Miniaturized photometrical methods for the rapid analysis of phosphate, ammonium, ferrous iron, and sulfate in pore water of freshwater sediments

Pore water analysis is a challenge for routine analysis methods, because of the small sample volume available and large sample numbers required for a high spatial resolution. To overcome the restrictions of established methods, this study presents a miniaturized photometrical method for the rapid analysis of phosphate, ammonium, ferrous iron, and sulfate in pore water of lake sediments. The method can cope with large sample sets (> 1000) and minimizes the sample volume to about 250 mu L. Standard photometric methods were modified for the use of microtiter plates (microphotometry), which allow the simultaneous determination of up to 100 samples by a microtiter plate reader. The advantage of this analytical technique is the minimal sample consumption, which enables new approaches for pore water sampling and analysis on a microscale level. In combination with a 2-dimensional dialysis sampler, it is now possible to obtain spatial patterns of pore water concentrations (SRP, NH4+, Fe2+, SO42-) with a high vertical and lateral resolution ( 9 mm). This approach shows the common 1-dimensional view of pore water profiles to be insufficient. Furthermore, the application examples yield new insights on lateral heterogeneity as well as nutrient mobilization and redox processes associated with the formation of microzones around biogenic structures, such as roots or macrofaunal burrows.