Landscape spatial configuration influences phosphorus but not nitrate concentrations in agricultural headwater catchments

Dupas, Rémi; Casquin, Antoine; Durand, Patrick; Viaud, Valérie

doi:10.1002/hyp.14816

Cited by 8 publications

(7 citation statements)

References 76 publications

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“…In addition, our RF models were constrained to explanatory variables currently available for the NTN stations, which satisfactorily captured the regional patterns of TP with no more than six features. However, the performance may further improve with additional features, which include but are not limited to management practices [20,51], legacy P [43,44], landscape configuration [52,53], and reservoir retention [54][55][56]. Lastly, we note that the river-segment predictions from the RF models should be interpreted with caution if any prediction does not have a high likelihood or if any river segment has a watersheds area that is beyond the range of the NTN watersheds.…”

Section: Discussionmentioning

confidence: 98%

Effects of point and nonpoint source controls on total phosphorus load trends across the Chesapeake Bay watershed, USA

Zhang,

Bostic,

Sabo

2023

Environ. Res. Lett.

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Reduction of total phosphorus (TP) loads has long been a management focus of Chesapeake Bay restoration, but riverine monitoring stations have shown mixed temporal trends. To better understand the regional patterns and drivers of TP trends across the Bay watershed, we compiled and analyzed TP load data from 90 Non-Tidal Network stations using clustering and random forest (RF) approaches. These stations were categorized into two distinct clusters of short-term (2013-2020) TP load trends, i.e., monotonic increase (n = 35) and monotonic decline (n = 55). RF models were developed to identify likely regional drivers of TP trend clusters. Reductions in point sources and agricultural nonpoint sources (i.e., fertilizer) both contributed to water-quality improvement in our period of analysis, thereby demonstrating the effectiveness of nutrient management and the importance of continuing such efforts. In addition, declining TP trends have a larger chance to occur in carbonate areas but a smaller chance in Coastal Plain areas, with the latter likely reflecting the effect of legacy P. To provide spatially explicit information, TP trend clusters were predicted for the entire watershed at the scale of river segments, which are more directly relevant to watershed planning. Among the 975 river segments, 544 (56%) and 431 (44%) were classified as “monotonic increase” and “monotonic decrease”, respectively. Furthermore, these predicted TP trend clusters were paired with our previously published total nitrogen (TN) trend clusters, showing that TP and TN both declined in 185 segments (19%) and neither declined in 337 segments (35%). Broadly speaking, large-scale nutrient reduction efforts are underway in many regions to curb eutrophication. Water-quality responses and drivers may differ among systems, but our work provides important new evidence on the effectiveness of management efforts toward controlling point and nonpoint sources.

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Section: Discussionmentioning

confidence: 98%

Effects of point and nonpoint source controls on total phosphorus load trends across the Chesapeake Bay watershed, USA

Zhang,

Bostic,

Sabo

2023

Environ. Res. Lett.

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“…Thus, agricultural headwaters and their catchments are ecosystem control points of stream networks, contributing significant loads of nutrients, suspended sediments, and other pollutants (e.g., pesticides, pharmaceuticals, microplastics) derived from agricultural activities . Despite common water quality pressures and similar land use trajectories within temperate areas, agricultural headwaters vary significantly in terms of water quality reflecting large spatial and temporal heterogeneity in the land-water interactions and land management. , This high hydrochemical variability is expressed for example in diverse concentration-discharge relationships observed for nutrients, carbon, and sediments in agricultural headwaters, varying from chemodynamic to chemostatic in contrast to high order streams with predominantly chemostatic slopes. , This variability results from variation in the way agricultural catchments are managed and how they modulate and transport solutes and sediments. The common driver is the long-term accumulation of legacy nutrients, in agricultural soils, saturated and unsaturated zones, and within bed sediments of headwater streams, but agricultural catchments and streams (riparian and hyporheic zones) can have varying pollution buffering capacity .…”

Section: Agricultural Headwaters Control Water Qualitymentioning

confidence: 99%

“… 26 Despite common water quality pressures and similar land use trajectories within temperate areas, 10 agricultural headwaters vary significantly in terms of water quality reflecting large spatial and temporal heterogeneity in the land-water interactions and land management. 12 , 14 This high hydrochemical variability is expressed for example in diverse concentration-discharge relationships observed for nutrients, carbon, and sediments in agricultural headwaters, varying from chemodynamic to chemostatic in contrast to high order streams with predominantly chemostatic slopes. 15 , 16 This variability results from variation in the way agricultural catchments are managed and how they modulate and transport solutes and sediments.…”

Section: Agricultural Headwaters Control Water Qualitymentioning

confidence: 99%

“…For example, aquatic ecology focuses on more pristine and larger water bodies, largely ignoring the ecological value and services that can be provided by agricultural headwaters . Likewise, hydrology and hydrochemistry often focus on large-scale land-water interactions, not capturing the heterogeneity of agricultural headwaters and their catchments . Overall, the lack of scientific focus together with monitoring gaps limit our understanding of underlying drivers of the large variability in hydrological and biogeochemical functions observed in agricultural headwaters (Figure ), and this hinders identification of the best strategies to remediate and restore the function of agricultural headwaters.…”

Section: Introductionmentioning

confidence: 99%

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Recognizing Agricultural Headwaters as Critical Ecosystems

Bieroza,

Hallberg,

Livsey

et al. 2024

Environ. Sci. Technol.

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Agricultural headwaters are positioned at the interface between terrestrial and aquatic ecosystems and, therefore, at the margins of scientific disciplines. They are deemed devoid of biodiversity and too polluted by ecologists, overlooked by hydrologists, and are perceived as a nuisance by landowners and water authorities. While agricultural streams are widespread and represent a major habitat in terms of stream length, they remain understudied and thereby undervalued. Agricultural headwater streams are significantly modified and polluted but at the same time are the critical linkages among land, air, and water ecosystems. They exhibit the largest variation in streamflow, water quality, and greenhouse gas emission with cascading effects on the entire stream networks, yet they are underrepresented in monitoring, remediation, and restoration. Therefore, we call for more intense efforts to characterize and understand the inherent variability and sensitivity of these ecosystems to global change drivers through scientific and regulatory monitoring and to improve their ecosystem conditions and functions through purposeful and evidence-based remediation.

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“…A number of recent papers have examined potential legacy P dynamics in streams and rivers; these studies have typically been deployed at the reach scale (i.e., stream reaches of a few hundred meters or less), or for individual small to medium-sized watersheds (e.g., Bieroza and Heathwaite, 2015;Casquin et al, 2020;Kreling et al, 2023;Siebers et al, 2023;Vissers et al, 2023;Dupas et al, 2023;Rode et al, 2023). These in-depth studies are important and highly 90 useful, as the microscale dynamics governing P mobility in river channels can be complex.…”

Section: Introductionmentioning

confidence: 99%

Phosphorus transport in a hotter and drier climate: in-channel release of legacy phosphorus during summer low flow conditions

Dolph,

Finlay,

Dalzell

et al. 2024

Preprint

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Abstract. The release of bioavailable phosphorus (P) during hot, dry summer periods when conditions are optimal for algal growth in lakes and rivers drives increased eutrophication risk. In addition to external P inputs, water quality is impacted by “legacy P”, i.e., the historical accumulation of P in soils and sediments due to past inputs. River networks represent a potential sink and/or source of legacy P, with many dynamic in-channel processes potentially governing the storage and mobilization of P over time. The objective of this study was to evaluate the potential contribution of in-channel release of legacy P to bioavailable P transport in streams during summer low flow conditions across a land use gradient in Minnesota, USA. We hypothesized that in-stream release of legacy P contributes to elevated concentrations of bioavailable P (i.e., soluble reactive P, SRP) during summer in streams with strong agricultural and/or urban influence, in addition to concurrent contributions from tile drainage systems and point source discharges. We addressed this hypothesis through synthesis of three water quality datasets: 1) water quality and stream flow (Q) data collected for 143 gaged watersheds across the state of Minnesota between 2007–2021 (22,750 total samples); 2) water quality data from 33 additional ditch, stream and river sites in Minnesota sampled under low flow conditions in summer of 2014; and 3) water quality data collected from tile drainage outlets for 10 monitored farm fields between 2011–2021. We used geospatial data and a machine learning (random forest) approach to identify possible drivers of bioavailable P concentrations during summer low flows for gaged watersheds. Our analysis indicates that between one third to one half of the gaged watersheds we studied exhibited SRP concentrations during low flows in late summer above previously identified thresholds for eutrophication of 0.02–0.04 mg/L. For many of these watersheds, stream SRP concentrations in late summer were above those observed in tile drainage outlets. Elevated SRP concentrations during late summer low flows weakened concentration-discharge relationships that would otherwise appear to indicate more strongly mobilizing SRP-Q responses across other seasons and flow conditions. We found that while wastewater discharge contributed to elevated P concentrations for watersheds with high densities of treatment plants, many did not have substantial wastewater impacts. The most important variables for predicting bioavailable P concentrations during late summer low flow conditions in a random forest model were land use in riparian areas (particularly crop cover), soil characteristics including soil erodibility, soil permeability, and soil clay content, agricultural intensity (reflected via higher pesticide use, higher phosphorus uptake by crops, and higher fertilizer application rates), as well as watershed precipitation and stream temperature. These findings suggest that, for stream and river sites heavily impacted by past and current P inputs associated with agriculture and urbanization, biogeochemical processes mediated by climate and geology result in the release of legacy P from in-channel stores during late summer low flow conditions. As summers become hotter and, at times, drier – predicted changes in this region – conditions for the release of legacy P stored in stream and river channels will likely become more prolonged and/or more acute, increasing eutrophication risk.

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Landscape spatial configuration influences phosphorus but not nitrate concentrations in agricultural headwater catchments

Cited by 8 publications

References 76 publications

Effects of point and nonpoint source controls on total phosphorus load trends across the Chesapeake Bay watershed, USA

Effects of point and nonpoint source controls on total phosphorus load trends across the Chesapeake Bay watershed, USA

Recognizing Agricultural Headwaters as Critical Ecosystems

Phosphorus transport in a hotter and drier climate: in-channel release of legacy phosphorus during summer low flow conditions

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