Inconspicuous Nutrient Laden Surface Runoff from Mature Forest Sierran Watersheds

Abstract

It is generally held that surface runoff in heavily forested ecosystems is minimal and therefore nutrient fluxes via runoff are unimportant. This is based in large measure on the absence of direct observation or remnant physical evidence. It is further held that protected forests with heavy understory and litter serve as a nutrient sink due to maximum uptake and interception. Our Sierran studies have detected the presence of surface runoff at several sites in the form of both overland and litter interflow with concentrations of NH 4 -N as high as 87.2 mg L −1 , NO 3 -N as high as 95.4 mg L −1 , and PO 4 -P as high as 24.4 mg L −1 . Data suggest that nutrients are derived from the mature O-horizons, and that there has been little contact with the mineral soil or root zone where strong retention and/or uptake of these ions would be expected. Such contributions from overland/interflow could be particularly important in areas where ultra-oligotrophic lakes (e.g., Lake Tahoe) are now trending towards meso-oligotrophic status. We believe that fire exclusion in these systems may have exacerbated N and P inputs to Lake Tahoe and elsewhere by allowing unnatural buildups of O-horizons that are apparently a source of nutrients to surface runoff.

Nutrient and mercury deposition and storage in an alpine snowpack of the Sierra Nevada, USA

“…Although much of snowpack-based chemical loads may not directly enter Lake Tahoe upon melt, snowpack loads are important for terrestrial chemical budgets. For example, nutrient-rich O-horizon runoff -measuring as high as 87.2 mg L −1 NH 4 -N, 95.4 mg L −1 NO 3 -N, and 24.4 mg L −1 PO 4 -P -has been observed in Lake Tahoe forests during snowmelt events due to leaching from the forest litter layer (Miller et al, 2005). In order to relate peak snowpack nutrient and pollutant loading to previous terrestrial and lake chemical budgets, we here estimate average peak basin-wide snowpack chemical storage using the peak SWE decadal average from 2000 to 2011 (Fig.…”

A Synthesis of Sierran Forest Biomass Management Studies and Potential Effects on Water Quality

“…The specific sources of nutrient and sediment loading to Lake Tahoe, although varied, are generally related to anthropogenic enhanced atmospheric deposition, overland flow surface runoff, and/or subsurface transport and discharge. If we are to arrest continued deterioration of the lake's famed water clarity, it is imperative that in addition to the current emphasis on urban sources of water pollution we also strive to better understand the interdependence among watershed nutrient cycling, groundwater and streamflow, overland flow surface runoff, precipitation (type, intensity, duration), atmospheric deposition, wildfire and anthropogenic manipulations such as biomass management [11][12][13][14][15][16][17][18][19][20][21][22].…”

“…At the same time large forest floor N and P pools may also contribute to increases in inorganic N and P pools in the summer dry O horizon [38][39][40][41]. Accumulating water soluble nutrients may leach into the soil or discharge from the area of by way of overland flow surface runoff and/or litter interflow [21,37]. Hence, the buildup of fuels in the understory has not only increased the potential for stand replacing wildfires, but has also resulted in the accumulation of much thicker, nutrient-rich organic residues.…”

“…Hence, the buildup of fuels in the understory has not only increased the potential for stand replacing wildfires, but has also resulted in the accumulation of much thicker, nutrient-rich organic residues. This excess accumulation of organic residues has apparently shifted the equilibrium such that the annual amount of internal nutrient cycling has increased, causing the organic mass to release more available nutrients into runoff and percolating solutions [21,37]. Although it is uncertain as to whether or not this nutrient laden runoff makes it into tributary water flow, the potential clearly exists [21].…”

Variation in reciprocal subsidies between lakes and land: perspectives from the mountains of California

“…As runoff from snowmelt or rain infiltrates and flushes the catchment, variability in soil structure and vegetation type plays an important role in nitrogen release. Nutrient release from soils is controlled by the accumulation of litter in the organic horizon (Miller et al 2005), the influence of snowpack on soil moisture and remineralization rates (Johnson et al 2009), and the magnitude of plant root development in the O horizon (Johnson et al 2009). In their review of nutrient cycling in forests of the eastern Sierra Nevada Mountains, Johnson et al (2009) suggest that very high concentrations of inorganic nitrogen and phosphorus in runoff waters resulted from nutrients mineralized from the soil O horizon that were not taken up by plants and that remained above hydrophobic mineral soils.…”