My research is focused on improving our understanding of the response of our increasingly human-altered ecosystems in this era of rapid global change. My current projects focus on the global mercury (Hg) contamination crisis and rising temperatures caused by global climate change. I am using the freshwater, mussel-driven ecosystems found in southeast Oklahoma as a model system to investigate the factors which regulate the amount of Hg in the environment and how Hg might combine with other environmental changes, particularly climate change, to affect the health of our ecosystems.
Do freshwater mussels alter the production of methyl mercury and contamination of aquatic food webs?
Methyl mercury (MeHg) is a potent neurotoxin with a global reach due to atmospheric emissions of inorganic mercury (Hg) from power plants, incinerators, and other antropogenic sources. This Hg is deposited across the landscape where it eventually washes into the sediment. Sulfate-reducing bacteria living in the sediments covert the relatively benign Hg into the highly toxic MeHg. Upon entering aquatic food webs, MeHg can bio-magnify posing a significant health risk to both humans and wildlife (Fig1).
Understanding the factors which regulate the production and release of MeHg into aquatic food webs is an important part of managing this pressing environmental issue. Freshwater mussels may play an important role in regulating the contamination of aquatic ecosystems. Mussels play a pivotal role in many aquatic ecosystems. Because mussels are large and occur in dense aggregates (beds) they often dominate the benthic biomass of the rivers they occur in. This allows mussels to have a strong effect on many ecosystem processes and functions. For instance, mussels can alter nutrient cycling regimes within mussel beds through their filter feeding and excretion, removing nutrients from the water column and depositing them in the sediments. They are also active burrowers and mix and agitate aquatic sediments altering properties such as oxygen content. These, and other, activities could have significant effects on the methylation activity of the sediment dwelling microbes (Fig2).
Do Multiple Stressors Combine to affect the health of ecosystems?
We live in a world which is heavily impacted by human activities that stress and degrade the environment. Two particularly widespread environmental stressors are mercury (Hg) contamination of the environment and climate change. While considerable research has addressed the effects of these stressors individually on ecosystems, we know little of how they will effect ecosystems in combination which is how they will be experienced by many natural systems globally in the coming decades. I am using a combination of mesocosm and laboratory studies to get answers to this problem. I plan to combine the results of these studies with current climate models, Hg emission models, and environmental flow models with structural equation modelling (SEM) to help better manage our freshwater resources.
Do Fish alter the flux of mercury from aquatic to terrestrial ecosystems?
Mercury (Hg) contamination of the environment has traditionally been thought to be a threat only to terrestrial consumers feeding in aquatic food webs (e.g. loons or raccoons). However, many studies have documented elevated levels of Hg contamination in birds that do not feed in aquatic food webs (e.g. sparrows, cardinals, or bats). These animals often consume the adult forms of emergent aquatic insects (e.g. dragonflies, damselflies, or gnats). The larval form of these insects live in aquatic ecosystems where they can become contaminated with Hg. When they leave the water in their adult form, they take the Hg present in their bodies with them, contaminating any terrestrial consumers that eat them.
For my M.S. Thesis at Texas Christian University I conducted a pond experiment to test two hypotheses. 1) The presence of fish in ponds (bass & bluegill) decreases the amount of Hg that leaves the pond and 2) Riparian (shore dwelling) spiders will mirror the contamination of the pond they are living by. We used floating emergence traps to quantify emergence over fish and fish-less ponds over the course of six weeks. We found that the presence of fish predators significantly decreases the amount of Hg leaving the pond through large insects like dragonflies and damselflies. We also found that the concentration of Hg found in riparian spiders was strongly correlated with the Hg of insects captured above that pond. You can read more about this study in the paper published in Environmental Science & Technology here.