J. N. Am. Benthol. Soc., 1993, 12(3):223-235 © 1993 by The North American Benthological Society Transient storage in Appalachian and Cascade mountain streams as related to hydraulic characteristics D. J. D'ANGELO 1 ' 4 , J. R. WEBSTER 2 , S. V. GREGORY 1 , AND J. L. MEYER 3 1 Fisheries and Wildlife Department, Oregon State University, Corvallis, Oregon 97331 USA 2 Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24060 USA 3 Institute of Ecology, University of Georgia, Athens, Georgia 30602 USA Abstract. Hydraulic characteristics were measured in artificial streams and in 1st- to 5th-order streams in the Appalachian and Cascade mountains. Appalachian Mountain stream sites at Coweeta Hydrologic Laboratory, North Carolina, were on six Ist-order streams and a 1st- through 4th-order gradient of Ball Creek-Coweeta Creek. Cascade Mountain sites were located on constrained and unconstrained reaches of Lookout Creek, a 5th-order stream in H. J. Andrews Experimental Forest, Oregon. At each site, a tracer solution (chloride or rhodamine WT) was released for 30-180 min and then discontinued. At the downstream end of the release site, the resulting rise and fall of the tracer concentration was measured. These data, along with upstream concentration and measured widths and depths, were used in a computer model to estimate several hydraulic parameters in- cluding transient storage and lateral inflow. Estimated transient storage zone size (A,) ranged from near zero in artificial streams to 2.0 m 2 in 5th-order streams. A, was largest relative to surface cross- sectional area (A) at Ist-drder sites where it averaged 1.2 x A, compared with 0.6 x A and 0.1 x A in unconstrained and constrained 5th-order sites, respectively. Where measured, lateral discharge inputs per metre of stream length ranged from 1.9%of instream discharge in Ist-order streams to 0.05% of instream discharge at 5th-order sites. Our results show that surface water exchange with storage zones is rapid and extensive in steep headwater streams and less extensive but still significant at 3rd- through 5th-order sites. An understanding of relationships between stream morphology, storage zone size, and extent of interactions between surface and subsurface waters will assist comparisons of solute dynamics in physically diverse streams. Key words: solutes, transient storage, transport model, retention, discharge, geomorphology. Solute dynamics often play a critical role in ering processes that influence transport and streams because many solutes (e.g., phosphorus transformation of biologically reactive solutes, and nitrogen) are present in short supply and and were limited by an inability to separate and thereby regulate primary and secondary pro- quantify physical and biological determinants ductivity (Stream Solute Workshop 1990). Ad- of solute transport. ditionally, linkages between terrestrial and Recent applications of transport equations aquatic ecosystems and between upstream and (Fischer et al. 1979, Bencala and Walters 1983, downstream reaches of streams strongly influ- Hart et al. 1990) to solute transport in streams ence solute concentrations (Meyer et al. 1988). allow us to explain transport dynamics quan- Evaluation of solute transport characteristics in titatively in terms of relationships between physically complex, small mountain streams has physical characteristics (e.g., geomorphology, typically been attempted with short-term tracer flow and substrate) and hydraulic variables (e.g., and nutrient releases (Stream Solute Workshop dispersion, transient storage, transient storage 1990). These studies (e.g., Elwood et al. 1981, exchange rate, and lateral inflow). A combina- Newbold et al. 1981, Elwood et al. 1983, Mul- tion of tracer studies and solute transport sim- holland et al. 1985, Triska et al. 1989, Mulhol- ulations provides a means to quantitatively sep- land et al. 1990, Munn and Meyer 1990, D'An- arate physical and biological controls, smooth gelo and Webster 1991, D'Angelo et al. 1991, out small scale variability, and compare studies Hart et al. 1992) primarily focused on discov- done at different scales (Stream Solute Work- shop 1990). 4 Present address: Institute of Ecology, University We suggest that dispersion, transient storage of Georgia, Athens, Georgia 30602 USA (pockets of slow water movement), transient 223