Turkey Lakes Watershed Research Articles

Foreword. The Turkey Lakes Watershed Study After Two Decades

Foreword. The Turkey Lakes Watershed Study After Two Decades

Prediction of groundwater characteristics in forested and harvested basins during spring snowmelt using a topographic index

AbstractConsistent relationships between groundwater conditions and topographic properties in small drainage basins would assist the study and modelling of basin hydrology and hydrochemistry. Hydrochemical simulation using topographically based models would benefit in particular from the linkage of groundwater residence times to topographic indices, such as the ln(a / tan β) index of Beven and Kirkby. Hypothesized associations between this index and groundwater characteristics were tested during the spring 2000 snowmelt in two sub‐basins in the Turkey Lakes Watershed near Sault Ste Marie, ON. One sub‐basin is in mature hardwood forest, and the other was clearcut in the fall of 1997. Piezometric surface elevations were monitored in each sub‐basin throughout the melt, and the topographic index value for each piezometer was determined. The δ18O signatures of input water and groundwater were also measured. Mean groundwater residence times were obtained using the exponential system response function, which generally produced good fits to the observed groundwater δ18O time series in both sub‐basins. There were significant contrasts in groundwater conditions between the sub‐basins. The forested sub‐basin exhibited higher and more temporally variable piezometric surface elevations and a greater contrast between δ18O signatures and water residence times in shallow versus deeper groundwater relative to the harvested sub‐basin. Patterns of groundwater residence times in the sub‐basins were supported by pre‐harvest groundwater chemistry; however, data from the two sub‐basins largely failed to support the hypothesized relationships between groundwater conditions and topographic index values. Methodological limitations that may have precluded a more rigorous test of the hypotheses are reviewed, and the potential for using groundwater residence times to evaluate the impacts of forest harvesting on basin hydrochemistry is briefly discussed. Copyright © 2001 John Wiley & Sons, Ltd.

Tracing the Sources of Exported Nitrate in the Turkey Lakes Watershed Using 15 N/ 14 N and 18 O/ 16 O isotopic ratios

Nitrate produced by bacterially mediated nitrification in soils is isotopically distinct from atmospheric nitrate in precipitation. 15N/14N and 18O/16O isotopic ratios of nitrate can therefore be used to distinguish between these two sources of nitrate in surface waters and groundwaters. Two forested catchments in the Turkey Lakes Watershed (TLW) near Sault Ste. Marie, Ontario, Canada were studied to determine the relative contributions of atmospheric and microbial nitrate to nitrate export. The TLW is reasonably undisturbed and receives a moderate amount of inorganic nitrogen bulk deposition (8.7 kg N · ha−1· yr−1) yet it exhibits unusually low inorganic nitrogen retention (average = 65% of deposition). The measured isotopic ratios for nitrate in precipitation ranged from +35 to +59‰ (VSMOW) for δ18O and −4 to +0.8‰ (AIR) for δ15N. Nitrate produced from nitrification at the TLW is expected to have an average isotope value of approximately −1.0‰ for δ18O and a value of about 0 to +6‰ for δ15N, thus, the isotopic separation between atmospheric and soil sources of nitrate is substantial. Nitrate produced by nitrification of ammonium appears to be the dominant source of the nitrate exported in both catchments, even during the snowmelt period. These whole catchment results are consistent with the results of small but intensive plot scale studies that have shown that the majority of the nitrate leached from these catchments is microbial in origin. The isotopic composition of stream nitrate provides information about N-cycling in the forested upland and riparian zones on a whole catchment basis.

Hydrologic Pathways during Snowmelt in First-order Stream Basins at the Turkey Lakes Watershed

The chemical composition of stream and soil water collected from two first-order stream basins in the Turkey Lakes Watershed (TLW) during the spring melt periods of 1992-1996 was examined to determine the flowpaths of snowmelt to the stream channel. Soil water was intensively sampled from within the soil organic layers as well as above (shallow soil water) and within (deep soil water) a compact basal till. Stream SiO 2 concentrations of the high-elevation basin 47 were the same as the levels found in shallow soil water, and forest-floor percolate SiO 2 concentrations were elevated to these levels during intense melting periods. The SiO 2 concentrations from the stream and the shallow and deep soil water were similar at the low-elevation basin 31. With the exception of deep soil water, water collected from the soil and stream at basin 47 had higher H + and Al and lower base cation concentrations than basin 31. Stream Al concentrations were significantly correlated with forest-floor percolate Al concentrations at the high-elevation basin, whereas stream Al concentrations were correlated with mineral soil water Al concentrations at the low-elevation site. There were significant positive correlations between stream and shallow soil water H + at both basins. Shallow soil water pathways, therefore, were an important contributor to streamflow, and influenced stream chemical response during the spring snowmelt at TLW.

Evaluating Critical Soil Acidification Loads and Exceedances for a Deciduous Forest at the Turkey Lakes Watershed

Critical soil acidification loads (CL) and related exceedances, base cation leaching, N leaching, and forest biomass growth were evaluated for a well-studied deciduous forest site within the Turkey Lake Watershed (TLW). The assessment was done by way of steady-state mass balance considerations of primary inputs for N, Ca, Mg, and K. Critical soil acidification rates were found to be high at TLW. These rates amounted to about 900 or 1400 eq/(ha yr) depending on the forest harvesting regime (selective harvest or maintainence of old-growth condition, respectively). The TLW soil substrate (till derived from basaltic bedrock) appeared to weather well, thereby buffering against natural and anthropogenic soil acidification. As a consequence, soil acidification exceedances were estimated to be relatively low for both the selective harvest and old-growth scenarios. In comparing overall S and N input/output data (atmospheric deposition data vs soil leaching losses), we found that the TLW site was essentially near or at S and N saturation. We also found that atmospheric deposition and soil leaching rates have been declining since about 1980. The figures for CL and exceedance varied to some extent depending on the quality of input data and related uncertainties. Estimated exceedances were increased when dry- as well as wet-deposition rates were considered. They varied depending on the yearly sulfate/nitrate/base-cation mix, and the definition of “acceptable acid leaching.” In addition, they were dependent on whether the forest was considered old growth or not.

Fifteen-year Change in Forest Floor Organic and Element Content and Cycling at the Turkey Lakes Watershed

To assess the long-term effects of atmospheric deposition on forest floor chemical composition, we took quantitative samplings of L-(Oi), F-(Oe), and H-(Oa) layers at an old-growth sugar maple-yellow birch stand on a till soil at the Turkey Lakes Watershed near Lake Superior, Ontario, Canada, in 1981 and 1996. We then assessed these samples for contents of organic matter (OM), total N, K, Ca, Mg, S, and Na, and exchangeable NH 4 + , NO 3 - , K + , Ca 2+ , Mg 2+ , SO 4 2- , and Na + . Over the 15-year period, total OM and element contents remained unchanged, with the exception of N, which increased significantly from 61.3 kmol/ha in 1981 to 78.4 kmol/ha in 1996. On an area basis, there were significant increases in exchangeable Ca 2+ (from 3.8 to 4.6 kmol/ha) and Na + (from 0.05 to 0.08 kmol/ha) and decreases in exchangeable NH 4 + -N (from 1.41 to 0.95 kmol/ha) and SO 4 2- -S (from 1.29 to 0.96 kmol/ha). There were no significant differences in average annual litterfall OM, N, Ca, Mg, S or Na inputs between 1980 and 1985 and between 1992 and 1997. Average annual wet-only SO 4 2- -S deposition during 1981-86 was 0.30; during 1992-97, it was 0.21 kmol/ha. Annual wet-only NO 3 - -N averaged 0.33 kmol/ha during 1981-86 and was similar during 1992-97. Throughfall was less rich in SO 4 2- and Ca 2+ , Mg 2+ , and Na + during 1992-97 than earlier. Throughfall NH 4 - and NO 3 - fluxes were unchanged. Efflux of cations from the forest floor reflected reduced throughput of SO 4 2- . Overall, the results suggest that in spite of atmospheric inputs, active biological processes-including litter input, fine-root turnover, and tree uptake-serve to impart stability to the mineral composition of mature sugar maple forest floor.

Trends in the Output of First-order Basins at Turkey Lakes Watershed, 1982-96

In 1981, we began to monitor the stream flow and chemistry of 13 first-order basins at the Turkey Lakes Watershed, with the objective of measuring the response of an undisturbed forested ecosystem to acid deposition. There was no trend in total annual precipitation received by the watershed, but the average annual water yield (percentage of annual precipitation) declined over the observation period. The proportion of runoff occurring in different seasons also changed, decreasing in the winter and increasing in the spring. In most streams the concentration of SO4 2− has decreased coincident with the decline in precipitation inputs. Recovery of the basins from acid deposition (as evidenced by increased pH, increased alkalinity, and decreasing base cation fluxes) has not been uniform. Basins that do not show signs of recovery are characterized by deeper flowpaths and greater potential neutralizing capacity, which minimizes the impacts of acid deposition. Basins that are dominated by shallow flowpaths and lower levels of potential neutralizing capacity are showing some signs of recovery, but their recovery is not complete and it is possible that cation depletion may prevent or retard it.

Atmospheric Deposition to the Turkey Lakes Watershed: Temporal Variations and Characteristics

We investigated the atmospheric concentrations and deposition fluxes of major ions to the Turkey Lakes Watershed (TLW) between 1980 and 1996. During that time, daily SO4 2− concentrations in precipitation decreased markedly, while NO3 −, NH4 +, and H+ concentrations remained roughly constant. It appears that precipitation acidity did not decrease in spite of declining SO4 2− concentrations due to a concurrent and counterbalancing decrease in the concentrations of Ca2+, Mg2+, and K+ in precipitation. The reasons for the decline in base cations are unknown, but this decline is probably related to decreasing emissions of soil-derived particles from agricultural, industrial, and road sources. A similar situation was seen during the same period in other parts of Canada, the eastern United States, and Europe. Wet, dry, and total (wet + dry) deposition fluxes of sulphur (S) and nitrogen (N) were estimated annually for the years 1980–96. The 17-year mean annual total (wet + dry) deposition of S to the watershed was estimated at 38.5 mmol m−2 y−1 (range 24.3–50.3). Total S deposition decreased by 35% from the early 1980s (1982–84) to the mid-1990s (1994–96), a decline consistent with the 23% decline in annual SO2 emissions in eastern North America during the same period. In contrast, the annual total (wet + dry) deposition of oxidized N ranged from 39.8 to 60.4 mmol m−2 y−1, with a 15-year mean of 50.1 mmol m−2 y−1 and a net increase of 10% between the early 1980s (1983–85) and the mid-1990s (1994–96). This is in keeping with a 10% increase in NOx emissions in eastern North America during the same period. For both S and N (oxidized), wet deposition dominated over dry deposition as the major mechanism for atmospheric input to the watershed. Annually, wet deposition accounted for approximately two-thirds of the total atmospheric deposition of both S and N. Dry S deposition was due more to gaseous SO2 deposition (two-thirds of dry S deposition) than to particulate SO4 2− deposition (one-third of dry S deposition). Dry deposition of oxidized N, however, was dominated (95%) by gaseous HNO3 deposition, with minimal input from particulate NO3 − deposition. Compared to several selected watershed/forest sites in Canada, the United States, and Europe, the estimated total deposition of S and N at the TLW was relatively high during the measurement period.

Erratum

The Turkey Lakes Watershed Study (TLWS) was initiated in 1980 to assess the effects of anthropogenic perturbation on Shield ecosystems. The goal of the study was to obtain a whole-ecosystem analysis of the biogeochemical processes that control pollutant–ecosystem interactions and thence to promote the development and validation of system models. It is a cooperative effort that includes investigators from Environment Canada (National Water Research Institute, Meteorological Service of Canada, and Canadian Wildlife Service), Natural Resources Canada (Great Lakes Forestry Centre), and Fisheries and Oceans Canada (Great Lakes Laboratory for Fisheries and Aquatic Science), as well as several universities. The initial impetus for research in the TLW arose from the desire to assess and understand the aquatic and terrestrial effects of acidic deposition. The TLW (Figure 1) is located 50 km north of Sault Ste. Marie, Ontario, on the Canadian Shield near the northern margin of the Great Lakes–St. Lawrence forest region. The basin, which is 10.5 km in area, is situated predominantly on metamorphic silicate bedrock (greenstone) overlain by thin to absent glacial tills. These geological conditions make the basin moderately sensitive to acidic deposition. The terrestrial and aquatic resources within the basin are representative of the surrounding Algoma district, although for an Ontario site, the TLW has relatively high relief (290 m) and precipitation (mean, more than 1200 mm y ). The forest is an uneven-aged, mature-toovermature, old-growth hardwood system dominated by sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britton). The drainage system is composed of many intermittent and perennial first-order streams draining into and through a chain of four dimictic lakes that range in size from 5.8 to 52.0 ha and in mean depth from 2.2 to 12.2 m. There is a chemical gradient in the aquatic system such that higherelevation waters are more dilute (that is, they have lower Ca and alkalinity concentrations) than lower-elevation waters. The TLW ultimately drains into the Batchawana River and thence to Lake Superior. For greater detail on basin characteristics, see Jeffries and others (1988). From time to time, study participants have conducted workshops to present, discuss, and integrate the findings from the scientific investigation now being done in the TLW (for example, see the Canadian Journal of Fisheries and Aquatic Sciences, 1988, vol. 45, Suppl. 1, pages 1–178,). This issue of Ecosystems presents six papers from a 1999 workshop that summarize the results from either long-term monitoring of conditions in the TLW or specific research projects. According to Sirois and others (2001), mean annual wet SO4 2 deposition declined from 31 mmol m 2 during 1981–1984 to 18 mmol m 2 during 1994–97. Two of the following papers address trends or responses in precipitation or surface-water chemistry that were contemporaneous with this change in acid input. Three other papers consider some of the physical and chemical processes that regulate watershed biogeochemistry, and another describes the development and application of a predictive soil acidification model that was designed to assess whether the reduced acid Received 19 September 2000; accepted 19 September 2000. *Corresponding author; e-mail: dean.jeffries@cciw.ca Ecosystems (2001) 4: 501–502 DOI: 10.1007/s10021-001-0023-2 ECOSYSTEMS

Forest research at the Turkey Lakes Watershed

The 10.5 km2 Turkey Lakes Watershed, located on the Precambrian Shield approximately 60 km north of Sault Ste. Marie, Ontario, is occupied by a typical Great Lakes-St. Lawrence sugar maple-yellow birch forest. Since late 1979, the watershed has been the site of an interdisciplinary study on impacts of long-range transported air pollutants on the biology of forests, lakes and streams, and the recovery of terrestrial and aquatic ecosystems in response to reduced pollutant deposition. A knowledge base on forest growth, soils and hydrology, with detailed climate and precipitation chemistry records dating back nearly twenty years has been developed. This history, plus an available infrastructure, makes the watershed an ideal site to study processes across the terrestrial-aquatic interface. A harvesting impacts project, for example, was started in 1997. This project is built around a field experiment comparing clear-felling, shelterwood, and single-tree selection versus uncut control, for appropriateness of application and for impacts on long-term soil productivity, stand function, diversity of plant and animal life, and hydrological and other on- and off-site impacts. The watershed is also a site for the ECOLEAP Project, which is attempting to improve overall understanding of mechanisms controlling forest productivity, and a site to test terrain and climate models to model temperature, moisture, energy and nutrients and the relationship of these to species distribution, abundance and productivity at different scales up to the watershed level. Key words: acid precipitation, air pollution, biogeochemistry, research site, watershed

Exploring functional similarity in the export of Nitrate‐N from forested catchments: A mechanistic modeling approach

Functional similarity of catchments implies that we are able to identify the combination of processes that creates a similar response of a specific characteristic of a catchment. We applied the concept of functional similarity to the export of NO3−‐N from catchments situated within the Turkey Lakes Watershed, a temperate forest in central Ontario, Canada. Despite the homogeneous nature of the forest, these catchments exhibit substantial variability in the concentrations of NO3−‐N in discharge waters, over both time and space. We hypothesized that functional similarity in the export of NO3−‐N can be expressed as a function of topographic complexity as topography regulates both the formation and flushing of NO3−‐N within the catchment. We tested this hypothesis by exploring whether topographically based similarity indices of the formation and flushing of NO3−‐N capture the observed export of NO3−‐N over a set of topographically diverse catchments. For catchments with no elevated base concentrations of NO3−‐N the similarity indices explained up to 58% of the variance in the export of NO3−‐N. For catchments with elevated base concentrations of NO3−‐N, prediction of the export of NO3−‐N may have been complicated by the fact that hydrology was governed by a two‐component till, with an ablation till overlying a basal till. While the similarity indices captured peak NO3−‐N concentrations exported from shallow flow paths emanating from the ablation till, they did not capture base NO3−‐N concentrations exported from deep flow paths emanating from the basal till, emphasizing the importance of including shallow and deep flow paths in future similarity indices. The strength of the similarity indices is their potential ability to enable us to discriminate catchments that have visually similar surface characteristics but show distinct NO3−‐N export responses and, conversely, to group catchments that have visually dissimilar surface characteristics but are functionally similar. Furthermore, the similarity indices provide a potentially powerful method to scale and generalize NO3−‐N export responses to other regions.

Impact of simulated acid rain on microbial respiration, biomass, and metabolic quotient in a mature sugar maple (Acersaccharum) forest floor

Effects of simulated acid rain on forest floor microbiological processes were investigated in an old-growth sugar maple (Acersaccharum Marsh.) woods at Turkey Lakes Watershed, northern Ontario, Canada. Sulphate and NO3− in ambient precipitation received on four replicate plots were augmented with additions of dilute (0.02 N) H2SO4 and HNO3, applied alone and in combination periodically during the growing seasons of 1993 and 1994. The equivalent load of SO42− applied in the present experiment was ca. 6 times that in ambient precipitation in the H2SO4-only treatment and half that in the combined treatment over the study period. In situ soil respiration measured during the summer and fall of 1994 showed no adverse effects of acid treatment. In the laboratory, soil microbial respiration, biomass (as determined by substrate-induced respiration), and microbial biomass carbon: organic carbon (Cmic/Corg ratios were significantly depressed in the L or FH layers of the forest floor when H2SO4 was applied alone or in combination with HNO3. No effects of HNO3 were detected when applied alone. Microbial respiration, substrate-induced respiration, and Cmic/Corg ratios were significantly correlated with forest floor pH. Microbial metabolic quotients (respiration:biomass ratios) were not adversely affected by any of the treatments. The observed deleterious effects of H2SO4 application under experimental conditions suggest the possibility of adverse effects in the field over the long-term.

Solution concentrations of nutrient ions below the rooting zone of a sugar maple stand: relations to soil moisture, temperature, and season

Temporal variations of ion concentrations in soil solution were analyzed in relation to soil percolate volume, soil water content, soil temperature, solution chemistry, and season. The study site was an uneven-aged, mature northern tolerant hardwoods dominated by sugar maple (Acersaccharum Marsh.) within the Turkey Lakes Watershed, Ontario. Six ions were investigated: nitrate (NO3−), sulfate (SO42−), calcium (Ca2+), magnesium (Mg2+), potassium (K+), and ammonium (NH4+). Nitrate concentrations in the soil solution depended on season during the nonfoliage period and responded directly to forest floor percolation, soil water content, and season during the foliage period. Variations of SO42−, Ca2+, and Mg2+ concentrations were mostly attributable to NO3− concentration, and to season to a lesser extent. Concentrations of K+ and NH4+ correlated only weakly to any of the "independent" variables included in the analysis, reflecting a high affinity between these ions and the soil colloids.

Impact of soil water deficits in a mature sugar maple forest: stand biogeochemistry

Computer simulations of moisture relationships in an uneven-aged, tolerant hardwood forest at the Turkey Lakes Watershed suggest that soil water deficits during 1982–1983 and 1988–1989 were among the most severe of the past 40 years. Examination of radial growth indices for sugar maple (Acersaccharum Marsh.) trees suggested that reductions in growth coincided with low volumetric soil water contents and with low NO3− concentrations in soil solution. The lowest mean monthly NO3− concentrations in soil percolate were observed during severe summer droughts. Nitrate concentrations were negatively correlated (r2 = −0.803) with SO42− levels in solution and positively correlated (r2 = 0.761) with Ca2+ levels. Nitrification, by stimulating adsorption of SO42− by the soil, may lead to temporary retention of atmospheric SO42− in soils that otherwise exhibit only limited capacity to retain SO42−. If warmer, drier summers become more frequent, nitrogen cycling will become more closed as the supply of nitrogen to the vegetation and leaching of nitrogen from the soil are reduced. Sulfate-moderated leaching from the soil, however, will increase; hence, net cation leaching is unlikely to change in response to drier summers.

Nutrient cycling in Huntington Forest and Turkey Lakes deciduous stands: nitrogen and sulfur

Biogeochemical cycling of S and N was quantified at two hardwood sites (Turkey Lakes watershed (TLW) and Huntington Forest (HF)) that have sugar maple (Acersaccharum Marsh.) as the major overstory component and are underlain by Spodosols (Podzols). TLW and HF are located in central Ontario (Canada) and the Adirondack Mountains of New York (U.S.A), respectively. Major differences between the TLW and HF sites included stand age (300 and 100 years for TLW and HF, respectively), age of dominant trees (150–300 and 100 years for TLW and HF, respectively), and the presence of American beech (Fagusgrandifolia Ehrh.) at HF as well as lower inputs of SO42− and NO3− (differences of 99 and 31 mol ion charge (molc)•ha−1•year−1, respectively) at TLW. There was an increase in concentration of SO42− and NO3− after passage through the canopy at both sites. A major difference in the anion chemistry of the soil solution between the sites was the much greater leaching of NO3− at TLW compared with HF (1300 versus 18 molc•ha−1•year−1, respectively). At HF, but not TLW, there was a marked increase in SO42− flux (217 molc•ha−1•year−1) when water leached from the forest floor through the mineral soil. The mineral soil was the largest pool (>80%) of N and S for both sites. The mineral soil of TLW had a C:N ratio of 16:1, which is much narrower than the 34:1 ratio at HF. This former ratio should favor accumulation of NH44+ and NO3− and subsequent NO3− leaching. Laboratory measurements suggest that the forest floor of TLW may have higher N mineralization rates than HF. Fluxes of N and S within the vegetation were generally similar at both sites, except that net requirement of N at TLW was substantially lower (difference of 9.4 kg N•ha−1•year−1). The higher NO3− leaching from TLW compared with HF may be attributed mostly to stand maturity coupled with tree mortality, but the absence of slow decomposing beech leaf litter and lower C:N ratio in the soil of the former site may also be contributing factors.

Cycling of acid and base cations in deciduous stands of Huntington Forest, New York, and Turkey Lakes, Ontario

Annual nutrient fluxes within two forests exposed to acidic deposition were compared for a 1-year period. Calcium (Ca2+) was the dominant cation in throughfall and soil solutions from tolerant hardwood dominated Spodosols (Podzols) at both Huntington Forest (HF), New York, and the Turkey Lakes watershed (TLW), Ontario. There was a net annual export of Ca2+ and Mg2+ from the TLW soil, whereas base cation inputs in precipitation equaled outputs at HF. In 1986, leaching losses of base cations were five times greater at TLW than at HF. A higher percentage of the base cation reserves was leached from the soil at TLW (5%) than at HF (1%). Relative to throughfall, aluminum concentrations increased in forest-floor and mineral-soil solutions, especially at HF. The TLW soil appears more sensitive to soil acidification. Deposited atmospheric acidity, however, was small in comparison with native soil acidity (total and exchangeable) and the reserves of base cations in each soil. Soil acidity and base saturation, therefore, are likely only to change slowly.

Influence of acid deposition on element cycling in mature sugar maple forest, Algoma, Canada

Forestry studies were undertaken within the Turkey Lakes Watershed to determine the impact of long-range transport of air pollutants on biogeochemical processes in old-growth sugar maple forest on shallow Precambrian-derived till soils in the Algoma District of Ontario, Canada. Distributions of organic matter and macroelements were determined in the tree- and field-layer vegetation, the forest floor and the mineral soil of the study site. Annual tree growth was largely offset by mortality, resulting in a relatively stable standing stock of ca. 245 t ha−1. Annual aboveground litter production averaged 3.7 t ha−1 yr−1, chiefly in the form of deciduous leaf fall. The average pH of the precipitation (4.3) was reduced considerably by contact with the forest canopy. Throughfall was enriched with other elements, principally K and, to a lesser extent, Ca and Mg. The cationic composition of the forest-floor percolates, on the other hand, was dominated primarily by Ca and only to a lesser extent by Mg and K. The stand receives moderate acid deposition, mainly from average inputs of 33–36 kg ha−1 yr−1 of SO42− and 24–29 kg ha−1 yr−1 of NO3− distributed throughout the year. Atmospheric inputs add to substantial natural NO3− production, notably within the forest floor and upper mineral soil, and contribute to leaching of bases, principally Ca and Mg, from the rooting zone. Active recycling of elements together with weathering of primary minerals should assist in preserving the base status of the site.

Ion Enrichment of Snowmelt Water by Processes within a Podzolic Soil

AbstractIon concentrations in snowmelt runoff, forest‐floor percolate and mineral‐soil percolate collected in a tolerant hardwood forest at the Turkey Lakes Watershed, ON, were determined during the spring snowmelt of 1986. The results were examined to assess the modification of snowmelt water after contact with the forest soil. Concentrations of NO3− increased from 17 to 201 µmolc L−1 and SO42− increased from 25 to 107 µmolc L−1 as meltwater passed through the organic layers and the upper mineral‐soil horizons. Mineralization of organic N and S, and desorption of SO42− from the soil, provide sources of these ions for leaching during the snowmelt period. Ion‐exchange reactions in the forest floor and upper mineral soil resulted in a decrease in H+ and an increase in Ca2+ concentration in solution. In the steep topography of this forested basin, the altered snowmelt solutions are rapidly transported downslope towards the aquatic system by lateral flow. Processes within the forest soil may therefore play an important role in determining the effects of snowmelt water on surface water chemistry in the spring.

Application of four watershed acidification models to Batchawana Watershed, Canada

Four watershed acidification models (TMWAM, ETD, ILWAS, and RAINS) are reviewed and a comparison of model performance is presented for a common watershed. The models have been used to simulate the dynamics of water quantity and quality at Batchawana Watershed, Canada, a sub-basin of the Turkey Lakes Watershed. The computed results are compared with observed data for a four-year period (Jan. 1981–Dec. 1984). The models exhibit a significant range in the ability to simulate the daily, monthly and seasonal changes present in the observed data. Monthly watershed outflows and lake chemistry predictions are compared to observed data. pH and ANC are the only two chemical parameters common to all four models. Coefficient of efficiency ( E), linear ( r) and rank ( R) correlation coefficients, and regression slope ( s) are used to compare the goodness of fit of the simulated with the observed data. The ILWAS, TMWAM and RAINS models performed very well in predicting the monthly flows, with values of r and R of approximately 0·98. The ETD model also showed strong correlations with linear ( r) and rank ( R) correlation coefficients of 0·896 and 0·892, respectively. The results of the analyses showed that TMWAM provided the best simulation of pH ( E = 0·264, r = 0·648), which is slightly better than ETD ( E = 0·240, r = 0·549), and much better than ILWAS ( E = −2·965, r = 0·293), and RAINS ( E = −4·004, r = 0·473). ETD was found to be superior in predicting ANC ( E = 0·608, r = 0·781) as compared to TMWAM ( E = 0·340, r = 0·598), ILWAS ( E = 0·275, r = 0·442), and RAINS ( E = −1·048, r = 0·356). The TMWAM model adequately simulated SO 4 over the four-year period ( E = 0·423, r = 0·682) but the ETD ( E = −0·904, r = 0·274), ILWAS ( E = −4·314, r = 0·488), and RAINS ( E = −6·479, r = 0·126) models all performed poorer than the benchmark model (mean observed value).

Hydrological modelling of acidified Canadian watersheds

Hydrology plays an important role in the acidification of watersheds in Canada by airborne pollutants such as the wet and dry deposition of sulfate and nitrate. The pathways of the anions through the soil layers, the contact times with soil matrix, the snow accumulation and melting sequences and the groundwater flows are all important hydrological factors that influence the acidification processes. A hydrogeochemical model has been developed (TMWAM) and applied to Turkey Lakes Watershed. Results are presented on the calibration and confirmation of the model using the data from these watersheds. Particulate emphasis is placed on the hydrological factors and their relationships to the varying degrees of acidification observed at these locations. Preliminary results of linking the hydrological and hydrogeochemical models are discussed in the context of model applications as part of the national acidification assessment efforts in Canada.