Current Research Projects

Water Quality and Biological Diversity Along an Urban Gradient
CO-PIs (Worcester State): Diana Sharpe, Allison Dunn, William Hansen, Meghna Dilip

From https://www.worcester.edu/stem-center/stem-center/aisiku-interdisciplinary-stem-research-team-initiative/: "Land-use change, and in particular, urban development, can strongly impact the health and biodiversity of freshwater ecosystems. This project examined temporal and spatial variability in water quality and biodiversity in the Tatnuck Brook watershed along an urbanization gradient. We measured a variety of land-use, physiochemical and biological metrics at 10 sites around Cooks, Patch, and Coes Reservoirs and their tributaries over the course of seven months (May to Nov 2022). Our more than 3000 individual data points on water quality preliminarily show that some aspects of water quality (conductivity, nitrates, ammonia) appear to be associated with land use dynamics, while other aspects are controlled by other factors.  Data on fish and macroinvertebrate community composition are still being collected, but analyses will focus on disentangling the relative importance of land use and water quality variables on the diversity and abundance of taxa, and on examining how proportions of ecologically-sensitive taxa vary along this urbanization gradient.

This project provided 4 undergraduate students with paid summer field experience, and 10 undergraduate students with independent study projects for Fall 2022. Throughout this project, we closely collaborated with academic, municipal, nonprofit, and community groups and are working to summarize the data to provide our partners with usable, actionable data on the sources of water quality impacts in this watershed."

Quantifying spatial and temporal variability in coastal sedimentation to improve models of tidal marsh response to sea level rise
Postdoc committee: Julie Lockwood, Rick Lathrop, Bob Kopp, Lisa Auermuller

As a Postdoctoral Associate at Rutgers University, I worked with an interdisciplinary group of geologists, ecologists, and stakeholders to understand how Mid-Atlantic tidal marshes have responded (and will respond) to sea-level rise and climate change. We compiled sedimentation and ecological data from tidal marshes to quantify variability and determine drivers of change. I also worked with a group of students to quantify spatial and temporal variability in carbon sequestration of tidal marshes along the Raritan River and Bay.

A Holocene Paleoflood Record from Coastal Southern California

In the coastal southwest, many ephemeral streams transport sediments only during or immediately following large precipitation events (storms). Therefore, fluvial-sourced paleoflood deposits in estuarine sediments may be good proxies for storm activity in the Holocene. Here we use diagnostic geochemical and grain size characteristics to differentiate marine-derived sand beds from fluvial-derived sand beds in Carpinteria Marsh, California. These fluvial-derived beds are interpreted to represent alluvial fans prograding into the marsh fringes during storm-induced flooding of the coastal plain. Three wet periods recorded in Carpinteria are contemporaneous with other records of pluvials throughout the southwest of North America, indicating a regional increase in storm activity during these time periods. Estuarine sediments provide an additional archive of past hydroclimate that demonstrates centennial to millennial scale storm frequency and magnitude may be similar across a wide geographic span of southwestern North America.

Past Research Projects

Estuarine Response to Coseismic Subsidence
(Reynolds et al., 2022 https://doi.org/10.1130/B35827.1)

We show lithological, geochemical, and biological evidence for an abrupt subsidence event in an estuary along the highly-urbanized southern California coastline at about 1000 years before present. A few meters below the marsh surface, an organic-rich mud containing marsh invertebrates and geochemical signatures indicative of terrestrial influence is sharply overlain by a blue-gray sand containing intertidal and subtidal invertebrates and geochemical signatures of marine influence. Using relative sea-level indicators, we interpret this contact to represent coseismic subsidence, sediment compaction, and/or subsequent erosion. Following subsidence, the estuary rapidly infilled and redeveloped into a marsh and mudflat environment within 500 years.

Coastal Flooding and the 1861-2 Storm Season
(Reynolds et al., 2018: https://doi.org/10.1016/j.margeo.2018.02.005)

A series of large storms attributed to Atmospheric River conditions struck the California coast in the winter of 1861-2. Here we show that the 1861-2 storms emplaced an extensive deposit of beach sand within a southern California salt marsh, suggesting that the 1861-2 storm season was erosive enough to remove coastal barriers, allowing for inundation of parts of the coastline currently developed.

 Late Quaternary relative sea level in Southern California and Monterey Bay
(Reynolds and Simms, 2015: 10.1016/j.quascirev.2015.08.003)
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This paper provides the first regional, uplift-corrected late Quaternary RSL history for southern California derived from a compilation of 132 previously published and unpublished radiocarbon ages from nearshore, estuarine, and freshwater deposits in sediment cores from coastal southern California. We also provide a local, uplift-corrected RSL history for Monterey Bay, central California, generated from 48 radiocarbon ages from Elkhorn Slough and surrounding environments.

Marine Radiocarbon Reservoir Values in Southern California Estuaries: Interspecies, Latitudinal, and Interannual Variability
(Holmquist et al., 2015: 10.2458/azu_rc.57.18389)

This project used AMS 14C dating on 40 pre-1950 salt marsh snail and clam shells previously collected from four California estuaries to determine interspecies and geographical variations in ∆R along the California coast.

Characterization of the Elephant Trees Formation, Anza Borrego with Implications for Determining the Depositional Environments of Conglomeratic Debris Flows
Elisabeth Steel, Lauren Simkins, Mary Kate Fidler, Laura Reynolds, GSA Meeting Vancouver, CA 2014

This project used 191 m of section measured within the Elephant Trees Formation, an alluvial fan succsession in Anza Borrego State Desesrt, to (1) identify evidence for depositional enviornmental change (subaqeous vs. subaerial) throughout the section, and (2) identify any relationship between maximum clast size and bed thickness within debris flow deposits. 

Palynology and Macrofossils from a Occom Pond sediment core, Hanover, NH
B.A. Honors Thesis, Dartmouth College, unpublished
Adviser: Meredith Kelly

This project examined Holocene environmental and climatic changes that occurred in Hanover, New Hampshire by analysis of pollen, charcoal, and macrofossil content of a sediment core taken from Occom Pond in 2009.