Effects of dissolved humic substances on the speciation of iron and phosphate at different pH and ionic strength.
be expected to be key factors in the complexation and release of Fe and Po43-. Consequently, variation of the pH and/or the ionic composition of humic lakes may affect the speciation and cycling of Fe and P04% and hence their availability for uptake by planktonic organisms. Numerous softwater lakes with varying DHS contents are known to have undergone substantial pH shifts in recent decades due to anthropogenic acidification. The variable response of the plankton community in these lakes to acidification may be in part due to alterations in the DHS-FWPO~~interactions. We have examined the effecta of pH and ionic strength on these interactions using a double isotope labeling technique introduced in a previous paper (IO).