Hydroperiod changes as clues to impacts on Cache River Riparian wetlands

Abstract

A hydrologic analysis of historic stream gage data collected on the Cache River at Patterson, Arkansas is presented as a basis for impact analysis of riverine wetlands. Subtle, long-term changes in hydroperiod that could collectively have major impacts on wetland functions are quantified. Harmonic analysis, time-scale analysis, and conventional methods of hydrologic analysis of gage data at decade intervals are employed. These various techniques indicate a steady decline in the magnitude and predictability of the base flow during low flow pericxts, beginning 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 developed that range from intuitively simple but generally insensitive indices based on means, medians, ranges, and discharge-duration curves to indices that are based on methods sensitive to subtle changes in hydrologic patterns. One set of sensitive indices generated by harmonic analysis is relatively simple to obtain and useful to explore changes in the pattern of discharges or stages in wetlands. The timescale analysis can be employed to provide a relatively high resolution quantification of changes in hydrology that can be related to long-term changes in land-or water-use patterns. The hydrologic methods presented in these analyses are simple enough for routine application (when adequate data are available) but sufficiently sophisticated to identify subtle changes in hydroperiod associated with impacts and passage of time. Changes 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.

Measurement of wetland hydroperiod using harmonic analysis

“…Each parameter corresponds to a recognizable characteristic of the overall pattern of water-level fluctuations; therefore, they can be understood intuitively. The utility of the harmonic parameters has been illustrated through their application, here, in the Everglades and by Long and Nestler (1996) in a bottomland hardwood swamp in eastern Arkansas. Results were obtained simply and directly, and this suggests the potential for harmonic analysis of hydroperiod as a general tool for wetland science.…”

“…When measured, hydroperiod is often defined to be the length of time that the wetland surface is inundated (e.g., Rowe andDunson 1995, David 1996). An exception is the recent paper by Long and Nestler (1996) in which they use harmonic analysis and other measures to investigate subtle changes in hydroperiod. Measuring hydroperiod only by the length of time of inundation does not capture all of the qualities evoked by "seasonal pattern" or "waterflow regime."…”

Associations between changes in agriculture and hydrology in the Cache River basin, Arkansas, USA

“…These analyses can be used to quantify the relative influence of climatic variation vs. human activities on river flow. Separate analyses were conducted for several time periods (WYs 1919(WYs 1928(WYs , 1941(WYs -1950(WYs , 1951(WYs -t960, 1961(WYs -1970(WYs , 1971(WYs -1980(WYs , and 1981(WYs -1988, which were defined according to the year-composition used in a related study (Nestler and Long 1994;Long and Nestler 1996). Thus, it was possible to determine if flows were consistently related to climatic variation over time.…”

Quantifying impacts to riparian wetlands associated with reduced flows along the Greybull River, Wyoming

“…Reductions in fiver flows associated with hydrologic changes from diversions may alter wetland hydrology and eventually cause some wetlands to revert to uplands. A few studies have examined effects of reduced river flows on riparian communities, including wetlands, using historical gage data (e.g., Long and Nestler 1996) or historical and current aerial photography (e.g., Shoemaker et al 1981). However, little research has been conducted that would allow for predicting and quantifying effects of reduced flows on riparian wetland area.…”

“…However, little research has been conducted that would allow for predicting and quantifying effects of reduced flows on riparian wetland area. The U.S. Army Corps of Engineers and other federal agencies involved with wetland preservation and management currently do not have appropriate tools to evaluate effects of hydrologic changes on wetlands (Long and Nestler 1996).…”