Nutrient uptake in a simplified stream channel: Experimental manipulation of hydraulic residence time and transient storage

Abstract

Stream restoration efforts have aimed at increasing hydraulic residence time (HRT) and transient storage (TS) to enhance nutrient uptake, but there have been few controlled studies quantifying HRT and TS influences on nutrient uptake dynamics. We assessed the effects of HRT and TS on ammonium (NH4+) and phosphate (PO43−) uptake through controlled experiments in an artificial channel draining a pristine tropical stream. We experimentally dammed the channel with artificial weirs, to progressively increase HRT, and performed NH4+ and PO43− additions to estimate uptake each time a weir was added. We also ran consecutive additions of NH4+ and PO43− with no weirs, to evaluate short‐term changes in uptake metrics. Also, NH4+ was injected alone to assess potential nitrification. We observed that NH4+ and PO43− uptake rates were much greater in the very first addition, probably due to luxury uptake. The weirs increased mean HRT (from 8.5 to 12 min) and depth (from 6.5 to 8.9 cm) and decreased mean water velocity (0.40–0.28 m s−1). Surprisingly, damming decreased the relative size of transient storage zone (storage zone area/channel area, As/A from 0.72 to 0.55), indicating that greater depth increased A, but not As. Greater HRT increased uptake rates and velocities of both nutrients (p < 0.05). The NH4+ conversion to NO3− was estimated at 18% of NH4+ consumption, indicating that joint additions to measure NH4+ and NO3− uptake would not be feasible in this system. Our results suggest that increases in HRT can lead to a greater short‐term retention of nutrients, with implications for stream management and restoration initiatives.

Comparative Adsorptive Removal of Phosphate and Nitrate from Wastewater Using Biochar-MgAl LDH Nanocomposites: Coexisting Anions Effect and Mechanistic Studies

“…Nitrate and phosphate are necessary nutrients for the growth of plants, wildlife, and humans. However, elevated concentrations of nitrate and phosphate in surface and groundwater is a severe global concern leading to devastating impacts on ecosystems [1,2]. General sources of nitrate and phosphate contaminants in water bodies usually arise from the waste products of human activities such as discharges from industrialized practices, agricultural uses like inorganic fertilizers, compost, and wastewater treatment effluents [3].…”

Land Use Change Influences Ecosystem Function in Headwater Streams of the Lowland Amazon Basin

“…The higher discharge in cropland streams during the wet season could have two potentially contrasting implications for P processing. Higher discharge increases stream velocity, which could reduce residence time and negatively affect uptake rates [114,117]. Our results indicate the opposite, however, with higher U and Vf in the higher discharge cropland streams and during the rainy season.…”

“…Similar to ER, the P demand increased proportionally more in the wet season in cropland streams than in forested streams. P uptake in streams can be a mix of biotic and abiotic processes, including sediment characteristics and stream conditions that promote abiotic P sorption [110,113]; hydrologic or geomorphic features of the stream that affect residence time and reactive surface area through altering transient storage or riparian connectivity [113][114][115]; rates of stream metabolic processing [116,117]; or background P concentrations that affect uptake kinetics by biological communities [118,119]. The capacity for sediment sorption does not likely differ between land uses.…”

“…Significant effects of land use on stream nutrient uptake have been widely observed [5,120,121], but studies of nutrient uptake in the tropics remain relatively rare compared to other biomes [110][111][112]117,122,123]. Of those studies that have evaluated land use effects on nutrient uptake dynamics in the Amazon-Cerrado region, most have shown increases in both N and P uptake with changes in land use in the Amazon [97,110,124] but have found mixed results in other regions of South America [122,124].…”

Agriculture influences ammonium and soluble reactive phosphorus retention in South American headwater streams

“…Geomorphic, hydrologic, and hydraulic factors such as discharge, channel size, and transient storage are also relevant for nutrient uptake because they influence water residence time and therefore the contact time between dissolved nutrients and reactive substrates (Cunha et al, ; Ensign & Doyle, ; Gücker & Boëchat, ; Thomas, Royer, Snyder, & Davis, ; Tromboni, Dodds, Neres‐Lima, Zandonà, & Moulton, ; Valett, Morrice, Dahm, & Campana, ). Increasing hydrologic connectivity between the channel and the hyporheic zone and promoting hydrological exchange between the stream and its floodplain increase nutrient retention through biological assimilation, denitrification, and/or adsorption to clay particles.…”