Streams play a pivotal role in the transport of energy and nutrients to terrestrial systems. For example, young aquatic insects consume algae in streams, fly into forests as adults, and are eventually consumed by terrestrial organisms. Despite the small area of rivers relative to land, materials produced within them feed many terrestrial consumers. Streams may be exporting more than just nutrients, however. Because of the widespread contamination of aquatic systems, aquatic insects can transport contaminants, such as mercury, to terrestrial food webs.
Mercury is a widespread problem in the U.S., particularly affecting the Northeastern portion of the country. While mercury exposure in fish-eating terrestrial consumers continues to be studied, little is known about the mechanisms of exposure to other terrestrial consumers. Recent studies have found high levels of mercury in terrestrial insectivorous predators, such as spiders, that may be consuming large amounts of adult aquatic insects.
Given that diet is the principal vector of mercury to wildlife, factors influencing mercury bioavailability in stream food webs could directly or indirectly determine mercury concentrations in terrestrial consumers. Dissolved organic matter (DOM), such as decaying leaf litter, has been identified by several studies as an important factor affecting the movement of mercury through aquatic ecosystems. The role of stream DOM in the accumulation of mercury in food webs is complex, and not yet well understood. The Alumni Research Award has allowed me to research the role of DOM on the movement of mercury through aquatic-terrestrial food webs. I have found that although DOM increases mercury concentration in stream water, it decreases mercury bioavailability within the food web. This dual role of DOM on mercury transport and bioaccumulation has been observed in aquatic food webs, but had not previously been shown to affect mercury transportation from streams to terrestrial food webs.
by Ramsa Chaves-Ulloa