Our research approach combines biogeochemical methods with paleoecology to provide a long-term perspective on understanding natural environmental variability and recent anthropogenically-induced changes. Our research is located across a wide range of environments from the sub-Arctic 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.
Seabirds as biovectors
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
Our ongoing work falls into several themes:
Environmental gradients across wetlands and drivers of past ecological change
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. 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
The influence of aquaculture effluent within wetlands and marine ecosystems
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 aquaculture-marine ecosystems to evaluate the impact of aquaculture runoff on coastal nutrient dynamics. We aim to: 1) characterize across multiple levels in the food web the relative contributions of carbon and nitrogen from aquaculture and marine-derived nutrients; and 2) use sediment cores to reconstruct the relative change in nutrient and carbon sources and storage over time.
Anthropogenic impacts to aquatic ecosystems
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). Using aquatic ecological and paleolimnological studies our research strives to understand how algal and invertebrate assemblages respond to anthropogenic impacts including climate change, nutrient pollution, and historical mining.
A mangrove forest in eastern Thailand
Piston coring on North Raft Lake