Ishi Buffam

Energy exchange and water budget partitioning in a boreal minerogenic mire

This study investigated patterns and controls of the seasonal and inter-annual variations in energy fluxes (i.e., sensible heat, H, and latent heat, lambda E) and partitioning of the water budget (i.e., precipitation, P; evapotranspiration, ET; discharge, Q; and soil water storage, Delta S) over five years (2001-2005) in a boreal oligotrophic fen in northern Sweden based on continuous eddy covariance, water table level (WTL), and weir measurements. For the growing season (May 1 to September 31), the 5 year averages (+/- standard deviation) of the midday (10:00 to 14:00 h) Bowen ratio (beta, i.e., H/lambda E) was 0.86 +/- 0.08. Seasonal and inter-annual variability of beta was mainly driven by lambda E which itself was strongly controlled by both weather (i.e., vapor pressure deficit, D, and net radiation, R-n) and physiological parameters (i.e., surface resistance). During the growing season, surface resistance largely exceeded aerodynamic resistance, which together with low mean values of the actual ET to potential ET ratio (0.55 +/- 0.05) and Priestley-Taylor alpha (0.89) suggests significant physiological constrains on ET in this well-watered fen. Among the water budget components, the inter-annual variability of ET was lower (199 to 298 mm) compared to Q (225 to 752 mm), with each accounting on average for 34 and 65% of the ecosystem water loss, respectively. The fraction of P expended into ET was negatively correlated to P and positively to R-n. Although a decrease in WTL caused a reduction of the surface conductance, the overall effect of WTL on ET was limited. Non-growing season (October 1 to April 30) fluxes of H, lambda E, and Q were significant representing on average -67%, 13%, and 61%, respectively, of their growing season sums (negative sign indicates opposite flux direction between the two seasons). Overall, our findings suggest that plant functional type composition, P and R-n dynamics (i.e., amount and timing) were the major controls on the partitioning of the mire energy and water budgets. This has important implications for the regional climate as well as for ecosystem development, nutrient, and carbon dynamics. Citation: Peichl, M., J. Sagerfors, A. Lindroth, I. Buffam, A. Grelle, L. Klemedtsson, H. Laudon, and M. B. Nilsson (2013), Energy exchange and water budget partitioning in a boreal minerogenic mire, J. Geophys. Res. Biogeosci., 118, 1-13, doi:10.1029/2012JG002073.

Seasonal TOC export from seven boreal catchments in northern Sweden

Abstract.Total organic carbon (TOC) concentrations from seven boreal catchments in northern Sweden were monitored between June 1996 and May 1998 to examine spatial and temporal variations in streamwater TOC export and its relationship with catchment characteristics. The annual average export of TOC ranged between 36 and 76 kg ha–1 yr–1 and correlated positively with the areal extent of wetlands (r2 = 0.72; p = 0.03). The daily output of TOC was 5–11 times higher during the spring than during any other season. In total, the four week long spring period contributed between 50% and 68% of the annual TOC export from the seven catchments. The relative importance of the spring snow melt period for the annual TOC export, however, correlated negatively with the percentage of wetlands (r2 = 0.83; p<0.01). We suggest that the smaller relative importance of the spring runoff period for the annual TOC export from wetland dominated catchments is a result of the hydrological flow paths associated with the snow melt period. While a large fraction of the spring runoff from forested areas reaches the stream via subsurface flow paths across riparian soils rich in TOC, the flow paths through wetland dominated systems include a much larger component of low-TOC snow melt water via surface flow over ice and frozen peat.

Importance of seasonality and small streams for the landscape regulation of dissolved organic carbon export

The regulation of the spatial and seasonal variation in terrestrial dissolved organic carbon (DOC) exports was studied in a 68 km2 boreal stream system in northern Sweden. A total of 1213 DOC sampl ...

A stormflow/baseflow comparison of dissolved organic matter concentrations and bioavailability in an Appalachian stream

Patterns of dissolved organic carbon (DOC) and nitrogen (DON) delivery were compared between times of stormflow and baseflow in Paine Run, an Appalachian stream draining a 12.4 km2 forested catchment in the Shenandoah National Park (SNP), Virginia. The potential in-stream ecological impact of altered concentrations and/or chemical composition of DOM during storms also was examined, using standardized bacterial bioassays. DOC and DON concentrations in Paine Run were consistently low during baseflow and did not show a seasonal pattern. During storms however, mean DOC and DON concentrations approximately doubled, with maximum concentrations occurring on the rising limb of storm hydrographs. The rapid response of DOM concentration to changes in flow suggests a near-stream or in-stream source of DOM during storms. Stormflow (4% of the time, 36% of the annual discharge) contributed >50% of DOC, DON and NO3− flux in Paine Run during 1997. In laboratory bacterial bioassays, growth rate constants were higher on Paine Run stormflow water than on baseflow water, but the fraction of total DOM which was bioavailable was not significantly different. The fraction of the total stream DOC pool taken up by water column bacteria was estimated to increase from 0.03 ± 0.02% h−1 during baseflow, to 0.15 ± 0.04% h−1 during storms. This uptake rate would have a minimal effect on bulk DOM concentrations in Paine Run, but storms may still have considerable impact on the bacterial stream communities by mobilizing them into the water column and by supplying a pulse of DOM.

Terrestrial inputs of organic matter to coastal ecosystems: An intercomparison of chemical characteristics and bioavailability

Dissolved and particulate organic matter (DOM and POM) collected from rivers or groundwater feeding five estuaries along the east and west coasts of the USA were characterized with a variety of biogeochemical techniques and related to bioavailability to estuarine microbes. Surface water was sampled from the Columbia, Satilla, Susquehanna and Parker Rivers and groundwater was sampled from the Childs River. Several geochemical descriptors (percent organic matter of suspended particulate matter, C/N, lignin phenol content, ratio of vanillic acid to vanillin) suggested an ordering of the systems with respect to POM lability: Satilla < Parker < Columbia < Susquehanna.DOC concentrations in these systems ranged from <100 μM for the Columbia River to >2000 μM for the Satilla River. Elemental analysis of DOM concentrates (>1000 D) was used to predict organic matter composition and to calculate degree of substrate reduction using two different modeling approaches. Models predicted aliphatic carbon ranging between 43 and 60% and aromatic carbon between 26 and 36%, with aliphatic content lowest in the Satilla and highest in the Columbia River. The degree of substrate reduction of the organic matter concentrates followed a pattern similar to that for aliphatic C, being lowest in the Satilla (3.5) and highest in the Columbia (4.0). Extracellular enzyme activity varied broadly across the systems, but again ordered sites in the same way as did aliphatic content and degree of substrate reduction. Bacterial growth rates ranged from 1.3 ug mg-1 d-1 DOC in the Satilla to 1.7 ug mg-1 d-1 DOC in the Parker River. Bioassays confirmed patterns of dissolved organic matter lability predicted by the chemical models. Between 67% to 75% of the variation in bacterial growth could be explained by differences in organic matter composition.

Landscape‐scale variability of acidity and dissolved organic carbon during spring flood in a boreal stream network

Landscape-scale variability of acidity and dissolved organic carbon during spring flood in a boreal stream network

Dissolved organic carbon characteristics in boreal streams in a forest-wetland gradient during the transition between winter and summer

The character and quantity of dissolved organic carbon (DOC) were studied in nine small boreal streams and adjacent soils during two years, with focus on the spring snowmelt period. The streams cov ...

Ecosystem Consequences of Changing Inputs of Terrestrial Dissolved Organic Matter to Lakes: Current Knowledge and Future Challenges

Lake ecosystems and the services that they provide to people are profoundly influenced by dissolved organic matter derived from terrestrial plant tissues. These terrestrial dissolved organic matter (tDOM) inputs to lakes have changed substantially in recent decades, and will likely continue to change. In this paper, we first briefly review the substantial literature describing tDOM effects on lakes and ongoing changes in tDOM inputs. We then identify and provide examples of four major challenges which limit predictions about the implications of tDOM change for lakes, as follows: First, it is currently difficult to forecast future tDOM inputs for particular lakes or lake regions. Second, tDOM influences ecosystems via complex, interacting, physical-chemical-biological effects and our holistic understanding of those effects is still rudimentary. Third, non-linearities and thresholds in relationships between tDOM inputs and ecosystem processes have not been well described. Fourth, much understanding of tDOM effects is built on comparative studies across space that may not capture likely responses through time. We conclude by identifying research approaches that may be important for overcoming those challenges in order to provide policy- and management-relevant predictions about the implications of changing tDOM inputs for lakes.

Photochemical and microbial processing of stream and soil water dissolved organic matter in a boreal forested catchment in northern Sweden

Abstract. Natural organic matter (NOM) from stream and soil water in a humic-rich headwater catchment in northern Sweden (initial total organic carbon (TOC) concentrations 10-40 mg C L–1) was rapidly degraded by light and microbial activity in an incubation experiment. Concentration losses were 33–50% after 12 days of exposure to 69 W m–2 artificial PAR and 16 W m–2 UV radiation. Natural, unshaded mid-day solar radiation in the region (68°N 18°E) during the month of june is 159 W m–2 for PAR. In contrast to microbial organic carbon removal, TOC exponentially decreased upon radiation, which suggests that TOC is more rapidly oxidized by light than by ambient microbes. Further, rapid decline in TOC concentration implies the presence of a dominant pool of photo-labile compounds (p > 95%). A measured mass balance for carbon identified 50–75% of the degraded TOC as carbon dioxide after 12 days of exposure to light. The observed conversion of organic to inorganic carbon was accompanied by increases in pH and alkalinity, suggesting that photo-degradation of NOM potentially contributes to in-stream buffering capacity. The remaining refractory TOC changed in chemical character, including an altered molecular weight distribution with decreased average weight and a change in the proportions of humics as evidenced by absorbance ratios (A254/A420). Extrapolation of the experiment to natural headwater conditions show that photo-degradation is an important in-stream process that should be considered in calculations of carbon turnover in surface waters because of its influence on both TOC amount and character.

Cold winter soils enhance dissolved organic carbon concentrations in soil and stream water

Concentrations of dissolved organic carbon ([DOC]) have increased in lakes, streams and rivers across a large part of the northern hemisphere and raised an animated scientific debate about the unde ...