Adenosine 5'-Triphosphate Flux Through the North Inlet

Transcription

1 APPLiED AND ENVIRONMENTAL MICROBIOLOGY, May 1979, p /79/ /08$02.00/0 Vol. 37, No. 5 Adenosine 5'-Triphosphate Flux Through the North Inlet Marsh Systemt THOMAS H. CHRZANOWSKI,'* L. HAROLD STEVENSON,' AND BJORN KJERFVE2 Belle W. Baruch Institute for Marine Biology and Coastal Research and Departments of Biology,' and Geology,2 University of South Carolina, Columbia, South Carolina Received for publication 26 February 1979 The distribution, fluctuation, and short-term transport of total microbial biomass (measured as adenosine 5'-triphosphate [ATP]) was investigated in a large salt marsh creek. Hourly samples were collected synoptically for 25 h from 10 boats positioned across the 320-m width of the creek. Samples were collected from three depths ranging from 0.2 to 8.0 m. Hourly data obtained from each station were graphed, plotting depth against ATP. Subsequently, interpolated ATP values were generated for every one-tenth depth from the surface to the bottom with the use of an 11-point proportional divider. A total of 2,750 values were generated, and a mean value of mg of ATP per m3 was determined. Maximum levels of ATP were found at high tide and minimal values were found at low tide. The distribution of ATP concentrations was found to be complex, with no suggestion of vertical stratification; however, horizontal divisions were apparent. ATP values corrected for direction of flow or velocity indicated two ebb-directed channels; however, when considered in total, there was a net import of ATP through the interface. The total import of ATP for this 25-h sampling period was calculated to be 3.58 kg, corresponding to a net transport of 39.8 mg of ATP per s through the cross section. Results suggest that detailed characterization of a creek transect in terms of ATP or any similar parameter requires the simultaneous measurements of both the concentration of the parameter in question and the velocity at the time and point from which the sample was taken. The terrestrial and aquatic components of a salt marsh community interact to make the environment an area of intense biological activity. The processes of primary production, degradation of marsh plants, ground water runoff, excrement of terrestrial animals, activity of intertidal organisms, disruptive action of benthic macrofauna, and the metabolism of microorganisms surely add to as well as alter the types and amounts of both inanimate organic and inorganic materials in the water that periodically cover the marsh. The fate of materials suspended in this water is in doubt. They may be transported or out-welled to pelagic communities of the inner continental shelf (15), or they may be sedimented in other areas of the marsh along with allochthonous materials of oceanic origins (19). However, dissolved and inanimate materials are not the only substances scoured from or added to the marsh sediment by tidal action. Viable microorganisms also represent a class of materials that can be either drawn from or deposited in a marsh system through the action of the tides. t Contribution no. 266 of the Belle W. Baruch Library in Marine Biology. The net movement of several classes of materials across a marsh-ocean interface has been investigated. These have included materials such as carbon (19, 20), suspended solids, ammonia, nitrate, nitrite, and phosphate (5), chlorophyll a (5, 7), detritus (8), and microbial biomass (I, 7, 9). Quantification of microbial biomass in aquatic systems has proceeded rapidly since the development of a reliable extraction and assay procedure for adenosine triphosphate (ATP). Despite the fact that ATP has been used for the quantification of microbial biomass for more than a decade, few studies using the nucleotide as a measure of the net exchange of microbial biomass between marsh and oceanic environments have been reported (1, 7, 9). The studies utilizing ATP were done in marshes under 60 ha and correspondingly small drainage creeks. The work reported herein involved high-density sampling at the junction of the Atlantic Ocean and a marsh of substantial area. This communication is intended to enhance the understanding of microbial biomass movements through a marsh-ocean interface by reporting the levels and fluctuations of ATP at the inter- 841

2 842 CHRZANOWSKI, STEVENSON, AND KJERFVE face as well as transport through the boundry on a short-term basis. MATERIALS AND METHODS All samples were collected on 11 and 12 November 1977 from Town Creek in the North Inlet Estuary near Georgetown, S.C. Descriptions of the marsh system are available (3, 14) and do not warrant further discussion. The sampling location and regime, however, require additional description. The mouth of the estuary is formed by two major creeks, Town Creek and Jones Creek. Town Creek, the larger of the two, drains the entire northern section of the marsh, approximately 1,800 ha (Fig. 1). Ten boats were positioned across the mouth of Town Creek between Debidue (east) and North Islands (west). The actual positions of the boats and the distance between them were determined from aerial photographs. The boats were augered to the bottom in such a way as to prevent rotational movement in response to tidal flow. Water was pumped (Guzzler pump, Dart Union Corp.) from three depths, 0.2 m below the surface, 0.2 m above the bottom, and from a point equidistant between the surface and bottom depths (Fig. 2). Water brought to the surface was collected in sterile, acidwashed, 500-ml bottles and immediately transported to laboratory facilities on shore. Hourly samples were collected synoptically from each of the 30 sampling points for 25 h, comprising two complete tidal cycles. Ten-milliliter aliquots were used for determinations of total microbial biomass (measured as ATP). The water was filtered using Whatman GF/F filters, and organisms retained on the filter were extracted according to the methods of Holm-Hansen (10) and Holm-Hansen and Booth (11). Extractions were performed in duplicate. Quantification of ATP was performed using FIG. 1. Map of North Inlet indicating the position of the transect from which samples were collected. APPL. ENVIRON. MICROBIOL. an SAI model 3000 photometer in the peak height mode in conjunction with Sigma firefly lantern extract (FLE-250 or FLE-50). The cross-sectional bathymetry (Fig. 2) was measured using a Raytheon DE735A recording fathometer. Also, at each site and sampling time, the water depth was measured with a lead-weighted line, allowing computations of a time-averaged (net) station depth and a time series of instantaneous deviations from the net depth. By knowing the time of the fathometer run relative to the sampling schedule, an independent check on the bathymetric variations was obtained. Additionally, by substracting the net depth from the sequence of instantaneous depth values at each station and computing a mean across the transect, a tide curve was constructed. Instantaneous vertical velocity profiles were determined from measurements obtained with biplane current crosses (16) made of stainless-steel sheets (20 by 50 by cm). Lead weights, 5 or 16 kg, were attached to the cross, when necessary, to allow current measurements over the range of 7 to 230 cm/s. The cross assemblies were designed to have ±2-cm/s precision and were all statistically intercalibrated. Velocity measurements were made from each boat comprising the transect, first at the surface and then at meter intervals to within 0.5 m of the bottom. At each depth, the angle between the current cross line and the vertical was measured by an inclinometer. The angle was smoothed by eye for 15 s to remove high-frequency velocity fluctuations. Vertical velocity profiles were computer fitted to the instantaneous velocity measurements using a cubic spline algorithm with a logarithmic bottom boundry fit (Kjerfve, in K. R. Dyer, ed., Hydrography and Sedimentation in Estuaries). Equispaced interpolated velocity values were used to compute net or timeaveraged velocities at 11 depths from surface to bottom at each station (12). Vertical ATP profiles were also calculated according to the methods of Kjerfve (12) with modifications. Mean hourly data obtained at each station were graphed plotting depth against ATP concentration, and with the use of an 11-point proportional divider, new ATP values were determined for every one-tenth of the depth from the surface to the bottom. These interpolated ATP values are herein referred to as interpolated data. The procedure of Kjerfve was modified by assuming the bottom value was not zero. Corresponding ATP and velocity data were available at three depths at each station. The interpolation allowed matching ATP-velocity data to be obtained at more frequent depth intervals. The instantaneous mass flux (F) of ATP through the cross section of the creek was computed from F= ff p C VdA A where V is velocity, C is the fractional concentration of ATP, and d is the water density (all three quantities measured at the same point). The triple product, pcv, was integrated over the entire cross-sectional area of the creek, denoted as A. As the density was almost constant relative to variations in C and V, density was

3 VOL. 37, 1979 assumed to equal unity since cgs units were used. The numerical procedure to evaluate flux has been outlined in a step-by-step fashion by Kjerfve (in K. R. Dyer, ed., Hydrography and Sedinentation in Estuaries). Statistical analyses and computer mapping were performed by an IBM-370 computer in conjunction with programs available in the SAS (2), SYMVU (13), and SYMAP (4) program packages. RESULTS The Town Creek transect is shown in Fig. 2. The distance across the transect was 320 m at the mean tide level. A primary channel on the eastern side of the transect had a depth of approximately 7.5 m at the mean tide level. The water velocity through the transect ranged from 0 to 230 cm per s. Descriptive statistics for direct and interpolated ATP data are presented in Table 1. For direct data, a total of 1,407 values were obtained (these values represent actual ATP assays), and a mean value of mg of ATP per m3 was determined. The data were found to be highly variable as indicated by the range of to mg of ATP per m3. The wide range of ATP values is, in part, due to natural fluctuations associated with rising and falling tides. When the data were interpolated, a total of 2,750 values were obtained, and a mean value of mg of ATP per m3 was determined with values ranging from to mg of ATP per m3. The fluctuations of ATP and tidal height for both direct and interpolated data are presented in Fig. 3. Considering the direct data, elevated West ATP FLUX 843 TABLE 1. Descriptive statistics for direct and interpolated ATP data mg of ATP per mi' Data n Mean Range Direct 1, Interpolated 2, levels were found at high tide, with depressed levels corresponding to low tide. The maximum levels of ATP were found at 1900 and 2100 h on 11 November and 0700 h on 12 November; the values were 1.379, 1.266, and mg of ATP per m3, respectively. Minimum levels were found at 1500 h on 11 November and 0200 and 1500 h on 12 November; the values were 0.523, 0.510, and mg of ATP per m3. The fluctuations of interpolated data were nearly identical to the direct data. Maximum and minimum values occurred at the same times, although the values were slightly different: 1.317, 1.227, and mg of ATP per m3 were the maximum values, and the minimum values were 0.522, 0.504, and mg of ATP per m3. To verify the validity of interpolating the hourly data, t tests were performed for each hour comparing direct with interpolating data. The Null hypothesis, Ho: U1 - U2 = 0, was tested and accepted at the significance level for data obtained at each hour. Due to the high degree of similarity between direct and interpolated data, only interpolated data were used in the characterization of the transect. AOI A02 A03 A04 A05 A06 A07 AOS A09 AIO 0 Om 21m 40m 68m 94m 113m 164m 191m 211m 25Sm 303m 320m MARS A * * A EACH 2-ii 0~~~~~~ PHOTOGRAPHS~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ t "I 3.39 VERTICAL EXAGGERATION 20 X DISTANCE BETWEEN BOATS FROM FOUR AERIAL -6m PHOTOGRAPHS BATHYMETRY FROM FATHOMETER - am FIG. 2. Bathymetry profile of the Town Creek cross section indicating the position of the sampling boats, distance between boats, and the approximate positions from which samples were collected (represented by squares). 4.27' m 7m East

4 844 CHRZANOWSKI, STEVENSON, AND KJERFVE APPL. ENVIRON. MICROBIOL. DARK M DIRECT C/) LLi HL 3 2 _ I I NRA TIME FIG. 3. Fluctuation ofatp and tidal height for both direct (top) and interpolated (bottom) data. The distribution of mean concentrations computed from values generated during the 25-h study indicates that the transect was very heterogeneous with respect to ATP levels (Fig. 4A). There were no patterns suggesting vertical stratification across the cross-sectional area; however, several horizontal divisions were apparent. Marked discontinuities in the mean values were evident between sites 5 and 6 as well as between sites 8 and 9 (Fig. 4B). In addition, a dissimilarity was noted in the upper depths between stations 7 and 8. The highest mean concentration was identified at the surface of site 4, whereas the lowest values were consistently recovered from site 9, the primary channel (Fig. 4B). When the ATP concentrations were corrected for directional movement such that concentrations associated with flooding waters were assigned a negative value and concentrations associated with ebbing waters were assigned a positive value, a distinctly different view of the transect emerged (Fig. 5A, B, and C). The distribution within the eastern half of the transect, from the vicinity of site 6, was relatively homogeneous, whereas the distribution was more heterogeneous in the western half. Two distinct areas of positive mean values (higher numbers '0-- ~~~~~~~~~~~DEPT H li INTE RPOLATED ATP DEPTH on ebbing tide) were revealed at the mid-depth areas at sites 3 and 9 (Fig. 5B). The only other area having a net positive (outward directed) distribution of ATP was found at the surface of site 8. All other sections of the transect had a net negative distribution, indicating higher ATP concentration moving from the ocean to the marsh (Fig. 50). Insights concerning the magnitude and the direction of biomass movement were obtained from the product of velocity and ATP concentration. These calculations permit the determination of areas where major transport occurred. Two distinct regions of this transect were apparent (Fig. 6A). The eastern section, again from the vicinity of site 6, was a predominately homogeneous exporting system with a strong exporting channel at the bottom of site 9 (Fig. 6B). There was a minor importing core at the surface of site 9 at which the net ATP flux was minimal (Fig. 6A, B). The western section was highly heterogeneous and predominately importing. The data suggested some horizontal stratification, with marked import occurring along the surface at sites 1 through 7 (Fig. 6C). Additionally, an exporting channel was found centered at the bottom of site 3 (Fig. 6B). I K) E a- E

5 VOL. 37, 1979 ATP FLUX 845 Eost - 2m - 3m -4. B - Sm - 6m am mg ATP/m3 Downloaded from FIG. 4. Distribution of mean ATP concentrations for the 25-h sampling period. (A) Two-dimensional isopleth; (B) three-dimensional contour. The computation of the net flux of ATP for the entire cross-sectional area indicated that ATP was imported at a rate of 39.8 mg per s. The total transport for the 25-h sampling period was calculated to be 3.58 kg of ATP. DISCUSSION Several previous studies have reported on the transport of materials into and out of marsh systems. These studies have, with few exceptions, dealt with brackish water marshes or poorly flooded marshes within the confines of larger low-salinity estuaries (1, 9, 20). Additionally, the marsh systems studied have been relatively small, usually under 60 ha (9, 18, 19), implying small drainage creeks with cross-sectional areas <100 m2 (see 9, 20). Sampling durations have generally been long, ranging from several months (8, 19) to a year or longer (9, 17, 20); however, during monthly or quarterly sampling regimes, samples have been taken from few depths and apparently from few positions along a selected sampling transect. This work is in sharp contrast to previous studies. The area of the marsh, approximately 1,800 ha, drained by Town Creek is substantial. The system is dominated by Spartina alterniflora and has no appreciable freshwater input. The transect had a cross-sectional area of 1,200 m2 and a peak discharge of 2,136 m3 per s during the study period. The sampling duration was relatively short, 25 h; however, the sampling regime was intensive: 30 sampling positions sampled synoptically each hour, requiring 125 people for the field work and 8 people to extract ATP. ATP has been used as a parameter for the quantification of total microbial biomass for more than a decade. Despite the relative ease of on October 2, 2018 by guest

6 A West East 2 m 3m 4m mg ATP/m3 \ 025-5m m FLOOD El El' 7rm m j mg ATP/m mg ATP/M3 FIG. 5. Distribution of mean ATP concentrations for the 25-h sampling period when the values were corrected for direction of flow. (A) Two-dimensional isopleth; (B) three-dimensional contour of the ebbdirected flow, with the observer facing the creek; (C) three-dimensional contour of the flood-directed flow, with the observer facing the ocean. 846

7 VOL. 37, 1979 ATP FLUX 847 A M VA3 AV5 A09 AIO East : -A-6' l / _3 C 0t Ool o3g 03e Downloaded from ~~=-vltl WC ~~~~~~~mg ATP/m2s FIG. 6. Distribution of mean ATP concentrations for the 25-h sampling period when the values were corrected for velocity. (A) Two-dimensional isopleth; (B) three-dimensional contour of the ebb-directed flow, with the observer facing the creek; (C) three-dimensional contour of the flood-directed flow, with the observer facing the ocean. on October 2, 2018 by guest extraction and quantification, as well as the reliability of the assay, very few studies are available using ATP as an indicator of microbial biomass transport. Perhaps the most prominent of the studies using ATP are those of Heinle and Flemer (9), Axelrad et al. (1), and, more recently, Erkenbrecher and Stevenson (7). The relatively short sampling duration of this study admittedly does not allow transport comparisons to these prominent studies or a comprehensive evaluation of the Town Creek drainage area as an importing or exporting system. However, both the large number of sampling sites and actual number of samples have yielded detailed distribution and transport data. The temporal fluctuation of ATP over the two tidal cycles reported in this paper is in conflict with that presented by Erkenbrecher and Ste-

8 848 CHRZANOWSKI, STEVENSON, AND KJERFVE venson (6). Working at Oyster Landing Creek, a high-marsh creek within North Inlet, they found ATP to fluctuate 1800 out of phase with the tide; ATP concentrations were minimal at high tide and maximal at low tide. These findings are opposite to our findings at Town Creek, where ATP concentrations were minimal at low tide and maximal at high tide. This discrepancy may be due to seasonal differences or, perhaps more importantly, they may reflect different populations detected in the water column. At low tide the sediment at Oyster Landing Creek is almost entirely exposed; the flooding and ebbing waters usually resuspend sediment and attendant microbial populations. ATP extracted from samples taken from this high-marsh creek was probably associated with sediment populations, whereas ATP extracted from samples taken at Town Creek was associated predominately with oceanic populations. Oyster Landing Creek is in the uppermost reaches of the marsh system, separated from the Town Creek transect by approximately 4 km of waterway. The distance between the creeks is strong circumstantial evidence in support of this proposal. The development of a detailed picture of the distributions of microbial biomass within the transect was one of the more valuable results of this study. The complex distribution cautions against the random selection of sampling sites within such a transect. This was dramatically emphasized when data corrected for direction of flow or velocity were compared to concentration data. Additionally, data corrected for direction of flow may supply distributional patterns that differ considerably from data intergrated with velocity. This was clearly demonstrated in this study as data corrected for direction indicated a majority of the eastern section of the transect to be inflowing (see Fig. 5A, B, and C); however, when velocity was accounted for, the majority of the eastern section of the transect was actually outflowing (see Fig. 6A, B, C). A salient point of this study is that detailed characterization of a creek transect in terms of ATP or any similar parameter requires the simultaneous measurements of both the concentration of the parameter in question and the velocity at the time and point from which the sample was taken. It is almost always impossible to characterize a location from concentration data alone and even more so if the concentration data are derived from a poorly constructed transect. As is apparent from data presented herein, conclusions based solely on concentration or directionally corrected data will be misleading. ACKNOWLEDGMENTS This work was supported by National Science Foundation grant DEB We thank the 133 students, faculty, and technicians of the APPL. ENVIRON. MICROBIOL. Marine Science Program and Department of Biology for their assistance in collecting the field data. We are especially grateful to Steven Knoche, Charles Wilson, and Jeffrey Proehl for capable technical assistance. LITERATURE CITED 1. Axelrad, D. M., K. A. Moore, and M. E. Bender Nitrogen, phosphorus and carbon flux in Chesapeake Bay marshes. Bull. 79, Virginia Water Resources Center, Blacksburg. 2. Barr, A. J., J. H. Goodnight, J. P. Sall, and J. T. Helwig A user's guide to SAS 76. Sparks Press, Raleigh, N.C. 3. Dame, R., F. Vernberg, R. Bonnell, and W. Kitchens The North Inlet marsh-estuarine ecosystem: a conceptual approach. Helgol. Wiss. Meeresunters. 30: Dougenik, J. A., and D. E. Sheehan SYMAP user's reference manual. Graduate School of Design, Harvard University, Cambridge, Mass. 5. Duedall, I. W., H. B. O'Connors, J. H. Parker, R. E. Wilson, and A. S. Robbins The abundances, distribution and flux of nutrients and chlorophyll a in the New York Bight Apex. Estuarine Coastal Mar. Sci. 5: Erkenbrecher, C. W., and L. H. Stevenson The influence of tidal flux on microbial biomass in salt marsh creeks. Limnol. Oceanogr. 20: Erkenbrecher, C. W., and L. H. Stevenson The transport of microbial biomass and suspended material in a high-marsh creek. Can. J. Microbiol. 24: Haines, E. B The origins of detritus in Georgia salt marsh estuaries. Oikos 29: Heinle, D. R., and D. A. Flemer Flows of materials between poorly flooded tidal marshes and an estuary. Mar. Biol. 35: Hohm-Hansen, Determination of total microbial biomass by measurement of adenosine triphosphate, p In L. H. Stevenson and R. R. Colwell (ed.), Estuarine microbial ecology. University of South Carolina Press, Columbia. 11. Holm-Hansen, O., and C. R. Booth The measurement of adenosine triphosphate in the ocean and its ecological significance. Limnol. Oceanogr. 11: Kjerfve, B Velocity averaging in estuaries characterized by a large tidal range to depth ratio. Estuarine Coastal Mar. Sci. 3: Laboratory for Computer Graphics and Spatial Analysis SYMVU manual. Graduate School of Design, Harvard University, Cambridge, Mass. 14. Lonsdale, D. J., and B. C. Coull Composition and seasonality of zooplankton of North Inlet, South Carolina. Chesapeake Sci. 18: Odum, E. P A research challenge: evaluating the productivity of coastal and estuarine water, p In Proceedings, Second Sea Grant Conference. Graduate School of Oceanography, University of Rhode Island, Newport. 16. Pritchard, D. W., and W. V. Burt An inexpensive and rapid technique for obtaining current profiles in estuarine waters. J. Mar. Res. 10: Settlemyre, J. L., and L. R. Gardner Suspended sediment flux through a salt marsh drainage basin. Estuarine Coastal Mar. Sci. 5: Shisler, J. L., and D. M. Jobbins Tidal variations in the movement of organic carbon in New Jersey salt marshes. Mar. Biol. 40: van Es, F. B A preliminary carbon budget for a part of the Ems estuary: the Dollard. Helgol. Wiss. Meeresunters. 30: Woodwell, G. M., D. E. Whitney, C. A. S. Hall, and R. A. Houghton The flax pond ecosystem study: exchanges of carbon in water between a salt marsh and Long Island Sound. Limnol. Oceanogr. 22: