NITRIFICATION POTENTIALS OF BENTHIC MACROFAUNAL TUBES AND BURROW WALLS - EFFECTS OF SEDIMENT NH4+ AND ANIMAL IRRIGATION BEHAVIOR

We examined the natural variation of nitrification potentials (NPs) of surface sediments and macrofaunal tubes and burrow walls in relation to sediment NH4+ level, season, and macrofaunal species. NP (the abili ty of a unit of sediment to oxidize NH4+ when NH4+ and O-2 are not lim iting) is an index of the abundance and activity of nitrifying bacteri a which we measured in slurries with the chlorate block technique (nmo l NO2--N produced g(-1) dry weight sediment h(-1)). The NP of the tube s of the polychaete Loimia medusa was positively related to sediment N H4+ (KCl-extractable) concentration at 3 sites where tubes were collec ted in June 1990 (Spearman rank correlation coefficient I-s = 0.90, p = 0.03), as was the NP of surface (0 to 1 cm) sediment (I-2 = 0.92, p = 0.002). The degree to which tube NP exceeded the NP of surface sedim ent was, however, negatively associated with sediment NH4+ (I-s = -0.8 4, p = 0.05). Tube NP of L. medusa did not vary significantly with dat e (February, April, and June 1990). Tubes or burrow walls of Macoma ba lthica (bivalve), Leptocheirus plumulosus (amphipod), and the polychae tes Macroclymene zonalis, Pectinaria gouldii, L. medusa, and Diopatra cuprea had NPs significantly greater (2 to 20 times) than that of adja cent sediment from the same depth interval, indicating that these spec ies stimulated nitrification. Except for burrows of M. balthica, the N Ps of these structures were significantly (p less than or equal to 0.0 5) greater (1.5 to 61 times) than that of surface sediment. The durati on of macrofaunal irrigation activity, but not irrigation rate, was po sitively associated (I-s = 0.72, p = 0.01) with the enhancement of NP in tubes and burrow walls relative to surface sediment. These findings indicate that macrofaunal tubes and burrows tend to be sites of enhan ced NP and that this enhancement varies among species due to Variation s in irrigation behavior. The NP of macrofaunal structures also varies among sites in relation to sediment NH4+ concentrations.