Estimating Benthic Light Regimes Improves Predictions of Primary Production and constrains Light-Use Efficiency in Streams and Rivers

Kirk, Lily; Hensley, Robert T.; Savoy, P.; Heffernan, James B.; Cohen, Matthew J.

doi:10.1007/s10021-020-00552-1

Cited by 25 publications

(51 citation statements)

References 76 publications

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“…[ 21 , 55 , 56 ]), potential light availability was the best predictor of GPP across sites in the summer/fall, regardless of their relation to a WWTP ( Fig 5 ). This relationship could further have been improved by accounting for variation in light attenuation with depth [ 19 ] as depths across sites can vary by a factor of two ( Table 2 ). Likely because of this strong spatial control on light availability, we observed that amplification effects were longitudinally limited, with rates returning to pre-WWTP levels after a few km ( Fig 3 ).…”

Section: Discussionmentioning

confidence: 99%

“…Multiple factors influence diel DO signals, from light to nutrient inputs, but their relative influence is poorly understood. High spatiotemporal variability in DO has been observed as a function of external drivers like light [ 19 ], frequency and timing of storms [ 20 ], and temperature [ 21 , 22 ]. In contrast, the effect of nutrient (i.e., carbon (C), nitrogen (N), and phosphorus (P)) concentrations on DO (via changes to GPP and ER) is less clear [ 21 , 23 ] and may only be evident when light and disturbance are not limiting to GPP [ 24 ].…”

Section: Introductionmentioning

confidence: 99%

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Large spatiotemporal variability in metabolic regimes for an urban stream draining four wastewater treatment plants with implications for dissolved oxygen monitoring

2021

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Urbanization and subsequent expansion of wastewater treatment plant (WWTP) capacity has the potential to alter stream metabolic regimes, but the magnitude of this change remains unknown. Indeed, our understanding of downstream WWTP effects on stream metabolism is spatially and temporally limited, and monitoring designs with upstream-downstream comparison sites are rare. Despite this, and despite observed spatiotemporal variability in stream metabolic regimes, regulators typically use snapshot monitoring to assess ecosystem function in receiving streams, potentially leading to biased conclusions about stream health. To address these important practical issues, we assessed the spatiotemporal variability in stream metabolism at nine sites upstream and downstream of four WWTPs in a suburban stream. We used one year (2017–2018) of high-frequency dissolved oxygen (DO) data to model daily gross primary productivity (GPP) and ecosystem respiration (ER). We found that GPP was 1.7–4.0 times higher and ER was 1.2–7.2 times higher downstream of the WWTPs, especially in spring when light was not limited by canopy shading. Critically, we observed that these effects were spatially limited to the kilometer or so just downstream of the plant. These effects were also temporally limited, and metabolic rates upstream of WWTPs were not different from sites downstream of the plant after leaf-out at some sites. Across sites, regardless of their relation to WWTPs, GPP was positively correlated with potential incident light suggesting that light is the dominant control on GPP in this system. Temporal windowing of DO to proposed regulatory monitoring lengths revealed that the violation frequency of water quality criteria depended on both the monitoring interval and start date. We conclude that spatiotemporal variability in metabolism and DO are crucial considerations when developing monitoring programs to assess ecosystem function, and that evidence of WWTP effects may only arise during high light conditions and at limited scales.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Large spatiotemporal variability in metabolic regimes for an urban stream draining four wastewater treatment plants with implications for dissolved oxygen monitoring

2021

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“…While nationally riparian attenuation only limited half of river length, this varied greatly across ecoregions and appears to covary with the percentage of forested reaches. Our model of light availability used turbidity as a measure of water clarity, but gradients of coloration also influence light availability and GPP (Kirk et al., 2020). We assumed that light was a first‐order control on GPP and sets the upper boundary of ecosystem productivity, but GPP is not solely determined by light.…”

Section: Discussionmentioning

confidence: 99%

Predicting Light Regime Controls on Primary Productivity Across CONUS River Networks

Savoy

Harvey

2021

Geophysical Research Letters

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Riparian zones limit light availability, and thus primary productivity, until channel width is 1.7 times the height of riparian trees • Light attenuation from water depth and clarity limit productivity for 50% of river length and 80% of river surface area • The percentage of river length and surface area limited by riparian zones and water column processes varies across ecoregions Supporting Information:

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“…Moreover, anthropogenic influences from land use (Glendell and Brazier 2014) and nutrient enrichment (Hilton et al 2006) increase particulate loads in streams and rivers. Quantification of benthic light regimes (i.e., integrating canopy and water column light attenuation) greatly improves predictions of stream primary production (Kirk et al 2020) and enables investigation of the role that changing light regimes play in modulating benthic community structure and function (Grubisic et al 2017, Bengtsson et al 2018.…”

Section: Model Limitationsmentioning

confidence: 99%

A seasonally dynamic model of light at the stream surface

et al. 2021

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Light is a primary constraint on primary production and drives many ecological processes in stream ecosystems, yet light regimes have received considerably less attention than other factors of the stream environment, such as hydrology or nutrient cycling. Light received by streams can be highly heterogeneous in both space and time resulting from changes in topography, channel characteristics, and riparian vegetation. Both the structure and phenology of riparian vegetation can be important determinants of the seasonality and magnitude of light reaching the stream surface, particularly in smaller forested streams. Despite the importance of riparian phenology on temporal patterns of stream light availability, existing models do not account for the seasonal dynamics of canopies. We developed a dynamic, biophysically based model (StreamLight) that incorporates canopy structure and phenology to predict light reaching the stream surface. We compared StreamLight to an existing model at 21 sites across the USA and found that, across sites, our biophysically based model produced light estimates that were more strongly correlated to observations and reduced the magnitude of errors in comparison to the existing model, particularly for streams that were relatively narrow compared to the height of riparian vegetation. Because smaller streams represent most global stream length, we expect that, in many smaller forested streams, the inclusion of canopy structure and phenology will enhance our ability to predict light regimes. We also used model simulations to examine the importance of controls on stream light environments and found that channel width was the strongest control on light environments. StreamLight represents an important incremental step forward in developing mechanistic models of river network productivity and in linking shifts in terrestrial vegetation structure and phenology to aquatic ecosystem productivity and thermal regimes.

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Estimating Benthic Light Regimes Improves Predictions of Primary Production and constrains Light-Use Efficiency in Streams and Rivers

Cited by 25 publications

References 76 publications

Large spatiotemporal variability in metabolic regimes for an urban stream draining four wastewater treatment plants with implications for dissolved oxygen monitoring

Large spatiotemporal variability in metabolic regimes for an urban stream draining four wastewater treatment plants with implications for dissolved oxygen monitoring

Predicting Light Regime Controls on Primary Productivity Across CONUS River Networks

A seasonally dynamic model of light at the stream surface

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