Retention and release of nutrients and dissolved organic carbon in a nutrient-rich stream: A mass balance approach

Abstract

The relevance of fluvial systems to process nutrients and carbon is widely accepted, but their role as sinks and sources of nutrients and dissolved organic carbon (DOC) is still under discussion especially in non-forested and highly productive streams. In this study, we used a mass balance approach at a reach scale in a Pampean stream to elucidate the major sources of water, nutrients and DOC as well as to determine net in-stream retention efficiencies of nutrients and DOC under different hydrological conditions. We measured conductivity, conservative ions (chloride and calcium), soluble reactive phosphorus (SRP), nitrate (NO 3), nitrite (NO 2), ammonium (NH 4) and DOC at the end-point of a reach of Las Flores stream (site A), at two upstream tributaries (B1 and B2), and at each potential hydrological contributors to stream flow (groundwater, overland and subsurface flows, and rainfall). In addition, we monitored one storm event where we collected samples during the rising and the recession limb of the hydrograph. Stream flow originated from groundwater (≈ 50%), upstream tributaries (B1 and B2) at baseflow, whereas overland flow contributed >20% during high flows. During baseflow, groundwater provided NO 3 to stream water, while B2, which received a point input of a dairy industry, was the main source of SRP and NH 4. Conversely, SRP and NH 4 were provided by B1, overland flow and subsurface flow during high flows. Overland flow also contributed DOC during high flow periods. Mass balance estimates revealed that the reach acts as a source of DOC, SRP and NO 3 (21.4, 37.4 and 53.5 % mean net in-stream release, respectively) and a sink of NH 4 (-36.8 % mean net instream retention). Relevant in-stream processes may be nutrient uptake (as in the case of SRP and NH 4) and biotic production (DOC), as well as decomposition (SRP) and nitrification (NH 4) in this Pampean stream. Our results stress the relevance of nutrient and DOC generation processes within the channel in non-forested and highly productive streams.

Predicting Nutrient Incontinence in the Anthropocene at Watershed Scales

“…The characteristics of river flow can indicate fundamental hydrological properties at watershed scales (Fang and Shen, 2017;Moatar et al, 2017). Higher peak flows during storm events can indicate greater near-surface runoff, while less responsive hydrographs and higher base flows between events can indicate longer residence time and greater proportion of subsurface flow (Feijoó et al, 2018;Kirchner, 2019). In this context, we calculated several, non-redundant hydrological metrics (see Table S2) based on daily stream flow: (i) the mean, (ii) coefficient of variation, (iii) skewness, (iv) kurtosis, (v) the autoregressive lag-one correlation coefficient (AR1), (vi) the amplitude, (vii) the phase of the seasonal signal (Archfield et al, 2014), and (viii) the W2.…”

“…In this instance, the positive correlation between nutrient attenuation and the W2 index could be associated with the weathering mechanism described previously (i.e., watersheds with a larger proportion of surface flow vs. groundwater flow could have less weathered and more reactive aquifers; Kolbe et al, 2019) or it could be associated with sediment legacies in and near the river network. In this region and many others, large stocks of nutrient-laden sediments have accumulated in streams, riparian zones, and small reservoirs (Song and Burgin, 2017;Feijoó et al, 2018). These sediments can be important or even primary sources of nutrients, particularly during low flow periods (Dupas et al, 2015;Gu et al, 2018).…”

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

“…Significant reduction of nutrient retention efficiency in streams draining agricultural landscapes is expected (e.g., see Royer, David, & Gentry, 2006, Weigelhofer, Welti, & Hein, 2013. Increases in incident light due to riparian deforestation, often associated with agricultural activity, can lead to higher rates of GPP and influence in-stream nutrient uptake (Feijoó et al, 2018). The loss of riparian vegetation also alters the temperature regime, supply of terrestrial leaf litter and large wood, and bank stability (Burrell et al, 2014), with significant consequences for aquatic metabolism and processing of phosphorus and nitrogen (Bleich, Piedade, Mortati, & André, 2015;Niyogi, Koren, Arbuckle, & Townsend, 2007).…”

Density effects on solute release from streambeds

“…Most contaminants, such as metals, colloids and/or nanoparticles, enter streams due to point and non‐point sources (Butler, ; Palumbo‐Roe, Wragg, & Banks, ; Ruiping, Huijuan, Dongjin, & Min, ). There are numerous studies on the input of metal, phosphorus, organic contaminates, gases, nanoparticles and microorganisms to streams (Butler, ; Feijoó et al, ; Fuller & Harvey, ; Jin, Jiang, Tang, Li, & Barry, ; Park, Pachepsky, Hong, Shelton, & Coppock, ; Quick, ; Saup et al, ), with consideration of different environmental factors such as pH, ionic strength and particle size (Butler, , ; Cheng, Zhu, Zhong, & Wang, ). A portion of the contaminants in the stream are transported into the hyporheic zone by convection and diffusion associated with hyporheic flow (Cardenas & Wilson, , ; Elliott & Brooks, ; Packman et al, ; Packman & Jerolmack, ; Salehin, Packman, & Paradis, ; Thibodeaux & Boyle, ).…”