River ecosystem phenology in a changing climateAs the climate warms, rivers are losing their ice rapidly; however, as ecologists, we do not understand what will happen to freshwater ecosystems once the ice is lost. In this study, we combined satellite image derived ice cover with installed dissolved oxygen sensors to evaluate how ice impacts river primary productivity. This project is funded by a NASA Future Investigators in Space Science and Technology grant.
The Ecology of River Ice |
What limits primary productivity in small, forested streams?In 1967, Stuart Fisher and Gene Likens conducted one of the first energy and organic matter budgets of an ecosystem. Surprisingly, they found that headwater streams at Hubbard Brook Experimental Forest derived 99% of their energy from leaf litter, ~1% of their energy from stream bryophytes, and there were no algae in the stream. Starting in the 1990s, researchers began documenting increased algal abundance in the headwaters. In this project, we sought to evaluate which factors may have led to this increase. Through a series of field experiments, we found that algae grow preferentially within bryophytes as bryophytes may provide refugia from major flow events. Because we have little long-term data on the bryophytes in these streams, it is presently unclear whether algae have increased along with the bryophytes, or whether algae have been there all along, hiding within the mosses.
[Publication in review for L&O] |
Light Use Efficiencies of RiversIn 1956, Howard Odum measured the total primary productivity of the extremely productive clearwater Florida springs and found that those ecosystems' autotrophs convert ~4% of their light energy into biomass. Recently, advances in new sensor technology has revolutionized the way we can measure primary productivity in rivers -- from measurements taken on single days to continuous measurements spanning several years. Using a synthesis (StreamPULSE) of 64 free-flowing US rivers and light modelled at the stream surface, we were able to estimate the yearly and daily light use efficiencies for rivers of many different types. We were surprised to find that on the river's "best day," they were able to achieve light use efficiencies much greater than 4%, meaning that those rivers were able to be more efficient than some of the most productive streams on the planet. While the river's potential was great, on "most days" the average river light use efficiency was much lower, only 1.5%.
High potential but low achievement: Frequent disturbance constrains the light use efficiency of river ecosystems |
Agricultural Ditch EcologyLand use change and the associated application of synthetic fertilizers to agricultural fields in the Midwestern U.S. have altered the cycling of bioavailable nutrients in aquatic ecosystems. This makes stream networks important sources of export for greenhouse gasses (GHG) and nutrients. To mitigate excess nutrient export from the agricultural landscape, best management practices (BMPs) have been developed to increase the physical retention of nutrients. By gaining a more accurate estimation of the role that these BMPs assume in surface-subsurface interactions, we can better understand reach-scale nutrient dynamics in these critical watersheds.
Publication led by Amelia Grose |
Heterotrophic LakesPeter and Paul Lake - Land O' Lakes, WI (UNDERC)
Previous studies established that lakes are sources of carbon dioxide to the atmosphere. Many of these studies predict that a majority of these inputs come from exogenously produced carbon transported to lakes through groundwater. By determining the amount of carbon stored in groundwater, accurate estimates can be made to determine groundwater’s role in the global carbon cycle. |