My research examines how aquatic ecosystems, ranging from freshwater to marine, respond to disturbance and environmental change. I am particularly interested in developing quantitative approaches to monitor spatial and temporal change in aquatic environments. Below are the main themes and questions I currently address in my research.

Aquatic Biogeochemistry at the Terrestrial-Aquatic Interface

How are changing means of material delivery to aquatic environments altering their transport and transformation?
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​​Aquatic ecosystem function at the terrestrial-aquatic interface is changing in response to longer-term climate change and more immediate land use change. For my doctoral research at UC Santa Barbara, I focused on reciprocal subsidies between terrestrial and marine environments and their effects on nutrient and organic matter cycling in recipient ecosystems. Following a historic drought in southern California, I tracked the transport of terrestrial organic matter (TOM) from mountain streams into marine sediment using a suite of biomarkers (lignin phenols). During wetter, El Niño conditions, results indicated that inputs to streams became more varied in source material and less degraded, and these trends were mirrored in recipient marine sediment samples (Lowman et al., 2021).

Rattlesnake Creek, a sampling location part of the Santa Barbara Coastal LTER.

I also examine distinct, human-mediated events that facilitate fluxes of upland material into aquatic systems and aim to advance our understanding of these materials’ impact on water quality and ecosystem function. Following a late-season wildfire and a subsequent debris flow, emergency responders in Santa Barbara County (CA) placed debris on local beaches during clean-up efforts. I used biomarkers of terrestrial (lignin phenols) and burned material (pyrogenic carbon) to examine the transport and degradation state of the debris. While wave action eventually removed most of the debris from the beach,  results suggest the debris was retained in nearshore marine sediment. Since the debris had bypassed in-stream processing, it was degraded relatively little which could have significant consequences on nearshore benthic communities and biogeochemical cycling (Lowman et al., 2022). This research was generously supported by the UC Santa Barbara Coastal Fund and was later featured on Santa Barbara's local KEYT News as well as in AGU's Eos Magazine.

Goleta Beach, where wildfire and debris flow material was placed. Note the distinct difference in coloration between beach sand and debris material.

How do changes to basal resources, at the base of the food chain, propagate across biological scales?

Giant kelp are adapted to high wave forces and changing currents; we found kelp's nutritional content is correlated with water temperature.

I investigate the effects of climate change and disturbance events on aquatic ecosystem function across multiple trophic levels.  Using a long-term dataset of giant kelp stoichiometry (Carbon:Nitrogen), I found that decreasing nutritional content of kelp tissue is correlated with warming temperatures (Lowman et al., 2021). I also demonstrated that beach invertebrates rapidly consume giant kelp deposited on beaches and elevate nutrient concentrations in surrounding beach pore waters (Lowman et al., 2019). Together, these studies suggest that changes in the nitrogen content of giant kelp could have far-reaching effects for both beach and offshore food webs. Declines in nutritional content could have compounding negative effects for consumers, since giant kelp abundance is also projected to decline due to warming  temperatures. Additional stories about this research were featured by local public radio station KCBX and Hakai Magazine.

Low nutrient, headwater streams can yield high numbers of emerging aquatic insects.

Furthermore, I study feedbacks across biological scales to inform predictions of how biotic interactions and associated biogeochemical cycles may respond under rapidly changing abiotic conditions. In the White Mountains of New Hampshire, changes in winter hydrology (smaller snowpacks, earlier snowmelt) are coinciding with changes in stream chemistry (lower nutrient concentrations, increasing pH). I am examining how these conditions may alter productivity dynamics (e.g., algal and bryophyte growth) in small, headwater streams in the region. I am also studying how past winter climate conditions may shift the timing and magnitude of aquatic insect emergence, an event that serves as a major subsidy of nutrients for aquatic and terrestrial consumers such as salamanders, bats, and birds. Please visit hbwater.org to learn more about ongoing data collection and additional research findings from the Hubbard Brook Water Ecosystem Record.

Aquatic Ecosystem Responses to and Memory of Disturbance

How do the types of biogeochemical responses vary according to local disturbances?
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I am interested in developing methods to quantify the type, magnitude, and duration of responses to disturbance in aquatic ecosystems. I am particularly focused on developing methods to quantify ecosystem memory, or the degree to which antecedent conditions are reflected in current ecosystem function. In many regions, wildfires are increasing in size and frequency, but their effects on aquatic ecosystems remain poorly studied. This is particularly true in arid climates, which are fire-prone and water-scarce. As a member of the Collaborative for Research in Aridland Stream Systems, I am developing quantitative methods to examine post-wildfire changes in water quality and a framework for future, post-fire aquatic biogeochemistry research. Arid lands typically experience high variability in annual precipitation, and our results highlight the potential for lagged and persistent water quality responses to wildfire, rather than immediate and short-lived (Lowman et al., 2024). This research has been supported by a Scientific Peers Advancing Research Collaborations grant from the National Center for Ecological Analysis and Synthesis.

A confluence in Sycamore Creek (AZ) following the Bush fire and subsequent rainstorm. (Credit: L. Gaines-Sewell)

How are responses to disturbance mediated by larger, or macro-scale, controls?
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I am also motivated to examine the macro-scale controls that determine how aquatic ecosystems respond to and recover following disturbance. As a member of the Modelscapes Consortium, I adapted a modeling technique to quantify recovery rates of productivity following high-flow storm events in 181 rivers across the continental U.S. Results indicate that larger, less regulated rivers (i.e., those with less interference from upstream dams) that experience high-flow disturbances more frequently are the rivers that recover most rapidly (Lowman et al., 2024). This work has enabled us to predict river resilience following disturbance at a broader spatial scale than ever before. Disentangling controls on the resilience of aquatic ecosystems will enable better predictions of how river ecosystem function will continue to change with warming, changing precipitation, and increased flow modification for irrigation and industry.

We found that river productivity (such as the benthic algae picture here) was most resilient in larger, less regulated rivers.