2002 Progress Report: The Influence of Climate-Induced Alterations in Dissolved Organic Matter on Metal Toxicity and UV Radiation in Rocky Mountain Streams

EPA Grant Number: R829640
Title: The Influence of Climate-Induced Alterations in Dissolved Organic Matter on Metal Toxicity and UV Radiation in Rocky Mountain Streams
Investigators: Clements, William , Baron, Jill S. , McKnight, Diane M. , Meyer, Joseph S.
Institution: Colorado State University , University of Colorado at Boulder , University of Wyoming
EPA Project Officer: Packard, Benjamin H
Project Period: April 1, 2002 through April 1, 2005
Project Period Covered by this Report: April 1, 2002 through April 1, 2003
Project Amount: $896,212
RFA: Assessing the Consequences of Global Change for Aquatic Ecosystems: Climate, Land Use, and UV Radiation (2001) RFA Text |  Recipients Lists
Research Category: Global Climate Change , Ecological Indicators/Assessment/Restoration , Water , Ecosystems , Climate Change


The primary goal of our research is to investigate the influence of climate-induced changes in hydrology and dissolved organic material (DOM) on responses of stream ecosystems to ultraviolet radiation (UVR) and heavy metals. We hypothesize that changes in climate and UVR will alter the quality and quantity of DOM in Rocky Mountain streams. Because DOM regulates light attenuation and metal bioavailability in these systems, we predict that exposure to UVR and metals will increase as a result of changes in DOM.

We will integrate climate and hydrologic modeling with an intensive field monitoring and experimental program to test the hypothesis that changes in DOM increase bioavailability of metals and exposure to UV-B (280-320 nm) radiation. We will estimate the effects of climate-induced alterations in stream hydrology on the timing and export of DOM using hydroecological and biogeochemical models that simulate carbon, water, and nutrient flux to streams. We will quantify metal-binding capabilities and light attenuation of DOM from different sources (e.g., allochthonous versus autochthonous) in the laboratory after exposure to a full-spectrum solar simulator. Finally, we will conduct field and microcosm experiments to test the hypothesis that reductions in DOM concentration and binding capabilities will increase exposure of benthic communities to heavy metals and UV-B radiation.

Progress Summary:

Modeling the Influence of Climate Change on DOM in Rocky Mountain Streams

We coupled an ecosystem biogeochemistry model (DayCent) with a soil and water chemical equilibrium model (PHREEQC) to predict physicochemical characteristics of alpine watersheds. We tested the coupled model using long-term data available from Loch Vale Watershed (LVWS) in Colorado. Measured values for LVWS include wet deposition, meteorology, forest biomass and nutrient ratios, soil microbial activity, soil and soil solution chemistry, stream discharge, and stream chemistry for a 20-year period. We used the model to simulate three representative sites in LVWS: forest, tundra, and rock. The contribution of each site to total discharge quantity and quality can be weighted by the percentage of the watershed occupied by each area. Preliminary results for the LVWS forest simulation showed that simulated forest net primary production (NPP) values were in the expected range of 200 gCm-2yr-1. Simulated forest soil, soil organic matter (SOM), and N-mineralization also were close to observed values. Simulated concentrations of chloride and sulfate generally were consistent in magnitude and timing to measured concentrations at the Loch outlet.

Field Monitoring of DOM and Other Physicochemical Characteristics

We measured a suite of physicochemical and habitat characteristics at 21 stream sites located in central Colorado. These sites encompass a range of metals and DOM concentrations. To characterize how metal complexation varied spatially and temporally with DOM source, we collected water samples at eight time intervals beginning before spring runoff and extending into the fall of 2003. Physicochemical analyses of water samples included pH, alkalinity, hardness, concentrations of DOM, cations (Ca2+, Mg2+, Na+, K+), anions (F-, Cl-, NO3-, PO43-, SO42-), and heavy metals (Cu, Cd, Zn, Fe).

To test whether source determines photochemical effects on the metal-binding characteristics of DOM and metal bioavailability, we collected DOM by reverse osmosis from three paired sets of wetland-stream complexes. DOM was collected during spring runoff, when terrestrial inputs likely dominate, and late in summer when microbial production has a greater influence on composition. For a majority of the monitoring sites, the percentage of fulvic acids was greater during snowmelt than in late summer. It is expected that changes in snowmelt resulting from climate changes will alter the composition of DOM flushed into alpine streams. For instance, more rapid snowmelt will result in a greater flush of humic materials. Changes in the flux of SOM into the stream also will affect the metal-binding and light-attenuation characteristics of aquatic DOM.

Field and Microcosm Experiments to Assess Effects of UV-B and Heavy Metals

Field and microcosm experiments were conducted to assess the interactive effects of UV-B radiation and heavy metals on the structure and function of benthic communities. To determine how exposure history influences community responses to the combined effects of UV-B and metals, two consecutive microcosm experiments were conducted. Macroinvertebrate and periphyton communities were collected from West Tennessee Creek (reference) and the Arkansas River (metal contaminated). Macroinvertebrate communities were collected using artificial substrates (10 x 10 x 6 cm plastic trays filled with pebble and small cobble), and periphyton communities were collected using 5 x 5 cm glazed ceramic tiles. After colonization, the trays and tiles were removed and transferred to the Stream Research Laboratory at Colorado State University, Fort Collins, CO. The 16 microcosms were randomly assigned to one of four treatments (control, metals only, UV-B only, metals plus UV-B) using a 2 x 2 factorial design (metals x UV-B exposure). Concentrations of metals were representative of those measured in the Arkansas River in Colorado. Streams were exposed to UV-B using lamps at levels that were approximately 50 percent of levels expected in the field. To assess the potential indirect effects of metals and UV-B on macroinvertebrate food resources, ash-free dry mass and chlorophyll a—indicators of periphyton biomass and quality—were measured. To determine the effects of metals and UV-B on stream metabolism, we estimated gross primary productivity (GPP) and community respiration.

UV-B had no direct effects on GPP in either microcosm experiment; however, communities from both the metal-impacted site (p = 0.046) and reference site (p = 0.021) had significantly lower GPP in the UV-B + metals treatment. Different metal exposure histories also played a role in community tolerance to metals. GPP in the reference community exposed to metals decreased, while GPP in the metal-treated streams from the impacted community was similar to the control.

Large-scale field experiments were conducted between July 30 and September 30, 2003 to investigate the effects of UV-B on the structure of macroinvertebrate and periphyton communities. Twelve sites were selected across a gradient of metal and DOM levels from the 21 monitoring stations described above. Replicate (n = 3) polyvinyl chloride frames (1.0 x 2.0 m) were placed in riffle areas at similar depths at each site. A greenhouse filter material that blocked UV-B was placed over half of each frame (treatment) while the other half remained uncovered (control). Substrate-filled trays and ceramic tiles were placed under each treatment. Depth, current velocity, and UV-B dose were measured every 4-6 days at each site. We measured UV-B using dosimeters and estimated the amount of UV-B striking the stream bottom based on attenuation coefficients and depth. GPP was estimated on day 30, and macroinvertebrate and chlorophyll a samples were collected on days 15, 30, and 60.

Colonization of blackfly larvae (mostly Simulium spp) was highly sensitive to UV-B exposure, especially at the metal polluted sites. The two sites with the highest Zn concentrations, Chalk Creek (245 µg/L Zn) and French Gulch (361 µg/L Zn), had significantly more blackflies present in the no UV-B treatments than in the controls (p<0.05). These data are consistent with results of microcosm experiments and indicate that the combination of UV-B and metals had greater impacts on aquatic communities than either stressor alone.

Future Activities:

In 2004, we will validate the coupled DayCent and PHREEQC models for the Loch Vale Watershed tundra simulations and improve our streamflow and soil solution DOM estimates at this site. We will simulate heavy metal reactions with DOM and use these models to predict how climate change will influence DOM flux and metal bioavailability at acid mine sites. We will characterize the source and chemistry of humic acids before and after irradiation using fluorescence spectroscopy and UV visible spectroscopy. We will measure Cd, Cu, and Zn complexation using DOM collected in the field before and after photodegradation. These data will be used to model seasonal patterns of free-ion concentrations of Cd, Cu, and Zn using the geochemical speciation program MINTEQA2. We will measure the influence of photodegradation on DOM and bioavailability of heavy metals to macroinvertebrates in the laboratory. Macroinvertebrate and periphyton samples currently are being processed from the field experiments conducted in the summer of 2003. Physicochemical data collected during the field experiments, including levels of DOM and heavy metals, currently are being analyzed. We will repeat these field experiments in the summer of 2004 using larger experimental frames placed at reference and metal-polluted sites.

Journal Articles on this Report : 2 Displayed | Download in RIS Format

Other project views: All 20 publications 5 publications in selected types All 5 journal articles
Type Citation Project Document Sources
Journal Article McKnight DM, Duren SM. Biogeochemical processes controlling midday ferrous iron maxima in stream waters affected by acid rock drainage. Applied Geochemistry 2004;19(7):1075-1084. R829640 (2002)
R829640 (2003)
  • Full-text: Science Direct Full Text
  • Abstract: Science Direct Abstract
  • Other: Science Direct PDF
  • Journal Article Prusha BA, Clements WH. Landscape attributes, dissolved organic C, and metal bioaccumulation in aquatic macroinvertebrates (Arkansas River Basin, Colorado). Journal of the North American Benthological Society 2004;23(2):327-339. R829640 (2002)
    R829640 (2003)
    R829640 (Final)
    R829515 (2003)
    R829515 (2004)
    R829515 (Final)
  • Abstract: Freshwater Science-Abstract
  • Supplemental Keywords:

    watersheds, ecological effects, bioavailability, toxicity, toxics, heavy metals, ecosystem indicators, aquatic, macroinvertebrates, benthic, ecology, hydrology, geology, limnology, modeling, monitoring, field experiments, microcosms, Rocky Mountains, Colorado, CO, EPA Region 8., RFA, Scientific Discipline, Air, Geographic Area, Water, Hydrology, Water & Watershed, climate change, State, Atmospheric Sciences, Ecological Risk Assessment, EPA Region, Watersheds, environmental monitoring, water resources, wetlands, dissolved organic matter, metal toxicity, regional hydrologic vulnerability, global change, aquatic food web, hydrologic models, climate models, UV radiation, Rocky Mountains, Rocky Mountain Streams, aquatic ecosystems, vulnerability assessment, watershed sustainablility, land and water resources, aquatic ecology, climate variability, ecological research, Global Climate Change, land use, climatic models, Colorado (CO)

    Relevant Websites:

    http://www.cnr.colostate.edu/~willc/index.htm Exit
    http://www.nrel.colostate.edu/projects/lvws/ Exit
    http://instaar.colorado.edu/people/bios/mcknight.html Exit
    http://uwadmnweb.uwyo.edu/Zoology/faculty/meyer/meyer.htm Exit

    Progress and Final Reports:

    Original Abstract
  • 2003 Progress Report
  • Final Report