15. Characteristic of the canopy throughfall and soil solutions in a pine stand in Chojnów Forest District

Magdalena Janek

Research conducted in the period from July to December 2003 pointed out to the high temporal and spatial variation in the amount of waters beneath tree crowns, so-called canopy throughfall (Fig. 22). The sum of atmospheric precipitation over the half year was 274 mm, thus the amount of annual throughfall waters was estimated at about 550 mm.

In 2003, seasonal changes in some chemical parameters of precipitation were observed. The value for pH of the throughfall waters during the winter season was more acid than in warmer months (Fig. 23). At the same time a steady increase in electrolytic conductivity was noted in the second half of the year. The values for pH in the throughfall water samples raged from 3.75 to 6.51 and for the conductivity - from 11 to 178 ľSˇcm^-1.

The concentrations of a many ions in the throughfall waters on the POP in the Chojnów Forest District were higher in the winter than in the summer. The maximal concentration of potassium, calcium, magnesium and phosphorus were recorded during the autumn season. This might be due to the leaching of ions from needles.

The amounts of the stemflow waters on pines in Chojnów Forest District was insignificant particularly for the trees representing lower diameter classes. The chemistry of the stemflow was more acid than the canopy throughfall. The value for pH of samples was within a range2.98 and 5.68. The concentrations ions in the stemflow were higher than those in the canopy throughfall and their conductivity reached the values even higher than 800 ľSˇcm^-1.

The amounts of soil waters collected in lysimeters during the research was highly varied and depended on climatic conditions, especially on the amount of atmospheric precipitation and temperature (Fig. 24). Seasonally the amount of waters collected in lysimeters was scarce or could not be collected particularly from the depth of 50 cm. During the summer season with persistent droughts, i.e. small amounts of water in the soil, samples could not be collected because of the strengths higher than 0.7 mB (subpressure in lysimeters). In the winter season, after the first frosts, water samples were not collected.

The electrolytic conductivity of soil waters collected from a depth of 25 cm and 50 cm was varied: the majority of measurements was within a range 40-130 ľS cm^-1. At the same time, pH of soil waters from the both depths ranged (in majority of cases) from 4.0 to 5.5. After six months, there was a notable decrease in the pH values and an increase in concentrations of aluminium and sulphate ions in soil waters from the summer to winter season.

A high variation in soil water chemistry between lysimeters (located on the diagonal of the observation plots) and lack of regular differences between horizons on which lysimeters had been located in the ecosystem was probably due to the occurrence of soils with many genetic horizons and layers.

The ability of soils to neutralise the acidic deposit is expressed in the molar ratio of calcium to aluminium or magnesium to aluminium in soil solutions. The calcium to aluminium ratio in the Chojnów Forest District was on average 1.16 in the soil waters from a depth of 25 cm and 3.03 from a depth of 50 cm (Fig. 25).

The greatest deposit of alkaline ions sums of these ions prevailed. Similar variation was found for the magnesium to aluminium ratio: 0.36 in the soil waters from a depth of 25 cm and 0.77 from a depth of 50 cm. The threshold values were 1.0 for the calcium to aluminium ratio and 0.1 for the magnesium to aluminium [18]. Measurements from the second-level POP located in the Chojnów Forest District account for the lack of threat to nutritional potential of trees with calcium and magnesium.

Special attention should be given to the ratio of calcium to sulphur in the soil water. The Ca:S ratio can indicate both the movement of sulphate ions from the surface downward the soil profile and an accompanying increase of calcium solubility .The value of the calcium to sulphur molar ratio in the soil waters in Chojnów stands was below one and deceased with the depth despite higher saturation of the sorption complex of lower soil horizons with alkaline ions (Fig. 25).