Gerardo M. E. Perillo

A sand wave field in the entrance to Bahia Blanca Estuary, Argentina☆

Abstract Sand waves in the mouth of the Bahia Bllanca Estuary show differences in wavelength, crestlength and crest shape characteristics between two sectors of the field. These differences may be explained by assuming that the residual ebboriented currents are stronger in the southern sector. Crest bifurcations on the centerline are suggestive of intermediate energy conditions and the development of secondary flows oblique to the main current direction. The large lee slopes and the presence of megaripple fans are indicative of flow separation, a condition seldom mentioned for subtidal sand waves. Boundaries of the sand wave field may be controlled by the thickness of the surficial sand layer, rapid reduction of the water depth as produced by a large marginal shoal, and variations in grain size. An average migration rate of 33 m yr−1 was calculated from repeated bathymetric surveys. Assuming that sand waves preserve shape and size, the established net sediment flux over the crests is 0.025 cm3 cm−1 s−1. Current measurements made during four individual tidal cycles yielded a net bedload sediment transport of 0.048 cm3 cm−1 s−1.

Geomorphological and Physical Characteristics of the Bahía Blanca Estuary, Argentina

Located at the southwest of the Buenos Aires Province, Argentina, the Bahia Blanca Estuary (Fig. 9.1) is considered the second largest estuary in the country after the Rio de la Plata. However, its geomorphologic and physical characteristics vary significantly from all other estuaries in Argentina and South America. Actually The Wash, located in the United Kingdom, is probably the only estuary in the world that have general characteristics quite similar to Bahia Blanca.

Influence of flooding and vegetation on carbon, nitrogen, and phosphorus dynamics in the pore water of a Spartina alterniflora salt marsh

Four sites were selected in a salt marsh in the Bahia Blanca Estuary (Argentina): (1) low marsh (flooded by the tide twice daily) vegetated by S. alterniflora; (2) non-vegetated low marsh; (3) high marsh (flooded only in spring tides) vegetated by S. alterniflora; (4) non-vegetated high marsh. The pH and Eh were measured in sediments, while dissolved nutrients (ammonium, nitrate, nitrite and phosphate) and particulate organic matter (POM) were determined in pore water. pH (6.2-8.7) was only affected by vegetation in low areas. Eh (from -300 to 250 mV) was lower at low sites than at high ones; in the latter, the values were higher in the non-vegetated sediments. The POM concentration was greater in the high marsh than in the low marsh, with no effect of vegetation. Ammonium was the most abundant nitrogen nutrient species in pore water, except in the non-vegetated high marsh where nitrate concentration was higher. All nitrogen nutrients were affected by both flooding and vegetation. Phosphate was always present in pore water at all sites throughout the year and its concentration varied within narrow limits, with no effect of flooding and greater values always at non-vegetated sites. Our results showed that the variability of the pore water composition within the marsh is greater than the temporal variation, meaning that both tidal flooding and vegetation are important in the dynamics of nutrients and organic matter in the sediment pore water.

The Argentina Estuaries: A Review

Despite of its long and extended coastline (5 700 km), the number of Argentine estuaries is relative small compared with other countries of comparable size. Mainly, the difference strives in the climate and the hydrological regime that characterize the country. Whereas the climate in the NE of Argentina is hot and humid with mean annual precipitation of 1950 mm and maximum of 2 437 mm; the NW is relatively dry and hot. In the center of the country the climate is mild with average precipitation on the order of 1000 mm, and in the South is dry and cold with annual precipitation of 300 mm or less.

Geomorphology of a sand wave in lower Chesapeake Bay, Virginia, U.S.A.

Morphologic and sedimentologic studies of a single sand wave within a sand wave field in the lower Chesapeake Bay suggest that the bedform was originally formed by ebb currents, and is presently in static equilibrium with the circulation pattern. In this report, the concept of “solitary” sand wave is introduced to describe the state of a sand wave when further evolution of the sedimentary structure is mostly independent of adjacent bedforms. This concept can be applied to several bedforms in the area that are isolated from others by flats. A particular sand wave that is included in this category is discussed.

What Do We Know About the Geomorphology and Physical Oceanography of South American Estuaries

As long as freshwater is discharged into the sea, there is the potential for the development of an estuary. Although this concept appears to be simple, the marked differences in geomorphologic, oceanographic, atmospheric and biogeochemical conditions that occur along the coasts of the world result in a wide variety of estuarine types. The variety is so large that several ways have been used as mean to define and classify them (Perillo 1995a).

Determination of optimal numbers of class intervals using maximum entropy

Based on the maximum entropy concept, optimal numbers of class intervals(K) for a closed array of samples has been determined. From the analysis, two values ofK (8 and 19) are selected as the most appropriate. ForK=8, the probability of occurrence on each unequal-size interval ispi=0.125, whereasK=19 results inpi=0.0526. An objective method for determining interval limits, modified from a previous method by Full et al. (1984), is also included.

Evaluation of the MODIS-Aqua Sea-Surface Temperature product in the inner and mid-shelves of southwest Buenos Aires Province, Argentina

Validation of sea-surface temperature (SST) provided by the MODIS-Aqua sensor (Moderate Resolution Imaging Spectroradiometer) for the inner and mid-shelves of the southwest of Buenos Aires Province (Argentina), is presented for the first time. In situ data obtained with a multi-parametric sonde YSI-6600 and a CTD SBE91 between 2002 and 2011 are used for comparison with the satellite SST product. The match-up exercise was established after comparing different spatial boxes, time difference windows, wind speeds, and also a coefficient of variation. The comparison exercise was made in the coastal zone and the rest of the inner and mid-shelves separately. In the coastal zone, applying a 3 × 2 pixel box and a time window of ±3 hours led to the most accurate results, with a coefficient of determination (R2) of 0.99, a bias of 0.62°C, and a root-mean-square-error (RMSE) of 0.79°C. In the inner-mid-shelves when applying a coefficient of variability <0.3, a time window of ±3 hours, and taking only values of wind speed > 6 m s−1, R2 is 0.97, bias is 0.46°C, and RMSE is 0.95°C. Wind speed plays a major role in the inner-mid-shelves as the SST product is affected by stratification and formation of a diurnal thermocline in the ‘skin and sub-skin layer’ when wind speed is below 6 m s−1. The results for the two shelves are very similar. Finally, the spatial and temporal variability of the SST satellite product was analysed in the study area for the period August 2002–December 2010. The results show that inter-annual variability is not significant and that there is no positive or negative trend for the 9 years of the study. Seasonality is the main component of temporal variability, with variation in amplitude signal depending on bathymetry changes, physical forcing, stability of the water column, and presence of flood plains.

Applications of maximum entropy and optimal number of class interval concepts: Two examples

Two data sets, one from surface sediment samples obtained from a subtidal sand wave and another consisting of three wave-height records representing different oceanographic conditions, are employed to test the application of maximum entropy (ME) and optimal number of class interval (K) concepts. Each data set was modified further to obtain a frequency distribution determined by eight unequal-size class intervals. Both original and modified sets were treated by a reliable statistical method. Comparison of relative entropies and results from statistical treatments show the advantage of the transformation of any original data set by means of ME and K methods before analyzing it further.

Implicancias de la variabilidad físico-biológica y la aplicación de normas legislativas sobre el recurso pesquero en la zona costera del sur de la Provincia de Buenos Aires, Argentina

Las condiciones hidrograficas y climatologicas de las aguas costeras son el principal factor a tener en cuenta cuando se analiza la abundancia de las especies icticolas. Ademas se deben considerar las leyes de proteccion pesquera, como las vedas y las limitaciones en permisos de pesca. El Rincon, localizado en el sur de la Provincia de Buenos Aires (Argentina) es un area costera compleja por las diferentes interacciones que se evidencian entre el continente y el mar y principalmente a traves de la susceptibilidad del sistema a la variabilidad climatica (eventos el Nino). En el presente estudio se analizan los desembarques pesqueros anuales en el periodo 2002-2010 en la zona de El Rincon asociado con las variaciones fisico ambientales del medio marino y las normas legislativas pesqueras de la zona. Como conclusion se infiere que las condiciones Nino benefician la abundancia de ciertas especies, mientras que el evento Nina beneficia el desarrollo de otras.