Below I detail some current and recent projects. Please also see my CV or contact me for more information on research questions I’ve worked on.
Complex life histories alter mercury exposure and accumulation in linked aquatic-terrestrial food webs
Pond-breeding amphibians fascinate me because they spend their larval period (1 month to 1+ years) as fully aquatic omnivores, then abruptly reabsorb their tail, grow limbs, and move on land to live as terrestrial carnivores. I’m part of a team exploring how this complex life history changes methylmercury (MeHg) concentrations in the Boreal chorus frog (Pseudacris maculata, pictured above). We found large increases in MeHg during times of physiological stress involving tissue catabolism. During metamorphosis and hibernation, these frogs rely on their stores of energy and MeHg bioamplified. More on this soon pending acceptance, but for a teaser check out our graphical abstract below.
Long-term aquatic ecosystem injury from legacy contaminants
Sauget (formerly known as Monsanto) and Cahokia, IL have a long history of industrial contamination. Although there have been remediations, current evidence suggests ongoing sediment release of mercury and PCBs. I’m part of a team exploring how contaminant flux from sediments in ponds and streams (such as Dead Creek pictured above) may enter the food web and be transported to terrestrial animals.
Pacific Chinook salmon thiamine deficiency
Chinook salmon (Oncorhynchus tshawytscha) in California have been experiencing precipitous declines. I’m part of a working group led by Rachel Johnson of NOAA, USGS, university, and fisheries scientists to holistically explore how thiamine (vitamin B1) deficiency affects spawning success, behavior, disease susceptibility, and survival of Chinook salmon populations, as well as investigations into sources of thiamine, food web shifts causing the deficiency, and how thiamine remediation could potentially reverse the negative effects. Read more about this work here.
At CERC we have the capability of analyzing samples for thiamine concentration as well as the thiamine-dependent enzyme transketolase which can give some information on whether thiamine is limited in tissues. We also run thiaminase, an enzyme produced de novo by some important forage fishes such as anchovy, alewife, and herring. We are currently expanding our research to include steelhead thiamine with Oregon fish health specialist Aimee Reed, and exploring whether thiamine deficiency may explain the lack of recruitment in endangered Klamath Basin suckers with USFWS’s Christie Nichols.
Long-term population dynamics of wood frogs
The Skelly lab has monitored more than 60 ponds at Yale-Myers Forest for wood frog (Rana sylvatica) population sizes for 21+ years. We are using these data to explore population dynamics and localized evolution. We just published the first paper from this work: Rowland et al. 2022. Long-story short: there is a surprising lack of synchrony in population boom/bust cycles for wood frogs, suggesting better resilience to major disturbances than we previously thought. Pond-scale factors including competition during the parental larval stage strongly influenced population growth rates.
Harmful algal blooms (HABs) in Lake Erie
I worked with Craig Stow (NOAA) and Tom Johengen (University of Michigan) to explore drivers of algal blooms and toxicity in western Lake Erie using high-quality monitoring data collected by the Cooperative Institute for Great Lakes Research and NOAA’s Great Lakes Environmental Research Lab from 2008-present.
We found spatial differences both in P concentration and the relationship between TP and chlorophyll a. Furthermore, despite loading targets based on spring P loads, our results indicate that spring phosphorus loads are a weak algal biomass predictor in the western basin of Lake Erie (Rowland et al. 2020).
Song Qian (U Toledo) led the effort to build a predictive model of microcystin concentrations using the same data, specifically chlorophyll a (an indicator of algal biomass). Now published in Ecological Indicators! Check out Qian et al. 2021.
The effects of neonicotinoid pesticides on non-target species
Neonicotinoid pesticides are touted as safe for non-target vertebrates like fish and amphibian larvae because of their low toxicity, but that doesn’t account for potential effects that are non-lethal. Former (w)undergraduate Jordan Holtswarth (now getting her Ph.D. at the University of Illinois), Holly Puglis (USGS), Lisa Webb (University of Missouri), Michelle Hladik (USGS), and I tested how a common neonicotinoid, clothianidin, affected tadpole movement after five days of exposure at field-realistic levels.
Tadpoles decreased how far they moved and velocity with increased exposure, which could have important population- and community-level effects. Read more in Holtswarth et al. (2019)!
Evaluating stream nutrient trends: a new statistical approach to compensate for changing streamflow
Large flow changes in wet and dry years can mask patterns of increasing or decreasing flux and concentrations, yet good estimates of changes over time are needed to inform policy. I worked with Bob Hirsch (USGS) and Craig Stow (NOAA) to look at long-term changes independent of flow changes in three tributaries to Lake Erie: the River Raisin, the Cuyahoga River, and the Maumee River. Spoiler: flow-normalizing using weighted regressions on time, discharge, and season regressions (WRTDS) on load and concentration estimates makes it much easier to detect long-term trends in the data. Read the full story in Rowland et al. 2021.
Nutrient limitation changes with season in sub-tropical lakes of Nepal
Most of the research on nutrient limitation in lakes has a temperate bias. The dogma is that tropical and sub-tropical lakes are N-limited, but most of these data were collected in the stratified season.
In collaboration with Jack Jones (University of Missouri) and Rebecca North (University of Missouri), I analyzed more than 70 nutrient stimulation experiments from two lakes in Nepal across all seasons in multiple years. It turns out that N-limitation is common in the monsoon season, but P-limitation often occurs pre- and post-monsoon. See Rowland et al. (2019) for more details.
Salamander larvae are as effective at short-term larval mosquito predation as mosquitofish
Managers often add non-native mosquitofish (Gambusia spp.) to ponds and wetlands to control mosquito larvae, but this can have strong negative effects on native amphibian larvae. Awesome former undergraduate Amanda Watters (now in vet school at the University of Illinois) compared the predatory ability of tadpoles, salamander larvae, and mosquito fish across a range of sizes.
We found that often salamander larvae were just as effective as mosquitofish, and could consume ~200 mosquito larvae in a 24 hr period. Tadpoles predated on mosquito larvae, too! Interested? Read more in Watters et al. (2018).
Freya E. Rowland, Ph.D. 