In recent decades, several standard colorimetric reactions for chemical analysis have been miniaturized to microwells on microplates, including methods useful for environmental measurements. Advantages of method miniaturization include a reduction in reagents required, improved safety, reduced waste stream, and increased sample throughput. However, the widespread use of microscale techniques employing microplates in classroom settings is likely limited by the high cost of microplate readers. Although spectrophotometers read peaks of specific wavelengths, absorbance spectra tend to be relatively broad and measurements at specific wavelengths are highly autocorrelated with those of nearby neighbors, which implies that broadband intensity data of red, green, and blue channels may indeed be adequate for digital colorimetric quantification. In this article, we demonstrate that digital image analysis of a scanned microplate image can substitute for a spectrophotometer for several common quantitative microscale procedures. This finding allows for cost effective and microscale quantification of several compounds to be demonstrated in the laboratory. Additionally, popular teaching and learning activities such as water quality monitoring can now be performed accurately and inexpensively using digital image analysis.

A sandy prairie remnant in the Lower Wisconsin River Valley, encroachment areas within the prairie, and an adjacent red pine (Pinus resinosa Aiton) plantation were studied to determine the influence of woody cover on C dynamics. Field transects, aerial imagery, and a geographic information system were used to quantify encroachment from 1979 to 2002. A linear encroachment model predicted 100% encroachment of the 6.0‐ha prairie in 50 yr. Four field plots in each of pine, prairie, and encroachment areas were sampled and soils collected (0–18, 18–38, and 38–75 cm) in 2004 and 2008. Total ecosystem C was greater in pine (126.6 Mg C ha−1) and encroachment areas (71.8 Mg C ha−1) than prairie (48.3 Mg C ha−1). In the 0 to 38 cm, coarse particulate organic matter (POM) (4.1, 6.3, and 7.5 Mg C ha−1) and the POM C/N ratio (15.1, 16.2, and 20.2) increased with woody encroachment (prairie, encroachment areas, and pine, respectively). Changes in POM suggest more organic inputs and slower decomposition, but due to minimal protection of C within aggregates, increased total soil C was not observed with woody advancement (46.4–47.2 Mg C ha−1). Microbial biomass (0–38 cm) was greatest in encroachment areas, followed by prairie, and then pine (108, 84, and 51 kg N ha−1, respectively), probably a result of more favorable microclimate and substrate at the ecotone boundary. Potential N mineralization (0.6, 2.8, and 4.8 kg N ha−1 d−1), extractable NH4+ (28, 33, and 57 kg ha−1), and Bray‐1 P (380, 402, and 541 kg ha−1) (0–38 cm) increased with woody cover, and increased nutrient availability could lead to a greater aboveground C sink through increased tree growth.

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Bromide (Br-) is commonly used as a tracer in studies of water and chemical transport in soil and rock because it is relatively nonreactive with soil and rock constituents and because of its low environmental background concentrations. Based upon a largely ignored modification of the standard colorimetric method for determining bromide using phenol red and chloramine-T, we correct an internal error and recast the technique for use with 96-well microplates. Furthermore, the addition of thiosulfate to quench the undesirable chlorination reaction as previously published is shown to be unnecessary and even detrimental following the use of ammonium to produce chloramine from excess chlorine species. By manipulating sample size and concentrations of phenol red and chloramine-T, the concentration range can be expanded from 12 mg L-1 Brto much as 300 mg L-1 Br- .