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Interactive Effects of Climate Change, Wetlands, and Dissolved Organic Matter on UV Damage to Aquatic Foodwebs

(Environmental Protection Agency STAR program RD-82964302-0), $937,009, July 2002 – June 2006.
Principal Investigators: Scott D. Bridgham (University of Oregon), Gary A. Lamberti (Notre Dame), Patricia A. Maurice (Notre Dame), David M. Lodge (Notre Dame), Carol A. Johnston (South Dakota State University), and Boris A. Shmagin (South Dakota State University)
Postdoctoral Associate:  Paul Frost (Notre Dame), Kangsheng Wu (South Dakota State University
Graduate Student:  James Larson (Notre Dame)
Technician:  Christine Cherrier (University of Oregon)
           
Project Overview

Understanding the factors controlling ultraviolet radiation (UVR) flux into aquatic ecosystems is critical given its deleterious effects on many ecological processes.  UVR is strongly attenuated in aquatic ecosystems by dissolved organic matter (DOM), and thus we hypothesized that landscape controls over DOM would ultimately control UVR exposure to, and subsequent effects on, stream biota.  Previous research suggests that the quantity and quality of DOM at the landscape scale is controlled primarily by:  (i) vegetation community and soil type, with wetland area being of particular significance, (ii) flow paths through soil, (iii) the discharge regimes of rivers and streams, and (iv) within-stream DOM degradation and production mechanisms.  Climate change will likely affect each of these DOM control factors in complex ways.  While a significant amount of previous research has focused on the separate roles of DOM and UVR in aquatic ecosystems, much less is known about the interactive effects of climate change, landscape, DOM, UVR, and aquatic food webs.

The overarching objective of this project was to enhance the understanding of how UVR affects foodweb structure in streams and rivers through its complex interactions with DOM, landscape characteristics, and climate in a northern forested watershed (Fig. 1).   

More specifically, we had five main objectives:

1. Determine the extent to which UVR exposure in streams is controlled by DOM concentration and chemistry.
2. Determine the response of stream foodwebs to the interactions among UVR intensity and DOM concentration and type.
3. Determine landscape controls over DOM concentration and chemistry (and, hence, UVR).
4. Determine how in-stream processing of DOM through biodegradation and photodegradation varies spatially and controls over that spatial variation.
5. Determine how various climate change scenarios will affect discharge and, thus, DOM concentration and UVR exposure.

Overall Experiment Design

We tested our central hypothesis and the linkages at a variety of spatial scales ranging from artificial streams and laboratory experiments to an entire watershed, as was appropriate to address the project’s five main objectives.  For our landscape analyses that related to Objectives 1 and 3, we sampled 60 catchments within the larger 3,460 km2 Ontonagon River watershed in northern Michigan and Wisconsin (Fig. 2) for DOM concentration and chemistry and related water chemistry variables in September, 2003.  Based upon this initial sampling, we sampled 35 catchments at 11 additional times in all seasons during the next two years.  We also measured discharge at each location at most time points.  Additionally, we sampled soil throughout the basin to obtain their carbon and nitrogen content.  We assembled a large GIS database of land cover and use, stream characteristics, wetland characteristics, soil type, and surficial
geology.  We then used this rich data in a variety of multivariate analyses to describe landscape controls over DOM concentration and chemistry to fulfill Objective 3 (Frost et al. 2006a, Larson et al. 2007, Johnston et al., in press, Bridgham et al., in preparation).  In a subset of these sites, we determined UVR penetration with depth in the water column and related it to DOM concentration and chemistry and other water quality variables to fulfill Objective 1 (Frost et al. 2005, 2006b).

To fulfill Objective 2, we constructed a large artificial stream facility at the University of Notre Dame Environmental Research Center, at the southern edge of the Ontonagon basin, to examine experimentally how DOM and UVR interact in controlling foodweb structure in streams.  We added DOM with natural UVR exposure and with UV-B removed and examined the effects on stream periphyton and algal communities (Frost et al. 2007).  We also used this facility for several other experiments to examine the effects of DOM concentration and chemistry on stream biota (Larson 2006, Frost et al., in preparation).

We performed a variety of experiments in the artificial streams, in the lab, and in situ to examine the effects of photodegradation and biodegradation on DOM concentration and chemistry to fulfill Objective 4 (Young et al. 2004, 2005, Docherty et al. 2006, Larson 2006, Cherrier et al., in preparation).

To fulfill Objective 5, we modeled discharge in the larger branches of the Ontonagon River and examined climatic and land cover controls over discharge in the basin (Wu et al. 2006, Wu and Johnston 2007, in press).  We also related DOM to discharge in the 35 repeatedly sampled catchments (Bridgham et al., in preparation).  However, as most of these catchments are not continuously gauged and thus we could not adequately parameterize the hydrologic model for them, we were somewhat limited in our ability to relate climate-driven changes in hydrology to DOM concentration (and hence UVR exposure) in smaller streams.  Furthermore, to put the Ontonagon basin within a larger geographic context, long-term stream flow records (1956-1988) from 32 U.S. Geological Survey gauging stations within the Great Lakes Basin were analyzed using multivariate statistical techniques (Johnston and Shmagin, in preparation).

Summary/Accomplishments

Landscape Controls over UVR Exposure in Streams

We examined the attenuation of UV-B and UV-A radiation flux and its environmental control directly using spectrometry in 32 streams in the Ontonagon River watershed in 2003 and 2004 (Frost et al. 2005).  Additionally, variation in UV-B and UV-A radiation within and among streams was examined using plastic dosimetry strips along longitudinal transects in seven streams in this same watershed in 2004 (Frost et al. 2006b).  Plastic dosimetry strips indicate a cumulative UV dose by changes in their absorbance characteristics, and deployed over 1-2 days allow for integrated UV measurements at different depths within a stream and under different forest canopy types. 

Both experiments demonstrated strong effects of DOM concentration on attenuation of UV-B and UB-A and the depth at which 1% of the incident UVR remained (Fig. 3).  Shading as determined by canopy cover and stream width also had strong effects on UVR exposure (Frost et al. 2005, 2006b).  We used this information to develop a model to predict UVR exposure in streams in this region (Fig. 4).

Interestingly, it appears that DOM is more effective at attenuating UV-B in streams than in other aquatic ecosystems, likely reflecting its largely terrestrial origin, short residence time, and limited photodegradation and biodegradation  (Frost et al. 2005).  Supporting this interpretation, we found that streams originating from lake outflows had lower DOM concentrations and higher UV-B exposure than streams without lake inputs (Larson et al. 2007).

Overall, our results indicate that the high DOM concentrations in the Ontonagon River watershed, and in other similar systems, strongly limit UVR exposure to aquatic biota in the vast majority of streams and rivers.

Response of Stream Biota to Interactions among UVR Intensity and DOM Concentration and Type

We constructed a large artificial stream facility at the University of Notre Dame Environmental Research Center, at the southern edge of the Ontonagon watershed, to examine experimentally how DOM and UVR interact in controlling food-web structure in streams.  The artificial stream facility consists of 24 channels fed with groundwater or lake water with motorized paddles providing current.  We conducted two artificial stream experiments in the summer of 2003 and two experiments in the summer of 2004. 

Overall, these experiments indicate minimal effects of UV-B on periphyton mass or algal community composition, but increased DOM concentrations caused greater accumulation of periphyton mass (Fig. 5), altered its C, N, and P stoichiometry, and changed algal community composition (Larson 2006, Frost et al. 2007). 

We also performed two experiments where we reciprocally transplanted the microbial communities from two to three
different aquatic DOM sources.  These experiments indicated strong effects of DOM source on microbial community structure and growth and large effects of microbial community structure on DOM biodegradation dynamics (Young et al. 2004, 2005, Docherty et al. 2006).

Overall, our results indicate that UVR has minimal effects on stream biota in these streams because of high natural DOM concentrations, but that DOM concentration and type is a primary driver of periphyton and microbial community structure and ecosystem function.

Landscape Controls over DOM Concentration and Chemistry 

Given the above results showing the central importance of DOM in controlling UVR exposure to stream biota, and in controlling overall stream structure and function, we spent considerable efforts to understand landscape controls over DOM concentration and chemistry.  We sampled 35 catchments in the Ontonagon River basin a dozen times over a 2-year period.  Additionally, we did an initial survey of 60 sampling locations within the Ontonagon River basin in September, 2003, upon which we based our final selection of the 35 sites that were sampled seasonally.  In each sample we measured DOM concentration and chemistry, dissolved and particulate nitrogen and phosphorus, cation concentrations, particulate carbon, total suspended solids, chlorophyll, and stream pH.  In addition, stream gauge height was recorded at each visit to a site, and discharge was also determined 4-6 times at each site to develop stage-discharge curves.

The second component to our watershed analysis was to relate DOM concentration and physiochemistry in tributaries of the Ontonagon River to discharge and landscape characteristics with multivariate statistics (multiple regressions, Akaike Information Criterion [AIC], and Classification and regression trees [CART]). We compiled an extensive GIS landscape database for each of the 60 catchments, including stream characteristics, wetland abundance and type,

upland landscape characteristics, land use, surficial geology, soil carbon and nitrogen, and topography. 

This landscape analyses showed a strong effect of wetland area on DOM concentration and physiochemistry, but the area of different types of wetlands may have positive or negative correlations with DOM concentrations (Frost et al. 2006a, Johnston et al., in press).  However, there are also important additional landscape controls over DOM concentration and physiochemistry, including upland land cover and topography (Frost et al. 2006a, Bridgham et al., in preparation).  The DOM concentration/discharge relation was widely variable among the catchments but it could be predicted well with % development, soil C:N ratios, stream density, and a limited number of surficial geology predictors (Bridgham et al., in preparation).  Many of the streams in this region originate as lake outflows, and such streams have lower DOM and molar absorptivity (UVR adsorbance per unit C) than streams not originating from lakes (Larson et al. 2007).

Controls Over In-Stream Processing of DOM

We performed two studies that examined the role of microbial community structure and the initial molecular-weight distribution of DOM in DOM biodegradation rates.  These studies have resulted in three publications (Young et al. 2004, 2005, Docherty et al. 2006).

We completed a long-term DOM biodegradation experiment that addressed three questions:

1. How do DOM concentration and quality interact to affect DOM biodegradation rates?
2. Does low nutrient availability constrain DOM biodegradation in some streams?
3. Is the effect of photodegradation on DOM biodegradation rates dependent on the DOM source?

We filtered water from six streams with different DOM concentration and chemistry characteristics and added a composite microbial community from all six sites to each sample.  We additionally had three treatments: (a) + nutrients, (b) no nutrients, and (c) photodegraded and then biodegraded, with five replicates of each stream-treatment combination.  Response variables included short-term DOM biodegradation by determining CO2 production and bacterial production over 72 hr and long-term DOM biodegradation by measuring the change in DOM concentration until it stabilized, with the remaining fraction indicating the recalcitrant portion of the DOM.  We are still in the final process of analyzing the results, but overall they indicate that most stream DOM is highly recalcitrant and not biodegradable even after prolonged decomposition, biodegradation of DOM is not nutrient limited, and prior photodegradation substantially enhances biodegradation.

In two other experiments, we examined the relative importance of photodegradation, biodegradation, and periphyton on the concentration of DOM and its photoreactions (Larson 2006).  Overall, these experiments indicated that all three mechanisms, and their interactions, are important in the consumption of stream DOM.

Effects of various climate change scenarios on discharge

The hydrology of the Ontonagon River is greatly influenced by the climate-sensitive phenomenon of snow melting (Wu et al 2006, Wu and Johnston 2007).  Long-term stream flow data from U.S.G.S. gauging stations and discharge data collected for this project consistently showed that peak monthly discharge occurred during April snowmelt events, when the accumulated snow pack rapidly released water into streams.  Because April discharge is typically three to six times that of flow during the rest of the year, snowmelt events dominate total annual discharge.  The high discharge that occurred during snowmelt in April 2003 caused a convergence of DOC concentrations in which normally low DOC streams increased in concentration and normally high DOC streams decreased in concentration (Johnston et al., in press).

Hydrologic response to climate change was evaluated by creating two versions of the Soil & Water Assessment Tool (SWAT) model for the 901 km2 South Branch Ontonagon River watershed: one calibrated for average climatic conditions (1969-70) and the other calibrated for drought conditions (1948-49) (Wu and Johnston 2007).  Snow melting parameters were altered by drought conditions, increasing snow melting rate and forcing peak flow timing to occur earlier in the spring.  The hydrology of the South Branch Ontonagon River was also influenced by the climate-sensitive phenomenon of evapotranspiration.  Monthly evapotranspiration in this forest-dominated watershed equals or exceeds monthly precipitation for five months of the year, making evapotranspiration an important factor in the annual water budget.  Our calibration results imply that drought conditions reduce the capacity of upper soil layers to meet soil evaporative needs, altering plant water uptake strategies under varying climatic conditions.  When the two versions of the SWAT model were applied to a validation data set (1950-65), the drought-calibrated version performed much better than did the average-calibrated version because of the dry conditions that prevailed during most of the validation period (Wu and Johnston 2007).

The SWAT model was also used to compare the hydrology of adjacent catchments dominated by wetlands and lakes (Middle Branch Ontonagon River) versus forest (East Branch Ontonagon River) (Wu and Johnston, in press). The wetland/lake dominated catchment exhibited substantially different temporal flow trends than did the adjacent forested wetland, with lower peak flows in April and higher baseflows during summer months (Fig. 6).  These results suggest an important storage function of wetlands and lakes, increasing a watershed's ability to moderate extreme flows and gradually release water into receiving streams through baseflow.  The snow melting algorithm in the SWAT model was essential to adequately simulate flow in this region of high snowfall.  Snow melt parameters were not transferable between the two adjacent watersheds, however, and suggested a significant impact of forest canopy and slope direction on snow-pack temperature.  Despite different seasonal patterns of monthly stream flow, the similarity in annual runoff efficiency between the two watersheds suggests a similar evapotranspiration demand and geologic structure in the adjacent watersheds, so that the watersheds produce a similar quantity of streamflow through different pathways.

To put the Ontonagon Basin within a larger geographic context, long-term stream flow records (1956-1988) from 32 U.S. Geological Survey gauging stations within the Great Lakes Basin were analyzed using multivariate statistical techniques (Johnston and Shmagin, in preparation). Factor analysis and cluster analysis of average annual flow revealed six patterns of river runoff within six distinct regions of the basin. Streams represented by pattern 1, including the Middle Branch Ontonagon River, occurred mostly in the upper peninsula of Michigan. This region exhibited relatively constant flow through the 1960s and 1970s, but decreasing flow during the 1980s. Streams represented by pattern 2 occurred mostly in New York State, and had pronounced cycles of low flow in the early 1960s and high flow in the 1970s, returning to average during the 1980s. Streams represented by pattern 3 occurred mostly in the lower peninsula of Michigan, and exhibited a continuous increase in flow over the 30-year time period.  The remaining three patterns distinguished watersheds in Ohio, Minnesota, and Wisconsin, respectively.  These historical results imply that the different flow regions of the Great Lakes Basin will respond differently to future climate change.

Significance of Accomplishments
We have thoroughly addressed each of our original five objectives and detailed the complex interactions among land use and land cover, climate, DOM, and UVR damage to aquatic foodwebs.  The streams in the northern Great Lakes region typically have very high concentrations of colored DOM, which is an effective attenuator of UVR.  Canopy cover also effectively reduces UVR exposure to streams.  Consequently, we conclude that the biota in the streams in this region likely experience minimal UVR exposure, except if they are shallow, have low DOM, and have a relatively open canopy.  However, even moderate amounts of DOM greatly reduce UVR exposure to stream biota. 

While UVR exposure appears to be of minor significance to stream biota in the northern Great Lakes region, DOM is extremely important in structuring stream foodwebs and in ecosystem services such as productivity.  Besides its effect on the attenuation of visible light and UVR, DOM acts as a carbon and nutrient subsidy.  At a landscape scale, DOM concentration and chemistry are controlled by a complex set of factors that include vegetation, soil, and surficial geology, but our findings reinforce those of previous studies that wetlands are a particularly important landscape control over DOM.  To our knowledge, this is the first study to demonstrate that different kinds of wetlands can have positive or negative effects on DOM concentration and properties.  The direct effects of future climate change on stream biota will be enhanced to the extent that they affect the landscape factors that control the production, transport, and cycling of DOM.  In particular, changes in wetland area and type and hydrology may be particularly important controls over future DOM dynamics in aquatic ecosystems.

Presentations
Bridgham, S. D. Jan. January 2004. Wetlands and global change: from microbes to watersheds.  Geography Department, University of Oregon.
Bridgham, S. D.  2005.  Interactive effects of climate change, wetlands, and dissolved organic matter on UV damage to aquatic foodwebs.  U.S. Environmental Protection Agency’s Global Change and Ecosystem Protection Research STAR Progress Review Workshop, Washington, DC. Nov. 3-4.
Bridgham, S. D.  2005.  Interactive effects of climate change, wetlands, and dissolved organic matter on UV damage to aquatic foodwebs.  U.S. Environmental Protection Agency’s Global Change and Ecosystem Protection Research STAR Progress Review Workshop, Washington, DC. Nov. 3-4.
Bridgham, S. D., P. C. Frost, J. H. Larson, C. A. Johnston, K. C. Young, C. T. Cherrier, G. A. Lamberti, P. A. Maurice, D. M. Lodge.  May 2004.  Landscape control of dissolved organic matter concentration and chemistry in a northern Michigan watershed.  Eos Trans. AGU,85(17), Jt. Assem. Suppl., Abstract B31B-04. American Geophysical Union Joint Assembly, Montreal Canada.
Frost, P. C. May 2003. Ecological stoichiometry and its potential uses for benthic ecologists. North American Benthological Society. Athens, Georgia.
Frost, P. C., G. A. Lamberti, J. H. Larson, D. M. Lodge, P. A. Maurice, S. D. Bridgham, C. A. Johnston, and B. A. Shmagin. 2003.  Landscape control of DOC and UV radiation and their effects on stream food webs in northern Michigan. Symposium on Notre Dame Environmental Education and Research. University of Notre Dame. Notre Dame, Indiana. Nov.
Frost, P. C., G. A. Lamberti, J. H. Larson, D. M. Lodge, P. A. Maurice, S. D. Bridgham, C. T. Cherrier, C. A. Johnston, and B. A. Shmagin. October 2003. Landscape control of DOC and UV radiation and their effects on stream food webs in northern Michigan. Dissertation Initiative for the Advancement of Limnology and Oceanography V Symposium. Bermuda Biological Station for Research, Bermuda. (poster)
Frost, P. C., J. H. Larson, C. T. Cherrier, G. A. Lamberti, D. M. Lodge, and S. D. Bridgham. 2004. Dissolved organic matter, ultraviolet radiation, and their interactive effects on the accumulation of stream periphyton. North American Benthological Society. Vancouver, B.C., June.
Frost, P. C., J. H. Larson, C. T. Cherrier, G. A. Lamberti, D. M. Lodge, and S. D. Bridgham. 2004. Effects of dissolved organic matter and ultraviolet radiation on the biomass and taxonomic composition of stream periphyton. Ecological Society of America. Portland, OR, Aug.
Frost, P. C., J. L. Larson, C. T. Cherrier, Z. Zheng, C. A. Johnston, S. D. Bridgham, G. A. Lamberti, and D. M. Lodge.  2005.  C:N ratios of organic particles in northern Michigan streams: effects of lakes, wetlands, and watershed size.  American Society for Limnology and Oceanography, Salt Lake City, Utah, Feb. 20-25.
Frost, P. C., J. L. Larson, C. T. Cherrier, Z. Zheng, C. A. Johnston, S. D. Bridgham, G. A. Lamberti, and D. M. Lodge.  2005.  Stoichiometry of suspended organic particles in northern Michigan streams:  effects of watershed landcover and geomorphology.  Society of Canadian Limnology, Jan.
Frost, P. C., J. H. Larson, K. C. Young, C. A. Johnston, S. D. Bridgham, P. A. Maurice, G. A. Lamberti, and D. M. Lodge. February 2003. Landscape control of DOC quantity and quality in northern Michigan streams. American Society of Limnology and Oceanography. Salt Lake City, Utah.
Frost, P. C., M. A. Xenopoulos, and J. H. Larson. July 2004. A three element (C, N, P) model of consumer growth and nutrient release. Gordon Research Conference. Bates College, ME. (poster)
Golden, S. M., P. A. Maurice, and S. D. Bridgham. 2003. Controls on dissolved organic matter in wetlands: Importance of hydrologic flow paths.  Annual meeting of the American Society of Limnology and Oceanography, Salt Lake City, UT.
Johnston, C. A., B. A. Shmagin, and S. D. Bridgham. May 2004. Hydrological regionalization of the U.S. Great Lakes Basin. Annual Conference on Great Lakes Research, Waterloo, ON.
Johnston, C. A., B. A. Shmagin, and S. D. Bridgham. 2004. Climate change effects on streamflow from wetland-dominated watersheds of the U.S. Great Lakes basin. Soil Science Society of America, Seattle, WA, Nov.
Johnston, C.A., B.A. Shmagin. P.C. Frost, J.H. Larson, G.A. Lamberti, S.D. Bridgham. Digital Wetland Databases Differ in Ability to Predict DOC Concentrations in Streams (poster). Biogeomon 2006, 5th Intenational Symposium on Ecosystem Behavior, Santa Cruz, CA. 25-30 June.
Kinsman, L. E., P. C. Frost, J. H. Larson, C. T. Cherrier, G. A. Lamberti, and S. D. Bridgham.  2005.  Attenuation of ultraviolet radiation in streams and lakes of northern Michigan: Effects of seasonal changes in dissolved organic carbon concentration and chemistry.  American Society for Limnology and Oceanography, Salt Lake City, Utah, Feb. 20-25.
Lamberti, G. A., S. D. Bridgham, C. Cherrier, P. C. Frost, C. A. Johnston, and J. H. Larson.  2006.  Landscape controls over seasonal dissolved organic matter concentration in a northern Michigan, USA watershed.  American Geophysical Union, San Francisco, CA, Dec. 11-15.
Larson J.H., D.M. Costello, K.J. Kulacki, and G.A. Lamberti.  2006.  The effect of ionic liquids on the retention of nutrients by aquatic invertebrates.  Ohio Valley Regional Chapter of the Society of Environmental Toxicology and Chemistry, Fort Wayne, IN, Apr. 20-21.  Note: won best student presentation
Larson, J., P. C. Frost, S. D. Bridgham, P. A. Maurice, G. A. Lamberti, D. M. Lodge, C. A. Johnston, and B. A. Shmagin.  2002. What are the critical controls over ultraviolet radiation (UVR) damage to aquatic organisms? Symposium on Notre Dame Environmental Education and Research. University of Notre Dame. Notre Dame, IN, Nov. (poster)
Larson, J.H., P.C. Frost, R. Buck, G.A. Lamberti, and D.M. Lodge.  2005.  Interactive effects of ionic liquids, dissolved organic matter, and nutrients on an aquatic plant.  Symposium on Notre Dame Environmental Education and Research.  University of Notre Dame, Notre Dame, IN, Nov. 8.
Larson, J.H., P.C. Frost, G.A. Lamberti, and D.M. Lodge.  2005.  The interactive effects of ionic liquids, dissolved organic matter and nutrient limitation on the growth of duckweed, Lemna minor.  2005.  Ionic Liquids Symposium.  University of Notre Dame, Notre Dame, IN, Feb. 15.
Larson, J.H., P.C. Frost, D.M. Lodge, and G.A. Lamberti. Photodegradation of dissolved organic matter from streams in northern Michigan.  2006.  North American Benthological Society, Anchorage, AK, June 4-9.
Larson, J. H., P. C. Frost, G. A. Lamberti, D. M. Lodge, S. D. Bridgham, C. A. Johnston, P. A. Maurice, and B. A. Shmagin. 2003. Landscape controls over dissolved organic carbon and ultraviolet penetration in streams of northern Michigan. North American Benthological Society. Athens, GA, May. (poster)
Larson, J. H., P. C. Frost, Z. Zheng, C. Johnston, S. D. Bridgham, G. A. Lamberti, and D. M. Lodge.  2005.  Do upstream lakes affect the quantity and absorbance of dissolved organic matter in streams?  North American Benthological Society and American Geophysical Union, New Orleans, LA, May 23-27.
Shmagin, B. A., and C. A. Johnston. 2004. Minnesota's place in hydrological regionalization of the U.S. Great Lakes basin. Minnesota Water 2004: Policy and Planning to Ensure Minnesota's Water Supplies. Minneapolis, MN, March.
Shmagin, B., C. Johnston and S. Bridgham. 2004. The spatial temporal regime of stream flow of the conterminous U.S. in connection with indices of global atmospheric circulation. Eos Trans. AGU, 85(17), Jt. Assem. Suppl., Abstract H33A-06. American Geophysical Union Joint Assembly, Montreal Canada, May.
Shmagin, B.A., C.A. Johnston, and S.D. Bridgham. 2005. Multidimensional structure of streamflow regime in a hierarchy of landscapes within the U.S. Great Lakes basin. 48th Annual Conference on Great Lakes Research. Ann Arbor, MI. 23-27 May.
Shmagin, B. A., C. A. Johnston, and S. D. Bridgham.  2005.  Ecohydrology or Hydroecology: time-space and scale-metric aspects.  Ecological Society of America/INTECOL, Montreal, August 7-12.
Shmagin, B. and R. Kanivetsky.  2006.  Regional hydrology:  tools vs.ideas. American Institute of Hydrology Annual Meeting & InternationalConference, Baton Rouge, LA. 21-24 May.
Young, K. C., K. M. Docherty, P. A. Maurice, and S. D. Bridgham. 2002. Biogeochemical controls of natural organic matter evolution in UNDERC wetlands.  Symposium on Notre Dame Environmental Education and Research. University of Notre Dame. Notre Dame, Indiana, Nov. (poster)
Young, K. C., K. M. Docherty, P. A. Maurice, and S. D. Bridgham. 2003. The dependence of dissolved organic matter biodegradation on microbial community structure in northern wetlands.  American Society of Limnology and Oceanography. Salt Lake City, Utah, Feb.
Young, K. C., P. A. Maurice, K. M. Docherty, S. D. Bridgham, and C. F. Kulpa.  2005.  A molecular-based study of bacterial degradation of dissolved organic matter from northern Michigan surface waters.  American Society for Limnology and Oceanography, Salt Lake City, Utah, Feb. 20-25.
Wu, K., B. Shmagin, and C. Johnston. 2005. Seasonal Patterns of Baseflow and Surface Runoff in the Ontonagon River Watershed, Michigan (poster). South Dakota/North Dakota EPSCoR 5th Biennial Joint Conference, Brookings, SD, Sept. 8-9.
Wu, K., C.A. Johnston, C. Cherrier, S. Bridgham, and B. Shmagin. 2006. Hydrologic calibration of the SWAT model in a Great Lakes coastal watershed. American Institute of Hydrology Annual Meeting & International Conference, Baton Rouge, LA, May 21-24 .
Zheng, Z., C. A. Johnston, P. C. Frost, J. H. Larson, S. D. Bridgham, and C. T. Cherrier.  2004. Effect of landscape characteristics on DOC concentration in streams of Ontonagon watershed (poster). Rushmore Regional Conference on Biocomplexity, Sioux Falls, SD, Aug.

Publications

Bridgham, S. D., C. T. Cherrier, C. A. Johnston, P. Frost, and J. H. Larson.  In Preparation.  Landscape and hydrological controls over dissolved organic carbon concentration in a northern Michigan watershed.
Cherrier, C. T., S. D. Bridgham, and J. H. Larson.  In Preparation.   Relative effects of source, nutrient availability, and photodegradation on long-term and short-term decomposition of dissolved organic matter in streams.
Docherty, K. M., K. C. Young, P. A. Maurice, and S. D. Bridgham.  2006. Dissolved organic matter concentration and quality influences upon structure and function of freshwater microbial communities.  Microbial Ecology 52:378-388.
Frost, P. C., C. T. Cherrier, J. H. Larson, S. Bridgham, and G. A. Lamberti.  2007.  Effects of dissolved organic matter and ultraviolet radiation on the accrual, stoichiometry, and algal taxonomy of stream periphyton.  Freshwater Biology 52:319-330.
Frost, P. C., J. H. Larson, C. A. Johnston, K. C. Young, P. A. Maurice, G. A. Lamberti, and S. D. Bridgham.  2006a.  Landscape predictors of stream dissolved organic matter concentration and physicochemistry in a Lake Superior river watershed.  Aquatic Sciences 68:40-51.
Frost, P. C., J. H. Larson, G. A. Lamberti, D. M. Lodge, and S. D. Bridgham.  2005.  Rapid attenuation of ultraviolet radiation by dissolved organic carbon in streams of northern Michigan.  Journal of the North American Benthological Society 24:246-255.
Frost, P. C., A. Mack, J. H. Larson, S. D. Bridgham, and G. A. Lamberti.  2006b.  Environmental controls of UV radiation in forested streams of northern Michigan.  Photochemistry and Photobiology 82:781–786.
Johnston, C.A., and B.A. Shmagin. In Preparation. Climate change effects on streamflow from wetland-dominated watersheds of the U.S. Great Lakes basin.
Johnston, C. A., B. A. Shmagin, P. C. Frost, C. Cherrier, J. H. Larson, G. A. Lamberti, and S. D. Bridgham.  In Press.  Wetland types and wetland maps differ in ability to predict dissolved organic carbon concentrations in northern Michigan streams.  Science of the Total Environment.
Kinsman, L. E., P. C. Frost, J. H. Larson, and G. A. Lamberti.  Submitted.  Temporal variation in dissolved organic carbon concentration and chemistry: Effects on attenuation of ultraviolet radiation in streams and lakes of northern Michigan.  Chemosphere.
Larson, J. H.  2006.  Interactions between dissolved organic matter sources and effects on stream ecosystems.  Ph.D. dissertation, University of Notre Dame, Notre Dame, IN. 
Larson, J. H., P. C. Frost, and G. A. Lamberti.  Submitted.  Variable toxicity of ionic liquids to Lemna minor and the influence of dissolved organic matter.  Environmental Toxicology and Chemistry.
Larson, J. H., P. C. Frost,  D. M. Lodge, and G. A. Lamberti. In Press.  Photodegradation of dissolved organic matter in forested streams of the northern Great Lakes region.  Journal of the North American Benthological Society.
Larson, J. H., P. C. Frost, Z. Zheng, C. A. Johnston, S. D. Bridgham, D. M. Lodge, and G. A. Lamberti.  2007.  Effects of upstream lakes on dissolved organic matter in streams.  Limnology and Oceanography 52:60-69.
Shmagin, B. and R. Kanivetsky.  2006.  Regional hydrology:  tools vs. ideas.  Pages 183-196 in Coastal Hydrology and Processes, V.P. Singh and Y. Jun Xu, eds., Proceedings of the American Institute of Hydrology 25th Anniversary Meeting & International Conference, “Challenges in Coastal Hydrology and Water Management.” Water Resources Publications, Highlands Ranch, CO.
Wu, K., C. Johnston, C. Cherrier, S. Bridgham, and B. Shmagin.  2006.  Hydrologic calibration of the SWAT model in a Great Lakes coastal watershed.  Pages 15-28 in Coastal Hydrology and Processes, V.P. Singh and Y. Jun Xu, eds., Proceedings of the American Institute of Hydrology 25th Anniversary Meeting & International Conference, “Challenges in Coastal Hydrology and Water Management.” Water Resources Publications, Highlands Ranch, CO.
Wu, K. and C. Johnston.  2007.  Hydrologic response to climatic variability in a Great Lakes Watershed: a case study with the SWAT model.  Journal of Hydrology 337:187-199.
Wu, K., and C.A. Johnston. In Press. Hydrologic comparison between a forested and a wetland/lake dominated watershed using SWAT.  Hydrological Processes.
Young, K. C., P. A. Maurice, K. M. Docherty, and S. D. Bridgham.  2004.  Bacterial degradation of dissolved organic matter from two northern Michigan streams.  Geomicrobiology Journal 21:521-528.
Young, K. C., P. A. Maurice, K. M. Docherty, and S. D. Bridgham.  2005.  Influences of carbon quality and microbial populations upon dissolved organic matter degradation in two streams and a dystrophic pond.  Hydrobiologia 539:1-11. 

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