A portable, noncontacting electromagnetic induction meter was employed to measure the apparent electrical conductivity (ECa) of nonsaline, medium‐ and coarse‐textured forest soils on Manitoulin Island, Ontario. In simple linear regressions, bulk soil ECa was strongly correlated with ECe (saturated‐extract electrical conductivity), as well as exchangeable Ca, exchangeable Mg, and cation exchange capacity. Within the limited study area, these soil characteristics were thought to be major determinants of forest soil quality for red oak (Quercus rubra L.) production. Multiple stepwise regression showed that variations in exchangeable Ca and total Kjeldahl N concentrations accounted for a large proportion of the variation in ECa meter response (R2 = 0.871). The potential of this geophysical terrain measurement method as an integrator of edaphic properties important to forest site productivity is discussed.

A study was undertaken to investigate leaf photosynthesis and stem growth responses of saplings of two broad‐leaf tree species to irrigation with municipal solid waste (MSW) leachate in a northern temperate climate at Ontario, Canada. The objective was to quantify plant stresses or changes in plant productivity that could be attributed to this low technology option for the treatment and disposal of groundwater contaminated by municipal refuse. Red maple (Acer rubrum L.) and hybrid poplar [Populus spp. nigra × maximowiczii (NM6)] were subjected to two consecutive seasons of leachate irrigation in a three factor, RCBD split‐plot field experiment. The three factors were irrigant type (MSW leachate, water), mode of application (spray, surface trickle, subsurface irrigation), and rate of application (3.5, 7.0, and 14.0 mm d−1). The main treatment plots in each of three blocks were split into subplots planted to different tree species. In the second irrigation season, the mean seasonal photosynthesis rates increased for irrigated saplings of both species relative to rain‐fed control saplings, irrespective of irrigant type. Mean seasonal photosynthesis rates for red maple increased with irrigant application rate, but were unaffected by irrigant type. Incremental stem diameter and height growth for this species were largely unaffected by the experimental treatments. Mean seasonal photosynthesis rates for hybrid poplar were unaffected by either irrigant type or application rate, but stem growth did increase significantly with leachate irrigation. The mode of irrigant application was not a significant factor in explaining plant response for either species. Direct exposure of leaves to potentially phytotoxic compounds in MSW leachate (volatile organics, and inorganics including metals) by spraying did not induce phytotoxic symptoms in the saplings. Irrigation of a MSW leachate of relatively high ionic strength can be carried out successfully on clay soils under Ontario climatic conditions without causing significant adverse effects on saplings of these tree species. Treatment and disposal of MSW leachates in tree plantations may offer a low technology, low cost option to municipalities.

Foliar gas exchange, water relations and spectral properties of understorey sugar maple ( Acer saccharum Marsh. ) sapling leaves were studied in a natural forested ecosystem subjected to spray irrigation of municipal solid waste (MSW) landfill leachate and compared to similar measures taken from leaves of unirrigated saplings. Photosynthetic rates in irrigated saplings were reduced 34% to 53% in comparison to unirrigated sapling rates. Similarly, water use efficiency of sapling leaves subjected to direct leachate exposure dropped an average of 70%, while transpiration rates were similar to, and leaf temperatures were 20% higher than, those found in unirrigated leaves. Spectral patterns of understorey leaves, distorted because of the accumulation of leachate precipitate residues on the adaxial surface, demonstrated increased absorbance in the near infrared waveband and reduced reflection in visible wavebands compared to abaxial surfaces. The adaxial spectral properties of mid-canopy leaves (above maximum spray height) of mature sugar maple trees were not distorted by these residues and revealed spectra that suggested increased nitrogen uptake and benefit derived from leachate irrigation. These findings on leaf tissue integrity and energy budgets are discussed in terms of the implications for design of leachate treatment and disposal systems on land and for forest ecology in general.

No abstract

An experiment was undertaken to examine the response of hydroponically-grown red maple ( Acer rubrum L.) saplings to a series of four flooding (sub-irrigation) treatments distributed over a 25-day period with an untreated (saline) municipal solid waste landfill leachate or deionized water. Net photosynthesis rates measured for water-treated saplings rapidly declined to 62% of the levels measured in untreated (control) saplings, but returned to pre-treatment levels with subsequent flooding treatments. Net photosynthesis rates measured for leachate-treated saplings decreased to about 50% of the levels measured for control saplings over the 25-day treatment period, and remained suppressed. Loss of turgor in leaves and a iron-oxyhydroxide plaque on root surfaces were also observed. Reasons proposed for this acute and apparently irreversible response to leachate exposure include: (i) extreme root anaerobiosis conditions caused by root system flooding and exacerbated by a high chemical oxygen demand leachate; (ii) increased root-soil interface resistance to transpiration water flow (osmotic potential gradient, iron oxyhydroxide plaque); (iii) metabolic intolerance to high solute concentrations in plant tissue; and (iv) exposure to potentially toxic volatile organic compounds. Water sub-irrigation had virtually no effect on nutrient and non-nutrient element concentrations in foliage or on the spectral reflectance characteristics of the leaves. Leachate treatment decreased the foliar content of many plant macro-and micro-nutrients significantly, and shifts in spectral reflectance patterns indicated declining plant vigour. Certain chemical constituents present in high concentrations in the leachate irrigant and which can be phytotoxic, such as Cl, accumulated to a significant degree in leachate-treated plant tissue.