Long‐term studies and reproducibility: Lessons from whole‐lake experiments

Pace, Michael L.; Carpenter, Stephen R.; Wilkinson, Grace M.

doi:10.1002/lno.11012

Cited by 14 publications

(12 citation statements)

References 74 publications

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“…Water color and P load together had an inverse statistical interaction with epilimnetic chlorophyll. This interaction is consistent with observations that the magnitude of chlorophyll response to P load was lower in years when g440 was relatively high (Pace et al In press).…”

Section: Discussionsupporting

confidence: 92%

Synthesis of a 33‐yr series of whole‐lake experiments: Effects of nutrients, grazers, and precipitation‐driven water color on chlorophyll

Carpenter

Pace

2018

Limnol Oceanogr Letters

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We conducted a 33‐yr series of whole‐lake experiments to measure ecosystem responses to food web structure and nutrient load, compare aquatic and terrestrial carbon flows to consumers, and evaluate indicators of ecosystem resilience. These manipulations showed that chlorophyll responded to nutrient loading and to grazing controlled by a trophic cascade. In this article, we synthesized experimental results using a new analysis of heretofore unrecognized variation in water color, measured as light absorbance at 440 nm. Long‐term data revealed fluctuations in precipitation that drive water color variation. We compared effects of nutrient loading, zooplankton biomass, zooplankton body size, and water color on chlorophyll. Water color was an important factor in the chlorophyll response. This driver of the chlorophyll response to manipulation was not resolved until decades of data were available. A long‐term context enriched insights from ecosystem experiments and exemplified the complementarity of experimental and long‐term approaches in limnology.

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Section: Discussionsupporting

confidence: 92%

Synthesis of a 33‐yr series of whole‐lake experiments: Effects of nutrients, grazers, and precipitation‐driven water color on chlorophyll

Carpenter

Pace

2018

Limnol Oceanogr Letters

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“…DOC and a440 were elevated in the lakes in 2013 and 2014 and more similar to data from previous years in 2015 (Pace et al 2019). FDOM was also elevated in the first 2 yr (i.e., 2013, 2014) relative to 2015.…”

Section: Discussionsupporting

confidence: 86%

Phytoplankton biomass, dissolved organic matter, and temperature drive respiration in whole lake nutrient additions

Pace

Buelo

Carpenter

2021

Limnology & Oceanography

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Lake respiration is supported by a mixture of autochthonous and allochthonous resources, but the relative significance and interaction of these sources are uncertain across gradients of primary production and organic matter inputs. We manipulated autochthonous resources by adding inorganic nitrogen and phosphorus to two lakes during three summers and monitored a third reference lake. Allochthonous resources were measured as fluorescent dissolved organic matter (FDOM). In the reference and two experimental lakes, daily estimates of respiration were made from continuously deployed oxygen sensors. Daily mean values of temperature and FDOM were determined from high‐frequency measurements along with daily measures of chlorophyll a, an index of phytoplankton biomass. We analyzed time series of respiration and tested models that used combinations of the independent variables chlorophyll, FDOM, and temperature. The best models included all three of the independent variables. Respiration increased twofold over the temperature range of 14.5–28.6°C. Respiration increased in association with phytoplankton blooms caused by the nutrient additions, but did not track blooms closely, because of large day‐to‐day variability. Respiration varied positively with FDOM that was primarily allochthonous and differed among lakes and years. We did not detect an interaction between chlorophyll and FDOM despite the large number of observations and range of chlorophyll and FDOM. Hydrologic, climatic, and land use changes are altering temperature and inputs of nutrients and organic matter to lakes. Our results indicate that these changes may lead to linear responses in ecosystem processes like respiration for the wide range of inputs represented in this study.

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“…We added 0.02 mL of dye per L of high-DOC water, increasing the chromophoricity of the high-DOC water by a factor of 2.5 relative to the low (ambient) chromophoricity treatment. We manipulated stoichiometry by adding to the tanks that supplied the high P:C stoichiometry treatments sufficient H 3 PO 4 and NH 4 NO 3 to double the P concentration of the high DOC water relative to the low (ambient) P:C stoichiometry treatment while maintaining a N:P ratio (~25:1 molar) high enough to prevent a switch from P to N as the primary limiting nutrient (Carpenter et al 2001;Pace et al 2019) (Fig. S2).…”

Section: Experimental Designmentioning

confidence: 99%

Shifting limitation of primary production: experimental support for a new model in lake ecosystems

2020

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The limits on primary production vary in complex ways across space and time. Strong tests of clear conceptual models have been instrumental in understanding these patterns in both terrestrial and aquatic ecosystems. Here we present the first experimental test of a new model describing how shifts from nutrient to light limitation control primary productivity in lake ecosystems as hydrological inputs of nutrients and organic matter vary. We found support for two key predictions of the model: that gross primary production (GPP) follows a hump‐shaped relationship with increasing dissolved organic carbon (DOC) concentrations; and that the maximum GPP, and the critical DOC concentration at which the hump occurs, are determined by the stoichiometry and chromophoricity of the hydrological inputs. Our results advance fundamental understanding of the limits on aquatic primary production, and have important applications given ongoing anthropogenic alterations of the nutrient and organic matter inputs to surface waters.

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Long‐term studies and reproducibility: Lessons from whole‐lake experiments

Cited by 14 publications

References 74 publications

Synthesis of a 33‐yr series of whole‐lake experiments: Effects of nutrients, grazers, and precipitation‐driven water color on chlorophyll

Synthesis of a 33‐yr series of whole‐lake experiments: Effects of nutrients, grazers, and precipitation‐driven water color on chlorophyll

Phytoplankton biomass, dissolved organic matter, and temperature drive respiration in whole lake nutrient additions

Shifting limitation of primary production: experimental support for a new model in lake ecosystems

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