State of the Greater Fundy Ecosystem - Hayward Brook Stream hydrochemistry

GREATER FUNDY ECOSYSTEM RESEARCH PROJECT

UNB Faculty of Forestry and Environmental Management

State of the Greater Fundy Ecosystem

Hayward Brook Watershed Study:
Stream Hydrochemistry

Joseph Pomeroy
Environment Canada, Environmental Conservation Branch
Moncton, N.B. E1A 6S8

Modern-day forestry can affect the ecology of streams by altering adjacent surface and groundwater flows, increasing water discharge rates, increasing streambank erosion and suspended sediment loads, increasing nutrient inflow, decreasing inputs of logs and other coarse woody debris, and increasing water temperatures through the removal of protective vegetation cover .

GOALS

The Hayward Brook hydrogeochemical study was established to determine changes in the chemistry and discharge of stream water as a result of ongoing forestry practices. Much of the following summary relates to pre-harvest conditions of these streams. Presently, the first year of post-harvest data is being approved for interpretation. The second year of post harvest monitoring will occur in 1997.

METHODS

Seven water monitoring stations were established downstream of the study plots that were being used for monitoring birds and small mammals in the watershed. Water quality and flow were measured at the stations. Surface water samples and various other physical measurements were also collected.

Surface water samples were taken at Hayward and Holmes Brooks on a monthly or more frequent basis since July 1993. From the time timber harvesting began in June 1995 to when it was completed in November 1995, sampling was undertaken weekly and during rain events. Since the winter of 1995, sampling has returned to a monthly schedule and during rain events. Automated monitoring stations have been used to record stream height and selected water quality variables every 30 minutes.

RESULTS

The discharge data from the six automated stations is summarized in Table 1. Sites 3 and 4, the no-treatment sites, had similar discharges over the 14 month period, although station 4 experienced more flash discharges. Site 5 (30 m buffer) had a drainage basin and mean and maximum rates of discharge three times higher than Site 6, a 30 m buffer site. Minimum rates of discharge for both sites, however, are identical, indicating that quantities of groundwater for both are similar.

The discharge per unit surface area for each site is obtained by dividing total discharge by basin size (Table 2). General similarity is shown in flow among the sites. The variability in maximum discharge comes from quick or flash floods.

Surface water samples were analyzed for 21 variables in five categories: 1) physical parameters (pH, conductance, turbidity, colour), 2) nutrients (nitrogen, phosphorus), 3) major ions (calcium, sulphate, chloride, sodium, etc...), 4) metals (zinc, aluminum), and 5) suspended sediment. Automated data consists of physical variables (pH, conductivity, temperature, turbidity, dissolved oxygen).

Stations located in the headwaters of Hayward and Holmes Brooks (stations 1,2,3) had lower conductance readings with less variation than stations located downstream. Conductance is a measure of the ability of a solution to carry an electrical charge. The stations with higher average conductivity tend to have larger sources of salt deposits in their basins. During wet seasons, high discharge dilutes the ions and lowers the conductance. Conductance reaches its highest levels during the dry seasons.

The pH in the streams are all near 7.0 . The characteristics of the surficial geology have much to do with the level of acidity in the soils and hence the waters.

The colour of the water samples taken from the streams at Hayward Brook were clear and turbidity was low indicating that disturbance is minimal.

Dissolved major ions or "components of salt" leach from soils into the water. Surface water samples were analyzed for sodium, sulphate, chloride, calcium, potassium, and magnesium. Calcium carbonate was highest in the southern tributaries whereas sodium carbonate was highest in the northern tributaries.

Nitrate is usually found in low concentrations because of its demand by growing plants. Nitrogen concentrations may vary due to the presence of plant and algae material which contains nitrogen compounds. Phosphorus is also usually present in low concentrations in a natural system. Phosphorous was present in the streams in low concentrations indicating that it was being taken up by growing vegetation.

In June 1995, timber harvesting in the Hayward Brook study area began. A road was constructed to access the area of stations 5 and 6 (30 m buffer zone). The road included the installation of a galvanized culvert 100 metres above station 6. The culvert resulted in a three fold increase in the zinc concentrations in the stream. Station 6 was also affected by the presence of an old woods road which crosses the stream just above it. The steepness of this road results in rapid water runoff and soil erosion above station 6. The change in the stream's water quality after a heavy rain storm in November 1995 demonstrates the impact of erosion and the importance of a riparian buffer strip.

Control Plots (No Treatment):

Stations 3 and 4 were located downstream of the plots which received no cutting. The plot above station 3 is composed of a forest of intolerant hardwoods and spruce while the plot above station 4 is a mixture of regenerating hardwood/softwood and intolerant hardwood-spruce. Geology tends to be the major influence on water chemistry variability in these plots. The pH average for both sites approaches 7.0. Turbidity and colour are low at both stations. Slightly lower concentrations of colour and turbidity at station 3 are due to its narrowness and the predominantly pebbled bed interspersed with vegetation. Suspended sediments tend to settle out of the water column in pools caused by fallen logs or other obstructions to stream flow.

During the pre-treatment measurements, nitrate at all sites was below 0.05 mg/L, indicating a high demand by plants and a growing forest.

30 m Buffer Plots:

Stations 5 and 6 are located downstream of plots which were clearcut with a 30 m wide forested buffer retained on both sides of the stream. Forest cover for both streams consisted of intolerant or regenerating hardwood-spruce. The elevation of the headwaters of stream 5 are much steeper than stream 6 and this contributes to a more rapid run off and shorter lag time. Stream 6 has a higher ionic content due to a spring with an elevated conductance. The pH of both streams is similar except for a minimum pH value at Station 6 due to the influence of organic acids from wetlands. Stream 6 is 1 m wide and 30 cm deep and has a low discharge. As such, minor inputs of organic acids can influence its chemistry during dry periods. Stream 5 is 3-4 m wide and 50 - 100 cm deep with small to medium sized rocks and pools occurring where trees have blocked the stream. Stream 6 has a higher turbidity and degree of colour than Stream 5 due to its size and bed type but also from an inflow of suspended sediment from the erosion of an abandoned road which crosses between plots 6 and 3.

Nitrogen and nitrate concentrations are low in both streams, suggesting that adjacent vegetation is utilizing available nutrients. Concentrations of metals are low in stream 5 because of the cobble stream bed. Station 6 experienced higher concentrations of zinc following the placement of a galvanised culvert during road construction. This culvert leached zinc 3-4 times above the detection limit for a period of five months following its construction. The zinc eventually accumulated in the stream bed. A storm in September 1995 released the zinc and resulted in a high concentration of the metal in the water. The concentration exceeded the 0.003 mg/L zinc guideline for the protection of aquatic life during this storm event.

60 m Buffer Plots:

Stations 9 and 10 are located downstream of plots which were clearcut with a 60 m wide forested buffer retained along both sides of the stream. The stream at station 9 is 4-5 m wide with a rocky bed and a forest along the banks of Spruce-Balsam Fir with regenerating hardwood. Station 10 is located upstream of station 9. Here the stream is 1-3 m wide with a sandy bed. Because of its position, station 9 measures the impacts of the treatments on both plots and was the only plot monitored for water chemistry and discharge. Station 9 is located on soils with abundant sodium and chloride ions. Station 9 experienced a low minimum pH during a storm in November 1995. The storm and the high discharge likely increased the concentrations of organic acids and bicarbonate buffer within the stream resulting in its increased alkalinity. Concentrations of metals were low at Station 9 and similar to concentrations at Station 5.

Best Management Plots:

Stations 1 and 2 are located downstream of plots which were treated with a combination of clearcut and selection cut within the buffer zone. Stream 2 is 0.5 m wide, 15-30 cm deep and heavily vegetated. The stream banks are steep with rock outcrops covered in vegetation and ridges covered with White and Red Pine. The slow moving stream forms many pools which accumulate plant matter. One part of the stream includes the remains of old logs used as a horse haul crossing. Stream 1 is 1 m wide, 25-50 cm deep and with a sandy, partially vegetated bottom. The forest cover along the banks consists of large Aspen, Fir and Red and White Pines.

The selective harvest plan for these plots was developed by Dr. Helmut Krause of UNB. The plan assumes that, depending on specific site conditions (stream edge slope, drainage, soil and vegetation) a degree of selective harvesting is possible within protected forest buffers without adverse impacts on the aquatic environment. Stream 1 was clear cut or selectively cut down to the riparian buffer. Within this buffer a selective harvest plan was followed. Stream 2 was also clear cut down to the buffer but no trees were removed within the buffer.

The waters at both stations showed low conductivity similar to the readings taken at Station 3, which is located on a similar forest soil unit. Acidity at both stations is similar with a pH value of 7.0. Lower concentrations of major ions result in lower concentrations of alkalinity and less buffering capacity. Concentrations of nitrate and nitrogen and metal are low and similar to the other stations.

IMPLICATIONS FOR MANAGEMENT

The pre-harvest data provides an important baseline data set by which to compare post-harvest effects. The pre-harvest data suggest that streams in the study area represent a healthy ecosystem. Although there are physical differences between the streams, these differences can be incorporated into the assessment of post-harvest data.

Further Reading:

Parker, G., J. Pomeroy and A. Chaisson. 1997. The Hayward Brook Watershed Study ( a research project of the Fundy Model Forest): Interim report (1993-1995). Fundy Model Forest, Sussex, N.B.

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