Soil water repellency: its causes, characteristics and hydro-geomorphological significance

How strongly can forest management influence soil carbon sequestration

Concentration–discharge relationships have been widely used as clues to the hydrochemical processes that control runoff chemistry. Here we examine concentration–discharge relationships for solutes produced primarily by mineral weathering in 59 geochemically diverse US catchments. We show that these catchments exhibit nearly chemostatic behaviour; their stream concentrations of weathering products such as Ca, Mg, Na, and Si typically vary by factors of only 3 to 20 while discharge varies by several orders of magnitude. Similar patterns are observed at the inter-annual time scale. This behaviour implies that solute concentrations in stream water are not determined by simple dilution of a fixed solute flux by a variable flux of water, and that rates of solute production and/or mobilization must be nearly proportional to water fluxes, both on storm and inter-annual timescales. We compared these catchments' concentration–discharge relationships to the predictions of several simple hydrological and geochemical models. Most of these models can be forced to approximately fit the observed concentration–discharge relationships, but often only by assuming unrealistic or internally inconsistent parameter values. We propose a new model that also fits the data and may be more robust. We suggest possible tests of the new model for future studies. The relative stability of concentration under widely varying discharge may help make aquatic environments habitable. It also implies that fluxes of weathering solutes in streams, and thus fluxes of alkalinity to the oceans, are determined primarily by water fluxes. Thus, hydrology may be a major driver of the ocean-alkalinity feedback regulating climate change. Copyright © 2009 John Wiley & Sons, Ltd.

/pdf/concentration-discharge-relationships-reflect-chemostatic-3k2jkxywa0.pdf

Concentration–discharge relationships reflect chemostatic characteristics of US catchments

Post-wildfire soil erosion in the Mediterranean: Review and future research directions

Wildfire effects on water quality in forest catchments: A review with implications for water supply

A wildfire burned through a previously sampled research site, allowing pre- and post-burn measurements of the forest floor, soils, and soil leaching near Lake Tahoe, Nevada. Fire and post-fire erosion caused large and statistically significant (P < or = 0.05) losses of C, N, P, S, Ca, and Mg from the forest floor. There were no statistically significant effects on mineral soils aside from a decrease in total N in the surface (A11) horizon, an increase in pH in the A11 horizon, and increases in water-extractable SO4(2-) in the A11 and A12 horizons. Burning caused consistent but nonsignificant increases in exchangeable Ca2+ in most horizons, but no consistent or statistically significant effects on exchangeable K+ or Mg2+, or on Bray-, bicarbonate-, or water-extractable P concentrations. Before the burn, there were no significant differences in leaching, but during the first winter after the fire, soil solution concentrations of NH4+, NO3-, ortho-P, and (especially) SO4(2-) were elevated in the burned area, and resin lysimeters showed significant increases in the leaching of NH4+ and mineral N. The leaching losses of mineral N were much smaller than the losses from the forest floor and A11 horizons, however. We conclude that the major short-term effects of wildfire were on leaching whereas the major long-term effect was the loss of N from the forest floor and soil during the fire.

Wildfire Effects on Soil Nutrients and Leaching in a Tahoe Basin Watershed

Wildfire effects on forest carbon and nutrient budgets

Fire is the dominant factor affecting C and N losses from the semiarid forests of the eastern Sierra Nevada. As prescription fire becomes a best management practice, it is critical to develop an estimate of these fluxes. The objectives of this study were (i) to test and refine methods to estimate the volatilized C and N losses from the forest floor following fire, (ii) to investigate the interactions between O-horizon temperature and nutrient loss, and (iii) to assess measured N losses in the context of atmospheric N deposition, leaching, and N fixation. The quantities of C and N volatilized from the forest floor by prescription fire in the Sierra Nevada were measured using two different field-based methods: weight loss estimation and Calelement ratio determination. Three sites were included in the study: Marlene, Sawtooth and Spooner. The weight method indicated C losses of 6.12, 7.39, and 17.8 Mg C ha -1 at the Sawtooth, Marlene, and Spooner sites, respectively. The ratio method indicated comparable C losses from the Sawtooth (6 Mg C ha -1 ) site, but greater losses at Marlene (16 Mg C ha -1 ) and Spooner (24 Mg C ha -1 ) sites. The weight method indicated N losses of 56.2, 60.8, and 362 kg N ha -1 , at the Sawtooth, Marlene, and Spooner sites, respectively. The ratio method indicated comparable N losses of 59.9 kg N ha -1 at the Sawtooth site, but considerably greater losses at Marlene (243 kg N ha -1 ), and Spooner (524 kg N ha -1 ) sites. The Ca-element method was preferred because of minimal needs for preburn sampling. Regardless of method, the estimated losses were significant, particularly for N, compared with deposition and leaching rates. Volatilization will represent the major mechanism for N loss from forest ecosystems of this region subjected to prescribed fire.

Forest Floor Carbon and Nitrogen Losses Due to Prescription Fire

The effects of wildfire, salvage logging, and post-fire N-fixation on the nutrient budgets of a Sierran forest.

http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.files/fileID/13970

Watkins W. Miller

Papers

Wildfire Effects on Soil Nutrients and Leaching in a Tahoe Basin Watershed

Wildfire effects on forest carbon and nutrient budgets

Forest Floor Carbon and Nitrogen Losses Due to Prescription Fire

The effects of wildfire, salvage logging, and post-fire N-fixation on the nutrient budgets of a Sierran forest.

Mercury distribution in two Sierran forest and one desert sagebrush steppe ecosystems and the effects of fire.