An excessive amount of nutrients is the top water quality concern in the Huron River watershed and the Great Lakes region, if not the entire county. This summer’s drinking water crisis in Toledo is a prime example of the potential impact. Waters in the Huron River watershed have suffered similar impacts, though somewhat less dramatic. Still, multiple millions of dollars have been invested within the watershed to reduce the sources of phosphorus (the growth-limiting nutrient in the region). So, where are we today, as we close out 2014? Have the programs, projects and other investments made any impact? HRWC’s Water Quality Monitoring Program results should shed some light on this question.
The first look at the phosphorus trends suggests that we have made little recent progress. As shown in the first chart, raw phosphorus concentrations in the middle Huron River watershed steadily declined from the beginning of the monitoring program (2003) through 2009, when the average phosphorus concentration rose above target levels (red line). From 2010 through this year, concentrations were much more variable, but averages were distinctly above the target. Phosphorus concentrations were also well above the target in the Lower Huron watershed over the last three years (not shown).
These raw results do not provide a complete picture, however. Concentrations can vary tremendously (just look at the error bars) depending on a number of variables, most importantly stream flow. 2008 was a particularly dry year, for example, while stream flows were well above average in 2011. HRWC storm sampling shows that, as stream flows increase during a rain storm, phosphorus concentrations increase, often dramatically.
When we account for the stream flow at the time of sampling, we get a somewhat different picture. The second chart shows phosphorus concentrations at Ford Lake, when adjusted for river flow (also shown as the blue line). The chart shows four periods — 1995 when the state DEQ sampled to set a phosphorus control policy, and three periods after the monitoring program began.
From this view, it is obvious that concentrations have come way down from original ’95 levels. Also, phosphorus concentrations have come back up since 2009, but by less than it seems from raw concentrations.
It is unclear why we have seen the recent increase in phosphorus concentrations. It does not appear to be linked to sediment concentration (i.e. erosion) as those data are not well correlated. Some national studies suggest that historical fertilizer application may be dissolved and slowly moving through the groundwater. If that is the case, while direct application of phosphorus in fertilizer has been addressed (through fertilizer policy in the City of Ann Arbor and later statewide law), we are still seeing the legacy effects of over-fertilization in our urban/suburban areas. There also has been an increase in phosphorus loading from the more heavily agricultural Mill Creek watershed, which could partially explain the increase.
HRWC provides a more detailed tributary evaluation in its annual monitoring report. For reports, presentations and 2014 raw data, see the Water Quality Monitoring page.