State of the Greater Fundy Ecosystem - Mass exports of the Point Wolfe River

GREATER FUNDY ECOSYSTEM RESEARCH PROJECT

UNB Faculty of Forestry and Environmental Management

State of the Greater Fundy Ecosystem

The Impact of Forest Practices on Chemical Mass Exports in the Point Wolfe River 1972-1994

Joseph Pomeroy, Tom Pollock, and D. Lockerbie
Environment Canada, Environmental Conservation Branch
Moncton, N.B. E1A 6S8

The chemical mass exports in the Point Wolfe River over the past 20 years were examined to assess the impacts of forestry practices on water quality and quantity. The data considered in the assessment included the chemistry and discharge of the river and areas of historic clear cuts, partial cuts, planted areas and roads. To compare the various types of forestry practices, the slope, soil, drainage, distance from the watercourses and location of activities were factored into each year of data.

The Point Wolfe River is located in south-east New Brunswick in the Fundy Plateau and Fundy Coastal ecodistricts. The upper part of the basin is privately owned whereas the lower section is protected by Fundy National Park.

Over the past century the Point Wolfe River basin has been continuously harvested. In 1970 the upper basin adjacent to Fundy National Park was purchased by J.D. Irving Pulp and Paper. This company has maintained records of forest activity type, area and dates of activities for the basin since that time. Prior to 1970 compiled records are not available although some information can be found in hand drafted maps kept on file at the Irving head office in Saint John, N.B. In the early 1970's Environment Canada began collecting discharge and stream chemistry data for the Point Wolfe River.

METHOD

Four main data sets were used in the forestry-mass export analysis for the Point Wolfe River. The water discharge, chemistry and precipitation data for 1970 to 1992 were obtained from Environment Canada (Atmospheric Environmental Branch and the Environmental Quality Laboratory). A digitized GIS map of the watershed was obtained from the Fundy Model Forest Project. The attributes selected from the GIS dataset include primary tree species, slope (calculated), soil and drainage, and type and date of forest activity at the time of digitizing. The GIS dataset had dates associated with forestry activity only after 1970. In 1970 the upper basin was bought by J.D. Irving Pulp and Paper and the type and date of each activity was recorded. Prior to 1970 the dates associated with the forest activities are not compiled. This report has grouped these as a "pre-1970" category.

To assimilate the impact of individual years of forest activity the GIS dataset was reclassified using the software SPANS so that for each year of forest activity there is an associated map. In all there were 14 maps. Several assumptions were made during the reclassifications in order to provide an accurate assessment of forestry practices. A clear cut, partial cut, road or plantation with an associated date is assumed to have a potential impact for five years. All activities will appear in five maps with the highest impact in the current year and the least impact in the last map or year five. The activity is then removed from the dataset. A plantation with an associated date is assumed to have been cut four years prior; therefore, the plantation is included in the database as a clear cut for four years prior to the current map.

Table 1 is an example of four of the 14 maps and their associated layers of information. Note that in 1975 the clear cut is current and so it is considered a primary impact activity. In the map "imp76" , the 1975 clearcut is one year old and so moves to a secondary impact activity. The 1975 clearcut appeared on maps for five more years before being removed in year 1981.

By transforming the data into a Spans quadtree each year of forestry activity can be associated with information on the area of activity in each class of slope, activity in proximity to a watercourse, activity within an individual sub-basin, and activity in relation to soil, drainage and tree species. Figure 1 shows a modified version of the Spans GIS map for plantations -1976 and clear cuts -1975. The original quadtree map differentiates between differing types of forest activities.

To associate the spatial data with changes in mass export, the monthly water chemistry data was used in a regression with the daily mean discharge to calculate daily mean mass export. A selection of the most appropriate water chemistry variables were then chosen to use as indicators. The daily mass exports were then summed to annual mass exports and graphed as a time series. Spatial changes were then associated with changes in mass exports.

RESULTS

Dissolved potassium was one of the variables chosen as a indicator of forest activity impact. The annual mass export of potassium clearly identify the years in which an elevated mass export occurred (Figure 2).

Elevated mass exports can be attributed to either a higher runoff or an increase in ion concentration in the stream. In this assessment the higher concentrations of ions are attributed to forestry activities. To determine if the cause of the increased mass exports was a higher runoff, the ratios of runoff to precipitation for the years of 1965 to 1992 were calculated (Figure 3). Generally, if the mass export is high and the ratio is low then an increase in ion concentration is suspected. If the mass export is high and the ratio is high then a increased runoff is suspected. Other factors are also considered in the analysis to support the conclusions.

PRELIMINARY DISCUSSION

The potassium mass exports peaked during 1967, 1973, 1975 to 1977, 1979, 1983 and 1990. The runoff /precipitation ratio indicates that the runoff was greater than the precipitation in 1967, 1973 and in 1981. The high ratio of 1967 may indicate theimpacts of forestry although mass exports are not available for this period. The high runoff/precipitation ratio of 1973 is associated with an elevated mass export which suggest that the mass export is attributed to the higher runoff. The influence of the greater amount of runoff is plausible because no forest activity was known to have occurred during the 1970-1973 period.

The elevated mass export which occurred in 1977 coincide with a 77 percent discharge/precipitation ratio. As there was no forest activity in 1977 the mass export is likely the results of forestry activities which occurred in 1975 and 1976. In 1975, 0.33 km2 was clear cut in three sub-basins and along the river. Most of the cutting occurred at a slope of less than 18 % although a small percentage occurred between a slope of 18 and 54 %. In the following year 1.12 km2 was planted in eight sub-basins along the southern side of the basin. Eighty-seven percent of the planting occurred on a slope of less than 10 % although planting did occur on slopes up to 34 %. Five percent of the planting occurred within 30 metres of the river and 73 % occurred between 100 and 250 metres.

The mass export between 1976 and 1977 increased more than between 1975 and 1976. The runoff/precipitation ratio decreased during the same period. In 1977 the clear cut was in a second year of growth therefore the release of potassium should be minimal. The 1976 planting was in its first post year and literature states that potassium release should be greatest during the first post year. Based on the above analyses and the probability that the areas were scarified prior to planting the practices used in 1976 appeared to have had a major impact on the mass exports of the Point Wolfe River.

CONCLUSION

Using data of discharge, precipitation, water chemistry and land features, the impact of forestry on the water of the Point Wolfe River is being assessed. The various yearly forestry activities are defined spatially using Spans GIS software and with consideration of landscape features (slope, buffer distance, soil). The runoff/precipitation ratio provides an indicator to determine if a particular year of mass export is associated with high or low runoff. The analysis of the 1973 to 1977 period indicates that the forest planting methods (scarification) in combination with the slope, and distance to the river caused potassium mass exports to peak in 1977. A more complete analysis is available in the original report.

- Table of Contents

- View other case studies

- Bibliography