Abstract
The detrital food web is a major nexus of energy flow in nearly all aquatic ecosystems. Energy enters this nexus by microbial assimilation of detrital carbon. To link microbiological variables with ecosystem process, it is necessary to understand the regulatory hierarchy that controls the distribution of microbial biomass and activity. Toward that goal, we investigated variability in microbial abundance and activities within the tidal freshwater estuary of the Hudson River. Surface sediments were collected from four contrasting sites: a mid-channel shoal, two types of wetlands, and a tributary confluence. These samples, collected in June to August 1992, were sorted into two to four size fractions, depending on the particle size distribution at each site. Each fraction was analyzed for bacterial biomass (by acridine orange direct counting), bacterial production (by 3H-thymidine incorporation into DNA), fungal biomass (by ergosterol extraction), fungal production (by biomass accrual), and the potential activities of seven extracellular enzymes involved in the degradation of detrital structural molecules. Decomposition rates for particulate organic carbon (POC) were estimated from a statistical model relating mass loss rates to endocellulase activity. Within samples, bacterial biomass and productivity were negatively correlated with particle size: Standing stocks and rates in the <63-μm class were roughly twofold greater than in the >4-mm class. Conversely, fungal biomass was positively correlated with particle size, with standing stocks in the largest size class more than 1OX greater than in the smallest. Extracellular enzyme activities also differed significantly among size classes, with high carbohydrase activities associated with the largest particles, while oxidative activities predominated in the smallest size classes. Among sites, the mid-channel sediments had the lowest POC standing stock (2% of sediment dry mass) and longest turnover time (approximately 1.7 years), with bacterial productivity approximately equal to fungal (56 vs. 46 μg C per gram POC per day, respectively). In the Typha wetland, POC standing stock was high (10%); turnover time was about 0.3 years; and 90% of the microbial productivity was fungal (670 vs. 84 μg C per gram POC per day). The other two sites, a Trapa wetland and a tributary confluence, showed intermediate values for microbial productivity and POC turnover. Differences among sites were described by regression models that related the distribution of microbial biomass (r 2 = 0.98) and productivity (r 2 = 0.81) to particle size and carbon quality. These factors also determined POC decomposition rates. Net microbial production efficiency (production rate/decomposition rate) averaged 10.6%, suggesting that the sediments were exporting large quantities of unassimilated dissolved organic carbon into the water column. Our results suggest that studies of carbon processing in large systems, like the Hudson River estuary, can be facilitated by regression models that relate microbial dynamics to more readily measured parameters.
Similar content being viewed by others
References
Almin K-E, Eriksson K-E (1967) Enzymic degradation of polymers 1. Viscometric method for the determination of enzymic activity. Biochim Biophys Acta 139:238–247
Antibus RK, Sinsabaugh RL (1993) The extraction and quantification of ergosterol from ectomy-corrhizal fungi and roots. Mycorrhizae 3:137–144
Austin K, Findlay S (1989) Benthic bacterial biomass and production in the Hudson River Estuary. Microbial Ecology 18:105–116
Benke AC, Hall CAS, Hawkins CP, Lowe-McConnell RH, Stanford JA, Suberkropp K, Ward JV (1988) Bioenergetic considerations in the analysis of stream ecosystems. J North Am Benthol Soc 7:480–502
Cole JJ, Findlay S, Pace ML (1988) Bacterial production in fresh and saltwater ecosystems: a cross-system overview. Mar Eco Prog Ser 43:1–10.
Dale NG (1973) Bacteria in intertidal sediments: factors related to their distribution. Limnol oceanogr 19:509–518
Findlay SEG, Meyer JL, Edwards RT (1984) Measuring bacterial production via rate of incorporation of 3H-thymidine into DNA. J Microbiol Methods 2:57–72
Findlay S, Pace ML, Lints D, Cole JJ, Caraco NF, Peierls B (1991) Weak coupling of bacterial and algal production in a heterotrophic ecosystem, the Hudson estuary. Limnol Oceanogr 36:268–278
Fuhrman J, Azam F (1982) Thymidine incorporation as a measure of heterotrophic bacterioplankton production in marine surface waters: evaluation and field results. Mar Biol 66:109–120i
Hargrave BT (1972) Aerobic decomposition of sediment and detritus as a function of a particle surface area and organic content. Limnol Oceanogr 17:583–596
Kirchman DL, Ducklow HW (1993) Estimating conversion factors for the thymidine and leucine methods for measuring bacterial production. In: Kemp PF, Sherr BF, Sherr EB, Cole JJ (eds) Handbook of methods in aquatic microbial ecology. Lewis Publishers, Boca Raton, Florida
Lints D, Findlay SEG, Pace ML (1992) Biomass and energetics of consumers in the lower food web of the Hudson River. In Smith CL (ed) Estuarine research in the 1980s. SUNY Press, Albany, pp 446–457
Newell SY, Arsuffi TL, Fallon RD (1988) Fundamental procedures for determining ergosterol content of decaying plant material by liquid chromatography. Appl Environmental Microbiol 54:1876–1879
Newell SY, Fallon RD (1991) Toward a method for measuring instantaneous fungal growth rates in field samples. Ecology 72:1547–1559
Schallenberg M, Kalff J (1993) The ecology of sediment bacteria in lakes and comparisons with other ecosystems. Ecology 74:919–934
Sinsabaugh RL, Antibus RK, Linkins AE, McClaugherty CA, Rayburn L, Repert D, Weiland T (1992) Wood decomposition over a first-order watershed: mass loss as a function of lignocellulase activity. Soil Biol Biochem 24:743–749
Sinsabaugh RL, Findlay S, Osgood M (1994) Enzyme activity-indexed models for estimating decomposition rates of particulate detritus. J North Am. Benthol Soc 13:160–169
Sinsabaugh RL, Linkins AE (1990) Enzymic and chemical analysis of particulate organic matter from a boreal river. Freshwater Biol 23:301–309
Sinsabaugh RL, Linkins AE (1993) Statistical modeling of litter decomposition from integrated cellulase activity. Ecology 74:1594–1597
Sinsabaugh RL, Moorhead DL (1994) Resource allocation to extracellular enzyme production: a model for nitrogen and phosphorus control of litter decomposition. Soil Biol Biochem 26:1305–1311
Sinsabaugh RL, Moorhead DL, Linkins AE (1994) The enzymic basis of plant litter decomposition: emergence of an ecological process. Appl Soil Ecol 1:97–111
Sinsabaugh RL, Weiland T, Linkins AE (1993) Enzymic and molecular analysis of microbial communities associated with lotic particulate organic matter. Freshwater Biol 28:393–404
Tyler SW, Wheatcraft SW (1992) Fractal scaling of soil particle-size distributions: analysis and limitations. Soil Sci Am J 56:362–369
Author information
Authors and Affiliations
Additional information
Correspondence to: R.L. Sinsabaugh
Rights and permissions
About this article
Cite this article
Sinsabaugh, R.L., Findlay, S. Microbial production, enzyme activity, and carbon turnover in surface sediments of the Hudson River estuary. Microb Ecol 30, 127–141 (1995). https://doi.org/10.1007/BF00172569
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF00172569