LANDSCAPE PLACEMENT, WETLAND FUNCTION, AND HYDROGEOMORPHOLOGYOF THE SUSAN CREEK WATERSHED
Susan Creek is the only perennial flowing water within an approximate 13 mile coastal reach of Lake Michigan that provides habitat suitable for potoanadromous fish populations. This Lake Michigan coastal area extends from T34N – R 6W, Section 4 to T34N – R8W, or basically from Bay Harbor to the mouth of the Pine River in the City of Charlevoix. The headwaters of Susan Creek are found within well drained drumlin topography, as such Susan Lake and Susan Creek are largely driven hydrologically by groundwater influences. As the stream discharges from Susan Lake it transverses an area of lacustrine sand and gravel. This landscape is chiefly composed of fine and medium sands with lenses of gravels. These lacustrine deposits resulted from the high post glacial levels of the Great Lakes. At one location on the stream reach, approximately 1,500′ south of US-31, the stream corridors increases its gradient as it bisects the Nippising lake terrace. The toe of the Nippising terrace is a location of numerous seeps, springs, and seepage faces that are regional groundwater discharge zones. This groundwater discharge zone drives the stream and wetland complex by providing a stable source of cool mineral rich groundwater.
WILDLIFE HABITAT
The Susan Creek stream corridor is largely a mixed forested wetland cover-type. For forested wetlands such as Susan Creek, size contributes to the ability of the wetland to support particular bird species which are considered “forest interior” species. Wetlands such as this, that are dominated by forested vegetation, are more likely to support a diversity or abundance of migrating and wintering wetland dependent birds. Vegetation cover types such as these support more wildlife by providing more habitat structure through vertical layering and increased patchiness resulting from horizontal overlap of layers. In forested wetlands, bird species diversity is directly tied to the number and density of foliage layers. The Susan Creek wetland contains special wildlife habitat features such as standing deadwood with cavities larger than 2″ in diameter, plants that bear fleshy fruits, and evergreen stands with canopy closure of 80% or more. Of particular note is the usage of standing deadwood and tall trees by bald eagle.
Riverine wetland systems such as Susan Creek are more likely to contain the habitat richness to support wetland dependent bird species. Wetlands where at least a portion of the wetland is temporarily flooded are more likely to support wildlife diversity. The zones of contact between the riverine system and vegetation improve conditions where by wetland dependent wildlife can take cover from predation as well as providing natural territorial boundaries. Additionally, these transition zones between water and vegetation are areas where species particularly adapted to ecotones thrive. In wetlands such as this, where the boundary between the upland and the wetland is sinuous, the ability of wildlife to migrate, breed, and feed increases. The Susan Creek wetlands, whose watersheds is not dominated by impervious or hardened surfaces is more likely to support wildlife diversity. This wetland has not be altered directly by filling or drainage and is without major or frequent disturbance so it is more likely to support a greater wildlife diversity.
These forested regions adjacent to Lake Michigan are prime feeding grounds for neo-tropical migrants that follow the Lake Michigan shoreline in their northerly migration. The massive hatch of freshwater (chironomidae) midges corresponds to the period in the spring when neo-tropical migrants such as warbles, vireos, and kinglets are moving through the area. These midge hatches, coupled with the abundance of forested vegetation, make these landscapes an important resting and feeding ground for these songbirds.
FLOOD CONTROL FUNCTIONS
This vast wetland complex provides important flood control functions for areas along US-31 and the Lake Michigan shoreline. Water moves through the wetland primarily as sheet flow, (with some channel flow) which promotes flood desynchronization. Vegetation spans the width of the wetland providing frictional resistance to water, further slowing it during period of high rainfall or rapid snow melt.
SEDIMENT AND NUTRIENT RETENTION
The thick stands of cedar and other forest vegetation act to trap sediments and nutrients from entering Susan Creek and ultimately Lake Michigan. Vegetation such as trees and shrubs, which are persistent in nature and that have ridged trunks and stems slow water velocity and are the best for providing sediment and nutrient retention. The vegetation provides frictional resistence allowing water to slow and sediments and nutrients to precipitate out of the water column.
Cedar, fir, and other trees are an important source of detritus, which is colonized by bacteria, fungi, and epiphytic algae communities, and consumed by insect larvae, crustaceans, and other aquatic invertebrates in Susan Creek. A portion of the detritus is swept downstream, where it is further processed. Overhanging trees found along Susan Creek also provide shade to shelter fish, and create snags when their twigs and branches fall into the stream. In addition, insects which drop into the stream provide an important food source for fish, in some cases forming their staple diet. Core forests potentially provide important and unique co-occurrence of habitat. Stream systems, such as the Susan Creek site, are degraded by cumulative stressors that operate at large scales, such as forest fragmentation. It is generally accepted that stream-side forests represent the best management practice for protecting aquatic ecosystems from outside pollution by filtering out nutrients, sediments and toxic contaminants before they get to the stream.
