Housatonic River Research Articles

Exploring landscape and geologic controls on spatial patterning of streambank groundwater discharge in a mixed land use watershed

AbstractPreferential groundwater discharge features along stream corridors are ecologically important at local and stream network scales, yet we lack quantification of the multiscale controls on the spatial patterning of groundwater discharge. Here we identify physical attributes that best explain variation in the presence and lateral extent of preferential groundwater discharges along two 5th order streams, the Housatonic and Farmington Rivers, and 32 1st to 4th order reaches across the Farmington River network. We mapped locations of preferential groundwater discharge exposed along streambanks using handheld thermal infrared cameras paired with high‐resolution topographic and land use land cover datasets, surficial soil characteristic maps, and depth‐to‐bedrock geophysical measurements. The unconfined Housatonic River, MA, USA (12 km) had fewer discharge locations and less lateral extent (41 discharge locations with 38 m of active discharge/km of river) compared to the partially confined Farmington River, CT, USA (26 km; 169 discharge locations with 129 m of active discharge/km of river). Using a moving window analysis, we found along both rivers that discharge was more likely to occur where bank slopes were steeper, floodplain extent was narrower, and degree of confinement was higher. Along the Farmington River, groundwater discharge was more likely to occur where saturated hydraulic conductivity was higher and depth‐to‐bedrock was shallower. Among the 32 stream reaches surveyed (33.2 km of total stream length) within the Farmington River watershed, preferential discharge was observed in all but two stream reaches, varied from 0 to 25% of lateral extent along stream banks (mean = 6%), and was more likely to occur where stream reach slopes were steep, saturated hydraulic conductivity was high, and watershed urbanization was low. Our results show that, though both surface (e.g., topographic, land use land cover) and subsurface (e.g., soil characteristics, bedrock depth) factors control the prevalence of streambank preferential groundwater discharge, the dominant controls vary across valley settings and stream sizes.

Disentangling effects of habitat on salmonid abundance in thermal refuges while accounting for imperfect detection

AbstractThermal refuges provide critical habitat for cold‐water‐dependent salmonids in marginal riverscapes during extreme heat events globally. Studies of thermal refuge use by salmonids are complicated by short‐term changes in weather conditions during heat waves, intermittent fish use, and the use of different analytical endpoints. We passively surveyed cold‐water‐dependent brown, rainbow, and brook trout (hereafter “trout”) thermoregulating in several thermal refuges along the Housatonic River, Connecticut, USA, during a two‐week heatwave using underwater action cameras (UACs). Using these data, we assessed the influence of various short‐term riverscape conditions on the abundance of trout within thermal refuges using a zero‐inflated Poisson, time‐stratified N‐mixture model in a Bayesian framework that accounts for imperfect detection. We detected at least one trout per sampling occasion, and estimated abundances summed across all thermal refuges ranged from 63.99 (95% credible interval [CRI] = 55.0–79.0) to 182.04 (167.0–199.0). We estimated higher trout abundances in larger thermal refuges located in low‐gradient river sections, and refuges that were deeper and cooler than the Housatonic River during the sampling occasion (all β estimates >0.0 and did not overlap zero). We also found evidence that less variable and cooler temperature regimes in the nearby Housatonic River led to higher estimated trout abundances within thermal refuges (all β estimates <0.0 and did not overlap zero). Last, we found that trout detection probabilities within thermal refuges were moderate (range = 0.521–0.634) when using UAC surveys and that the video image brightness negatively influenced detection (αbright = −0.193, 95% CRI = −0.330 to −0.058). To aid in trout population persistence in dynamic, marginal riverscapes as the climate changes, focusing on modifiable refuge attributes (e.g., depth, cold‐water plume area), and strategically targeting refuges in riverscape segments beneficial to trout may be tactics that could enhance conservation strategies globally.

Camera traps reveal that terrestrial predators are pervasive at riverscape cold-water thermal refuges.

Perceived predation risks by terrestrial predators are major ecological forces in aquatic systems, particularly for aggregating fish. Riverscape thermal refuges are discrete, localized cold-water patches where fish temporarily aggregate to buffer against heat events. Predation pressures by terrestrial predators at thermal refuges may decrease the thermoregulatory benefits of refuge use, but quantifying such effects can be challenging and controversial when sampling can impose additional stress on fish. We passively monitored terrestrial predator visitation patterns and predation at four thermal refuges in the Housatonic River, Connecticut, USA, between May 18th and September 29th, 2022, with camera traps, a common wildlife monitoring method. Specifically, we (1) assessed diel visitation patterns by different categories of terrestrial predators at thermal refuges and determined if patterns varied among predator categories or with prevailing environmental conditions, and (2) estimated the probability of predation by hour of the day combined across all predator categories, quantifying general predation pressures at refuges. We detected at least one terrestrial predator at a thermal refuge each day, and mean hourly visitation rates (count/h) were highly variable across predator categories and sampling dates. The most supported generalized additive mixed model indicated that terrestrial predator visitation rates (count/h/day) varied with mean daily river discharge and water temperature differential, and relationships differed across categories of terrestrial predators. We observed 22 separate predation attempts on thermoregulating salmonids and predicted that the probability of predation by any terrestrial predator increased from 0.002 to 0.017 throughout a 24 h day (p = .004). Camera traps provided novel evidence that terrestrial predators are pervasive at riverine thermal refuges, which is relevant for refuge conservation and management globally. We recommend the implementation of a coordinated monitoring network across riverine thermal refuges using camera traps, further enriching our ecological understanding of cumulative predator effects in refuges across complex riverscapes.

Major River Floodplain Forest Restoration: A Case Study in Western Massachusetts

Although efforts to restore floodplain forests are becoming more popular in the northeastern United States, best management practices are not well defined. In this study, we demonstrate the success of a planting effort in western Massachusetts to increase the extent of a floodplain forest along the Housatonic River. Over 1700 floodplain-adapted tree saplings were planted in an old field and in two hayfields at Bartholomew's Cobble, a property located in Sheffield, Massachusetts, and individually tagged to follow their growth and survival. Planted trees had relatively high rates of survival over a 6 y period, especially the two most commonly planted tree species: silver maple (Acer saccharinum, 42.5% survival) and boxelder (Acer negundo, 71.7%), although plantings were more successful in the old field compared to the two hayfields. Tree dbh after 6 y differed across fields for silver maples and boxelders with those planted within the old meadow significantly larger than those planted into hayfields (silver maple dbh 9.8 cm old field vs. 6.5–6.6 cm hayfields; boxelder dbh 10.4 cm old field vs. 4.4–6.6 cm hayfields). By documenting which floodplain-adapted tree species were successful in establishing under which conditions, our observational study provides valuable insights for future restoration efforts.

Exploring Local Riverbank Sediment Controls on the Occurrence of Preferential Groundwater Discharge Points

Groundwater discharge to rivers takes many forms, including preferential groundwater discharge points (PDPs) along riverbanks that are exposed at low flows, with multi-scale impacts on aquatic habitat and water quality. The physical controls on the spatial distribution of PDPs along riverbanks are not well-defined, rendering their prediction and representation in models challenging. To investigate the local riverbank sediment controls on PDP occurrence, we tested drone-based and handheld thermal infrared to efficiently map PDP locations along two mainstem rivers. Early in the study, we found drone imaging was better suited to locating tributary and stormwater inflows, which created relatively large water surface thermal anomalies in winter, compared to PDPs that often occurred at the sub-meter scale and beneath riparian tree canopy. Therefore, we primarily used handheld thermal infrared imaging from watercraft to map PDPs and larger seepage faces along 12-km of the fifth-order Housatonic River in Massachusetts, USA and 26-km of the Farmington River in Connecticut, USA. Overall, we mapped 31 riverbank PDPs along the Housatonic reach that meanders through lower permeability soils, and 104 PDPs along the Farmington reach that cuts through sandier sediments. Riverbank soil parameters extracted at PDP locations from the Soil Survey Geographic (SSURGO) database did not differ substantially from average bank soils along either reach, although the Farmington riverbank soils were on average 5× more permeable than Housatonic riverbank soils, likely contributing to the higher observed prevalence of PDPs. Dissolved oxygen measured in discharge water at these same PDPs varied widely, but showed no relation to measured sand, clay, or organic matter content in surficial soils indicating a lack of substantial near-surface aerobic reaction. The PDP locations were investigated for the presence of secondary bank structures, and commonly co-occurred with riparian tree root masses indicating the importance of localized physical controls on the spatial distribution of riverbank PDPs.

The importance of oxbow lakes in the floodplain storage of pollutants

Abstract Oxbow lakes are important stores for fine-grained sediment, which potentially makes them critical sinks for sediment-associated pollutants. We leverage an exhaustive public archive of coring data, supplemented by our data collection, to provide a quantitative assessment of the role of oxbows as off-channel sinks. We investigated loading trends of sediment-sorbed polychlorinated biphenyls (PCBs) within oxbows of the Housatonic River, an actively meandering river in western Massachusetts, USA. Our results reveal the efficiency of oxbows as sinks, with average PCB concentrations (14.8 ppm) that are nearly twice that of the surrounding floodplain (7.56 ppm). Even though the 5.83 km2 floodplain is the largest sink of PCB-laden material, storing as much as 14.1 t of PCBs or 2.42 g m−2, oxbows store more than 20% of all PCBs (3.63 t of PCBs or 11.2 g m−2) while making up just over 5% of the floodplain surface area. Nearly 85% of the oxbow storage of PCBs occurs within the first 50 m of floodplain, making clear the significance of regular oxbow production to the off-channel storage of sediment-associated pollutants.

EEMD- and VMD-based hybrid GPR models for river streamflow point and interval predictions

Abstract Reliable river streamflow (RSF) forecasting is an important issue due to its impact on planning and operation of the water resources system. In this study, based on Lower Upper Bound Estimation (LUBE), hybrid artificial intelligence methods were used for point and interval prediction of monthly RSF. Two states based on stations' own data and upstream stations' data were considered for RSF modeling of the Housatonic River during the period of 1941–2018. Ensemble Empirical Mode Decomposition (EEMD) and Variational Mode Decomposition (VMD) methods were used for enhancing the streamflow point forecasting accuracy. Interval Prediction (PI) was applied for tolerating increased uncertainty. Results showed that in state 1, the error criterion value for the superior model decreased from 0.155 to 0.082 and 0.09 for the EEMD- and VMD-based models, respectively. Generally, hybrid models increased the modeling accuracy between 20% and 40%. Via the integrated approaches, the upstream stations' data was successfully used for streamflow prediction of stations without data. In this state, the PI coverage probability values for the VMD-based model were approximately 12% higher than the single model. Generally, the VMD-based model led to more desirable results due to having higher PI coverage probability and lower mean PI width values.

A comparative study of wavelet and empirical mode decomposition-based GPR models for river discharge relationship modeling at consecutive hydrometric stations

Abstract The river stage–discharge relationship has an important impact on modeling, planning, and management of river basins and water resources. In this study, the capability of the Gaussian Process Regressions (GPR) kernel-based approach was assessed in predicting the daily river stage–discharge (RSD) relationship. Three successive hydrometric stations of the Housatonic River were considered, and based on the flow characteristics during the period of 2002–2006 several models were developed and tested via GPR. To enhance the applied model efficiency, two pre-processing techniques, namely Wavelet Transform (WT) and Ensemble Empirical Mode Decomposition (EEMD), were used. Also, two states of the RSD modeling were investigated. In state 1, each station's own data was used and in state 2, the upstream stations’ datasets were used as input to model the RSD downstream of the river. The single and integrated model results showed that the integrated WT- and EEMD-GPR models resulted in more accurate outcomes. Data processing enhanced the models' capability between 25% and 40%. The results showed that the RSD modeling in state 1 led to better results; however, when the station's own data were not available the integrated methods could be applied successfully for the RSD modeling using the previous stations’ data.

Indigenous People and the New England Town Meeting: Stockbridge, Massachusetts, 1730-1775

In the 1730s, Mahicans along the Housatonic River settled the mission town of Stockbridge, Massachusetts. They participated in town meetings and elected “traditional” leaders to typical New England offices. Even after a growing population of English settlers began dominating town offices, the Indians remained a strong presence in meetings, which was conducted in the Mahican as well as English language, and all voting done viva voce. In 1763, a major battle when an English faction tried to take control by introducing secret balloting; the Indians complained and mostly won their case. Stockbridge thus provides a case study comparing Indian and colonial New England decision-making, and highlighting the evolution of the town meeting during the 18th century.

Dark False Mussel,Mytilopsis leucophaeata(Bivalvia: Dreissenidae), in the Lower West River, New Haven, New Haven County, Connecticut

In October 2015, the dark false mussel, Mytilopsis leucophaeata, was encountered in the Duck Pond of the West River at Edgewood Park in New Haven, New Haven County, Connecticut, USA. The natural endemic range of Mytilopsis leucophaeata is the Gulf of Mexico and the temperate Atlantic coast of North America from Tampico, Mexico, northward to the Chesapeake Bay. In the late 1930s, Mytilopsis leucophaeata became established in the Hudson River basin in New York. The only previous reports of Mytilopsis leucophaeata from New England are from the Charles River near Boston, Massachusetts, in 1981 and from the Housatonic River in Fairfield County, Connecticut, in the 1990s. Mytilopsis leucophaeata has been characterized as the brackish-water equivalent to the zebra mussel, Dreissena polymorpha, and has been associated with severe fouling problems of water-cooling systems in Europe where it has been introduced. It is hypothesized that Mytilopsis leucophaeata was introduced by ballast water of ships from New Haven Harbor and established in the lower West River subsequent to the installation of two-way tidal gates in the course of a tidal marsh and channel restoration project completed in 2012. Other invertebrates collected were the hydrozoan Cordylophora caspia; the polychaetes Hobsonia florida and Polydora cf. ciliata; the amphipods Gammarus fasciatus and Apocorophium simile; the ivory barnacle, Amphibalanus eburneus; and Say's mud crab, Dyspanopeus sayi. The blue crab, Callinectes sapidus, was commonly observed. The freshwater leech, Helobdella modesta, which was once abundant in the Duck Pond, was not collected. Given the invasive potential of Mytilopsis leucophaeata, in conjunction with the paucity of knowledge of many aspects of its natural history, especially in introduced settings, it is important to monitor this population.

Local vs. cross station simulation of suspended sediment load in successive hydrometric stations: heuristic modeling approach

The present paper aims at modeling suspended sediment load (SSL) using heuristic data driven methodologies, e.g. Gene Expression Programming (GEP) and Support Vector Machine (SVM) in three successive hydrometric stations of Housatonic River in U.S. The simulations were carried out through local and cross-station data management scenarios to investigate the interrelations between the SSL values of upstream/downstream stations. The available scenarios were applied to predict SSL values using GEP to obtain the best models. Then, the best models were predicted by SVM approach and the obtained results were compared with those of GEP. The comparison of the results revealed that the SVM technique is more capable than the GEP for modeling the SSL through the both local and cross-station data management strategies. Besides, local application seems to be better than cross-station application for modeling SSL. Nevertheless, the cross-station application demonstrated to be a valid methodology for simulating SSL, which would be of interest for the stations with lack of observational data. Also, the prediction capability of conventional Sediment Rating Curve (SRC) method was compared with those of GEP and SVM techniques. The obtained results revealed the superiority of GEP and SVM-based models over the traditional SRC technique in the studied stations.

Ecological risk assessment for mink and short-tailed shrew exposed to PCBs, dioxins, and furans in the Housatonic River area.

A probabilistic risk assessment was conducted to characterize risks to a representative piscivorous mammal (mink, Mustela vison) and a representative carnivorous mammal (short-tailed shrew, Blarina brevicauda) exposed to PCBs, dioxins, and furans in the Housatonic River area downstream of the General Electric (GE) facility in Pittsfield, Massachusetts. Contaminant exposure was estimated using a probabilistic total daily intake model and parameterized using life history information of each species and concentrations of PCBs, dioxins, and furans in prey collected in the Housatonic River study area. The effects assessment preferentially relied on dose-response curves but defaulted to benchmarks or other estimates of effect when there were insufficient toxicity data. The risk characterization used a weight of evidence approach. Up to 3 lines of evidence were used to estimate risks to the selected mammal species: 1) probabilistic exposure and effects modeling, 2) field surveys, and 3) species-specific feeding or field studies. The weight of evidence assessment indicated a high risk for mink and an intermediate risk for short-tailed shrew.

Comparison of marine sampling methods for organic contaminants: Passive samplers, water extractions, and live oyster deployment

Laboratory and field trials evaluated the efficacy of three methods of detecting aquatic pesticide concentrations. Currently used pesticides: atrazine, metolachlor, and diazinon and legacy pesticide dieldrin were targeted. Pesticides were extracted using solid-phase extraction (SPE) of water samples, titanium plate passive samplers coated in ethylene vinyl acetate (EVA) and eastern oysters (Crassostrea viginica) as biosamplers. A laboratory study assessed the extraction efficiencies and precision of each method. Passive samplers yielded the highest precision of the three methods (RSD: 3–14% EVA plates; 19–60% oysters; and 25–56% water samples). Equilibrium partition coefficients were derived. A significant relationship was found between the concentration in oyster tissue and the ambient aquatic concentration. In the field (Housatonic River, CT (U.S.)) water sampling (n = 5) detected atrazine at 1.61–7.31 μg L−1, oyster sampling (n = 2×15) detected dieldrin at n.d.–0.096 μg L−1 SW and the passive samplers (n = 5×3) detected atrazine at 0.97–3.78 μg L−1 SW and dieldrin at n.d.–0.68 μg L−1 SW.

Long-Term Trends in Water Quality in a New England Hydroelectric Impoundment

Lake Lillinonah, a hydroelectric impoundment on the Housatonic River, CT, is characterized by frequent and extensive algal blooms during the summer months, and historical accounts from the lake's early years document the fact that algal blooms (dominated by cyanobacteria) have been a concern since the lake's creation in 1955. Algal blooms create lethal oxygen conditions for aquatic organisms, impair recreation, and produce toxins that are harmful to people, pets, and wildlife. To help understand current and future trends in water quality, we reconstructed the historical water quality of Lake Lillinonah from 1974 to 2009. Our results suggest that water temperature, phosphorus concentration, and nitrogen concentration all play a role in determining summer water clarity. Additionally, although total phosphorus concentration has decreased since the early 1970s, total nitrogen concentration has remained constant likely due to differences in watershed nutrient-management strategies, and water clarity in the lake remains poor. We suggest that a continued effort to reduce both nitrogen- and phosphorus-loading is necessary in order to improve water clarity, particularly considering the observed increase in storm-loading events and warmer temperatures predicted as the climate warms.

Persistence in Massachusetts of the veined white butterfly due to use of the invasive form of cuckoo flower

The native pierid butterfly Pieris oleracea underwent a large range reduction in New England in the twentieth century, likely due to the introduction the invasive butterfly Pieris rapae (Lep.: Pieridae) to North America in 1860, and later the oligophagous parasitoid Cotesia glomerata (Hymenoptera: Braconidae) in 1884. Thought extirpated from the state by the 1970s, one large dense population of the butterfly was found in the mid 1980s in a flood plain meadow along the Housatonic River in Lenox, Berkshire Co., Massachusetts. We examined how this native pierid was able to maintain a relatively dense local population by feeding on a novel, invasive host plant, Cardamine pratensis (cuckoo flower), in a meadow habitat despite known parasitoid presence. We approached this question in three ways. First, we deployed trap host plants (cuckoo flower and collards) stocked host larvae (first and second instars of either P. rapae or P. oleracea) at the Lenox site and other locations to determine current rates of C. glomerata attack, for comparison with historical information. Second, we used olfactometer experiments to determine if C. glomerata females could detect the cuckoo flower volatiles released during P. oleracea larval feeding. Third, we used field-cage experiments to determine if the plant architecture found in the flood plain meadow inhibited the ability of C. glomerata females to locate and parasitize hosts. Specifically, we asked if overtopping vegetation prevented or reduced parasitism of P. oleracea larvae feeding on the covered basal rosettes of C. pratensis, which is the physical form of host plant for three of the four butterfly generations at the site.

Polybrominated diphenyl ether congeners in the young-of-the-year bluefish, Pomatomus saltatrix, from several nursery habitats along the US Atlantic coastline

Spatial trends of polybrominated diphenyl ether (PBDE) congeners were examined by using high resolution gas chromatography – low resolution electron impact mass spectrometry (GC-EIMS) in 414 samples of young-of-the-year (YOY) bluefish (Pomatomus saltatrix) collected from a total of 29 nursery habitats along the US Atlantic coastline from Massachusetts to Florida. Of the 26 target PBDE congeners, BDE-47 (4 Br), BDE-100 (5 Br), BDE-49 (4 Br), BDE-99 (5 Br), and BDE-154 (6 Br) were the five most frequently detected congeners in the order of decreasing importance. The sum of the concentrations of five major PBDE congeners, referred to as ΣPBDEs, varied between estuaries and also among samples from a given estuary. ΣPBDEs were lowest in YOY bluefish from Vineyard Sound, Nantucket Sound, Great Bay, Delaware Bay, Lynnhaven Bay, Cape Lookout, and Crescent Beach, with maximum ΣPBDE concentrations below 10ng/g wet weight. ΣPBDEs in three bluefish samples from Stamford Harbor were detected at relatively high to unusually high concentrations of 69.1, 205, and 561ng/g wet weight. ΣPBDE values for other Stamford Harbor bluefish were generally low. Highest PBDE concentrations were detected in the vicinity of industrial and urban locations within the New York – New Jersey metropolitan complex. Among them, bluefish from Newark Bay were generally the most contaminated with an average ΣPBDE value of 56.6±30.8ng/g wet weight. ΣPBDEs in bluefish from Newark Bay were numerically greater than ΣPBDEs in bluefish from all locations, however these differences were not statistically significant. Modest to good correlations between ΣPBDEs and lipids were observed for YOY bluefish from Buzzards Bay, Upper New Bedford Harbor, Lower New Bedford Harbor, Outer New Bedford Harbor, Providence Harbor, Housatonic River, Norwalk Harbor, Little Neck Bay, Newark Bay, Sandy Hook Bay, Great Bay, Delaware Bay, Patuxent River and Crescent Beach. Poor correlations between ΣPBDE and lipids were observed for bluefish from other estuaries. ΣPBDEs were not always correlated with fish length or weight. ΣPBDEs in YOY bluefish along the US Atlantic coastline modestly paralleled ΣPBDEs in mussels and oysters, from not exact but geographically loosely similar locations, reported in the NOAA Mussel Watch Program. A number of researchers who used the high resolution mass spectrometry reported additional PBDE congeners. Although PBDE congeners we report do appear to be the prominent congeners in these studies, it is likely that the comparisons will be skewed in certain instances.

Effects of egg order on organic and inorganic element concentrations and egg characteristics in tree swallows, Tachycineta bicolor

The laying order of tree swallow eggs was identified from the Housatonic River, Berkshire County, Massachusetts, USA, and eggs were chemically analyzed individually to document possible effects of laying order on organic contaminant and inorganic element concentrations. Effects of laying order on other parameters such as egg weight, size, and lipid and moisture content also were assessed. Some effects of egg order on total polychlorinated biphenyls (PCBs) were detected, but the effect was not uniform across individual females or between years. In 2004, clutches with higher total PCBs tended to have concentrations decline across egg order, whereas clutches with lower concentrations of PCBs tended to increase across egg order. In contrast, in 2005, there was a tendency for concentrations to increase across egg order. Polychlorinated biphenyl concentrations were highly variable within and among clutches in both years. The directionality of egg order associations (i.e., slopes) for trace elements was element dependent, was positive for Mn and Zn, was negative for B, and had no slope for Cr. Whole egg weight increased across egg order. Percentage lipid was variable within a clutch, with no pattern common across all females. Percentage lipid was also correlated with organic contaminant concentration. In highly contaminated environments, higher lipid content could have the unanticipated corollary of having higher concentrations of lipophilic contaminants such as PCBs. To reduce the effect of high variation within a clutch when assessing contamination exposure, it is recommended that two eggs per clutch be collected and pooled for chemical analysis. We further recommend that, as long as the two eggs are randomly collected, the additional effort needed to identify and collect specific eggs is not warranted.

Corticosterone stress response in tree swallows nesting near polychlorinated biphenyl‐ and dioxin‐contaminated rivers

We assayed baseline and stress-induced corticosterone concentrations from adult female and nestling tree swallows, Tachycineta bicolor, from New England, U.S.A., sites with different levels of contamination with polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Corticosterone was compared over 2 years from a highly contaminated PCB site along the Housatonic River (Berkshire County, MA, USA), a midrange contaminated site upstream, and a reference site. Adult females (n=29), sampled only in 2003, showed an inverted-U association with PCBs, with higher stress-induced corticosterone with midrange contamination than at the high-contamination site. In nestlings, stress-induced corticosterone was highest for the highly contaminated site compared with the other sites in 2003 (n=53, 29 nests), with no difference among sites in 2004 (n=93, 27 nests). In 2004, we began testing mechanisms underlying these changes in nestlings at the high- and low-PCB sites. Corticosterone response to dexamethasone injection (used to test negative feedback) was not different between sites, but stress-induced corticosterone was reduced at the contaminated site after adrenocorticotropin hormone injection (used to test adrenal responsiveness), suggesting an inhibited ability to mount a stress response. We also compared nestlings from a stretch of the Woonasquatucket River, Rhode Island, U.S.A., heavily contaminated with TCDD (n=80, 43 nests) with nestlings from an upstream site that had lower levels of TCDD and the Berkshire County reference site. Although there were no stress-induced differences, baseline corticosterone was lower at the higher TCDD site than at the reference site. Altogether these findings suggest that tree swallows chronically exposed to high PCB and TCDD levels exhibit altered baseline and stress-induced corticosterone responses, but the patterns of alteration might not be predictable.

A Case Study for Microbial Biodegradation: Anaerobic Bacterial Reductive Dechlorination of Polychlorinated Biphenyls—From Sediment to Defined Medium

The history of anaerobic microbial polychlorinated biphenyl (PCB) dechlorination is traced over 20 years using a case study of PCB dechlorination in the Housatonic River (Massachusetts) as an example. The history progresses from the characterization of the PCBs in the sediment, to cultivation in sediment microcosms, to the identification of four distinct types of PCB dechlorination, to a successful field test, to the cultivation in defined medium of the organisms responsible for extensive dechlorination of Aroclor 1260, and finally to the identification of a Dehalococcoides population that links its growth to the dechlorination of Aroclor 1260. Other PCB dechlorinators have also been identified. Two bacterial strains, o-17 and DF-1, that link their growth to the dechlorination of several PCB congeners belong to a novel clade of putative dechlorinating bacteria within the phylum Chloroflexi. Dehalococcoides ethenogenes strain 195 also dechlorinates several PCB congeners when grown on chlorinated ethenes. Evidence is mounting that Dehalococcoides and other dechlorinating Chloroflexi may play a significant role in the dechlorination of commercial PCBs in situ.

Adult tree swallow(Tachycineta bicolor)survival on the polychlorinated biphenyl‐contaminated Housatonic River, Massachusetts, USA

Tree swallows (Tachycineta bicolor) were captured and banded at six sites that differed in polychlorinated biphenyl (PCB) contamination levels in the Housatonic River watershed, western Massachusetts, USA, from 2000 through 2004 to test the prediction that apparent survival rates of females in more contaminated areas were lower than those from less contaminated areas. We also tested whether plumage coloration affected over-winter survival and whether concentrations of PCBs in eggs differed between birds that did and that did not return the following year. Apparent survival rates were calculated using mark-recapture methods and compared using Akaike's Information Criterion. Model-adjusted survival rates ranged from 0.365 to 0.467 for PCB-contaminated females and between 0.404 and 0.476 for reference females. Models with either survival or capture probability modeled as functions of treatment (degree of PCB contamination), year, and age received some support. The model-averaged parameter estimate reflecting a treatment effect for high-PCB birds was negative (beta = -0.046, SE(beta) = 0.0939). Fifty-four percent of the total model weights involved models in which survival was a function of PCB treatment. Eggs were collected for contaminant analyses from a random sample of females that did and that did not return the following year. Concentrations of total PCBs were the same or higher in the eggs of females that returned compared to the eggs of those that did not return at both the highly and the moderately contaminated PCB sites. This may have resulted from higher-quality females with higher lipid reserves being more likely than lower-quality females to return the following year. Percentage lipid was positively correlated with total PCBs in eggs. Survival rates were similar among swallows with brown versus blue plumage.