Abstract
Abstract. Stream ecosystem processes such as nutrient cycling may vary with stream position in the network. Using a scaling approach, we examined the relationship between stream size and nutrient uptake length, which represents the mean distance that a dissolved solute travels prior to removal from the water column. Ammonium (NH4+) uptake length increased proportionally with stream size measured as specific discharge (discharge/stream width) with a scaling exponent = 1.01. In contrast, uptake lengths for nitrate (NO3−) and soluble reactive phosphorus (SRP) increased more rapidly than increases in specific discharge (scaling exponents = 1.19 for NO3− and 1.35 for SRP). Additionally, the ratio of inorganic nitrogen (N) uptake length to SRP uptake length declined with stream size; there was relatively lower demand for SRP compared to N as stream size increased. Finally, we related the scaling of uptake length with specific discharge to that of stream length using Hack's law and downstream hydraulic geometry. Ammonium uptake length increased less than proportionally with distance from the headwaters, suggesting a strong role for larger streams and rivers in regulating nutrient transport.
Highlights
One of the most elegant applications of the ecosystem concept (O’Neill, 2001) has been to define the boundary or edge of an ecosystem and quantify the functioning within this spatially explicit unit, as did Bormann and Likens (1967) for a small watershed
Soluble reactive phosphorus scaled with Q / w with a slope of 1.35, which like that for NO−3 was > 1, but the relationship for soluble reactive phosphorus (SRP) had much less variation and smaller confidence intervals compared to the other two solutes (Fig. 1, Table 1)
We have provided a scaling framework to examine how an ecosystem process such as nutrient uptake can vary as a func
Summary
One of the most elegant applications of the ecosystem concept (O’Neill, 2001) has been to define the boundary or edge of an ecosystem and quantify the functioning (e.g., material cycling or energy flow) within this spatially explicit unit, as did Bormann and Likens (1967) for a small watershed. Dissolved solute concentrations in streams varied with the size of the drainage basin (Likens and Buso, 2006). Despite previous recognition of these patterns, there are few quantitative relationships linking ecosystem processes and, for example, position in a drainage network (Ensign and Doyle, 2006). We use an allometric scaling approach applied to stream ecosystems to examine how nutrient uptake in streams varies as a function of ecosystem size measured as specific discharge and position in the network
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