Near Infrared Aerial Image - Spring Lake Rain Garden
3. Water Quality Problems
Records of water quality examinations in York Creek have been located for the years 1925, 1969, 1987, 1989, and 1992. Each of these studies are related to fish or other biological surveys, however. No previous water chemistry data is believed to exist. As such, AWRI conducted a number of studies to gain a better understanding of the water quality status of York Creek. Among the various assessments of stream conditions are the following:
Detailed description of the methodology used and data assembled during these and other studies can be found in A Technical Supplement to York Creek Watershed Project Watershed Management Plan. Results of the water chemistry analysis are found in Appendix B of this report.
Conclusions from data collection and analysis efforts describe a variety of current and potential threats to water quality in the York Creek Watershed. Among these are:
The sources of NPS pollutants are as varied as the pollutants themselves. Agricultural practices and land disturbing activities related to new development are the primary contributors of sediment, automobiles contribute numerous chemicals and heavy metals through normal operation and inadequate maintenance; road maintenance contributes salts, toxins, and oils; and homes, golf courses, and businesses contribute nutrients, pesticides, and other pollutants through fertilization and maintenance of turf grass areas. These situations and others currently exist in the York Creek watershed. As the current trend of development continues, the levels and concentrations of pollutants reaching the stream can be expected to increase.
NPS pollutants affect water quality in different ways. They may generate excessive plant growth, interrupt feeding or reproductive activities of aquatic organisms, or contain a variety of toxins. Many common NPS pollutants are plant nutrients. The resultant accelerated growth of algae and other aquatic vegetation reduces oxygen levels in surface waters, denying fish and other aquatic organisms their required oxygen levels. A number of metals found in surface runoff are toxic to many aquatic species. In addition, sedimentation in water bodies decreases the number of species of benthic macroinvertebrates in those areas. It has been shown that coldwater indicator species such as mayflies and stoneflies are drastically affected by siltation. (Peckarsky, Barbara L. 1984. Do predaceous stoneflies and siltation affect the structure of stream insect communities colonizing enclosures? Canadian Journal of Zoology 63:1523, 1528-29). These aquatic insects are a critical link in the aquatic food chain, and decreases in their numbers greatly impact the fish that feed upon them. Another negative impact of NPS pollutants is the sedimentation of spawning areas of many fish species. The effects of stream sedimentation are apparent in York Creek, as described in the most recent MDNR biological survey of the stream, conducted in the summer of 1992. (Michigan Department of Natural Resources. 1993. p2.). In order to expand upon the results of the 1992 survey, WRI staff conducted a similar biological survey in roughly the same portions of the stream (Figure 11).
It is believed that the principle causes for the decline in water and habitat quality in York Creek are twofold and functions of one another. These causes are: 1) extreme hydrologic fluctuations, and 2) sedimentation of habitat areas. Each of these situations result from the alteration of stable, vegetated areas to impervious surfaces such as roads, rooftops, and parking lots. Associated with the development is an increase in surface runoff from those areas. The runoff carries additional sediment and erodes the banks and bed of the stream.
Streambank erosion is also caused by an unnaturally accelerated meandering rate that result from sand bars and other areas of deposition generated by the increased sediment inputs to the stream system. In addition, there are numerous locations within the watershed where bank erosion has caused trees to fall into the channel, artificially increasing the rate of meandering, eroding additional streambank during the process. While meandering is a natural occurrence and large woody debris in natural streams is a very important factors in habitat stability, York Creek cannot currently be considered a natural setting. As such, the removal of debris in some areas is required to protect the fragile streambanks from redirected flows. Once flows rates and streambanks have been stabilized, woody debris should be allowed to remain in the stream.
In addition to these problems are many lesser current and potential threats to water quality, such as thermal inputs, pesticides and fertilizers, and the non-sediment fraction of NPS pollutants associated with runoff from impervious surfaces. Included in this group are automobile fluids, road salt, and general debris. While these threats to water quality are recognized, they currently seem to impact the stream less than the principle problems discussed. In addition, the management of such NPS pollutants is often accomplished by default during stormwater runoff and sediment control procedures. As such, these pollutants should receive a proportionally lesser focus during BMP implementation than the principle pollutants.