One of the often-stated functions of wetlands is their ability to remo
ve sediments and other particulates from water, thus improving water q
uality in the adjacent aquatic system. However, actual rates of suspen
ded sediment removal have rarely been measured in freshwater wetland s
ystems. To address this issue, suspended sediment dynamics were measur
ed in a 85-km(2) bottomland hardwood (BLH) wetland adjacent to the hig
hly turbid Cache River in eastern Arkansas during the 1988-1990 water
years. A suspended sediment mass balance was calculated using depth-in
tegrated, flow-weighted daily measurements at wetland inflow and outfl
ow points. Over the three-year period, suspended sediment load decreas
ed an average of 14% between upstream and downstream sampling points.
To test the idea that the suspended sediments were retained by the adj
acent wetland and to determine what portion of the BLH forest was most
responsible for retaining the suspended sediments, concurrent measure
ments of sediment accretion were made at 30 sites in the wetland using
feldspar clay marker horizons, sedimentation disks, the (137)cesium m
ethod, and dendrogeomorphic techniques. Sedimentation rates exceeding
1 cm/yr were measured in frequently flooded areas dominated by Nyssa a
quatica and Taxodium distichum. Maximum sedimentation rates did not oc
cur on the natural levee, as would be predicted by classical fluvial g
eomorphology, but in the ''first bottom,'' where retention time of the
water reached a maximum. Multiple regression was used to relate sedim
entation rates with several physical and biological factors. A combina
tion of distance from the river, flood duration, and tree basal area a
ccounted for nearly 90% of the variation in sedimentation rates.