Stream Hydrologic Regimes
Streamflow patterns are a major feature of stream ecosystems and are critical in shaping aquatic communities (Resh et al. 1988, Poff and Ward, 1989, Poff et al. 1997). In Michigan, considerable hydrologic diversity exists across the State, with many rivers receiving considerable groundwater contributions (Richards 1990, Wiley et al. 1997, Zorn et al. 1998). The structure and function of riverine systems are based on five components affected by flow: hydrology, geomorphology, biology, water quality and connectivity. The objective of maintaining an adequate flow should be to sustain, rehabilitate or restore ecosystem processes through seasonal and annual regimes. Stream flow regimes must address instream and out-of-stream needs and integrate biotic and abiotic processes (Annear et al. 2004). As a consequence of changes in streamflow patterns, many rivers no longer support native species or sustain healthy ecosystems that can provide important goods and services (Poff et al. 1997).

When altered, streamflows exhibit changes in magnitude, timing, duration, frequency, and rate of change (Poff et al. 1997). Loss of water retention capacity within a watershed through land clearing, increased impervious surfaces (e.g., urban development), wetland drainage, and stream channelization leads to increased magnitude and frequency of high flows, more extreme low flows, and generally flashier conditions (Karr and Schlosser 1978, Menzel 1983, Poff et al. 1997). Groundwater pumping can also result in more extreme low flows and can generally destabilize streamflow (Poff 1997, Wiley et al. 1997). Dam operation for flood control results in reduced magnitude and frequency of high flows (Poff 1997), which results in the loss of floodplain connectivity and habitat diversity (Copp 1989, Sparks 1995). Dam operation for hydropower generation can result in large daily changes in water releases (hydropeaking), which can have severe effects on aquatic ecosystems and organisms (Cushman 1985, Gislason 1985, Bovee et al. 1994, Freeman et al. 2001).

Lake Hydrologic Regimes
Water levels in many lakes throughout Michigan fluctuate naturally as a result of changes in precipitation, snow melt, groundwater inflow, and evaporation. In some instances, lakeshore property owners prefer a fixed lake level to ensure recreational access or to protect property vulnerable to water level changes. Michigan currently has more than 300 lakes with regulated lake levels. Lake levels are maintained through the use of either lake-level control structures or augmentation wells.

Natural fluctuation of water levels in lakes and streams contributes significantly to ecosystem health and integrity (Wilcox and Meeker 1992, Poff et al. 1997). Lakeshore vegetation, beaches, shorelines, and associated plant and animal assemblages were established through cycles of high and low water levels and these attributes may be lost when natural water level fluctuation is prevented. Lake-level control constricts the margin or transition zone between water and land that is often rich in aquatic species diversity, provides high quality habitat for fish productivity, reptiles, amphibians and birds, and provides a buffer that protects the shoreline from extensive erosion during wind and wave events.

Operation of augmentation wells may lower regional groundwater tables, negatively affecting nearby wells and water bodies (streams, lakes, wetlands and springs) through reduction or complete loss of water supply or deteriorated water quality (Alley et al. 1999, Grannemann et al. 2000, MDEQ 2003c). A reduced flow or change in water chemistry can result in a loss of wildlife habitat (Lindorff et al. 1997). Environmental research on effects of groundwater pumping is limited; however, several case studies show effects such as diminished wetland area and streamflow and impaired water quality (Lindorff et al. 1997, Born et al. 2000).

Groundwater Hydrology in Terrestrial Systems
Hydrologic processes are very critical to the vegetative structure of several wetland and marginally upland natural communities (e.g., lakeplain prairie, prairie fen, floodplain forest, relict conifer swamp) and the wildlife that depends on them (Albert and Kost 1998, Spieles et al. 1999, Kost 2001, Tepley et al. 2004). These communities tend to be disturbance dependent and experience seasonal/periodic flooding due to low topography and relatively high water tables. When groundwater flow is altered by agricultural and residential drains and wells, however, the underlying groundwater table is often lowered because of lack of recharge due to drained surface water and groundwater extraction. Prairie fens and relict conifer swamps also depend on a high water table to supply necessary permeation of calcareous groundwater (Spieles et al. 1999, Kost 2001).

Trees growing in anaerobic conditions associated with a high water table and muck and peat soils tend to be shallowly rooted and are therefore, especially prone to windthrow. Light gaps created by windthrow help to regenerate dominant tree species and maintain understory layers in forested systems. In addition, the coarse woody debris that results from windthrow also adds to the complex structures of these communities (Kost 2001). Lowered water tables in such systems can disrupt these natural processes.

Avoiding surface water inflows from drainage ditches and agricultural fields and protecting groundwater recharge areas by maintaining native vegetation types in the uplands around these communities are essential for their conservation. Healthy woodlands, savannas and prairies in uplands adjacent to wetlands allow infiltration of precipitation into groundwater, whereas lawns, agricultural fields, and impervious surfaces contribute warm, nutrient and sediment-laden surface runoff (Spieles et al. 1999).

Conservation Needs to Address Altered Hydrologic Regime Threats:

Land & Water Protection

• Protect springs and seeps from ground-disturbing activities

Land, Water & Species Management

• Restore areas where hydrologic regimes are significantly altered
  
  
• Protect areas where ecological conditions are particularly susceptible to hydrologic changes
  
  
• Protect the local hydrology in areas with high quality groundwater-dependent communities
  
  
• Implement best management practices that restore natural watershed processes while supporting human needs
  
  
• Require use of retention or detention basins in urban areas to reduce flashiness of stream flows
  
  
• Incorporate aquatic species passage into existing lake-level control structures
  
  
• Follow the recommendations of the International Joint Commission (1999) to "apply the precautionary principle with respect to removals and consumptive use of groundwater in the (Great Lakes) Basin"
  
  
• Create buffer strips around wells, lakes, streams, creeks and rivers

Law & Policy

• Consider downstream streamflow alterations during land-use planning and development of zoning regulations
  
  
• Discourage construction of lake-level controls and establishment of legal lake-levels
  
  
• Develop land-use recommendations to prevent hydrologic modifications and share these with local planning agencies
  
  
• Encourage green space development to promote water infiltration and on-site water retention

Research, Surveys & Monitoring

• Identify areas where hydrologic regimes are significantly altered
  
  
• Identify areas where ecological conditions are particularly susceptible to hydrologic changes
  
  
• Identify areas with high quality groundwater-dependent communities
  
  
• Develop and test best management practices that restore natural watershed processes while supporting human needs
  
  
• Develop and test best management practices, with respect to existing lake-level controls, that minimize disruption to annual or seasonal hydrological regimes, protect and maintain natural aquatic communities, protect downstream aquatic habitat, and maintain natural water temperatures
  
  
• Document or model historical hydrologic disturbance regimes and assess their potential for restoration
  
  
• Monitor streamflows for changes in natural range of variation
  
  
• Conduct research on effects of groundwater withdrawals
  
  
• Conduct research to identify the nature, extent and source of streamflow alterations
  
  
• Study groundwater recharge in landscape features that have the potential for high infiltration
  
  
• Conduct research to determine how changes in hydrologic regimes affect wildlife use of wetlands
  
  
• Conduct research to examine imperviousness in watersheds and develop tools, guidelines and methodologies to decrease it
  
  
• Develop hydrologic models and monitor hydrologic (e.g., groundwater, streamflow, dam operation) dynamics