Channelizing Streams for Agricultural Drainage Impairs their Nutrient Removal Capacity

Abstract

In agricultural basins, fluvial ecosystems can work as filters when retaining the nutrient excess from agricultural activities, mitigating the impacts downstream. In frequently flooded areas, like the Pampas Region of Argentina, natural streams are being channelized to reduce flood frequency and intensity, thus increasing land suitability for crop production, but the impact of these interventions on nutrient removal capacity by streams is unknown. To evaluate the effects of channelizing streams on the assimilation rate of nitrate, ammonia, and phosphorus, nutrient addition experiments were performed in streams of the southern Pampas under three different conditions: (i) channelized reaches without Schoenoplectus californicus (C.A. Mey.) Palla (reeds), (ii) unchannelized reaches without reeds, and (iii) unchannelized reaches with reeds. Assimilation rates were estimated by applying the one-dimensional transport with inflow and storage (OTIS) model, which considers the solute transport with lateral flow and storage. Nitrate and ammonia uptake rates were higher in unchannelized than in channelized stream reaches, and a higher nitrate assimilation rate was found in the presence of reeds, indicating an important role of this macrophyte in the nitrate uptake. In the case of phosphorous, uptake rates were higher in unchannelized reaches with reeds than in the channelized reaches. These results suggest that channelizing first-order streams in agricultural landscapes of the Argentine Pampas may significantly reduce the ability of streams to mitigate nutrients loss to continental and marine water sinks.

Sediment phosphorus buffering in streams at baseflow: A meta‐analysis

“…Despite the potential for P sorption, fine sediments restrict advective flows through the streambed while dispersive transport through the benthic substrate is often insignificant relative to the stream's hydraulic load (Aubeneau et al., 2014; Weigelhofer et al., 2018a). Indeed, stream P uptake can increase with greater hyporheic exchange (Orr et al., 2009) and volume of transient storage (Bohrman & Strauss, 2018; Ensign & Doyle, 2006), thus leading to reduced P uptake in streams whose geomorphology is limited in these hydrological characteristics (Booman & Laterra, 2019; Weigelhofer, 2017).…”

Sensor-Equipped Unmanned Surface Vehicle for High-Resolution Mapping of Water Quality in Low- to Mid-Order Streams

“…Specific conductivity was steady along the middle part of the reach, which was highly channelized, and values then decreased along the downstream, sinuous section of the reach (Figure C,D). The spatial patterns in specific conductivity may reflect differing geomorphology if the increased sinuosity of the downstream reach resulted in slower water velocity and greater short-term storage of water and solutes relative to the channelized reach, as has been observed in other streams. − …”

Differences in Phytobenthic Diatom Community between Natural and Channelized River Sections

“…Szczepocka et al [18] claim that for diatom communities as well, such pseudo-mountain conditions favor the establishment of taxa that prefer cold water with high O2 concentrations. Another consequence of the channelization of rivers is their reduced ability to deal with pollutants in the form of degradable organic matter and inorganic nutrients [19]. Channelized rivers have lower efficiency of self-purification processes due to the lower Straightened and constricted river channels have higher flow velocities, resulting in differences in species composition and their proportions in aquatic communities compared to intact sites [16].…”