My research approach combines biogeochemical methods with paleoecology to provide a long-term perspective on understanding natural environmental variability and recent anthropogenically-induced changes. My research is located across a wide range of environments from the subarctic and Arctic Canada to tropical coastal Thailand. These environments face many anthropogenic stressors from land-use changes to global warming, which can manifest in several ways within aquatic and terrestrial ecosystems. For example, northern ecosystems are undergoing significant changes with warming including increases in the length of the ice-free period, increased water column stability, the northward shifts of species ranges, increases in the rates of weathering and decomposition, changes in snowmelt, and shifting water balances, to name a few. In Southeast Asia, the rapid expansion of shrimp aquaculture in the last few decades has deteriorated coastal ecosystems including mangrove forests. Often many of these recent changes require knowledge on environmental conditions prior to the onset of impact or introduction of an ecosystem stressor, but monitoring records can be scarce, especially in inaccessible regions of the world. This is where the importance of paleolimnological and paleoecological records come in.
Biovectors - new tracer methods (e.g. lipid biomarkers) & ecosystem regime shifts
A biovector is any organism that transports a substance (e.g., nutrient, contaminant, virus) from one ecosystem to another. In particular, birds feed almost exclusively off shore but nest on land, often forming large breeding colonies or roosts where they can number in the tens or even hundreds of thousands. The wastes released from bird colonies provide critical nutrient subsidies for many coastal ecosystems, often creating thriving biological communities that would not exist otherwise. An unfortunate irony is that this transport pathway also concentrates contaminants that are biomagnified and bioaccumulated through the marine or aquatic food webs, thereby threatening the very ecosystems it supports and sustains. For this research, I am working to develop many proxies, including metals, diatoms, and lipophilic biomarkers to understand the land-sea linkages created by biovectors, as well as to reconstruct long-term population records of sensitive species.
A sediment core and eider pond, Hudson Strait'15
My ongoing work falls into several themes:
Environmental gradients across organic wetlands and identifying drivers of past successional changes
With climate change, studies of northern peatlands are now more important than ever owing to the vast quantities of carbon stored within these regions and their future role as net carbon sinks. All biological indicators are limited by their responses to environmental factors (e.g. moisture, pH, etc.), and these responses will differ among proxies. A multi- proxy approach allows comparisons and corroboration among the indicators, thereby strengthening paleoecological interpretations. Although peatlands provide a challenging and harsh environment, fossil diatom assemblages preserved in peat sequences have been used successfully to further understanding of autogenic processes and climatic changes over the Holocene. For this research, we are studying the response of diatoms across northern peatlands to small differences in microhabitats, including varying pH, moisture and bryophyte type. In conjunction with other proxies, this knowledge on modern diatom autecology will improve our interpretations on past environmental changes captured in peat archives.
A bog in Hudson Bay Lowlands'11
The influence of aquaculture effluent within natural and engineered wetlands
Mangrove forests perform many functions that are beneficial to people, including buffering excess nutrients received from land-use activities, and storing carbon as organic matter. However, few studies have evaluated the linkages between excess nutrient runoff from aquaculture and the capacity of mangrove forests to utilize these nutrients to store greater carbon. For this research we are utilizing a comprehensive suite of chemical tracers in a coupled shrimp farm-mangrove system to evaluate the impact of aquaculture runoff on mangrove nutrient dynamics. We aim to: 1) characterize across multiple levels in the food web the relative contributions of carbon and nitrogen form shrimp-farm runoff, marine-derived nutrients, and in situ production; and 2) use sediment cores to reconstruct the relative changes of these nutrient sources and carbon storage through time.
The responses of lake phytoplankton and invertebrate communities to anthropogenic impacts
Knowing historical baseline conditions in aquatic ecosystems is critical for setting realistic recovery targets and conservation goals. Many aquatic ecosystems may be naturally productive or cycle through different steady states (e.g., clear with macrophytes or turbid with algal blooms). In Lake of the Woods, I found that phosphorus loading to the lake has been reduced over the past ~30 years, and that that there is likely a greater stressor or multiple stressors in addition to phosphorus that are promoting cyanobacteria blooms. Now, paleolimnological studies show with warming, enhanced lake thermal stratification and longer growing seasons, have likely exacerbated algal blooms. Through paleolimnological research, I continue to address several remaining critical research questions, such as how aquatic algal and invertebrate assemblages respond overtime to the interaction between climate change and nutrient pollution, including utilizing these proxies to understand how hypolimnetic oxygen concentrations and the quality of cold-water fishery habitat is changing with warming temperatures and shorter winters.
A mangrove forest in eastern Thailand'18
Piston coring on North Raft Lake'11