Primary Research Objectives
- Quantify long-term trends in lake and/or stream water, precipitation, and snowpack hydrology and chemistry.
- Examine the role of vegetation, surface organic layers, and shallow soils in modifying precipitation solute concentration and flux.
- Define terrestrial-aquatic linkages for nutrient and energy transfers.
- Examine the effects of global change, especially climate and precipitation, on terrestrial carbon and nitrogen cycles.
- Quantify terrestrial production of dissolved organic carbon and nitrogen, and its input to the aquatic ecosystem.
- Quantify trends in above-ground vegetation diversity, biomass, and nutrient content.
- Quantify long-term trends in terrestrial and aquatic ecosystem production, and define the major processes accounting for observed changes.
The Northern Watershed Ecosystem Project conducts long-term research, inventory, and monitoring in a small network of legally-protected research sites located in National Parks and Preserves. The project goal is to gain understanding of the structure and function of representative ecosystems and their response to stressors. Most sites have been under study for 20+ years. The network of sites represents a diverse set of natural ecosystems from the northern hardwood-boreal ecotone to the taiga-tundra tree line.
Ecological Systems as Interacting Units
Since the 1930's, scientists have recognized that ecological systems have richly detailed energy and nutrient input and output budgets. Nutrient supply is generally the factor most limiting to biological growth and production in temperate and high latitude ecosystems. But without understanding of internal function or processes regulating nutrient and energy transformations and movements within the system, it was difficult to quantitatively separate the effects of different regulatory processes including human activity. The biotic structure and diversity, geologic substrate, climate, and season control the flux of water, nutrients, and energy in ecosystems. For some decades it was recognized that to gain insight into such complex systems a new conceptual research approach was necessary, one which would consider ecological systems as interacting units rather than a set of individual components.
Most human-induced ecosystem responses arise from a plethora of subtle, chronic, and often synergistic stresses rather than the simpler "cause-effect" relationship. A review of the literature for the last several decades suggests that to statistically detect incipient change in terrestrial ecosystems, which can occur decades before above-ground symptoms are apparent, one studies functions (processes). The principal processes studied are production, decomposition, and biogeochemical cycles. Conversely, in the aquatic system shifts in community composition, particularly plankton and benthic crustaceans, often has the most potential to detect incipient change in response to stress. In practical terms, a combination of both strategies is often applied. For policy and perhaps political reasons early detection of incipient response, and the statistical quantification of the magnitude of response, is essential. The ecosystem approach evaluates not just potential responses in one or a few species, but assesses the magnitude of effect throughout the system over the longer-term.
In the 1950's, an ecosystem model was developed where major parameters could be directly measured in the field. By linking hydrology with other ecosystem processes, the "small watershed ecosystem" model permitted quantification of biogeochemical cycles, i.e. the movement and transformation of nutrients and energy (carbon) between the biotic and abiotic components, and other ecosystem processes sensitive to change. The comparison of biogeochemistry among systems provides an index of their functional "health".
To measure nutrient and energy flux one must also understand water movement and the sequential shifts in ecosystem water quality. Understanding hydrology is essential to quantify system nutrient and energy flow, their variation with time, and to detect trends in stream and lake physical and chemical character (Fig. 1). Most nutrient, energy, and water flux occurs as shallow subsurface flow which is difficult, if not impossible, to quantify outside of the watershed context. At least 90+% of surface water in boreal ecosystems passes through the terrestrial component before entering a stream, pond, or lake. In temperate watersheds, it is closer to 98+%.
The Northern Watershed Ecosystem Project also places emphasis on terrestrial below-ground physicochemical and biological processes and functional biodiversity. Greater than 99% of ecosystem biodiversity usually occurs in the sub-surface organic and shallow mineral soil layers. Typically half of the terrestrial system total production occurs below-ground in the form of microbial (bacteria, fungi) biomass and small and fine root growth. The below-ground microbial community regulates the quality and quantity of most nutrients and almost half the energy available to the above-ground biota. Higher latitude terrestrial ecosystems generally have greater than 90% of system carbon and nitrogen in organic form below-ground. Factors affecting below-ground microbial functional diversity, such as nutrient and energy quality or quantity, will in time affect above-ground biomass and its diversity.
The 176 – ha Calumet watershed (47o 17' N, 88o 34' W) is adjacent the south shore of Lake Superior 16 km north of Michigan Technological University (Fig. 2) The watershed is in the sensitive ecotone between northern hardwood and boreal forest. It has a NW aspect, uniform slope, moderate topographic relief with elevation from 190 m at the mouth to 370 m in the headwaters. The bedrock is Cambrian Freda sandstones overlain with alkaline till and old beach deposits. Soils are Typic Haplorthods, sandy, mixed, frigid. The watershed is vegetated by sugar maple (Acer saccharum Marshall) and white birch (Betula papyrifera Marshall), and includes hardwood-dominated and white cedar (Thuja occidentalis) wetlands. Continuous monitoring of watershed hydrology, meteorology, precipitation and stream chemistry began in autumn 1979. Instrumentation includes an upper and lower stream gage; air, snowpack, stream and soil temperature; PAR; and weekly precipitation and snowpack water equivalent (SWE) along an elevation gradient. In 1985, we added replicated instrumented vegetation/soil plots to measure SWE, snowmelt, forest floor and soil water; and instrumented wells to measure change in soil water height with snowmelt (Fig. 3). Precipitation, snowpack, forest floor leachate, soil water, well and stream water chemistry are monitored weekly for macro ions and dissolved organic carbon (DOC) and nitrogen (DON).
Continuous watershed-level monitoring and research began in 1982 (Fig. 4). The 115-ha watershed is located in the northeastern third of Isle Royale National Park in northwestern Lake Superior about 130 km north of Houghton, Michigan.
Included within the gauged first-order watershed is the 5-ha Wallace Lake (Fig. 5). Watershed elevation ranges from 195 to 275 m above sea level, and the watershed has a northern aspect. The watershed topography is broken by a series of small (<5 m elevation) bedrock ridges exposed by glaciation. Wallace Lake is formed behind one such ridge.
Soils are sandy to coarse loamy, mixed, and frigid Alfic Haplorthods deposited during the post-glacial Lake Nipissing stage about 3000 years ago. The overstory is dominated by trembling aspen (Populus tremuloides), white birch (Betual papyrifera), balsam fir (Abies balsamea) and white spruce (Picea glauca). Half of the watershed is vegetated by birch-aspen with the remainder in spruce-fir, tag alder (Alnus rugosa), northern white cedar (Thuja occidentalis), and wetlands.
In 1990 we began continuous monitoring and study of the Asik watershed (lat 67° 58', long 162° 15') located 95 km northeast of Kotzebue, Alaska.
The 800-ha watershed is one of few longer-term study sites located at the taiga-tundra tree line (Fig. 6). The bedrock is sedimentary and metamorphic rock. About 5-7% of the watershed consists of talus slopes. The Noatak River drainage was not glaciated during the last ice age. The soil association is gravelly, hilly to steep Pergelic Cryaquepts – Pergelic Cryorthents, and consists of poorly drained to well-drained soils most with discontinuous permafrost. Upper elevation portions of the lower one-third and most of the middle half of the watershed are dominated by white spruce (Picea glauca) (Fig. 7).
Forest understory consists primarily of Hylocomium splendens, Equisetum arvense, and Boykinia richardsonii, with shrubs of willow (Salix spp.) and Vaccinium uliginosum. The understory of the taiga-tundra transition zone and tundra is dominated by tussocks of Eriophorum vaginatum, Vaccinium uliginosum, Potentilla fruticosa, and birch (Betula nana).
The upper 20% of the watershed area is dominated by shrubs as birch and scattered alder (Alnus crispa) on more northern aspects, and mesic non-tussock tundra. The stream flood zone is dominated by willow.
- Binkley, D., R. Stottlemyer, F. Suarez, and J. Cortina. 1994. Soil nitrogen availability in some arctic ecosystems in Northwest Alaska: responses to temperature and moisture. Ecoscience 1(1):64‑70.
- Binkley, D., F. Suarez, C. Rhoades, R. Stottlemyer, and D. W. Valentine. 1995. Parent material depth controls ecosystem composition and function on a riverside terrace in northwestern Alaska. Ecoscience 2(4):377-381.
- Binkley, D., F. Suarez, R. Stottlemyer, and B. Caldwell. 1997. Ecosystem development on terraces along the Kugururok River, northwest Alaska. Ecoscience 4(3):311-318.
- Rhoades, C. C., H. Oskarsson, D. Binkley, and R. Stottlemyer. 2001. Alder (Alnus crispa) effects on soils in ecosystems of the Agashashok River valley, northwest Alaska. 8(1):89-95.
- Rutkowski, D., and R. Stottlemyer. 1993. Composition, biomass and nutrient distribution in mature northern hardwood and boreal forest stands, Michigan. Am. Midl. Nat. 130:13-30.
- Stottlemyer, R. 1997. Streamwater chemistry in watersheds receiving different atmospheric inputs of H+, NH4+, NO3-, and SO42-. J. Amer. Water Resour. Assoc. 33(4):767-780.
- Stottlemyer, R. 2001. Biogeochemistry of a treeline watershed, Northwest Alaska. J. Environ. Qual. 30(6):1990-1998.
- Stottlemyer, R. 2002. Ecosystem processes and nitrogen export in northern U.S. watersheds. In: Optimizing nitrogen management in food and energy production and environmental protection, J. Galloway, E. Cowling, J. W. Erisman, J. Wisniewski, and C. Jordan (eds), A.A. Balkema Publishers, Tokyo, pp. 581-588.
- Stottlemyer, R., D. Binkley, and H. Steltzer. 2002. Treeline biogeochemistry and dynamics, Noatak National Preserve. In: Studies by the U.S. Geological Survey in Alaska, 2000, F. H. Wilson and J. P. Galloway (eds), USGS Prof. Pap. 1662, pp. 113-122.
- Stottlemyer, R., C. Rhoades, and H. Steltzer. 2003. Soil temperature, moisture, carbon and nitrogen mineralization at treeline, Noatak National Preserve, Alaska. In: Studies by the U.S. Geological Survey in Alaska, 2001, Galloway, J. P. (ed), USGS Prof. Pap. 1678, pp. 127-137.
- Stottlemyer, R., and Toczydlowski, D. 1991. Stream chemistry and hydrologic pathways during snowmelt in a small watershed adjacent Lake Superior. Biogeochemistry 13:177-197.
- Stottlemyer, R., and Toczydlowski, D. 1996 a. Modification of snowmelt chemistry by forest floor and mineral soil, Northern Michigan. J. Environ. Qual. 25:828-836.
- Stottlemyer, R., and Toczydlowski, D. 1996 b. Precipitation, snowpack, stream-water ion chemistry, and flux in a northern Michigan watershed, 1982-1991. Can J. Fish. Aquatic Sciences 53:2659-2672.
- Stottlemyer, R., and Toczydlowski, D. 1999. Seasonal change in precipitation, snowpack, snowmelt, soil water, and streamwater chemistry, northern Michigan. Hydrol. Process. 13:2215-2231.
- Stottlemyer, R., and D. Toczydlowski. 1999. Seasonal relationships between precipitation, forest floor, and stream water nitrogen, Isle Royale, Michigan. Soil Sci. Soc. Amer. J. 63(2):389-398. #2651
- Stottlemyer, R., and D. Toczydlowski. 2006. Effect of reduced winter precipitation and increased temperature on watershed solute flux, 1988-2002, Northern Michigan. Biogeochemistry 77(3):409-440.
- Stottlemyer, R., Toczydlowski, D. and Herrmann, R. 1998. Biogeochemistry of a mature boreal ecosystem: Isle Royale National Park, Michigan. Scient. Monogr. NPS/NRUSGS/NRSM-98/01, U.S. Dept. Interior, National Park Service, Washington, D.C., 116 pp.
- Suarez, F., D. Binkley, M. Kaye, and R. Stottlemyer. 1999. Expansion of forest stands into tundra in the Noatak National Preserve, northwest Alaska. Ecoscience 6(3):465-470.
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