Evaporation as a nutrient retention mechanism at Sycamore Creek, Arizona

Abstract

Studies of nutrient cycling in streams have typically focused on patterns and mechanisms of retention because retention can result in temporary or permanent removal of biologically important nutrients. Biogeochemical studies of nitrate in stream ecosystems have focused primarily on biotic uptake and sequestration, while little is known about abiotic mechanisms of nitrogen retention. Evaporation is one abiotic mechanism that can contribute to nutrient retention with nutrients stored as precipitated solutes in sandbars. The objective of this study was to assess the significance of evaporation-driven nitrate retention in sandbars to reach-scale nutrient budgets at Sycamore Creek, Arizona. The vertical profile of chloride and nitrate evaporties were used as a tool to evaluate abiotic retention. I found that salts accumulated in surface layers (0-2 cm) of exposed sandbar sediments. Calculated evaporative retention rate was 0.7-5.4% of average rate of uptake by biota in the surface stream. However, the area of influence of these two mechanisms varies greatly. Taking into account this spatial and seasonal variation in areal extent of the surface stream versus exposed sandbar surfaces, evaporite formation accounted for 14.8% of retention in the study reach and up to 46.0% of annual retention compared to instream biotic uptake. Nitrate retention via evaporation is important because of the temporary disconnection of nutrients stored in sandbars to the surface stream delaying further biological processing until hydrological reconnection occurs.

Quantifying the effects of stream channels on storm water quality in a semi-arid urban environment

“…Heffernan and Sponseller, 2004;Larned et al, 2010;McLaughlin, 2008;Rankin et al, 1999;Vidon et al, 2010), our study suggests that the characteristics of the substrate and cycles of stream channel wetting and drying control solute retention and mobilization during runoff. However, unlike these studies, this study was conducted in semi-arid urban channels that are heavily modified and managed by humans.…”

Emerging concepts in temporary‐river ecology

“…Periodic hypoxia in pools causes microbial metabolism to fluctuate between aerobic and anaerobic pathways (Chan et al, 2005). When pools dry, the POM stored in them also dries, and solutes form evaporites on sediment and POM surfaces (McLaughlin, 2008). At this stage, terrestrial microbial and metazoan communities take over as organic matter consumers, and solar radiation and desiccation enhance degradation (Boulton, 1991;Austin & Vivanco, 2006;Sangiorgio, Fonnesu & Mancinelli, 2007).…”

When the river runs dry: human and ecological values of dry riverbeds

“…Microbial mortality during sediment drying releases large amounts of nitrogen and phosphorus (Amalfitano et al 2008). Nutrients may be further stored as precipitated solutes through evaporation (McLaughlin 2008). Moreover, temporary rivers that run through forested areas receive a substantial input of leaf litter from riparian vegetation as a result of water stress during the dry phase (Figure 3f; Acuña et al 2007).…”