Development of Stream Water Chemistry during Spring Melt in a Northern Hardwood Forest

The role of snowmelt and subsurface hydrology in determiningthe chemistry of a small headwater stream in the TurkeyLakes Watershed (TLW) was evaluated for the spring meltperiods 1992 to 1996. Spring runoff is the dominanthydrological event at the TLW each year. Processesoccurring within the snowpack during snowmelt wereprincipally responsible for the above-ground changes inchemical fluxes relative to bulk deposition (the effect ofwinter throughfall was minimal). Large changes in chemicalfluxes occurred below ground. Organic matter decomposition,weathering, nitrification, and element cycling are some ofthe more important below-ground processes that operateduring the snow accumulation and ablation season and controlthe composition of the water ultimately appearing in thestream. Maximum stream discharge was accompanied byelevated concentrations of H⁺, NO₃ ^-, K⁺,NH₄ ⁺, DOC, Al and Mn, but reduced levels ofCa²⁺, Mg²⁺, SO₄ ^2- and SiO₂. Theconcentration-discharge relationships were consistent withwater movement through and above the forest floor duringpeak discharge, a flowpath facilitated by rapid infiltrationof meltwater and the existence of a relatively impermeablelayer in the mineral soil creating a perched water table. Averaged over the five periods of snow accumulation andablation, it was estimated that pre-melt stream flow, andwater routed through the forest floor and through the uppermineral soil contributed 9, 28 and 63%, respectively, ofthe discharge measured at the outlet of the catchment. Theforest floor contribution would be greater at peak dischargeand at higher elevations. An end-member mixing modelestimated concentrations of SO₄ ^2-, NO₃ ^-,Cl^-, Ca²⁺, Mg²⁺, Na⁺ and Al that werecomparable to average values measured in the stream. Othervariables (NH₄ ⁺, H⁺, K⁺ and DOC) wereover-estimated implying retention mechanisms operatingoutside the model assumptions.     

Issues with ozone attainment methodology for Houston, TX

To comply with the federal 8-hr ozone standard, the state of Texas is creating a plan for Houston that strictly follows the U.S. Environmental Protection Agency's (EPA) guidance for demonstrating attainment. EPA's attainment guidance methodology has several key assumptions that are demonstrated to not be completely appropriate for the unique observed ozone conditions found in Houston. Houston's ozone violations at monitoring sites are realized as gradual hour-to-hour increases in ozone concentrations, or by large hourly ozone increases that exceed up to 100 parts per billion/hr. Given the time profiles at the violating monitors and those of nearby monitors, these large increases appear to be associated with small parcels of spatially limited plumes of high ozone in a lower background of urban ozone. Some of these high ozone parcels and plumes have been linked to a combination of unique wind conditions and episodic hydrocarbon emission events from the Houston Ship Channel. However, the regulatory air quality model (AQM) does not predict these sharp ozone gradients. Instead, the AQM predicts gradual hourly increases with broad regions of high ozone covering the entire Houston urban core. The AQM model performance can be partly attributed to EPA attainment guidance that prescribes the removal in the baseline model simulation of any episodic hydrocarbon emissions, thereby potentially removing any nontypical causes of ozone exceedances. This paper shows that attainment of all monitors is achieved when days with observed large hourly variability in ozone concentrations are filtered from attainment metrics. Thus, the modeling and observational data support a second unique cause for how ozone is formed in Houston, and the current EPA methodology addresses only one of these two causes.     

Assessment of a regulatory model's performance relative to large spatial heterogeneity in observed ozone in Houston, Texas

In Houston, some of the highest measured 8-hr ozone (O3) peaks are characterized by sudden increases in observed concentrations of at least 40 ppb in 1 hr or 60 ppb in 2 hr. Measurements show that these large hourly changes appear at only a few monitors and span a narrow geographic area, suggesting a spatially heterogeneous field of O3 concentrations. This study assessed whether a regulatory air quality model (AQM) can simulate this observed behavior. The AQM did not reproduce the magnitude or location of some of the highest observed hourly O3 changes, and it also failed to capture the limited spatial extent. On days with measured large hourly changes in O3 concentrations, the AQM predicted high O3 over large regions of Houston, resulting in overpredictions at several monitors. This analysis shows that the model can make high O3, but on these days the predicted spatial field suggests that the model had a different cause. Some observed large hourly changes in O3 concentrations have been linked to random releases of industrial volatile organic compounds (VOCs). In the AQM emission inventory, there are several emission events when an industrial point source increases VOC emissions in excess of 10,000 mol/hr. One instance increased predicted downwind O3 concentrations up to 25 ppb. These results show that the modeling system is responsive to a large VOC release, but the timing and location of the release, and meteorological conditions, are critical requirements. Attainment of the O3 standard requires the use of observational data and AQM predictions. If the large observed hourly changes are indicative of a separate cause of high O3, then the model may not include that cause, which might result in regulators enacting control strategies that could be ineffective.     

Biogeochemical signatures in the lichen Hypogymnia physodes in the mid Urals

Multi-element content and uranium (U) isotopes were investigated in the lichen Hypogymnia physodes (native and transplants) sampled across a 60-km transect, centred on Karabash smelter town, from Turgoyak Lake (SW) to Kyshtym (NE) to investigate the origin of U. Kyshtym was the site of a major nuclear accident in 1957. (234)U/(238)U activity ratios in native thalli sampled during July 2001 were within the natural isotopic ratio in minerals. Uranium/thorium (U/Th) ratios were higher in native thalli towards the NE (average 0.73) than those in the SW (average 0.57). Element signatures in native thalli and transplants suggest U was derived from fossil fuel combustion from Karabash and sources lying further to the east. Systematic and significant U enrichment indicative of a nuclear fuel cycle source was not detected in any sample. Element signatures in epiphytic lichen transplants and native thalli provide a powerful method to evaluate U deposition.     

Automated sizing,counting and identification of zooplankton by pattern recognition

A computerized system was developed to automate the analysis of zooplankton samples. Classification to major taxonomic group was based on discriminant analysis of morphological features. Images were generated either from preserved organisms or from silhouette photographs. The latter technique simplified large-scale sample storage. Accuracy of correct classification, among organisms regularly occurring in New England coastal waters, exceeded 90%. Critical problems were due to limitations inherent to the imaging of low contrast, randomly oriented objects by a vidicon camera. One solution would utilize an incoherent-to-coherent transducer in a binocular field of observation through which plankton entrained in a flowing medium passed.This work was supported in part by NOAA grant NA80AA-4 00023     

Assessing the recovery of lakes in southeastern Canada from the effects of acidic deposition

Reductions in North American sulfur dioxide (SO2) emissions promoted expectations that aquatic ecosystems in southeastern Canada would soon recover from acidification. Only lakes located near smelters that have dramatically reduced emissions approach this expectation. Lakes in the Atlantic provinces, Quebec and Ontario affected only by long-range sources show a general decline in sulfate (SO4(2-)) concentrations, but with a relatively smaller compensating increase in pH or alkalinity. Several factors may contribute to the constrained (or most likely delayed) acidity response: declining base cation concentrations, drought-induced mobilization of SO4(2-), damaged internal alkalinity generation mechanisms, and perhaps increasing nitrate or organic anion levels. Monitoring to detect biological recovery in southeastern Canada is extremely limited, but where it occurs, there is little evidence of recovery outside of the Sudbury/Killarney area. Both the occurrence of Atlantic salmon in Nova Scotia rivers and the breeding success of Common Loons in Ontario lakes are in fact declining although factors beyond acidification also play a role. Chemical and biological models predict that much greater SO2 emission reductions than those presently required by legislation will be needed to promote widespread chemical and latterly, biological recovery. It may be unrealistic to expect that pre-industrial chemical and biological conditions can ever be reestablished in many lakes of southeastern Canada.     

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 SO4 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).     

Monitoring the results of Canada/U.S.A acid rain control programs: some lake responses

Aquatic acidification by deposition of airborne pollutants emerged as an environmental issue in southeastern Canada during the 1970s. Drawing information from the extensive research and monitoring programs, a sequence of issue assessments demonstrated the necessity of reducing the anthropogenic emissions of acidifying pollutants, particularly sulphur dioxide (SO₂). The 1991 Canada-U.S. Air Quality Agreement (AQA) was negotiated to reduce North American SO₂ emissions by 40% relative to 1980 levels by 2010, and at present, both countries have reduced emissions beyond their AQA commitment. In response to reduced SO₂ emissions, atmospheric deposition of sulphate (SO₄ ^2–) and SO₄ ^2– concentrations in many lakes have declined, particularly in south-central Ontario and southern Québec. Sulphate deposition still exceeds aquatic critical loads throughout southeastern Canada however. Increasing pH or alkalinity (commonly deemed recovery) has been observed in only some lakes. Several biogeochemical factors have intervened to modify the lake chemistry response to reduced SO₄ ^2– input, notably release of stored SO₄ ^2– from wetlands following periods of drought and reduction in the export of base cations from terrestrial soils. Three examples from Ontario are presented to illustrate these responses. Significant increases in pH and alkalinity have been observed in many lakes in the Sudbury area of Ontario due to the large reductions in local SO₂ emissions; early-stage biological recovery is evident in these lakes. An integrated assessment model predicts that AQA emission reductions will not be sufficient to promote widespread chemical or biological recovery of Canadian lakes. Monitoring and modeling are mutually supporting assessment activities and both must continue.