Papers by Beverly Johnson
To begin, I would like to thank the most important person for this process, my advisor, Beverly J... more To begin, I would like to thank the most important person for this process, my advisor, Beverly Johnson. Thank you for guiding me through not only my senior thesis but my senior year. If not for her knowledge both on the subject and writing, this work would not be possible. Further, I would like to thank Philip Dostie for guiding me through the lab work and helping to refine the methods used for the completion of this work. Phil was always a calming presence in even the most hectic of field days.
Beverly J Johnson, Department of Geology, Bates College, Lewiston ME, 04240; [email protected] C... more Beverly J Johnson, Department of Geology, Bates College, Lewiston ME, 04240; [email protected] Curtis Bohlen, Casco Bay Estuary Partnership, Portland ME 04140; [email protected] Cailene Gunn, Department of Geology, Bates College, Lewiston ME, 04240; [email protected] Erin Beirne, Department of Geology, Bates College, Lewiston ME, 04240; [email protected] Colin Barry, Department of Geology, Bates College, Lewiston ME, 04240; [email protected] Matthew Craig, Casco Bay Estuary Partnership, Portland ME 04140; [email protected] Phillip Dostie, Department of Geology, Bates College, Lewiston ME, 04240; [email protected]
Anadromous fish, such as alewives (Alosa pseudoharengus) can provide an important link between co... more Anadromous fish, such as alewives (Alosa pseudoharengus) can provide an important link between coastal watersheds and the Atlantic Ocean along the Gulf of Maine. Alewives contribute marine-derived nutrients (MDN) in the form of nitrogen to freshwater lakes via excretion and mortality as they migrate upstream during spawning season. Previous attempts to detect MDN in the sedimentary record have provided equivocal results. Freshwater biota or the size of current alewife migrations may have a significant effect on the sedimentary MDN signal. The focus of this project is to determine the degree to which MDN were imported into Nequasset Lake, Woolwich Maine. These data represent the initial findings of an expanded, multi-institutional, multi-year study currently underway. The Nequasset Lake watershed covers an area of ~50 square kilometers and provides drinking water to the city of Bath and three other communities in Maine. Every spring, alewives return to Nequasset Lake to spawn, accessing the lake through a fish ladder adjacent to the water control dam. In April and May 2012, alewife counts were performed at the top of the fish ladder by volunteers of Trout Unlimited and Kennebec Estuary Land Trust. Water samples were collected from the top of the fish ladder, and from the 4 major stream inlets, and analyzed for nutrient concentrations (TDN, NO 3-, NH 4 +) to construct a nitrogen budget. Additional samples were collected for δ 15 N of water NO 3 analysis from April to June to trace marine-derived nitrogen from the alewives in the lake. δ 15 N of water NO 3 − (+1.6 ‰) suggests the only detectable MDN signal is at the top of Nequasset Dam. However, NH 4 + concentrations may suggest Nequasset Brook and Sucker Brook be targeted for restoration management. Nutrient cycling models shows that the implications of MDN may be insignificant because nutrient loading from the 2012 migration only accounts for approximately 1% of the total nitrogen inputs.
Earth's Future, 2016
A mixing model derived from first principles describes the bulk density (BD) of intertidal wetlan... more A mixing model derived from first principles describes the bulk density (BD) of intertidal wetland sediments as a function of loss on ignition (LOI). The model assumes that the bulk volume of sediment equates to the sum of self-packing volumes of organic and mineral components or BD = 1/[LOI/k 1 + (1-LOI)/k 2 ], where k 1 and k 2 are the self-packing densities of the pure organic and inorganic components, respectively. The model explained 78% of the variability in total BD when fitted to 5075 measurements drawn from 33 wetlands distributed around the conterminous United States. The values of k 1 and k 2 were estimated to be 0.085 ± 0.0007 g cm −3 and 1.99 ± 0.028 g cm −3 , respectively. Based on the fitted organic density (k 1) and constrained by primary production, the model suggests that the maximum steady state accretion arising from the sequestration of refractory organic matter is ≤ 0.3 cm yr −1. Thus, tidal peatlands are unlikely to indefinitely survive a higher rate of sea-level rise in the absence of a significant source of mineral sediment. Application of k 2 to a mineral sediment load typical of East and eastern Gulf Coast estuaries gives a vertical accretion rate from inorganic sediment of 0.2 cm yr −1. Total steady state accretion is the sum of the parts and therefore should not be greater than 0.5 cm yr −1 under the assumptions of the model. Accretion rates could deviate from this value depending on variation in plant productivity, root:shoot ratio, suspended sediment concentration, sediment-capture efficiency, and episodic events.
Frontiers in Marine Science, 2015
Tight coupling between pelagic and benthic communities is accepted as a general principle on Arct... more Tight coupling between pelagic and benthic communities is accepted as a general principle on Arctic shelves. Whereas this paradigm has been useful for guiding ecological research, it has perhaps led to a disproportionate focus on POM and ice algae as the most likely sources of carbon for the benthic food web. Arctic shelves are complex systems, including banks, fjords, and trough systems up to 350 m or more in depth. In this stable-isotope study, 13 different potential carbon sources were analyzed for their contribution to the food-webs of Isfjorden, Svalbard. A mixing model with herbivorous copepods and grazing sea urchins as end-members was applied to determine the relative contributions of the most likely carbon sources to pelagic and benthic taxa. Most taxa from the benthos feed on a broad mixture of POM and macroalgal detritus, even at depths down to 410 m. Most suspension-feeding bivalves had isotopic signals consistent with more than a 50% contribution from kelps and rockweeds. In contrast, nearly all pelagic species had diets consistent with an overwhelming contribution of pelagic POM. These results indicate that macroalgal detritus can contribute significantly to near-shore Arctic food-webs, a trophic link that may increase if macroalgae increase in the Arctic as predicted. These weaker quantitative links between pelagic and benthic components of coastal systems highlight the need for thorough sampling of potential carbon-baselines in food-web studies. A large detrital-carbon component in diets of Arctic benthos may dampen the impacts of strong seasonality in polar primary producers, leading to higher ecosystem resilience, but may also result in lower secondary productivity.
40 3 general ConsIderatIons Once the details of the project and sampling requirements have been d... more 40 3 general ConsIderatIons Once the details of the project and sampling requirements have been determined, field sampling of the ecosystem carbon pools can begin. Field techniques for measuring the aboveground and belowground living biomass in different ecosystems vary between mangroves, tidal salt marshes, and seagrass meadows and are described in the ecosystem specific sections of Chapter 4. however, the techniques for sampling carbon contained in the soils, discussed in this chapter, are generally applicable to all three ecosystems. It is important to note that belowground carbon is sometimes referred to as sediment carbon or as soil carbon. For the purposes of this document, we use these terms interchangeably. belowground carbon pools usually termed soil carbon—dominated largely by the living and decomposing roots, rhizomes, and leaf litter—are usually the largest pool in vegetated coastal ecosystems and their measurement is critical for determining long-term changes in carbon ...
Organic Geochemistry, 2007
A 3.1 meter sediment core was analyzed for stable carbon isotope composition of organic matter an... more A 3.1 meter sediment core was analyzed for stable carbon isotope composition of organic matter and higher plant leaf wax (HPLW) lipid biomarkers to determine Holocene shifts in C 3 (higher high marsh) and C 4 (low and/or high marsh) plant deposition at the Sprague River Salt Marsh, Phippsburg, Maine. The carbon isotope composition of the bulk sediment and the HPLW parallel each other throughout most of the core, suggesting that terrestrial plants are an important source of organic matter to the sediments, and diagenetic alteration of the bulk sediments is minimal. The current salt marsh began to form 2500 cal yr BP. Low and/or high C 4 marsh plants dominated deposition at 2000 cal yr BP, 700 cal yr BP, and for the last 200 cal yr BP. Expansion of higher high marsh C 3 plants occurred at 1300 and 600 cal yr BP. These major vegetation shifts result from a combination of changes in relative sea-level rise and sediment accumulation rates. Average annual carbon sequestration rates for the last 2500 years approximate 40 g C yr-1 m-2 , and are in strong agreement with other values published for the Gulf of Maine. Given that Maine salt marshes cover an area of ~79 km 2 , they represent an important component of the terrestrial carbon sink. More detailed isotopic and age records from a network of sediment cores at Sprague Marsh are needed to truly evaluate the long term changes in salt marsh plant communities and the impact of more recent human activity, including global warming, on salt marsh vegetation.
Marine Pollution Bulletin, 2009
Identifying patterns and drivers of natural variability in populations is necessary to gauge pote... more Identifying patterns and drivers of natural variability in populations is necessary to gauge potential effects of climatic change and the expected increases in commercial activities in the Arctic on communities and ecosystems. We analyzed growth rates and shell geochemistry of the circumpolar Greenland smooth cockle, Serripes groenlandicus, from the southern Barents Sea over almost 70 years between 1882 and 1968. The datasets were calibrated via annually-deposited growth lines, and growth, stable isotope ( 18 O, 13 C), and trace elemental (Mg, Sr, Ba, Mn) patterns were linked to environmental variations on weekly to decadal scales. Standardized growth indices revealed an oscillatory growth pattern with a multi-year periodicity, which was inversely related to the North Atlantic Oscillation Index (NAO), and positively related to local river discharge. Up to 60% of the annual variability in the Ba/Ca could be explained by variations in river discharge at the site closest to the rivers, but the relationship disappeared at a more distant location. Patterns of 18 O, 13 C, and Sr/Ca together provide evidence that bivalve growth ceases at elevated temperatures during the fall and recommences at the coldest temperatures in the early spring, with the implication that food, rather than temperature, is the primary driver of bivalve growth. The multi-proxy approach of combining the annually integrated information from the growth results and higher resolution geochemical results yielded a robust interpretation of biophysical coupling in the region over temporal and spatial scales. We thus demonstrate that sclerochronological proxies can be useful retrospective analytical tools for establishing a baseline of ecosystem variability in assessing potential combined impacts of climatic change and increasing commercial activities on Arctic communities.
Marine Ecology Progress Series, 2006
Marine Ecology Progress Series, 2008
Photosynthetic pigments and stable isotopes from suspended particulate organic matter (POM) and s... more Photosynthetic pigments and stable isotopes from suspended particulate organic matter (POM) and surface sediment of the southeast Beaufort Sea, including the Mackenzie shelf and the Amundsen Gulf, were studied during fall 2003 and summer 2004. This multiple-biomarker approach led to an increased understanding of spatial and seasonal variation in pelagic-benthic coupling, as these 2 biomarkers reflect inherent differences in the time scales over which they integrate. Sedimentary pigments highlighted the importance of local water-column production as a source of phytodetrital inputs to the sea floor. In the summer, the dominance of diatoms in the water column was reflected in the sediment by the abundance of fucoxanthin, a pigment broadly found in diatoms. In the fall, a more variable suite of sedimentary pigments reflected inputs from smaller cells such as haptophytes and prasinophytes. While stable isotope composition of the POM showed seasonal variations, i.e. a more marine signature in the summer and a more terrestrial signature in the fall, sedimentary stable isotopes revealed geographical differences. Sediment on the Mackenzie shelf suggested a terrestrial source of organic matter, while in the Amundsen Gulf, sources of organic matter had a more marine origin. Finally, benthic community compositions and activity (sediment carbon demand) seemed affected by both spatial and seasonal variations in organic matter inputs to the benthos. This study stresses the importance of both physical factors (water depth and riverine inputs) and biological production (primary productivity and secondary production) in the determination of organic matter inputs to the benthos.
Geochimica et Cosmochimica Acta, 2019
Developing high resolution, well-dated marine proxies of environmental, climatic, and oceanograph... more Developing high resolution, well-dated marine proxies of environmental, climatic, and oceanographic conditions is critical in order to advance our understanding of the ocean's role in the global climate system. While some work has investigated bulk and compound specific stable nitrogen isotopes (δ15N) in bivalve shells as proxies for environmental variability, the small concentrations of nitrogen found in the organic matrix of the shell calcium carbonate (CaCO3) makes developing high resolution records challenging. This study investigates the potential of using the bulk and amino acid δ15N of bivalve periostracum, the protein layer on the outside of the shell, as a proxy archive of nitrogen cycling processes and water source variability. Bulk δ15N values were measured on the periostracum, aragonitic CaCO3, and adductor muscle of Arctica islandicashells collected in the Gulf of Maine. Increased variability of isotopic values across growth lines compared to along growth lines support mechanistic reasoning based on growth processes that periostracum is recording changes in δ15N over the course of the clam's lifetime (up to 500 years). In addition, the statistically significant relationship between periostracum δ15N and contemporaneous carbonate δ15N of the same shell (r= 0.82, p Compound specific δ15N analyses of the periostracum of A. islandica shells were used to determine that the calculated trophic position of the clams in this study (1.4±0.4) did not change significantly between 1783 and 1997. Phenylalanine δ15N values over the last 70 years show similar trends to that of the bulk record, suggesting that changes in bulk δ15N of that time period are related to changes in baseline δ15N. Periostracum δ15N values from shells collected in the western Gulf of Maine have decreased by ∼1‰ since the mid-1920s. This trend (-0.008‰/year) is not statistically different from the trend of previously published δ15N values of deep-sea corals from the entrance to the Gulf of Maine over the same time period. This coral record has been shown to indicate a shift in water mass source to the region and therefore the similarity between the two records suggest that changes in periostracum δ15N values are reflecting broader North Atlantic hydrographic changes. Our study introduces a new, high-resolution and absolutely dated paleoceanographic proxy of baseline δ15N, presenting the opportunity for future reconstructions of aspects of nitrogen cycling and water source changes in the global oceans.
The Holocene, 2005
Stable carbon isotopes in emu eggshell (EES) reflect emu diets and consequently the vegetation av... more Stable carbon isotopes in emu eggshell (EES) reflect emu diets and consequently the vegetation available for food sources. At Lake Eyre, South Australia, isotopic data suggest that there has been a rapid and dramatic change in vegetation at some point over the last 200 years when compared with the rest of the Holocene. The proportion of C4 plants in emu diets has been reduced by approximately 20% in response to an overall shift in C4/C3 biomass at Lake Eyre. Isotopic measurement of the dominant plants at Lake Eyre indicate that the C4 plants are almost entirely comprised of grasses and some chenopods and the C3 plants are comprised of the dominant chenopods, shrubs, trees and forbs. We surmise that the -20% reduction in C4 plant biomass reflects landscape degradation and loss of C4 grasses resulting from a combination of effects, including overgrazing by both introduced (e.g., sheep, cattle and rabbits) and native (e.g., kangaroos) animals, increasing drought and a change in fire re...
New England Intercollegiate Geological Conference 2017
The photo is from Rumford Whitecap more or less in the middle of the region covered by this guide... more The photo is from Rumford Whitecap more or less in the middle of the region covered by this guidebook and itself part of the subject of trip B5 (Spigel et al, this volume; photo credit Eusden). The back cover is a collage of author-submitted representative images for the trips that define this year's NEIGC conference. The NEIGC logo is courtesy of Lindley Hanson. The field guides for this Conference are offered under the terms of the Creative Commons Attribution-Non-Commercial 3.0 Unported All field trips are available for free download through the Bates College Repository SCARAB (scarab.bates.edu/neigc2017). DISCLAIMER Before visiting any of the sites described in New England Intercollegiate Geological Conference guidebooks, you must obtain permission from the current landowners. Landowners only granted permission to visit these sites to the organizers of the original trips for the designated dates of the conference. It is your responsibility to obtain permission for your visit. Be aware that this permission may not be granted. Especially when using older NEIGC guidebooks, note that locations may have changed drastically. Likewise, geological interpretations may differ from current understandings. Please respect any trip stops designated as "no hammers", "no collecting" or the like. Consider possible hazards and use appropriate caution and safety equipment. NEIGC and the hosts of these online guidebooks are not responsible for the use or misuse of the guidebooks.
40 3 general ConsIderatIons Once the details of the project and sampling requirements have been d... more 40 3 general ConsIderatIons Once the details of the project and sampling requirements have been determined, field sampling of the ecosystem carbon pools can begin. Field techniques for measuring the aboveground and belowground living biomass in different ecosystems vary between mangroves, tidal salt marshes, and seagrass meadows and are described in the ecosystem specific sections of Chapter 4. however, the techniques for sampling carbon contained in the soils, discussed in this chapter, are generally applicable to all three ecosystems. It is important to note that belowground carbon is sometimes referred to as sediment carbon or as soil carbon. For the purposes of this document, we use these terms interchangeably. belowground carbon pools usually termed soil carbon—dominated largely by the living and decomposing roots, rhizomes, and leaf litter—are usually the largest pool in vegetated coastal ecosystems and their measurement is critical for determining long-term changes in carbon ...
Organic Geochemistry, 1997
Oecologia, 2005
The stable isotopic composition (d 13 C) of sediments from lakes are frequently analyzed to recon... more The stable isotopic composition (d 13 C) of sediments from lakes are frequently analyzed to reconstruct the proportion of the regional vegetation that used either the C 3 or C 4 photosynthetic pathways, often without conducting a detailed survey of the current local vegetation. We performed a study on the modern vegetation composition within the Wolfe Creek Meteorite Crater to complement our future paleoecological investigation of the crater. A bull's-eye pattern exists where C 4 grasses dominate an outer ring and salt tolerant species, including shrubs, herbs, chenopods, and halophytic algae, dominate the inner pan of the crater. The ecotone between the inner and outer zones is narrow and occupied by tall (>7 m) Acacia ampliceps, with some C 4 grasses in the understory. Along with the highest water table and most saline soils the center of the crater has C 3 plants present with the highest d 13 C and d 15 N values. The range of d 13 C and d 15 N values from the analysis of surface soil organic matter (OM) was much smaller compared with the range of values from plant materials implying that either: (1) the current plant OM has not yet been integrated into the soils, or (2) processes within the soil have acted to homogenize isotopic variability within the crater. The application of a two end member mixing model to calculate %C 4 and %C 3 biomass from the d 13 C of surface soil OM was complicated by: (1) the crater containing both a dry habitat with C 4 grasses and a central pan with C 4 halophytic plants and, (2) the large variation in the d 13 C of the plants and soil OM.
Geochimica et Cosmochimica Acta, 1998
An isotopic study of modern ostrich eggshell (OES) is presented as a calibration for terrestrial ... more An isotopic study of modern ostrich eggshell (OES) is presented as a calibration for terrestrial paleoenvironmental applications. The stable carbon and nitrogen isotope fractionations of OES were determined for various organic fractions of eggshell by measuring the isotopic ratios of modern OES samples collected from controlled settings (i.e., zoos and farms) and corresponding ostrich diet. These fractionations were used to evaluate the relationship between the isotope composition of OES laid by free-range birds living in South Africa and their environment. The carbon isotope composition of the total organic and inorganic fractions of OES were enriched by 2 and 16‰, respectively, relative to the diet. In natural settings, the ␦ 13 C values of both the organic and inorganic fractions of OES reflected that of ambient vegetation, with a noted dietary preference for C 3 plants. The nitrogen isotope composition of the total organic fraction of OES was 3‰ enriched relative to the diet, and varied inversely with mean annual precipitation (MAP) in natural settings. A decrease in MAP of 100 mm was accompanied by an increase in ␦ 15 N values of approximately 1‰. The oxygen isotope composition of the inorganic fraction of the OES varied linearly with that of the drinking water in controlled settings. However, in natural settings, the ␦ 18 O of OES values were highly variable and are thought to be controlled primarily by the ␦ 18 O of ingested plant leaf-water. The stability of the isotopic signal in the organic fraction of OES through geologic time was evaluated through a series of heating experiments. The ␦ 13 C and ␦ 15 N values of the total organic fraction of heated OES increased by less than 0.6 and 0.2‰ for carbon and nitrogen, respectively, in spite of extensive diagenetic alteration and changes in the amino acid composition of the samples. The results of this study indicate that the stable carbon and nitrogen isotope composition of OES is relatively stable under the experimental conditions used and may be used to derive a plethora of paleoenvironmental information, including changes in C 3 and C 4 vegetation and paleorainfall estimates.
Palaeogeography, Palaeoclimatology, Palaeoecology, 1997
The stable carbon and nitrogen isotopes from organic compounds, and stable oxygen and carbon isot... more The stable carbon and nitrogen isotopes from organic compounds, and stable oxygen and carbon isotopes from inorganic carbonate in modern and fossil ostrich eggshell (OES) at Equus Cave, South Africa, were used to determine relative changes in C3 and C4 vegetation, rainfall, and temperature throughout the last 17 ka. Amino acid racemization and three new radiocarbon dates were used to assign ages to the individual OES fragments analyzed for stable isotopes, and to evaluate the stratigraphic integrity of the samples. The amino acid racemization and radiocarbon data indicate that most of the OES fragments are not in correct stratigraphic context, and may have been upwardly and downwardly mixed; thus, each fragment was placed in chronological sequence using radiocarbon-calibrated amino acid racemization. The stable carbon isotope data from the fossil OES do not change systematically through the last 17 ka. The ostriches primarily consumed C3 plants (between 70% and 90%), and smaller quantities of C4 plants (between 30% and 10%), indicating that a mixture of C3 and C4 plants has been in the vicinity of Equus Cave for the last 17 ka. Stable nitrogen isotope data from OES indicate that at 17 ka, mean annual precipitation (MAP) was at a minimum (190+50 mm/yr), increased steadily to modern values by 6 ka (600+ 150 mm/yr), and remained relatively unchanged until present. Stable oxygen isotope data coupled with nitrogen isotope data indicate that paleotemperatures were at a minimum between 14 and 17 ka, and reached their maximum in the latest Holocene. This study demonstrates the plethora of paleoenvironmental information that can be derived from analysis of three different stable isotopes (carbon, nitrogen, and oxygen) in the same sample-type (OES), and presents a new tool with wide applicability for reconstructing paleoenvironments in semi-arid and arid regions of Africa. © 1997 Elsevier Science B.V.
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Papers by Beverly Johnson