THE EFFECT OF EL NIÑO-RELATED DROUGHT ON THE RECOVERY OF ACIDIFIED LAKES

Although SO₂ emissions and deposition rates havedeclined substantially since the implementation of sulphuremission control programmes in North America [1], recovery(measured as decreases in concentrations) of affected lakes in central Ontario has been much less substantial thananticipated based on the decrease in deposition. The slowrecovery is attributed to the reoxidation and release of storedsulphur in catchments. Reduced sulphur retained in previousyears when sulphur deposition was higher is exposed to air andoxidized during severe droughts, then exported duringsubsequent wet periods. Elevated stream concentrations and export rates occur in the autumns of yearswith prolonged severe droughts, particularly in catchments withextensive wetlands. Drought in our study catchments occurred inyears following strong El Niño events. When the SouthernOscillation Index (SOI) was strongly negative (1976–77, 1982–83,1986–87, 1991–92, 1993–94) the frequency of occurrence ofdrought the following summer in small catchments with shallowoverburden was extremely high. A lakes rate of recovery fromacidification depends upon the amount of excess reduced Sthat has been stored in anoxic zones in the catchment (largely afunction of the extent of wetlands) during years of elevated Sdeposition rates, and the frequency and severity of droughts. Iflong-term changes in global or regional climate alter thefrequency or magnitude of El Niño-related droughts, therecovery of acidified lakes will be affected.     

IMPACTS OF VISITORS ON SOIL AND VEGETATION OF THE RECREATIONAL AREA “NACIMIENTO DEL RÍO MUNDO” (CASTILLA-LA MANCHA, SPAIN)

This study examines the effects of recreational use on the soil and vegetation at a site of ecological importance (Nacimiento del Río Mundo, Albacete, Spain). The most visited sites showed increased soil compaction of approximately 50%, bare ground increase to 61 ± 10% and a decrease in richness (from 25 ± 2 to 15 ± 2 species), diversity (from 4.0 ± 0.1 to 2.7 ± 0.4) and stratification of plant species (from 80 ± 11 to 21 ± 4%). The most visited sites had 90% less plant species as compared to the least visited. Intense use was associated with the presence of nitrophilous plant and vegetal species with a morphology adapted to heavy trampling. The recreational areas showed a distribution pattern of impact radiating outwards from the most used and degraded point. At the most visited point, Los Chorros (the spring of the river), the impact radiated outwards for about 20 m. A pilot experiment examining the effects of one-year restriction to visitors for access to a formerly impacted area showed a plant cover increase by anthropic and not by native species of 57 percent units.     

CHANGES IN ACID PRECIPITATION-RELATED WATER CHEMISTRY OF LAKES FROM SOUTHWESTERN NEW BRUNSWICK, CANADA, 1986–2001

Between 1986 and 2001, thirty-nine lakes in southwestern New Brunswick in Atlantic Canada were surveyed for acid precipitation-related water quality changes. Most of the study lakes are located on granite bedrock and represent the most acid sensitive lakes in the province. Between 1987 and 1992, hydrogen ion deposition to the lake study area averaged 452 eq ha^–1 yr^–1, compared to 338 eq ha^–1 yr^–1 between 1993 and 2000, a 25% reduction. The lake chemistry data were evaluated by dividing the lakes into four clusters for each survey year based on their acid neutralizing capacity. Twenty percent of the lakes (cluster IV) had an average ANC of 40 eq L^–1or greater and maintained an average pH of greater than 6 over the duration of the study period. A pH of 6 or greater is considered a healthy benchmark for maintaining biodiversity. The remaining 31 lakes (clusters I to III) had an average ANC of less than 40 eq L^–1and maintained an average pH of less than 6. Other lake chemistry changes included a general decline in lake sulphate and colour over the duration of the survey period, followed by more recent improvements in calcium ion, pH and ANC, and notably higher but declining aluminum levels in lower ANC and pH lakes. Nitrate accounted for 37% of the acid deposition to the study area, however it was not detectable in the lakes. Although acid deposition has declined and these lakes are beginning to show signs of acid recovery, 80% of the study lakes remain acid sensitive having little buffering capacity with low calcium, pH and ANC.     

A SAS® CODE TO CORRECT FOR NON-NORMALITY AND NON-CONSTANT VARIANCE IN REGRESSION AND ANOVA MODELS USING THE BOX–COX METHOD OF POWER TRANSFORMATION

A computer program written in SAS ® code for theBox–Cox family of powertransformations is presented. The purpose of the program is tosuggest a powertransformation for the positive continuous response variablesin only regression and ANOVAmodels. A brief overview of data transformation in regressionand analysis of variance is given.An example using real data from the U.S. EnvironmentalProtection AgencysEnvironmental Monitoring and Assessment Program/Estuaries(EMAP-E) illustrates the useof the program.