing
chemical properties within the lake optical environment
The role of wetlands in the chromophoric dissolved organic matter release and its relation to aquatic ecosystems optical properties. A case of study: Katonga and Bunjako Bays (Victoria Lake; Uganda)
No full textChromophoric Dissolved Organic Matter (CDOM) is an important component in freshwater and marine ecosystems
and plays direct and indirect role in biogeochemical cycles. CDOM originates from the degradation process of organic
materials, usually macrophytes and planktons. The present work examines the importance of wetland derived CDOM
on the optical and bio-optical properties of two bays of Lake Victoria (Uganda, Africa). This was achieved by determining
the attenuation and extinction coefficients of filtered and unfiltered water samples from two equatorial bays on the Ugandan
coastline of Lake Victoria. Katonga Bay is a wetland lined bay that receives water from the Katonga river, while Bunjako
Bay is an outer bay between Katonga Bay and Lake Victoria. The results showed that attenuation was highest in
Katonga Bay and the role ofCDOMis most dominant near the river inlet. The quantity and quality ofCDOMis extremely
different in the two bays: in Katonga Bay it is possible to hypothesize a terrestrial origin of CDOM (transported by the
wetland river). On the contrary, in Bunjako Bay, spectral measurements of absorption indicate a modified CDOM and/
or alternative CDOMsource. The terrestrial CDOMin Katonga Bay is more capable of absorbing harmful UV radiation
than theCDOMpresent in the Bunjako Bay. The resulting optical environment in the former bay presented a water column
with a very limited penetration of harmful UV radiation, while a higher penetration was observed in the Bunjako Bay
ToF-SIMS investigation of ancient ceramics from the Quartaia Site, Tuscany (Italy)
No full textThe study of ancient ceramic fragments provides important information about the production technology that characterized a certain civilization. In this work, time-of-flight secondary ion mass spectrometry (ToF-SIMS), atomic absorption spectroscopy(AAS) and scanning electron microscopy (SEM) were used to study two types of ceramics having different impasto (depurata and non-depurata ceramics). Ancient fragments, belonging to the archeological site of Quartaia (Tuscany, Italy), were examined to obtain chemical and spatial information on inorganic and organic components. The results revealed the presence of the major elements, i.e. Al, Mg, Na, K, Ca, Si, Fe; minor elements, i.e. Cr, Cu, Mn, Pb; and organic components adsorbed during the firing process, both in depurata and non-depurata ceramics. In addition, through ToF-SIMS imaging, it was possible to highlight inorganic components, i.e. Na, Ca, Fe, K and Mg, that showed an inhomogeneous spatial distribution in non-depurata ceramics. These chemical elements appear to be concentrated inside the inclusions of the non-depurata ceramics impasto. These unique results demonstrated that ToF-SIMS is a potential tool to reveal important aspects of the Quartaia ceramic production technology and it results in a very promising technique for the archeological studies
- …
