Lower Susquehanna River Research Articles

Legacy sediment as a potential source of orthophosphate: Preliminary conceptual and geochemical models for the Susquehanna River, Chesapeake Bay watershed, USA

Nutrient pollution from agriculture and urban areas plus acid mine drainage (AMD) from legacy coal mines are primary causes of water-quality impairment in the Susquehanna River, which is the predominant source of freshwater and nutrients entering the Chesapeake Bay. Recent increases in the delivery of dissolved orthophosphate (PO4) from the river to the bay may be linked to long-term increases in pH, decreased acidity of precipitation, and decreased acidity, iron, and aluminum loading from widespread AMD. Since the 1950s, baseline pH increased from ~6.5 to ~8 in the West Branch and “North Branch” of the Susquehanna River, which drain bituminous and anthracite coalfields of Pennsylvania. A current baseline pH of ~8 and daily maxima exceeding 9 have been documented along the lower Susquehanna River. In response to improved river quality, bioavailable PO4 now may be released into solution from legacy sediment that has filled major impoundments in lower reaches of the river. At typical pH (5–8) of natural water, aqueous PO4 species tend to be adsorbed by hydrous iron, aluminum, and manganese oxides that coat soil and sediment particles; however, PO4 may be substantially desorbed at pH >8. We created a geochemical model that simulates equilibrium aqueous/solid distributions of PO4 as pH and other solution characteristics change. Considering current conditions in the lower Susquehanna River, the model demonstrates potential for extensive release of adsorbed PO4 at pH >8. Empirical data from laboratory experiments corroborate model results. The transfer of PO4 into the water column may increase algae growth, which removes CO2 and drives pH to higher values, facilitating additional PO4 release and exacerbating the potential for harmful algal blooms. Thus, legacy sediment is a currently unquantified source of PO4 that warrants consideration by resource managers and programs collaborating to reduce phosphorus loads to the bay and similar settings worldwide.

Relative Roles of Sediment Transport and Localized Erosion on Phosphorus Load in the Lower Susquehanna River and Its Mouth in the Chesapeake Bay, USA

AbstractParticle size greatly influences the fate of phosphorus (P) in estuaries as P adheres more readily to the larger surface area in smaller sized particles. Here, data on two size fractions of particulate matter, permanently suspended particulate matter (PSPM, ≤40 μm) and resuspended particulate matter (RSPM, >40 μm), from field and controlled laboratory erosion experiments were analyzed to determine their relative contribution to water column P in the mouth of the Susquehanna River in the upper Chesapeake Bay. Based on the composition of sequentially extracted P pools, C and N isotopes, and elemental data, all PSPM and the majority of RSPM are most likely derived from allochthonous sources through river transport. A minor fraction of particulate matter in the water column was derived from sediment resuspension, which had a dominant role above the sediment‐water interface in the river's mouth. The proportion of biologically available P pools to recalcitrant P pools in suspended particulate matter decreased with water column depth, indicating their preferential removal or biological utilization during settling. Suspended particulate matter (SPM) mobilized during sediment erosion experiments, regardless of particle size, was richer in biologically available P pools than SPM in the field, suggesting higher mobility of these pools in the field. These complementary results from field and field‐simulated laboratory erosion experiments provide unique insights into the composition of particulate matter under different hydrodynamic regimes in the river estuary.

Challenging Colonial Narratives: Nineteenth-Century Great Lakes Archaeology

Challenging Colonial Narratives: Nineteenth-Century Great Lakes Archaeology

The Susquehannocks: New Perspectives on Settlement and Cultural Identity

The Susquehannocks: New Perspectives on Settlement and Cultural Identity

Population Genomics and Conservation of Erigenia bulbosa (Apiaceae), an Edge-of-Range Species in Pennsylvania

Premise of research. Erigenia bulbosa, or the harbinger of spring, is one of the earliest-blooming wildflowers in eastern North America. As a spring ephemeral of forests and woodlands, it is a common species throughout the Midwest. In Pennsylvania, E. bulbosa exhibits an east-west disjunct distribution, where widespread western populations are contiguous with the midwestern range and a handful of smaller populations in the eastern part of the state are restricted to the lower Susquehanna River Valley. The relative isolation of the eastern populations suggests a possible conservation concern; the smaller, less connected populations may be threatened by fluctuations in size and the potential for low genetic diversity. As a consequence, establishing regulatory measures in Pennsylvania has been problematic because of disagreement regarding how to treat E. bulbosa during the Pennsylvania Department of Conservation and Natural Resources (PA DCNR) environmental review process. Currently, populations in the east are subject to regulation, while populations in the west are not.Methodology. To better understand the population genetics of the species, we coupled field assessments of E. bulbosa with a population genomics approach. We sampled multiple individuals from eight populations and generated a genotyping-by-sequencing data set of single-nucleotide polymorphisms (SNPs) that we used to calculate population statistics (genetic variation [FST], inbreeding coefficient [FIS], and heterozygosity), estimate population structure (sparse nonnegative matrix factorization), identify clusters of genetically related individuals (discriminant analysis of principal components), estimate a NeighborNet, look at signatures of isolation by distance (IBD), and detect population differentiation (analysis of molecular variance) using the filtered SNP data set.Pivotal results. Our data reveal structure in all populations and suggest genetic isolation between the groups of populations in the eastern and western portions of the state. Genetic groups identified using multivariate methods correspond to populations. Within populations, we estimate low levels of heterozygosity, a significant signature of IBD, and that most of the genetic variation we find is due to differences between populations.Conclusions. Our results indicate that any conservation measures undertaken by the PA DCNR should be applied evenly throughout Pennsylvania. We expect that most populations will continue to be threatened by land use and other development activities. This work illustrates the strength of academic and nonacademic partnerships in fostering outcomes that inform conservation activities for local species of concern.

The Susquehannocks: New Perspectives on Settlement and Cultural Identity ed. by Paul A. Raber

Reviewed by: The Susquehannocks: New Perspectives on Settlement and Cultural Identity ed. by Paul A. Raber Andrew Newman (bio) The Susquehannocks: New Perspectives on Settlement and Cultural Identity paul a. raber, ed. Pennsylvania State University Press, 2019 200 pp. The Susquehannocks were an Iroquoian people who, before and during the colonial era, inhabited the Susquehanna River watershed. The chronology, distribution, and extent of their settlements within this region, spanning present-day New York and Pennsylvania and the upper reaches of Chesapeake Bay, are research questions addressed by this edited volume. For readers of Early American Literature who are involved in Native American and Indigenous Studies, the Susquehannocks may have been just beyond the periphery of our field of inquiry, as neighbors of the Powhatan Confederacy, the Haudenosaunee, or the Delawares. A single passage in John Smith's account of his 1608 expedition from Jamestown, in his Generall Historie (1624), recounts his encounter with the "Sasquesahanocks," a "gyant-like people" (cited by Becker 160). They appear less explicitly in French, Swedish, and Dutch colonial accounts. Tragically, they have really only drawn the attention of early Americanist historians and literary scholars at their apparent moment of extinction in 1763, when the Paxton Boys infamously massacred the last "remnant community" (Raber 4) of Susquehannocks near Conestoga. So there is no present-day Susquehannock community that non-Native scholars might consult, collaborate with, and perhaps be accountable to. In the introduction to this volume, published in the Recent Research in Pennsylvania Archaeology series for which he is also the series editor, Paul Raber notes that given the dearth of sources, "exploration of the Susquehannocks has been left largely to archaeologists" (4). He suggests that in light of the unreliability of these textual records, it is perhaps better that way: he mentions a French Jesuit account from 1647 that presents what he demonstrates to be an impossibly high count of warriors for a Susquehannock village, concluding: "We are better off depending on archaeological evidence rather than putting much stock in rare documentary sources of dubious veracity" (5). The basis for this dismissal also illustrates how the questions that archaeologists bring to textual sources may be of little interest to literary scholars, and vice versa. Similarly, colonialist literary [End Page 612] scholars would find little of value to our own inquiries in the contributors' analyses of pottery sherds—their primary medium—and human bones. Nevertheless, although I am for the most part unqualified to evaluate the validity of their findings, I found The Susquehannocks to be illuminating as a sort of case study of a highly specialized community of inquiry. The Susquehannocks positions itself as an update on the twentiethcentury body of scholarship, whose summation was Barry Kent's Susquehanna's Indians (Pennsylvania Historical and Museum Commission, 1984). Accordingly, it announces a departure from the "culture history" model that characterized that era. As I understand it, this approach infers a group cultural identity on the basis of archaeological remains. In this case, pottery styles—"the fuel of culture history," according to April M. Beisaw (81)—may tell the story of the emergence of a "proto-Susquehannock" people, with ancestors in common with the northern Iroquois in the Upper Susquehanna River Valley, their migration and settlement in the Lower Susquehanna River Valley, their contacts with other Native American peoples and with colonists, and their demise during the colonial era. Some of the contributions depart more markedly from this model than others. The first of three parts in the volume is devoted to the first phase in this history, the sixteenth-century transition from the Upper to Lower Susquehanna Valley and perhaps from "Proto-" to "Susquehannock." In chapter 1, Jasmine Gollup points to the central research question of whether "the tribe left New York as culturally recognized Susquehannocks or if they formed their group identity during their journey south" (20). However, she demonstrates that this determination is complicated by a reassessment of the materials, insofar as the classification of the pottery is more indeterminate and inclusive than previous researchers have suggested. She therefore challenges the "idea of a monolithic Susquehannock culture reflected by a unique, identifiable, and culturally delineated set of materials" (21). Nevertheless, the subsequent chapter...

Balancing exploration, uncertainty and computational demands in many objective reservoir optimization

Abstract Reservoir operations are central to our ability to manage river basin systems serving conflicting multi-sectoral demands under increasingly uncertain futures. These challenges motivate the need for new solution strategies capable of effectively and efficiently discovering the multi-sectoral tradeoffs that are inherent to alternative reservoir operation policies. Evolutionary many-objective direct policy search (EMODPS) is gaining importance in this context due to its capability of addressing multiple objectives and its flexibility in incorporating multiple sources of uncertainties. This simulation-optimization framework has high potential for addressing the complexities of water resources management, and it can benefit from current advances in parallel computing and meta-heuristics. This study contributes a diagnostic assessment of state-of-the-art parallel strategies for the auto-adaptive Borg Multi Objective Evolutionary Algorithm (MOEA) to support EMODPS. Our analysis focuses on the Lower Susquehanna River Basin (LSRB) system where multiple sectoral demands from hydropower production, urban water supply, recreation and environmental flows need to be balanced. Using EMODPS with different parallel configurations of the Borg MOEA, we optimize operating policies over different size ensembles of synthetic streamflows and evaporation rates. As we increase the ensemble size, we increase the statistical fidelity of our objective function evaluations at the cost of higher computational demands. This study demonstrates how to overcome the mathematical and computational barriers associated with capturing uncertainties in stochastic multiobjective reservoir control optimization, where parallel algorithmic search serves to reduce the wall-clock time in discovering high quality representations of key operational tradeoffs. Our results show that emerging self-adaptive parallelization schemes exploiting cooperative search populations are crucial. Such strategies provide a promising new set of tools for effectively balancing exploration, uncertainty, and computational demands when using EMODPS.

River ice monitoring with MODIS: Application over Lower Susquehanna River

Spatially detailed characterization of the distribution, amount and timing of river ice is important for identifying and predicting potential ice hazards. Although information on the ice cover over inland water bodies is provided within MODIS snow products (MOD10 and MYD10), this information has little practical value for river ice monitoring. First, many rivers are not properly resolved in the MODIS land/water mask. Second, the cloud mask incorporated in the product is conservative and therefore results in reduced effective area coverage of the product. Third, the accuracy of the incorporated cloud mask (MOD35) depends on the particular setting and underlying land/water mask. The MODIS cloud mask is not suitable for this particular setting, if frequent ice observations are desired.In this study we present an alternative river ice monitoring algorithm for MODIS that identifies river ice both in cloud-free conditions and through some semitransparent clouds. As input the semitransparent cloud algorithm (STC) uses an improved land/water mask accurately delineating the river channel along with bands 4 and 7 data from the MODIS surface reflectance product. The algorithm was developed for the MODIS instrument and comprehensively tested with MODIS Aqua data over the Lower Susquehanna River for the 2014 winter season. It is shown that river ice cover retrievals made with STC are highly consistent with in situ observed ice processes, for both individual scenes and the overall winter period. Owing to a better-suited cloud masking algorithm, the new technique yields nearly twice as many usable river observations during the ice-bearing period as compared to the MODIS cloud cover product. The presented approach provides potential for more timely identification of river ice changes and hence more accurate prediction of ice-related hazards using MODIS data.

Conowingo Reservoir Sedimentation and Chesapeake Bay: State of the Science.

The Conowingo Reservoir is situated on the Susquehanna River, immediately upstream of Chesapeake Bay, the largest estuary in the United States. Sedimentation in the reservoir provides an unintended benefit to the bay by preventing sediments, organic matter, and nutrients from entering the bay. The sediment storage capacity of the reservoir is nearly exhausted, however, and the resulting increase in loading of sediments and associated materials is a potential threat to Chesapeake Bay water quality. In response to this threat, the Lower Susquehanna River Watershed Assessment was conducted. The assessment indicates the reservoir is in a state of "dynamic equilibrium" in which sediment loads from the upstream watershed to the reservoir are balanced by sediments leaving the reservoir. Increased sediment loads are not a threat to bay water quality. Increased loads of associated organic matter and nutrients are, however, detrimental. Bottom-water dissolved oxygen declines of 0.1 to 0.2 g m are projected as a result of organic matter oxidation and enhanced eutrophication. The decline is small relative to normal variations but results in violations of standards enforced in a recently enacted total maximum daily load. Enhanced reductions in nutrient loads from the watershed are recommended to offset the decline in water quality caused by diminished retention in the reservoir. The assessment exposed several knowledge gaps that require additional investigation, including the potential for increased loading at flows below the threshold for reservoir scour and the nature and reactivity of organic matter and nutrients scoured from the reservoir bottom.

A diagnostic assessment of evolutionary algorithms for multi-objective surface water reservoir control

Globally, the pressures of expanding populations, climate change, and increased energy demands are motivating significant investments in re-operationalizing existing reservoirs or designing operating policies for new ones. These challenges require an understanding of the tradeoffs that emerge across the complex suite of multi-sector demands in river basin systems. This study benchmarks our current capabilities to use Evolutionary Multi-Objective Direct Policy Search (EMODPS), a decision analytic framework in which reservoirs’ candidate operating policies are represented using parameterized global approximators (e.g., radial basis functions) then those parameterized functions are optimized using multi-objective evolutionary algorithms to discover the Pareto approximate operating policies. We contribute a comprehensive diagnostic assessment of modern MOEAs’ abilities to support EMODPS using the Conowingo reservoir in the Lower Susquehanna River Basin, Pennsylvania, USA. Our diagnostic results highlight that EMODPS can be very challenging for some modern MOEAs and that epsilon dominance, time-continuation, and auto-adaptive search are helpful for attaining high levels of performance. The ϵ-MOEA, the auto-adaptive Borg MOEA, and ϵ-NSGAII all yielded superior results for the six-objective Lower Susquehanna benchmarking test case. The top algorithms show low sensitivity to different MOEA parameterization choices and high algorithmic reliability in attaining consistent results for different random MOEA trials. Overall, EMODPS poses a promising method for discovering key reservoir management tradeoffs; however algorithmic choice remains a key concern for problems of increasing complexity.

Spotlight on Sediments: How is the Chesapeake Bay affected by storm flows from the Conowingo Reservoir?

Spotlight on Sediments: How is the Chesapeake Bay affected by storm flows from the Conowingo Reservoir?

The spread of zebra mussel (Dreissena polymorpha) from the lower Susquehanna River into the upper Chesapeake Bay, Maryland, USA

The invasion of North American waters by Dreissena polymorpha (zebra mussel) and its subsequent ecological impacts has been well documented. Their spread continues to new states and watersheds despite a wealth of research and outreach campaigns, albeit at a slowed pace. We describe the spread and proliferation of zebra mussel into one of the more recently invaded states, Maryland, USA. Veliger counts and fixed hard surface monitoring suggest that a population is established within the lower Susquehanna River to the head of the Chesapeake Bay. A relatively narrow tidal-freshwater habitat envelope with suitable salinity may serve to restrict zebra mussel dispersal further downstream. Dispersal to other freshwater habitats in Maryland seems likely as the current area of infestation is highly used by commercial and recreational boaters, although regulations are in place that could help slow or prevent spread. Successful invasion will likely be a function of water chemistry, which may be limiting in some parts of the state.

A Simulation-Based Approach for Evaluating Cost and Performance of a Sediment Removal and Processing System for the Lower Susquehanna River Dams

A series of three major dams and reservoirs located along the Lower Susquehanna River have historically acted as a system of sediment and nutrient pollution traps. However, episodic pulses of these pollution loads are released following short-term extreme storm events, affecting subaquatic vegetation, benthic organisms, and the overall water quality in the Upper Chesapeake Bay. In addition, all three reservoirs have reached a state of near maximum storage capacity termed as dynamic equilibrium. Based on prior research, this study seeks to reduce the sediment buildup behind the dams through a sediment removal and processing operation, and thereby reduce the ecological impact of major storms. A set of scour performance curves derived from a regression analysis, and a stochastic lifecycle cost model were used to evaluate the sediment scouring reduction and economic feasibility of three processing alternatives: Plasma Vitrification, Cement-Lock, and Quarry/Landfill, and three removal amount cases: Nominal, Moderate, and Maximum. Since the scour performance curves treat the dams as static, a fluid system dynamics model was used to determine if the dynamic interaction between the capacitance of the dams during major scouring events is negligible or considerable. A utility vs. cost analysis factoring in time, performance, and suitability of the alternatives indicates that a Cement-Lock processing plant at moderate dredging for the Safe Harbor and Conowingo Dams is the most cost-performance effective solution.

Many‐objective reservoir policy identification and refinement to reduce policy inertia and myopia in water management

AbstractThis study contributes a decision analytic framework to overcome policy inertia and myopia in complex river basin management contexts. The framework combines reservoir policy identification, many‐objective optimization under uncertainty, and visual analytics to characterize current operations and discover key trade‐offs between alternative policies for balancing competing demands and system uncertainties. The approach is demonstrated on the Conowingo Dam, located within the Lower Susquehanna River, USA. The Lower Susquehanna River is an interstate water body that has been subject to intensive water management efforts due to competing demands from urban water supply, atomic power plant cooling, hydropower production, and federally regulated environmental flows. We have identified a baseline operating policy for the Conowingo Dam that closely reproduces the dynamics of current releases and flows for the Lower Susquehanna and thus can be used to represent the preferences structure guiding current operations. Starting from this baseline policy, our proposed decision analytic framework then combines evolutionary many‐objective optimization with visual analytics to discover new operating policies that better balance the trade‐offs within the Lower Susquehanna. Our results confirm that the baseline operating policy, which only considers deterministic historical inflows, significantly overestimates the system's reliability in meeting the reservoir's competing demands. Our proposed framework removes this bias by successfully identifying alternative reservoir policies that are more robust to hydroclimatic uncertainties while also better addressing the trade‐offs across the Conowingo Dam's multisector services.

Improving the protection of aquatic ecosystems by dynamically constraining reservoir operation via direct policy conditioning

Water management problems generally involve conflicting and non-commensurable objectives. Assuming a centralized perspective at the system-level, the set of Pareto-optimal alternatives represents the ideal solution of most of the problems. Yet, in typical real-world applications, only a few primary objectives are explicitly considered, taking precedence over all other concerns. These remaining concerns are then internalized as static constraints within the problem's formulation. This approach yields to solutions that fail to explore the full set of objectives tradeoffs. In this paper, we propose a novel method, called direct policy conditioning (DPC), that combines direct policy search, multi-objective evolutionary algorithms, and input variable selection to design dynamic constraints that change according to the current system conditions. The method is demonstrated for the management problem of the Conowingo Dam, located within the Lower Susquehanna River, USA. The DPC method is used to identify environmental protection mechanisms and is contrasted with traditional static constraints defining minimum environmental flow requirements. Results show that the DPC method identifies a set of dynamically constrained control policies that overcome the current alternatives based on the minimum environmental flow constraint, in terms of environmental protection but also of the primary objectives.

Long-term seasonal trends of nitrogen, phosphorus, and suspended sediment load from the non-tidal Susquehanna River Basin to Chesapeake Bay

Reduction of nitrogen (N), phosphorus (P), and suspended sediment (SS) load has been a principal focus of Chesapeake Bay Watershed management for decades. To evaluate the progress of management actions in the Bay's largest tributary, the Susquehanna River, we analyzed the long-term seasonal trends of flow-normalized N, P, and SS load over the last two to three decades, both above and below the Lower Susquehanna River Reservoir System. Our results indicate that annual and decadal-scale trends of nutrient and sediment load generally followed similar patterns in all four seasons, implying that changes in watershed function and land use had similar impacts on nutrient and sediment load at all times of the year. Above the reservoir system, the combined loads from the Marietta and Conestoga Stations indicate general trends of N, P, and SS reduction in the Susquehanna River Basin, which can most likely be attributed to a suite of management actions on point, agricultural, and stormwater sources. In contrast, upward trends of SS and particulate-associated P and N were generally observed below the Conowingo Reservoir since the mid-1990s. Our analyses suggest that (1) the reservoirs' capacity to trap these materials has been diminishing over the past two to three decades, and especially so for SS and P since the mid-1990s, and that (2) the Conowingo Reservoir has already neared its sediment storage capacity. These changes in reservoir performance will pose significant new kinds of challenges to attainment of total maximum daily load goals for the Susquehanna River Basin, and particularly if also accompanied by increases in storm frequency and intensity due to climate change. Accordingly, the reservoir issue may need to be factored into the proper establishment of regulatory load requirements and the development of watershed implementation plans.

Farm Boundaries as Agroecological Systems

South-central Pennsylvania, framed by the great folds of the Appalachians to the north and west, by the Mason-Dixon Line to the south, and by the rise of hills that bound the lower Susquehanna River to the east, was claimed by settler-farmers of western European descent during the early and mid-eighteenth century. They utilized river and stream valleys to gain access to the fertile lowlands and rich uplands of the region, following in the steps of surveyors to mark farm boundaries with timber fences cut from the cloak of forest. The social and ecological imprint of these boundary structures has endured for hundreds of years.

Driftwood dropstones in Middle Miocene Climate Optimum shallow marine strata (Calvert Cliffs, Maryland Coastal Plain): Erratic pebbles no certain proxy for cold climate

Sparse lithic erratics (pebbles to cobbles) sampled from three shallow marine strata deposited during the Middle Miocene Climate Optimum (MMCO, ca. 16–14Ma) along the western Atlantic margin (exposed in the Calvert Cliffs, Maryland) suggest transport and deposition not from ice but from the roots of trees uprooted during floods and carried out to sea. Evidence for driftwood transport includes carbonized wood in the same strata. More than half the ca. 225 erratics were quarried in the largely metamorphic Piedmont province (including a few from the Port Deposit Gneiss, still outcropping on the lower Susquehanna River).The lowest sampled bed (Parker Creek Bone Bed) is assigned to the ca. 15.7–15.5Ma peak warmth of the MMCO, which we attribute in part to CO2 from the coevally erupted Grande Ronde flood basalts (GRFB), the peak effusiveness episode of the Columbia River Flood Basalts (CRFB) The three sampled beds predate the ca. 13.9Ma Antarctic cryosphere expansion, which may be recorded in the Calvert Cliffs by a unique buried channel.

Diet of Northern Map Turtles (Graptemys geographica): Relationship to Sexual Dimorphism and Potential Impacts of an Altered River System in Maryland

Last recorded in Maryland in the early 1990’s, the Northern Map Turtle (Graptemys geographica) is listed as state endangered and is currently only known in the lower Susquehanna River drainage. This river is divided by a hydroelectric dam, used for recreation, and has increasing shoreline development, all of which may negatively impact this population. Knowing this population’s diet and if alterations to the river affect their prey base is important to understanding the species’ current status. Northern Map Turtles are mostly molluscivorous but will also consume other invertebrates. Studies have shown that map turtle species will subsidize their diet with invasive mussels, potentially decreasing dietary diversity. The Susquehanna River contains both native and nonnative mollusks species. Recently, Zebra Mussels (Dreissena polymorpha), an invasive species known to have large effects on aquatic food webs and nutrient cycling, have been found in the lower Susquehanna. Given the absence of basic data on Northern Map Turtle diet in Maryland, fecal samples of 32 turtles were examined. Three operational taxanomic units predominated across samples: gastropods, trichopteran larvae, and Corbicula fluminea. Pronounced sexual differences occurred for these taxa, as adult males (n=14) fed primarily on trichoptera, a small unidentified gastropod species (~2 mm), and Corbicula sp. while the females (n=18) fed almost exclusively on Pleurocerid snails. This research has provided us baseline data on Northern Map Turtle diet and monitoring of the diet will allow us to not only understand impacts of dam operations on composition of their prey base, but the potential shift to zebra mussels as well.

Diet of Northern Map Turtles (Graptemys geographica): Relationship to Sexual Dimorphism and Potential Impacts of an Altered River System in Maryland

AbstractLast recorded in Maryland in the early 1990’s, the Northern Map Turtle (Graptemys geographica) is listed as state endangered and is currently only known in the lower Susquehanna River drainage. This river is divided by a hydroelectric dam, used for recreation, and has increasing shoreline development, all of which may negatively impact this population. Knowing this population’s diet and if alterations to the river affect their prey base is important to understanding the species’ current status. Northern Map Turtles are mostly molluscivorous but will also consume other invertebrates. Studies have shown that map turtle species will subsidize their diet with invasive mussels, potentially decreasing dietary diversity. The Susquehanna River contains both native and nonnative mollusks species. Recently, Zebra Mussels (Dreissena polymorpha), an invasive species known to have large effects on aquatic food webs and nutrient cycling, have been found in the lower Susquehanna. Given the absence of basic data on Northern Map Turtle diet in Maryland, fecal samples of 32 turtles were examined. Three operational taxanomic units predominated across samples: gastropods, trichopteran larvae, and Corbicula fluminea. Pronounced sexual differences occurred for these taxa, as adult males (n=14) fed primarily on trichoptera, a small unidentified gastropod species (~2 mm), and Corbicula sp. while the females (n=18) fed almost exclusively on Pleurocerid snails. This research has provided us baseline data on Northern Map Turtle diet and monitoring of the diet will allow us to not only understand impacts of dam operations on composition of their prey base, but the potential shift to zebra mussels as well.