2012 was a dry year for the watershed. No significant storms occurred after mid-April, and very little precipitation fell at all through the entire month of July. Flows in the river and tributary streams hit record lows in late July and early August. What effect did this dry spring and summer have on the water quality in the watershed? Results from HRWC’s Water Quality Monitoring Program help answer this question.
The program had a banner year in 2012 with the greatest number of volunteers (49) trained and deployed to the most sites (36) across three counties. HRWC added 14 new sites in 2012 alone as the program expanded into Wayne County. This diligent corps of dedicated volunteers collected nearly 500 sets of water quality samples for analysis at municipal labs administered by the cities of Ann Arbor and Brighton and the Ypsilanti Communities Utility Authority (YCUA).
The state of Michigan does not have a numerical standard for phosphorus levels, but 50 µg/l is used for area lakes as a level to stay below in order to avoid serious algae blooms and fish kills. Concentrations of total phosphorus (TP) in monitored streams were roughly the same, on average, as the past two years. Wayne County streams (which include some that drain directly to the Detroit River) had the highest mean concentration at 100 µg/l, while Washtenaw County streams averaged 80 µg/l, and Livingston County streams were much lower at 30 µg/l. The portion of the watershed in Livingston County retains more wetland area (wetlands filter phosphorus), and a smaller developed or urbanized area than in Washtenaw or Wayne County. Mean stream flow, or discharge, was much less in 2012 than in previous years resulting in an overall “load” of phosphorus (i.e., the total mass of phosphorus moving downstream over a given period of time) from these streams that was lower than in previous years. Also, sediments (measured as Total Suspended Sediments or TSS) were slightly lower on average this year. Fewer storms means less erosion, or soil runoff, which may have also helped to keep phosphorus levels down, since phosphorus readily attaches to soil particles.
Bacteria Still a Health Concern
Bacteria levels, as measured by Eschericia coli, continue to be high in several areas of the watershed during 2012. Levels regularly exceeded state standards for human health in most monitored tributary streams in Washtenaw and Wayne counties. Notable exceptions were Woods Creek, Fleming Creek, and the Huron River upstream of Ann Arbor. Efforts to identify specific sources of bacteria in Honey Creek in Scio Township were not particularly fruitful. Bacteria counts were high throughout the streams of Honey Creek, and genetic tracking showed that a wide variety of animals contributes to the problem (including humans).
Stormwater Runoff Problem Persists
While the lack of major storms this season may have reduced the overall amount of erosion and other runoff pollution, tributary streams continue to exhibit unnatural flows. Streams throughout Wayne County (with the exception of Woods Creek) and the urbanized areas of Washtenaw County exhibited much higher peak flows following storms than would be expected from the size of their watersheds, and the flows returned to low flow much more quickly. Notably, at the driest points in July and August, some smaller creeks stopped flowing altogether. Typically, unaltered perennial streams should continue to receive sufficient groundwater in-flow even through the drought experienced in 2012.
Some of these flow characteristics also led to dissolved oxygen levels that were below state standards set to protect aquatic life. The streams in question are ones that were severely channelized (straightened and deepened), and the low water levels isolated sections from in-flow of oxygen-rich water, causing them to stagnate for long periods. Bugs, fish and other aquatic life will return to these creeks as flow returns, but they will have a difficult time sustaining a healthy, diverse population over the long term with such periodic oxygen starvation. While a number of programs and projects to reduce stormwater runoff are encouraging, these results suggest there is still a long way to go.
The Water Quality Monitoring Program is funded by local government agencies through HRWC partnerships for stormwater and watershed management.