Paul D. Brooks

Inorganic nitrogen and microbial biomass dynamics before and during spring snowmelt

AbstractRecent work in seasonally snow covered ecosystems has identifiedthawed soil and high levels of heterotrophic activity throughout the winterunder consistent snow cover. We performed measurements during the winter of1994 to determine how the depth and timing of seasonal snow cover affectsoil microbial populations, surface water NO

Snowpack controls on nitrogen cycling and export in seasonally snow-covered catchments

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Winter and early spring CO2 efflux from tundra communities of northern Alaska

loss during snowmelt, and plant Navailability early in the growing season. Soil under early accumulating,consistent snow cover remained thawed during most of the winter and bothmicrobial biomass and soil inorganic N pools gradually increased under thesnowpack. At the initiation of snowmelt, microbial biomass N pools increasedfrom 3.0 to 5.9 g n m-2,concurrent with a decrease in soil inorganic N pools. During the latterstages of snowmelt, microbial biomass N pools decreased sharply without aconcurrent increase in inorganic N pools or significant leaching losses. Incontrast, soil under inconsistent snow cover remained frozen during most ofthe winter. During snowmelt, microbial biomass initially increased from 1.7to 3.1 g N m-2 and thendecreased as sites became snow-free. In contrast to smaller pool sizes,NO

Cascading impacts of bark beetle‐caused tree mortality on coupled biogeophysical and biogeochemical processes

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Hydrological Partitioning in the Critical Zone: Recent Advances and Opportunities for Developing Transferable Understanding of Water Cycle Dynamics

export during snowmeltfrom the inconsistent snow cover sites of 1.14 (±0.511) g N m-2 was significantly greater (p< 0.001) than the 0.27 (±0.16) g N m-2 exported from sites with consistent snowcover. These data suggest that microbial biomass in consistentlysnow-covered soil provides a significant buffer limiting the export ofinorganic N to surface water during snowmelt. However, this buffer is verysensitive to changes in snowpack regime. Therefore, interannual variabilityin the timing and depth of snowpack accumulation may explain the year toyear variability in inorganic N concentrations in surface water theseecosystems.

Quantifying the role of climate and landscape characteristics on hydrologic partitioning and vegetation response

Experiments were conducted during 1993 at Niwot Ridge in the Colorado Front Range to determine if the insulating effect of winter snow cover allows soil microbial activity to significantly affect nitrogen inputs and outputs in alpine systems. Soil surface temperatures under seasonal snowpacks warmed from −14 °C in January to 0 °C by May 4th. Snowmelt began in mid-May and the sites were snow free by mid June. Heterotrophic microbial activity in snow-covered soils, measured as C02 production, was first identified on March 4, 1993. Net C02 flux increased from 55 mg CO2-C m−2 day−1 in early March to greater than 824 mg CO2-C m-2 day−1 by the middle of May. Carbon dioxide production decreased in late May as soils became saturated during snowmelt. Soil inorganic N concentrations increased before snowmelt, peaking between 101 and 276 mg kg−1 soil in May, and then decreasing as soils became saturated with melt water. Net N mineralization for the period of March 3 to May 4 ranged from 2.23 to 6.63 g N m−2, and were approximately two orders of magnitude greater than snowmelt inputs of 50.4 mg N m−2 for NH4+ and 97.2 mg N m−2 for NO3−. Both NO3− and NH4+ concentrations remained at or below detection limits in surface water during snowmelt, indicating the only export of inorganic N from the system was through gaseous losses. Nitrous oxide production under snow was first observed in early April. Production increased as soils warned, peaking at 75 μg N2O-N m−2 day−1 in soils saturated with melt water one week before the sites were snow free. These data suggest that microbial activity in snow-covered soils may play a key role in alpine N cycling before plants become active.