Unpolluted Estuary Research Articles

Links between elevated zinc levels, diet and muscle melanisation in sand flathead (Platycephalus bassensis) from polluted estuaries

Muscle melanisation in sand flathead is defined as the presence of abnormal black spots in the fish's flesh and the phenomenon has been associated with Zn pollution in the environment. In this study, Zn levels in the fish muscle and crabs were analysed to investigate the role of Zn in causing muscle melanisation and the fish's uptake of Zn via its diet, crabs. An improved technique for extracting melanised fish muscle from fillets with black spots was developed. It enabled Zn levels in melanised muscle to be more accurately determined when compared to previous study and showed Zn levels were 2.1–3.5 times higher in melanised regions of muscle than non-melanised regions of muscle from fish with melanisation and fish unaffected by melanisation. This indicated elevated levels of Zn were localised in the melanised muscle. Muscle melanisation was potentially caused by Zn ions binding to the active site of tyrosinase, an enzyme involved in melanin production, likely facilitated by the presence of higher Zn than Cu in the polluted estuaries. A digestion reagent mixture suitable for microwave assisted acid digestion and analysis of Zn in the whole crab was developed using a mixture of HNO3 and H2O2. Zn levels in the whole crab were 1.5 times higher in 50% of the crab species studied from a polluted estuary compared to the same species from an unpolluted estuary. As sand flathead primarily feed on crabs, the fish's diet was a likely source of elevated Zn for the fish. Overall, this study has described new techniques useful for the study of melanised fish and heavy metal levels in the whole crab. The findings from this study also provided insights that will inform and guide the direction of future research on muscle melanisation in sand flathead.

Tracing platinum accumulation kinetics in oyster Crassostrea gigas, a sentinel species in coastal marine environments

Platinum Group Elements (PGEs) are extremely scarce in the Earth's Crust and of strong interest for high-end technologies due to their specific properties. They belong to the Technology Critical Elements (TCEs) for which use is forecast to increase, implying growing emissions into the environment in the following years. In particular, with the intensive use of platinum (Pt) in car catalytic converters, the anthropogenic geochemical cycle of this element has surpassed the natural cycle. Yet, environmental Pt levels are still in the sub picomolar range, making its analytical detection a challenge. Few studies cover the behavior of Pt in marine waters in terms of speciation, reactivity and possible transfer to the biota. In this study, oysters (Crassostrea gigas) from an unpolluted estuary were exposed to the stable isotope 194Pt in seawater at a range of concentrations during 35days. Seawater was renewed daily and spiked to three nominal Pt concentrations (50, 100, and 10,000ng·L−1) for two replicate series. In addition, control conditions were monitored. Five oysters from each tank were dissected after 3, 7, 14, 21, 28, 35days of Pt exposure, and analyzed by ICP-MS. Accuracy of this analytical method applied to biological matrix was checked by an inter-method comparison with a voltammetrical technique. A concentration-dependent accumulation of Pt in oysters increasing with exposure time occurred. After 28days, oyster Pt accumulation from low and intermediate exposure conditions reached a plateau. This was not the case of the highest exposure condition for which oyster tissues showed increasing concentrations until the last day of the experiment. A linear correlation exists between seawater concentrations and Pt content in oysters for low and intermediate exposure concentrations i.e. closer to environmental concentrations. By showing high Pt accumulation potential, oysters may serve as sentinels, ensuring biomonitoring of Pt concentrations in marine coastal waters.

Screening strategy of producers of proteases with proteins of the haemostasis system activity among micromycetes

Platinum Group Elements (PGEs) are extremely scarce in the Earth's Crust and of strong interest for high-end technologies due to their specific properties. They belong to the Technology Critical Elements (TCEs) for which use is forecast to increase, implying growing emissions into the environment in the following years. In particular, with the intensive use of platinum (Pt) in car catalytic converters, the anthropogenic geochemical cycle of this element has surpassed the natural cycle. Yet, environmental Pt levels are still in the sub picomolar range, making its analytical detection a challenge. Few studies cover the behavior of Pt in marine waters in terms of speciation, reactivity and possible transfer to the biota. In this study, oysters (Crassostrea gigas) from an unpolluted estuary were exposed to the stable isotope 194Pt in seawater at a range of concentrations during 35 days. Seawater was renewed daily and spiked to three nominal Pt concentrations (50, 100, and 10,000 ng·L− 1) for two replicate series. In addition, control conditions were monitored. Five oysters from each tank were dissected after 3, 7, 14, 21, 28, 35 days of Pt exposure, and analyzed by ICP-MS. Accuracy of this analytical method applied to biological matrix was checked by an inter-method comparison with a voltammetrical technique. A concentration-dependent accumulation of Pt in oysters increasing with exposure time occurred. After 28 days, oyster Pt accumulation from low and intermediate exposure conditions reached a plateau. This was not the case of the highest exposure condition for which oyster tissues showed increasing concentrations until the last day of the experiment. A linear correlation exists between seawater concentrations and Pt content in oysters for low and intermediate exposure concentrations i.e. closer to environmental concentrations. By showing high Pt accumulation potential, oysters may serve as sentinels, ensuring biomonitoring of Pt concentrations in marine coastal waters.

Multivariate analysis applied to agglomerated macrobenthic data from an unpolluted estuary

We agglomerated species into higher taxonomic aggregations and functional groups to analyse environmental gradients in an unpolluted estuary. We then applied non-metric Multidimensional Scaling and Redundancy Analysis (RDA) for ordination of the agglomerated data matrices. The correlation between the ordinations produced by both methods was generally high. However, the performance of the RDA models depended on the data matrix used to fit the model. As a result, salinity and total nitrogen were only found significant when aggregated data matrices were used rather than species data matrix. We used the results to select a RDA model that explained a higher percentage of variance in the species data set than the parsimonious model. We conclude that the use of aggregated matrices may be considered complementary to the use of species data to obtain a broader insight into the distribution of macrobenthic assemblages in relation to environmental gradients.

Modulation of ASK1 expression during overexpression of Trx and HSP70 in stressed fish liver mitochondria

Mitochondrial heat shock protein 70 (mtHSP70) is found to play a primary role in cellular defense against physiological stress like exposure to environmental contaminants and helpful in the maintenance of cellular homeostasis by promoting the cell survival. In the present investigation, the environmental-stress-induced increase in mtHSP70 levels along with the quantification of apoptosis signal regulating kinase 1 (ASK1) and thioredoxin (Trx) were measured in the liver mitochondria of grey mullets (Mugil cephalus) collected from the polluted Ennore estuary and the unpolluted Kovalam estuary for a period of 2 years. The results showed elevated lipid peroxide (LPO) and decreased total antioxidant capacity along with the decrease in mitochondrial viability percentage. Mitochondrial HSP70, ASK1, and Trx levels were increased under this stress condition. A 42% increase in LPO levels and 18% decrease in mitochondrial survivality were observed in the polluted-site fish liver mitochondria when compared to the results of unpolluted estuary. We also report that, under observed oxidative stress condition in Ennore fish samples, the ASK1 levels are only moderately elevated (13% increase). This may be due to mitochondrial-HSP70-induced adaptive tolerance signaling for the activation of Trx (22% increase) which suppresses the ASK1 expression thereby promoting the cell survival that leads to the maintenance of the cellular homeostasis.

Pollution induced nitrative stress and heat shock protein 70 overexpression in fish liver mitochondria

Exposure to heavy metals and organic pollutants in natural water bodies can have detrimental effects on fish health. A combination of biochemical and energy studies were used to observe the changes in fish liver mitochondria in response to environmental pollutant induced nitrative stress in natural field conditions . The fish samples Mugil cephalus were collected from polluted (Ennore) and unpolluted (Kovalam) estuaries for a period of two years. The results revealed elevated nitrite (NO 2 −) and nitrate (NO 3 −) levels, increased nitric oxide (NO) synthesis and 3-nitrotyrosine expression, decreased respiratory chain enzyme activities and ATP/ADP ratio, reduced mitochondrial superoxide dismutase (MnSOD), glutathione peroxidase (Gpx) levels, diminished thiol status that leads to alterations in the mitochondrial function and elevated mitochondrial heat shock protein 70 (mtHSP70) expression (30%) to a significant extent in fish from the polluted estuary than in the unpolluted estuary. The overexpression of HSP70 under stress may aid mitochondrial survival by protecting against nitrative stress induced damage. The results also reveal the percentage increase in fish liver mitochondrial HSP70 in response to cumulative effect of environmental pollutants.

Liver oxidative stress of the grey mullet Mugil cephalus presents seasonal variations in Ennore estuary

The objective of this study was to determine the liver oxidative stress status of grey mullets living in heavy-metal-rich polluted Ennore estuary compared with unpolluted Kovalam estuary. Fish were collected from both estuaries during the monsoon and summer seasons from October 2004 to September 2006. Fish liver homogenate (N = 20 per group) was prepared for evaluating oxidative stress parameters. Fish living in the polluted estuary had significantly higher lipid oxidation products, conjugated dienes (0.346 +/- 0.017 vs 0.141 +/- 0.012 DA233/mg protein), lipid hydroperoxides (0.752 +/- 0.032 vs 0.443 +/- 0.03 nmol/mg protein), and lipid peroxides (3.447 +/- 0.14vs 1.456 +/- 0.096 nmol MDA/mg protein) than those of the unpolluted estuary during the summer. In contrast, significantly lower levels of superoxide dismutase (20.39 +/- 1.14 vs 53.63 +/- 1.48 units/mg protein) and catalase (116 +/- 6.87vs 153 +/- 8.92 units/mg protein) were detected in the liver of fish from the polluted estuary (Ennore) compared to fish from the unpolluted estuary (Kovalam) during the summer. Variations in most of the oxidative stress parameters were observed between the summer and monsoon seasons, indicating the importance of seasonal variation for estuaries and their inhabitants.

The impact of a salinity barrier on the partitioning of heavy metals in sediments of a tropical backwater system

Concentrations of heavy metals (Cd, Co, Cr, Cu and Fe) in surface sediments and their partitioning behaviour between exchangeable, reducible (Fe-Mn oxide bound) and organic/residual phases of the sediments in a typical backwater system of Kerala, viz. the southern upstream part of Cochin Estuarine System (South India), have been studied. Spatial and temporal variations of trace metals are discussed with special reference to pH, dissolved oxygen, salinity, organic carbon and texture of sediment. Metal concentrations in the tide gated part of the estuary were found to be significantly higher when compared to metal concentrations reported from the unrestricted part of the Cochin estuarine system and also those from many of the unpolluted estuaries worldwide. The higher levels of heavy metals in the study area and their characteristic distribution and partitioning behaviour in the surficial sediments were attributed to the presence of a salinity barrier across the backwater system and also by the massive use of pesticides and chemical fertilizers in the vast area of agricultural land near the backwater system.

Mercury levels in muscle of two fish species and sediments from the Cartagena Bay and the Ciénaga Grande de Santa Marta, Colombia

Mercury (Hg) content in sediments and muscle from two fish species were determined in Cartagena Bay and Ciénaga Grande de Santa Marta, an industrialized bay and an unpolluted estuary in the Caribbean coast of Colombia. Sampling was conducted four times during March–November 1996, including both the dry and rainy seasons. Significant differences in Hg concentration were detected both for fish and sediments between the two waterbodies. Hg values ranged from 94 to 10,293 μg/kg dry weight (dw) in sediments from Cartagena Bay and between 20 and 109 μg/kg dw in Ciénaga Grande de Santa Marta. Highest Hg concentrations were observed for the omnivorous species Eugerres plumieri, and lowest concentrations were found in the detritivorous Mugil incilis. High Hg concentrations in sediments of Cartagena Bay were detected in front of the sewage discharge of an extinct chlor-alkali plant, with decreasing concentrations in stations far from the source. Our results suggest that Hg can be persistent in the sediments of previously exposed ecosystems and that the use of their biological resources should be avoided until decontamination programs guarantee safe levels of the metal in the environment.

Exploring the relationships between abiotic variables and benthic community structure in a polluted estuarine system

Assessed was the effect of a man-induced interference in an estuarine system by monitoring a set of hydrographic and sedimentary variables together with a faunal survey of intertidal mudflats. A reference site was established in a nearby unpolluted estuary. A principal components analysis (PCA) reduced the original environmental data to a few more manageable factors. PCA factor I, defined by changes in salinity at the surface of the water column and dissolved oxygen at the bottom, explained 40% of the total variance. Pair-wise correlations between different structural metrics and PCA factor I explained up to 70% of the variability observed in the community metrics. Macrobenthic communities were simpler (with minor values of abundance, diversity, evenness and a much lower value of biomass) where dissolved oxygen at the bottom of the water column was minimum. An afaunal stage developed along intertidal mudflats where anoxic conditions prevailed. There was a large “weight-of-evidence” that a depletion of dissolved oxygen was causing a severe stress to the estuarine biota.

Epizoology of Hepatic Neoplasia in Atlantic Tomcod (Microgadus tomcod) from the Hudson River Estuary

Atlantic tomcod (Microgadus tomcod) collected from the Hudson River estuary during the winter spawning season revealed neoplastic and preneoplastic lesions in livers from 44% of the age 1 individuals and 93% of the age 2 individuals collected. These lesions appear as a continuum ranging from basophilic foci with little cellular alterations to hepatocellular carcinoma frequently involving the entire liver. Lesions were more prevalent in larger individuals within the same age group, suggesting a relationship between growth rate and tumor expression. Atlantic tomcod from a relatively unpolluted estuary in Connecticut did not reveal a comparable prevalence of hepatic lesions. Juvenile tomcod collected from the Hudson during the summer, only 4–5 mo prior to the winter spawning season had no hepatic lesions, suggesting that these lesions form rapidly, coincident with gonadal maturation. Chemical analysis of liver tissue revealed high levels of PCBs (2.5–38.2 mg/kg) and the presence of several pesticides including DDT (and metabolites), chlordane, and dieldrin (<0.1–3.0 mg/kg) and several heavy metals (<0.1–6.5 mg/kg). These results suggest that chemical contamination of the lower estuary nursery areas, coupled with high-temperature stresses of summer, may contribute to the high levels of hepatic lesions observed.

Nitrogen biogeochemistry in an unpolluted estuary: the importance of benthic denitrification

Nitrogen biogeochemistry in an unpolluted estuary: the importance of benthic denitrification

Upwelling and river runoff as sources of dissolved nitrous oxide to the Alsea estuary, Oregon

Surface waters of Alsea Bay, an unpolluted estuary on the Oregon coast, were analysed for nitrous oxide, nitrate and nitrite on a weekly or biweekly basis during the summer of 1979. The estuary was found to be a variable source of N 2O to the atmosphere. Large and rapid increases in the concentrations of N 2O, NO 3 −, and NO 2 − occurred at the beginning of the sampling period and are attributed to the influx of nutrient-rich upwelling water into the estuary with the tide. The subsequent decline in concentrations of nitrate, nitrite and nitrous oxide over the remainder of the summer is attributed to a decrease in upwelling intensity, a decline in nitrification rates and to assimilatory nitrate reduction. Measurements of nitrous oxide at six stations along the Alsea River were also made in September and October before and after the onset of the rainy season. Samples taken after flood conditions were established were systematically 50% higher than pre-flood samples. The data suggest that soil runoff results in elevated concentrations of N 2O in rivers.

Trophic Response of Fishes to Habitat Variability in Coastal Seagrass Systems

Shallow coastal areas of the northeast Gulf of Mexico are physically unstable in terms of short—term, seasonal, and year—to—year changes in temperature, salinity, nutrient concentration, and other water quality features. A 9—yr comparison was made of two estuaries, one polluted and one in the natural state, to determine the response of fish assemblages to habitat alteration in space and time. During the study period, extreme natural habitat changes due to storm water runoff and low winter temperatures were superimposed over water quality changes (increased color, turbidity, nutrients; reduced dissolved oxygen) associated with release of pulp mill effluents. Various grassbed fishes followed regular seasonal, age—specific feeding patterns, which did not change substantially in terms of qualitative food composition in the unpolluted estuary over a 7—yr period of observation. Such feeding behavior helped to explain temporally conservative cycles of relative abundance despite extreme (natural) habitat change. Anthropogenous habitat alterations, though seemingly slight, were associated with reductions in benthic macrophyte distribution, enhanced phytoplankton productivity, and changes in the relative dominance and numerical abundance of associated fish assemblages. Grassbed species were replaced by plankton—feeding fishes, and disruption of feeding habits of various species was apparent in the affected area relative to the unpolluted estuary. Those fishes dependent on specific benthic food organisms altered their feeding habits during the years of pollution in the affected estuary. Subsequent water quality improvement over time was associated with shifts in the age—specific dietary patterns of various species toward those observed in the unaffected estuary, although such recovery varied from species to species according to habitat utilization and trophic needs. From these results, it is clear that a relatively complex coastal seagrass system exposed to periodic, extreme natural disturbance is relatively resilient to such changes in terms of relative dominance and food web structure. However, apparently slight water quality changes due to pollution, which are outside the evolutionary experience of the biotic components, can cause serious disruptions of the basic habitat structure, energy flow, and community composition of the grassbed assemblages at various levels of biological organization.

Environmental Impact Assessment of the Strangford Lough Tidal Power Barrage Scheme in Northern Ireland

A tidal power barrage on Strangford Lough, would supply about 10% of Northern Ireland's energy requirements in the year 2000. However, the Droject will have serious environmental consequences for the largely unpolluted estuary which contains rare floral and faunal elements, provides a major bird feeding ground and has considerable recreation potential. This article reviews the likely environmental impact of the project.

Fluoride pollution in French rivers and estuaries

Fluoride concentrations have been determined in major French rivers and estuaries. The unpolluted estuary in the Loire has been compared with the Seine, Gironde and Charente where important discharges occur. Natural dissolved concentration can be multiplied by a factor of 30. Particulate fluorine concentration reach almost 2000 ppm in the Seine estuary. The percentage between free and complexed dissolved fluoride is not affected by the anthropic discharge. The present French rivers discharge of fluoride is 700% higher than the pristine value. At a global scale, dissolved fluoride has probably increased by 25% compared with the natural situation.

Overlap and Pollution-Induced Variability in the Feeding Habits of Filefish (Pisces: Monacanthidae) from Apalachee Bay, Florida

The distribution and feeding habits of two species of filefish, Monacanthus ciliatus and Stephanolepis hispidus, were examined. Spatial and temporal distribution and feeding habits of the two species overlapped broadly. The apparent similarity in diet was reduced when prey were identified to species. Analysis of ontogenetic variation of each species indicated a tendency toward herbivory with increasing standard length. The feeding habits ofM. ciliatus taken from areas affected by pulp mill effluents were compared to those from a nearby unpolluted estuary. Cluster analysis of stations within the two systems, based on feeding habits of M. ciliatus, were similar to those based on numbers of fishes and macrophyte biomass. Differences in the feeding habits between the two systems may be due to pollution-induced habitat modifications and resulting changes in prey distribution.

Uranium isotopes in rivers, estuaries and adjacent coastal sediments of western India: their weathering, transport and oceanic budget

The two major river systems on the west coast of India, Narbada and Tapti, their estuaries and the coastal Arabian sea sediments have been extensively studied for their uranium concentrations and 238U 238U activity ratios. The 238U concentrations in the aqueous phase of these river systems exhibit a strong positive correlation with the sum of the major cations, σ Na + K + Mg + Ca, and with the HCO 3 − ion contents. The abundance ratio of dissolved U to the sum of the major cations in these waters is similar to their ratio in typical crustal rocks. These findings lead us to conclude that 238U is brought into the aqueous phase along with major cations and bicarbonate. The strong positive correlation between 238U and total dissolved salts for selected rivers of the world yield an annual dissolved 238U flux of 0.88 × 10 10 g/ yr to the oceans, a value very similar to its removal rate from the oceans, 1.05 × 10 10 g/ yr, estimated based on its correlation with HCO 3 − contents of rivers. In the estuaries, both 238U and its great-grand daughter 234U behave conservatively beyond chlorosities 0.14 g/l. These data confirm our earlier findings in other Indian estuaries. The behavior of uranium isotopes in the chlorosity zone 0.02–0.14 g/l, was studied in the Narbada estuary in some detail. The results, though not conclusive, seem to indicate a minor removal of these isotopes in this region. Reexamination of the results for the Gironde and Zaire estuaries (Martin et al., 1978a and b) also appear to confirm the conservative behavior of U isotopes in unpolluted estuaries. It is borne out from all the available data that estuaries beyond 0.14 g/l chlorosities act neither as a sink nor as a source for uranium isotopes, the behavior in the low chlorosity zones warrants further detailed investigation. A review of the uranium isotope measurements in river waters yield a discharge weighted-average 238U concentration of 0.22 μg/l with a 234U 238U activity ratio of 1.20 ± 0.06 is missing. The residence time of uranium isotopes in the oceans estimated from the 238U concentration and the 234U 238U A. R. of the rivers yield conflicting results; the material balance of uranium isotopes in the marine environment still remains a paradox. If the disparity between the results is real, then an additional 234U flux of about 0.25 dpm/cm 2·10 3 yr into the oceans (about 20% of its river supply) is necessitated.

Granulometric dependence of chromium accumulation in estuarine sediments in Maine

Variation of chromium concentrations with grain size in estuarine sediments comples use of a sediment textural indicator in examination of pollutant chromium distribution. Sediment specific surface area is shown to be superior to measurements of the proportion of fine-grained sediment in defining regional variations of chromium concentration with sediment texture in three relatively unpolluted estuaries. Mineralogy is the prime control on chromium levels in these estuaries. The application of a textural normalization technique using specific surface areas in an estuary receiving a chromium-rich effluent allows differentiation of polluted from nonpolluted sediments. Accumulation of effluent chromium occurs within the estuary, not in adjacent coastal sediments, and concentration occurs in intertidal rather than subtidal zones.

Problems in the assessment of heavy-metal levels in estuaries and the formation of a pollution index

Most estuaries receive a high heavy-metal input from industries. This is reflected in the relatively high levels found in numerous estuarine organisms and in sediments. Many indicators have been suggested for facilitating the detection of heavy-metal pollution, but the problems in using these indicators to evaluate the metal loading of estuaries are considerable. Variations in species composition, and conditions at different sites, differences in season of sampling, and age of organism, as well as different metal levels in different parts of the organism, make the interpretation of results difficult. The levels reported here, similar to those in other unpolluted estuaries, have been used to suggest a baseline concentration for heavy metals in estuaries. The concept of a baseline is fundamental to the formation of a “Biological Quality Index” and “Pollution Load Index,” and a formula for such an index is suggested and tested at a preliminary level against published data for an English and a European estuary.