Comment on “Dilution of ²¹⁰Pb by organic sedimentation in lakes of different trophic states, and application to studies of sediment‐water interaction“ (Binford and Brenner)

Reply to comment by Benoit and Hemond

“…A recent paper by Benoit and Hemond (1987) supports this observation. They state that in a small, artificial lake in central Massachusetts (p. 1453) "total stream input and output of *lOPb are nearly equal.…”

“…comm.). Benoit and Hemond's (1987) study infers, properly in our view, that the source of 210Pb in incoming stream water was from groundwater ?lOPb produced and supplied by alpha-recoil in the aquifer matrix or ***Rn dissolved in groundwater that recharges a brook that could decay to 210Pb within the stream. This source makes sense to us, but may or may not have any bearing on the *lOPb delivery to sediments, as previous discussion has emphasized.…”

“…Fourth, the source of sedimentary *lOPb in individual lakes must be understood. Benoit and Hemond (1987) observed that although streamflow added a substantial portion of 2*0Pb to the water of one lake, sedimentary flux approximately equaled atmospheric flux. This observation must be examined to determine the mechanism and for its generality.…”

“…Our citations on this point were inconclusive, largely because mass-balance studies have been carried out on only a handful of lakes. McCall et al (1984), Stiller and Imboden (1986), and Benoit and Hemond ( 1987) are the only studies that we are aware of that demonstrate inflowing streams to be a major source of *'OPb to lake water. However, none of these three indicate that rivers are a major source of sedimentary 210Pb.…”

“…The latter two studies were on lakes with extremely large ratios of drainage basin to lake area and are fed by large rivers. Benoit and Hemond's (1987) study was on a reservoir with a water residence time of 84 d, which implies that the lake is fed by a river with a discharge that is large relative to lake volume.…”