Vanesa L. Negrin

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.

Tidal time-scale variation of inorganic nutrients and organic matter in Bahía Blanca mesotidal estuary, Argentina

Land-derived materials are regulated by coastal and shelf environmental conditions before being transported to the open sea. It is of great concern to understand the processes and to establish the extent in which they modify terrestrial compound fluxes, such as nutrients, that end up in the oceans. At present, one of the topics that arouses the highest interest within environmental coastal studies is the direction and magnitude of inorganic nutrients and the exchange fluxes of organic matter between the water column and the associated tidal plains during the daily tidal cycle. These processes, together with the local hydrographic conditions, define the key role of this type of environment: its function as a nutrient and organic matter reservoir and/or as a source. A research programme directed to understand this mechanism within mesotidal estuaries was developed in the Bahía Blanca estuary, on the coast of Buenos Aires (Argentina). On a tidal time-scale basis, levels of DIN (nitrate + nitrite + ammonium), DIP, DISi, and organic matter were measured in the estuarine water column and tidal plain porewater, for two years. Results showed no significant variations during the tidal cycle, even though the temporal variation of these compounds was clearly identified. In addition, the biological production of the estuary was considered and taken into account, so as to understand the organic matter cycle within the system. Particular conditions of the environment (sediment characteristics, porewater chemical environment, hydrodynamics, anthropogenic sources, etc.) were also considered to help fully understand the results.

Above- and belowground biomass and nutrient pools of Spartina alterniflora (smooth cordgrass) in a South American salt marsh

In order to examine the role of position in the tidal range on biomass production and nutrient pools in Spartina alterniflora in an Argentinian estuary, we estimated productivity, the concentration of C, N and P in tissues and pools (concentration×biomass) of these elements in low (LM) and high (HM) zones. Aboveground biomass of S. alterniflora was higher in HM than in LM. Aboveground primary productivity was 106 and 439 g dry wt m−2 year−1 in LM and HM, respectively. Belowground biomass was similar in LM and HM. Belowground primary productivity was 526 and 744 g dry wt m−2 year−1 for LM and HM, respectively. Nutrient pools were higher in HM than in LM. Biomass and productivity values were low, which makes nutrient pools low. The lower values of the parameters analysed in LM than in HM indicate that position in the tidal range is an important factor in this system, possibly due to the effect of flooding. Moreover, this pattern is opposite to the general one observed in the northern hemisphere, meaning that studying marshes from different environments is worth doing. Because pools were higher in HM, this zone would be more important for nutrient input to the estuary.

The role of Sarcocornia perennis and tidal flooding on sediment biogeochemistry in a South American wetland

Abstract The roles of Sarcocornia perennis and tidal flooding on sediment biogeochemistry were evaluated within a wetland in the Bahía Blanca estuary. pH and Eh were measured in sediments while particulate organic carbon (POC) and dissolved inorganic nutrient concentrations were determined in porewater, at three sites with different conditions according to vegetation and flooding. Grain size was also analysed. pH varied in a narrow range (7–8.2) and was lower in the vegetated site. Eh values (50–250 mV) imply that sediment conditions were moderately reduced, in agreement with the relatively high percentage of sand; it was influenced by both factors. POC concentration was high (26.24±1.62 mg/l), especially at the vegetated site. The concentrations of ammonium and nitrate were similar (21.30±1.83 and 18.77±3.06 µmol/l, respectively) and not affected by flooding; only nitrate was affected by vegetation. Phosphate was rather constant (13.43±1.19 µmol/l) and affected mainly by flooding. Silicate was high (566.45±76.06 µmol/l) and not affected by either factor. These results suggest that the sediment biogeochemistry of this environment is significantly influenced by flooding and, especially, by S. perennis, as vegetation affected a higher number of parameters.

Decomposition and nutrient dynamics in a Spartina alterniflora marsh of the Bahia Blanca estuary, Argentina

, Descomposicao, Nutrientes, Marisma Argentina. Salt marshes are among the most productive systems in the world. As a consequence, they also produce great amounts of litter (e.g. BOUCHARD; LEFEUVRE, 2000; MONTEMAYOR et al., 2011), which becomes a large and renewable pool of organic matter and nutrients. Litter alternately releases and absorbs nutrients (especially of C, N and P) as it decomposes (JORDAN et al., 1989). Hence, detritus is a considerable energy source for microorganisms in the marsh and the adjacent estuary, being the basis of the food web in these ecosystems (MOORE et al., 2004). On the other hand, the concentration of C, N and P in the tissues and, most importantly, the ratios between them, are factors that determine the rate of decomposition (ENRIQUEZ et al., 1993; REJMANKOVA; HOUDKOVA, 2006).

Uptake and accumulation of metals in Spartina alterniflora salt marshes from a South American estuary

Salt marshes are capable of reducing metal pollution in coastal waters, but this capacity is highly dependent on the metal, the physico-chemical characteristics of the sediment, the plant species, the production of biomass, the time of the year, etc. The aim of this study was to assess the uptake and accumulation of Pb, Ni, Cu and Zn in Spartina alterniflora from three salt marshes within the Bahía Blanca estuary (BBE), a human-impacted Argentinean system. Metal concentrations in sediments and plants showed the same order at all sites: Zn > Cu > Pb ≥ Ni. The site with lower organic matter and fine sediment content had lower metal concentrations in the sediments, but not a lower metal content in the plant tissues, meaning that the sediment characteristics influenced the metal concentrations in the sediment and their uptake by plants. Despite differences in sediment characteristics between sites, metals were always higher in the belowground tissues than in aboveground ones and, in general, higher in dead than in live tissues. Some metals were accumulated in plant tissues, but not others, and this is dependent on the metal and the sediment characteristics. Allocation patterns of metals in tissues of S. alterniflora were mainly dependent on metal concentrations, determining higher belowground pools, but the aboveground pools were important in some cases due to higher biomass. Partitioning of metals in above or belowground pools determines their fate within the estuarine system, since tissues can decompose in situ (belowground) or be exported (aboveground). Seasonal dynamics were important for some variables but were less noticeable than the differences between sites and tissues. Our results indicate that S. alterniflora from the BBE is efficient in accumulating some metals, despite usually low metal concentrations in sediments and plants. This accumulation capacity has implications for the whole system through the fate of the tissues.