Dl. Childers et al., SPATIAL AND TEMPORAL VARIABILITY IN MARSH WATER COLUMN INTERACTIONS IN A SOUTHEASTERN USA SALT-MARSH ESTUARY, Marine ecology. Progress series, 95(1-2), 1993, pp. 25-38
We measured the exchange of inorganic nutrients and particulate matter
between the Spartina alterniflora marshes and the adjacent estuary of
Cumberland Island, Georgia, USA, beginning in January 1991. Tidal flu
xes were quantified using throughflow flumes at 3 sites within 10 km o
f one another. These sites represent a spatial gradient in geologic ag
e, sediment characteristics, marsh topography and elevation, and expos
ure to open water that is often found in transgressive marsh-barrier c
omplexes. They exhibited large variability in frequency and duration o
f tidal inundation and in susceptibility of the marshes to wind and wa
ve erosion. The flumes were sampled seasonally and on consecutive days
, and we present flux data from 7 samplings. We also investigated shor
t-term temporal variability in nutrient and particulate fluxes by samp
ling one flume 4 times in 6 days. Temporal variability in total and or
ganic suspended sediment fluxes, which was largely related to quickly
changing wind and wave conditions, was greater than spatial variabilit
y measured during the same time. Dissolved constituent fluxes were gen
erally more variable across space, suggesting that day-to-day variabil
ity in dissolved nutrient exchanges was not a major contribution to sp
atial variability. Dissolved inorganic nutrient fluxes (as ammonium, n
itrate+nitrite, and soluble reactive phosphorus) followed a spatial pa
ttern of highest nutrient uptake at the geologically young marsh site.
This marsh also consistently imported dissolved organic carbon. This
site has the lowest absolute elevation of the 3 sites and a ramp-like
topographic profile, and its young geologic age suggests that it is al
so ecologically immature. Fluxes of dissolved constituents at this sit
e were negatively related to the area of marsh inundated, switching to
export when large areas of the young marsh were inundated for long pe
riods of time. This marsh also generally exported total and organic se
diments; data from the other 2 sites were more variable. Sediment flux
es from the older marsh sites were positively related to slack high ti
de water level and area inundated, switching from particulates release
to uptake only when the highest portions of these marshes were inunda
ted. Most Cumberland Island marshes thus appear to take up sediments o
nly when tidal heights exceed about 2.3 m above National Geodetic Vert
ical Datum, corresponding to tides where the moon is within 20 % of ne
w or full phase, Our data also suggest definite differences in the way
the geologically young marshes interact with the inundating water col
umn compared to geologically older marshes in the same estuarine syste
m.