Field evaluation of a micro-extraction technique for measuring chlorophyll in lake water without filtration.
A recently described technique for measuring chlorophyll biomass in small water samples (Phinney and Yentsch, 1985) was evaluated on a set of lakes in northcentral Wisconsin. Since the new technique requires only 1.5 mL of unconcentrated lake water, it eliminates several steps and sources of error in the traditional protocol and it permits a very high degree of spatial precision for point estimates of chlorophyll concentration. For the midsummer plankton of six lakes (oligotrophic to mesotrophic), agreement between the new whole-water micro-extraction and the traditional filtered-sample techniques was quite good (r2 = 0.82 to 0.88) but recovery by the whole-water method was generally higher, perhaps because some plankton passed through the filters. Using unmodified, generally available instrumentation, limits of detection were about 0.3 µg Chl L-1in situ; and the literature suggests that these limits can be improved easily by a factor of three. Our results indicate that whole-water micro-extraction of chlorophyll is an acceptable technique to use for many lakes.