Nitrogen Dynamics During Succession in a Desert Stream

Open Access
Publisher Website
Google Scholar
Abstract
Nitrogen dynamics of Sycamore Creek, Arizona, a lowland Sonoran Desert stream, are described by seven diel input—output budgets at different stages of postflood succession. Hydrologic inputs and outputs of nitrogen and N storage in periphyton, macroinvertebrates, and fish were measured over 24—h periods. Total nitrogen storage in this desert stream (3—9 g/m2) was lower than that in forest streams of Oregon (12 g/m2) and Quebec (22 g/m2). While >99% of nitrogen in the latter systems is in allochthonous detritus, benthic algae and autochthonous detritus comprised °90% of the total nitrogen pool in the desert stream. Up to 14% of nitrogen was in consumer organisms. Inputs of nitrogen to the stream ecosystem were dominated by dissolved nitrogen, of which 19—60% was inorganic, primarily nitrate. Particulate nitrogen in transport (4—15%of total input) was mostly autochthonous. Inputs of nitrogen exceeded outputs on most study dates. Rates of ecosystem nitrogen retention were as high as 400 mg°m2°d—1 and outputs exceeded inputs on only one study date. Retention was primarily of inorganic nitrogen and was presumed due to autotrophic assimilation. Nitrogen retention data from the seven budgets were used to evaluate the Vitousek and Reiners (1975) model that patterns of nitrogen retention during succession reflect patterns of net ecosystem production and biomass accumulation. Biomass and stored nitrogen increased asymptotically during a postflood successional sequence at a single site; nitrogen retention during this period accounted for increases in storage. Nitrogen retention among the seven study dates exhibited the predicted successional patterns of increases from early to middle successional stages, followed by late stage declines.