Rl. Marinelli et Bp. Boudreau, AN EXPERIMENTAL AND MODELING STUDY OF PH AND RELATED SOLUTES IN AN IRRIGATED ANOXIC COASTAL SEDIMENT, Journal of marine research, 54(5), 1996, pp. 939-966
Macrofaunal irrigation is an important process in nearshore sediments,
facilitating greater exchange between sediments and seawater and impa
rting significant lateral heterogeneity to the porewater profiles of m
any constituents. Like many macrofaunal activities, irrigation is a tr
ansient behavior, i.e. tubes and burrows are flushed periodically, at
frequencies that generally are species-specific. As a result, transien
t concentrations within the dwelling arise, potentially impacting grad
ients, fluxes and reaction rates in the vicinity of the dwelling. We i
nvestigated the impact of periodic burrow irrigation on the distributi
on of several diagenetically important porewater constituents. Laborat
ory experiments evaluated irrigation periodicity using artificially ir
rigated tubes embedded in nearshore organic-rich sediments, and microd
istributions of oxygen and pH in laboratory experiments were measured
with microelectrodes. To help interpret our results, we also construct
ed a simplified time and space-dependent transport-reaction model for
oxygen, pH and sulfide in irrigated sediments. Laboratory results show
substantial differences in the pH field of sediments surrounding an i
rrigated tube as a function of irrigation frequency. Higher pH values,
indicative of an overlying water signature, were observed in the vici
nity of the tube wall with increasing duration of irrigation. Converse
ly, oxygen concentrations did not vary significantly with the amount o
f irrigation, most likely a result of extremely high sediment oxygen d
emand. Model results are consistent with laboratory findings in predic
ting differences in the measured variables as a function of irrigation
frequency. However, the nature and extent of the model-predicted diff
erences are often at variance with the experimental data. Overall, exp
erimental and modeling results both suggest irrigation periodicity can
substantially influence porewater distributions and diagenetic proces
ses in sediments. Future studies should examine the influence of irrig
ation periodicity on the types and rates of reactions, and the attenda
nt biological features, in the environment encompassing the tube or bu
rrow wall.