Climate Change and the Possible Effects to the Vermillion River

Transcription

1 Climate Change and the Possible Effects to the Vermillion River Travis Thiel Dakota County Water Resources Galaxie Avenue Apple Valley, MN (952) Prepared for the Vermillion River Watershed Joint Powers Organization, Apple Valley, MN Under a U.S. Environmental Protection Agency Targeted Watersheds Grant (#WS ) November 30, 2008 The Vermillion River is a Mississippi River tributary in Dakota County, MN, within the Twin Cities Metropolitan Area (TCMA) of significant importance to the local communities, many interest groups, and residents. The main stem of the Vermillion River is 38 miles in length with numerous miles of tributaries that add significant amounts of water to the main branch. The river drains to the Mississippi River after receiving water from 20 communities (cities and townships). The significance of the Vermillion River is that not only is it seen as a recreational resource for locals, but the river has portions of designated trout stream. Brown trout and Rainbow trout are present within the river and the river is known as a trophy class trout stream, with Brown trout up to 27 inches being recently captured during electrofishing surveys. Trophy class trout streams rarely exist in urban or urbanized areas, especially in Minnesota. Although drainage from heavily developing urban areas occurs in the upper Vermillion River Watershed, the mid and lower portions of the watershed are comprised mostly of agricultural and row-crop land use. The current trout populations within the Vermillion River exist because of habitat conditions present within the river, especially with regards to water temperature. Trout populations are more vulnerable to warm water temperatures than many species of fish that exist in Minnesota. Due to large groundwater inputs at different points in the river and its tributaries, the temperature is maintained as satisfactory for trout. Temperatures above 18 C are considered by local experts to exert stress on trout. 1 Climate Change and the Possible Effects to the Vermillion River

2 The Minnesota Pollution Control Agency (MPCA) identifies water-quality impairments within surface-water resources. Currently, the MPCA is evaluating data collected on the Vermillion River to determine the extent, if any, of temperature impairment. The water-quality criterion for temperature impairment on a class 2A cold water stream is a narrative non-degradation goal of no material increase in temperature. Although discussions have taken place among the Vermillion River Watershed Joint Powers Organization (VRWJPO), the local government authority over water quality and quantity within the watershed, and the MPCA as to what no material increase means on a technical basis, for the purpose of this research effort, we are focusing on this established standard meaning that the temperature does not increase above current baseline temperatures. In other words, temperature inputs to the river from anthropogenic sources that significantly increase the temperature above baseline temperatures threaten to exceed the water quality standard. To manage the watershed, the VRWJPO has developed standards and rules to mitigate changes within the watershed while still allowing development and growth. With limited watershed resources and room for economic development, an evaluation of the potential for a waterquality trading program is being conducted to determine if it is feasible to initiate a trading program to mitigate temperature impacts to the Vermillion River. While science can tell us whether on-the-ground changes could potentially impact the river, the uncertainty of change outside of implemented practices is a concern to the stakeholders involved in maintaining the water quality of the river. Climate change is a primary concern associated with increased uncertainty when it comes to maintaining optimal temperatures within the Vermillion River. The predictability of changes in air temperatures, precipitation, and other factors and their impacts on the stream is something that must be evaluated. The rules and standards developed to maintain the optimal water temperatures may or may not be enough to mitigate the potential impacts climate change may bring. Many scientists have published evidence showing that the climate of the world is changing. Although critics may disagree with the evidence or conclusions, within the scientific community the uncertainty is not whether climate change is happening but rather, now that it is happening, what are the causes, and what can be done to reduce the impacts. According to the Intergovernmental Panel on Climate Change (IPCC), among many sectors and regions in North America, northern ecosystems and habitats and low latitude cool- and cold-water fisheries are two sectors which will be significantly affected by climate change (IPCC, 1997). Data show that during the last century, the average temperature in Minneapolis, Minnesota, has increased from 43.9 F ( average) to 44.9 F ( average), and precipitation in some areas of the state has increased by up to 20 percent, especially in the southern half (MPCA unpublished data, 2008). If these trends continue, the impacts to the Vermillion River could be significant, if not properly mitigated. There are three primary categories of impacts that could significantly affect the Vermillion River as a result of climate change; stormwater/land use impacts, groundwater impacts, and transitional impacts. Stormwater and Land Use Impacts A recent objective of scientists in the hydrologic community has been to revise Technical Paper No. 40 or TP40 (USDA, 1961). This paper identifies rainfall return frequencies for the United 2 Climate Change and the Possible Effects to the Vermillion River

3 States and is the current basis for most stormwater modeling, infrastructure design, and policy. In Minnesota, summer storm rainfall patterns have changed and rainfall intensity in these storms has increased, affecting the ratio of total rainfall/return frequency. These changes are important with regards to response in modeling, infrastructure design, and policy. Minnesota climatologists currently have data supporting these changes in summer rainfall. Recent climatological data have shown that higher dew points, temperatures, and stalled or stationary frontal boundaries are often present on a regular basis when higher intensity, larger event storms occur (Minnesota Climate Almanac, 2006). With changes to these return frequencies and realization of climate change for planning purposes, materials are being developed that assist with stormwater and hydrologic design. These changes will integrate appropriate rate and volume control designs for storm intensities that are realistic to the climate we are currently experiencing and what we can expect in the future. Land use changes within the watershed will not only have stormwater impacts, but will also alter the natural hydrology, hydrogeology, and ecology. Although temperature impacts will be discussed separately within this document, the temperature impacts discussed in this section will be due to changes in the landscape as a direct result of land use. The result of changes in ground cover has a significant impact on the temperature of soils beneath. One study shows that maximum groundwater temperatures, to a depth of about 22 m beneath a field, were C higher than groundwater temperatures at comparable depths below a mature forest. In addition to having a decreased temperature range, the mean annual groundwater temperatures were also 0.8 C cooler at the wooded site (Pluhowski and Kantrowitz 1963). The amount of organic detritus covering a forest floor also tends to reduce temperature variability in the soil (Lee 1978; Smith 1975), due to its insulative properties. Temperature Impacts According to research, there is a growing consensus that the temperature of the troposphere will increase in response to the steadily increasing concentrations of atmospheric CO 2 and other greenhouse gases (Canadian Climate Centre 1986; Clark 1982; Jager 1986). Although some of the modeling simulations to predict temperature change may be somewhat crude, the models project increases in mean annual air temperature of up to 5.5 C in North America in years (Mintzer 1987). In the Great Lakes basin, which is a more appropriate representation for the climate of the Vermillion River watershed s geographical area, projected increases are between 3.2 and 4.8 C (Maarouf 1985). Greater increases are expected in winter due to a positive feedback effect of reduced albedo from decreases in snow and ice. Most of North America is predicted to have a decrease in the duration and extent of snow cover, and the Great Lakes region is predicted to have a decrease in the duration and extent of ice cover (IPCC, 2008). These changes in mean temperature will have direct impacts on the temperature within the Vermillion River, as well as the temperature of the water contributed to the Vermillion River in the form of groundwater. River water temperature will increase by a slightly lesser amount than air temperature (Pilgrim et al., 1998), with the smallest increases in catchments with large contributions from groundwater. Biological and chemical processes in river water are dependent on water temperature: Higher temperatures alone would lead to increases in concentrations of some chemical species, but decreases in others. Dissolved oxygen concentrations are lower in warmer 3 Climate Change and the Possible Effects to the Vermillion River

4 water, and higher temperatures also would encourage the growth of algal blooms, which consume oxygen on decomposition. Not only will water temperatures more closely mirror air temperatures when increases do occur, but groundwater and stormwater will also play a significant role in river temperature changes. In the Vermillion River watershed, shallow groundwater aquifers are the primary contributors to cold water discharge. Groundwater temperatures are a direct reflection of mean annual air temperatures. Surface soil temperatures follow seasonal air temperature fluctuations with a time lag that is related to depth. The fluctuation in soil temperature decreases with increasing depth until the temperature of soil remains constant with no seasonal variation. This depth is known as the neutral zone (Matthess 1982). The effect of seasonal fluctuations in air temperature on an aquifer depends on its depth and the depth of the water table. If the water table is deeper than the neutral zone, then aquifer temperatures will be invariable and will continue to change with depth according to the local geothermal gradient. If the water table is above the neutral zone, the temperature of the upper layer of the aquifer will fluctuate seasonally. The temperature of discharge from shallow aquifers will exhibit greater seasonal variability than those from deep aquifers (Meisner, Rosenfeld, and Regier 1988). With greater seasonal variability in the shallow aquifers feeding the Vermillion River, we can expect a temperature change to the river over time with the potential to impact trout and other biota that require colder temperatures for survival. Numerous species of macroinvertebrates, plants, and animals are dependent on groundwater resources or cold water resources for survival. These groundwater-dependent resources rely heavily on factors besides temperature (i.e. soil mineral composition), but the temperature impacts from changes in groundwater temperature would certainly have an effect on many of these biota. Stormwater runoff temperatures will also play an integral role in potential temperature impacts to the Vermillion River. Modeled runoff from large commercial buildings has been found to be a large exporter of heat to the Vermillion River watershed (K.A. Chapman, personal communication). Stormwater runoff will need to be mitigated with specific practices to address heat export and the potential impact that heat may have on the Vermillion River. Infiltration has been the standard practice for volume control and ultimately temperature control to this point, but little is known about temperature effects on groundwater related to infiltrating stormwater over long periods of time during warm air temperature periods. Transitional Vegetation Impacts Climate impacts on transitional vegetation are changes in vegetation and crop types over time. Although no research has concluded at this time that rising temperature and precipitation volume and intensity trends will continue, current trends point in that direction. With increased temperature and precipitation volume and intensity changes, the current vegetation present on the landscape is likely to change in response. Native vegetation will likely have more competition with warm-weather-adapted vegetation. Current stands of timber could be replaced by grasslands and/or arid land (MPCA unpublished data, 2008). Vegetation in many riparian areas in this region typically consists of small stands of riparian timber that provide 4 Climate Change and the Possible Effects to the Vermillion River

5 shade benefits to the water resource. If replaced by grasses or arid-soil-tolerant species, cooling effects due to shading could be lost. A couple of possibilities exist in the way transition could take place in agricultural crop-types. Currently, this region s agricultural land is used primarily for corn and soybean production. Warmer temperatures and more intense rainfall could lead to scenarios where longer growing seasons may exist. If that scenario became reality, runoff impacts from more intense rainfalls and the possibility of rainfalls during the winter on these croplands could create pollutant impacts to the Vermillion River that do not currently exist or exacerbate any current pollutant loading. Longer growing seasons create scenarios where croplands are in use for longer periods of time during the year with concurrent additions of fertilizers and chemicals such as herbicides and pesticides. Changes in human behavior, reductions in abundance of species, can lead to changes in the structure and functioning of affected ecosystems. These changes can, in turn, lead to the loss of further species, a cascading effect on biodiversity, and the invasion of nonnative species and further disruption (IPCC, 2002). Another potential scenario that could result from warmer temperatures and more intense rainfall events is an increase in irrigation. More intense rainfall may not have the opportunity to infiltrate into the soil and replenish groundwater supply properly. The Vermillion River is dependent on a consistent groundwater supply for its discharge volume and its support to unique biota. Groundwater usage for irrigation could lessen the groundwater discharge contributing to base flow in the Vermillion River or possibly eliminate it, if demand is high enough. Conclusions Although the scientific community has not concluded that current climate change trends will continue, most individuals and groups are currently working to develop policy to prepare for a potential change. Many of the effects previously described could have a significant impact on the Vermillion River and other similar resources in this region. Secondary impacts could arise from the aforementioned primary impacts, but the possible effects are nearly infinite and difficult to predict. Proper planning and policy development will be crucial to buffer and, if possible, eliminate the effects of climate change on our region. Additional monitoring of climate, as well as practices to attenuate climate impacts on our air, soil, and water will be important to planning and policy development to lessen or eliminate climate change effects. References: Canadian Climate Centre Understanding CO 2 and climate. Annual report, Canadian Atmospheric Environment Service of Environment Canada, Downsview, ON. Clark. W. C Carbon dioxide review: Oxford Univ. Press, New York, NY. IPCC Working Group II The Regional Impacts of Climate Change: An Assessment of Vulnerability. Intergovernmental Panel on Climate Change. IPCC Working Group II Climate Change and Biodiveristy. Intergovernmental Panel on Climate Change. 5 Climate Change and the Possible Effects to the Vermillion River

6 IPCC Working Group II Climate Change and Water. Intergovernmental Panel on Climate Change. Jager, J Climate change: floating new evidence in the CO 2 debate. Environment 28(7). Lee, R Forest microclimatology. Columbia University Press, New York, NY. Mintzer, I. M A matter of degrees: the potential for controlling the greenhouse effect. World Resources Institute, Res. Rep. #5, Washington, DC. Maarouf, A. R Carbon dioxide effects on climate with emphasis on climate model results for Canada. Canadian Climate Centre, Canadian Atmospheric Environment Service, Downsview, Ontario, Canada. Matthess, G The properties of groundwater. John Wiley and Sons, New York, NY. Meisner, J. D., J. S. Rosenfeld, and H. A. Regier The role of groundwater in the impact of climate warming on stream salmonines. Fisheries 13(3): 2-8. Minnesota Pollution Control Agency Global climate change and its impact on Minnesota. Pilgrim, J.M., X. Fang, H. G. Stefan Stream temperature correlations with air temperatures in Minnesota: Implications for climate warming. J. Am. Wat. Resourc. Res. Assoc. 34: Pluhowski, E.J., and I.H. Kantrowitz Influence of land surface conditions on ground water temperatures in southwestern Suffolk County, Long Island, N.Y. Professional Paper 475-B. Washington, DC: USGS. Seeley, M Minnesota Weather Almanac. Minnesota Historical Society Press. ISBN Smith, M. W Microclimate influences on ground temperatures and permafrost distribution, Mackenzie Delta, NWT. Can. J. Earth Sci. 12: U.S. Weather Bureau Technical paper no. 40, rainfall frequency atlas of the United States for durations from 30 Minutes to 24 Hours and Return Periods from 1 to 100 Years. Washington, DC. 6 Climate Change and the Possible Effects to the Vermillion River