Dissolved organic carbon

Organic carbon, total nitrogen, and water-soluble ions in clouds from a tropical montane cloud forest in Puerto Rico

G.J. Reyes-Rodriguez, A. Gioda, O.L. Mayol-Bracero and J. Collett, Organic carbon, total nitrogen, and water-soluble ions in clouds from a tropical montane cloud forest in Puerto Rico, Atmospheric Environment 43 (2009), pp. 4171–4177. Abstract | Article | PDF (530 K) | View Record in Scopus | Cited By in Scopus (3)

samples collected in a mountaintop site in Puerto Rico. Cloudwater samples showed average concentrations of 1.09 mg L1 of total organic carbon (TOC), of 0.85 mg L1 for dissolved organic carbon (DOC) and of and 1.25 mg L1 for total nitrogen (TN). Concentrations of organic nitrogen (ON) changed with the origin of the air mass. Changes in their concentrationswere observed during periods under the influence of African dust (AD). The ON/TN ratios were 0.26 for the clean and 0.35 for the AD periods. Average concentrations of all these species were similar to those found in remote environments with no anthropogenic contribution. In the AD period, for cloud water the concentrations of TOC were 4 times higher and TN were 3 times higher than during periods of clean air masses associated with the trade winds. These results suggest that a significant fraction of TOC and TN in cloud and rainwater is associated to airborne particulate matter present in dust. Functional groups were identified using proton nuclear magnetic resonance (1H NMR) spectroscopy. This characterization led to the conclusion that water-soluble organic compounds in these samples are mainly aliphatic oxygenated compounds, with a small amount of aromatics. The ion chromatography results showed that the ionic specieswere predominantly of marine origin, for air masses with and without African dust influence, with cloud water concentrations of NO3  and NH4 þ much lower than from polluted areas in the US. An increase of such species as SO42, Cl, Mg2þ, Kþ and Ca2þ was seen when air masses originated from northwest Africa. The changes in the chemical composition and physical properties of clouds associated with these different types of aerosol particles could affect on cloud formation and processes.

biogeochemistry of dissolved organic carbon entering streams

Kaplan, L. A., and J. D. Newbold, Biogeochemistry of dissolved organic
carbon entering streams, in Aquatic Microbiology: An Ecological Approach,
edited by T. E. Ford, pp. 139 – 165, Blackwell Sci., Malden,
Mass., 1993.

Variability of DOC and nitrate responses to storms in a small Mediterranean forested catchment

Bernal, S., A. Butturini, and F. Sabater (2002), Variability of DOC and
nitrate responses to storms in a small Mediterranean forested catchment,
Hydrol. Earth Syst. Sci., 6, 1031– 1041.

Severe drought periods followed by intense rainfall often leads to major floods in Mediterranean catchments. The resulting hydrology is complex and the response of solutes in the streams is often unpredictable. This study aimed to identify the most relevant factors controlling the hydrological responses to storms of an intermittent Mediterranean stream and to link those factors with dissolved organic carbon (DOC) and nitrate during storm events. Measurements of climate, hydrology, DOC and nitrate concentrations during 26 storm events over three hydrological years were analysed. The contribution of the storm events to the total DOC and nitrate annual export was also calculated. Nitrate was mainly mobilised during high flow, while most of the DOC export occurred during baseflow. Solute concentrations peaked after drought periods and the solute export was maximal during the largest rainfalls (i.e.>100 L m-2). One single large storm contributed some 22% of the total annual export of DOC, and about 80% of that of nitrate. Discharge was a good predictor of neither DOC nor nitrate responses, so variables other than discharge were considered. Factor Analysis was used to identify the main factors controlling the biogeochemical responses. Antecedent moisture conditions and the magnitude of the storm event were the most relevant factors and accounted for 63% of the total variance. Solute responses during high flow were highly variable. However, solute concentration changes showed a significant and moderate relationship with the factors controlling the hydrological responses (i.e. Δ DOC v. the antecedent moisture conditions and Δ NO3-N v. the magnitude of the storm event).

Hydrologic flowpaths influence inorganic and organic nutrient leaching in a forest soil

Asano, Y., Compton, J. E. & Church, R. M. Hydrologic flowpaths influence
inorganic and organic nutrient leaching in a forest soil. Biogeochem. 81,
191-204 (2006).

Hydrologic pathways through soil affect element leaching by determining the relative importance of biogeochemical processes such as sorption and decomposition. We used stable hydrogen isotopes of water (dD) to examine the influence of flowpaths on soil solution chemistry in a mature spruce–hemlock forest in coastal Oregon, USA. Soil solutions (50 cm depth, n = 13) were collected monthly for 1 year and analyzed for dD, major ions and dissolved organic carbon (DOC) and nitrogen (DON). We propose that the variability of dD can be used as an index of flowpath length and contact time. Throughfall variability in dD was much greater than soil solution variability, illustrating that soil solution integrates the variation in inputs. Lysimeters with greater variation in dD presumably have a greater proportion of flow through rapid flowpaths such as macropores. The variation in soil solution dD for individual lysimeters explained up to 53% of the variation in soil solution chemistry, and suggests that flowpaths influence leaching of some constituents. Soil solutions from lysimeters with greater dD variation had higher DOC and DON (r2 = 0.51 and 0.37, respectively), perhaps because transport via macropores reduces interaction of DOM with the soil matrix. In contrast, nitrate concentrations were highest in lysimeters with a small variation in dD, where long contact time and low DOC concentrations may yield higher net nitrification. Our results demonstrate the utility of stable isotopes to link flowpaths and soil solution chemistry, and illustrate how the spatial complexity of soils can influence ecosystem- level nutrient losses.
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