Duluth-Superior Harbor Research Articles

The effects of intensive trapping on invasive round goby densities.

The round goby (Neogobius melanostomus) is an invasive benthic fish first introduced to the Laurentian Great Lakes in 1990 that has negatively impacted native fishes through increased competition for food and habitat, aggressive interactions, and egg predation. While complete eradication of the round goby is currently not possible, intensive trapping in designated areas during spawning seasons could potentially protect critical native fish spawning habitats. Baited minnow traps were spaced 10 meters apart in shallow water along a 100-meter stretch of shoreline within the Duluth-Superior Harbor during the round goby breeding period (June to October) with captured round gobies removed from interior traps (N = 10) every 48 hours. These traps were bracketed by two pairs of reference traps deployed weekly for 48 hours, from which round gobies were also tagged and released. The number of round gobies captured in the interior traps declined by 67% compared to reference traps over the course of the study, with extended periods of no captures. The tagged round gobies showed high site affinity, with 82.8% of tagged fish recaptured at the previous release site. The results indicate that even at open water sites, which allow natural migration of round gobies into the area, extensive trapping could reduce local population numbers.

Field testing of an enzymatic quorum quencher coating additive to reduce biocorrosion of steel.

Microbial colonization can be detrimental to the integrity of metal surfaces and lead to microbiologically influenced corrosion. Biocorrosion is a serious problem for aquatic and marine industries in the world and severely affects the maritime transportation industry by destroying port infrastructure and increasing fuel usage and the time and cost required for maintenance of transport vessels. Here, we evaluate the potential of a stable quorum quenching lactonase enzyme to reduce biocorrosion in the field. Over the course of 21 months, steel samples coated with lactonase-containing acrylic paint were submerged at two different sites and depths in the Duluth-Superior Harbor (Lake Superior, MN, USA) and benchmarked against controls, including the biological biocide surfactin. In this experiment, the lactonase treatment outperformed the surfactin biocide treatment and significantly reduced the number of corrosion tubercles (37%; P < 0.01) and the corroded surface area (39%; P < 0.01) as compared to the acrylic-coated control coupons. In an attempt to evaluate the effects of signal disruption of surface microbial communities and the reasons for lower corrosion levels, 16S rRNA sequencing was performed and community populations were analyzed. Interestingly, surface communities were similar between all treatments, and only minor changes could be observed. Among these changes, several groups, including sulfate-reducing bacteria (SRB), appeared to correlate with corrosion levels, and more specifically, SRB abundance levels were lower on lactonase-treated steel coupons. We surmise that these minute community changes may have large impacts on corrosion rates. Overall, these results highlight the potential use of stable quorum quenching lactonases as an eco-friendly antifouling coating additive. IMPORTANCE Biocorrosion severely affects the maritime transportation industry by destroying port infrastructure and increasing fuel usage and the time and cost required to maintain transport vessels. Current solutions are partly satisfactory, and the antifouling coating still largely depends on biocide-containing products that are harmful to the environment. The importance of microbial signaling in biofouling and biocorrosion is not elucidated. We here take advantage of a highly stable lactonase that can interfere with N-acyl homoserine lactone-based quorum sensing and remain active in a coating base. The observed results show that an enzyme-containing coating can reduce biocorrosion over 21 months in the field. It also reveals subtle changes in the abundance of surface microbes, including sulfate-reducing bacteria. This work may contribute to pave the way for strategies pertaining to surface microbiome changes to reduce biocorrosion.

Evaluating restoration success in a Great Lakes embayment: A case study for addressing beneficial use impairments

Aquatic habitats within the St. Louis River estuary were impacted when developing the Duluth-Superior Harbor (MN/WI USA) and through decades of unregulated industrial and municipal discharge. An effort to remediate and restore sediment quality in the harbor began by implementing projects designed to address Beneficial Use Impairments (BUI) identified in this Area of Concern. Habitat restoration in the 21st Avenue West project site was implemented to improve overall aquatic community health and address a degradation of benthos BUI. Restoration objectives focused on creating more complex bathymetric surfaces and mitigating contaminant exposure by capping with clean dredged material. Before and after construction, samples were collected to assess the benthic community within 21st Avenue West compared to results from least-impaired, reference locations. A scaled trimetric index (s-TMI), scored between 0 and 1, was used to track an impaired benthic community before and after construction.A median s-TMI value for 21st Avenue West prior to construction (value = 0.51) improved following restoration (site median = 0.65), reaching a site-wide value that was not significantly different from the least impaired removal target (reference median = 0.68, when calculated from pooled reference data). Results from post construction sample collections at 21st Avenue West suggest macroinvertebrate community index scores increased by more than 10% two years following construction. These results indicate that the 21st Avenue West habitat restoration effort successfully reached a degradation of benthos BUI goal and demonstrates that dredge material is a cost-effective alternative for construction.

Evaluation of a method that uses one cubic meter mesocosms to elucidate a relationship between inoculation density and establishment probability for the nonindigenous, invasive zooplankter, Bythotrephes longimanus

The introduction and spread of aquatic invasive species by ships is a global concern, and development and implementation of effective prevention measures are an urgent priority. Two questions plague science and policy. First, what level of reduction in live organism discharges from ships yields a given desired level of reduction in species establishment probability? Second, how can this question be empirically tested in a practicable and replicable manner? We evaulated the extent to which experiments using 1 m3 mesocosms could help elucidate a relationship between inoculation density and reproductive output (a proxy for establishment probability) of a surrogate invader, Bythotrephes longimanus (Crustacea: Cladocera). The inoculation densities were 1, 5, 10, 20, or 40 individuals m−3. All individuals in each inoculum were added as a single event at the start of each of four, two-week-long experiments. B. longimanus were inoculated into ambient water pumped from the Duluth-Superior Harbor at the start of each experiment between June and August, 2015. The mesocosm volume and range of inoculation densities has relevancy to the International Maritime Organization’s Ballast Water Management Convention D2 standard which allows a density of 50 μm minimum dimension. Reproductive output was detected among 78 of 80 mesocosms after 2 weeks. Among 13 abiotic and biotic variables, inoculation density was overwhelmingly the best predictor, and water temperature was the second best predictor, of B. longimanus reproductive output. Net reproductive value of the inoculants was ≥ 1 among 35 of 80 mesocosms after 2 weeks. There was evidence for density-dependent reduction in population growth rate in the higher inoculation density mesocosms. We examined various parts of our method for robustness. Translation of the results into meaningful estimates of establishment probability in the field remains a vivid challenge. We introduce the idea of using annual hatching rates of natural banks of dormant eggs in lake sediments as a method to characterize relationships between propagule pressure and establishment probability at the scale of an ecosystem for seasonally transient species such as B. longimanus.

Evaluation of biological and enzymatic quorum quencher coating additives to reduce biocorrosion of steel.

Microbial colonization can be detrimental to the integrity of metal surfaces and lead to microbiologically influenced corrosion (MIC). Biocorrosion is a serious problem for aquatic and marine industries in the world. In Minnesota (USA), where this study was conducted, biocorrosion severely affects the maritime transportation industry. The anticorrosion activity of a variety of compounds, including chemical (magnesium peroxide) and biological (surfactin, capsaicin, and gramicidin) molecules were investigated as coating additives. We also evaluated a previously engineered, extremely stable, non-biocidal enzyme known to interfere in bacterial signaling, SsoPox (a quorum quenching lactonase). Experimental steel coupons were submerged in water from the Duluth Superior Harbor (DSH) for 8 weeks in the laboratory. Biocorrosion was evaluated by counting the number and the coverage of corrosion tubercles on coupons and also by ESEM imaging of the coupon surface. Three experimental coating additives significantly reduced the formation of corrosion tubercles: surfactin, magnesium peroxide and the quorum quenching lactonase by 31%, 36% and 50%, respectively. DNA sequence analysis of the V4 region of the bacterial 16S rRNA gene revealed that these decreases in corrosion were associated with significant changes in the composition of bacterial communities on the steel surfaces. These results demonstrate the potential of highly stable quorum quenching lactonases to provide a reliable, cost-effective method to treat steel structures and prevent biocorrosion.

Evaluation of a method for ballast water risk–release assessment using a protist surrogate

Understanding the risk–release relationship (the relationship between density of organisms released and associated risk of establishment of a population) of aquatic invasive species is important for setting policy standards to protect natural water bodies from species spread through human-mediated vectors, in particular ballast discharge. To test the viability of an experimental and analytical approach to investigate this relationship, we conducted a mesocosm-based experiment using a test organism, Melosira varians (a freshwater phytoplanktonic diatom native to the Great Lakes). Varying densities of the test organism were added to 19-l mesocosms of water from the Duluth-Superior Harbor at Superior, Wisconsin, in three consecutive trials over 4 months. Each mesocosm was sampled weekly for 4 weeks, and the size of the M. varians population and phytoplankton community was measured via assessments of cell densities. Population responses varied by initial M. varians density. Based on a logistic model, the inoculation density necessary for establishment of M. varians was approximately 12 cells/ml. These findings suggest mesocosm experiments coupled with logistic modeling have the potential to characterize risk–release relationships. Additional investigations using similar methods should be undertaken with a variety of test organisms and environmental conditions to further vet this method and extend understanding of risk–release relationships.

The benthic fish assemblage of the soft-bottom community of the Duluth-Superior Harbor before and after round goby invasion (1989–2011)

Abstract The soft-bottom benthic fish community of the St. Louis River and Duluth-Superior Harbor was examined yearly (20 of 23 years) from 1989 through 2011 using bottom trawling. Catch per unit effort (CPUE) and fish lengths were used to assess the impact of the round goby, which appeared in trawl records in 1998, on benthic native fishes. Logperch ( Percina caprodes ), spoonhead sculpin ( Cottus ricei ), johnny darter ( Etheostoma nigrum ), channel catfish ( Ictlarus puncatus ), tadpole madtom catfish ( Noturus gyrinus ) and bullhead catfish ( Ictalurus spp.) plus the invasive Eurasian ruffe ( Gymnocephalus cernuus ) populations were assessed. After detection in the trawl record in 1998, round goby continued to increase in abundance through 2006. Logperch showed a 65% decline in median CPUE from 2.4 to 0.85, while johnny darter increased almost three-fold from 0.24 to 0.68 CPUE following round goby detection. Bullheads dropped from 7.5 CPUE to being virtually extirpated from the study area. However, their decline preceded round goby appearance, and was linked to the stocking of predator fish to combat the Eurasian ruffe. It is hypothesized that the presence of the Eurasian ruffe contributed to depressing the native fish population to the extent that the round goby appearance had less impact on the community. However, after 20 years of decline, the native fish appear to be rebounding due to declines in the Eurasian ruffe and round goby populations and improvements in water quality.

Effort and potential efficiencies for aquatic non-native species early detection

Our objective was to determine the effort required for high-probability early detection of non-native zooplankton, benthic invertebrates, and fish using Duluth–Superior Harbor — a Great Lakes port under intense non-native species introduction pressure — as a case study. Initially, we allocated samples using a spatially balanced random design. We then resampled the harbor, but allocated samples to a few targeted areas. We detected 21 non-native invertebrate and 10 non-native fish species; however, many rare zooplankton and benthic invertebrates were likely missed. The two designs did not have significantly different species accumulation curves, but the targeted area design samples had higher species richness and detected non-native species with a significantly higher probability. It was possible to reduce the effort required to detect established non-native species. In contrast, the effort required to detect an ultra-rare, newly arrived species remained large. Based on statistical estimation theory, the effort required to detect 95% or more of species present could exceed enumerating 750 zooplankton samples (~500 000 individuals, ~90 species), 150 benthic invertebrate samples (~100 000 individuals, ~250 species), and 100 fish samples (~75 000 individuals, ~40 species).

Waterfowl Abundance Does Not Predict the Dominant Avian Source of Beach Escherichia coli

The horizontal, fluorophore enhanced, rep-PCR (HFERP) DNA fingerprinting technique was used to identify potential sources of in water, nearshore sand, and sediment at two beaches in the Duluth-Superior Harbor, near Duluth, MN, and Superior, WI, during May, July, and September 2006. An animal or environmental source could be identified for 35, 29, and 30% of strains in water, sand, and sediments, respectively. Waterfowl, including Canada geese, ring-billed gulls, and mallard ducks, were the largest source of that could be identified in water (55-100%), sand (59-100%), and sediment (92-100%) at both beaches. Although ring-billed gulls were more abundant in this harbor, Canada geese were usually the dominant source of waterfowl found at these beaches. The percentage of identified from treated wastewater was always less than the percentage of originating from waterfowl. At both beaches, the percentage of in water contributed by treated wastewater was higher in May compared with July and September. The larger proportion of wastewater-derived seen in May probably reflected a smaller contribution of from geese when these birds were less abundant rather than an absolute increase in from treated wastewater. Microbial source analysis and bird census data both indicated that waterfowl were a major source of at beaches in the Duluth-Superior Harbor. These data also indicated it is risky to assume that the most abundant waterfowl species present in waterways will also be the largest source of avian-derived in water, nearshore sand, and sediments at beaches.

Tertiary-Treated Municipal Wastewater is a Significant Point Source of Antibiotic Resistance Genes into Duluth-Superior Harbor

In this study, the impact of tertiary-treated municipal wastewater on the quantity of several antibiotic resistance determinants in Duluth-Superior Harbor was investigated by collecting surface water and sediment samples from 13 locations in Duluth-Superior Harbor, the St. Louis River, and Lake Superior. Quantitative PCR (qPCR) was used to target three different genes encoding resistance to tetracycline (tet(A), tet(X), and tet(W)), the gene encoding the integrase of class 1 integrons (intI1), and total bacterial abundance (16S rRNA genes) as well as total and human fecal contamination levels (16S rRNA genes specific to the genus Bacteroides ). The quantities of tet(A), tet(X), tet(W), intI1, total Bacteroides , and human-specific Bacteroides were typically 20-fold higher in the tertiary-treated wastewater than in nearby surface water samples. In contrast, the quantities of these genes in the St. Louis River and Lake Superior were typically below detection. Analysis of sequences of tet(W) gene fragments from four different samples collected throughout the study site supported the conclusion that tertiary-treated municipal wastewater is a point source of resistance genes into Duluth-Superior Harbor. This study demonstrates that the discharge of exceptionally treated municipal wastewater can have a statistically significant effect on the quantities of antibiotic resistance genes in otherwise pristine surface waters.

Seasonal abundance and movement of the invasive round goby (Neogobius melanostomus) on rocky substrate in the Duluth–Superior Harbor of Lake Superior

Abstract – Despite its small size [adult: 60–130 mm, total length (TL)] and limited home range, the round goby (Neogobius melanostomus) has quickly become established throughout the Laurentian Great Lakes. Little information is available, however, on the natural dispersal pattern of this species. This capture–mark–recapture study utilised alphanumeric tags subcutaneously inserted into round gobies (n = 1228) along a 550‐m stretch of the Duluth–Superior Harbor shoreline to observe their movement over a 13‐month period. Recaptured round gobies (n = 415) exhibited highly leptokurtic movement distributions, and movement events were not correlated with fish size, gender or month. Our work indicates that round gobies &gt;50 mm (TL) generally occupy an area less than the minimum sampling interval (25 m); however, occasional movement up to 50 m per day could facilitate range expansion in the Laurentian Great Lakes.

The anatomy of tubercles: A corrosion study in a fresh water estuary

AbstractThe structure and mineralogy of corrosion products formed on carbon steel coupons exposed in Duluth Superior Harbor (DSH, USA), were investigated and compared with corrosion products on similar substrata from other locations. Corrosion products in DSH form within a few months each year and are removed by ice scour and reform. The corrosion products formed in DSH are tubercles with an outer surface, an inner shell of magnetite, and a core of iron(III) oxyhydroxides, goethite, and lepidocrocite, in association with stalks produced by bacteria. In general, the tubercles formed in DSH are similar in morphology and mineralogy to corrosion products described for carbon steel and cast iron exposed to treated waters in decades‐old drinking water and cooling water systems. DSH tubercles are unique in several structural details. DSH tubercles increase areal coverage of the substratum by consolidation of tubercles. Furthermore, the core material extends into the pit and is an exact replica of the pit profile.

Status of non-indigenous benthic invertebrates in the Duluth–Superior Harbor and the role of sampling methods in their detection

As part of a study to develop recommendations for non-indigenous species (NIS) monitoring in Great Lakes areas at risk of invasion, we conducted intensive sampling in the Duluth–Superior Harbor and lower St. Louis River in 2005 and 2006. Of the ~240 benthic invertebrate taxa identified, 19 were non-indigenous, including 8 first detection records for this system: New Zealand mud snail Potamopyrgus antipodarum; African/Asian-origin cladoceran Daphnia lumholtzi; Eurasian-origin amphipod Echinogammarus ischnus; Eurasian-origin bivalves Dreissena bugensis, Pisidium henslowanum and Pisidium supinum; and possibly range expanding oligochaetes Paranais frici and Pristina acuminata. Dreissenids were by far the most abundant NIS. Several other NIS were also common, but others were detected in only a few of the >200 samples taken. Non-indigenous amphipods and Dreissena were most frequently detected in sweep net and colonization plate samples of littoral vegetation, while NIS oligochaetes, gastropods, and non-dreissenid bivalves were most frequently detected in ponar and bottom sled samples of sediments. Our findings confirm that this major shipping port remains a NIS “hotspot” and emphasize that regular surveys covering a range of habitats with multiple sampling gears and thorough taxonomic effort are needed to detect and monitor non-indigenous species.

Factors Contributing to Corrosion of Steel Pilings in Duluth-Superior Harbor

Abstract Field observations and laboratory testing were used to conclude that aggressive localized corrosion of carbon steel pilings in Duluth-Superior Harbor, Minnesota and Wisconsin, is caused by...

Distribution, Abundance, and Range of the Round Goby, Apollina melanostoma, in the Duluth-Superior Harbor and St. Louis River Estuary, 1998–2004

Round gobies were first discovered in the Duluth-Superior Harbor, Lake Superior, in 1995. Anecdotal sightings by anglers and others suggested that the infestation was growing and expanding; however, direct evidence of the distribution and expansion rate in the harbor was largely unknown. Distribution and range of the round goby, Apollonia melanostoma, (formerly Neogobius melanostomus) was assessed using bottom trawl sampling throughout the Duluth-Superior Harbor, and portions of the lower St. Louis River from 1998 to 2004. Previous to 1998, round gobies only were reported to occupy the harbor between the two shipping entries (river kilometer 1 to 7). By 2004, they expanded throughout the harbor and upstream to river kilometer 13, but remained absent in western Lake Superior. The number of round gobies captured per 5 minutes of trawling (catch per unit effort, CPUE) increased from less than 1 fish in 1998 to an average 5.4 ± 1.2 SE fish in 2004, indicating a large increase in the population. The median yearly fish total length varied from 56.0 to 81.5 mm and wet weight varied from 2.3 to 7.0 g. As nest guarding male round gobies were located in rocky habitats inaccessible to trawling, the initial years were dominated by female round gobies with a 16:1 female to male ratio, but by 2002 the maximum ratio was 2:1. The ratio change may be indicative of the increasing population forcing males from their preferred rocky habitat onto open substrates that were more accessible to trawling.

Sources and Sinks of Escherichia coli in Benthic and Pelagic Fish

Escherichia coli and fecal coliform bacteria were isolated from five benthic and four pelagic fish species to determine their role in the fecal contamination of recreational waters. All fish were collected during fall 2006 from Southworth Marsh in the Duluth-Superior Harbor, a public beach that is commonly posted to minimize water contact due to high E. coli levels. Although fecal coliform bacteria were isolated from each fish species, they were only isolated from 66% and 72% of the individual benthic and pelagic fish, respectively. While 42% of the fecal coliforms from benthic fish were E. coli, only 4% of these bacteria from pelagic fish were E. coli. Cluster analysis showed different fish species harbored identical strains of E. coli and some fish contained multiple E. coli strains. The potential source for 65% of the E. coli isolates obtained from fish were identified by using the HFERP DNA fingerprinting method and libraries of E. coli DNA fingerprints from warm-blooded animals and environmental isolates collected in the area. The E. coli strains whose source could be identified were most similar to strains isolated from sediments, Canada geese, mallard ducks, and wastewater. None of the fish E. coli had DNA fingerprints matching those from any water or beach sand isolates. Although our results demonstrate that benthic fish contain E. coli, it may be more appropriate to consider these fish as a vector of E. coli from other sources, rather than a new source of E. coli contamination in aquatic environments.

MINNESOTA NORTH SHORE AND DULUTH-SUPERIOR HARBOR SPILL RESPONSE STRATEGIES

ABSTRACT The Minnesota Lake Superior shoreline (Minnesota'S “North Shore”) is characterized by a rocky shoreline with stretches of sand, gravel and cobble as well as several stream and ditch inlets into Lake Superior. The risk of spills is from both land and water. The 150 plus mile stretch of shoreline has a very limited amount of response equipment or nearby responders. The Duluth-Superior Harbor is at the estuarine mouth of the St. Louis River and is divided by the Minnesota and Wisconsin border. The harbor includes sensitive shorelines and habitats, numerous stream, ditch and storm sewer outfalls, as well as an active shipping industry. Geographic Information System (GIS) is a great tool for conducting data analysis and planning. GIS allows users to analyze and visualize large volumes of data to make decisions quickly. While many spill response planners use GIS as a planning response tool, many responders do not have the training and equipment to make efficient use of the capabilities of GIS. This project uses GIS to gather and analyze available data and then put it into a useful “hardcopy” visual format for responders to use in the field. Maps produced from various GIS data sources outline the response strategies for sensitive areas to be protected; types and quantities of response equipment needed; access areas; and other important features. These “hardcopy” displays can be included in contingency plans. Larger laminated versions can be stored with response equipment caches. For response planners that are more familiar with GIS, the tool includes several useful features including “clickable” hyperlinks that connect to georeferenced oblique aerial photos of the Lake Superior shoreline. Also included are GIS data from U.S. EPA and NOAA, including sensitive environment, economic and cultural resources; potential spill sources; and response resources. Where available, sewer data for both sanitary and storm sewers is included, along with high resolution aerial photos; navigation charts; highway stream crossing data; and other habitat information. These various data sources are valuable tools for spill response planners to more accurately and effectively develop workable response strategies and also for use during an actual response to more effectively and efficiently direct responders and resources. This GIS product also incorporates an Access database which allows for easy report generation and information updating.

Decay model for biocide treatment of unballasted vessels: Application for the Laurentian Great Lakes

A biocide decay model was developed to assess the potential efficacy and environmental impacts associated with using glutaraldehyde to treat unballasted overseas vessels trading on the Laurentian Great Lakes. The results of Monte Carlo simulations indicate that effective glutaraldehyde concentrations can be maintained for the duration of a vessel’s oceanic transit (approximately 9–12 days): During this transit, glutaraldehyde concentrations were predicted to decrease by approximately 10% from initial treatment levels (e.g., 500 mg L −1). In terms of environmental impacts, mean glutaraldehyde concentrations released at Duluth-Superior Harbor, MN were predicted to be 100-fold lower than initial treatment concentrations, and ranged from 3.2 mg L −1 (2 SD: 2.74) in April to 0.7 mg L −1 (2 SD: 1.28) in August. Sensitivity analyses indicated that the reballasting dilution factor was the major variable governing final glutaraldehyde concentrations; however, lake surface temperatures became increasingly important during the warmer summer months.

Burrowing mayflies as indicators of ecosystem health: Status of populations in two western Lake Superior embayments

The U.S. Environmental Protection Agency and Environment Canada are supporting the development of indicators of ecosystem health that can be used to report on progress in restoring and maintaining the Great Lakes ecosystem, as called for in the Great Lakes Water Quality Agreement between the United States and Canada. One indicator under development for Great Lakes mesotrophic environments is based on burrowing mayflies (Hexagenia: Ephemeroptera: Ephemeridae). In this paper, we report the results of a benthic survey in spring 2002 to determine the status of nymphal populations of Hexagenia in two western Lake Superior embayments, the St. Louis River estuary, an area with significant water-use impairments, and Chequamegon Bay, an area with no known water-use impairments. Ponar grab samples collected throughout these embayments showed nymphs were generally abundant in finely particulate, cohesive substrate (clay or mixtures of clay and sand) in both embayments. However, in the St. Louis River estuary nymphs were absent in those preferred substrates at 11 stations in the eastern portion of St. Louis Bay and the adjoining northwestern portion of the Duluth-Superior Harbor, where the sediments were variously contaminated with visible amounts of taconite pellets, paint chips, oil, or combusted coal waste (clinkers). Our results suggest that human activities have rendered those portions of the St. Louis River estuary unsuitable for habitation by Hexagenia nymphs and we recommend that trend monitoring of the nymphal population there be conducted to permit reporting on progress in restoring and maintaining the health and integrity of this Great Lakes ecosystem embayment, consistent with the intent of the Great Lakes Water Quality Agreement.

Screening for PAHs by fluorescence spectroscopy: A comparison of calibrations

Total PAHs were estimated by UV-fluorescence spectroscopy in sediments from the Duluth-Superior Harbor Area of Concern in the Western arm of Lake Superior (USA). The screening method used a simple hexane extraction followed by fluorescence analysis using a standard, un-modified, Turner TD-10 fluorometer equipped with a short wavelength hydrocarbon kit. Three calibration scenarios were evaluated. The accuracy of the method was dependent on the calibration method selected that depended on the knowledge of the site. The method had good overall accuracy for designating “hot spots”(with Total-PAHs > 2,000 μg/Kg dry weight) and for plume delineation, with a relatively low rate of “false positives” (17%) and “false negatives” (18%) at the designated sediment criteria. In addition the method had significant cost advantages over standard GC/MS methodology for sediment assessment.