HYDROPERIOD CHANGES AS CLUES TO IMPACTS ON CACHE RIVER RIPARIAN WETLANDS

A hydrologic analysis of historic stream gage data collected on the Ca che River at Patterson, Arkansas is presented as a basis for impact an alysis of riverine wetlands. Subtle, long-term changes in hydroperiod that could collectively have major impacts on wetland functions are qu antified. Harmonic analysis, time-scale analysis, and conventional met hods of hydrologic analysis of gage data at decade intervals are emplo yed. These various techniques indicate a steady decline in the magnitu de and predictability of the base flow during low flow periods, beginn ing with the 1920s and becoming increasingly more pronounced into the 1980s. Complementary information suggests that hydroperiod alterations can be associated with increased ground-water pumping and associated land use changes in the Cache River basin. Hydrologic indices wer deve loped that range from intuitively simple but generally insensitive ind ices based on means, medians, ranges, and discharge-duration curves to indices that are based on methods sensitive to subtle changes in hydr ologic patterns. One set of sensitive indices generated by harmonic an alysis is relatively simple to obtain and useful to explore changes in the pattern of discharges or stages in wetlands. The timescale analys is can be employed to provide a relatively high resolution quantificat ion of changes in hydrology that can be related to long-term changes i n land- or water-use patterns. The hydrologic methods presented in the se analyses are simple enough for routine application (when adequate d ata are available) but sufficiently sophisticated to identify subtle c hanges in hydroperiod associated with impacts and passage of time. Cha nges in hydroperiod identified by these methods may have the potential to explain changes in biotic communities or wetland structure as part of comprehensive wetland studies.