Contribution of Hydrologic Opportunity and Biogeochemical Reactivity to the Variability of Nutrient Retention in River Networks

Marcé, Rafael; Schiller, Daniel von; Aguilera, Rosana; Martı́, Eugènia; Bernal, Susana

doi:10.1002/2017gb005677

Cited by 49 publications

(34 citation statements)

References 52 publications

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“…However, the % nutrient retention is the outcome of both hydraulics as well as biogeochemical reactivity. The factors influencing biogeochemical reactivity, such as NO 3 and organic carbon supply, temperature, or hyporheic flow path do change from headwaters to large rivers [7,62] and have been found to be more important for N retention variability than previously thought [63]. Hence, the high biogeochemical reactivity of the Elbe may also explain the comparably high % retention rates found here.…”

Section: N-retention Efficiency In Large Riverssupporting

confidence: 44%

A Mass Balance of Nitrogen in a Large Lowland River (Elbe, Germany)

Ritz

Fischer

2019

Water

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Nitrogen (N) delivered by rivers causes severe eutrophication in many coastal waters, and its turnover and retention are therefore of major interest. We set up a mass balance along a 582 km river section of a large, N-rich lowland river to quantify N retention along this river segment and to identify the underlying processes. Our assessments are based on four Lagrangian sampling campaigns performed between 2011 and 2013. Water quality data served as a basis for calculations of N retention, while chlorophyll-a and zooplankton counts were used to quantify the respective primary and secondary transformations of dissolved inorganic N into biomass. The mass balance revealed an average N retention of 17 mg N m−2 h−1 for both nitrate N (NO3–N) and total N (TN). Stoichiometric estimates of the assimilative N uptake revealed that, although NO3–N retention was associated with high phytoplankton assimilation, only a maximum of 53% of NO3–N retention could be attributed to net algal assimilation. The high TN retention rates in turn were most probably caused by a combination of seston deposition and denitrification. The studied river segment acts as a TN sink by retaining almost 30% of the TN inputs, which shows that large rivers can contribute considerably to N retention during downstream transport.

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Section: N-retention Efficiency In Large Riverssupporting

confidence: 44%

A Mass Balance of Nitrogen in a Large Lowland River (Elbe, Germany)

Ritz

Fischer

2019

Water

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“…Other potentially important factors include variation of river network structure, flow regimes, the effect of disturbance, loading distributions (in space and time), seasonality of process rates, internal aquatic sources, role of water column processes, and their interactions. All these factors can differ among watersheds and among biomes (Mineau et al 2015;Ruegg et al 2016;Helton et al 2017;Marcé et al 2018;Park et al 2018;Gardner and Doyle 2018).…”

Section: Implications Of the Rnsmentioning

confidence: 99%

River network saturation concept: factors influencing the balance of biogeochemical supply and demand of river networks

et al. 2018

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River networks modify material transfer from land to ocean. Understanding the factors regulating this function for different gaseous, dissolved, and particulate constituents is critical to quantify the local and global effects of climate and land use change. We propose the River Network Saturation (RNS) concept as a generalization of how river network regulation of material fluxes declines with increasing flows due to imbalances between supply and demand at network scales. River networks have a tendency to become saturated (supply) demand) under higher flow conditions because supplies increase faster than sink processes. However, the flow thresholds under which saturation occurs depends on a variety of factors, including the inherent process rate for a given constituent and the abundance of lentic waters such as lakes, ponds, reservoirs, and fluvial wetlands within the river network. As supply increases, saturation at network scales is initially limited by previously unmet demand in downstream aquatic ecosystems. The RNS concept describes a general tendency of river network function that can be

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“…Previous work examining the watershed patch size at which variance collapse occurs found smaller extent patches (3–61 km 2 ) for labile constituents and larger extent patches (113–216 km 2 ) for conservative constituents (Abbott et al, 2018; Shogren et al, 2019), which correspond with second‐ to third‐order watersheds in the Kuskokwim (47–208 km 2 ). For labile nutrients like PO 4 3− and NO 3 − , this pattern of variance collapse is likely due to some combination of higher cumulative uptake with distance downstream and shorter residence times in larger channels (Ensign & Doyle, 2006; Marcé et al, 2018; Mulholland et al, 2009), in addition to the expected spatial averaging that occurs as small tributaries combine into larger streams. Variance collapse in [DOC] has been attributed to net gains of allochthonous instream organic matter inputs along the network (Shogren et al, 2019).…”

Section: Discussionmentioning

confidence: 99%

Headwater Catchments Govern Biogeochemistry in America's Largest Free‐Flowing River Network

et al. 2020

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Riverine chemistry reflects both watershed conditions and instream processing, both of which vary across river networks, yet little is known about the scales at which watershed attributes regulate biogeochemical constituents. We used spatial stream network (SSN) models to quantify both watershed and instream effects on streamwater constituents in the Kuskokwim River (western Alaska), the largest free-flowing river in the United States. We assessed chemical constituents spanning from labile nutrients (nitrate [NO 3 − ] and orthophosphate [PO 4 3− ]) to biologically and chemically conservative tracers (calcium [Ca 2+ ], strontium [Sr 2+ ], and Sr isotopes [ 87 Sr/ 86 Sr]). We also examined the behavior of dissolved organic carbon (DOC) relative to these constituents to understand whether bulk DOC behaved conservatively in a large boreal river network, where future changes in DOC and nutrient loading are expected under a shifting climate. We derived watershed spatial covariates comprising land cover, geology, and geomorphic characteristics at 14 different spatial extents based on stream order and relative to position in the river network to understand the effect of distant and proximal watershed attributes on streamwater constituents. For all constituents but 87 Sr/ 86 Sr, watershed attributes in low-order headwater catchments yielded the best predictive ability for streamwater constituent concentrations across the entire network. Spatial patterning for conservative tracers and bulk DOC showed strong spatial autocorrelation, whereas PO 4 3− and NO 3 − exhibited spatial patchiness indicative of instream processing. Our work shows that headwater streams are disproportionately important contributors to network-wide biogeochemical constituents supporting aquatic food webs and that conservation and management of aquatic systems should include these small and often remote watershed areas. Plain Language Summary Streamwater chemistry is influenced by watershed attributes like geology, gradient, and land cover and biochemical changes occurring within the stream channel, but how the relative importance of these factors changes as water moves through a river network is not known. We used a statistical model that accounts for water flows and the spatial layout of the river to study how stream chemistry is influenced by both watershed attributes and instream conditions at local to watershed-wide scales. We studied the Kuskokwim River in Alaska, America's largest free-flowing river, and found that conditions in small, headwater streams play a disproportionately important role in shaping streamwater chemistry throughout the river network. We also found that chemicals that are rapidly used by algae and microbes are spatially more variable in the river network when compared to passively transported chemicals that have lower biological demand. This work is important because streamwater chemical patterns can influence how different organisms are distributed in rivers, and certain watershed attributes will influence how changing clima...

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Contribution of Hydrologic Opportunity and Biogeochemical Reactivity to the Variability of Nutrient Retention in River Networks

Cited by 49 publications

References 52 publications

A Mass Balance of Nitrogen in a Large Lowland River (Elbe, Germany)

A Mass Balance of Nitrogen in a Large Lowland River (Elbe, Germany)

River network saturation concept: factors influencing the balance of biogeochemical supply and demand of river networks

Headwater Catchments Govern Biogeochemistry in America's Largest Free‐Flowing River Network

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