Exploring Potential Spatial-Temporal Links Between Fluvial Geomorphology and Nutrient-Periphyton Dynamics in Streams Using Simulation Models

Abstract

Understanding stream ecosystem processes necessitates an awareness of not only the physical, chemical, and biological systems, but also how these separate systems interact with each other. Using a nutrient retention and periphyton growth model coupled to a dynamic geomorphic template, we explore the potential role of channel shape, slope, and sediment texture on downstream nutrient retention, and attempt to determine if physical changes alone can drive or influence changes in nutrient-periphyton dynamics. The overall model results suggest there is a strong potential control of both nutrient retention and periphyton biomass by channel morphology. For example, with constant biochemical process rates, geomorphic variations alone could alter spatial distribution of nutrient retention over a 4-km study reach by between 11 percent and 52 percent. These results suggest channel geomorphology has a potentially strong influence on both nutrient retention and basal food sources in streams.

Key Words:

• biogeochemistry
• ecohydrology
• ecosystem ecology
• river restoration

Acknowledgments

We are grateful to Don DeAngelis for guidance on modeling nutrient-periphyton dynamics, and for reviews of an earlier manuscript by Jim Pizzuto, Jack Schmidt, and two anonymous reviewers.

Notes

Source: All coefficients are taken from DeAngelis et al. (1995) except those marked, which were taken from a subset of the data presented in Laenen and Bencala (2001).

^aÄS=length of model stream segment (10 m).

^bFG=function of geomorphology, and therefore spatially and temporally dynamic.

^c A _s was calculated using A _w and ê=A _s /A _w =0.14 and 0.31 for sand-bed and gravel-bed channels, respectively (Laenen and Bencala 2001).

^d k _w =2.6 × 10⁻⁵ and 9.9 × 10⁻⁵ sec⁻¹ for sand-bed and gravel-bed channels, respectively (Laenen and Bencala 2001).

^e k _s was computed to maintain steady-state diffusional transport: V _s /V _w =k _w /k _s (DeAngelis et al. 1995).

Note: Results are for T1 and T3 channel conditions. Percentages in parentheses indicate the difference from model output using the original parameter value. See Table 1 and the text for complete definitions of parameters.