Reading The Buffer Tea Leaves

Since "they" won't show us the problem, we can try to read tea leaves instead. I reckon we can read tea leaves mathematically by back-calculating. The buffer abacus targets 70% to 75% pollutant removal. It is largely based on the Mayer paper (Mayer et al, 2007). The Mayer paper considered only nitrates, so let's consider nitrate regulatory limits.* The drinking water standard for nitrates, the maximum contaminant level (MCL), is 10 mg/L, which is the same level established as the aquatic life criterion set by EPA.

Presumably, "they" sized our buffers so that our water would be safe coming out of the buffer, meaning nitrate levels no higher than 10 mg/L. At efficiencies of 75% removal, that would imply that our pre-buffered water from development areas could have ambient nitrate concentrations around 40 mg/L. For 70% removal, that would imply a figure as high as 33.3 mg/L.

Is that a lot?

Yes, it is, especially for surface waters. I believe it is unreasonable to think concentrations around here could ever be that high. Those levels are high even for aquifers in heavy use areas, such as the Salinas Valley in California, where there has been decades of intensive nitrogen fertilizer use associated with agriculture.

The USGS says the background concentration of nitrate in groundwater in the Puget Sound region is only about 3 mg/L. As for surface water data from the San Juans specifically, there is no mention of nitrates in the 303d reports. However, a study by Huxley College monitored nitrates and several other constituents in the islands, and they found nitrate concentrations to be around 2 mg/L or less. They had just one data point that was significantly higher in concentration, a 7 mg/L reading that they attributed to alders, not an anthropogenic source.

The Huxley comment about alders raises an interesting point. Many plants fix nitrogen into the soil, like alders. Other plants take it out, like grasses. A typical crop rotation schedule has a plant from the grass family (e.g. corn) followed by a legume (e.g., alfalfa). The grasses use nitrogen, and legumes put it back into the soil. Despite the fact that grasses are well-known consumers of nitrogen, our proposed County buffer calculator assumes lawn buffers are less effective than other vegetation at removing nitrogen. That is a peculiar conclusion since grasses are very good at withdrawing nitrogen from soil, and that is why people apply nitrogen fertilizer to lawns in the first place. Grass is so good at taking up nitrogen, it needs extra.

Is it possible that with fertilizer use or other behaviors that we might develop a nitrate problem somewhere in the county at some time? Sure, anything is possible. In fact, a 2008 Eastsound water supply report from the County Health Department suggests that nitrates may be slowly accumulating in the Eastsound aquifer, but levels are still quite low.  Further research (e.g., isotopic analysis of nitrogen and oxygen) may be needed to better define the source, and the situation is being monitored.

But it is fantasy to think that our county-wide pre-buffered ambient environmental concentrations of nitrate could be in the range of 30 to 40 mg/L (measured as nitrogen). Yet, by back-calculating, that appears to be the unspoken design criterion for all our buffers.

Even if we ignore all the other questions about the derivation of the buffer calculator, I still have to wonder why "they" sized buffers for 70% to 75% removal? Where is the justification for a problem so large and widespread that we all need buffers that robust? 

Why are our buffers so big? For the same reason "they" consider grass to be relatively ineffective at nitrogen removal. That is to say, for no reason at all apparently.


* - the MCL and aquatic life criterion express nitrate as nitrogen. Nitrate can be measured as nitrogen or as nitrate, the difference being the ratios of their molecular weights.  The same concentration of nitrate, measured as nitrate instead of nitrogen, is roughly 4.5 times higher than that same concentration of nitrate measured as nitrogen.  A 10 mg/L limit for nitrate as nitrogen is equivalent to a level of 45 mg/L for nitrate measured as nitrate.  If you click the link for the Salinas Valley data, they show nitrate measured as nitrate, so a 90 mg/L data point in their figures corresponds to a 20 mg/L level as compared to the MCL provided here.