Determination of total phosphorus in lake sediments

During Bob Sandford’s presentation at the Comox Valley Eco-Asset Management Symposium on March 14-15, 2017, he stated “cyanobacteria is affecting all lakes in Canada.” Bob Sandford is the EPCOR Chair, Water and Climate Security United Nations University Institute for Water, Environment & Health. To identify whether cyanobacteria can gain a foothold in our lakes we need to test the level of phosphorus in the lake’s sediment and there are four different methods experts use. Click here to read the full study or an excerpt below.

 

page-4 Figure 1

 

Abstract Several methods are in use to measure total phosphorus in lake sediments making cross-study comparisons tenuous, and may lead to potential errors in calculating other phosphorus fractions. Four methods in common use in the limnological literature were compared using sediments spanning a range of organic content from 2 to 35% C. No significant differences were found in within-lake comparisons, although a method using persulfate oxidation was highly variable, and this variability was correlated with organic content suggesting inconsistent oxidation. The other methods (combustion, acid digestion with HClO4, H2SO4 ? H2O2) gave uniformly small variances.

Results

The collection of sediments ranged from 2 to 34.9% carbon (Table 1), and encompassed the range of organic matter found in most lake sediment investigations. Columbus Bog is a small (0.37 ha) dystrophic, seepage bog lake with no inlet or outlet. The overwhelming portion of its sediments is derived autochthonously, or is delivered as wind-blown detritus (e.g., pollen). At the other extreme, Juniper Basin of Lake Champlain is a deep offshore site in a large oligo-mesotrophic lake where the major portion of the sediments is composed of clastic material from streams draining the Adirondack and Green Mountains to the west and east, respectively, and the Champlain Valley with its extensive agricultural development adjacent to the lake.

The results of the four analytical methods are shown in Fig. 1. Although there were significant differences in the TP concentrations among the lakes, ranging from a low of 850 lg/g in Columbus Bog sediments to a high of 2,750 lg/g in Sugar Lake, there were no significant differences among the analytical methods (two-way ANOVA; Flake = 110.3, P\0.0001; Fmethod = 1.57, P = 0.2046). Although the methods gave the same mean TP concentrations, the persulfate method had greater variability than the other three, with an average coefficient of variation (SD/mean) across all lakes of 0.31. The other three methods had a combined average coefficient of variation of only 0.038. Variability within the persulfate method increased with increasing organic content of the sediments suggesting that the method was ineffective in consistently oxidizing all organic-bound P to reactive PO4. No such pattern was observed with any of the other methods.

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