3.6 Decreased Biological Diversity

The most notable water quality problems with York Creek are associated with the disappearance of the trout population, which has historically been characterized as good. (Michigan Department of Natural Resources. 1969. Fisheries Division York Creek Field Survey Results.)

The decrease in trout during recent years has been documented by MDNR staff during periodic biological surveys of the stream. The results of an MDNR bioassessment conducted in 1987 showed markedly decreased numbers of trout, and the 1991 MDNR survey revealed a complete absence of trout species. (MDNR. 1993.)

AWRI staff conducted an additional bioassessment during the summer of 1994 to provide the most current biological data possible. The locations of the surveys, as well as those of water quality sampling and stormwater monitoring sites, are shown in Figure 16. The results of the AWRI survey support the most recent MDNR biological survey, as there continues to be sedimentation of stream bottom habitat areas, very little diversity among aquatic macroinvertebrate species and no trout observed (Tables 4-6). (Grand Valley State University. Water Resources Institute. 1994. A technical supplement to York Creek Watershed Project Watershed Management Plan. Publication No. MR 94-8.)

While there were several taxa present, the vast majority of individuals observed is comprised of species which are relatively tolerant of degraded stream conditions.

The sedimentation of gravel areas on the stream bed prevents successful spawning and reproduction of trout and other fish species. Low scores in the habitat assessment reflect the relatively poor condition of the stream bed in York Creek (Table 5). Aquatic macroinvertebrates are also negatively impacted by sedimentation of the stream bed. The unnatural hydrologic extremes flush many young fish and macroinvertebrates from the stream system into the warmer Grand River, further decreasing populations. (Harvey. 1987. )

These situations received the most thorough investigation during the study, and should receive the most attention during implementation of best management practices toward the return of York Creek to viability as habitat for indigenous species.

While many water quality problems affect a variety of species, often remedial actions are not undertaken until a game species is impacted. Although the decrease in trout numbers served to draw interest to York Creek, the fact that trout are a popular and commercially valuable fish is less important to the study of water quality than the fact that trout and the macroinvertebrates on which they feed are relatively intolerant of degraded water quality, and therefore are excellent indicators of water quality problems.

Figure 16. Water Quality Sampling Locations - York Creek Watershed

Table 4. Qualitative Macroinvertebrate Sampling Results For York Creek