The Recursion Scheme from the Cofree Recursive Comonad

AbstractWe instantiate the general comonad-based construction of recursion schemes for the initial algebra of a functor F to the cofree recursive comonad on F. Differently from the scheme based on the cofree comonad on F in a similar fashion, this scheme allows not only recursive calls on elements structurally smaller than the given argument, but also subsidiary recursions. We develop a Mendler formulation of the scheme via a generalized Yoneda lemma for initial algebras involving strong dinaturality and hint a relation to circular proofs à la Cockett, Santocanale

Land Use Affects Carbon Sources to the Pelagic Food Web in a Small Boreal Lake

<div><p>Small humic forest lakes often have high contributions of methane-derived carbon in their food webs but little is known about the temporal stability of this carbon pathway and how it responds to environmental changes on longer time scales. We reconstructed past variations in the contribution of methanogenic carbon in the pelagic food web of a small boreal lake in Finland by analyzing the stable carbon isotopic composition (δ¹³C values) of chitinous fossils of planktivorous invertebrates in sediments from the lake. The δ¹³C values of zooplankton remains show several marked shifts (approx. 10 ‰), consistent with changes in the proportional contribution of carbon from methane-oxidizing bacteria in zooplankton diets. The results indicate that the lake only recently (1950s) obtained its present state with a high contribution of methanogenic carbon to the pelagic food web. A comparison with historical and palaeobotanical evidence indicates that this most recent shift coincided with agricultural land-use changes and forestation of the lake catchment and implies that earlier shifts may also have been related to changes in forest and land use. Our study demonstrates the sensitivity of the carbon cycle in small forest lakes to external forcing and that the effects of past changes in local land use on lacustrine carbon cycling have to be taken into account when defining environmental and ecological reference conditions in boreal headwater lakes.</p></div

Invertebrate assemblages in the upper part of the Mekkojärvi sediment record.

<p>Percentage of the remains of selected invertebrate taxa relative to the total number of picked remains (size fraction > 100 μm) and number of picked remains per gram of dry sediment plotted against sediment depth are shown. The age based on ²¹⁰Pb dating is indicated on a separate scale bar. No information on sediment weight for the depths 3 to 4 cm and 29 to 30 cm is available.</p

δ¹³C values of <i>Daphnia</i> ephippia relative to the most relevant pollen indicators, charcoal, and historical events in the catchment.

<p>The main events include occupation of the Savijärvi farm in the beginning of the 19^th century, drainage and tillage of Mekkojärvi meadow in the 1910s, and abandonment of the tillage in the 1940s. The age based on ²¹⁰Pb dating on a separate scale bar and the calibrated ¹⁴C dates in the sediment depths from 7 to 9 cm are indicated. Since the age of sediments older than 1950 is poorly constrained, the historical events are drawn in the diagram at approximate locations based on modern sediment accumulation rates and the presented interpretation of sediment record.</p

Dating of the Mekkojärvi sediment record.

<p>(A) Age-depth model based on a constant rate of supply model for ²¹⁰Pb (black line, uncertainties represent one standard deviation) and ¹³⁷Cs activity for comparison (red line, not used for the age model). (B) Probability distributions of ¹⁴C dates. X-axis represents ²¹⁰Pb and calibrated ¹⁴C ages. Only the five uppermost ¹⁴C dates in agreement with ²¹⁰Pb (black line) are presented.</p

Sediment geochemical properties and δ¹³C values of invertebrate remains in the upper part of the Mekkojärvi sediment record.

<p>(A) Bulk sediment C:N ratio. (B) Bulk sediment organic carbon content. (C) δ¹³C values of bulk sediment, <i>Daphnia</i> ephippia and <i>Plumatella</i> statoblasts. (D) The difference between <i>Plumatella</i> statoblast and <i>Daphnia</i> ephippia δ¹³C values and between bulk sediment and <i>Daphnia</i> ephippia δ¹³C values. The age based on ²¹⁰Pb dating is indicated on a separate scale bar.</p

Historical map and aerial images showing the land-use changes in the catchment of Mekkojärvi.

<p>In the map from 1870, the shores of Mekkojärvi are categorized as wet meadow. The gradual afforestation in the catchment is shown in the aerial images from 1949, 1979, and 2012. Sources: The National Archives of Finland, Metsähallituksen historialliset kartat, Karta öfver Savijärvi block af Evois kronopark i Lampis socken och Tavastehus län (25S 01/07) and National Land Survey of Finland, Aerial photographs 04/2014. The map is reprinted from The National Archives of Finland under a CC BY license, with permission from The National Archives of Finland, original copyright 2014. The aerial images are reprinted from National Land Survey of Finland under a CC BY license in accordance with the National Land Survey open data license, version 1.0, 1 May 2012.</p