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  • 1. Berger, S. A.
    et al.
    Diehl, S.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Stibor, H.
    Trommer, G.
    Ruhenstroth, M.
    Wild, A.
    Weigert, A.
    Jager, C. G.
    Striebel, M.
    Water temperature and mixing depth affect timing and magnitude of events during spring succession of the plankton2007Inngår i: Oecologia, Vol. 150, nr 4, s. 643-654Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In many lakes, the most conspicuous seasonal events are the phytoplankton spring bloom and the subsequent clear-water phase, a period of low-phytoplankton biomass that is frequently caused by mesozooplankton (Daphnia) grazing. In Central European lakes, the timing of the clear-water phase is linked to large-scale climatic forcing, with warmer winters being followed by an earlier onset of the clear-water phase. Mild winters may favour an early build-up of Daphnia populations, both directly through increased surface temperatures and indirectly by reducing light limitation and enhancing algal production, all being a consequence of earlier thermal stratification. We conducted a field experiment to disentangle the separate impacts of stratification depth (affecting light supply) and temperature on the magnitude and timing of successional events in the plankton. We followed the dynamics of the phytoplankton spring bloom, the clear-water phase and the spring peak in Daphnia abundance in response to our experimental manipulations. Deeper mixing delayed the timing of all spring seasonal events and reduced the magnitudes of the phytoplankton bloom and the subsequent Daphnia peak. Colder temperatures retarded the timing of the clear-water phase and the subsequent Daphnia peak, whereas the timing of the phytoplankton peak was unrelated to temperature. Most effects of mixing depth (light) and temperature manipulations were independent, effects of mixing depth being more prevalent than effects of temperature. Because mixing depth governs both the light climate and the temperature regime in the mixed surface layer, we propose that climate-driven changes in the timing and depth of water column stratification may have far-reaching consequences for plankton dynamics and should receive increased attention.

  • 2. Jager, C. G.
    et al.
    Diehl, S.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Matauschek, C.
    Klausmeier, C. A.
    Stibor, H.
    Transient dynamics of pelagic producer grazer systems in a gradient of nutrients and mixing depths2008Inngår i: Ecology, Vol. 89, nr 5, s. 1272-1286Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Phytoplankton grazer dynamics are often characterized by long transients relative to the length of the growing season. Using a phytoplankton-grazer model parameterized for Daphnia pulex with either flexible or fixed algal carbon:nutrient stoichiometry, we explored how nutrient and light supply (the latter by varying depth of the mixed water column) affect the transient dynamics of the system starting from low densities. The system goes through an initial oscillation across nearly the entire light nutrient supply space. With flexible (but not with fixed) algal stoichiometry, duration of the initial algal peak, timing and duration of the subsequent grazer peak, and timing of the algal minimum are consistently accelerated by nutrient enrichment but decelerated by light enrichment (decreasing mixing depth) over the range of intermediate to shallow mixing depths. These contrasting effects of nutrient vs. light enrichment are consequences of their opposing influences on food quality (algal nutrient content): algal productivity and food quality are positively related along a nutrient gradient but inversely related along a light gradient. Light enrichment therefore slows down grazer growth relative to algal growth, decelerating oscillatory dynamics; nutrient enrichment has opposite effects. We manipulated nutrient supply and mixing depth in a field enclosure experiment. The experimental results were qualitatively much more consistent with the flexible than with the fixed stoichiometry model. Nutrient enrichment increased Daphnia peak biomass, decreased algal minimum biomass, decreased the seston C:P ratio, and accelerated transient oscillatory dynamics. Light enrichment (decreasing mixing depth) produced the opposite patterns, except that Daphnia peak biomass increased monotonously with light enrichment, too. Thus, while the model predicts the possibility of the "paradox of energy enrichment" (a decrease in grazer biomass with light enrichment) at high light and low nutrient supply, this phenomenon did not occur in our experiment.

  • 3.
    Jäger, Christoph G.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Diehl, Sebastian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Resource competition across habitat boundaries: asymmetric interactions between benthic and pelagic producers2014Inngår i: Ecological Monographs, ISSN 0012-9615, E-ISSN 1557-7015, Vol. 84, nr 2, s. 287-302Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In shallow aquatic systems, benthic and pelagic primary producers typically compete for light and nutrients along opposing vertical supply axes: pelagic algae shade the benthic habitat; conversely, benthic algae intercept the nutrient flux from the sediment to the pelagic habitat. We present a general framework for analyzing such spatially asymmetric resource competition across habitat boundaries using a mechanistic, dynamical model. We visualize the mechanisms determining the outcome of these cross-habitat interactions using zero-net-growth isoclines, resource supply points, and resource consumption vectors. In extensive invasion analyses, we characterize the abiotic and competitive persistence boundaries of pelagic and benthic primary producers, which are set by environmental factors determining nutrient and light supply and are modified by resource use by the competitor in the respective other habitat. We note several qualitative differences between cross-habitat and "classical" within-habitat resource competition. First, coexistence of cross-habitat competitors is facilitated by, but does not require niche differentiation with respect to, the utilization of resources. Because each species has a competitive edge for the resource that is supplied from "its" side of the system, a competitor that is inferior in utilizing both resources can sometimes coexist with, or even exclude, a superior competitor. Second, increasing the external supply of one resource (the nutrient) may initially favor both competitors, until a breakpoint is reached where the benthic producer goes abruptly extinct. Finally, whether a given pair of cross-habitat competitors coexist or shows alternative states may depend on the environment. Specifically, benthic and pelagic algae may coexist at low nutrient and light supply but produce alternative states at high nutrient and light supply. Alternative states are, in turn, promoted by any algal trait combination that increases the spatial asymmetry in resource consumption, i.e., leads to a higher nutrient consumption in the benthic habitat and/or a higher light consumption in the pelagic habitat. In a first empirical application, we show that predictions from our model give a good fit to published data on benthic and pelagic primary production in temperate and arctic lakes spanning a broad range of nutrient environments.

  • 4.
    Jäger, Christoph G
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Diehl, Sebastian
    Emans, Maximilian
    Physical Determinants of Phytoplankton Production, Algal Stoichiometry, and Vertical Nutrient Fluxes2010Inngår i: The American naturalist, ISSN 1537-5323, Vol. 175, s. E91-E104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Abstract: Most phytoplankters face opposing vertical gradients in light versus nutrient supplies but have limited capacities for vertical habitat choice. We therefore explored a dynamical model of negatively buoyant algae inhabiting a one-dimensional water column to ask how water column depth and turbulence constrain total (areal) phytoplankton biomass. We show that the population persistence boundaries in water column depth-turbulence space are set by sinking losses and light limitation but that nutrients are most limiting to total biomass in water columns that are neither too shallow or too weakly mixed (where sinking losses prevail) nor too deep and turbulent (where light limitation prevails). In shallow waters, the most strongly limiting process is nutrient influx to the bottom of the water column (e.g., from sediments). In deep waters, the most strongly limiting process is turbulent upward transport of nutrients to the photic zone. Consequently, the highest total biomasses are attained in turbulent waters at intermediate water column depths and in deep waters at intermediate turbulences. These patterns are insensitive to the assumption of fixed versus flexible algal carbon-to-nutrient stoichiometry, and they arise irrespective of whether the water column is a surface layer above a deep water compartment or has direct contact with sediments.

  • 5.
    Jäger, Christoph G.
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Diehl, Sebastian
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Schmidt, Gertraud M.
    Influence of water-column depth and mixing on phytoplankton biomass, community composition, and nutrients2008Inngår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, nr 6, s. 2361-2373Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We independently manipulated mixing intensity (strong artificial mixing vs. background turbulence) andwater-column depth (2 m, 4 m, 8 m, and 12 m) in order to explore their separate and combined effects in a fieldenclosure experiment. To accentuate the vertical light gradient, enclosures had black walls, resulting in a euphoticdepth of only 3.7 m. All enclosures were placed in a well-mixed water bath to equalize temperature acrosstreatments. Phytoplankton responded to an initial phosphorus pulse with a transient increase in biomass, whichwas highest in the shallowest, least light-limited water columns where dissolved mineral phosphorus subsequentlybecame strongly limiting. As a consequence, the depth-averaged mineral phosphorus concentration increased andthe seston carbon (C) : phosphorous (P) ratio decreased with increasing water-column depth. Low turbulenceenclosures became quickly dominated by motile taxa (flagellates) in the upper water column, whereas mixedenclosures became gradually dominated by pennate diatoms, which resulted in higher average sedimentation ratesin the mixed enclosures over the 35-d experimental period. Low turbulence enclosures showed pronouncedvertical structure in water columns .4 m, where diversity was higher than in mixed enclosures, suggesting verticalniche partitioning. This interpretation is supported by a primary production assay, where phytoplanktonoriginating from different water depths in low-turbulence treatments had the relatively highest primaryproductivity when incubated at their respective depths of origin.

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