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					                                                           NITRATE AND PHOSPHATE EXCHANGE IN AN
                                                           EXPERIMENTALLY FERTILIZED TIDAL CREEK
                                                                          C.R. Picard, B.J. Peterson, C.S. Hopkinson and L.A. Deegan

                                                          The Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA 02543

                                                                                                                             NITRATE                                                                                                   NITRATE                                                                                             RESULTS
       Eutrophication is currently one of the most influential                                                  29-Jun                             29-Jul                                                                      Flooding     Ebbing      Net Flux
                                                                                                                Average Depth                      Marsh Flooding Depth
stressors effecting estuarine ecosystems. The TIDE project uses a                                                                                                                                                       40                                         .32
                                                                                                   70                                                                     4.0                                                                                                                                                       REFERENCE CREEK

multi-disciplinary approach to investigate the effects of                                          60                                                                     3.5
                                                                                                                                                                                                                        30                                         .24

eutrophication on marshes of Plum Island Estuary,                                                  50
                                                                                                                                                                          3.0                                           20                                         .16                                                              Nitrate   Phosphate        Depth

                                                                                     NO3 (uM/L)

                                                                                                                                                                                 Depth (m)
                                                                                                                                                                                Depth (m)
Massachusetts. Moderate to high nutrient loads were added                                          40
                                                                                                                                                                                                                        10                                         .08                                                  5                                                       3.0
directly to the flooding water of a treatment creek system during                                  20
                                                                                                                                                                          1.5                                            0                                          0
                                                                                                                                                                                                                                                                                                                        4                                                       2.5

                                                                                                                                                                                                                                                                                                       NO3/PO4 (uM/L)
each incoming tide from May to October 2004. This methodology


                                                                                                                                                                                                                                                                                                                                                                                       Depth (m)
                                                                                                                                                                                                                       -10                                         -.08

                                                                                                                                                                                                                                                                                                                                                                                      Depth (m)
                                                                                                   10                                                                     0.5                                                                                                                                                                                                   2.0
differs from plot fertilization experiments by simulating the                                       0                                                                     0.0
                                                                                                                                                                                                                       -20                                         -.16
                                                                                                        0       2        4          6         8             10     12                                                                                                                                                                                                           1.5
hydrological delivery of elevated nutrients into tidal creeks and the                                                        Time In Tide (hr)
                                                                                                                                                                                                                              29-JUN                 29-JUL
adjoining systems. We present a preliminary flux calculation for
NO3 and PO4 in this fertilized creek.                                                                                    PHOSPHATE                                                                                                 PHOSPHATE                                                                                                                                    0.5
                                                                                                                                                                                                                          7                                             56                                              0                                                       0.0

       We found a positive flux of both NO3 and PO4 in June (2.6 kg                               5.0
                                                                                                                                                                          4.0                                             6
                                                                                                                                                                                                                                                                                                                            0          5                  10               15
NO3-N/tide, 0.1 kg PO4-P/tide) and July (22 kg NO3-N/tide, 3.5 kg                                 4.0
                                                                                                                                                                                                                          4                                             32                                                               Time In Tide (h)
                                                                                                  3.5                                                                                                                     3                                             24
PO4-P/tide). These early calculations suggest a high percentage
                                                                                PO4 (uM/L)

                                                                                                                                                                                 Depth (m)
                                                                                                                                                                                Depth (m)
                                                                                                  3.0                                                                     2.5                                             2                                             16                Figure 5: Typical nutrient concentration profile of a reference
                                                                                                                                                                                                                          1                                             8
of the added nutrients were imported into the system. Variations in                               2.5                                                                     2.0
                                                                                                                                                                                                                          0                                           0
                                                                                                                                                                                                                                                                                          creek in the Plum Island Estuary system. NO3 concentrations vary
                                                                                                  2.0                                                                     1.5
the flux values for each sampling event may be due to                                             1.5
                                                                                                                                                                                                                         -1                                          -8                   from 1 to 5 µM/L while PO4 values are usually around 1 µM/L.

                                                                                                                                                                          1.0                                            -2                                          -16
hydrodynamic differences and changes in ecosystem metabolism.                                     0.5                                                                     0.5                                            -3                                          -24
                                                                                                                                                                                                                         -4                                          -32
                                                                                                  0.0                                                                     0.0
                                                                                                        0       2        4          6         8             10    12                                                          29-JUN                 29-JUL
                                                                                                                             Time In Tide (hr)

                               METHODS                                                                                                                                                                                                                                                                                                                          N
                                                                                                                                                                                                                                          WATER                                                        70
                                                                                                                             WATER                                                                                                                                                                                                                                     P
– Tidal cycles were chosen to ensure at least 10 cm of water on                                                                                                                                                        80                                                                              60

                                                                                                   25                                                                     4.0

                                                                                                                                                                                                                                                                                         % Imbalance
  the marsh surface                                                                                                                                                       3.5                                                                                                                          50

                                                                                                                                                                                                   H2O (103 m3/tide)
                                                                                                   20                                                                                                                  40
                                                                                H2O (103 m3/h)


                                                                                                                                                                                Depth (m)
– Hourly water column nutrient samples were taken at multiple

                                                                                                                                                                                 Depth (m)
                                                                                                   15                                                                     2.5
                                                                                                                                                                          2.0                                           0                                                                              30
  points in the creek system during two tidal cycles (June 29 and                                  10                                                                     1.5                                          -20
  July 29) on both the flooding and ebbing tides                                                    5
                                                                                                                                                                                                                       -40                                                                                                             P

                                                                                                                                                                          0.5                                                                                                                          10
– ADCP used to monitor water velocity and depth to calculate
                                                                                                    0                                                                     0.0
                                                                                                            0   2        4           6        8             10     12                                                  -80                                                                              0
  hourly water volume fluxes during each tidal cycle                                                                            Time In Tide (h)                                                                              29-JUN                    29-JUL
                                                                                                                                                                                                                                                                                                                                29-JUN                           29-JUL
– Hourly nutrient concentrations were pooled and volume
  weighted hourly fluxes determined                                            Figure 3: Nutrient concentration and water                                                                    Figure 4: Nutrient and water flux values for the two                                          Figure 6: Percent of experimentally added nutrients
                                                                               volume profiles during the two tidal cycles. The                                                              tidal cycles. The flooding flux is designated by a                                            imported into the tidal creek system during each tidal cycle.
– Flooding fluxes (+ values) and ebbing fluxes (- values) were                 predicted high tides were 3.08 m and 3.14 m                                                                   positive value and the ebbing flux a negative
  determined for each sampling date                                            respectively for June 29 and July 29. Previous                                                                value. Nutrient fluxes are expressed with relation
                                                                               data on this system suggests that a tidal height                                                              to the whole system (kg/tide) and per unit area
– Net flux calculated by comparing the individual flooding and                 of approximately 2.9 m floods the surrounding                                                                 (g/m2/tide) for each tide. The tidal creek system is
  ebbing fluxes. A positive value represents an import to the                  marsh with 10 cm of water.                                                                                    12.5 ha in area.
  creek system and a negative value represents an export from
  the creek system
                                                                                                                                                                 PRELIMINARY CONCLUSIONS                                                                                               CURRENT AND FUTURE DIRECTIONS
                                                                                                                                         – Early data suggests a large import of nutrients in this                                                                        – Continued fertilization and monitoring of two tidal creeks and two
                                                                              Point of                                                   experimentally loaded tidal creek                                                                                                reference creeks
                                                                                                                                         – Variations in fluxes between the two tidal cycles may be                                                                       – Ecosystem scale 15N enrichment project on a fertilized and
                                                                                                                                         due to differences in tidal height, incoming nutrient                                                                            reference creek to investigate differences in biogeochemistry
                                                                                                                                         concentrations and ecosystem metabolism                                                                                          between the two systems
                                                                                                                                         – More precise hydrological data and monitoring of a variety                                                                     – Continued collection of hydrological data on all creeks using a
                                                                                                                                         of tidal cycles will aid in the final flux analyses                                                                              variety of instruments and methods
                                                                                                                                                                                                                                                                          – Development of an ecosystem model that will predict the cumulative
                                                                                                                                                                                                                                                                          effects of marsh eutrophication on a decadal scale
Figure 1: Pump station at treatment                                                                                                                                       FURTHER INFORMATION
creek where a fertilizer solution was                                                                                                                                                                                                                                                                                           ACKNOWLEDGEMENTS
added directly to the water column on                                                                                                    For project updates and information visit the following websites:
                                                                                                                                                                                                                                                                          This material is based upon work supported by the National Science Foundation under Grants No. 0213767
each incoming tide.                         Figure 2: Map of treatment creek system.                                                     TIDE: http://ecosystems.mbl.edu/tide                                                                                             and 9726921. Any opinions, findings, and conclusions or recommendations expressed in this material are
                                                                                                                                                                                                                                                                          those of the authors and do not necessarily reflect the views of the National Science Foundation.
                                                                                                                                         Plum Island LTER: http://ecosystems.mbl.edu/pie

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