Relative sediment elevations have been measured seasonally since Sprin
g, 1990, in three estuaries representing a range of estuarine geomorph
ologies, sizes, and watershed inputs: the North Inlet estuary, South C
arolina (SC), the Patuxent River estuary, Maryland (MD), and the Rhode
River estuary, Maryland (MD). Sediment elevations were quantified usi
ng a levelling-arm device that allowed accurate, repeatable measuremen
ts at four arm orientations per site (with nine replicates per orienta
tion), a number of habitat sites per location, and a number of locatio
ns in each estuary. This hierarchical design allowed variability to be
partitioned into nested spatial scales. At North Inlet, we establishe
d six locations characterizing a range of freshwater and oceanic influ
ences, and marsh ages. Water level gauges continuously recorded inunda
tion rates at three of the six locations. Six sediment elevation locat
ions along the Patuxent River estuary (one habitat site each) differen
tiated tributary marshes from main channel marshes, marshes from mudfl
ats, and upper from lower river geomorphologies. Seven sediment elevat
ion sites in the Rhode River estuary were all within the same 0.25 ha
area (spatially equivalent to a single habitat site in the other two e
stuaries), and we used these data to investigate small-scale variabili
ty in brackish marsh sediment elevations over time. Results from North
Inlet showed sediment elevations increasing at the greatest rates at
locations nearest to freshwater influence. These rates were two to thr
ee times apparent sea level rise (ASLR), which is 2-4 mm yr-1 in all t
hree estuaries. Sediment elevations in dead end tidal creek marshes-th
ose without direct freshwater inputs-generally increased at rates comp
arable to ASLR. Geologically older marshes showed little or no net acc
retion over 2.5 years. A large decline in sediment elevations (-9.4 mm
yr-1) at a mudflat located in the headwaters of a geologically young
tidal creek appeared to represent the ''birth'' of a transgressively s
ubtidal creek from an intertidal mudflat. Sediment elevations generall
y increased at Patuxent River tributary marsh sites, but at greater ra
tes in lower river than upper river tributaries. In contrast, a lower
river main channel marsh and upper river mudflat appeared to be erodin
g while a middle river marsh and mudflat appeared to be accreting. Thi
s pattern suggests that the extensive mid-channel tidal freshwater mar
shes of the upper river and the isolated tributary headwater marshes o
f the lower river may be sediment sinks, while others may be sediment
sources. The Rhode River study, on the other hand, showed that small-s
cale variability in brackish marsh sediment elevations may be much gre
ater than seasonal or long-term differences. The consistent use of thi
s accurate and repeatable technique to quantify estuarine sediment ele
vation dynamics in a number of systems will continue to generate data
critical to future comparisons of Atlantic and Gulf Coast estuaries.