North Carolina Estuaries Research Articles

Ecological mechanisms generating variable first-year growth in Paralichthys lethostigma, a coastal flatfish

Determining the relative influence of, and possible synergistic relationships among, environmental and biotic processes on individual growth rates can identify key mechanisms that contribute to variation in body size observed among similar-aged individuals. The timing of ontogenetic shifts in diet or habitat, which themselves can be size-dependent, can have considerable impacts on individual growth trajectories, survival, and year class formation. The southern flounder Paralichthys lethostigma is a coastal flatfish species with juvenile cohorts that occupy diverse estuarine settlement habitats and commonly display 2-3 fold variation in body size by the end of the first growing season. We examined abiotic and biotic factors contributing to differences in early juvenile growth for the 2018 year-class of southern flounder in a North Carolina estuary. Following peak larval settlement (Febuary/March), flounder body sizes began to diverge by April, with differences between settlement habitats contributing to roughly 3-fold variation by August. Stomach content analyses indicated a greater occurrence of fish prey in the diets of southern flounder recovered in mesohaline versus oligohaline settlement habitats. Increased piscivorous foraging in mesohaline habitats was linked to nitrogen (δ15N)-enriched tissues and faster growth rates relative to fish collected in oligohaline habitats. Results from a controlled laboratory experiment provided evidence for the strong effects of diet, with only minor direct effects of salinity on juvenile southern flounder growth. Our findings support the critical role of ontogenetic shifts to piscivorous feeding for growth in young-of-the-year southern flounder and highlights the potential for growth-mortality tradeoffs to exist among estuarine settlement habitats.

Introducing a "core steel microbiome" and community functional analysis associated with microbially influenced corrosion.

Microorganisms attached to aquatic steel structures play key roles in nutrient cycling and structural degradation processes. Corrosion-causing microbes are often the focus of studies involving microbially influenced corrosion, yet the roles of remaining community members remain unclear. This study characterizes the composition and functional potential of a 'core steel microbiome' across stainless steel types (304 and 316) and historic shipwreck steel along salinity gradients in North Carolina estuaries. We found higher phylogenetic evenness and diversity on steel surfaces compared to sediment, and at lower salinities. The core steel microbiome was composed of heterotrophic generalist taxa, and community composition was most strongly influenced by salinity. Substrate type was a secondary factor becoming more influential at higher salinities. The core steel microbiome included members of Sphingobacteriia, Cytophagia, Anaerolineaceae, Verrucomicrobiaceae, Chitinophagaceae, and Rheinheimera. While salinity differences led to phylogenetic separations across microbial community assemblages, functional genes were conserved across salinity and steel type. Generalist taxa on steel surfaces likely provide functional stability and biofilm protection for the community with limited functional trade-offs compared to surrounding environments. Further, characterization of a core steel microbiome increases the understanding of these complex steel surface microbial communities and their similarities to core microbiomes in other environments.

Examining coastal dynamics and recreational water quality by quantifying multiple sewage specific markers in a North Carolina estuary

Fecal contamination is observed downstream of municipal separate storm sewer systems in coastal North Carolina. While it is well accepted that wet weather contributes to this phenomenon, less is understood about the contribution of the complex hydrology in this low-lying coastal plain. A quantitative microbial assessment was conducted in Beaufort, North Carolina to identify trends and potential sources of fecal contamination in stormwater receiving waters. Fecal indicator concentrations were significantly higher in receiving water downstream of a tidally submerged outfall compared to an outfall that was permanently submerged (p < 0.001), though tidal height was not predictive of human-specific microbial source tracking (MST) marker concentrations at the tidally submerged site. Short-term rainfall (i.e. <12 h) was predictive of E. coli, Enterococcus spp., and human-specific MST marker concentrations (Fecal Bacteroides, BacHum, and HF183) in receiving waters. The strong correlation between 12-hr antecedent rainfall and Enterococcus spp. (r = 0.57, p < 0.001, n = 92) suggests a predictive model could be developed based on rainfall to communicate risk for bathers. Additional molecular marker data indicates that the delivery of fecal sources is complex and highly variable, likely due to the influence of tidal influx (saltwater intrusion from the estuary) into the low-lying stormwater pipes. In particular, elevated MST marker concentrations (up to 2.56 × 104 gene copies HF183/mL) were observed in standing water near surcharging street storm drain. These data are being used to establish a baseline for stormwater dynamics prior to dramatic rainfall in 2018 and to characterize the interaction between complex stormwater dynamics and water quality impairment in coastal NC.

Ecosystem Capacity for Microbial Biodegradation of Munitions Compounds and Phenanthrene in Three Coastal Waterways in North Carolina, United States.

Munitions compounds (i.e., 2,4,6-trinitrotoluene (TNT), octahy-dro-1,3,5,7-tetranitro-1,3,5,7-tetrazocin (HMX), and hexadydro-1,3,5-trinitro-1,3,5-triazin (RDX), also called energetics) were originally believed to be recalcitrant to microbial biodegradation based on historical groundwater chemical attenuation data and laboratory culture work. More recently, it has been established that natural bacterial assemblages in coastal waters and sediment can rapidly metabolize these organic nitrogen sources and even incorporate their carbon and nitrogen into bacterial biomass. Here, we report on the capacity of natural microbial assemblages in three coastal North Carolina (United States) estuaries to metabolize energetics and phenanthrene (PHE), a proxy for terrestrial aromatic compounds. Microbial assemblages generally had the highest ecosystem capacity (mass of the compound mineralized per average estuarine residence time) for HMX (21–5463 kg) > RDX (1.4–5821 kg) ≫ PHE (0.29–660 kg) > TNT (0.25–451 kg). Increasing antecedent precipitation tended to decrease the ecosystem capacity to mineralize TNT in the Newport River Estuary, and PHE and TNT mineralization were often highest with increasing salinity. There was some evidence from the New River Estuary that increased N-demand (due to a phytoplankton bloom) is associated with increased energetic mineralization rates. Using this type of analysis to determine the ecosystem capacity to metabolize energetics can explain why these compounds are rarely detected in seawater and marine sediment, despite the known presence of unexploded ordnance or recent use in military training exercises. Overall, measuring the ecosystem capacity may help predict the effects of climate change (warming and altered precipitation patterns) and other perturbations on exotic compound fate and transport within ecosystems and provide critical information for managers and decision-makers to develop management strategies based on these changes.

Examining coastal dynamics and recreational water quality by quantifying multiple sewage specific markers in a North Carolina estuary

Examining coastal dynamics and recreational water quality by quantifying multiple sewage specific markers in a North Carolina estuary

Antecedent precipitation influences the bacterial processing of terrestrial dissolved organic matter in a North Carolina estuary

Estuaries and coastal waters ultimately receive the terrestrial dissolved organic matter (DOM) exported from coastal watersheds, more directly during extreme precipitation events. Recent work suggests DOM's degradation in coastal waters varies with its quality, which also might vary as a function of precipitation, activating contributions from different sources within a watershed. The aim of this study was to determine the extent to which microbial degradation of terrestrial DOM in the Newport River Estuary, eastern North Carolina, was influenced by precipitation events occurring within the preceding seven days from sampling. We hypothesized that DOM stored in forested wetlands (e.g., pocosins and Cypress swamps) that become connected to the main channel of the Newport River during high precipitation events was more labile than DOM flowing into the estuary under low precipitation events. DOM quality was assessed with optical and stable C isotope (δ13C) measurements, while DOM lability was assessed by measurements of bacterial production (BP) and mineralization of 14C-labeled phenanthrene (Pmin), a polyaromatic tracer compound. Aromatic content of DOM, assessed by specific ultraviolet absorbance at 254 nm (SUVA254) was highest in the river with values well over 5.0 L mg C−1 m−1, and decreased with salinity. Antecedent precipitation (AP) of at least 100 mm in the seven days prior to sampling resulted in dissolved organic carbon (DOC) concentrations >20 mg L−1, at salinities <10. Similarly, fluorescence humification index (HIX) values were highest in the estuary after the highest AP. Generally depleted δ13C-DOC values (−26 to −28‰) in the estuary up to a salinity of 30 indicated a substantial source of DOM likely originating from the forested swamps and tidal wetlands fringing the estuary. BP exhibited wide variability yet declined with salinity, while median values after higher AP (40 μg C L−1 d−1) were double that under lower AP. By contrast, aromatic mineralization (Pmin) rates increased as both DOC and CDOM concentrations, and SUVA254 and HIX values, declined with salinity. However, Pmin rates were highest after the highest AP for the three events sampled. Results indicate that flooding of coastal wetlands mobilizes a large pool of labile DOM which have a large impact on the carbon cycle in estuaries. By altering the quality, as well as quantity of terrestrial organic matter inputs to estuarine systems, extreme events may also affect utilization of aromatic organics by estuarine microbial assemblages, an intriguing research question worthy of further study.

Decadal-Scale Acidification Trends in Adjacent North Carolina Estuaries: Competing Role of Anthropogenic CO2 and Riverine Alkalinity Loads

Decadal-scale pH trends for the open ocean are largely monotonic and controlled by anthropogenic CO2 invasion. In estuaries, though, such long-term pH trends are often obscured by a variety of other factors, including changes in net metabolism, temperature, estuarine mixing, and riverine hydrogeochemistry. In this study, we mine an extensive biogeochemical database in two North Carolina estuaries, the Neuse River estuary (NeuseRE) and New River estuary (NewRE), in an effort to deconvolute decadal-scale trends in pH and associated processes. By applying a Generalized Additive Mixed Model (GAMM), we show that temporal changes in NewRE pH were insignificant, while pH decreased significantly throughout much of the NeuseRE. In both estuaries, variations in pH were accompanied by increasing river discharge, and were independent of rising temperature. Decreases in bottom-water pH in the NeuseRE coincided with elevated primary production in surface waters, highlighting the importance of eutrophication on long-term acidification trends. Next, we used a simple mixing model to illustrate the impact of changing river discharge on estuarine carbonate chemistry. We found that increased riverine alkalinity loads to the NewRE likely buffered the impact of CO2-intrusion-induced acidification. In the NeuseRE, however, elevated dissolved inorganic carbon loads further decreased the buffering capacity, exacerbating the effects of CO2-intrusion-driven acidification. Taken together, the findings of this study show that future trajectories in estuarine pH will be shaped by complex interactions among global-scale changes in climate, regional-scale changes in precipitation patterns, and local-scale changes in estuarine biogeochemistry.

Flood-driven CO2 emissions from adjacent North Carolina estuaries during Hurricane Joaquin (2015)

Extreme climatic events like floods and hurricanes have the potential to significantly alter coastal carbon cycling. However, due to the challenges associated with sampling these events, they can be difficult to incorporate into regional and global carbon budgets. To address this data gap, we bracket a major flooding event associated with the passing of Hurricane Joaquin (October 2015) with direct and high-resolution pCO2 measurements in the Neuse (NeuseRE) and New River Estuary (NewRE), North Carolina. Enhanced river discharge quickly flushed the relatively small NewRE, causing residence time to fall from 90 to 9 days, while the larger NeuseRE responded relatively slowly to flooding. This period of rapid flushing coincided with a significant increase in CO2 fluxes. The effect of cooler flood-waters, which reduce pCO2, was counteracted by allochthonous DIC inputs, which drove large increases in pCO2 relative to dissolved O2. The spatial distribution of carbonate buffering differed between estuaries, enhancing CO2 fluxes in the NewRE (178 mmol C m−2 d−1), while partially limiting air-water exchange in the NeuseRE (62 mmol C m−2 d−1). While windy storms may drive larger CO2 fluxes from estuaries, we show that flooding events can also contribute significantly to annual carbon budgets. CO2 emissions during this ~14-day flood period accounted for 31% (NeuseRE) to 44% (NewRE) of the total annual CO2 flux. Our findings show that sufficient spatial and temporal coverage during storms is necessary for estuarine CO2 fluxes to be reliably assessed over annual or longer time scales.

Distribution and population structure in the naked goby Gobiosoma bosc (Perciformes: Gobiidae) along a salinity gradient in two western Atlantic estuaries.

Many species of fish produce larvae that undergo a prolonged dispersal phase. However, evidence from a number of recent studies on demersal fishes suggests that the dispersal of propagules may not be strongly correlated with gene flow. Instead, other factors like larval behavior and the availability of preferred settlement habitat may be more important to maintaining population structure. We used an ecologically important benthic fish species, Gobiosoma bosc (naked goby), to investigate local and regional scale population structure and gene flow along a salinity gradient (∼3 ppt to ∼18 ppt) in two North Carolina estuaries. G. bosc is an abundant and geographically widespread species that requires complex but patchy microhabitat (e.g. oyster reefs, rubble, woody debris) for reproduction and refuge. We sequenced 155 fish from 10 sites, using a common barcoding gene (COI). We also included recent sequence data from GenBank to determine how North Carolina populations fit into the larger biogeographic understanding of this species. In North Carolina, we found a significant amount of gene flow within and between estuaries. Our analysis also showed high predicted genetic diversity based upon a large number of rare haplotypes found within many of our sampled populations. Moreover, we detected a number of new haplotypes in North Carolina that had not yet been observed in prior work. Sampling along a salinity gradient did not reveal any significant positive or negative correlations between salinity and genetic diversity, nor the proportion of singleton haplotypes, with the exception of a positive correlation between salinity standard deviation and genetic diversity. We also found evidence that an introduced European population of naked gobies may have originated from an Atlantic source population. Altogether, this system offers a compelling way to evaluate whether factors other than dispersal per se mediate recruitment in an estuarine-dependent species of fish with a larval dispersal phase. It also demonstrates the importance of exploring both smaller and larger scale population structure in marine organisms to better understand local and regional patterns of population connectivity and gene flow.

Watershed-Scale Drivers of Air-Water CO2 Exchanges in Two Lagoonal North Carolina (USA) Estuaries

Watershed-Scale Drivers of Air-Water CO2 Exchanges in Two Lagoonal North Carolina (USA) Estuaries

Watershed‐Scale Drivers of Air‐Water CO2 Exchanges in Two Lagoonal North Carolina (USA) Estuaries

AbstractRiverine loading of nutrients and organic matter act in concert to modulate CO2 fluxes in estuaries, yet quantitative relationships between these factors remain poorly defined. This study explored watershed‐scale mechanisms responsible for the relatively low CO2 fluxes observed in two microtidal, lagoonal estuaries. Air‐water CO2 fluxes were quantified with 74 high‐resolution spatial surveys in the neighboring New River Estuary (NewRE) and Neuse River Estuary (NeuseRE), North Carolina, which experience a common climatology but differ in marine versus riverine influence. Annually, both estuaries were relatively small sources of CO2 to the atmosphere, 12.5 and 16.3 mmol C m−2 d−1 in the NeuseRE and NewRE, respectively. Large‐scale pCO2 variations were driven by changes in freshwater age, which modulates nutrient and organic carbon supply and phytoplankton flushing. Greatest pCO2 undersaturation was observed at intermediate freshwater ages, between 2 and 3 weeks. Biological controls on CO2 fluxes were obscured by variable inputs of river‐borne CO2, which drove CO2 degassing in the river‐dominated NeuseRE. Internally produced CO2 exceeded river‐borne CO2 in the marine‐dominated NewRE, suggesting that net ecosystem heterotrophy, rather than riverine inputs, drove CO2 fluxes in this system. Variations in riverine alkalinity and inorganic carbon loading caused zones of minimum buffering capacity to occur at different locations in each estuary, enhancing the sensitivity of estuarine inorganic C chemistry to acidification. Although annual CO2 fluxes were similar between systems, watershed‐specific hydrologic factors led to disparate controls on internal carbonate chemistry, which can influence ecosystem biogeochemical cycling, trophic state, and response to future perturbations.

Flood-driven CO2 emissions from adjacent North Carolina estuaries during Hurricane Joaquin (2015)

Flood-driven CO2 emissions from adjacent North Carolina estuaries during Hurricane Joaquin (2015)

Habitat partitioning and diurnal-nocturnal transition in the elasmobranch community of a North Carolina estuary

In marine communities, resource partitioning can be as important as abiotic environmental preferences in determining habitat use patterns. Elasmobranchs are generally assumed to be crepuscular or nocturnal, but diel temporal habitat partitioning is poorly studied in this group. We attempted to identify habitat preferences and find evidence of resource partitioning among the elasmobranch community in Back and Core Sounds, North Carolina, using a multi-gear, fishery-independent survey with a temporal focus on the diurnal-nocturnal transition. Gillnet, longline, drumline, and rod-and-reel sampling captured a total of 160 elasmobranchs, representing 12 species within the estuary, and differences between the seven most abundant species were assessed in terms of temporal, environmental, and spatial habitat factors. The elasmobranch community was broadly divided into cool and warm temperature assemblages. Most species showed evidence of generalist habitat preferences, but spatial overlap between species was generally low. Blacknose sharks [Carcharhinus acronotus (Poey,1860)] appeared to be nocturnal, and aggregations of smooth dogfish [Mustelus canis (Mitchill,1815)] and spiny dogfish (Squalus acanthias Linnaeus, 1758) were found during mid-afternoon hours. Blacknose sharks and blacktip sharks [ Carcharhinus limbatus (Muller and Henle,1839)] showed evidence of spatial resource partitioning based on distance from the nearest inlet. Temperature appears to be a strong influence on the presence of elasmobranch species within Back and Core Sounds, but behavioral interspecific avoidance may be a greater influence on fine-scale habitat use by elasmobranchs in this estuarine system.

Impact of hypoxia on gene expression patterns by the human pathogen, Vibrio vulnificus, and bacterial community composition in a North Carolina estuary.

Estuarine environments are continuously being shaped by both natural and anthropogenic sources which directly/indirectly influence the organisms that inhabit these important niches on both individual and community levels. Human infections caused by pathogenic Vibrio species are continuing to rise, and factors associated with global climate change have been suggested to be impacting their abundance and geographical range. Along with temperature, hypoxia has also increased dramatically in the last 40 years, which has led to persistent dead zones worldwide in areas where these infections are increasing. Thus, utilizing membrane diffusion chambers, we investigated the impact of in situ hypoxia on the gene expression of one such bacterium, Vibrio vulnificus, which is an inhabitant of these vulnerable areas worldwide. By coupling these data with multiple abiotic factors, we were able to demonstrate that genes involved in numerous functions, including those involved in virulence, environmental persistence, and stressosome production, were negatively correlated with dissolved oxygen. Furthermore, comparing 16S ribosomal RNA, we found similar overall community compositions during both hypoxia and normoxia. However, unweighted beta diversity analyses revealed that although certain classes of bacteria dominate in both low‐ and high‐oxygen environments, there is the potential for quantitative shifts in lower abundant species, which may be important for effective risk assessment in areas that are becoming increasingly more hypoxic. This study emphasizes the importance of investigating hypoxia as a trigger for gene expression changes by marine Vibrio species and highlights the need for more in depth community analyses during estuarine hypoxia.

Can bycatch in a flatfish gillnet fishery be reduced with rectangular mesh?

Gillnets fished in North Carolina, USA, estuaries have high rates of bycatch relative to the target catch of southern flounder, Paralichthys lethostigma Jordan & Gilbert. This study tested whether rectangular-mesh gillnets would maintain catch rates of southern flounder and reduce fish bycatch relative to conventional diamond-mesh gillnets in two North Carolina estuaries. In the Neuse River estuary, catch rates of legal southern flounder were not different between the two mesh shapes, but the bycatch of red drum, Sciaenops ocellatus (Linnaeus) and other fish species was reduced with rectangular-mesh net. In the Newport River estuary, southern flounder and red drum catches were reduced in rectangular-mesh net, but the decrease was greater for red drum. Catches of sublegal southern flounder were reduced in the rectangular-mesh net in both estuaries. Reduced catch rates of sublegal southern flounder and bycatch species suggest rectangular mesh may help manage stocks of estuarine fish species in areas where gillnets are used to target flatfishes.

Estuarine Residency and Migration of Southern Flounder Inferred from Conventional Tag Returns at Multiple Spatial Scales

AbstractAn improved understanding of the spatial structure and movements of harvested populations can promote more efficient management of marine resources. Conventional tagging is a valuable approach to study the movements of marine fishes due to its relatively low expense and the typically broad spatial extent over which movements can be characterized. We present the findings of multiple tag return studies initiated in the estuaries of North Carolina during the past two decades to better understand habitat residency and migration patterns of Southern Flounder Paralichthys lethostigma, an economically important marine flatfish in the southeastern USA. Tag return data indicated large‐scale (&gt;50 km) movements of relatively large fish in the fall, which were presumably associated with offshore winter spawning migrations. Nearly all Southern Flounder that demonstrated large‐scale movement were recovered to the south of the system in which they were tagged, suggesting that the spawning activity of fish using North Carolina estuaries may be concentrated mostly off the southeastern U.S. continental shelf. Tag returns from within multiple estuarine systems during the spring and summer were in close proximity to release sites (typically &lt; 1 km), suggesting limited movement during estuarine residency. Recaptures in the spring of fish tagged the previous summer or fall were also in close proximity to release sites, in some cases within the same estuarine creek, indicating limited movement of fish overwintering in the estuary as well. Our findings reveal saltatory movement dynamics of Southern Flounder characterized by limited movement during estuarine residency and large‐scale movements in the fall associated with spawning migrations. Our synthesis of several tag return studies across multiple spatial scales should contribute to a better alignment of Southern Flounder management with their spatial dynamics.Received April 13, 2015; accepted July 20, 2015

Observations on spiny dogfish ( Squalus acanthias) captured in late spring in a North Carolina estuary.

Five spiny dogfish were captured in early-mid May during gillnet and longline sampling targeting juvenile coastal sharks in inshore North Carolina waters. Dogfish captures were made within Back Sound and Core Sound, North Carolina. All dogfish were females measuring 849-905 mm total length, well over the size at 50% maturity. Dogfish were caught at stations 1.8-2.7 m in depth, with temperatures 22.9-24.2 °C, 32.8-33.4 ppt salinity, and 6.9-8.0 mg/L dissolved oxygen. These observations are among the latest in the spring for spiny dogfish in the southeastern U.S. and occurred at higher temperatures than previously recorded for this species. It is unclear whether late-occurring spiny dogfish in this area represent a cryptic late-migrating or resident segment of the Northwest Atlantic population.

Observations on spiny dogfish ( Squalus acanthias) captured in late spring in a North Carolina estuary

Five spiny dogfish were captured in early-mid May during gillnet and longline sampling targeting juvenile coastal sharks in inshore North Carolina waters. Dogfish captures were made within Back Sound and Core Sound, North Carolina. All dogfish were females measuring 849-905 mm total length, well over the size at 50% maturity. Dogfish were caught at stations 1.8-2.7 m in depth, with temperatures 22.9-24.2 °C, 32.8-33.4 ppt salinity, and 6.9-8.0 mg/L dissolved oxygen. These observations are among the latest in the spring for spiny dogfish in the southeastern U.S. and occurred at higher temperatures than previously recorded for this species. It is unclear whether late-occurring spiny dogfish in this area represent a cryptic late-migrating or resident segment of the Northwest Atlantic population.

Observations on spiny dogfish (Squalus acanthias) captured in late spring in a North Carolina estuary

Five spiny dogfish were captured in early-mid May during gillnet and longline sampling targeting juvenile coastal sharks in inshore North Carolina waters. Dogfish captures were made within Back Sound and Core Sound, North Carolina. All dogfish were females over the size at maturity, and were caught at stations 1.77-2.74 m in depth, with temperatures 22.9-24.2 °C, 32.8-33.4 ppt salinity, and 6.9-8.0 mg/L dissolved oxygen. Stations where dogfish were captured were approximately 6.5-15.7 km from the nearest inlet and 43.4-247.1 m from the nearest seagrass bed. These observations are among the latest in the spring for spiny dogfish in the southeastern U.S. and occurred at higher temperatures than previously recorded for this species. It is unclear whether late-occurring spiny dogfish in this area represent a cryptic late-migrating or resident segment of the Northwest Atlantic population.

Comparisons of statistical models to predict fecal indicator bacteria concentrations enumerated by qPCR- and culture-based methods

Recently, the United States Environmental Protection Agency (USEPA) revised their recreational water quality criteria, in which adjustments were made by approving enterococci (ENT) quantitative PCR (qPCR) as an alternative, rapid method and advocating the use of predictive models for water quality management. The implementation of qPCR-based methods and prediction models are meant to decrease the time between sample collection and public advisories and notifications. To date, few studies have compared qPCR-based models to culture-based prediction models and none of these studies have been conducted in coastal estuarine systems. In this study, we created prediction models using qPCR-based fecal indicator bacteria (FIB) data in dual-use recreational and shellfish harvesting waters and compared them to published ENT and Escherichia coli (EC) culture-based prediction models in eastern North Carolina estuaries. Furthermore, an empirical statistical model was created to predict qPCR inhibition levels so that proper remediation techniques can be applied when it is a problem. Predictor variable selection in both qPCR- and culture-based ENT models was very similar; both models included 14-day rain total, dissolved oxygen, and salinity/conductivity, with 89 and 90% of qPCR and culture data described, respectively. Using ENT management action thresholds, qPCR- and culture-based models showed high accuracy in management decisions. The qPCR model had 92 and 96% accuracy using the 110 and 1000 cell equivalents (CE)/100 ml thresholds, respectively, and the culture model had 90% accuracy in management decisions with the 110 MPN/100 ml threshold. EC models for qPCR- and culture-based concentrations used similar independent variables (14-day humidity, salinity/conductivity, a rain/storm variable, and a measure of air temperature), with each model explaining 26 and 55% of the data variation, respectively. When using different thresholds that were logs apart for management decisions, the two EC models accurately predicted management decisions; qPCR models correctly predicted management decisions 96 and 77% of the time (using 31 and 320 CE/100 ml, respectively) while culture models correctly predicted management decisions 96 and 88% percent of the time (with 31 and 320 MPN/100 ml, respectively). Equivalency between models was shown in our non-point source impacted estuaries, with ENT models performing slightly better than EC models. In addition, inhibition of the qPCR was a major issue that had to be addressed. An inhibition model was created with easily obtained meteorological data and accounted for a high level of data variability (adjusted R2 = 0.82).