Hydro-Climatological Influences on Long-Term Dissolved Organic Carbon in a Mountain Stream of the Southeastern United States

AbstractThe standard procedure for storing/preserving seawater dissolved organic carbon (DOC) samples after field collection is by freezing (–20°C) until future analysis can be made. However, shipping and receiving large numbers of these samples without thawing presents a significant logistical problem and large monetary expense. Access to freezers can also be limited in remote field locations. We therefore test an alternative method of preserving and storing samples for the measurement of DOC concentrations ([DOC]), stable carbon (δ13C), and radiocarbon (as ∆14C) isotopic values via UV photooxidation (UVox). We report a total analytical reproducibility of frozen DOC samples to be [DOC]±1.3 µM, ∆14C±9.4‰, and δ13C±0.1‰, comparable to previously reported results (Druffel et al. 2013). Open Ocean DOC frozen versus acidified duplicates were on average offset by ∆DOC±1.1 µM, ∆∆14C± –1.3‰, and ∆δ13C± –0.1‰. Coastal Ocean frozen vs. acidified sample replicates, collected as part of a long-term (380-day) storage experiment, had larger, albeit consistent offsets of ∆DOC±2.2 µM, ∆∆14C±1.5‰, and ∆δ13C± –0.2‰. A simple isotopic mass balance of changes in [DOC], ∆14C, and δ13C values reveals loss of semi-labile DOC (2.2±0.6 µM, ∆14C=–94±105‰, δ13C=–27±10‰; n=4) and semi-recalcitrant DOC (2.4±0.7 µM, ∆14C=–478±116‰, δ13C=–23.4±3.0‰; n=3) in Coastal and Open Ocean acidified samples, respectively.

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Effect of long-term phosphorus addition on the quantity and quality of dissolved organic carbon in a freshwater wetland of Northeast China

The Science of The Total Environment ◽

10.1016/j.scitotenv.2017.02.084 ◽

2017 ◽

Vol 586 ◽

pp. 1032-1037 ◽

Cited By ~ 6

Author(s):

Rong Mao ◽

Si-Yue Li ◽

Xin-Hou Zhang ◽

Xian-Wei Wang ◽

Chang-Chun Song

Keyword(s):

Organic Carbon ◽

Dissolved Organic Carbon ◽

Northeast China ◽

Freshwater Wetland ◽

Phosphorus Addition

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Long-Term Timber Contracts in the Southeastern United States: Updating the Primer Valuation Framework

Forest Science ◽

10.1093/forsci/fxaa020 ◽

2020 ◽

Vol 66 (6) ◽

pp. 653-665

Author(s):

Hector I Restrepo ◽

Bin Mei ◽

Bronson P Bullock

Keyword(s):

United States ◽

Interest Rates ◽

Southeastern United States ◽

Price Volatility ◽

Forest Products ◽

The United States ◽

Raw Material ◽

Conditional Volatility ◽

Material Supply

Abstract Timberland ownership has drastically changed in the United States since the 1980s, driven by the divestitures of vertically integrated forest products companies. Having sold their timberland, forest products companies have exposed themselves more to the risk of raw material supply. To hedge against this risk, forest products companies usually use long-term timber contracts (LTTC). The objective of this article is to update the valuation framework for LTTCs proposed by Shaffer (1984) by including alternative option price models and refining the estimates of some key economic variables. In particular, conditional volatility from the generalized autoregressive conditional heteroscedasticity model and quasi-conditional volatility from rolling estimation windows, in addition to simple standard deviation, are used for the volatility estimates in the option pricing models. Contrary to the previous result by Shaffer (1984), our analysis suggests that LTTCs that were once profitable for forest products companies in the 1980s are no longer so under current market conditions. This is primarily because both timber price volatility and the risk-free interest rates have declined significantly. Thus, to be better off, forest products companies need to either lower the administration and management costs of those LTTCs or rely more on the open market for timber procurement. Study Implications: Forest products companies have traditionally relied on long-term timber contracts (LTTC) negotiated with forest landowners to mitigate the risk of raw material supply. The value of these LTTCs highly depends on the economic context. This research provides some insights into the valuation of LTTCs in the southeastern United States. Forest products companies can use this updated framework to aid their decisionmaking in timber procurement.

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