Current Areas of Research
Superficial characteristics are what provide initial impression of ecosystem impairment: are invasive species present, is there an algal bloom, can we detect harmful chemicals? These snapshot measurements are useful for initial assessments but can be disconnected from how well an ecosystem is functioning (e.g., capacity to clean water, store nutrients, produce biomass). Resilience and redundancy inherent in ecosystems allow stressors to be present without necessarily affecting important ecosystem processes. Conversely, ecosystems that “look” normal on the surface or through initial assessments may not be providing key functions due to emergent properties that disconnect population and community traits from ecosystem processes.
In our lab, we spend substantial effort finding ways to directly measure how ecosystem process rates respond to stressors, which in addition to structural assessments can give a complete picture of ecosystem impairment. We find that field and mesocosm experiments are one of the best tools for understanding mechanisms of impairment at the ecosystem scale.
In our lab, we spend substantial effort finding ways to directly measure how ecosystem process rates respond to stressors, which in addition to structural assessments can give a complete picture of ecosystem impairment. We find that field and mesocosm experiments are one of the best tools for understanding mechanisms of impairment at the ecosystem scale.
Metal limitation of algal biofilms
The first evidence of ecosystem-scale trace metal limitation of algae was discovered in the ocean three decades ago, and this discovery revolutionized how we understand the "bottom-up" drivers of marine primary production. An appreciation for the role of trace metals has been extended to large lakes, but to date there is little effort to study whether trace metal limitation is important in stream ecosystems. In-stream experiments completed by our lab show that trace metals can limit primary producers in streams and trace metals are often co-limiting with N and P. This work was recently funded by NSF through a CAREER grant and we are looking for students to work on this project.
- NSF award information [abstract]
Restoring function in urban streams
Urban streams are characterized by flashy hydrology and impaired water quality which results in diminished ecosystem functioning. Stormwater managers use a diversity of interventions with goals of improving hydrology and water quality but the degree to which those dispersed and often disconnected management actions influence whole stream health is unknown. Our lab is part of an NSF-funded interdisciplinary effort to study urban stream management from stormwater actions through hydrology, water quality and ecosystem health (Stream Outcomes Resulting from Management of Stormwater [STORMS]). Our lab is measuring whole-stream metabolism and characterizing whole-ecosystem resistance and recovery to storm events with a goal of identifying hydrologic thresholds that managers can set as targets for restoration.
- More about the STORMS project from PI Anne Jefferson here.
- To measure whole-stream metabolism and water quality we use an array of sensors for dissolved oxygen, turbidity, and conductivity. Metabolism modeling for the STORMS project is further supported by solar irradiance data from Solcast.
Global-scale measures of stream ecosystem function
Although wadable streams take up a relatively small footprint on the globe, they contribute substantially to global cycles of C, N, and P. In particular, decomposition of detrital C returns CO2 to the atmosphere and can sequester nutrients in microbial biomass. I am part of a global team of researchers studying decomposition in streams from the arctic to the tropics. We are using cotton strips for as leaf surrogates for standardized experiments across the globe, which have provided unique insights into microbial decomposition. Our lab is expanding the decomposition assay to understand how N and P availability drives decomposition.
- Global patterns in litter decomposition [abstract]
Ecotoxicology of metals in streams
At high concentrations, metals (e.g., Ni, Cu, Zn) are toxic to aquatic organisms. However, metals are dynamic pollutants that react with naturally occurring compounds (e.g., FeS, DOC) which can greatly modify their toxicity. Our lab uses biogeochemistry to understand how natural elemental cycles interact with pollutant cycling, which ultimately has consequences for aquatic organisms. We have also completed unique experiments that demonstrate how ecosystem processes are altered by pollutants.
Examples from our lab: