Limnol. 0 1992, by the American Oceanogr., 37(2), 1992, 280-295 Society of Limnology and Oceanography, Inc. Early diagenesis of protein: A seasonal study Lawrence M. Mayer Department of Oceanography, University of Maine, Darling Marine Center, Walpole 04573 Donald L. Rice Chesapeake Biological Laboratory, Center for Environmental and Estuarine Studies, University of Maryland, Solomons 20688 A bstract The diagenetic behavior of proteins, defined as large polypeptides, was examined over a 2-yr period at a mudflat site subject to intense bioturbation. Protein concentrations in the surface sediment correlated well with deposition of algal detritus from the water column. Cellular biomass made up a significant, though likely not a major, component of protein in the sediments; likewise, changes in biomass could not account for the bulk of protein losses downcore. These protein losses made up most of the total acid-hydrolyzable amino acid losses and about a quarter of the total N losses. Loss rates of protein are proportional within cores to previously reported estimates of extracellular proteolytic activity at this site, though with variation among sampling times. The combination of high organic matter input and rapid bioadvection allows detection of changing kinetics of decomposition during very early stages of diagenesis, analogous to those observed in algal decay experiments. Specific decay rates, similar to first-order decay constants, ranged from 0.2 to 8 yr-’ for protein, total organic C and N, and pheophytin in the labile fraction of organic matter found in the top few centimeters. This labile fraction, which is dominated by nonprotein forms of N, is lost with progressively lower specific decay rates downcore. Various lines of evi- dence-such as ammonification experiments and low C : N ratios of the remineralized material- suggest that these changing kinetics are at least partially due to replacement of algal detritus by more slowly decaying products of microbial resynthesis rather than simply to varying lability of fractions of the original algal detritus. Sediments are zones of primarily trophic activity in which nitrogenous pounds often make up an important of nutrition. The organic N that provides this nutrition in sediments has not been well characterized to date, being parameterized in the literature primarily nitrogen (TN) or, in some cases, as total acid-hydrolyzable amino These two parameters often show parallel behavior during downcore Henrichs and Farrington Martens 1988) and include a considerable amount of refractory susceptible to heterotrophic early diagenesis. Mayer et al. (1986) sought hetero- com- source as total organic acids (THAA). diagenesis (e.g. 1987; Burdige and material that is not processes in Acknowledgments We thank Linda Schick for the bulk of the analytical work reported here, J. Dibb for assistance with ‘Be ana’lyses, and S. Macko and G. King for discussions. Useful comments on earlier drafts were made by G. Cowie, J. Hedges, M. Goni, P. Coble, and two anon- ymous reviewers. This work was supported by NSF grants OCE 85- 1 1383, 87-00358, and 89-12433. Contribution 234 from the Darling Marine Center. to provide a measure of a smaller and more labile component of the organic N pool by means of an analysis based on a combina- tion of enzymatic hydrolysis and Coomassie Blue dye detection. ‘This combination sults in an assay of only those larger poly- peptides (i.e. proteins) matic attack, materials indicative of the labile component. We have previously shown that this measure spa- tially correlates well with indicators atively labile organic matter such as plant pigments (Mayer et al. 1988) and shows rap- id loss downcore relative to TN (Mayer et al. 1986). In this paper we examine early diagenesis of proteins this analytical method. Our purposes are to determine rates of decay of this material and the relations among protein decay, the en- zymes responsible for their hydrolysis, the decay of other organic matter pools. We examine decay rates in a sediment system in which dense populations belt feeding polychaetes of the genus Lei- tmcoloplos create a high rate of particle sub- 280 re- amenable to enzy- that should be of rel- in detail the as defined by and of conveyor-
