Showing papers in "Virginia journal of science in 2012"

A Centennial Record of Paleosalinity Change in the Tidal Reaches of the Potomac and Rappahannock Rivers, Tributaries to Chesapeake Bay

Abstract: Gravity and push cores from the Potomac and Rappahannock Rivers (Virginia Tidewater) were collected from central and proximal estuarine zones with known seasonal salinity stratification. The lowermost microfossil associations in the cores comprise alternating ostracode populations of Cyprideis salebrosa and Cytheromorpha. This microfossil association gives way to an oligohaline association dominated by the freshwater ostracode Darwinula stevensoni. Stable oxygen isotope values (ä O) of Rapphannock Cyprideis salebrosa are 18 highly variable ranging between -6.6 to -3.2‰ VPDB. ä O values for 18 Potomac Cytheromorpha fuscata range from -8.2 to -3.2‰ VPDB. Positive excursions in ä O values are synchronous with population peaks for both 18 Cyprideis and Cytheromorpha indicative of increased marine influence and/or higher salinities. Microfossil paleoecology coupled with oxygen isotope values record a marked shift towards gradual freshening and deterioration of the salinity structure in the tidal tributaries during the mid-to late 19 century. th We attribute these trends to both decadal climate trends and aggressive land use practices in the Chesapeake Bay watershed during the late 19 to middle th 20th centuries. INTRODUCTION Estuaries are physically, chemically, and biologically complex environments at the convergence of continental and marine processes. In the Chesapeake Bay, the recent combination of anthropogenic watershed modification and sea-level rise are forcing mechanisms that have potentially influenced mixing of fresh and marine waters in the tidal reaches of the major tributaries (Colman and Bratton 2003; Boon 2012). To test this hypothesis, sediment cores were collected from the proximal and central reaches Corresponding author: Neil E. Tibert, ntibert@umw.edu Virginia Journal of Science, Vol. 63, No. 3, 2012 http://digitalcommons.odu.edu/vjs/vol63/iss3 112 VIRGINIA JOURNAL OF SCIENCE of the Potomac and Rappahannock estuaries for microfossil and stable isotopic analyses. Paleosalinity indicators were established on the basis of ostracode paleoecology (population abundances and pore morphometrics) and oxygen isotope values (ä O). The paleosalinity trends were considered in the context of sedimentation 18 history based on Cs dating, organic matter concentrations, and magnetic 137 susceptibility of collected cores. Cumulative results of these analyses indicate that salinity gradients in both estuaries have changed markedly since the beginning of the 19 century which is suggestive of anthropogenic influence on estuarine processes in th the Chesapeake Bay. BACKGROUND Geographic Location The Chesapeake Bay is the largest estuarine system in the United States that is located between Virginia and Maryland on the Atlantic Coastal Plain (Colman and Mixon 1988). This study focuses on the upper tidal reaches of the Potomac and Rappahannock Rivers where they transition from estuarine-to fluvial conditions (Fig. 1). Sediment cores were collected near the boundary between proximal (oligohaline) and central estuary (mesohaline) near Aquia Creek in the Potomac estuary and Blandfield Point in the Rappahannock estuary (Ellison and Nichols 1970, 1976; Ellison 1972; USEPA 1998). Since the 1980s, these estuaries have produced the highest annual FIGURE 1. Sediment cores were collected from the Potomac and Rappahannock estuaries, both of which are tributaries to Chesapeake Bay, the largest estuary in the eastern United States (Colman and Mixon, 1988). Virginia Journal of Science, Vol. 63, No. 3, 2012 http://digitalcommons.odu.edu/vjs/vol63/iss3 Centennial Record of Paleosalinity Change 113 sediment yields for all major Chesapeake Bay tributaries (Langland and Cronin 2003). In general, the relatively high sedimentation rates in Chesapeake Bay are related to ongoing sea-level rise and anthropogenic watershed modification (Fig. 2) (Colman and Mixon 1988; Brush 1989; Colman and Bratton 2003; Boon and others 2010; Boon 2012). Estuarine Circulation The convergence of fluvial and marine waters creates a dynamic circulation pattern that impacts sedimentary processes in estuarine environments. Where freshwater outflow meets incoming saltwater in a partially mixed estuary like the Chesapeake Bay, the seasonal halocline (salinity gradient) forms a relatively impermeable surface to sediment transport that frequently coincides with the estuarine turbidity maximum (ETM)(Langland and Cronin 2003). In the Potomac estuary, the maximum extent of saltwater intrusion occurs near Aquia Creek (Elliott 1976). In the Rappahannock estuary, the maximum extent of saltwater intrusion occurs near Blandfield Point (Ellison and Nichols 1970). Our preliminary assessment of modern salinity structure revealed oligohaline conditions and/or weak haloclines near Aquia Creek and Blandfield Point during June 2009 (Fig. 3). Microfossils Ostracodes are aquatic crustaceans that are sensitive to changes in salinity and temperature (Frenzel and Boomer 2005) and their ecological associations have been used to make inferences about past environmental conditions in the Chesapeake Bay (Elliott and others 1966; Cronin and Grinbaum 1999; Cronin and others 2005, 2010). When used in conjunction with ä O values of their calcite carapaces, ostracodes can 18 be used to develop paleosalinity proxies in the context of both climate induced evaporation and mixing of marine and freshwaters (Anderson and Arthur 1983; Anadón FIGURE 2. Historic sea level data for Washington, D.C. illustrates a constant rise in sea level over the last century for the Potomac estuary (NOAA 2008). Virginia Journal of Science, Vol. 63, No. 3, 2012 http://digitalcommons.odu.edu/vjs/vol63/iss3 114 VIRGINIA JOURNAL OF SCIENCE and others 2002; Holmes and Chivas 2002; Ito and others 2003). Studies by Medley and others (2008) demonstrated that the shape of the sieve pores on the external surface of the carapace (Type C of Puri 1974) varies significantly with salinity which further improves the potential for past salinity determinations using ostracoda. METHODS Sediment cores were collected from the Rappahannock and Potomac estuaries with Ogeechee and Gravity (Wildco Inc.) corers (Fig. 1). The longer Ogeechee cores (>100 FIGURE 3. Late spring salinity (mg/L) and temperature ( C) profiles measured from o the (A) Potomac and (B) Rappahannock estuaries. This analysis was part of an unpublished assessment of water quality during June 2009. Virginia Journal of Science, Vol. 63, No. 3, 2012 http://digitalcommons.odu.edu/vjs/vol63/iss3 Centennial Record of Paleosalinity Change 115 cm) were analyzed with a Bartington MS2C Core Logging Sensor, and subsequently partitioned into 1 cm segments for loss on ignition and microfossil processing. The shorter gravity cores (40 cm) were divided into 2 cm segments and samples sent to Core Scientific International (Winnipeg, MB, Canada) for Cs analysis via gamma 137 spectrometry. Microfossil census counts were completed at 2 cm intervals using the methods outlined in Medley and others (2008). Sediment samples were rinsed on a 125 ìm mesh sieve and wet samples were examined with a stereoscopic zoom microscope (Nikon SMZ1500). Select ostracodes were photographed using a variable pressure scanning electron microscope (Hitachi S-3400N). Morphometric shape analysis was completed according to the methods described by Medley and others (2008). Sieve pores on external valves of Cyprideis were traced to determine the areas and shapes using ImageJ 1.3.1v (National Institutes of Health by Wayne Rasband). Values for circularity were calculated using the following formula: Circularity = 4ð (area/perimeter ). The 2 best-fit trendline of circularity versus area crossplots was used to determine the pore slope values. Ostracode carapaces were bathed in deionized water and sent to the Saskatchewan Isotope Laboratory (Saskatoon, SK, Canada) for oxygen and carbon isotope analysis via stable isotope ratio mass spectrometry (SIRMS). SIRMS preparation entails the heating of samples in vacuo to dissipate contaminants (e.g. organic matter and water that may influence isotope values) prior to analysis with a Finnigan Kiel-IV carbonate preparation device directly coupled to a Finnigan MAT 253 isotope ratio mass spectrometer. Data is expressed relative to the VPDB scale and calibrated to the NBS19 standard (ä C=1.95‰ VPDB; ä O=-2.2‰ VPDB). 13 18 Sediment accumulation rates were determined following the Cs analysis method 137 of Robbins and Edgington (1975). Cesium-137 is a radioactive isotope (half life=~30 years) that was released into the atmosphere during nuclear testing and simple gamma spectrometry can measure its concentration in sediment (USEPA 2010). Given that atmospheric levels of Cs peaked in 1963, a sampling site’s average sedimentation 137 rate can be calculated using the simple stratigraphic thickness above the peak divided by the time in years since 1963. To ensure accurate gamma spectroscopy results, at least 2 g of sediment were removed from the center of each core segment. Forty samples from two Potomac estuary cores were analyzed by Core Scientific International (Winnipeg, Manitoba). Select samples were pretreated for radiocarbon dating at the University of Pittsburgh following the methods outlined by Abbott and Stafford (1996). AMS C analyses were performed at the University of Arizona’s 14 Accelerator Mass Spectrometry Laboratory. RESULTS Physical Stratigraphy Core PT-09-C3 from Aquia Creek (Potomac River) comprises 134 cm of dark grey clay with a layer of fine sand in the basal 10 cm (Figs. 1, 4). Magnetic susceptibility values average 38.7 SI Units with a minimum value of 18.7 (124 cm) and a maximum value of 166.7 (134 cm). Total organic matter (TOM) averages 6.59 % with a minimum value of 1.42% (132 cm) and a maximum value of 9.68% (11 cm). The maximum concentration of Cs occurs between the 20-22 cm cored interval (Fig. 5). 137 Virginia Journal of Science, Vol. 63, No. 3, 2012 http://digit

Late Holocene Sedimentation and Paleoenvironmental History for the Tidal Marshes of the Potomac and Rappahannock Rivers, Tributaries to Chesapeake Bay

Abstract: Instrumental tide gauge records indicate that the modern rates of sea-level rise in the Chesapeake Bay more than double the global average of 1.2-1.5 mm yr-1. The primary objective for this study is to establish a relative depositional history for the tidal marshes of the Potomac and Rappahannock Rivers that will help us improve our understanding of processes that influence sedimentation in the proximal tributaries of Chesapeake Bay. Marsh cores were collected from Blandfield Point VA, Tappahannock VA, and Potomac Creek VA. The sedimentary facies include: 1) a lower unit of organic-poor, grey clay with fine sand and silt layers and estuarine foraminifera; and 2) an upper unit of organic-rich clay and peat with abundant brackish to freshwater marsh foraminifera and thecamoebians. AMS 14C dating of bulk marsh sediments yield sedimentation rates at Potomac Creek ranging from 3.04-4.20 mm yr-1 for the past 2500 years. Rates of sedimentation calculated for Blandfield Point indicate 1.37-2.19 mm yr-1 in the basal clays and peat for the past ~3000 years. Foraminiferal census counts indicate a freshening upward trend with a transition from an estuarine Ammobaculites crassus assemblage to a marsh Ammoastuta salsa assemblage with abundant freshwater Thecamoebians. The late Holocene history of sedimentation for the marshes indicates that differential compaction, recent land use practices, and climate change have contributed to the resultant freshening-upward environmental trend and variability in sediment accumulation rates between coring sites. Corresponding author: Neil E. Tibert ntibert@umw.edu 92 VIRGINIA JOURNAL OF SCIENCE INTRODUCTION The Chesapeake Bay watershed comprises numerous tributaries draining from the eastern Appalachian Mountains. The central axis to the Chesapeake has been evaluated in the context of decadal, centennial, and millennial climate changes (Cronin and others 2005, 2010). In the historic Northern Neck region of Virginia, the tidal reaches of the Rappahannock and Potomac Rivers (Fig. 1) have received little detailed study with respect to the nature of the sedimentary record spanning the past several thousand years. Recent estimates for eustatic sea level are estimated to be as high as 1.5-1.88 mm yr (Church and White 2006, Nerem and others 2006) whereas the instrumental tidal -1 FIGURE 1. Location map for the tidal reaches of the Potomac and Rappahannock Rivers. Table1 lists the coordinates and detailed coring information for Sites A-C. Table 2 list coordinates and details for the tide gauge stations (Sites 1-4). Inset shows our location along the eastern Atlantic coast of the USA. Late Holocene Sedimentation 93 records from the Chesapeake Bay indicate rates as high as ~3-4 mm yr (Boon 2012). -1 The disparity between global and regional base level change in the Chesapeake Bay is not well understood and likely reflects the combined effects of allogenic, autogenic, and anthropogenic processes in the region (Cronin 2012). The primary objective for this paper is to establish a late Holocene sedimentation and paleoenvironmental history for the tidal reaches of the Potomac and Rappahannock Rivers in the Northern Neck region of Virginia, USA. Our primary analytical tools include physical stratigraphy (loss on ignition, grain size, and magnetic susceptibility), foraminiferal paleoecology, and AMS C geochronology applied to cores collected from the central estuarine region of the 14 tidal Potomac and Rappahannock Rivers. BACKGROUND The Chesapeake Bay is the largest estuary in the United States, with shores bordering the states of Virginia, Maryland, and the District of Columbia. The watershed area of this coastal plain estuary is 167,000 km that includes the following major 2 tributaries: Susquehanna, Potomac, Rappahannock, York, and James Rivers (Boesh and others 2001). The Chesapeake Bay is the product of Holocene sea-level rise formed by fluvial incision coupled with the inundation of river valleys following the terminus of the last glacial maximum (Schubel and Pritchard 1986). The Chesapeake Bay is located in an apparently inactive tectonic region on the North American passive margin. However, many Cretaceous age faults have been identified in close proximity to our localities in the Fredericksburg, VA (Table 1) which marks the transition from the Piedmont region (west) to the coastal plain (east) in Virginia (Fig. 1) (Berquist and Bailey 1999). Lower Tertiary sedimentary deposits in the region include fine-to coarse glauconitic quartz sand and clay-silt of the Lower Tertiary Pamunkey Group (Brightseat, Aquia, Marlboro, Nanjemoy, and Piney Point formations) (Mixon and others 1989). TABLE 1. List of sampling localities from the Potomac and Rappahannock tidewater region of Virginia and Maryland. Site Location Longitude Latitude Geographic Info Site A Blandfield Point VA 76°54'40.436\"W 38°0'6.911\"N Blandfield Marsh on Rappahannock River (proximal estuarine zone 0-5 ppt) Site B Tappahannock Harbor VA 76°51'15.368\"W 37°55'16.723\"N Coleman's Island, Hoskin's Creek tributary to Rappahannock River (distal tributary to central estuarine zone) Site C Potomac Creek VA 77°20'7.619\"W 38°21'6.972\"N Potomac Creek tributary to Potomac River (central estuarine zone 5-15 ppt) 94 VIRGINIA JOURNAL OF SCIENCE During the past several decades, the National Oceanic and Atmospheric Administration (NOAA, 2009) has maintained tidal gauging stations at Colonial Beach and Washington DC (Table 1). The sea level rates calculated from the instrumental records on the Potomac River range from 3.16-4.78 mm yr from Washington DC and -1 Colonial Beach respectively (Table 2), which are significantly higher than eustatic values of 1.0-1.5 mm yr (Table 2) (NOAA 2009; Boon 2012). The instrumental -1 records from the lower Rappahannock at Sewell’s point record a relative sea-level rise of 4.44 mm yr spanning the past 84 years. -1 Cronin and others (2000, 2005, and 2010) and Cronin and Vann (2003) reported microfossils from cores (~2-6 m in thickness) located at the mouths of the major tributaries in the central regions of the bay (e.g., Patuxent, Choptank, and the Potomac Rivers). Willard and others (2003) and Cronin and others (2003) reported a highresolution historical microfossil record that apparently discriminates important anthropogenic events such as the Medieval Warm Period and deforestation of the bay region with the arrival of European settlers. METHODS Marsh cores were collected from the Rappahannock and Potomac Rivers that includes Blandfield Point (Site A), Tappahannock Harbor (Site B), and Potomac Creek (Site C) (Table 1) (Fig. 1). A square-rod piston coring device was used to collect continuous 1-meter long core drives down a single coring hole (Wright 1967). Individual core sections were split along a longitudinal axis to produce two equal halves. Potomac Creek cores were evaluated for microfossils at 10 cm intervals. Approximately eighty 1cm sediment samples were soaked in a beaker of warm water 3 and mild detergent to disperse the clays (Scott and Leckie 1990). Samples were rinsed over a 63 μm sieved and picked wet using conventional microfossil methods (Scott and Medioli 1980). Each sample was then examined for foraminifera and relative abundances were calculated for species and select genera to simplify the trends. Exceptionally preserved specimens were examined on the scanning electron microscope (SEM) for identification and illustration purposes. TABLE 2. Tidal gauge data for the Chesapeake Bay (NOAA, 2009). Locality Instrumental Records SL Rate mm yr-1 YBP Tidal Station & Data Set Info NOAA Monthly Mean 1 Washington DC 3.16+0.35 87 8594900 (1924-2006) 2 Colonial Beach VA 4.78+1.21 39 8635150 (1972-2003) 3 Sewells Point VA 4.44+0.27 84 8638610 (1927-2006) 4 Solomons Island MD 3..41+0.29 74 8577330 (1937-2006) x Global average 1.5+0.5 0 Late Holocene Sedimentation 95 The total organic matter (TOM) was determined by using loss on ignition (LOI) (Dean 1974). Grain size analyses were conducted using methods modified from McManus (1988). Volume magnetic susceptibility was conducted on sediments using a Bartington MS2E surface scanner following the method of split-core logging of Last and Smol (2001). Select bulk sediment samples were pretreated for radiocarbon dating at the University of Pittsburgh following the methods outlined by Abbott and Stafford (1996). AMS C analyses were performed at the University of Arizona’s Accelerator 14 Mass Spectrometry Laboratory and the dates calibrated using Calib 6.1.0 (Reimer and others 2009). RESULTS Sedimentary Facies Grey Clay Facies: The basal sediments at all coring sites comprise clay and sparse interbeds of silt and sand (Fig. 2). The grey clay facies ranges in thickness from ~7.54.25 m at Potomac Creek to ~5.5-2.5 at Tappahannock Harbor (Fig. 2). TOM values in the organic-rich clay range from ~8-28%. Magnetic susceptibility values are relatively low with positive excursion peaks in the silt-rich layers. Grain size analyses at Tappahannock Harbor indicate a coarsening-up trend from mud-to-silt and fine sand (Fig. 2). Foraminifera in the organic-rich grey clay are dominated by Trochammina inflata, and Ammobaculites spp. in association with sparse Ammoastuta salsa and Miliammina fusca. (Fig. 3). Peat & Clay Facies: All cores contain an upper unit of alternating peat and grey clay with TOM values that range from ~20% to 85% (Fig. 2). Magnetic susceptibility values are relatively low with little variability. Microfossil populations in this facies are dominated by Ammoastuta salsa and Miliammina fusca. Trochammina inflata and Jadaminna macrescens are also common while Haplophragmoides is the least abundant (Fig. 3). Sedimentary cores from Blandfield Marsh and Potomac Creek (Fig. 2) are capped with an uppermost rooted zone of the grass Phragmites and the freshwater thecamoebian Arcellacea sp. (Figs. 2, 3). Core Chronology & Sedimentation Rates Accelerator Mass Spectrometry (AMS) C dat

Effect of Greenhouse Temperature on Tomato Yield and Ripening

Abstract: High fuel costs have encouraged producers of greenhouse tomato (Solanum lycopersicum L.) in the mid-Atlantic region to reduce air temperatures during the day. However, effects on fruit ripening and yield are not known, especially under the low light conditions found in off-season production. This 2-yr study compared fruit ripening and yield of tomato under two temperature regimes during the fall season. Two sets of 18 tomato plants, three rows of six, were grown in soilless culture under either a warm or cool temperature regime. Temperatures were similar during night hours but allowed to rise to at least 2124 oC in the cool greenhouse section and 23-26 oC in the warm section, depending on daily solar heating. Mean 24 hour temperature difference between zones was less than 2 oC. Ripe tomato fruit were harvested and weighed 3 times per week for 8 weeks and the remaining un-ripened green tomatoes were weighed at the termination of the experiment to obtain total fruit biomass. The warm zone produced significantly greater weight of ripe tomatoes (23%) than the cool zone. However, total fruit weight (ripe and green), was not significantly different. Thus, a relatively small increase in temperature (2 oC) during the mid-day was associated with a significant increase in fruit ripening but not in total fruit weight. This study showed that greenhouse temperature could be used to better manage fruit production to match weekly market demand without affecting total fruit weight and that consistently maintaining a cool greenhouse would delay tomato ripening and likely increase the potential for plant stress due to high fruit loads remaining on the vines.

Exploratory Modeling Indicates Red-Backed Salamander Detections are Sensitive to Soil pH at C. F. Phelps Wildlife Management Area, Virginia

Abstract: Red-backed salamanders represent an important component of Virginia ecosystems, but there are few habitat models that can reliably predict the presence/absence of this species. We surveyed the habitats of red-backed salamanders at one site in the Piedmont region of Virginia and collected data on an array of habitat variables with which this species is normally associated. We used logistic regression to develop a model predicting the presence or absence of the species at a given 50m-transect. Our final model incorporated soil organic layer pH variability and mineral layer average pH, and accounted for 30% of the variation in our data. We conclude that soil pH is a limiting determinant of habitat use for this study site, and that it may affect adaptive behaviors for highly acidic soils. INTRODUCTION As researchers address the issues of amphibian decline, there is an increasing need to better understand how salamanders in terrestrial ecosystems interact with their habitat. Greater understanding of the habitat ecology of these species would likely improve our ability to manage and conserve amphibian diversity in local watersheds, thereby reducing the ecosystem damage that would result from the loss of these species (Cushman 2005, Wyman 1990). In the Rappahannock River watershed of Northern Virginia, both Mitchell (1998) and McGhee and Killian (2010) have surveyed amphibian, and specifically, salamander diversity, but little has been done to assess the habitat relationships of commonly detected species. To address this need, we conducted a preliminary study of salamander habitat for a single site in the Rappahannock River drainage at the C. F. Phelps Wildlife Management Area (WMA) concurrent with a species diversity survey and developed a simple habitat model for our most commonly detected terrestrial salamander, Plethodon cinereus Green 1818 (red-backed salamander). Corresponding author: Jay D. McGhee jmcghee@nwmissouri.edu Virginia Journal of Science, Vol. 63, No. 3, 2012 http://digitalcommons.odu.edu/vjs/vol63/iss3 138 VIRGINIA JOURNAL OF SCIENCE The red-backed salamander is common to Virginia forests and the Rappahannock River watershed, and is considered an important component of the local ecosystems in which they occur (Burton and Likens 1975, Davic and Welsh 2004). While several studies have noted particular habitat features associated with this species, such that a hypothetical niche-gestalt can be conceptualized (James 1971), only a few studies have actually developed predictive models of habitat use, primarily to compare the effects of silviculture treatments (Demaynadier and Hunter 1998, Morneault et al. 2004, McKenney et al. 2006). The red-backed salamander occurs in the leaf-litter and well-drained soil underlying deciduous, northern conifer, and mixed deciduous-coniferous forests with numerous cover objects (logs and rocks) and little underbrush (Burger 1935, Petranka 1998, Richmond and Trombulak 2009). This lungless salamander is dependent on gas exchange through the skin for respiration, and is sensitive to moisture and temperature shifts, typically adjusting to these changes by moving vertically through the soil column (Taub 1961, Heatwole 1962, Spotila 1972). They tend to prefer a neutral soil pH, cooler temperatures and ready access to lower soil layers as predation refugia (Bogert 1952, Heatwole 1962, Spotila 1972, Wyman and Hawksley-Lescault 1987). Females attach eggs within natural crevices or beneath embedded rocks or decaying logs (Petranka 1998). We wished to determine whether we could successfully predict red-backed salamander occurrence at a given site using variables associated with these general habitat features known to be key components in their ecology. We hypothesized that red-backed salamanders would be detected in leaf litter associated with cover objects and moist, cool soil conditions of neutral pH. We predicted that a logistic regression model would include variables measuring the amount of coverage by cover objects, soil moisture, and soil ph. METHODS We used transect sampling to locate salamanders (Jaeger 1994, Jaeger and Inger 1994, Mitchell 2000). We randomly selected the starting location of transects using a GPS. We sampled transects by searching five 1-m quadrats placed randomly within 2 10m increments (Jaeger 1994, Jaeger and Inger 1994, Mitchell 2000). We searched quadrats by removing large cover objects (rocks and decaying wood) and searching leaf litter (Mitchell 2000). We identified captured salamanders to species, and measured snout-vent length and total length to estimate and assign age-classes (Petranka 1998, Moore and Wyman 2010). We collected habitat data at both the transect-level and the quadrat-level. Transectlevel data included air temperature, air pressure, relative humidity, vapor pressure deficit (vapor pressure deficit represents the difference between the actual moisture in the air and the amount of moisture the air could hold when saturated at a given temperature: Bellis 1962), degree and direction of slope, general weather (clear, partly cloudy, overcast, light rain, heavy rain), and habitat (coniferous, mixed deciduous, mixed coniferous-deciduous, open-field/Rosa multiflora brush). Quadrat-level data included soil pH, soil moisture, soil temperature, leaf litter depth, and percent cover (bare ground, leaf litter, natural cover, ground vegetation, and woody stem). We determined soil pH and soil moisture of cored soil samples in a laboratory. Soil samples were obtained by taking 31.7 mm diameter soil probe cores from a quadrat Virginia Journal of Science, Vol. 63, No. 3, 2012 http://digitalcommons.odu.edu/vjs/vol63/iss3 Habitat Modeling of Red-Backed Salamander 139 until sufficient soil was obtained to fill two collection tubes (50 mL centrifuge tubes) with separate organic and mineral fractions. In the laboratory each fraction was thoroughly mixed followed by division into two approximately equal parts—one for percent soil moisture and one for ph. Percent soil moisture was determined by massing the wet samples followed by drying for 24 hours in a 50 C oven. Soil pH was determined using a Barnant 20 digital pH meter. The sample (placed in the centrifuge tube) was covered with enough distilled water to keep the pH probe above the sediment. We waited for 20 minutes to allow the more coarse soil particles to settle out. We then measured the pH after the reading stabilized, but not to exceed 1 minute. We measured leaf litter depth using a ruler placed once within a randomly chosen quadrant of the quadrat. We used the Daubenmire (1959) method to estimate ground cover within quadrats. As we had little information from which to base hypotheses regarding habitat selection at this site, we used logistic regression as an exploratory modeling approach to determine which predictor variables were most associated with captured salamanders at the transect level. For variables measured at the quadrat level, we tested both mean values and their standard deviations as predictors. From our data we created new multiplicative variables where synergistic effects seemed likely (synergistic variable 1: soil temperature*organic layer soil moisture*mineral layer soil moisture, synergistic variable 2: organic-layer soil pH*organic layer soil moisture). We used forward stepwise selection (P = 0.05 to enter and 0.10 to remove) in SPSS (SPSS Inc., Chicago IL). Variable coefficients were assessed using the change in -2 loglikelihood (Hosmer and Lemeshow 1989). The explanatory value of the selected model was evaluated using Nagelkerke’s r (Hosmer and Lemeshow 1989, Nagelkerke 1991, Ryan 1997). For all 2 statistical analyses, detection refers to whether a species was captured or not, as opposed to the number of captures; = 0.05. RESULTS From 13 April 2007 – 21 April 2009, we sampled 91 transects and 455 quadrats, locating 42 red-backed salamanders. We found individuals in 26 of 91 transects (29% encounter rate). Mean SVL for captured adults was 40.06mm ± 0.90 SE while mean SVL for captured juveniles was 27.33mm ± 1.40 SE. Our logistic regression selected a model that explained 30% of the variation in the data (r = 0.30) and produced two 2 predictor variables. The first was the standard deviation of organic soil layer pH (SDOrgpH: 6.50 ± 2.38 SE, change in -2 log likelihood = 9.350, df = 1, P = 0.002, Fig. 1). The second was the average mineral soil layer pH (AvgMinpH: -1.80 ± 0.92 SE, change in -2 log likelihood = 6.376, df = 1, P = 0.012, Fig 2). The model defined the probability of predicting the detectable presence of a red-backed salamander within a transect as equal to . It correctly predicted the absence of salamanders in 81% of cases, and correctly predicted their presence in 37% of cases. Soils throughout the study site tended to be acidic. The average organic layer soil pH across all transects was 4.62 ± 0.10 SE, and the average mineral layer soil pH was Virginia Journal of Science, Vol. 63, No. 3, 2012 http://digitalcommons.odu.edu/vjs/vol63/iss3 140 VIRGINIA JOURNAL OF SCIENCE FIGURE 1. Detection of red-backed salamanders as a function of the variability (standard deviation) in pH of the organic layer of soil for transects on C. F. Phelps Wildlife Management Area, Fauquier and Culpeper County, Virginia, April 2007 – April 2009. Detections tend to increase with increased variation in soil acidity. 4.57 ± 0.08 SE. The pH of the organic and mineral layers were highly correlated (r = 0.93) and 77% of our sites had organic fractions with pH 5 and 83% of the sites had mineral fractions with pH 5. All of our captures were in soils with a pH between 3.5 and 6.5 for the organic layer and between 3.9 and 5.3 for the mineral layer. DISCUSSION The model explained a substantial amount of the variation in presence and absence data. Haan et al. (2007) found similar results in their investigation of Aneides hardii Taylor 1941 (Sacramento salamander) where the best of 18 models were able

Camera Trap Success Among Carnivores and Prey Animals in Tazewell County, Virginia

Abstract: Obtaining basic ecological information on occurrence and activity levels in cryptic and elusive species is often difficult. Camera trapping provides a relatively inexpensive opportunity to acquire such data. We used infraredtriggered cameras to assess trap success and activity levels of several species across four consecutive seasons, including: Ursus americanus (black bear), Lynx rufus (bobcat), Canis latrans (coyote), Vulpes vulpes (red fox), Urocyon cinereoargenteus (gray fox), Procyon lotor (raccoon), Odocoileus virginianus (white-tailed deer), Didelphis virginiana (opossum), Sciurus carolinensis (gray squirrel), and Meleagris gallopavo (wild turkey). With a total of 396 trap nights (TN) at one station over the span of four consecutive seasons, overall trap success rate was 86.87 captures per 100 TN. Trap success was highest in wild turkeys (31.57/100 TN), followed by raccoons (15.66/100 TN), gray squirrels (10.86/100 TN), gray foxes (8.59/100 TN), white-tailed deer (8.08/100 TN), opossums (5.56/100 TN), coyotes (1.52/100 TN), red foxes (1.26/100 TN), and bobcats (0.76/100 TN). Overall trap success significantly varied across all target species combined (Kruskal Wallis ChiSquare = 349, d.f. = 10, p < 0.0001). However, trap success did not vary across all seasons for all target species combined (Kruskal Wallis Chi-Square = 0.99, d.f. = 3, p = 0.78). This study is the first to use camera trapping to examine species presence and activity levels in a longitudinal manner for cryptic and elusive species of southwest Virginia. INTRODUCTION Camera trapping is an excellent non-invasive tool for identifying cryptic or elusive species (Yasuda, 2004; Rowcliffe et al. 2008). While this approach to elusive species identification is not a recent revelation in ecological methodologies (e.g., Chapman, 1927), camera trap usage has picked up momentum in recent years (Karanth and Nichols, 1998). In fact, published papers utilizing some degree of camera trapping have seen an estimated 50% annual growth over the past decade (Rowcliffe and Carbone, Corresponding author: David L. Chambers chambersdl@longwood.edu 130 VIRGINIA JOURNAL OF SCIENCE 2008). Much of this growth can be attributed to increased technological and analytical advances that allow ecologists to determine population densities, dispersal behaviors, and relative abundance – all from a distance (Karanth and Nichols, 2000; Kelly et al. 2012). Trap success is one common index of activity level that can be obtained using camera trap data. Trap success calculated per species can provide insight into species presence or, at a more interactive scale, potential species interactions among predators/prey (Kelly and Holub, 2008), despite recent debate about its use as an index of abundance (Anderson, 2003; O’Brien et al., 2003). Regardless of debate, it is impractical to ignore the importance of understanding predator/prey dynamics particularly in the wake of increasing anthropogenic disturbances that are altering natural community composition and interactions (Sala et al., 2000; Walker et al., 2005). Thus, the value of camera trapping becomes magnified for elusive species that act as predators and/or prey in their respective systems. Such value is further magnified when camera trapping is employed in highly understudied locations, such as Virginia, in order to elucidate cryptic species interactions. Our study used camera trapping to survey medium to large-sized mammalian and terrestrial avian species known to occur at our study site. Specifically, we targeted Ursus americanus (black bear), Lynx rufus (bobcat), Canis latrans (coyote), Vulpes vulpes (red fox), Urocyon cinereoargenteus (gray fox), Procyon lotor (raccoon), Odocoileus virginianus (white-tailed deer), Didelphis virginiana (opossum), Sciurus carolinensis (gray squirrel), and Meleagris gallopavo (wild turkey). We report overall and seasonal trap success for each target species in the understudied state of Virginia. MATERIALS AND METHODS Our study site was located on private property in Tazewell County, near the town of Richlands, Virginia (Fig. 1). The site is situated at approximately 615 m in elevation within a mostly deciduous forest. Trap camera location (one station) was along a fence that bisected a north-facing forested hillside consisting of predominately yellow poplar (Liriodendron tulipifera). However, northern red oak (Quercus rubra), white oak (Q. alba), American ash (Fraxinus americana), and eastern red cedar (Juniperus virginiana) were also in the adjacent area. Cameras were mounted approximately 80 cm above the ground in a location that would funnel animals in the pathway of the lens that was approximately 3 m away. Two types of cameras were used throughout the duration of this study: a StealthCam MC2-G and a DeerCam 200, both of which are passive infrared-triggered 35 mm film cameras. These cameras are triggered by heat and motion detectors. The StealthCam MC2-G, programmed with 1 min intervals between each image capture, was used from 1 October 2005 to 25 January 2006. The DeerCam 200, programmed with 15 sec intervals between each image capture, was used from 26 January 2006 until the end of the study. Both cameras, when active separately, were active 24 hours a day. Cameras were routinely checked for basic maintenance and battery and film replacement. No bait or lures were used to attract target species. No camera malfunctions were noted throughout this longitudinal study. Trap success for each targeted species was calculated as the number of trap events per 100 trap-nights. In order to prevent duplicate counting of images taken over short periods of time (i.e., less than 30 min apart; Kelly, 2003; Silver et al., 2004), date/time Camera Trapping in Tazewell County 131 stamps on each photograph and individual animal size, position, and markings were examined. Special care was taken to accurately estimate the number of wild turkeys (M . gallopavo) for each camera trap event since they periodically appear as a flock that, subsequently, triggered multiple image captures. Because data did not meet assumptions of normality, nonparametric statistical analyses were conducted. Specifically, we used a nonparametric Kruskal-Wallis test to compare overall trap success amongst all targeted species to compare trap success among seasons for each target species. We conducted this study over an entire year, thus all four seasons are represented. Spring season consists of March, April, and May image captures. Summer season reflects image captures from June to August. Fall season includes all image captures from September to November. Finally, winter season includes all image captures from December to February. All statistical analyses were conducting using SAS JMP 9.0 (SAS Institute, Cary, North Carolina). RESULTS In total, we photographed nine species (eight mammals and one bird) without the use of lures or baits. Specifically, six (bobcat, coyote, red fox, gray fox, raccoon, and opossum) are considered to be predatory species while the remaining three (white-tailed deer, gray squirrel, and wild turkey) are considered to be prey. We amassed a total of 396 trap nights (TN) and recorded 344 trap events, with a total of 637 target animal photographs (Table 1). Overall trap success for all animals photographed was 86.87 per FIGURE 1. Study site location. 132 VIRGINIA JOURNAL OF SCIENCE 100 TN (Table 1). In terms of individual species contributing to successful trap events, the majority of raw photographic events were M. gallopavo (wild turkey; 36.34%), followed by P. lotor (raccoon; 18.02%), S. carolinensis (gray squirrel; 12.5%), U. cinereoargenteus (gray fox; 9.88%), O. virginianus (white-tailed deer; 9.3%), D. virginiana (opossum; 6.4%), C. latrans (coyote; 1.74%), V. vulpes (red fox; 1.45%), and L. rufus (bobcat; 0.87%). No U. americanus (black bear) were photographed. Trap success significantly varied across all targeted animals (Kruskal Wallis ChiSquare = 349, d.f. = 10, p < 0.0001) (Fig. 2). Trap success was highest in M. gallopavo (wild turkey; 31.57/100 TN). Procyon lotor (raccoon; 15.66/100 TN) had the second highest trap success, followed by S. carolinensis (gray squirrel; 10.86/100 TN), U. cinereoargenteus (gray fox; 8.59/100 TN), O. virginianus (white-tailed deer; 8.08/100 TN), D. virginiana (opossum; 5.56/100 TN), unknown/unidentifiable photographs due to poor quality (3.03/100 TN), C. latrans (coyote; 1.52/100 TN), V. vulpes (red fox; 1.26/100 TN), and L. rufus (bobcat; 0.76/100 TN). Trap success did not significantly vary across seasons for all targeted species combined (Kruskal Wallis Chi-Square = 0.99, d.f. = 3, p = 0.78)(Fig. 3.). Unfortunately, rigorous comparisons of seasonal trap success within each individual targeted species were not possible due to low sample sizes among individual seasons. TABLE 1. Total number of trap events, number of animals photographed, and overall trap success. Species (common name) Total number of trap events Total number of