Dynamics of arrays of floating point-absorber wave energy converters with inter-body and bottom slack-mooring connections

If point absorbers are employed in the extensive exploitation of the offshore wave energy resource, they should be deployed in arrays, the distance between the elements in the array being possibly tens of meters. In such cases, it may be more convenient that the array is spread moored to the sea bottom through only some of its elements, located in the periphery, while the other array elements are prevented from drifting and colliding with each other by connections to adjacent elements. An array of identical floating point absorbers located at the grid points of an equilateral triangular grid is considered in the paper. A spread set of slack-mooring lines connect the peripheric floaters to the bottom. A weight is located at the centre of each triangle whose function is to pull the three floaters towards each other and keep the inter-body mooring lines under tension. The power take-off system (PTO) is a linear damper activated by the buoy heaving motion. The whole system–buoys, moorings and power take-off systems–is assumed linear, so that a frequency domain analysis may be employed. Hydrodynamic interference between the oscillating buoys in array is accounted for. Equations are presented for a set of three identical point absorbers. This is then extended to more complex equilateral triangular grid arrays. Results from numerical simulations, with regular and irregular waves, are presented for the motions and power absorption of hemispherical converters in arrays of three and seven elements and for different mooring parameters and wave incidence angles. Comparisons are given with the unmoored and independently-moored buoy situations.     

Biogeochemical processes and nutrient cycling within an artificial reef off Southern Portugal

This study (2002/2004) examines the effect of artificial reef (AR) structures off the southern coast of Portugal on biogeochemical process and nutrient cycling. Organic and inorganic carbon, nitrogen, phosphorus and chlorophyll a were determined monthly in sediment cores and settled particles for a two-year period. Ammonium, nitrates, phosphates, silicates, total organic nitrogen and phosphorus, chlorophyll a and phaeopigments were also determined monthly in water samples within AR and control sites. Results of the two-year study showed that: (i) there was a significant exponential fit between organic carbon and chlorophyll a (r2=0.91; p<0.01) in reef sediment suggesting an increase of benthic productivity; (ii) organic carbon and nitrogen content in settled particles within AR environment was about four times higher two years after reef deployment; (iii) nutrients and chlorophyll a in the water column were higher at AR than control site. Two years after AR deployment, dissolved organic and inorganic compounds in near bottom water were 30-60% higher, emphasizing benthic remineralization processes at AR's organically rich sediment. Marked chemical changes in the ecosystem were observed during the two-year study period, reinforcing the importance of these structures for sandy coastal areas rehabilitation through trophic chain pull-out.     

The use of the marine biotic index AMBI in the assessment of the ecological status of the Obidos lagoon (Portugal)

This study reports the longitudinal distribution of sediment properties, including inorganic and organic contaminants, and the structure of the benthic community in Obidos lagoon, a coastal system permanently connected to the sea and with negligible freshwater sources. Sediments from the upper to central lagoon consist of fine particles (91%) and from the lower lagoon of sands (94%). Chemical composition is strongly correlated to the percentage of fine particles. Contamination is relatively low in those sediments suggesting the effect of diffuse sources. The increase in organic matter content from down- to upstream areas was associated with the dominance of opportunistic species, while sensitive and indifferent species to organic enrichment were mainly associated to the clean sandy downstream area. The marine biotic index (AMBI) was suitable for the discrimination of the biological and environmental gradients in the Obidos lagoon and was highly related with the gradient of organic matter content in this system.     

Pathogenic fungi: an unacknowledged risk at coastal resorts? New insights on microbiological sand quality in Portugal

Whilst the potential impact on beach users from microorganisms in water has received considerable attention, there has been relatively little investigation into microbial contaminants in sand. Thirty three beaches across Portugal were analyzed during a five year period (2006-2010) to determine the presence of yeasts, pathogenic fungi, dermatophytes, total coliforms, Escherichia coli and intestinal enterococci in sand.Our results showed that 60.4% of the samples were positive for fungi and that 25.2% were positive for the bacterial parameters. The most frequent fungal species found were Candida sp. and Aspergillus sp., whereas intestinal enterococci were the most frequently isolated bacteria. Positive associations were detected among analyzed parameters and country-regions but none among those parameters and sampling period.Regarding threshold values, we propose 15 cfu/g for yeasts, 17 cfu/g for potential pathogenic fungi, 8 cfu/g for dermatophytes. Eighty four cfu/g for coliforms, 250 cfu/g for E. coli, and 100 cfu/g for intestinal enterococci.     

Comparative hydrochemistry of five nested catchments located in the upper part of the Barcés river watershed (A Coruña,NW Spain)

259 stream water and 21 bulk precipitation samples have been studied between April 2008 and December 2010 in order to assess baseline hydrochemical conditions in a rural area of NW Spain. Stream waters are related to five nested catchments (<10 km²) with apparent low mean residence times. Their hydrochemical characteristics are closely related to bulk precipitation although clear evidences of seasonal (flushing, dilution, sediment desorption, etc.), lithological (schist vs. granite substrate) and anthropogenic (land use, contamination) effects are also described.     

Convection theory before relaxation

The well known mixing length theory of convection is revised for times shorter than the effective time of relaxation into diffusion.Using the Cattaneo equation for the heat flux, we show that the revised theory predicts, before relaxation, a convective flux which is quite different from the flux obtained with the Maxwell-Fourier law.Implications of this result in the outcome of some astrophysical processes are commented upon.     

Effects of infauna harvesting on tidal flats of a coastal lagoon (Ria Formosa, Portugal): implications on phosphorus dynamics

The systematic collection of benthic organisms in tidal flats of coastal lagoons should be taken into account for the management of these systems, once sediment disturbance affects biogeochemical processes by favouring pore water renewal during tidal inundation. The objective of the present work was to evaluate the effects of infauna harvesting on the phosphorus dynamics of muddy and sandy intertidal areas in the Ria Formosa. Sediment cores and overlying water were collected during August 2000 and February 2001 from reworked and undisturbed sediment before and after flooding. Results obtained showed that during the first minutes of flooding there was a marked decrease of phosphate in pore water of disturbed sediments. However, phosphate tidal fluxes from sandy sediment were clearly higher (17 nmol cm(-2) d(-1) in summer and 3 nmol cm(-2) d(-1) in winter) than in muddy sediment (0.4 nmol cm(-2) d(-1) in summer and -0.01 nmol cm(-2) d(-1) in winter). After muddy sediment disturbance concentrations of iron oxides increased quickly (from 5 to 16 micromol g(-1)) and phosphate was sorbed onto these iron oxides, resulting in a buffering of phosphate pore water concentrations at low values in the oxidized sediment zone. The estimated P-output from muddy sediment decreased one to two orders of magnitude after sediment disturbance in contrast to sandy sediments in which the impact of infauna harvesting was minimal. Consequently, the P-cycle is influenced by the disruption of muddy habitats in tide-driven systems. Such information could be useful for the management of the lagoon.     

Impact of coal tar pavement on polycyclic hydrocarbon distribution in lacustrine sediments from non-traditional sources

The evaluation of potential environmental impacts from polycyclic aromatic hydrocarbon is a subject that requires investigation, especially related to emission sources from highway roads with high traffic. In this paper, the distribution of polycyclic aromatic hydrocarbons was investigated in the surface sediments from a subtropical lake, located in the south of Brazil and away from urban areas. The results showed that all sediments presented such compounds in significant concentration, ranging from 9.50 to 29.88???g/g. The highest total concentration was found in those sites close to the highway (bridges) and the deepest area of the lake. Moreover, a high concentration of polycyclic aromatic hydrocarbons of high molecular weight, such as benzo(a)anthracene and dibenzo(a,h)anthracene was found. It was laso found that high concentrations might be related to asphalt and coal tar pavement used in the highway construction close to the lake. In addition, the potential capacity of sediment toxicity was compared with values of the interim sediment quality guidelines values. The results indicate that most of the sediment presents concentrations of hydrocarbons above these limits. Only fluoranthene and chrysene were found in concentrations below the guideline values. The concentrations of most of the polycyclic hydrocarbons are higher than the quality guidelines. However, the main concern is associated with the presence of benzo(a)anthracene whose concentration is 416 times higher than the limit establisehed by guidelines. The same observation can be done to traces of benzo(a)pyrene and dibenz(a,h)anthracene, with concentration values of 13 and 1,993 times higher.     

Vertical distribution of two sympatric labrid fishes in the Western Mediterranean and Eastern Atlantic rocky subtidal: local shore topography does matter

Changes in the shore topography (e.g. slope) occur at a scale of hundreds of meters in several locations in the Lusitanian and the Mediterranean Sea provinces. We tested whether differences in the bottom inclination might affect the vertical distribution patterns of two sympatric coastal labrid fishes, the rainbow wrasse Coris julis and the ornate wrasse Thalassoma pavo. Visual censuses were used to determine the distribution and abundance of these labrid species in high (≥30°) and low (≤3°) slope rocky substrates covered by brown macroalgae and at two different depths (shallow, 4–7 m, and deep 14–20 m). Pectoral fin aspect ratio was used as an estimate of swimming performance to potentially explain the patterns observed. Despite the intrinsic biogeographical differences in the overall density of T. pavo and C. julis, on steep coasts the ornate wrasse dominated in shallow waters, whereas the two species coexisted both in shallow and deeper depths on gentle slope coasts. These distribution patterns were consistent across locations, and fin aspect ratio was not a good predictor of between‐habitat use for wrasses. We show that, under specific topographical conditions, the depth segregation pattern seems to be an interactive segregation (likely related to resource competition) rather than a result of selective segregation due to morphological differences in the pectoral fin. Significant ecological changes might occur in locations where the density of T. pavo has recently increased as a result of water warming.