Pristine Reference Sites Research Articles

Multiple microbial guilds mediate soil methane cycling along a wetland salinity gradient.

Estuarine wetlands harbor considerable carbon stocks, but rising sea levels could affect their ability to sequester soil carbon as well as their potential to emit methane (CH4). While sulfate loading from seawater intrusion may reduce CH4 production due to the higher energy yield of microbial sulfate reduction, existing studies suggest other factors are likely at play. Our study of 11 wetland complexes spanning a natural salinity and productivity gradient across the San Francisco Bay and Delta found that while CH4 fluxes generally declined with salinity, they were highest in oligohaline wetlands (ca. 3-ppt salinity). Methanogens and methanogenesis genes were weakly correlated with CH4 fluxes but alone did not explain the highest rates observed. Taxonomic and functional gene data suggested that other microbial guilds that influence carbon and nitrogen cycling need to be accounted for to better predict CH4 fluxes at landscape scales. Higher methane production occurring near the freshwater boundary with slight salinization (and sulfate incursion) might result from increased sulfate-reducing fermenter and syntrophic populations, which can produce substrates used by methanogens. Moreover, higher salinities can solubilize ionically bound ammonium abundant in the lower salinity wetland soils examined here, which could inhibit methanotrophs and potentially contribute to greater CH4 fluxes observed in oligohaline sediments.IMPORTANCELow-level salinity intrusion could increase CH4 flux in tidal freshwater wetlands, while higher levels of salinization might instead decrease CH4 fluxes. High CH4 emissions in oligohaline sites are concerning because seawater intrusion will cause tidal freshwater wetlands to become oligohaline. Methanogenesis genes alone did not account for landscape patterns of CH4 fluxes, suggesting mechanisms altering methanogenesis, methanotrophy, nitrogen cycling, and ammonium release, and increasing decomposition and syntrophic bacterial populations could contribute to increases in net CH4 flux at oligohaline salinities. Improved understanding of these influences on net CH4 emissions could improve restoration efforts and accounting of carbon sequestration in estuarine wetlands. More pristine reference sites may have older and more abundant organic matter with higher carbon:nitrogen compared to wetlands impacted by agricultural activity and may present different interactions between salinity and CH4. This distinction might be critical for modeling efforts to scale up biogeochemical process interactions in estuarine wetlands.

Water soluble organic aerosols in the Colorado Rocky Mountains, USA: composition, sources and optical properties.

Atmospheric aerosols have been shown to be an important input of organic carbon and nutrients to alpine watersheds and influence biogeochemical processes in these remote settings. For many remote, high elevation watersheds, direct evidence of the sources of water soluble organic aerosols and their chemical and optical characteristics is lacking. Here, we show that the concentration of water soluble organic carbon (WSOC) in the total suspended particulate (TSP) load at a high elevation site in the Colorado Rocky Mountains was strongly correlated with UV absorbance at 254 nm (Abs254, r = 0.88 p < 0.01) and organic carbon (OC, r = 0.95 p < 0.01), accounting for >90% of OC on average. According to source apportionment analysis, biomass burning had the highest contribution (50.3%) to average WSOC concentration; SOA formation and motor vehicle emissions dominated the contribution to WSOC in the summer. The source apportionment and backward trajectory analysis results supported the notion that both wildfire and Colorado Front Range pollution sources contribute to the summertime OC peaks observed in wet deposition at high elevation sites in the Colorado Rocky Mountains. These findings have important implications for water quality in remote, high-elevation, mountain catchments considered to be our pristine reference sites.

Effects of metal contamination in situ on osmoregulation and oxygen consumption in the mudflat fiddler crab Uca rapax (Ocypodidae, Brachyura)

The contamination of estuaries by metals can impose additional stresses on estuarine species, which may exhibit a limited capability to adjust their regulatory processes and maintain physiological homeostasis. The mudflat fiddler crab Uca rapax is a typical estuarine crab, abundant in both pristine and contaminated areas along the Atlantic coast of Brazil. This study evaluates osmotic and ionic regulatory ability and gill Na+/K+-ATPase activity in different salinities (<0.5, 25 and 60‰ S) and oxygen consumption rates at different temperatures (15, 25 and 35°C) in U. rapax collected from localities along the coast of São Paulo State showing different histories of metal contamination (most contaminated Ilha Diana, Santos>Rio Itapanhaú, Bertioga>Picinguaba, Ubatuba [pristine reference site]). Our findings show that the contamination of U. rapax by metals in situ leads to bioaccumulation and induces biochemical and physiological changes compared to crabs from the pristine locality. U. rapax from the contaminated sites exhibit stronger hyper- and hypo-osmotic regulatory abilities and show greater gill Na+/K+-ATPase activities than crabs from the pristine site, revealing that the underlying biochemical machinery can maintain systemic physiological processes functioning well. However, oxygen consumption, particularly at elevated temperatures, decreases in crabs showing high bioaccumulation titers but increases in crabs with low/moderate bioaccumulation levels. These data show that U. rapax chronically contaminated in situ exhibits compensatory biochemical and physiological adjustments, and reveal the importance of studies on organisms exposed to metals in situ, particularly estuarine invertebrates subject to frequent changes in natural environmental parameters like salinity and temperature.

Poor ecological quality of urban ponds in northern England: causes and consequences

The value of ponds in urban areas historically has been overlooked. While some recent studies have described considerable biodiversity in urban areas, it is unclear as to how far this extends to different urban habitats. The aims of this study were to determine the condition of 21 urban ponds in Bradford (northern England) and to quantify the connectivity of wetlands in the district. The study showed that macroinvertebrate and plant biodiversity was substantially lower than would be expected based on pristine reference sites. Of the 21 ponds surveyed, 15 were found to be classified as having very poor ecological quality, with 5 being classed as poor and just 1 was classed as moderate. The number of aquatic plant species found in the ponds ranged from 0 to 6 and the number of macroinvertebrate families found ranged from 4 to 13. It was suspected that the aquatic plant diversity was low due to management techniques such as the removal of emergent vegetation. The average distance to a wetland was found to be higher in urban areas (533 m) compared to rural areas (448 m) although this difference was small, which indicates that the low diversity found in urban ponds is likely due to habitat variables.

Transplantation of epiphytic bioaccumulators (Tillandsia capillaris) for high spatial resolution biomonitoring of trace elements and point sources deconvolution in a complex mining/smelting urban context

Monitoring atmospheric trace elements (TE) levels and tracing their source origin is essential for exposure assessment and human health studies. Epiphytic Tillandsia capillaris plants were used as bioaccumulator of TE in a complex polymetallic mining/smelting urban context (Oruro, Bolivia). Specimens collected from a pristine reference site were transplanted at a high spatial resolution (∼1 sample/km2) throughout the urban area. About twenty-seven elements were measured after a 4-month exposure, also providing new information values for reference material BCR482. Statistical power analysis for this biomonitoring mapping approach against classical aerosols surveys performed on the same site showed the better aptitude of T. Capillaris to detect geographical trend, and to deconvolute multiple contamination sources using geostatistical principal component analysis. Transplanted specimens in the vicinity of the mining and smelting areas were characterized by extreme TE accumulation (Sn > Ag > Sb > Pb > Cd > As > W > Cu > Zn). Three contamination sources were identified: mining (Ag, Pb, Sb), smelting (As, Sn) and road traffic (Zn) emissions, confirming results of previous aerosol survey.

Biomonitoring study of an estuarine coastal ecosystem, the Sacca di Goro lagoon, using Ruditapes philippinarum (Mollusca: Bivalvia)

Coastal lagoons are constantly subjected to releases of chemical pollutants, and so organisms may be exposed to such toxicants. This study investigated through a multivariate approach the physiological status of bivalve Ruditapes philippinarum, farmed in Sacca di Goro lagoon. Biomarkers at different levels of biological organization (catalase, superoxide dismutase, genotoxicity, reburrowing behavior) were evaluated at three sites exposed to different environmental conditions. A seasonal trend was observed, and micronucleus frequency was significantly lowest at the relatively pristine reference site. Enzymatic activity toward oxyradicals be quite efficient since variations in responsiveness were not consistent. However, behavioral impairment was observed in reburrowing rates. Sediment concentrations showed low PAH levels and high natural levels of trace metals Cr and Ni. DistLM statistical analysis revealed a non-significant relationship between selected biomarkers and xenobiotics. Therefore other potentially toxic compounds in admixture at low doses may be involved in driving differing spatial distribution of physiological impairment.

A Starting Point: An Ecosystem of Reference for Habitat Restoration of the Northern Idaho Ground Squirrel, Urocitellus brunneus brunneus

The Northern Idaho Ground Squirrel (NIDGS, Urocitellus brunneus brunneus) is threatened by habitat loss due to fire exclusion in west-central Idaho. Increases in Ponderosa Pine (Pinus ponderosa) density and extent have closed historically open meadows. Management practices for NIDGS recovery include thinning and burning to reduce tree encroachment. Baseline habitat data help create restoration goals and refine present management plans, but no pristine reference sites exist for the NIDGS, due to 100 y of land use and a lack of historical records. Therefore, we provided the first quantitative habitat descriptions of NIDGS habitat at 7 currently occupied sites that may be useful as an ecosystem of reference. We chose habitat attributes that are likely important to NIDGS, as well as attributes that are potentially altered by restoration treatments, which included overstory canopy cover, tree density, ground cover, litter depth, and soil texture. Habitat attributes were described with Bayesian 95% credibility intervals. Sites occupied by NIDGS had tree canopy cover of 10 to 15%, tree densities of 64 to 118 trees/ha, and understory height was 20 to 25 cm. Understory vegetation of occupied habitat consisted of 20 to 30 species, while across-site richness was 153 species. We also identified 15 understory species with the highest constancy and cover across the 7 sites. Litter depth was 0.7 to 0.9 cm, and the soil texture was clay loam. Our study provides valuable baseline information about NIDGS habitat. Managers may use our results to develop appropriate restoration targets when implementing habitat restoration. Information on occupied habitat may increase the efficacy of currently implemented restoration techniques and provide knowledge to be used in an adaptive management framework.

Persistent Metal Contamination Limits Lotic Ecosystem Heterotrophic Metabolism after More Than 100 Years of Exposure: A Novel Application of the Resazurin Resorufin Smart Tracer

Persistent stress from anthropogenic metal deposition in lotic ecosystems is a global concern. This long-term selective pressure shapes hyporheic microbial assemblages and influences ecosystem functional integrity. We hypothesized that, even after 100 years of adaptation opportunity, ecosystem function remains inhibited by sediment-associated metal stress and that the Resazurin Resorufin Smart Tracer can be used to quantify this impact. The Resazurin Resorufin Smart Tracer system is applied here in a novel capacity as an indicator of ecosystem function by quantifying ecosystem respiration of microbial communities. Hyporheic microbial communities exposed to differing magnitudes of chronic metal stress were compared to pristine reference sites in controlled column experiments. A Markov chain Monte Carlo technique was developed to solve the inverse smart tracer transport equation to derive community respiration data. Results suggest metals inhibit respiration by 13-30% relative to reference sites and this inhibition is directly related to the level of in situ metal stress. We demonstrate the first application of a hydrologic smart tracer as a functional indicator of ecological integrity within anthropogenically influenced flowing water systems and provide data suggesting resilience is limited in hyporheic ecosystems even after more than a century of microbial adaption to chronic pollutants.

High Variability in Sediment Characteristics of a Neotropical Stream Impacted by Surface Mining and Gully Erosion

This study examined patterns of stream sediment granulometry, organic matter (OM) and metal concentration, and surface water characteristics in a catchment in the Brazilian Iron Quadrangle that is highly impacted by surface iron mining and gully erosion. Sediment granulometry indicated fine sediment deposition at impacted stream sites, i.e., tendencies towards bimodal particle size distributions with an additional peak in the sand fraction at impacted stream sites that did not occur at pristine reference sites, as well as towards smaller mean sediment particle sizes at impacted sites than at reference sites. Impacted sites also had significantly lower sediment OM contents than reference sites. Sediment heavy metal and arsenic concentrations did not differ between impacted and reference sites and were generally below published target or threshold effect concentrations. Impacts on surface water characteristics occurred only locally at a site that received tailings pond effluent from an iron mine and had very low pH and conductivity values. Sediment characteristics exhibited substantial spatial variability in the studied tropical catchment, showing that land use impacts can hardly be detected in routine monitoring and impact assessment studies that adopt a before–after control-impact approach and do not consider pristine reference streams. These results underline the importance of high-resolution and long-term sediment monitoring as well as integrated basin-scale sediment management programs.

Utility of a single a priori river typology for reference conditions of boreal macroinvertebrates and diatoms

The ecological quality of river habitats is increasingly assessed using multiple taxonomic groups. As widely recognised, assessments should be based on the reference condition approach where potentially impaired sites are compared to pristine or near pristine reference sites. To enable valid comparisons, natural variability of habitat characteristics and biotic assemblages should be controlled for, by using either an a priori river typology as suggested by the European Union Water Framework Directive (WFD) or by some other reference framework. We examined a simple WFD river typology, based on two broad-scale ecoregions, catchment area, and geology, as a basis for reference conditions of macroinvertebrates and diatoms in Finland. The ability of this a priori typology to account for natural variation in assemblage composition was evaluated by comparing it with null models (no typology) and with a posteriori clusters ('optimal' biological typology). The biological clusters were clearly more effective than the WFD typology in partitioning assemblage variation for diatoms, whereas differences among the groupings were less evident for macroinvertebrates. Similarly, the number of observed versus expected type-specific taxa (O/E-ratio) was more precise with the a posteriori clusters than with the WFD typology for diatoms, while there were no clear differences among the groupings for macroinvertebrates. For diatoms, the typology was virtually inefficient in improving the precision of O/E from that of the null model. Strong biogeographical patterns in assemblage composition of both biotic groups were evident between and within the two ecoregions. Variation in macroinvertebrate assemblages was primarily related to geographical location and river size, whereas geographical location and water chemistry were the most important environmental factors for diatoms. Our results suggest that simple a priori typologies could be used as a framework for reference condition in freshwater bioassessment. However, when assessments are conducted using multiple taxonomic groups, typologies should be based on factors important for each individual group.

Evaluation of geochemical associations as a screening tool for identifying anthropogenic trace metal contamination

Geochemical association plots are used as a screening tool for environmental site assessments and use empirical log-log relationships between total trace metal concentrations and concentrations of a major (i.e., reference) soil metal constituent, such as iron (Fe), to discern sites with naturally elevated trace metal levels from sites with anthropogenic contamination. Log-log relationships have been consistently observed between trace metal and reference metal concentrations and are often considered constant. Consequently, we used a regional geochemistry data set to evaluate background trace metal/Fe log-log associations across soils with highly diverse composition. Our results indicate that, although geochemical associations may be proportional, they significantly differ across predominant United States Department of Agriculture (USDA) soil orders. This suggests that highly complex interactions between soil-forming factors and variable secondary clay mineral composition affect the ratio of trace metals to Fe concentrations in soils. Also, intra-order variability in trace metal/Fe ratios generally ranged multiple orders of magnitude which suggest that the order level of the USDA soil taxonomic system is insufficient to reasonably classify background trace metal concentrations. Consequently, geochemical association plots are a useful screening tool for environmental site assessments, but ubiquitous application of generic background metal data sets could result in erroneous conclusions. Because significantly different ratios were observed across predominant USDA soil orders, an agglomerative clustering technique was used to elucidate hierarchical patterns of association. We present these results as a mechanism to aid environmental assessors in screening candidate background metal data sets for their applicability to site-specific soil composition; although site-specific background metal data should be utilized if ample pristine reference sites with similar (i.e., sub-order) soil composition can be identified and sampled.

Prediction of riverine fish assemblages through the concept of environmental filters

Although the taxonomic composition and richness of fish assemblages are important properties to be considered in freshwater bioassessment, conservation and rehabilitation, it can be difficult to establish a natural benchmark for these properties because of widespread human impact and a lack of pristine reference sites or pre-impact data. As an alternative to the reference site approach, the concept of multiple environmental filters was used to predict the assemblages of fish taxa expected in the absence of anthropogenic stress at 85 sites on rivers in north-eastern New South Wales, Australia. The predicted native fish assemblages were compared with the assemblages recorded by backpack and boat electrofishing at each site. The number of native species predicted by the filters model at each site was highly correlated with the observed number of native species (R2 = 0.75; P &lt; 0.001) but the observed number was generally lower. The model had an average sensitivity of 93% and specificity of 87%, but sensitivity and specificity were considerably less for a few species, including some that are known to have suffered historical declines or been translocated outside of their natural ranges. Comparisons between predicted and observed richness and composition can be used to identify areas of high conservation value and areas where native fish assemblages have been adversely affected by anthropogenic impacts.

Crude oil-induced structural shift of coastal bacterial communities of rod bay (Terra Nova Bay, Ross Sea, Antarctica) and characterization of cultured cold-adapted hydrocarbonoclastic bacteria

For preliminary screening of human impact on Antarctic coasts, the compositions of microbial communities were analyzed in seawater at two sites located in the Terra Nova Bay of Antarctica (Ross Sea) by a combination of 16S rRNA gene sequencing and culture techniques. The bacterial community in the sample from the Rod Bay site, located at the proximity to the Italian Station, was characterized by a high abundance of 16S rRNA gene sequences belonging to the microflora typically found in soil and freshwater environments. In contrast, the seawater sample from the Adelie Cove station, a pristine reference site, contained 16S rRNA gene sequences typically found in marine areas affected by algal blooms and sea ice decay. The addition of crude oil to the Rod Bay seawater sample rapidly induced a shift in the composition of the bacterial community with appearance of novel taxonomic groups and a dramatic increase in the relative abundance of γ- Proteobacteria sequences, whereas no significant changes were detected in the bacterial community of the Adelie Cove sample under the same conditions. Bacteria-exhibiting features with potential interest for industrial and environmental applications were isolated from the Rod Bay oil-enriched sample. In particular, hydrocarbon-degrading, cold-adapted bacteria were selectively enriched, isolated and screened for their ability to synthesize polyunsaturated fatty acids. Twenty two bacterial strains were isolated from the oil enrichment culture and identified. Eighteen isolates were found to be members of γ- Proteobacteria, while the remainder were representatives of α- Proteobacteria, CFB and high G + C divisions.

Crude oil-induced structural shift of coastal bacterial communities of rod bay (Terra Nova Bay, Ross Sea, Antarctica) and characterization of cultured cold-adapted hydrocarbonoclastic bacteria

For preliminary screening of human impact on Antarctic coasts, the compositions of microbial communities were analyzed in seawater at two sites located in the Terra Nova Bay of Antarctica (Ross Sea) by a combination of 16S rRNA gene sequencing and culture techniques. The bacterial community in the sample from the Rod Bay site, located at the proximity to the Italian Station, was characterized by a high abundance of 16S rRNA gene sequences belonging to the microflora typically found in soil and freshwater environments. In contrast, the seawater sample from the Adelie Cove station, a pristine reference site, contained 16S rRNA gene sequences typically found in marine areas affected by algal blooms and sea ice decay. The addition of crude oil to the Rod Bay seawater sample rapidly induced a shift in the composition of the bacterial community with appearance of novel taxonomic groups and a dramatic increase in the relative abundance of γ-Proteobacteria sequences, whereas no significant changes were detected in the bacterial community of the Adelie Cove sample under the same conditions. Bacteria-exhibiting features with potential interest for industrial and environmental applications were isolated from the Rod Bay oil-enriched sample. In particular, hydrocarbon-degrading, cold-adapted bacteria were selectively enriched, isolated and screened for their ability to synthesize polyunsaturated fatty acids. Twenty two bacterial strains were isolated from the oil enrichment culture and identified. Eighteen isolates were found to be members of γ-Proteobacteria, while the remainder were representatives of α-Proteobacteria, CFB and high G + C divisions.

Short Note

Using process‐orientated parameters to assess degradation.

Mercury exposure to passerine birds in areas close to local emission sources in Slovakia and Norway

Mercury concentrations in vegetation, insects and insectivorous birds were studied in the vicinity of a mercury production plant at Rudnany, Slovakia and a zinc smelter at Odda, Norway. Comparison was made with pristine reference sites in both countries. Sampling of eggs and juvenile birds was facilitated through the use of nest boxes. In Norway the migrating species Ficedula hypoleuca was studied, whereas in Slovakia both migrating and resident birds were represented. While the Hg levels in vegetation and insects corresponded well to the expectations based on previous knowledge of contamination levels, the levels in passerine bird eggs seemed to depend mainly on whether the bird was migratory or resident. In chicks liver Hg levels at different sites in Norway showed no clear correspondence with egg levels at the same sites. At the background site an initial Hg burden provided through the egg was rapidly reduced, probably through excretion during feather development, whereas at the most contaminated site intake of Hg through contaminated food outweighed the excretion effect.

Toxicological evaluation of constructed wetland habitat sediments utilizing [formula omitted] 10-day sediment toxicity test and bacterial bioluminescence

A toxicological evaluation was conducted on wetland habitats created as a result of run-off from agricultural areas. These temporary wetlands were created by using drop pipes as a means of reducing erosional cutting in agricultural fields. Toxicity bioassays utilizing bacterial bioluminescence and Hyalella azteca were used to assess sediment pore water and whole sediment, respectively. Inhibition of bacterial bioluminescence was initially used to determine relative toxicities of pore water from ten wetland sites. Constructed wetland sites were compared to the University of Mississippi Biological Field Station, a relatively pristine reference site. The H. azteca ten day sediment toxicity test was utilized to assess sediment from four selected sites using survival and growth as toxicological endpoints. Results from the toxicological evaluation, along with extensive ecological evaluations, were used to assess the best approach for implementation of temporary wetland habitats with existing agricultural practices.

Linkages Between Chemical Contaminants and Tumors in Benthic Great Lakes Fish

Cutaneous papilloma have been observed at high prevalences in populations of brown bullheads ( Ameiurus nebulosus) and white suckers ( Catostomus commersoni) distributed throughout the Great Lakes, with no clear-cut delineation between prevalences in fish populations from industrialized sites in comparison to more pristine sites. However, bullhead papilloma prevalences greater than 20% were never observed at pristine reference sites, while high prevalences of sucker papilloma (> 20%) were only observed in populations from the lower Great Lakes. It is probable that there is a viral etiology for papilloma affecting bullheads and suckers, although chemical contaminants may influence the development of these neoplasms through some mechanism. Hepatic neoplasms of both cholangiocytic and hepatocytic origin have been observed at relatively high prevalences in Great Lakes populations of brown bullheads and white suckers. Prevalences of total hepatic neoplasms of > 9% in bullheads and > 3% in suckers were usually only observed in populations from industrialized areas of the Great Lakes. However, relatively high prevalences of hepatic neoplasms were also observed in suckers and bullheads from pristine areas where there is a preponderance of older fish in the population. In the case of both bullheads and suckers, high prevalences of hepatic neoplasms appear to be associated with severe biliary disease (e.g. cholangiofibrosis, cholangiohepatitis). It is highly probable that the etiology of hepatic cancers in bullheads and suckers from the Great Lakes is associated with exposure to chemical contaminants, and in some areas, specifically with exposure to polynuclear aromatic hydrocarbons. However, other chemical contaminants may indirectly influence hepatic tumor rates by increasing the severity of biliary disease in fish from contaminated areas. Overall, cutaneous papilloma prevalences above approximately 25% and hepatic neoplasm prevalences above approximately 5% in these species should be interpreted as an indicator of environmental degradation in the area where fish were surveyed.

Chromosome damage in wild rodents inhabiting a site contaminated with aroclor 1254

AbstractAn in situ investigation of structural chromosomal damage in wild rodents from a site contaminated with Aroclor 1254 was undertaken to compare effects observed in nature to those documented in previous laboratory studies. Laboratory assays indicate that Aroclor 1254 does not cause structural damage to chromosomes. However, the many variables at work in actual waste‐site environments and receptor populations led us to question whether exposures under natural conditions could potentially lead to different results using the same assay systems. Individuals of three rodent species, Peromyscus leucopus, Sigmodon hispidus, and Reithrodontomys fulvescens, were collected from the contaminated site and three matched, pristine reference sites. Standard somatic metaphase chromosome preparations from bone marrow were examined for chromosomes lesions. Comparisons were made between conspecifics from the Aroclor‐contaminated site and the reference sites. Significant increases in chromosome damage were not observed in animals from the Aroclor‐contaminated site, indicating agreement between laboratory assays and an in situ application of this assay system.

Biological markers in fish: DNA integrity, hematological parameters and liver somatic index

In a field study, DNA damage, hematological parameters, and liver somatic index were measured in fish collected from freshwater creeks contaminated with polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs) (East Tennessee) and from estuarine and marine waters contaminated with PAHs and cadmium (Mississippi Sound). For comparison, specimens were examined from two pristine reference sites near the impacted Tennessee and Mississippi sites. Significantly more strand-breaks were found in DNA isolated from liver tissue of redbreast sunfish ( Lepomis auritus) from contaminated creeks than in DNA from sunfish from two pristine creeks. Hemoglobin concentration ( C Hb) and mean corpuscular hemoglobin concentration (MCHC) were significantly higher in both male and female sunfish from the pristine creeks. Furthermore, the liver somatic index (LSI) of sunfish from contaminated creeks was higher than that of specimens from reference sites. In adult male, female, and juvenile hardhead catfish ( Arius felis) from suspected contaminated sites in the Mississippi Sound, high LSI and lowered C Hb and MCHC were found. A higher percentage of double-stranded DNA was measured in specimens from the pristine reference sites. Individual differences in responses of the biological markers, however, were large, as reflected by high standard deviations. The biological responses measured were obviously valuable to indicate differences in the environmental quality expressed in molecular and physiological terms.