CONFERENCE CONTRIBUTION:

NABS/ASLO 2010

METHYLMERCURY BIOACCUMULATION ACROSS A PRODUCTIVITY GRADIENT IN STREAMS  

Conceptual models have identified periphyton as a potentially important pathway for biomagnifying pollutants in streams. This hypothesis, however, has neither been tested experimentally, nor investigated for methylmercury (MeHg), a ubiquitous aquatic contaminant. We conducted a mesocosm experiment to measure MeHg uptake from water to basal resources and primary consumers across a productivity gradient established by differences in light exposure. Simple two-level food webs were introduced to mesocosms consisting of periphyton, suspended algae, a grazer (snails), leaves, a shredder (Hyalella), and filter feeder (Corbicula). Mesocosms were amended with MeHg and fertilized with N and P. Phytoplankton biomass increased with light, but periphyton did not. With greater productivity, MeHg levels increased in phytoplankton and were reduced in water, periphyton, and consumers, including snails despite no difference in periphyton density. In stream ecosystems, where MeHg availability may not limit bioaccumulation, phytoplankton growth appears to govern bioaccumulation and transfer to associated consumers.  

FEDERAL AGENCY:

ENVIRONMENTAL PROTECTION AGENCY 2010

AQUATIC INSECTS TRANSFER PCBS TO RIPARIAN FOOD WEBS CREATING EXPOSURE RISK IN BIRDS  

Consumption of emergent aquatic insects by terrestrial invertebrates is a poorly resolved, but potentially regulating, mechanism of contaminant flux across ecosystem borders leading to contaminant exposure in terrestrial invertivores. We characterized the spatial extent and magnitude of contaminant transfer from aquatic sediments to terrestrial invertebrate predators by examining riparian araneid spiders, terrestrial insects, and emergent aquatic insects for stable isotopes and polychlorinated biphenyls (PCBs, sum of 141 congeners) at Lake Hartwell, (Clemson, SC, USA). PCB concentrations in aquatic insects were orders of magnitude higher than in terrestrial insects. Aquatic insect consumption by spiders (as indicated by d13C and d15N), PCB concentrations in spiders, and aquatic prey availability were greatest at the shoreline and declined inland, while terrestrial prey availability was invariant with distance. We calculated spider-based wildlife values (WVs, the minimum spider PCB concentrations causing physiologically significant doses in consumers) to assess exposure risks for arachnivorous birds. Spider concentrations exceeded WVs for most birds at heavily contaminated sites and were 14-fold higher for the most sensitive species (chickadee nestlings).These results illustrate the importance and limiting nature of consumption of emergent insects as a vector of contaminant transfer from lake sediments to riparian food webs, and that spiders are key predators in this process.  

SEMINAR:  

UNIVERSITY OF CINCINNATI DEPARTMENTS OF BIOLOGY AND GEOLOGY  2010

and

UNITED STATES GEOLOGICAL SURVEY 2010

QUANTIFYING ECOSYSTEM CONNECTIVITY 

One of the major trends in ecology over the last 40 years has been an increasing integration of space into explanations of ecological patterns and processes. Landscape-scale examination shows that ecological phenomena are not only a function of conditions at a site, but a function of materials that travel to the site, or connectivity. Methods for the explicit spatial delineation of source areas for water-borne materials in watersheds and open water, however, lag behind those for atmospheric chemistry and groundwater. I’m going to talk about examinations of connectivity using modeling of the “resource shed”. For example, independent hydrologic and hydrodynamic models, coupled with a particle tracking model, were used to delimit resource shed total spatial extent and relative contributory importance for selected receptors in Lake Erie (North America) over varying time intervals. Resource shed size, orientation, and internal structure varied with receptor location, in-lake circulation, terrestrial precipitation, time interval, and season. Source areas within the Fox River watershed (WI, USA) were mapped for individual discharge events. The spatial distribution of source areas varied between, and over the duration of, individual discharge events. Therefore a source area-based approach may yield more accurate spatial analyses of connectivity than a watershed-based approach. 

PUBLIC LECTURE:  

POWDERMILL NATURE RESERVE  2009

LEGACY CONTAMINATION OF STREAMS: FORGOTTEN BUT NOT GONE

 While other issues of ecological concern, like climate change, receive popular attention, the problems that initially raised environmental awareness take a back seat. Yet these problems are not only still with us, they are spreading. This seminar will focus on the contamination of aquatic sediments, a legacy of the 20th century. Having been around for decades, such pollutants can escape the water through the emergence of aquatic insects. Thus ironically, legacy contamination of aquatic sediments provides a powerful tool for studying food webs. I will present new work on PCB transfer to land-based food webs, in which spiders are crucial to the process of linking ecosystems, resulting in particular exposure risk to birds.