THE IMPACT OF ANTHROPOPREASSURE AND WEATHER CONDITIONS ON THE MINERAL NITROGEN CONTENT IN THE ORGANIC SOILS FROM FEN PEATLANDS ( STOŁOWE MOUNTAINS , SW POLAND )

1234Abstract. At the turn of the 19th and 20th centuries large peatland areas of the Stołowe Mountains were drained for the forestry use. The aim of the study was to assess the real impact of the natural (climate) and anthropogenic (forestry drainage) factors on the actual nitrogen mineralization in the shallow organic soils in the Stołowe Mountains National Park (SMNP). For the needs of the study, two research transects were established on the fen peatlands located in the central part of the SMNP. Each transect consisted of three sampling plots. The soil samples for the basic soil properties analysis were sampled in April, while undisturbed soil samples for mineral nitrogen were collected in April (spring), July (summer) and October (autumn) to show the seasonal dynamics of nitrogen mineralization. The obtained results revealed that the currently investigated fen peatland soils were rather slightly affected by the drainage network remains. A vast domination of ammonium over the nitrate form observed in the study soils during the growing season might indicate a periodical soil moisture increase limiting the mineralization process. The amount of precipitation and soil moisture had dominant impact on the N mineralization process, especially on the N-NO3 concentrations.


INTRODUCTION
The peatland soils, primarily for the last two centuries, were exposed to drainage for agricultural or forestry use (Ferrati et al. 2005;Limpens et al. 2008).This harmful process also concerned mountain peatlands, drained mainly for forestry use (Bogacz et al. 2012;Łajczak 2013).At the turn of the 19 th and 20 th centuries peatland ecosystems in the Stołowe Mountains (Central Sudetes) were drained to obtain a new area for afforestation by spruce monoculture (Stark 1936;Jędryszczak and Miścicki, 2001).Due to artificial drainage, a rapid decrease of the groundwater table is observed (Ferrati et al. 2005).This phenomenon increases aerobic conditions in organic soils, which promotes physical and chemical changes (Sokołowska et al. 2005;Markiewicz et al. 2015).Particular the mineralization of soil organic matter resulted in great amount of biogenic components released are the most common phenomenon (Pawluczuk and Szymczyk, 2008).In the soil organic matter mineralization process mainly mineral nitrogen forms (N-NO 3 and N-NH 4 ) are release.Actual weather conditions (Jason et al. 2004), soil moisture (Devito et al. 1999), organic matter type (Purvanto et al. 2005) and type of peatland management mainly affect the intensity of the indicated process (Tripathi and Sighn, 2009).In Poland, up till then, the aforementioned problem was described mainly with respect to lowland peatlands drained for agriculture (e.g., Pawluczuk 2006; Pawluczuk 2008; Smólczyński and Orzechowski, 2009).However, it is also an important problem for degraded mountain mires ecosystems (e.g., Basiliko  The main objective of the study was to investigate which natural (climate) or anthropogenic (drainage, forestry use) factors have dominant impact on actual nitrogen mineralization in the organic soils from the fen peatlands in the Stołowe Mountains National Park.Additionally, the paper will tackle the problem of the marked organic soil horizons with mineral material admixture according to the Polish Soil Classification (PSC 2011).

MATERIALS AND METHODS
For the needs of the study two research transects were established on the fen peatlands (A and B) located on the northern slope of Skalniak ridge -the second highest elevation in the SMNP.Each transect consisted of three sampling plots (Fig. 1, Tab. 1).The study site A is a spring fen peatland supply in water by seepages of highly mineralized groundwater (soligenic), while the fen peatland B in the edge parts is also seasonally fed by a local stream (Czerwona Woda) -fluviogenic type (Glina, 2014).The peatland B is covered by spruce monoculture, with addition of birch and beech.In the site A, all the tree species were cut down in 2010, nowadays the indicated peatland is covered mainly by sedge communities, grasses and shrubs.Both peatlands were developed over the sandstone-siltstone bedrock (Glina 2014).The field works were conducted and the samples were collected during the growing season in 2012, when the mean annual air temperature was 6.7°C, amounting to 17.0°C in the warmest month (July), and decreasing to -7.5°C in the coldest one (February).The annual sum of precipitation in 2012 was 786 mm, reaching a maximum level in July (169 mm) and a minimum one in March (14 mm) -the data come from the meteorological station in Kudowa Zdrój (Fig. 2).The soil samples for the basic soil properties analysis (Tab.2) were sampled in March.The undisturbed soil samples were collected in stainless steel rings (100 cm 3 ) in April (spring), July (summer) and October (autumn) to show the seasonal dynamics of nitrogen mineralization.Additionally, six piezometers were installed along the research transects for actual water table measurement.Before the laboratory analysis each soil sample was divided into two pieces.In fresh material the degree of peat decomposition was determined using the fiber volume method (Lynn et al. 1974).The remaining soil samples, after being dried at 105 °C, mixed and freed from plant remains facilitated the determination of the following soil properties: ash content after placing dried samples for 5h in a muffle furnace at 550 o C (Heiri et al. 2001), pH in distilled water and 1M KCl solutions (soil to water ratio 1:2.5) potentiometrically, total organic carbon (TOC) by catalytic dry combustion at 600°C in Ströhlein CS-mat 5500 analyzer and total nitrogen (TN) by Kjeldahl method using Büchii analyzer.The contents of N-NO 3 and N-NH 4 were measured spectrometrically in 1% K 2 SO 4 extracts with Nessler's reagent (for NH 4 ) and phenol disulfonic acid (for NO 3 ) after 14 days incubations at 28°C (Gotkiewicz 1974) in climatic chambers (THe AG-1440), with daily controls of the soil moisture.All the soil samples were analyzed in triplicate.Based on the morphological features and physico-chemical properties, the soils were classified according to the Polish Soil Classification (PSC 2011) and FAO-WRB (IUSS Working Group WRB, 2015).The sta-tistical analysis of variance (ANOVA) was made using the Statistica 12 software system (StatSoft Inc., Tulsa, OK).The obtained results of nitrogen mineralization were collated with the actual soil moisture and meteorological data (monthly mean air temperature and monthly sum of precipitation).

Soil classification and morphology
Based on the field survey and the basic laboratory analysis (Tab.2) the investigated shallow organic soils were classified as Sapric Histosols, with addition of various principal and supplementary qualifiers (IUSS Working Group WRB, 2015).In the PSC (2011) soil profiles 1, 3 and 6 represented sapric murshic peat soils (in Polish: gleby organiczne saprowo-murszowe), while soil profiles 2, 4 and 5 were classified as shallow sapric peat soils (in Polish: gleby torfowe saprowe płytkie) (see Tab. 1).Moorsh horizons with aggregate structure observed in the topsoil of profiles 1, 3 and 6 constitute a visible effect in soil morphology of the long-term forestry drainage in SMNP.The indicated soils were under medium stage of mursh process -MtII (profile 1 and 3) and strong stage of mursh process -MtIII (profile 6) according to classification proposed by Okruszko (1993).The PSC (2011) assumes that admixture of fluvial mineral material in the organic soils should be marked as C.This symbol is also used for marking underlying mineral material of organic soils, which frequently have different texture and genesis than fluvial material in the topsoil.The described situation occurs in the study soil profiles 4 and 6, where underlying bedrock (C) is loamy textured material, while in the topsoil admixture of sandy material (derived from weathering of sandstones) transported by local stream "Czerwona Woda" is observed.The substantial admixture of mineral material in the surface horizons of organic soils from the Stołowe Mountains were also described by Bogacz and Roszkowicz (2010).According to the actual definition in the PSC (2011) the soil horizons should be marked as Oa/C, which indicates that admixture of underlying material occurs in the topsoil of the investigated soil profiles.For that reason, it is proposed to add "+" to organic horizon symbol with significant mineral material admixture in the upper 50 cm of the soil profile -Oa(+),which improves the readability of organic soil morphology.This proposal should be considered in the next development of the Polish Soils Classification update.

Seasonal dynamics of nitrogen mineralization
The organic matter mineralization, as indicated by the TOC/TN ratio, showed a differentiation between the studied soils (Tab.2).The lowest ratios, mainly below 20, were observed in the shallow organic soils from the study site A. It indicates a periodical drying of soils and slightly organic matter mineralization (Bogacz and Roszkowicz, 2010).The values of TOC/TN ratio below 16 (upper 35 cm in the profile 3), according to Bieniek et.al. (2007) might indicate low susceptibility to further transformation of soil organic matter.In the soil profiles 4, 5 and 6 (site B) the measured ratios were slightly higher and ranged between 18.1 and 30.4.A lower TOC/TN value in the fen peatland A than that in the peatland B may be the result of local land relief.The rapid water outflow in the sloped (4°) treeless area (site A) might reinforce the drainage of peatland.
The results of seasonal dynamics of the measured mineral nitrate forms (N-NH 4 and N-NO 3 ) demonstrated weak seasonal variability of N mineralization.The recorded content of ammonium and nitrate forms in the fen peatlands soils from SMNP were very low, but vast domination of N-NH 4 over the N-NO 3 form was observed (Tab. 3 and 4).The highest mean content of N-NO 3 among study soils were found during the spring period, except soil profile 6, where the highest concentrations of nitrate forms were observed in summer (Table 4).In this work statistically weak and significantly negative correlations between nitrate form concentrations and precipitation (r= -0.27; p<0.0001) were observed.In the study A the mean concentration of N-NO 3 in spring (the lowest amount of precipitation) was significantly higher than in summer and autumn, while for the site B, seasonal dependency was not statistically proven (Fig. 3).
No seasonal statistically significant effect on mean N-NH 4 concentration was found, both in soils form the study A and B (Fig. 4).
The comparison of study sites disclosed that during the growing season in 2012 the content of nitrate forms was higher in soils from the transect A, while the ammonium form displayed higher values along the transect B (Tab. 5).The ANO-VA analysis showed statistically significant difference between the mean N-NO 3 (F=7.96;p=0.001) and N-NH 4 (F=15.ation is the effect of periodic high groundwater table, which limits the microbial activity (Bieniek et al. 2007;Makarov et al. 2010).Although it should be noted that the increase of the ammonium form in the topsoil layers may result from the atmospheric deposition in the mountain peatlands (Evans et al. 2000).The N-mineralization in study soils was strongly correlated with the soil moisture (r = -0,65; p<0.0001) and precipitation.The highest concentration of the N-NO 3 was noticed in spring, when low soil moisture level was observed (Tab.3).Davenport and DeMorainvile (2004) reported in a laboratory experiment that the organic soil (peat or mursh), in higher temperature (above 18 0 C) is associated with the increased N mineralization rate.CONCLUSIONS 1.The weak nitrogen mineralization observed in the investigated soils indicated that currently the fen peatland soils in the Stołowe Mountains are under minor impact of the drainage network remains.
2. The vast domination of ammonium over the nitrate form indicates a periodical soil moisture increase, which limits the mineralization process.
3. The statistical analysis showed that the amount of precipitation and actual soil moisture had dominant impact on the N mineralization process, especially the N-NO 3 concentrations in organic soils.

Fig. 1 .
Fig. 1.Localization of the study area and transects sketch

Fig. 2 .
Fig. 2. Temperature and precipitation in the year 2012 5; p=0.00001) concentrations in different seasons (Tab.5).The described results indicate that actual investigated organic soils undergo rather a weak mineralization process.It is confirmed by a great dominance of the ammonium N-NH 4 over the nitrate N-NO 3 forms (Gao et al. 2009).As it was reported by Smólczyński and Orzechowski, (2009), such situ-

Fig. 3 .Fig. 4 .
Fig. 3. Comparison of mean N-NO 3 content between sites A and B during the growing season

TABLE 1 .
STUDY SITES CHARACTERISTIC

TABLE 2 .
BASIC PROPERTIES OF STUDY SOILS (MEAN VALUES) Explanation: RF -rubbed fiber content; TOC -total organic carbon, TN -total nitrogen

TABLE 3 .
STUDY SITE A -DYNAMICS OF NITROGEN MINERALIZATION (MEAN VALUES)

TABLE 4 .
STUDY SITE B -DYNAMICS OF NITROGEN MINERALIZATION (MEAN VALUES)

TABLE 5
Explanation: M -mean, SD -standard deviation; F -analysis of variance ANOVA; p -significance