The role of the smooth cordgrass Spartina alterniflora and associated sediments in the heavy metal biogeochemical cycle within Bahía Blanca estuary salt marshes

Background, aim, and scope

Bahía Blanca estuary is characterized by the occurrence of large intertidal areas, including both naked tidal flats and salt marshes densely vegetated with Spartina alterniflora. The estuary is strongly affected by human activities, including industrial and municipal discharges, harbor maintenance, cargo vessels and boat navigation, oil storage and processing, etc. Even numerous studies have reported the occurrence and distribution of heavy metals in sediments and biota from this estuary, although the function of the halophyte vegetation on metals distribution was at present not studied. The main objective of the present study was to understand the potential role of the salt marshes as a sink or source of metals to the estuary, considering both the obtained data on metal levels within sediments and plants from the studied areas at naked tidal as well as vegetated flats.

Materials and methods

The selected study area, named Villa del Mar, was located in the middle estuary coast. The sampling was carried out under low tide conditions, and the sampling area was divided into two parts: A (close to Villa del Mar) and B (north-westerly of Villa del Mar). In each part, two integrated samples of S. alterniflora (the first in the medium-salt marsh and the second in the higher one) were collected. Also sediments associated with the roots of S. alterniflora were taken at the same locations, in addition to another sediment sample from the naked zones of the tidal flats (without any vegetation). After corresponding treatment at the laboratory, plant and sediment samples were mineralized according to Marcovecchio and Ferrer, J Coast Res 21:826–834, 2005), in order to measure their metal concentrations by atomic absorption spectroscopy (AAS). Analytical quality (AQ) was checked against certified reference materials from NIES, Tsukuba (Japan).

Results

Most of the Spartina samples have shown highest Cd and Mn concentrations in the aerated parts of the plants, indicating an allocation process from the roots up to the leaves. Most of the samples have presented non-detectable Pb and Cr values. Cu, Fe, Ni, and Zn have presented highest concentrations in the underground parts of the plant, suggesting an accumulation process in the roots and rhizomes. In the case of sediments, samples from those sites located far away from Villa del Mar have presented greater concentrations on the sediments associated with underground parts of Spartina than those from the naked tidal flat, for almost all of the metals studied. Unlike this, the samples from the site close to Villa del Mar have shown the higher concentrations in sediments from the naked tidal flat.

Discussion

Marsh plants are known to absorb and accumulate metals from contaminated sediment, and this is one reason that allows wetlands to be used for wastewater treatment. It was observed that those sets of samples from the same salt marsh levels (e.g., A.1 and B.1, or A.3 and B.3) have shown similar heavy metal distribution trends, although even their corresponding concentrations could be different. Thus, the concentrations of Cu, Zn, Ni, and Fe in the medium-salt marshes were higher in the underground tissues (roots plus rhizomes), with the exception of Mn, which was seen to be higher in the aboveground parts. The same tendency occurs at high-salt marshes for these heavy metals, with the exception of Ni. This fact was sustained regarding the fact that the levels mentioned (medium-salt marsh and high-salt marshes) must have the same exposition to heavy metal sources, similar physical-chemical conditions regulating metal distribution within the compartments on the salt marshes or, simultaneously, both mentioned processes. Moreover, metals in this macrophyte can remain after the leaves have died and turned into detritus. The metals present in the detritus can be passed on to consumers (Quan et al., Mar Environ Res 64:21–37, 2007)). Keeping in mind that Bahía Blanca estuary’s salt marshes are inundated twice each day by tidal water for 3–4 h, macrophytes may act as a conduit for the movement of metals from the sediment to the estuarine body and near-coastal system.

Conclusions and recommendations

Considering the comments on the previous paragraphs, salt marshes from Bahía Blanca estuary are sources or sinks for metals? It can be sustained that both are the case, even if it is often stated that wetlands serve as sinks for pollutants, reducing contamination of surrounding ecosystems (Weis and Weis, Environ Int 30:685–700, 2004)). In the present study case, the sediments (which tend to be anoxic and reduced) act as sinks, while the salt marshes can become a source of metal contaminants. This is very important for this system because the macrophytes have been shown to retain the majority of metals in the underground tissues, and particularly in their associated sediments. This fact agreed well with previous reports, such as that from Leendertse et al., Environ Pollut 94:19–29, 1996) who found that about 50% of the absorbed metals were retained in salt marshes and 50% was exported. Thus, keeping in mind the large spreading of S. alterniflora salt marshes within Bahía Blanca estuary, it must be carefully considered as a re-distributor of metals within the system.     

Feeding physiology and scope for growth of the oyster Crassostrea corteziensis (Hertlein, 1951) acclimated to different conditions of temperature and salinity

There is a particular interest in Mexico for the grow-out and breeding in captivity of the native oyster Crassostrea corteziensis. However, there is a lack of knowledge of the effect of temperature and salinity on the feeding physiology that maximizes the growth and eventually achieves the maturation of C. corteziensis. Our aim was to evaluate the filtration and clearance rates, oxygen consumption, ammonium excretion rates, assimilation efficiency, and scope for growth of the oyster C. corteziensis acclimated during 2 weeks to different combinations of temperature (23, 26, 29, and 32 °C) and salinity (20, 30, 40, and 50 psu). Oysters were fed with a standard suspension of the microalga Chaetoceros muelleri as total particulate matter, which was supplied at 4.2 L h^?1 into 10 1-L tanks used as experimental chambers. The results showed that filtration and clearance rates increased with increasing temperature and decreased with increasing salinity, with the highest values obtained at 29 °C and 20 psu. Ammonium excretion and, to lesser extent, oxygen consumption matched with the variations in the feeding rate. The values of the scope for growth (SFG) suggested that C. corteziensis is able to grow out in all combinations of temperatures and salinities tested in this work. However, the SFG decreased at higher salinity (50 psu) in both extreme temperatures (23 and 32 °C), with highest value occurring at intermediate temperature and the lowest salinity. The SFG increased with increasing temperature and decreased with increasing salinity, which was explained by the increase in the feeding rates and ammonium excretion, coupled with higher absorption efficiency of the food. We concluded that higher filtrations and scope for growth of oysters occurred at 29 °C in brackish-water (20 psu) rather than in marine-water conditions. The results obtained can be considered highly useful information for aquacultural management of this oyster species, and useful to establish suitable sites to enhance their cultivation and maximize the growth of C. corteziensis.     

Forecasting of jack mackerel landings (Trachurus murphyi) in central‐southern Chile through neural networks

In the present study, the performance of neuronal networks models in monthly landing forecasting of jack mackerel (Trachurus murphyi) in central‐southern Chile (32°S–42°S) was assessed. Thus, monthly estimations for 10 environmental variables, fishing effort (fe) and jack mackerel landings for the period 1973–2008 were used. A preliminary analysis was done in order to remove strongly correlated variables. Sea surface temperature (SST) and fe are established as input variables, then, a non‐linear cross correlation analysis was performed to estimate the lag between the input variables and jack mackerel landings. Two models were adjusted: model one includes both training and testing cases randomly selected using all data involved in the analysed period; for model 2, the data is divided into two time series: the first from 1973 to 2002 used for training and the second between 2003 and 2008 used for validation. The external validation process for model 1 showed an explained variance of 92%, with a standard forecasting error of 30%. The explained variance for model 2 was 81%, with a standard forecasting error of 38%. Finally, the sensitivity analysis for both models showed the fe as the most influential variable to jack mackerel landings, which presents functionality depending on anthropogenic effects rather than environmental conditions.     

Pharmacokinetics of injectable marbofloxacin after intravenous and intramuscular administration in red-eared sliders (Trachemys scripta elegans)

Fluoroquinolone antibacterial drugs are currently used in reptilian medicine because of their broad spectrum of activity including the most frequent pathogens of these species. The disposition kinetics of marbofloxacin (MBX) at a single dose of 2 mg/kg were determined in healthy red-eared sliders after intravenous (IV) and intramuscular (IM) administration. The influence of renal portal system on the bioavailability of the drug was investigated by using forelimb and hindlimb as IM injection sites. Apparent volume of distribution at steady-state (V_ss) and systemic clearance (Cl) of marbofloxacin after IV administration were estimated to be 48.21 ± 5.42 ml/kg and 23.38 ± 2.90 ml/hr·kg, respectively. The absolute bioavailabilities after IM route were 45.96% (forelimb) and 52.09% (hindlimb). The lack of statistically significant differences in most of the pharmacokinetic parameters after the two IM injection sites suggests a negligible influence of renal portal system in clinical use of MBX, although the C_max after IM_fore administration is advantageous, having into account the concentration-dependent action of this antibiotic. The absence of visible adverse reactions in the animals and the advantageous pharmacokinetic properties suggest the possibility of its safe and effective clinical use in red-eared sliders.     

Isomerization of lactose-derived oligosaccharides: a case study using sodium aluminate

Galactooligosaccharides (GOS) obtained during the enzymatic hydrolysis of lactose contain large amounts of glucose, galactose, and unreacted lactose, which do not have prebiotic properties and increase the calorific value of the product. In this work, the isomerization of the GOS mixture by the action of sodium aluminate has been studied. During the reaction, lactose, glucose, and galactose were isomerized to lactulose, fructose, and tagatose, respectively, and in addition allolactose, 6-galactobiose, and 6'-galactosyl-lactose were also converted to the corresponding keto-sugars. The effect of time, temperature, and aluminate/initial lactose ratio has been studied. After 9 h at 40 degrees C and molar ratio aluminate/lactose 3:1, the isomerization yield was >60%, and the amount of final carbohydrates was close to 90% of the initial product. This process considerably decreases the amount of lactose, glucose, and galactose.     

Evaluating trap cropping strategies for insect pest control through simulation models

Trap cropping is a habitat management strategy where the aim is to reduce damage to the crop of interest by mixing it with other plants that are highly attractive to insect pests. However, despite its potential, the application of this strategy has been limited mainly due to a lack of consistent effectiveness. Here, we developed an individual-based spatially explicit model that accounts for reproduction, movement and mortality of insects within a mixed crop system. This model was used to evaluate the effects of varying trap crop spatial configurations (border, stripes and patches), cover (2, 4 and 10 %) and supplemental management strategies (early harvest and pesticide application) to gain insight into the best control options offered by trap cropping. As a case study, we considered Liriomyza huidobrensis, a world known leafminer pest. Our results showed a maximum reduction of about 34 % in the pest population of the main crop when using trap plants. The supplemental management strategy had a stronger effect than other factors, with pesticide use being the best option. A sensitivity analysis showed that demographic parameters were more relevant than the behavioral ones in determining the success of the method. Our model suggests that trap cropping is only suitable for controlling L. huidobrensis if a pesticide application is added to the trap crop. Individual-based models, which are cheaper and less laborious than direct field testing, might provide an important tool to help define management schemes for the control of herbivorous pests.     

Effects of biochars produced from different feedstocks on soil properties and sunflower growth

The use of biochar as a soil amendment is gaining interest to mitigate climate change and improve soil fertility and crop productivity. However, studies to date show a great variability in the results depending on raw materials and pyrolysis conditions, soil characteristics, and plant species. In this study, we evaluated the effects of biochars produced from five agricultural and forestry wastes on the properties of an organic‐C‐poor, slightly acidic, and loamy sand soil and on sunflower (Helianthus annuus L.) growth. The addition of biochar, especially at high application rates, decreased soil bulk density and increased soil field capacity, which should impact positively on plant growth and water economy. Furthermore, biochar addition to soil increased dissolved organic C (wheat‐straw and olive‐tree‐pruning biochars), available P (wheat‐straw biochar), and seed germination, and decreased soil nitrate concentration in all cases. The effects of biochar addition on plant dry biomass were greatly dependent upon the biochar‐application rate and biochar type, mainly associated to its nutrient content due to the low fertility of the soil used. As a result, the addition of ash‐rich biochars (produced from wheat straw and olive‐tree pruning) increased total plant dry biomass. On the other hand, the addition of biochar increased the leaf biomass allocation and decreased the stem biomass allocation. Therefore, biochar can improve soil properties and increase crop production with a consequent benefit to agriculture. However, the use of biochar as an amendment to agricultural soils should take into account its high heterogeneity, particularly in terms of nutrient availability.     

Sequence analysis within the RNA 3 of seven Spanish tomato isolates of Parietaria mottle virus (PMoV-T) reveals important structural differences with the parietaria isolates (PMoV)

The genomic regions encoding the putative movement protein (MP), coat protein (CP) and intergenic region (IGR) of seven Spanish isolates of the Parietaria mottle virus which infects tomato plants (PMoV-T) were sequenced. Values for the genetic diversity of the PMoV-T isolates were 0.056, 0.047 and 0.013 for the CP, MP genes and IGR, respectively. Nucleotide and amino acid sequence comparison of the seven PMoV-T isolates with those of PMoV revealed significant differences. All of them had a cytosine deletion at position 1366, also confirmed in an Italian tomato isolate, which involves a start codon for the CP gene different from that for the PMoV sequence, resulting in a CP 16 amino acids shorter than the PMoV CP. The certainty of a cytosine deletion only associated to the tomato isolates or the possibility of a mistake in the PMoV published sequence are the two hypotheses that could explain this difference. Structural motifs highly conserved in Ilarviruses were identified in PMoV-T MP and CP. A stable hairpin structure is proposed for IGR, by the initiation site for subgenomic RNA 4 synthesis. Phylogenetic analysis of CP and MP amino acid sequences showed that Spanish PMoV-T isolates form a separate group from PMoV and other members of the Ilarvirus genus. Comparative analysis with different PMoV isolates including tomato isolates from other regions and isolates from different hosts are necessary to confirm this differentiation.     

Multiscalar land suitability assessment for aquaculture production in Uruguay

This article presents a highly detailed territorial assessment for aquaculture production in Uruguay and a methodology to identify the most suitable areas in order to develop the activity. Furthermore, it proposes the basis to generate a dynamic modelling tool of high spatial resolution to support the decision‐making process regarding national aquaculture activities. The modelling structure of aquaculture suitability was developed by the construction of a hierarchical model, combining a multicriteria assessment and a geographic information system. Forty‐one attributes were integrated in six aptitude models: one model for each one of the five common production systems intended to be the most viable in Uruguay and a sixth aptitude indicator that summarizes those five systems, representing the maximum suitability for aquaculture activities. In addition, the hierarchical model allows measurement and identification of relative weights of each model, according to the planning scale, ranging from basin to cell.