Long before she joined my lab to work on microbial communities in some of Maine’s coastal salt marshes, Heather was an ecologist, educator, and bioinformatician. Over her career, she’s used hands-on experiences in nature (a.k.a. living labs or nature’s classroom) to inspire a love of the natural world while teaching the process of scientific inquiry to students of all ages. Her enthusiasm for environmental science similarly helped her unite people during public outreach and policy work towards common goals of information sharing and evidence-based conservation strategies to benefit communities and the ecosystems around them. And, her unwavering fascination with nature and her dedication to understanding (i.e. science) led her along a path of scientific inquiry to solve problems. In fact, her PhD program was just one leg of her lifelong journey in conservation. As she is coming to the end of her PhD project and looking for her next opportunity, Heather landed a position at Scarborough Land Trust where she will oversee the management and coordination of various restoration and science projects with multiple interest groups starting this fall, as she wraps up her dissertation and resulting scientific manuscripts.

Heather’s focus at UMaine has been to catalogue the microbiomes associated with coastal salt marsh ecosystems in Maine. There are approximately 800 locations in Maine where roads and bridges cross tidal creeks, which requires culverts or other infrastructure to direct the flow of water, and 90% of these structures are considered undersized. These restrictive crossings impound freshwater upstream of the restriction site, keeping it flooded and lowering salinity. This disrupts the native vegetation and soil microbes adapted to salty conditions, making the marshes highly vulnerable to invasive plants. Healthy salt marshes act as blue carbon ecosystems by trapping and storing large amounts of atmospheric carbon in their soils. However, tidal restrictions disrupt this process and can turn these areas into major hotbeds for potent greenhouse gas production. Understanding how microbes react to restrictions in marshes, and whether they can still sequester carbon instead of losing chemical resources from the marsh, can help us learn how to more effectively use infrastructure that does not negatively impact water flow, native plants, or microbes. Microbial communities can be viewed as an integrated response to environmental conditions over time, whereas variables such as salinity and carbon flux are instantaneous measurements that capture only a snapshot of a dynamic system. That means these methods can potentially be very useful and informative for those who protect, monitor and restore salt marsh habitats.

Heather studied soil/sediment as these areas host a high diversity of microbes, which are responsible for a majority of the chemical processing that happens there, such as breaking down the plant, animal, or chemical waste into simpler compounds or elements which can be sequestered into the soil, taken up by the plants, or fuel more microbial activity. The bacteria, archaea, and fungi that live in the sediment of marshes are somewhat specific to the plants, animals, chemicals, environment, and humans around the marsh, thus each marsh must be “microbially mapped” to know which microbes are present and where specifically, and what they are doing. This is important for knowing how microbes are affected by change: will they sequester carbon or release methane if the community is changed by a storm, or by the installation of a culvert? What will the microbes do if the marsh dries out or gets flooded?

Heather discovered too much to name here, but here are some highlights: The microbiomes found in the regularly flooded marsh adjacent to tidal channels at depths within the rhizosphere (plant roots) are likely to be particularly sensitive to hydrology alterations because of the low elevation in these areas and close proximity to tidal creeks. Hydrologic restrictions that increase water residence time can prolong anoxic conditions and reduce tidal flushing, promoting environments that favor methanogenic and other anaerobic microorganisms while suppressing aerobic processes. These changes may also reduce the capacity of the marsh plant Spartina alterniflora to oxygenate the rhizosphere under highly reduced conditions and, where sulfide accumulates, may further reinforce redox-driven shifts in microbial community composition. The presence of natural marsh microbial communities at some restricted sites should not be interpreted as evidence that these tidal restrictions have no ecological impact: restrictions at sites with less freshwater influence that reduce tidal inundation upstream without impounding freshwater may have similar oxygen and salinity conditions as the natural sites in the lower/downstream part of marshes while increasing aerobic carbon mineralization at deeper depths and increasing salinity stress in the higher/upstream part of the marshes.

Now that she’s wrapping up, Heather will condense what she learned and how she did it into a dissertation, the chapters of which will be formed into several manuscripts. This will include one with the information about the microbial communities present and which environmental conditions were associated with certain taxa or biochemical pathways, one on a particular marsh before and after it was restored, and one on the process of setting up a collaborative marsh-conservation network across multiple states and institutions to facilitate evidence-based restoration strategies.