Terrestrial dominance of organic matter in north temperate lakes

Abstract

[1] Aquatic ecosystems are hotspots of decomposition and sources of carbon dioxide to the atmosphere that are globally significant. Carbon exported from land (allochthonous) also supplements the carbon fixed by photosynthesis in aquatic ecosystems (autochthonous), contributing to the organic matter (OM) that supports aquatic consumers. Although the presence of terrestrial compounds in aquatic OM is well known, the contribution of terrestrial versus aquatic sources to the composition of OM has been quantified for only a handful of systems. Here we use stable isotopes of hydrogen and carbon to demonstrate that the terrestrial contribution (Φ Terr ) to particulate organic matter (POM) is as large or larger (mean = 54.6% terrestrial) than the algal contribution in 39 lakes of the northern highlands region of Wisconsin and Michigan. Further, the largest carbon pool, dissolved organic matter (DOM), is strongly dominated by allochthonous material (mean for the same set of lakes approximately 100% terrestrial). Among lakes, increases in terrestrial contribution to POM are significantly correlated with more acidic pH. Extrapolating this relationship using a survey of pH in 1692 lakes in the region reveals that, with the exception of eutrophic lakes, most of the OM in lakes is of terrestrial origin. These results are consistent with the growing evidence that lakes are significant conduits for returning degraded terrestrial carbon to the atmosphere.

Stable carbon isotope biogeochemistry of lakes along a trophic gradient

“…The oligo-mesotrophic lakes are surrounded by forest (C 3 vegetation) and δ 13 C DOC was −28.0 ± 0.5 ‰, corresponding to a C 3 vegetation signal, suggesting that the DOC pool is dominantly terrestrially derived, consistent with a combined carbon and hydrogen isotope study of Wisconsin and Michigan lakes by Wilkinson et al (2013). The other proxy for allochthonous carbon, δ 13 C det , was slightly more negative (−29.6 ± 2.1 ‰), but the two proxies for allochthonous carbon were well correlated ( Table 2).…”

“…The 1.6 ‰ lighter isotopic composition might reflect a relatively larger contribution of autochthonous detritus to the total detrital particulate organic matter pool than to the dissolved pool. Consistently with this, Wilkinson et al (2013) reported that a lower contribution of terrestrial organic matter to the particulate pool than to the dissolved organic matter pools in North American lakes.…”

“…When vegetation is dominated by C 4 plants, however, common in tropical areas and agricultural areas with maize production (δ 13 C of ∼ −14 ‰; Fry, 2006), the isotopic composition of allochthonous carbon can be significantly enriched in 13 C. In lakes with large terrestrial input, δ 13 C of DOC can be used as a proxy for δ 13 C allo , since terrestrial carbon forms the largest fraction of DOC (Kritzberg et al, 2004;Wilkinson et al, 2013).…”

Spatio-seasonal variability of chromophoric dissolved organic matter absorption and responses to photobleaching in a large shallow temperate lake

“…Much of the dissolved organic matter (DOM) found in lakes typically represents between 90 and 100 % of the total carbon pool (Wilkinson et al, 2013) and is derived from terrestrial inputs, transported through streams, rivers and wetlands. This allochthonous component of the DOM originates from soils, sediments and plants and is primarily composed of humic substances.…”

Chemodiversity of dissolved organic matter in lakes driven by climate and hydrology

“…In lakes, DOM is largely derived from terrestrial sources 3 and is central to food web dynamics [4][5][6] and global carbon cycling 7,8 . While oceans are the final receptacles of terrestrial DOM, transformations during transport through freshwater systems are important regulators of the ultimate quantity and quality of DOM delivered to marine systems [7][8][9][10] .…”