Toxicological and physiological responses of the fish,Leiostomus xanthurus,exposed to chlorine produced oxidants

The sublethal and lethal effects of chlorine produced oxidants (CPO) on juveniles of the estuarine teleost,Leiostomus xanthurus, were investigated in flowing water tests conducted at 30 ±1°C and 26 to 31‰ salinity. Short-term LT50 tests were conducted at two nominal concentrations of NaOCl, 1.0 and 1.4 mg/l (respective measured CPO concentrations 0.09 and 0.12 mg/l) which were sublethal in 2,880 minute exposures; and three nominal concentrations, 1.6, 1.8 and 3.2 mg/l NaOCl (respective measured CPO concentrations 0.13, 0.20 and 0.37 mg/l) which were acutely toxic. Opercular ventilation rates in exposed spot were much higher than in control fish, but returned to rates only slightly above those of controls during the latter portion of the 2,880 minute exposure to the two sublethal CPO concentrations. Opercular rates at the three acutely toxic CPO concentrations remained much higher than control rates until the exposed fish died. Blood pH after 2,880 minutes of exposure to the sublethal concentrations of CPO; or at the respective estimated LT50 for lethal concentrations, showed significant decreases ( \(\bar X\) as low as 6.84) compared to controls \((\bar X 7.35)\) . No significant changes in the % methemoglobin were observed. Oxygen uptake by spot was depressed at all of the measured concentrations of CPO tested. Histopathological examination showed that gill respiratory epithelial tissues sloughed away from the underlying pillar cells. Complete denudation of circulatory tissues and hemangiectic secondary lamellae were observed in gill tissues from fish exposed to the highest CPO concentration of 0.37 mg/l.     

Relations between sinkhole density and anthropogenic contaminants in selected carbonate aquifers in the eastern United States

The relation between sinkhole density and water quality was investigated in seven selected carbonate aquifers in the eastern United States. Sinkhole density for these aquifers was grouped into high (>25 sinkholes/100 km²), medium (1–25 sinkholes/100 km²), or low (<1 sinkhole/100 km²) categories using a geographical information system that included four independent databases covering parts of Alabama, Florida, Missouri, Pennsylvania, and Tennessee. Field measurements and concentrations of major ions, nitrate, and selected pesticides in samples from 451 wells and 70 springs were included in the water-quality database. Data were collected as a part of the US Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program. Areas with high and medium sinkhole density had the greatest well depths and depths to water, the lowest concentrations of total dissolved solids and bicarbonate, the highest concentrations of dissolved oxygen, and the lowest partial pressure of CO₂ compared to areas with low sinkhole density. These chemical indicators are consistent conceptually with a conduit-flow-dominated system in areas with a high density of sinkholes and a diffuse-flow-dominated system in areas with a low density of sinkholes. Higher cave density and spring discharge in Pennsylvania also support the concept that the high sinkhole density areas are dominated by conduit-flow systems. Concentrations of nitrate-N were significantly higher (p < 0.05) in areas with high and medium sinkhole density than in low sinkhole-density areas; when accounting for the variations in land use near the sampling sites, the high sinkhole-density area still had higher concentrations of nitrate-N than the low sinkhole-density area. Detection frequencies of atrazine, simazine, metolachlor, prometon, and the atrazine degradate deethylatrazine indicated a pattern similar to nitrate; highest pesticide detections were associated with high sinkhole-density areas. These patterns generally persisted when analyzing the detection frequency by land-use groups, particularly for agricultural land-use areas where pesticide use would be expected to be higher and more uniform areally compared to urban and forested areas. Although areas with agricultural land use and a high sinkhole density were most vulnerable (median nitrate-N concentration was 3.7 mg/L, 11% of samples exceeded 10 mg/L, and had the highest frequencies of pesticide detection), areas with agricultural land use and low sinkhole density still were vulnerable to contamination (median nitrate-N concentration was 1.5 mg/L, 8% of samples exceeded 10 mg/L, and had some of the highest frequencies of detections of pesticides). This may be due in part to incomplete or missing data regarding karst features (such as buried sinkholes, low-permeability material in bottom of sinkholes) that do not show up at the scales used for regional mapping and to inconsistent methods among states in karst feature delineation.     

Import of coastally-derived chlorophylla to South Slough, Oregon

Material transfer between estuaries and the nearshore zone has long been of interest, but information on the processes affecting Pacific Northwest estuaries has lagged behind other areas. The west coast of the U.S. is a region of seasonally variable upwelling that results in enhanced phytoplankton production in the nearshore zone. We examined estuarine-nearshore links over time by measuring physical oceanographic variables and chlorophylla concentration from an anchor station in South Slough, Oregon. Data was collected during 24-h cruises conducted at approximately weekly intervals during summer 1996 and spring 1997. The results demonstrate that the physical oceanography of this estuarine site was strongly influenced by the coastal ocean. Marine water reached the estuarine site on every sampled tide, and chlorophylla was clearly advected into the estuary with this ocean water. In contrast, phytoplankton concentrations were comparatively reduced in the estuarine water. There were, however, large fluctuations in the import of chlorophyll over the course of the summer. These variations likely reflect upwelling-generated phytoplankton production in the coastal ocean and subsequent cross-shelf transport to the estuary. Suspension feeding organisms in South Slough likely depend on the advection of this coastally-derived phytoplankton. The large allochthonous chlorophyll input measured for this system appears dissimilar from most estuaries studied to date. Previous investigations have focused on the outwelling and inwelling of materials in estuaries. We must now consider the influence of coastal upwelling and downwelling processes on estuarine material exchange.     

Methylmercury Bioaccumulation in an Urban Estuary: Delaware River,USA

Spatial variation in mercury (Hg) and methylmercury (MeHg) bioaccumulation in urban coastal watersheds reflects complex interactions between Hg sources, land use, and environmental gradients. We examined MeHg concentrations in fauna from the Delaware River estuary, and related these measurements to environmental parameters and human impacts on the waterway. The sampling sites followed a north to south gradient of increasing salinity, decreasing urban influence, and increasing marsh cover. Although mean total Hg in surface sediments (top 4 cm) peaked in the urban estuarine turbidity maximum and generally decreased downstream, surface sediment MeHg concentrations showed no spatial patterns consistent with the examined environmental gradients, indicating urban influence on Hg loading to the sediment but not subsequent methylation. Surface water particulate MeHg concentration showed a positive correlation with marsh cover whereas dissolved MeHg concentrations were slightly elevated in the estuarine turbidity maximum region. Spatial patterns of MeHg bioaccumulation in resident fauna varied across taxa. Small fish showed increased MeHg concentrations in the more urban/industrial sites upstream, with concentrations generally decreasing farther downstream. Invertebrates either showed no clear spatial patterns in MeHg concentrations (blue crabs, fiddler crabs) or increasing concentrations further downstream (grass shrimp). Best-supported linear mixed models relating tissue concentration to environmental variables reflected these complex patterns, with species specific model results dominated by random site effects with a combination of particulate MeHg and landscape variables influencing bioaccumulation in some species. The data strengthen accumulating evidence that bioaccumulation in estuaries can be decoupled from sediment MeHg concentration, and that drivers of MeHg production and fate may vary within a small region.     

Enhanced toxicity of atrazine to Daphnia magna in the presence of nano-CeO2

In this study,aquatic toxic effect of atrazine,and nano-CeO2,the accumulation,reproduction and adsorp-tion of atrazine onto nano-CeO2 and the facilitated transport of atrazine into D.magna by nano-CeO2 were exam-ined.The results showed that atrazine concentrations of 3.0,4.0,and 10.0 mg/L exhibited 43%,56%,68% mortali-ties,respectively,which indicated the mortality was 56% while the concentration of nano-CeO2 was 4.0 mg/L.D.magna accumulated considerably more atrazine when exposed to atrazine-contaminated water in the presence of nano-CeO2.At the same time,atrazine and nano-CeO2 yielded a significant reduction of the reproduction rate at all concentrations tested.What is more,the co-exposure of nano-CeO2 and atrazine was observed to significantly de-crease the reproduction rate of D.magna,and atrazine adsorbed on nano-CeO2 quickly.Therefore,attention should be paid to their associations with other contaminants for the risk assessment of nano-CeO2 and it is worthy of notice that the sorption of atrazine on nano-CeO2 would enhance the toxicity of atrazine to D.magna.     

Relationships between Nutrient Enrichment and Benthic Function: Local Effects and Spatial Patterns

Eutrophication-induced changes to benthic faunal activities are problems of significant ecological impact, affecting global nutrient budgets as well as local trophic connections. We address the question of how nitrogen loads to estuarine embayments alter the bioturbation activities of benthic fauna. Specifically, we related local benthic activities to calculated local nitrogen concentrations for 22 northeastern US estuaries. These local nitrogen concentrations were derived from the calculated nitrogen loading for the embayment together with the spatial distribution of the local flushing time. Our results showed a maximum bioturbation rate at intermediate nitrogen concentrations or a “hump-shaped” pattern of response. This behavior was evident in all embayments that had a range of concentrations including low, intermediate, and high values. Embayments where sampling did not include this full range did not show this behavior. This work provides methods and guidance to help managers make decisions concerning the effects of nitrogen loading on the activities and well-being of benthic fauna in coastal embayments. The novelty of this approach lies in identifying the response of bioturbation to nitrogen loading in many systems, without costly and time-consuming speciation of benthic fauna, and also in rapidly identifying embayments and aquatic areas with vulnerable fauna. These results are ecologically significant in supporting the hypothesis that benthic organism abundance and activity will peak at mid-levels of nitrogen due to the interplay of food availability and oxygen levels, noting that the critical levels of these factors differ among water bodies.     

Influence of salinity on atrazine toxicity to a Chesapeake Bay copepod (Eurytemora affinis) and fish (Cyprinodon variegatus)

The objective of this study was to determine the influence of a range of salinities (5%., 15%., and 25%.) on the acute toxicity of atrazine to nauplii of the copepodEurytemora affinis and larvae of the sheepshead minnow,Cyprinodon variegatus. Ninety-six-hour LC50 values for the copepod were 0.5 mg 1^?1, 2.6 mg 1^?1, and 13.2 mg 1^?1 at salimities of 5%., 15%. and 25%. respectively. A comparison of LC50 values between adjacent salinities showed a statistical difference between 15%. and 25%. but not between 5%. and 15%.. Atrazine was more toxic toE. affinis at the lowest salinity. The 96-h LC50s for the sheepshead minnow were 16.2 mg 1^?1, 2.3 mg 1^?1, and 2.0 mg 1^?1 at salinities of 5%., 15%., and 25%., respectively. There was a statistical difference between LC50 values at 5%. and 15%. but not between 15%. and 25%.. In contrast toE. affinis results, atrazine was more toxic toC. variegatus at the highest salinity. The toxicity data from these species suggest that development of estuarine water quality criteria is warranted.     

Determination of atrazine isotherms on agricultural soils

For determination of atrazine isotherms in agricultural soils of Fars Province, composite soil samples from 0 to 5 cm depth with textures of silty clay loam, clay loam and loam were collected. In order to form the atrazine isotherms, 10, 50 and 100 µg atrazine g^?1 soil was added to the soil samples. Soluble atrazine in water:soil ratios of 10:1, 50:1 and 200:1 was measured after 3-h shaking. Finally, for each cases of applied atrazine, water extractable atrazine was determined and quantified using gas chromatography instrument. The results indicated that there was a linear relationship between the logarithms of water extractable atrazine and added atrazine for different water:soil ratios. A general equation of WEA = K(WS) ^α (AA) ^β is obtained experimentally between water extractable atrazine, µg g^?1(WEA), and added atrazine, µg g^?1 (AA), where K, α and β are absorption constants; WS is the water:soil ratio, g g^?1. For the loam, silty clay loam and clay loam soil textures, the α were 0.49, 0.23 and 0.13, respectively, the β were 0.55, 0.806 and 0.21, respectively, and the K were 1.44, 0.78 and 25.38, respectively.     

Rearing Shrimps in Pens: A Predictive Model for Impact Assessment

A predictive model for impact assessment of shrimp (Farfantepenaeus paulensis) culture in pen enclosures was developed. Experiments were carried out at Saco da Mangueira, a small embayment at the Patos Lagoon estuarine area (southern Brazil). Nitrogen budget was assessed considering inputs and outputs from the culture system. The measured parameters were water flow, shrimp density, pen mesh size and clogging effect, artificial diet quality, and food conversion rates. Shrimp excretion was estimated from literature available. A N-NT concentration of 0.07 mg L⁻¹ of was assumed as a conservative critical reference value to assess environmental impact and water deterioration. Trials showed that for Saco da Mangueira conditions, a total number of 70 pen enclosures of 0.3 ha (i.e., a total production of 32.2 ton) is recommended as a maximal number. This model is a useful tool for impact assessment and coastal management and may be applied to other estuarine areas.     

Carbon dynamics of estuarine ponds receiving treated sewage wastes

The carbon dynamics of six estuarine ponds at Morehead City, North Carolina, were measured from August 1969 through August 1970. Three waste ponds received secondary treated sewage effluent and three served as controls. Total organic levels were determined by combustion with a Beckman total carbon analyzer. Inorganic levels were calculated from temperature, pH, and carbonate alkalinity. Carbon dioxide diffusion across the air-water interface was measured with a floating plastic dome and an infrared gas analyzer. Carbon metabolism was determined from diurnal changes in total inorganic carbon. From October through April the wastereceiving ponds were characterized by an intense bloom of a small alga,Monodus guttula. During the bloom organic levels reached 75 mg C per 1. The warmer months were characterized by a more diverse flora and organic concentrations averaging 25 mg per 1. Organic levels in the control ponds seldom were greater than 10 mg per 1. CO₂ diffused constantly out of the control ponds due to input of high alkalinity water supersaturated with inorganic carbon. During the bloom in the waste ponds diffusion of CO₂ from the atmosphere was as high as 0.5 g C per m² per day. CO₂ diffused into the water constantly because the high uptake rate of inorganic carbon by the small algae reduced the levels in the water to less than 5 mg per 1. Gross production of the waste receiving ponds avearaged 2,86 g C per m² per day during the bloom and 2.44 during the non-bloom period. The average productivity of the control ponds was 1.7. Corrections for CO₂ diffusion were significant in the control ponds and in the waste ponds during theMonodus bloom. Availability of carbon from diffusion and respiratory regeneration seemed to limit phytoplankton productivity during the bloom. The annual budgets for the two sets of ponds were distinctly different. For the control ponds, the input of organic matter was nearly equal to losses indicating almost no net production of organic material. A high net loss of organic material and a net gain of inorganic carbon for the waste ponds reflected the net productive nature.     

Short-term water quality variability in two tropical estuaries,central Sumatra

We examined high frequency fluctuations in water quality parameters in two tropical coastal plain estuaries in response to changing tidal flow conditions. The variability in total suspended sediments (TSS), volatile suspended solids (VSS), total organic carbon (TOC) concentrations, and indicators of water quality, including pH, temperature, salinity, and dissolved oxygen, over one spring tidal cycle during the early wet monsoon season was measured in two estuaries in eastern Sumatra. The relatively high rainfall experienced throughout the year, in combination with the recent extensive vegetation clearing and modification of the landscape, resulted in significant concentrations of TSS, VSS, and TOC being discharged to coastal waters. Maximum values are reached on the ebb tide (TSS > 1,013 mg l⁻¹; VSS > 800 mg l⁻¹; TOC >60 mg l⁻¹). The influence of freshwater discharge and tidal flow on water properties of the lower estuaries is also marked by the variability in salinity, dissolved oxygen, and pH over the tidal cycle, with minimum values for each of these parameters following maximum current velocities and after the completion of the strong ebb tide. Estimation of seaward sediment fluxes, which are of significant interest in a region where rapid environmental change is occurring, would require further examination of sedimentary processes, such as resuspension and advection of sediment, as well as a consideration of neap-spring tidal variations and the effect of seasonality on estuarine circulation.     

The effects of hematite nanoparticles on phytoavailability of arsenic and corn growth in contaminated soils

This study was carried out to assess the effects of hematite nanoparticles (α-Fe₂O₃) on the motility and phytoavailability of arsenic in contaminated soils and corn growth. A factorial experiment was conducted using a completely randomized design and three replications. The examined factors were the application rates of hematite nanoparticles (0, 0.05, 0.1 and 0.2%) and the levels of soil arsenic (0, 6, 12, 24, 48, and 96 mg/kg). Before sowing of corn seeds, the concentrations of soil available arsenic were measured in all soil samples. Corn plant was used as a biological indicator of arsenic phytoavailability and 75 days after sowing, it was harvested, and dry weights of aerial parts and roots and concentrations of arsenic and phosphorus of these parts were measured. The results showed that the concentration of soil available arsenic and arsenic concentrations of root and aerial parts increased as the concentration of soil total arsenic increased. Contamination of soil by arsenic increased the concentration of phosphorus in root but decreased it in the aerial parts of corn. In contaminated soils, the application of hematite nanoparticles significantly decreased the concentrations of arsenic in soil and in root and aerial parts of corn and increased the dry weights of root and aerial parts. But in uncontaminated soils, the application of hematite nanoparticles decreased the concentration of phosphorus and the dry weights of root and aerial parts of corn.     

Feeding rates of the sea nettle,Chrysaora quinquecirrha,under laboratory conditions

The scyphomedusa, Chrysaora quinquecirrha, preys on a variety of estuarine organisms. A series of experiments were conducted to measure the feeding rate of adult medusae on zooplankton prey. Artemia was used as a substitute for the endemic and abundant copepod, Acartia tonsa. The feeding rates ranged from three Artemia per hour per ml of medusae volume to 107 per hour per ml in 51 trials. The consumption was also linearly related to the initial prey concentration. Certain results suggested that a toxic factor might be exuded by the medusae, affecting the observed feeding rates. The results verify the possibility that Acartia may be a major prey organism in estuarine environments.     

The chironomid (Insecta: Diptera) and other fauna of aMyriophylum spicatum L. plant bed in the lower Hudson River

The benthic fauna of a small cove of the Hudson River containing the aquatic plantMyriophyllum spicatum L. was studied for a one-year period. The fauna was characteristic of oligohaline zones of United States east coast estuaries. Total abundance of invertebrates retained on a 0.12 mm mesh sieve averaged 124,631 organisms m^?2 (sediment and plant populations combined) and ranged up to 196,000 m^?2. During the May–August period, invertebrates living on the plants comprised 16–35% of the invertebrate fauna in the cove. Chironomid larvae were the most abundant organisms on plants and the third most abundant in the sediments. Two assemblages of chironomid species were recognized; one lived solely in the sediments, the other lived primarily on the plants.Chironomus decorus andTanytarsus sp. dominated the former group andCricotopus sylvestris the latter. The chironomidDicrotendipes modestus utilized both habitats. During the May–August period, chironomid biomass on the plants comprised approximately 50% of total chironomid biomass in the cove. The mean dry-weight biomass of chironomids in the cove (1.6 g m^?2) is estimated to be sixteen times greater than that of the fauna in the deeper areas of the river. Because chironomid larvae are eaten by fish and invertebrates, shallow water regions with their rich chironomid (and other fauna) may contribute importantly to the trophic dynamics of estuarine systems. *** DIRECT SUPPORT *** A01BY009 00004     

Effects of a photosynthesis inhibitor,atrazine, on the salt-marsh fiddler crab,Uca pugnax (Smith)

Atrazine (2-chloro-4-ethylamino-6-isopropylamine-s-triazine) concentrations of 1,000 ppm either killed or eliminated the escape response (considered to be analogous to death) ofUca pugnax in laboratory experiments in August 1977. Adverse effects were observed at concentrations as low as 100 ppm and the severity was dependent on size and sex of the crab. However, in subsequent experiments, each with a new group of crabs, the effects of atrazine became smaller and smaller until a November experiment when no deleterious effects were observed even when exposed to 1,000 ppm. Experiments in August, 1978 confirmed the data obtained 1 year earlier. Ecological and physiological considerations of this seasonal variation in response are discussed. Crabs fed for 20 days with detritus wetted with 10^?4 M atrazine were not adversely affected. Crabs exposed to a single application of 0, 100, 1,000, and 10,000 ppm atrazine in the field and in microecosystems were adversely affected only by the 10,000-ppm rate. Toxicity of atrazine to the larval stage of the crab was not investigated.     

Dissolved Boron in the Tapi,Narmada and the Mandovi Estuaries,the Western Coast of India: Evidence for Conservative Behavior

The concentrations of dissolved boron have been measured during different seasons in three estuaries, the Tapi, Narmada and the Mandovi situated on the western coast of India, to investigate its geochemical behavior and inputs from the localized anthropogenic pressures of industrial effluents and sewage discharge. The measured boron concentrations in these estuaries (except the Tapi during non-monsoon) at salinity ≤0.1 fall in a narrow range?～?2–4 μmol/kg (average B?～?2.4?±?0.8 μmol/kg) within the reported wide range?～?0.1–18.6 μmol/kg for global rivers. The much higher estimate of boron concentration in the Tapi River during non-monsoon is attributed to its possible additional supply from the sewage and/or industrial effluents discharged along the river course. During monsoon, the rains seem to be a significant source of dissolved boron to all the three rivers. The distribution of dissolved boron in each estuary exhibits a conservative behavior during the seasons sampled suggestive of no measurable addition or removal of boron in the estuarine region. The orders of magnitude differences in boron concentration between the river waters and seawater, and the conservative behavior of dissolved boron indicate that its major contributor to the estuaries sampled is seawater.     

Application of Species Distribution Models to Identify Estuarine Hot Spots for Juvenile Nekton

Modeling the distribution and habitat capacities of key estuarine species can be used to identify hot spots, areas where species density is significantly higher than surrounding areas. This approach would be useful for establishing a baseline for evaluating future environmental scenarios across a landscape. We developed species distribution models for early juvenile life stages of brown shrimp (Farfantepenaeus aztecus), white shrimp (Litopenaeus setiferus), blue crab (Callinectes sapidus), and spotted seatrout (Cynoscion nebulosus) in order to delineate the current coastal hot spots that provide the highest quality habitat conditions for these estuarine-dependent species in Louisiana. Response curves were developed from existing long-term fisheries-independent monitoring data to identify habitat suitability for fragmented marsh landscapes. Response curves were then integrated with spatially explicit input data to generate species distribution models for the coastal region of Louisiana. Using spatial autocorrelation metrics, we detected clusters of suitable habitat across the Louisiana coast, but only 1% of the areas were identified as true hot spots with the highest habitat quality for nekton. The regions identified as hot spots were productive fringing marsh habitats that are considered the most vulnerable to natural and anthropogenic impacts. The species distribution models identify the coastal habitats which currently provide the greatest capacity for key estuarine species and will be used in the Louisiana coastal planning process to evaluate how species distributions may change under various environmental and restoration scenarios.     

High-resolution profiles of iron, manganese, cobalt, cadmium, copper and zinc in the pore water of estuarine sediment

The remobilization of iron, manganese, cobalt, cadmium, copper and zinc in the pore water of estuarine sediment cores at Yingkou was assessed using diffusive equilibrium in thin films and diffusive gradients in thin films techniques. A relatively anoxic system (+33.7 to ?224.1 mV) in the sediment cores might cause the reductive release of iron, manganese and cobalt into pore water from the estuarine sediment. High-average concentrations of iron (47.85 μg ml^?1) and manganese (3.81 μg ml^?1) were observed using diffusive equilibrium in thin films on the sediment core, but the concentration of cobalt (18.02 ng ml^?1) was relatively low. A strong correlation between iron and cobalt was observed based on the vertical profiles of the metals. Manganese and iron were more readily released from the solid phase to the solution. The peak cobalt, copper and zinc concentrations were observed in the upper layer (2–4 cm) measured using diffusive gradients in thin films. However, the peak iron, manganese and cobalt concentrations were located in the deeper layer (≥7 cm). In addition, the concentration profiles measured using diffusive gradients in thin films of cobalt, copper and zinc were independent of the iron, manganese and cobalt distribution with respect to depth.     

Occurrence and spatial distribution of metals in intertidal sediments of a temperate estuarine system (Bahía Blanca,Argentina)

Intertidal sediments of the inner and middle zone from the Bahía Blanca estuary were sampled for geochemical and environmental assessment of metals (Cd, Cu, Pb, Zn, Mn, Ni, Cr and Fe). Results indicate that both the organic matter content and the sediment grain size plays an important role in controlling the differential concentrations of the metals found in sediments from both zones. For most of the elements (except Mn), sediment metal concentrations were greater in the middle zone, although the concentrations did not exceed the maximums for quality of marine sediments. In this sense, anthropogenic impact (i.e., sewage drain) appears to be a key factor in the distribution of metals within the estuarine system. Comparing the levels obtained with quality levels (LEL and SEL), except Cu that showed levels slightly above the LEL, the rest of the concentrations of metals were lower to those levels. The low metal concentrations obtained within this highly impacted estuarine system suggest that the great volume of water that flooding the extensive flats in each tidal cycle has much importance. Although the potential risks of metals to the estuarine environment were low, taking into account the toxicity of some of these metals, continuity of monitoring is highly recommended.     

The effects of a photosynthesis inhibitor atrazine,on salt marsh edaphic algae,in culture,microecosystems, and in the field

A 10^?5 M (2.2 ppm) concentration of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) reduced the rate of photosynthesis, chlorophyll content, and cell numbers in unialgal cultures of Nitzschia sigma Grun. and Thalassiosira fluviatilis Hustedt isolated from a salt marsh habitat. Results with lower atrazine concentrations indicated an ability to maintain chlorophyll production and cell division with reduced photosynthesis. The effects of a 10^?5 M concentration of atrazine in unialgal cultures were also evident in microecosystems and in the field at the same concentration, although atrazine effects were less severe in the field than in microecosystems or cultures. Cell number and productivity of the diatoms from microecosystems not treated with atrazine agreed well with field data and previously published data. Diatom species diversity was not affected by 10^?5 M atrazine in microecosystems or in the field but the number of Cymatosira belgica Grun. was increased. Diatom assemblages in atrazine-treated vs non-treated microecosystems were very similar (SIMI>0.838). Results were less conclusive in the field but the trend was toward a lower level of similarity. Based on the least effect level of atrazine to diatoms, the maximum safe level for atrazine in the salt marsh is 10 ppb.