Mercury Availability & Exposure

Many area lakes have fish consumption advisories for mercury (see links from MN DNR Lakefinder for details on particular lakes). Mercury is a potent neurotoxin that has especially adverse consequences for developing brains (which is why consumption advisories are more stringent for young children and women of child-bearing age). Because mercury accumulates in muscle tissue there is no way to reduce exposure through cleaning or cooking techniques.

One of the puzzling things about these advisories is how different they are from lake to lake. Because most mercury enters lakes through atmospheric deposition of mercury released from coal burning power plants we might expect similiar mercury levels across all lakes in an area but this is not the case. Recently reported research from UW-Madison suggests at least a partial explanation for observed differences -- levels of dissolved organic carbon (DOC) apparently enhance the biological availability of mercury. Exact mechanisms are still not well understood but the pattern is undeniable.

From the standpoint of expectations or predictions, high DOC lakes often have a tea-stained appearance. Consequently, fish from such lakes are likely to have higher mercury levels. In addition, in more oligotrophic lakes fish generally grow slower and live longer and are thus likely to have higher mercury levels at any given size than fish from more productive waters. So, to reduce exposure to mercury you should in general (1) eat smaller specimens of (2) fish species lower on the food chain from (3) relatively productive lakes with (4) unstained waters. /dps

Honors Council Lecture

I delivered a public Honors Council Lecture at Bemidji State last night. My talk focused on demographic and climatic factors predisposing some area lakes to regime shifts and I also talked a bit about the summer dissolved oxygen impairment in the Mississippi from Itasca to the Schoolcraft river. C-map notes for my talk are available on-line. /dps

Snow depth map

Hydroclim Minnesota just emailed another update (should be posted to the web soon) and one of the most interesting features is a series of weekly snowdepth maps from this and past years. Given the seemingly continuous snowfalls of the past week it will be fun to compare current levels with those of recent winters. /dps