Similar to the sediment research, the goal of the bacterial sampling was to pinpoint the location of origin of the bacteria. Water samples were collected over the course of eight weeks in the summer of 2011 both in Lake Macatawa and along the major tributaries to better understand the nature of the infestations. During dry periods, bacterial levels in the water were generally within the safe limit for recreational contact. However, shortly after the start of rain events, large concentrations of the bacteria – often more than 100 times the safe contact level – were found in the eastern end of Lake Macatawa, along with most of the upstream tributaries. Interestingly, these high levels never got out into the central and western parts of the lake, likely confined to the eastern area by Dunton Park due to the prevailing westerly winds. Since these bacteria traditionally originate in animal gut, samples were genetically sequenced in order to determine what organism they came from. The initial results were:
- Human markers were found in a few samples during dry periods, but never in high levels. This suggests perhaps a leaking septic system or other small-scale source. Positive hits were also found downstream of an accidental sewage discharge.
- Cow markers were found in samples collected from streams that have cow pastures located nearby. Levels were low and only found during dry periods.
- Pig markers were not found during routine testing. The marker did show up downstream of a discharge of pig manure, but never during normal environmental samples.
The vast majority of the bacteria found in the watershed is not from a known source.
The bacteria found in the lake are likely not from a wild animal, since the levels correlate with changes in precipitation so closely. So where is it coming from? A possible explanation is that there are environmental sources of bacteria that have adapted to survive in either the soil or in tile drains. Further research is being performed to further understand the origins of the bacteria, and since they do not originate in a mammalian gut, how dangerous to humans they actually are.
This research has given our partners an unprecedented set of data from which we can begin to effectively fix the problems that occur in the watershed. With these findings, we have a much more complete picture of the factors that contribute to the deteriorated health of Lake Macatawa. Further monitoring work will continue, and as remediation measures are put into place, the ODCMG will work with our partners to watch how the health of the watershed improves. This will lead to a healthier lake and watershed, which all residents and visitors and enjoy year-round.
Reference: Phillips, J.M, Russell M.A. & Walling, D.E.. “Time-integrated sampling of fluvial suspended sediment: a simple methodology for small catchments.” Hydrological Processes. 14, 2589-2602 (2000).
Sediment and Nutrients
Sediment samplers were constructed based on the design of Phillips et al. (2000), allowing us to collect a known ratio of the sediment that was coming downstream following heavy rain. Following a period of high stream flow, samples were gathered from the collection chambers and taken back to the lab for processing and analysis. The first piece of data the samplers provide is simply the mass of sediment collected, which allows for a quick comparison between sites to identify which streams contain the highest sediment levels. Taking these measurements has allowed us to come up with estimates of how much sediment each area is contributing, thereby allowing us to come up with a map of areas contributing the most sediment. In general, we found that most of the sediment washes into the streams in the outer edges of the watershed and is carried down the tributaries and empties into Lake Macatawa. Peters Creek and the Upper Macatawa River in particular had very high concentrations, but significant levels of sediment were found in the vast majority of streams.
Further forensic techniques and analyses, collectively referred to as sediment fingerprinting, are being implemented on the sediment in order to get a unique “fingerprint” for the sediment. Similar to how fingerprints can point to a specific person, a sediment fingerprint will allow us to distinguish between different types and identify areas of origin. These analyses include examining chemical composition, biological content, minerals, color, radioisotopic content, grain size and shape, and phosphate content. Preliminary work has shown chemical composition, color, radioisotopic content, and phosphate measurements to be particularly promising. Adding these techniques to the sampling will allow for the sediment that is collected on a particular stream branch to further pinpoint what area(s) upstream is the point of origin.