Young, Old, and Weathered Carbon-Part 1: Using Radiocarbon and Stable Isotopes to Identify Carbon Sources in an Alkaline, Humic Lake

Abstract

This article presents a case study of Lower Lough Erne, a humic, alkaline lake in northwest Ireland, and uses the radiocarbon method to determine the source and age of carbon to establish whether terrestrial carbon is utilized by heterotrophic organisms or buried in sediment. Stepped combustion was used to estimate the degree of the burial of terrestrial carbon in surface sediment. Δ14C, δ13C, and δ15N values were measured for phytoplankton, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and particulate organic carbon (POC). Δ14C values were used to indicate the presence of different sources of carbon, including bedrock-derived inorganic carbon, “modern,” “recent,” “subsurface,” and “subfossil” terrestrial carbon in the lake. The use of 14C in conjunction with novel methods (e.g. stepped combustion) allows the determination of the pathway of terrestrial carbon in the system, which has implications for regional and global carbon cycling.

Young, Old, and Weathered Carbon—Part 2: Using Radiocarbon and Stable Isotopes to Identify Terrestrial Carbon Support of the Food Web in an Alkaline, Humic Lake

“…Carbon dynamics in Lower Lough Erne (Figure 1) are complicated by seasonal changes in terrestrial subsidies and productivity (Keaveney et al 2015). The lake was chosen as a suitable study site to build on the substantial amount of research carried out in the lake (Maguire and Gibson 2010).…”

“…There is no indication in these studies whether this terrestrial carbon is derived from modern or detrital material. Field sampling was conducted in February, March, May, August and October of 2011 and details of methodology are described in supplemental information (also, Keaveney et al 2015). The lake did not stratify during the study.…”

Characterization ascertained from δ¹³C and Δ¹⁴C of particulate organic matter in surface water from a shallow and semi-closed Lake Kiba

“…Radiocarbon abundance increased in the natural environment after nuclear weapons testing in the 1950s and 1960s injected large quantities of 14 C into the atmosphere [1,2]. The ∆ 14 C values of organic matter in river suspended particles are -980 to +75‰, but plankton and particulate organic carbon in marine environments have enriched 14 C values of -45 to +110‰ [1][2][3].…”

“…Radiocarbon abundance increased in the natural environment after nuclear weapons testing in the 1950s and 1960s injected large quantities of 14 C into the atmosphere [1,2]. The ∆ 14 C values of organic matter in river suspended particles are -980 to +75‰, but plankton and particulate organic carbon in marine environments have enriched 14 C values of -45 to +110‰ [1][2][3]. Radiocarbon is useful as a tracer of the dynamics of organic matter in river systems and lake environments because of differences in the contribution of each source with a wide range of ∆ 14 C values [4][5][6].…”

Assimilation of ancient organic carbon by zooplankton in Tibetan Plateau lakes is depending on watershed characteristics

“…The ongoing glacier mass loss and permafrost thawing have important implications for the quantity, age, and reactivity of organic carbon (OC) in proglacial freshwater (Hood and Scott ; Caraco et al ; Mann et al ; Qu et al ). By measuring natural abundance of radiocarbon ( 14 C), highly aged ( 14 C depleted) organic material has been found in some rivers and lakes, from Arctic (Schell ; Guo et al ), tropical (Mayorga et al ) to temperate rivers and lakes (Raymond et al ; Drenzek et al ; Keaveney et al a,b ; Zigah et al ), and Tibetan alpine streams and lakes (Spencer et al ; Hu et al ). A few studies have provided compelling evidence that ancient allochthonous OC may be an important food source for microbial heterotrophs (Cherrier et al ; Singer et al ; Mann et al ; Bellamy and Bauer ), invertebrates, and higher trophic consumers such as fish and waterfowl (Schell ; Hågvar and Ohlson ; Fellman et al ) and that it may be a significant resource for food webs in rivers and estuaries (McCallister et al ; Caraco et al ).…”