The Yahara River watershed of south-central Wisconsin drains 1389 km2 and contains five major lakes that have been significantly impacted by changes in seasonal climate over the past 60 years, agricultural land use, and a growing urban environment. Changing land-use, management, urbanization, and policy are placing competing demands on the water system, and may affect the resilience of built and natural environments under a changing climate. Many players typically aroused by competing water management goals are present in the watershed, including farmers, urban and suburban residents, developers, realtors, recreationists, policy-makers, neighborhood associations, environmental NGOs, and business associations.
Water and land use governance in the watershed is complex and multilayered. Although most resource sectors are managed independently, efforts to link land use with water quality impacts have prompted the establishment of regional authorities. This watershed also exemplifies three features that often stymie implementation of environmental reform: (1) a complex ecological system where cause-and-effect relationships are not easily understood, (2) benefits and costs of different land management scenarios accrue largely in the future, and (3) a situation where actors degrading the water system are different from the users who suffer the costs.
The watershed’s physiography is strongly influenced by glaciation that occurred as recently as 14,000 years ago leading to a relatively flat landscape characterized by former glacial lake beds, meltwater deposits, moraines, drumlins, and hummocky till. Paleozoic bedrock is generally covered by up to 100 meters of glacial sediment, which is mostly till consisting of gravelly, clayey, silty sand (Clayton and Attig, 1997).
Land use is largely agricultural (principally corn, soybean, and dairy) but includes a densely populated urban area (Madison) and some remnant native vegetation. The mix of urban areas, croplands, forests, pastures, wetlands, and prairie make for a complex environment to interact with water.
Drivers of Recent Change
Stresses on ecosystem services of the Yahara watershed typify many agricultural landscapes (Turner et al. 1998). Organic C storage in watershed soils has declined by ~50% (Kucharik et al. 2003, Kucharik 2007). Groundwater extraction, loss of wetlands, reduced infiltration, and increased runoff from impervious surfaces have altered the hydrology and increased flood frequency (Soranno 1996, Wegener 2001). Nitrate is contaminating groundwater, and P loads from nonpoint runoff substantially exceed those that occurred prior to agriculture (Carpenter et al. 2006, Lathrop 2007). Today, a high incidence of use of pesticides, fertilizers and manure have contributed to water quality issues in area lakes, as well as increased “flashiness” of runoff from heavy rainfall events. Climate change is already occurring; since 1950, the growing season has lengthened, the number of extremely cold days has declined, and rainfall on frozen soil conditions and the frequency of intense rainfall events have both increased (Kucharik et al., 2010). Plant phenology has also changed, with emergence and flowering occurring earlier for many species (Bradley et al., 1999).
Remote sensing studies (Zhang et al., 2004) have also confirmed an early season green-up by 3-6 days in the Madison area, attributed to an Urban Heat Island (UHI). The dynamics of ET, infiltration, and runoff may be significantly different within the urban setting vs. agricultural regions due to temperature differences in addition to direct effects of the built environment (i.e. increased impervious area and engineered drainage systems). Residential water use in summer may also increase as UHI footprints expand (Guhathakurta and Gober, 2007). These drivers interact to challenge the sustainability of freshwater resources and other ecosystem services throughout the region.
Bradley, N. L., A. C. Leopold, J. Ross, and W. Huffaker. 1999. Phenological changes reflect climate change in Wisconsin, Proceedings of the National Academy of Sciences of the United States of America, 96(17), 9701-9704.
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Guhathakurta, S., and P. Gober. 2007. The impact of the phoenix urban heat island on residential water use, J. Am. Plan. Assoc., 73(3), 317-329.
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Turner, M. G., S. R. Carpenter, E. J. Gustafson, R. J. Naiman, and S. M. Pearson. 1998. Land Use. Pages 37-61 in M. J. Mac, P. A. Opler, C. E. Puckett Haecker, and P. D. Doran, editors. Status and trends of the nation's biological resources. U. S. Department of the Interior, USGS.
Wegener, M. W. 2001. Long-term land use/cover change patterns in the Yahara Lakes region and their impact on runoff volume to Lake Mendota, MS thesis, University of Wisconsin-Madison, Madison, WI.