0295-B1

The Role of Forests in Regulating Water Quality: The Turkey Lakes Watershed Case Study

N.W. Foster^[1], F.D. Beall and D.P. Kreutzweiser

Abstract

Increased concerns over diminishing renewable freshwater supplies have prompted global interest in watershed research and management. In some parts of the world, including Canada, much of the accessible freshwater supply is derived from forested watersheds. The development of forest watershed management policies for the maintenance of freshwater supplies and aquatic habitats requires science-based knowledge of land/water linkages and their underlying, hydrological, biogeochemical, and ecological processes. A number of large-scale watershed studies have been established in North America to examine these linkages and processes in support of watershed management decisions. Among these the Turkey Lakes Watershed (TLW), a rare example of a long-term fully integrated examination of the biology and chemistry of the atmosphere, forests, soils, streams, and lakes, is presented as a case study. Multi-agency, interdisciplinary research at the TLW, that has strong links internationally, has included hydrological studies, examination of landscape influences on nutrient export to surface waters, and impacts of catchment disturbance on water yield, nutrient flux, carbon cycling, and sedimentation in streams. Results have contributed to international policy on acid rain reductions and air quality agreements. Results can be utilized in other boreal and north temperate countries for the design and implementation of forest management practices that ensure the protection of aquatic ecosystems and water resources. The TLW research approach can be used globally to scientifically assess how natural and human actions affect the important services provided by forested watersheds.

Introduction

A renewed focus on issues of water and watershed management is occurring worldwide in preparation for the “International Year of Water Resources” in 2003. There is a growing international concern that shortages of fresh water and the increasing pollution of water bodies are limiting economic development in many countries (Sedell et al. 2000). Demand for water is growing in Canada and other jurisdictions and the provision of abundant and safe drinking water must be a top priority of land-use decisions. The most significant water quality problems resulting from unrestricted logging, and land clearing are increases in sediment, nutrients, and temperature of first-order streams.

Why is the provision of clean water from forest watersheds so important? The global economy (energy, transportation), quality of life, and cultural identity are highly dependent on forest watersheds and water resources. As a result of expanding human activity there will be an increased global demand for forests to provide clean water for a multiplicity of purposes, including agriculture, fisheries, and recreation. With 10% of the world's forests and 7 % of the world's usable freshwater resources (much of it in forested areas), Canada's forests play critical roles in the regulation of stream flow and the maintenance of water quality. Watershed management in any nation must strike a balance between protection of water quality and quantity and the production of other values (timber, recreation, wildlife habitat etc.).

Decisions on watershed management must be supported by both traditional and scientific knowledge of watershed functioning. Often watershed management standards in forestry are based on professional judgment because research has not defined the best management practices to integrate wood extraction with sustainable silviculture and the protection of other watershed values. It is imperative to understand the interaction of the hydrological cycle, geology, topography, soils, vegetation and the effects of human activities to design and implement safe, efficient land-use practices. To ensure that development does not result in water contamination or shortages, water management programs must be developed worldwide that emulate the results of research and monitoring, that have demonstrated how forests can be managed to sustain the supply of clean water for many needs. Synthesis of long-term research from watershed case studies is the foundation for a watershed management knowledge base, for translating science into practice and for developing policy to support sound management practices. We will use the Turkey Lakes Watershed (TLW), a headwater system with late-succession tolerant hardwood forest on steep terrain in humid, mid-continental America, to illustrate the utility of multidisciplinary research watersheds.

Policy Contributions

Around the world, countries continue to develop institutional responses to combat air pollution threats to ecosystems and human health. Effects research at TLW has developed and applied models simulating acidification effects on aquatic chemistry and biology (Lam et al. 1988); assessed the role on nitrogen-based pollutants in water and soil acidification (Foster and Hazlett 2002), and examined the process, reversibility, and extent of chemical and biological recovery in streams and lakes (Jeffries et al. 2002). Scientific findings from the TLW have reported on the effectiveness of domestic SO₂ emission controls implemented in the 1980’s (Table 1), supported the negotiations that culminated in the Canada/US Air Quality Agreement (Canada/US 1983), and contributed to a national strategy for a post-2000, long-term domestic Acid Rain Program (Environment Canada 1997). The latter report concludes that acidic deposition is a continuing threat to aquatic biota in eastern Canada and that further emission reductions are needed across eastern North America. Discharge water losses of sulphate from headwater basins remain high at TLW (Beall et al. 2001), thereby slowing recovery of surface waters from acidification.

Table 1. Pre-harvest mean annual soil water NO₃^- concentrations (ueqL^-1) at the Turkey Lakes Watershed and mean annual changes due to different intensities of harvest.

In 1998 the New England Governors and Eastern Canadian Premiers Conference formulated an Acid Rain Action Plan to address concern relating to soil acidification and forest health impacts. This action plan identified the mapping of forest sensitivity to acid deposition across eastern North America as a priority to enhance policy dialogue on further emission reductions. Biogeochemical data from the TLW and another 20 Canadian and 15 American plots and watersheds will be used along with spatial interpolation methods for mapping (Arp et al. 2001). By the completion of the project new technologies will have been developed and applied to integrate process studies and scale process information spatially and temporally. Maps will be developed that show the spatial distribution of sustainable acid deposition rates, where these rates are likely exceeded, and by how much.

Forest Management Contributions

Globally policy makers continue to face important decisions relating to the effects of forest management practices on water quality and quantity. A key to improving the knowledge base on forest management impacts on aquatic systems is to incorporate paired-basin manipulative experiments and process studies into watershed research. Acquisition of this knowledge is relevant to the development of several Criteria and Indicators (C & I) that are being used in the Montreal Process to evaluate sustainable forestry in 12 countries with more that 70 % of the boreal forest (Canadian Forest Service 1995). The operational relevance of research results must be improved in order to develop cost-effective techniques for monitoring water quality and meet reporting requirements under C & I. In a summary of research on forest disturbance impacts, Buttle et al. (2000) listed the TLW and 7 other paired-basin studies that were distributed in four ecozones of Canada (Pacific Maritime, Montane Cordillera, Boreal Plain, and Boreal Shield). Additional examples of multidisciplinary research on the effects of land management on water quality are the U.S. Forest Service experimental forest watersheds (e.g., Coweeta, Fernow, H.J. Andrews, and Hubbard Brook).

At the TLW, a Harvesting Impacts Project included stem-only harvesting (clear-cut), a shelterwood cut, a selection cut, and a control (no cut). The main objective with respect to water management was to quantify harvest intensity impact on water yield, quality and fauna in forest streams. Selective harvesting at up to 50% removal mitigated most of the 3-yr increases in nitrate, calcium, and sedimentation that were produced in streams by clearcut logging (Fig. 1;Table 2). Annual water yield was not affected by harvesting, although an increase in streamflow during the summer low-flow period was observed (Fig. 1a). Gradual removal harvesting operations offered greater protection of soils and natural regeneration and thereby increased protection of water quality. In contrast to long-lasting impacts of other land-use changes, a return to pre-harvest levels in headwater streams was observed on all treatments for nitrate and calcium concentrations 3 years after harvest. The magnitude and duration of impacts on secondary and tertiary streams can be controlled by the timing, size, and dispersion of harvesting within the watershed.

Table 2. Mean annual sulfate fluxes (kg/ha) in 1981 at the Turkey Lakes Watershed and mean five-year changes due to reductions in SO₂ emissions in North America.

Stream data in last column is for 1997-2000 calendar years.

Figure 1. Annual yield of water, nitrate-N, calcium and dissolved organic carbon (DOC) from headwater catchments at TLW. Treatment catchments were harvested in August/September, 1997. Water years at TLW are defined as the period between June 1 and May 31 of the following year.

Soils, especially those on steeper slopes, are sensitive to disturbance and mismanagement of land because they are prone to erosion. Commercial forestry operations (especially the roads associated with these practices) within watersheds can result in changes in water quality due to increased silt deposition (Waters, 1995). In the TLW Harvesting Impacts Project, fine sediment deposition in streams was measured across the gradient of harvesting intensity (Kreutzweiser and Capell, 2001). Clearcut harvesting caused significant increases in sediment deposition as a result of heavy ground disturbance and channeled flowpaths from skidder activity in riparian areas. Sediment increases at other sites were attributable to road construction and maintenance, underscoring the need for designing and implementing effective sediment control strategies for road building in forest watersheds. At the shelterwood site (about 50 % removal) where roads were not a factor, no measurable increases in sediment deposition were detected even in the absence of protective buffer zones (Fig. 2). The TLW results demonstrate that selective hardwood harvesting at up to 50 % removal can be conducted without causing sediment inputs to streams by following best management practices and careful skid trail orientation. This science-based information contributes to the development of forest management guidelines for the protection of water resources.

Figure 2. Stream inorganic fine sediment bed load (mean ± 1 SE, n=10) collected before and after harvesting in the Turkey Lakes Watershed.

Sustainability of Watershed Services

International inter-site comparisons between watersheds are one of the most valuable approaches that can be used to test hypotheses and to advance knowledge on how anthropogenic, as well as natural factors influence forested watersheds. Such an approach may involve the application of a standardized experiment with a common set of measurements. An example is the Integrated Forestry Study, an international interdisciplinary study of processes of nutrient transfer linking the atmosphere, living plants and animals, soil and soil water (Electric Power Research Institute 1986). Atmospheric acid inputs and their impacts on nutrient movement to ground and surface waters were quantified simultaneously across a range of vegetation and soil types across North America (including TLW) and Norway during 1986-89. An across-site comparison revealed that retention of atmospheric nitrogen was amongst the lowest in TLW soils (Johnson and Lindberg 1992). Such comparisons foster interdisciplinary collaboration between scientists and can become a focal point for communicating information about water quality issues globally.

Alternatively, comparisons may take the form of sharing perspectives and results with others involved in similar research and the development of larger scale, more comprehensive research projects. An example is the Northeastern Ecosystem Research Cooperative (NERC), which supports research on watersheds across the eastern Canadian provinces and New England states. The TLW is one of 30 partners in the cooperative with sites from an area with an underlying similarity in vegetation, soils, and climate. The collaboration takes the form of (1) sharing data and results, (2) developing regional data bases, (3) initiating joint research projects, (4) analysis and synthesis of regional environmental issues, and (5) increasing communication among researchers, resource managers and policy-makers (NERC, 2000). The focus of the cooperative is on the health of the forest and aquatic ecosystems in the region. The primary scientific issues to be addressed involve hydrological and biogeochemical processes in forested ecosystems and surface waters.

Changes in watersheds can increase or decrease their capacity to contribute to human needs. Long-term records from the relatively undisturbed TLW have revealed much about natural rates of change in surface water quality and quantity, and about aquatic and terrestrial biology. A certain amount of change is “normal” or “acceptable” since forests, streams and lakes are continually exposed to natural (pests, pathogens, drought, flooding, windstorms, icestorms) and anthropogenic (air pollution, climate change) disturbances. For example, at the TLW the average annual water yield (percentage of annual precipitation) declined and the proportion of runoff occurring in different seasons changed between 1982 and 1996 (Beall et al. 2001). Likewise a long-term examination of a fish community at the TLW in the absence of experimental perturbation has revealed declines in species in response to natural shifts at the community level (Smokorowski and Kelso 2002).

In Canada, fire and insect infestations are the dominant stand-renewing agents for forests in many of the nine distinct terrestrial ecozones. There are dramatic differences in hydrological and hydrochemical processes among these ecozones (Buttle et al. 2000). The whole-ecosystem investigative approach (Morrison et al.1999), which was initiated at the TLW in 1980, has resulted in increased understanding of the functioning and linkages between terrestrial and aquatic ecosystems. The prediction of water movement and soil development variation with topographic position is essential for linking terrestrial nutrient exports to surface water response in high relief catchments (Hazlett and Foster 2002). Natural variations in N export among catchments within the TLW have been documented and the processes that lead to these variations have been explored (Creed and Band 1998). For greater detail on TLW basin characteristics and scientific findings see the Canadian Journal of Fisheries and Aquatic Sciences, 1988, vol.45, Suppl.1, pages 1-178, Ecosystems, 2001, vol. 4, pages 501-567, and Water, Air, and Soil Pollution: Focus, 2002, vol. 2, pages 1-168.

Summary and Conclusions

Decisions made now and in the next decade are immensely important with respect to the global protection and sound management of forested watersheds to provide clean water for many purposes to future generations. The TLW is an example, one of many in North America, where recent advances in the understanding of natural processes and human impacts on services provided by watersheds have contributed to international policies and the adoption of sustainable watershed management. Watershed research and monitoring has demonstrated how forests can be managed to maintain or increase water yields for many purposes. Selective harvesting at up to 50 % removal mitigated most of the 3-yr increase in nitrate, calcium, and sedimentation that were produced in streams by clearcut logging at the TLW. Acidification effects of atmospheric nitrogen and sulphur on aquatic chemistry and biology and the slow process of recovery in streams and lakes at TLW in response to reductions in SO₂ emissions across North America have been reported.

Canada is a world leader in producing and exporting forest science and technology. Future land use decisions for the millions of people living in forested watersheds and down-stream areas may benefit from the sound scientific information derived from watershed research in Canada. Dissemination will help ensure that new projects can benefit from the experiences learned and avoid duplication of effort. There is a need for a more coordinated international effort for communicating information on the management of freshwater availability.

References

Arp, P.A., W. Leger, M.H. Moayeri and J.E. Hurley. 2001. Methods for mapping forest sensitivity to acid deposition for northeastern North America. Ecosystem Health 7: 35-47.

Beall, F.D., R.G. Semkin, and D. S. Jeffries. 2001. Trends in the output of first-order basins at Turkey lakes watershed, 1982-1996. Ecosystems 4: 514-526.

Buttle, J.M., I.F. Creed, and J.W. Pomeroy. 2000. Advances in Canadian forest hydrology, 1995-1998. Hydrol. Process 14: 1551-1578.

Canada/US 1983. Memorandum of intent on transboundary air pollution. Report of the Impact Assessment Working Group I, Section 3-Aquatic Effects. 259 p.

Canadian Forest Service. 1995. Criteria and indicators for the conservation and sustainable management of temperate and boreal forests. The Montreal Process. Can.For. Serv., Hull, QC. 28p.

Creed, I.F., and L.E. Band. 1998. Exploring functional similarity in the export of nitrate-N from forested catchments: a mechanistic modeling approach. Water Resour. Res. 34: 3079-3093.

Electric Power Research Institute. 1986. Integrated Forestry Study. Tech. Brief, Electric Power Res. Inst., Palo Alto, CA. 4p.

Environment Canada. 1997. 1997 Canadian acid rain assessment Vol.3 The effects on Canada’s lakes, rivers, and wetlands. D.S. Jeffries (ed.) Supply and Services Canada, Ottawa.

Foster, N.W. and P.W. Hazlett. 2002. Trends in water chemistry in a maple forest on a steep slope. Water, Air, soil Pollut.: Focus 2: 23-36.

Hazlett, P.W., and N.W. Foster. 2002. Topographic controls of nitrogen, sulfur, and carbon transport from a tolerant hardwood hillslope. Water, Air, Soil Pollut: Focus 2: 63-80.

Jeffries, D.S., R.G. Semkin, F.D. Beall, and J. Franklyn. 2002. Temporal trends in water chemistry in the Turkey Lakes Watershed, Ontario, Canada, 1982-1999. Water, Air, Soil Pollut.: Focus 2: 5-22.

Johnson, D.W. and S.E. Lindberg (eds). 1992. Atmospheric Deposition and Forest Nutrient Cycling. Springer-Verlag, New York, NY, Ecol. Studies 91.707 p.

Kreutzweiser, D.P. and S.S. Capell. 2001. Fine sediment deposition in streams after selective forest harvesting without riparian buffers. Can. J. For. Res. 31: 2134-2142.

Lam, D.C.L., A.G. Bobba, D.S. Jeffries, and D. Craig. Modelling stream chemistry for the Turkey Lakes Watershed: comparison with 1981- 84 data. Can. J. Fish. Aquat. Sci. 45 (Suppl. 1): 72-80.

Morrison, I.K., D. A. Cameron, N.W. Foster and A. Groot. 1999. Forest Research at the Turkey Lakes Watershed. For. Chron. 75: 395-399.

NERC. 2000. Northeastern Ecosystem Research Cooperative. Draft Prospectus.

Sedell, J., M. Sharpe, D. Apple, M. Copenhagen, and M. Furniss. 2000.Water and the Forest Service. USDA For. Serv., Washington Office, FS-660. 26p.

Smokorowski, K.E., and J.R.M. Kelso. 2002. Trends in fish community structure, biomass, and production in three Algoma, Ontario, lakes. Water, Air, Soil Pollut.: Focus. 2: 129-150.

Waters, T.F. 1995. Sediment in streams: sources, biological effects, and control. American Fisheries Society, Bethesda, Maryland. 251 pp.