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Channelizing Streams for Agricultural Drainage Impairs their Nutrient

Removal Capacity

Article  in  Journal of Environmental Quality · March 2019

DOI: 10.2134/jeq2018.07.0264

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AbstractIn 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.

Channelizing Streams for Agricultural Drainage Impairs their Nutrient Removal Capacity

Gisel C. Booman and Pedro Laterra*

Natural streams can act as filters by retaining the excess nutrients from agricultural activities and thus mitigate the impact downstream. In particular,

headwater streams play an important role in the watersheds, as they constitute up to 85% of the total length of watercourses (Horton, 1945; Naiman, 1983; Naiman et al., 2010; Weigelhofer 2017) and collect most of the water and dissolved nutrients from adjacent terrestrial ecosystems. These small streams have a high capacity for biogeochemical water quality regulation, mainly due to their large surface/volume ratio, which favors rapid uptake and transformation of nutrients (Alexander et al., 2000; Peterson et al., 2001).

Despite their importance in the provision of ecosystem ser-vices related to water quality, headwater streams within agricul-tural and urban environments are the most affected ecosystems by human disturbances such as diversions, drainage, and disposal (Meyer and Wallace, 2001), which negatively affect the stream’s capacity for nutrient uptake (Hall et al., 2013; Meals et al., 2010).

Stream channelization usually involves the straightening, deep-ening, and widening of the channels to remove water from agri-cultural fields or minimize the area occupied by natural meanders. Channelization might also involve the alteration of the riverbank structure, as well as the removal of instream and riparian vegeta-tion (Hohensinner et al., 2018). This practice is common in agri-cultural regions of the world, like US cropland areas and farmlands in Northwest Europe (Blann et al., 2009). The use of channeliza-tion for drainage is concentrated in landscapes prone to flooding. For example, 25% of the streams in Illinois (USA) have been chan-nelized (Mattingly et al. 1993), and 15 to 42% reduction in the flooded areas of Córdoba Province, Argentina, has been attributed to the impact of channelization practices (Brandolin et al., 2013). In Mar Chiquita’s basin in the Pampas Region of Argentina, at least 17% of the watercourses (315 km total length) have been channelized and rectified (Booman et al., 2012).

Since channelizing practices have a direct impact on hydrology, alterations of riparian vegetation, aquatic biota,

Abbreviations: C, channelized reaches without reeds; NC, unchannelized reaches, without reeds; NCR, unchannelized reaches, with reeds; OTIS, one-dimensional transport with inflow and storage; P-SRP, soluble reactive phosphorus.

G.C. Booman and P. Laterra, Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET, Argentina, Facultad de Ciencias Agrarias, Univ. Nacional de Mar del Plata, CC 276, 7620 Balcarce, Argentina, EEA Balcarce, National Institute of Agricultural Technology, INTA, CC 276, 7620 Balcarce, Argentina; G.C. Booman, current address, Institute of Materials Science and Technology, INTEMA, Av. Juan B. Justo 4302. B7608FDQ Mar del Plata, Buenos Aires, Argentina; P. Laterra, current address, Fundación Bariloche, Av. Bustillo 9500, 8400 San Carlos de Bariloche. Prov. Rio Negro. Argentina. Assigned to Associate Editor Jaehak Jeong.

Copyright © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. J. Environ. Qual. doi:10.2134/jeq2018.07.0264 Received 7 July 2018. Accepted 21 Dec. 2018. *Corresponding author (pedro.laterra@conicet.gov.ar).

Journal of Environmental QualityLAndscApe And WAtershed processes

technicAL reports

core ideas

• Channelizing streams significantly reduces their capacity of nutrient removal.• Assimilation velocity and areal uptake rate (U) were the main affected parameters.• Median reductions of nitrogen U due to channelization varied between 34 and 86%.• Median reductions of phosphorus U due to channelization varied between 63 and 75%.• Nutrients removal in nonchannelized streams is enhanced by reed cover.

Published online February 14, 2019

Journal of Environmental Quality

and biogeochemical processes in headwater streams are also expected. For example, there have been increases in the peak flows after storms due to channelizing and rectification (Shields and Cooper, 1994; Rheinhardt et al., 1999; Powell et al., 2007; Brooks et al., 2012), as well as increases in the water velocity and changes in biological communities, which may affect both biotic and abiotic nutrient removal (Bukaveckas, 2007; Smiley and Dibble, 2008; Rambaud et al., 2009; Lennox and Rasmussen, 2016; Käiro et al., 2017). Therefore, a possible direct conse-quence of stream channelization in a basin is the reduction or loss of the ability of nutrient uptake, and an increased transport of nutrients to sinks (lakes, ponds, marshes, and gulfs) located downstream (David et al., 2010).

Macrophyte communities, one of the most conspicuous losses from channelized streams, play a key role in the uptake, process-ing, and storage of nutrients via several mechanisms (Greenway, 2007). The stems and leaves reduce water velocity and turbu-lence, causing the filtering and settling of particles (sediment, organic compounds) and provide a substrate for the adherence of epiphytic algae and microorganisms. They also facilitate the uptake of bioavailable inorganic nutrients from the water column and sediment, both by direct uptake and through the adhered biofilm. Also, oxygen transferred from the stem to the roots is released into the rhizosphere, facilitating nitrification–denitrification processes. Emergent macrophyte species of large size such as Schoenoplectus californicus (C.A. Mey.) Palla (giant bulrush) exhibit a high water purifying capacity, by removing heavy metals (Murray-Gulde et al., 2005), organochlorine pes-ticides (Miglioranza et al., 2004), and nutrients (Busnardo et al., 1992). In the Pampas, S. californicus forms compact reed beds (Iriondo and Scotta, 1988; Parker and Marcolini, 1992) (hereaf-ter, reeds) and thus might influence the nutrient removal capac-ity of Pampean first-order streams.

Here, we hypothesize that channelization of first-order streams has a long-term negative impact on their removal capacities of nitrate, ammonia, and phosphorus. In addition, we hypothesize that the presence of S. californicus reeds in unchan-nelized streams is able to increase the nutrient removal rates during the growing season of this macrophyte. Therefore, chan-nelization has more severe effects on meandering reaches with reeds than on those without reeds. To test these hypotheses, nutrient addition experiments were performed in streams of the southern Pampas under three different conditions: (i) channel-ized reaches without reeds, (ii) unchannelized reaches without reeds, and (iii) unchannelized reaches with reeds.

Below, we offer novel insights about the impact of stream channelization and the role of S. californicus on the nutrient uptake capacity of first-order streams, which drain into the Mar Chiquita coastal lagoon. The Mar Chiquita costal lagoon is currently endangered by the transport of different agricul-tural pollutants (Marcovecchio et al., 2006). High concern exists about the ecological health of this lagoon, because it is the core of the Mar Chiquita Biosphere Reserve under the Man and the Biosphere United Nations Educational, Scientific and Cultural Organization (UNESCO) Program and is a key element supporting ecosystem services for resi-dent and tourists, like provision of species for sport fishing and bird watching, and clean water for different aquatic sports (Isacch et al., 2011).

Materials and MethodsStudy Area and General Design

The study was conducted in the basin of the Mar Chiquita coastal lagoon, within the southeast of the Buenos Aires prov-ince (Argentina), including ?1 million ha, composed by por-tions of the southern Pampa in the upper basin and the Flooding Pampa in the lower basin (León, 1991). Most of the Flooding Pampa is currently covered by native grasslands and permanently cultivated pastures on flat relief and poorly drained soils, and by a minor portion of annual crops usually associated to agricultural drainage. The southern Pampa reflects the opposite trend because its well-drained soils are desirable for agricultural production. The climate is temperate (Köppen–Geiger classification), with an average cumulative annual rainfall of ?900 mm, the mean air temperature of the warmest month is <22°C, and the region does not experience significant water deficits along the year.

Hydrology of the study basin is characterized by an extensive groundwater system, and typical Pampas plain streams, which have their recharge zone and headers in the mountain ranges of the Tandilia System and drain to the east–southeast into interior wetlands, shallow lagoons, and the Mar Chiquita coastal lagoon (37°43¢ S, 57°24¢ W) (Glok Galli et al., 2014). Stream vegeta-tion varies within both the riparian and the main channel zones. Riparian vegetation along streams consists of different combina-tions of native grasslands dominated by Paspalum quadrifarium Lam. and Bromus auleticus Trin. ex Nees, and modified grasslands invaded by exotic grass species [e.g., Schedonorus arundinaceus (Schreb.) Dumort., Cynodon dactylon (L.) Pers., Phalaris arun-dinacea L.] and an invasive tree species (Salix fragilis L.) (Giaccio et al., 2015, 2017). Wetted portions of the streams strongly differ according to the cover of S. californicus, as well as the cover of floating and submerged macrophytes [e.g., Ludwigia peploides (Kunth) P.H. Raven, Lemma spp, Potamogeton spp., Rorippa nasturtium-aquaticum (L.) Hayek, Juncus pallescens Lam.].

We selected four first-order streams with three stream reaches each (Fig. 1). Three of the streams ( Junco, Dulce, Vivoratá) were located in the Mar Chiquita watershed, and one was located in an adjacent watershed (Malacara). Each stream contained one of each of the three reach types that consisted of: (i) channelized reaches without reeds (i.e., cover of S. californicus < 5%; here-after, C); (ii) unchannelized reaches, without reeds (i.e., cover of S. californicus < 5%; hereafter, NC), and (iii) unchannelized reaches, with reeds (i.e., cover of S. californicus ³ 20%; hereafter, NCR). Since the channelized reaches that we found in our study area were almost free of reeds, we assumed that it is the natural condition of channelized streams. Therefore, a factorial experi-mental design for testing the interaction of channelization and reeds factors was not possible and lacked interest.

Channelized and unchannelized reaches were differentiated according to their shape (linear vs. meandrous) and signs of severe streambed substrate disturbance. Additionally, we checked for channelization evidence during the six previous years, using Google Earth images. Length of selected stream reaches varied between 50 and 150 m, according to the hydraulic residence time and/or the maximum length of continuous reed cover avail-able (Fig. 2). Different stream reaches can be compared when the theory of the nutrient spiraling is applied (Martí and Sabater 2009; Newcomer Johnson et al., 2016; and elsewhere).

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Fig. 1. Location of studied streams and stream reaches where addition experiments were performed. J, d, and V identify the Junco, dulce, and Vivoratá streams, respectively, within the Mar chiquita basin (dark gray area), and M identifies the Malacara stream in the south-occidental basin (light gray area). c, nc, and ncr identify the placement of channelized reaches without reeds, unchannelized reaches without reeds, and unchan-nelized reaches with reeds, respectively. * Location of the study area within Argentina, south America.

Fig. 2. Selected reaches in Junco stream. Black bars labeled as C, NC, and NCR identify the placement of channelized reaches without reeds, unchannel-ized reaches without reeds, and unchannelized reaches with reeds, respectively. The length of black bars does not exactly match the length of these particular reaches, but it reflects the general mean length of studied stream reaches. Image was taken from Google Earth.

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Modeling Solute Dynamics in Streams: The Nutrient Spiraling Theory

Nutrient uptake or removal from the water column of streams is explained by both abiotic and biotic processes, which mainly con-sist of adsorption (especially for phosphate), heterotrophic uptake, and attached algal uptake (Hauer and Lamberti, 2007). Nitrogen in water columns is not only subjected to assimilatory uptake and adsorption, but also to denitrification, and volatilization (Bernot and Dodds, 2005). As nutrients cycle from the uptake of inorganic forms to their mineralization and return to the water column, they are transported downstream, better resembling a spiraling than a circular motion. Since nutrient recycling is largely a biotic process, the shape of the spiral along a watercourse is a result of the relation-ship between the retentiveness and the assimilation of nutrients by the biota. Following the theory of the nutrient spiraling (Webster and Patten, 1979; Royer et al., 2004), the shape of nutrient spirals basically depends on (i) the spiraling length, that is, the sum of the distance of assimilation (or nutrient uptake, Sw) and the return dis-tance (or nutrient retentiveness by the consumers, Sc), and (ii), the assimilation rate per unit area or U (mg m−2 min−1) (Newbold et al., 1981; Newbold, 1992; Sabater and Martí, 2000). The assimila-tion rate is an indicator of the nutrient uptake capacity of the eco-system, which allows correcting the effect of basal nutrient loading and thus enables comparison of nutrient uptake between different streams (Fellows et al., 2006).

Nutrient Addition ExperimentsTo estimate the nutrient uptake rates in the different reaches

under study, we conducted one short-term nutrient addition experiment for each selected reach. This technique basically con-sists of an instantaneous (i.e., slug) nutrient addition of a known volume of a solution containing nutrients and hydrologic tracer, and the subsequent monitoring of the nutrient plus tracer plume at a known distance downstream from the point of addition.

Experiments were performed between December 2010 and January 2011 and completed in each stream within the same week and under similar weather conditions before initiating nutrient addition experiments in another stream. No rainfall events occurred between addition experiments within a stream. To avoid interference between different experiments within the same stream, they were performed from downstream to upstream reaches. One addition point was located at a narrow zone of each study reach, and the sampling point was located 50 to 120 m downstream of each addition point. The day before performing the experiments, velocity, volume, and dilution measurements were performed on each reach by injecting a known amount of rhodamine WT in the addition point and measuring changes in rhodamine concentration as a function of time at the end point of the reach. rhodamine WT was selected as a conserva-tive tracer (Covino et al., 2010; Hubbard et al., 2010), because of its environmental safety, proven efficacy, and widespread adop-tion in nutrient addition experiments. Additionally, we selected rhodamine WT because salt tracers were not appropriate due to the high salt content of soils and groundwater in our study sites (Lavado and Taboada, 1988).

Nutrient salts were weighed in the laboratory and mixed onsite with stream water. Before the addition started, water sam-ples were taken for estimating basal concentration of nutrients.

The solution was then poured at once at the point of addition, trying to avoid the resuspension of sediments. The time of the addition was recorded and used as the starting point for timing the sampling at the endpoint of the reach. From the moment of the addition, the rhodamine tracer was monitored at the end-point at regular time intervals every 10 to 20 s using a portable, handheld field fluorometer (Aquafluor, Turner Designs).

Collection of water for nutrient measurements began with the first record of the tracer, by sequentially filling 125-mL plas-tic bottles arranged in numerical order, while recording the time of sampling in each case during the breakthrough curve from the slug (Covino et al., 2010). Sampling ended when rhodamine values returned close to baseline, yielding between 40 and 120 samples per reach. The samples were stored on ice and returned to the laboratory.

Laboratory EstimationsBack in the laboratory and within 12 h of the addition experi-

ment, all the samples were measured for turbidity and rhodamine WT content with the fluorometer. Also, dissolved ammonium and nitrate were measured with a handheld multiparameter water quality meter (YSI Professional Plus). A 5-mL aliquot of each sample was filtered using syringes with filter holders and Whatman GF/F filters and stored in a freezer for later analysis of soluble reactive phosphorus (P-SRP) content. Then, within 30 d, the phosphorus content analysis was performed with the molyb-denum blue method (Murphy and Riley, 1962).

Calculation of ParametersNutrient Concentrations

For each reach and each analyzed nutrient, two concentration curves were obtained: (i) the curve of the conservative tracer (rho-damine WT), which allowed drawing a theoretical curve for the nutrient behavior in the watercourse in the absence of chemical and/or biological assimilation over time, and (ii) the real nutri-ent curve over time at the end point of the reach. The estimated concentrations within the theoretical curve assume the trans-port of a conservative element and therefore are only affected by advection, dispersion, and dilution processes. Conversely, real (observed) nutrient concentrations are also affected by biologi-cal and chemical uptake or assimilation processes. The difference in the area between the two nutrient concentration curves (theo-retical and real) can be integrated, and thus the chemical and/or biological uptake velocity is calculated for a stream reach.

The nutrient concentration was calculated from the con-servative tracer curve following the equation from Martí and Sabater (2009):

Net = [(Rt − Rb)/Rs]Ns + Nb [1]

where it is assumed that changes in nutrient concentration at time t corrected for basal nutrient levels (Nb) in relation to the concentration of the added solution (Ns) are equal to the changes in the concentration of the Rhodamine tracer concentration at time t (Rt − Rb ) in relation to the concentration of the added tracer solution (Rs).

It is expected that if the nutrients are retained along the reach, then the estimated theoretical concentrations will be greater than the observed (real) concentrations. The difference between the

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integrated areas of the two curves multiplied by the flow rate gives the nutrient mass retained in the reach during the experiment.

Nutrient Assimilation RatesUptake rate coefficient (Kt), uptake velocity (Vf ), and areal

uptake rate (U) were calculated for each nutrient at each experi-ment following the equations described in Martí and Sabater (2009). Some parameters were calculated with the one-dimen-sional transport with inflow and storage (OTIS) model and its modified version OTIS-P (Runkel, 1998; USGS, 2018). These models were chosen because of their suitability and widespread adoption for this kind of studies, and their better performance for modeling transport and nutrient kinetics than other approaches (O’Connor et al., 2010).

Statistical AnalysisSince the assumptions of parametric statistics were not met,

the concentrations and assimilation rates of nitrate, ammonium, and P-SRP were separately compared among treatments (C, NC, and NCR) using Friedman’s test. Our experimental design was a randomized complete block design, with reach type as the factor

of interest and streams as the block. We applied post-hoc com-parison procedures based on ranges by treatment and variance of the ranges as described in Conover (1999), using Infostat (Di Rienzo et al., 2012). A 5% significance level was used in all cases.

ResultsThe Vf and U were significantly higher in NC and/or NCR

than in C (Fig. 3–5). Median uptake rates (U) were reduced by 82% for ammonium, by 34% for nitrate, and by 63% for P-SRP in C reaches compared with NC reaches, and U was reduced by 82% for ammonium, by 86% for nitrate, and by 75% for P-SRP in C reaches compared with NCR reaches. In general, these dif-ferences were even higher in C reaches compared with NCR reaches. Therefore, median uptake was also reduced by 78% for nitrate and 33% for P-SRP in NC reaches compared with NCR reaches. Similar trends of median U values were observed for mean U values, and similar differences among treatments were observed for Vf. In contrast with the observed channelization impact on Vf and U, no differences were observed among C, NC, and NCR for Kt nor for Sw (Fig. 3c, 4c, and 5c).

Fig. 3. Variation in concentration and assimilation parameters of ammonium among channelized stream reaches without reeds (c), unchannel-ized stream reaches without reeds (nc) and unchannelized stream reaches with reeds (ncr). Kt is the nutrient uptake coefficient, Sw is the uptake length, U is the areal uptake rate, and Vf is the uptake velocity. samplings for ammonium concentration estimates were made immediately before the start of the addition experiment.

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The observed channelization impacts on the nutrient uptake cannot be explained by simple physical and chemical differences between stream channelized and unchannelized stream reaches, since nutrient loads (original concentrations), transport, storage, and physical parameters for the stream reaches studied here did not significantly differ among treatments (Table 1, Fig. 3a, 4a, and 5a). As was expected, the cover of reeds in NCR reaches pro-moted higher nitrate and P-SRP uptake rates than in C and NC stream reaches (both without reeds).

DiscussionResults of assimilation velocity and aerial uptake rate were con-

sistent with the hypothesis of negative impact of channelization of streams on their nutrient (ammonium, nitrate, and P-SRP) assimi-lation capacities in the long term. The results for nitrate were also consistent with the hypothesis that these reductions in assimila-tion capacity are higher when channelization affects stream reaches with reeds than when it affects stream reaches without reeds.

Although many studies have quantified the effects of chan-nelizing on the hydrology of watercourses (Shields and Cooper, 1994; Rheinhardt et al., 1999; Powell et al., 2007; Brooks et al.,

2012), the impact of this widespread practice on stream nutri-ent uptake has received less attention. Our results partly agree with the observed impact of stream channelization on the strong reductions in P-SRP uptake reported elsewhere (Bukaveckas, 2007; Weigelhofer, 2017), as well as with studies focused on the influence of vegetation and coarse wood debris in unchannelized streams (Ensign and Doyle, 2005), and studies on channels res-toration (Hines and Hershey, 2011). For example, the influence of channelization on phosphorus uptake in headwater streams of northeastern Austria altered Sw but did not alter U. Therefore, the observed responses of unchannelized stream reaches to chan-nelization contrast with those observed in channelized streams, where nutrients loads can be significantly reduced in the months after dredging events (Smith and Huang, 2010).

Lack of treatment differences in transport, storage, and physical parameters for the studied stream reaches (Table 1) suggest a minor relevance of mechanisms slowing water veloc-ity, whereas the high sensitivity of the nutrient uptake velocity (Vf ) and the areal uptake rate (U) suggest a major relevance of biochemical mechanisms involved in the nutrient assimilation. Nutrient uptake in low-order streams is basically explained by

Fig. 4. Variation in concentration and assimilation parameters of nitrate among channelized stream reaches without reeds (c), unchannelized stream reaches without reeds (nc), and unchannelized stream reaches with reeds (ncr). Kt is the nutrient uptake coefficient, Sw is the uptake length, U is the areal uptake rate, and Vf is the uptake velocity. samplings for nitrate concentration estimates were made immediately before the start of the addition experiment.

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microorganism and macroinvertebrate activity in benthic and hyporheic zones (Fellows et al., 2001; Sabater et al., 2002; Rode et al., 2015; Yao et al., 2017). Disentangling the relevance of dif-ferent mechanisms of compartment-specific nutrient uptake is beyond the reach of whole-ecosystem nutrient uptake studies (von Schiller et al., 2017), but our results suggest that under-standing of channelization impacts on streams nutrient uptake, as well as their restoration, deserves closer consideration in dif-ferent ecohydrological interfaces (Krause et al., 2017).

In contrast with the relatively well-known influence of macro-phytes on the nutrient dynamics of lentic water systems (Laterra et al., 2018), the role of macrophytes in riverine nutrient dynam-ics is still poorly known and offer contradictory results (Clarke, 2002; recently reviewed in García et al., 2017). For example, Moore et al. (2010) observed lower P-SRP loads in vegetated than in nonvegetated agricultural drainage ditches in the United States, whereas a minor role of macrophytes for nutrient removal has been found in Pampean streams (García et al., 2017). The

Fig. 5. Variation in concentration and assimilation parameters of soluble reactive phosphorus (p-srp) among channelized stream reaches without reeds (c), unchannelized stream reaches without reeds (nc), and unchannelized stream reaches with reeds (ncr). Kt is the nutrient uptake coef-ficient, Sw is the uptake length, U is the areal uptake rate, and Vf is the uptake velocity. samplings for p-srp concentration estimates were made immediately before the start of the addition experiment.

table 1. transport, storage, and physical parameters for the stream reaches under study.

treatment†transport and transient storage means (sd)‡ channel property means (sd)§

D A As a W H Q¶ V¶

m2 s−1 —————— m2 —————— ´ 10−4 s−1 —————— m —————— m3 s−1 m s−1

C 0.02 (0.02) 0.31 (0.26) 0.58 (0.27) 1.9 (1.9) 4.21 (1.52) 0.29 (0.34) 0.02 (0.02) 0.02 (0.01)NC 0.08 (0.08) 0.16 (0.16) 0.05 (0.06) 2.4 (2.6) 4.19 (1.66) 0.07 (0.06) 0.02 (0.03) 0.07 (0.06)NCR 0.11 (0.13) 0.26 (0.14) 0.03 (0.05) 15 (22) 5.97 (2.31) 0.06 (0.06) 0.04 (0.04) 0.08 (0.06)

† C, channelized stream reaches without reeds; NC, unchannelized stream reaches without reeds; NCR, unchannelized stream reaches with reeds.

‡ D, dispersion coefficient; A, mainstream cross-sectional area; As, storage zone cross-sectional area; a, storage zone exchange coefficient.

§ W, width of the wet streambed; H, average water depth; Q, stream discharge; V, water velocity.

¶ Discharge and water velocity values were calculated from the hydraulic parameters resulting from the addition of rhodamine WT (one-dimensional transport with inflow and storage [OTIS] simulations).

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positive effect of S. californicus cover on the uptake capacity of nitrates and phosphorus found here agrees with previous results obtained in wetland mesocosms (Busnardo et al., 1992), so this study confirms a relevant positive role of this species in the nutri-ent uptake capacity of first-order streams. Other tall emergent macrophytes, such as Phragmites australis (Cav.) Trin. ex Steud., have also shown to promote denitrification by providing better conditions for the development and activity of bacterial commu-nities, which are responsible for nitrate dissipation (Castaldelli et al., 2018).

The increment of nutrients uptake reported by restored streams may be also considered as an indirect test of channeliza-tion impacts, but caution needs to be taken with results inter-pretation, since restoration treatments involve very different techniques that do not lead to the recreation of the hydroeco-logical conditions of undisturbed streams. Variable effects over uptake capacity of phosphorus and nitrogen were found in a recent global review in response to a wide array of restoration techniques, including raising stream bottoms, lowering flood-plains, wetland reconnections, and increasing sinuosity, among others (Newcomer Johnson et al., 2016).

The uptake velocities and rates found for the various nutri-ents studied here (Fig. 1–3) were higher than those reported by other authors in headwater streams (Ensign and Doyle, 2006; Mulholland et al., 2008), probably because our study was performed during a period of high temperatures and con-sequently high biological activity. In fact, in a Pampean stream of the Rio Lujan, very high P-SRP assimilation rates were also found in spring compared with other first-order reaches in the Northern Hemisphere, although fall values were significantly lower and found within the range of such studies (Feijoó et al., 2011). Therefore, the Pampas ecoregion is characterized by naturally eutrophic water bodies (Quirós et al., 2006; Feijoó and Lombardo, 2007), which could favor the development of biota with a greater efficiency of nutrient uptake or higher metabolic levels than in waters with a reduced availability of nutrients.

It is worth noting that our results reflect the consequences of stream channelization during the growing season, so they cannot be extrapolated to all year round. Seasonal variations in water flow, nutrient loads, vegetation structure and activity, and micro-organism and macroinvertebrate activity may affect the nutrient assimilation efficiencies (Kröger et al., 2007, 2008). However, the observed effect of stream channelization on agricultural drainage is particularly relevant because of current trends in agricultural expansion over native grasslands and cultivated pastures of the Mar Chiquita basin (Lima et al., 2011; Zelaya et al., 2016). In particular, agriculture intensification and expansion over the study area during the last decades has been accompanied by the imple-mentation of practices of wetland drainage and stream channeliza-tion, affecting at least 17% of the basin (Booman et al., 2012).

ConclusionsCurrent and forthcoming agricultural intensification in agro-

exporting countries, and the subsequent increase of fertilization rates and stream channelization, call for a better understanding of their negative environmental externalities. Faced with scarcity and limited extrapolability of studies evaluating the effects of channelization practices on the capacity of both nitrogen and phosphorus uptake by first-order streams, this study provides

novel evidence for the support of the environmental manage-ment of streams in the Argentine Pampas and comparable regions of the world.

Our results indicate that stream channelization leads to long-term impairment of nutrient uptake with variable reductions levels according to nutrient forms (between 34 and 82%), which are even higher when compared with stream reaches with >25% cover of reeds (between 82 and 86%). These results were not associated with changes in transport, storage, and physical parameters in the stream reaches, suggesting that channelization effects on nutrient uptake rates are mainly due to biochemical processes, where the role of macrophytes deserves further attention.

The utility of our study to support environmental policies and management practices for mitigating the impacts of channeliza-tion on nutrient transport in agricultural headwater streams still depends on further research steps; two of them are now clearly envisaged. The next step is to validate our results by repeating similar experiments in different seasons and different discharge conditions. A more distant but no less necessary step is to model channelization effects and mitigation practices at the basin scale, including the conservation of riparian vegetation strips and of stream reaches with a high coverage of S. californicus, as well as the identification, protection, and/or restoration of key reaches and key riparian wetlands.

AcknowledgmentsThis study was supported by the Fondo para la Investigación Científica y Tecnológica (FONCYT), Agencia Nacional de Promoción Científica y Tecnológica (ANPCYT) (PICT 12-0607 and PICT 15_0672), and the Bridging Ecosystem Services and Territorial Planning (BEST-P) Inter-American Institute for Global Change Research (CRN3095), which is supported by the US National Science Foundation (Grant GEO 1128040). We thank the three anonymous reviewers for their valuable comments on a previous version of this paper. The authors would like to express particular thanks to Oscar Iribarne, Eugenia Fanjul, Mauricio Escapa, and Eugenia Orúe for their early advice and discussions on project design and implementation, to Cecilia Videla and Liliana Picone for their advice on laboratory procedures, and to Sebastián Muñoz for his invaluable help during the field work.

ReferencesAlexander, R.B., R.A. Smith, and G.E. Schwarz. 2000. Effect of stream channel

size on the delivery of nitrogen to the Gulf of Mexico. Nature 403:758–761. doi:10.1038/35001562

Bernot, M.J., and W.K. Dodds. 2005. Nitrogen retention, removal, and saturation in lotic ecosystems. Ecosystems 8:442–453. doi:10.1007/s10021-003-0143-y

Blann, K.L., J.L. Anderson, G.R. Sands, and B. Vondracek. 2009. Effects of agri-cultural drainage on aquatic ecosystems: A review. Crit. Rev. Environ. Sci. Technol. 39:909–1001. doi:10.1080/10643380801977966

Booman, G.C., M. Calandroni, P. Laterra, F. Cabria, O. Iribarne, and P. Vázquez. 2012. Areal changes of lentic water bodies within an agricultural basin of the Argentinean Pampas. Disentangling land management from climatic causes. Environ. Manage. 50:1058–1067. doi:10.1007/s00267-012-9943-1

Brandolin, P.G., M.A. Ávalos, and C. Angelo. 2013. The impact of flood con-trol on the loss of wetlands in Argentina. Aquat. Conserv. 23:291–300. doi:10.1002/aqc.2305

Brooks, K.N., P.F. Ffolliott, and J.A. Magner. 2012. Hydrology and the management of watersheds. John Wiley & Sons, Hoboken, NJ. doi:10.1002/9781118459751

Bukaveckas, P.A. 2007. Effects of channel restoration on water velocity, transient storage, and nutrient uptake in a channelized stream. Environ. Sci. Tech-nol. 41:1570–1576. doi:10.1021/es061618x

Busnardo, M.J., R.M. Gersberg, R. Langis, T.L. Sinicrope, and J.B. Zedler. 1992. Nitrogen and phosphorus removal by wetland meso-cosms subjected to different hydroperiods. Ecol. Eng. 1:287–307. doi:10.1016/0925-8574(92)90012-Q

Journal of Environmental Quality

Castaldelli, G., V. Aschonitis, F. Vincenzi, E.A. Fano, and E. Soana. 2018. The ef-fect of water velocity on nitrate removal in vegetated waterways. J. Environ. Manage. 215:230–238. doi:10.1016/j.jenvman.2018.03.071

Clarke, S.J. 2002. Vegetation growth in rivers: Influences upon sediment and nutrient dynamics. Prog. Phys. Geogr. 26:159–172. doi:10.1191/0309133302pp324ra

Covino, T.P., B.L. McGlynn, and R.A. McNamara. 2010. Tracer Additions for Spiraling Curve Characterization (TASCC): Quantifying stream nutrient uptake kinetics from ambient to saturation. Limnol. Oceanogr. Methods 8:484–498. doi:10.4319/lom.2010.8.484

Conover, W.J. 1999. Practical nonparametric statistics. John Wiley & Sons, Hoboken, NJ.

David, M.B., L.E. Drinkwater, and G.F. McIsaac. 2010. Sources of nitrate yields in the Mississippi River basin. J. Environ. Qual. 39:1657–1667. doi:10.2134/jeq2010.0115

Di Rienzo, J.A., F. Casanoves, M.G. Balzarini, L. Gonzalez, M. Tablada, and C.W. Robledo. 2012. InfoStat version 2012. InfoStat Group, Facultad Cienc. Agropecu., Univ. Nacl. Córdoba, Córdoba, Argentina. http://www.infostat.com.ar/ (accessed 17 Apr. 2012).

Ensign, S.H., and M.W. Doyle. 2005. In‐channel transient storage and associated nutrient retention: Evidence from experimental manipulations. Limnol. Oceanogr. 50:1740–1751. doi:10.4319/lo.2005.50.6.1740

Ensign, S.H., and M.W. Doyle. 2006. Nutrient spiraling in streams and river net-works. J. Geophys. Res. Biogeosci. 111(G4). doi:10.1029/2005JG000114

Feijoó, C., A. Giorgi, and N. Ferreiro. 2011. Phosphate uptake in a macro-phyte-rich Pampean stream. Limnologica 41:285–289. doi:10.1016/j.limno.2010.11.002

Feijoó, C.S., and R.J. Lombardo. 2007. Baseline water quality and macrophyte as-semblages in Pampean streams: A regional approach. Water Res. 41:1399–1410. doi:10.1016/j.watres.2006.08.026

Fellows, C.S., M.H. Valett, and C.N. Dahm. 2001. Whole-stream metabolism in two montane streams: Contribution of the hyporheic zone. Limnol. Oceanogr. 46:523–531. doi:10.4319/lo.2001.46.3.0523

Fellows, C.S., H.M. Valett, C.N. Dahm, P.J. Mulholland, and S.A. Thomas. 2006. Coupling nutrient uptake and energy flow in headwater streams. Ecosys-tems 9:788–804. doi:10.1007/s10021-006-0005-5

García, V.J., P. Gantes, L. Giménez, C. Hegoburu, N. Ferreiro, F. Sabater, and C. Feijoó. 2017. High nutrient retention in chronically nutrient-rich lowland streams. Freshw. Sci. 36:26–40. doi:10.1086/690598

Giaccio, G.C.M., P. Laterra, V.C. Aparicio, and J.L. Costa. 2015. Glyphosate re-tention in grassland riparian areas is reduced by the invasion of exotic trees. (In Spanish, with English abstract.) Phyton 85:108–116.

Giaccio, G.C.M., P. Laterra, and F. Cabria. 2017. Floristic associations and filter-ing ability of riparian vegetation strips. (In Spanish, with English abstract.) Phyton 86:4–11.

Glok Galli, M., D. Martínez, E. Kruse, S. Grondona, and M. Lima. 2014. Hy-drochemical and isotopic characterization of the hydrological budget of a MAB reserve: Mar Chiquita lagoon, province of Buenos Aires, Argentina. Environ. Earth Sci. 72:2821–2835. doi:10.1007/s12665-014-3187-8

Greenway, M. 2007. The role of macrophytes in nutrient removal using con-structed wetlands. In: S.N. Singh and R.D. Tripathi, editors, Environ-mental bioremediation technologies. Springer, New York. p. 331–351. doi:10.1007/978-3-540-34793-4_15

Hall, R.O., Jr., M.A. Baker, E.J.J. Rosi-Marshall, L.J. Tank, and D. Newbold. 2013. Solute-specific scaling of inorganic nitrogen and phosphorus uptake in streams. Biogeosciences 10:7323–7331. doi:10.5194/bg-10-7323-2013

Hauer, F.R., and G. Lamberti, editors. 2007. Methods in stream ecology. 2nd ed. Acad. Press, Amsterdam.

Hines, S.L., and A.E. Hershey. 2011. Do channel restoration structures promote ammonium uptake and improve macroinvertebrate-based water quality classification in urban streams? Inland Waters 1:133–145. doi:10.5268/IW-1.2.395

Hohensinner, S., C. Hauer, and S. Muhar. 2018. River morphology, channeliza-tion, and habitat restoration. In: S. Schmutz and J. Sendzimir, editors, Riv-erine ecosystem management. Aquatic Ecol. Ser. Vol. 8. Springer, Cham, Switzerland. p. 41–65. doi:10.1007/978-3-319-73250-3_3

Horton, R.E. 1945. Erosional development of streams and their drainage ba-sins; hydrophysical approach to quantitative morphology. Geol. Soc. Am. Bull. 56:275–370. doi:10.1130/0016-7606(1945)56[275:EDOSAT]2.0.CO;2

Hubbard, K.A., Jr., L.K. Lautz, M.J. Mitchell, B. Mayer, and E.R. Hotchkiss. 2010. Evaluating nitrate uptake in a Rocky Mountain stream using labelled 15N and ambient nitrate chemistry. Hydrol. Processes 24:3322–3336. doi:10.1002/hyp.7764

Iriondo, M.H., and E. Scotta. 1988. A comparison between the Amazon and Paraná River systems. Mitt. Bayerischen Staatssammlung Palaontol. Hist. Geol. 5:77–92.

Isacch, J.P., M. Escapa, E. Fanjul, and O. Iribarne. 2011. Valoración ecológica de bienes y servicios ecosistémicos en marismas del Atlántico Sudoccidental. In: J. Paruelo et al., editors, Valoración de servicios ecosistémicos. concep-tos, herramientas y aplicaciones para el ordenamiento territorial. Ediciones INTA, Buenos Aires, Argentina. p. 529–551. http://inta.gob.ar/docu-mentos/valoracion-de-servicios-ecosistemicos.-conceptos-herramientas-y-aplicaciones-para-el-ordenamiento-territorial/ (accessed 1 July 2018).

Käiro, K., M. Haldna, H. Timm, and T. Virro. 2017. The effect of chan-nelization on the biological quality of lowland streams using macro-invertebrates as proxies. Hydrobiologia 794:167–177. doi:10.1007/s10750-017-3091-9

Krause, S., J. Lewandowski, N.B. Grimm, D.M. Hannah, G. Pinay, K. McDonald, et al. 2017. Ecohydrological interfaces as hot spots of ecosystem processes. Water Resour. Res. 53:6359–6376. doi:10.1002/2016WR019516

Kröger, R., M.M. Holland, M.T. Moore, and C.M. Cooper. 2007. Hydrological variability and agricultural drainage ditch inorganic nitrogen reduction ca-pacity. J. Environ. Qual. 36:1646–1652. doi:10.2134/jeq2006.0506

Kröger, R., M.M. Holland, M.T. Moore, and C.M. Cooper. 2008. Agricultural drainage ditches mitigate phosphorus loads as a function of hydrological variability. J. Environ. Qual. 37:107–113. doi:10.2134/jeq2006.0505

Laterra, P., G.C. Booman, L. Picone, C. Videla, and M.E. Oúe. 2018. Indica-tors of nutrient removal efficiency for riverine wetlands in agricultural landscapes of Argentine Pampas. J. Environ. Manage. 222:148–154. doi:10.1016/j.jenvman.2018.05.070

Lavado, R.S., and M.A. Taboada. 1988. Water, salt and sodium dy-namics in a natraquoll in Argentina. Catena 15:577–594. doi:10.1016/0341-8162(88)90008-2

Lennox, P.A., III, and J.B. Rasmussen. 2016. Long-term effects of channeliza-tion on a cold-water stream community. Can. J. Fish. Aquat. Sci. 73:1530–1537. doi:10.1139/cjfas-2015-0561

León, R.J.C. 1991. Vegetation. In: R.T. Coupland, editor, Natural grasslands: Introduction and western hemisphere. Elsevier, Amsterdam. p. 380–387.

Lima, L., K. Zelaya, P. Laterra, H. Massone, and N. Maceira. 2011. A dynamic simulation model of land cover in the Dulce Creek Basin, Argentina. Pro-cedia Environ. Sci. 7:194–199. doi:10.1016/j.proenv.2011.07.034

Marcovecchio, J., H. Freije, S. De Marco, M.A. Gavio, L. Ferrer, S. Andrade, et al. 2006. Seasonality of hydrographic variables in a coastal lagoon: Mar Chiquita, Argentina. Aquat. Conserv. 16:335–347. doi:10.1002/aqc.719

Martí, E., and F. Sabater. 2009. Retención de nutrientes en ecosistemas fluviales. In: A. Elosegi and S. Sabater, editors, Conceptos y técnicas en ecología flu-vial. Fund. BBVA, Bilbao, Spain. p. 117–132.

Mattingly, R.L., E.E. Herricks, and D.M. Johnston. 1993. Channelization and levee construction in Illinois: Review and implications for management. Environ. Manage. 17:781–795. doi:10.1007/BF02393899

Meals, D.W., S.A. Dressing, and T.E. Davenport. 2010. Lag time in water quality response to best management practices: A review. J. Environ. Qual. 39:85–96. doi:10.2134/jeq2009.0108

Meyer, J.L., and J.B. Wallace. 2001. Lost linkages and lotic ecology: Rediscover-ing small streams. In: M.C. Press et al., editors, Ecology: Achievement and challenge. Blackwell, New York. p. 295–317.

Miglioranza, K.S., J.E. de Moreno, and V.J. Moreno. 2004. Organochlorine pes-ticides sequestered in the aquatic macrophyte Schoenoplectus californicus (CA Meyer) Sojak from a shallow lake in Argentina. Water Res. 38:1765–1772. doi:10.1016/j.watres.2004.01.017

Moore, M.T., R. Kröger, M.A. Locke, R.F. Cullum, R.W. Steinriede, Jr., S. Testa, III, et al. 2010. Nutrient mitigation capacity in Mississippi Delta, USA drainage ditches. Environ. Pollut. 158:175–184. doi:10.1016/j.envpol.2009.07.024

Mulholland, P.J., A.M. Helton, G.C. Poole, R.O. Hall, S.K. Hamilton, B.J. Peter-son, et al. 2008. Stream denitrification across biomes and its response to an-thropogenic nitrate loading. Nature 452:202. doi:10.1038/nature06686

Murphy, J., and J.P. Riley. 1962. A modified single solution method for the de-termination of phosphate in natural waters. Anal. Chim. Acta 27:31–36. doi:10.1016/S0003-2670(00)88444-5

Murray-Gulde, C.L., G.M. Huddleston, K.V. Garber, and J.H. Rodgers. 2005. Contributions of Schoenoplectus californicus in a constructed wetland system receiving copper contaminated wastewater. Water Air Soil Pollut. 163:355–378. doi:10.1007/s11270-005-1297-3

Naiman, R.J. 1983. A geomorphic approach for examining the role of pe-riphyton in large watersheds. In: R. Wetzel, editor, Periphyton of fresh-water ecosystems. Springer, Dordrecht, the Netherlands. p. 191–198. doi:10.1007/978-94-009-7293-3_26

Naiman, R.J., H. Decamps, and M.E. McClain, editors. 2010. Riparia: Ecology, conservation, and management of streamside communities. Acad. Press, London.

Journal of Environmental Quality

Newbold, J.D. 1992. Cycles and spirals of nutrients. In: P. Calow and G.E. Petts, editors, The rivers handbook. Vol. 1. Blackwell Science, London. p. 379–408.

Newbold, J.D., J.W. Elwood, R.V. O’Neill, and W.V. Winkle. 1981. Measur-ing nutrient spiralling in streams. Can. J. Fish. Aquat. Sci. 38:860–863. doi:10.1139/f81-114

Newcomer Johnson, T.A., S.S. Kaushal, P.M. Mayer, R.M. Smith, and G.M. Si-virichi. 2016. Nutrient retention in restored streams and rivers: A global review and synthesis. Water 8:116. doi:10.3390/w8040116

O’Connor, B.L., M. Hondzo, and J.W. Harvey. 2010. Predictive model-ing of transient storage and nutrient uptake: Implications for stream restoration. J. Hydraul. Eng. 136:1018–1032. doi:10.1061/(ASCE)HY.1943-7900.0000180

Parker, G., and S. Marcolini. 1992. Geomorfología del Delta del Paraná y su ex-tensión hacia el Río de la Plata. Rev. Asoc. Geol. Argent. 47:243–269.

Peterson, B.J., W.M. Wollheim, P.J. Mulholland, J.R. Webster, J.L. Meyer, J.L. Tank, et al. 2001. Control of nitrogen export from watersheds by headwa-ter streams. Science 292:86–90. doi:10.1126/science.1056874

Powell, G.E., A.D. Ward, D.E. Mecklenburg, and A.D. Jayakaran. 2007. Two-stage channel systems: Part 1, a practical approach for sizing agricultural ditches. J. Soil Water Conserv. 62:277–286.

Quirós, R., M.B. Boveri, C.A. Petracchi, A.M. Rennella, J.J. Rosso, A. Sosnovsky, and H.T. Von Bernard. 2006. Los efectos de la agriculturización del humedal pampeano sobre la eutrofización de sus lagunas. In: J.G. Tundisi et al., editors, Eutrofização na América do Sul: Causas, conseqüências e tecnologias de ger-enciamento e controle. Inst. Int. Ecol., Inst. Int. Ecol. Gerenciamento Amb., Acad. Bras. Ciênc., Conselho Nacl. Desenvolvimento Científico Tecnol., In-terAcademy Panel Int. Issues, InterAmerican Netw. Acad. Sci. p. 1–16.

Rambaud, M., I. Combroux, J. Haury, J. Moret, N. Machon, M. Zavodna, and S. Pavoine. 2009. Relationships between channelization structures, environ-mental characteristics, and plant communities in four French streams in the Seine–Normandy catchment. J. North Am. Benthol. Soc. 28:596–610. doi:10.1899/08-139.1

Rheinhardt, R.D., M.C. Rheinhardt, M.M. Brinson, and K.E. Faser. 1999. Appli-cation of reference data for assessing and restoring headwater ecosystems. Restor. Ecol. 7:241–251. doi:10.1046/j.1526-100X.1999.72017.x

Rode, M., M. Hartwig, D. Wagenschein, T. Kebede, and D. Borchardt. 2015. The importance of hyporheic zone processes on ecological functioning and sol-ute transport of streams and rivers. In: L. Chicharo, F. Müller, and N. Fohrer, editors, Ecosystem services and river basin ecohydrology. Springer, Dor-drecht, the Netherlands. p. 57–82. doi:10.1007/978-94-017-9846-4_4

Royer, T.V., J.L. Tank, and M.B. David. 2004. Transport and fate of nitrate in headwater agricultural streams in Illinois. J. Environ. Qual. 33:1296–1304. doi:10.2134/jeq2004.1296

Runkel, R.L. 1998. One-dimensional transport with inflow and storage (OTIS): A solute transport model for streams and rivers. Water Resour. Invest. Rep. 98-4018. USGS, Reston, VA.

Sabater, S., H. Guasch, A. Romaní, and I. Muñoz. 2002. The effect of biological factors on the efficiency of river biofilms in improving water quality. Hy-drobiologia 469:149–156. doi:10.1023/A:1015549404082

Sabater, F., and E. Martí. 2000. Towards a holistic view of nutrient dynamics in fluvial ecosystems. Verh. - Int. Ver. Theor. Angew. Limnol. 27:3111–3116. doi:10.1080/03680770.1998.11898250

Shields, F.D., Jr., and C.M. Cooper. 1994. Riparian wetlands and flood stages. In: G.V. Cotroneo and R.R. Rumer, editors, Proceedings of the 1994 Hy-draulic Engineering Conference, Buffalo, NY. Am. Soc. Civil Eng., Reston, VA. p. 351–355.

Smiley, P.C., and E.D. Dibble. 2008. Influence of spatial resolution on assessing channelization impacts on fish and macroinvertebrate communities in a warmwater stream in the southeastern United States. Environ. Monit. As-sess. 138:17–29. doi:10.1007/s10661-007-9787-y

Smith, D.R., and C. Huang. 2010. Assessing nutrient transport following dredging of agricultural drainage ditches. Trans. ASABE 53:429–436. doi:10.13031/2013.29583

USGS. 2018. USGS water resources applications software: OTIS. USGS. https://water.usgs.gov/software/OTIS/ (accessed 9 Apr. 2018).

von Schiller, D., V. Acuña, I. Aristi, M. Arroita, A. Basaguren, A. Bellin, et al. 2017. River ecosystem processes: A synthesis of approaches, criteria of use and sensitivity to environmental stressors. Sci. Total Environ. 596–597:465–480. doi:10.1016/j.scitotenv.2017.04.081

Webster, J.R., and B.C. Patten. 1979. Effects of watershed perturbation on stream potassium and calcium dynamics. Ecol. Monogr. 49:51–72. doi:10.2307/1942572

Weigelhofer, G. 2017. The potential of agricultural headwater streams to retain soluble reactive phosphorus. Hydrobiologia 793:149–160. doi:10.1007/s10750-016-2789-4

Yao, J., F. Colas, A.G. Solimini, T.J. Battin, S. Gafny, M. Morais, et al. 2017. Mac-roinvertebrate community traits and nitrate removal in stream sediments. Freshwater Biol. 62:929–944. doi:10.1111/fwb.12913

Zelaya, K., J. van Vliet, and P.H. Verburg. 2016. Characterization and analysis of farm system changes in the Mar Chiquita basin, Argentina. Appl. Geogr. 68:95–103. doi:10.1016/j.apgeog.2016.02.001

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