Quantitative Analysis of the Rate of Geochemical Weathering of Sulfur from Sedimentary Rocks Using Atmospheric Deposition , Concentration and River Discharge Data — A Case Study of the Mountainous Basin of the Tedori River , Japan , over a 16-Year Period

Quantitative analysis of the rate of geochemical weathering of sulfur (S) from sedimentary rocks (GeoS) was conducted using concentration (Cs) and discharge (Qs) data from the Tedori River and atmospheric deposition (AtdepS) in the basin. First, S fluxes were calculated using 16 years of Cs and Qs data. The annual average discharge of S (TotalS) was estimated at 8597 ton·year (117.3 kg·ha·year). Of this, 1331 ton·year was AtdepS (18.2 kg·ha·year) and another 7266 ton·year was GeoS (99.1 kg·ha·year). Monthly changes in TotalS were investigated, which showed that GeoS was highest in summer, because of the air temperature, while AtdepS peaked in winter because of seasonal wind. Using Qs and AtdepS corrected for altitude, TotalS, AtdepS and GeoS were estimated at six sites, and among these sites we found that the TotalS per unit area values were random, depending on the site characteristics. In particular, the discharge from the Kuwajima site was remarkably high suggesting that the sedimentary rocks at this site had higher pyrite content than at the other sites. Finally, we also assessed the relationship between the characteristics of sedimentary rocks and GeoS in a range of rivers in the Hokuriku Region, and found that there was a close relationship between concentrations of greater than 10 mg·l and sedimentary rocks containing the pyrite group. In addition, we estimated that the influence of GeoS was present when the concentration of 2 4 SO  2 4 SO  in river water was greater than 2 3 mg·l in the Hokuriku region.


Introduction
There is great concern about sulfur (S) cycling in a river basin because it is closely related to acid deposition in soil, leads to sulfate contamination of irrigation water and has possible damaging consequences for human health.The S cycle in a mountainous river basin is governed by atmospheric deposition (AtdepS) and geochemical weathering of sedimentary rocks (GeoS).The annual average discharge of S (TotalS) from a basin can be estimated by taking the product of the discharge (Qs) and the concentration of S (Cs) in the river.
Based on the above, the objectives of this research were as follows: 1) to establish weathering rates of the sulfur mineral defined as GeoS using Qs and Cs of the river and AtdepS in the study area; 2) to estimate TotalS discharge from a river basin at various sites both within and beyond the study area; and 3) to investigate the effect of GeoS from sedimentary rocks on different sulfate concentrations in river.
Many studies on geochemical cycling of S have been conducted, including large-scale marine studies.Jamieson et al. carried out a study on the concentrations of sulfate in seawater from sulfur isotopes in sulfide ore [1], while Newton et al. reported large shifts in the isotopic composition of seawater sulfate across the Permian-Triassic boundary in northern Italy [2].Ooki reported size resolved sulfate and ammonium measurements in marine boundary layer from November 2001 to March 2002 over the North and South Pacific [3].
Much research has also been carried out on sulfur cycling in river basins.For example, Norman et al. examined the biogenetic contribution to aerosols and precipitation using isotopes and oxygen [4].Elimaers et al. investigated the effects of climate on sulfate fluxes from forested catchments in south-central Ontario [5].William et al. investigated the change in ion outputs from watersheds resulting from acidification of precipitation [6].Beaulieu et al. modeled the interactions between water and rocks in the Mackenzie Basin; and highlighted the competition between sulfuric and carbonic acid [7].Huang et al. investigated weathering and soil formation rates based on geochemical mass balances in a small forested watershed [8].
Mine drainage water has also been studied by many researchers.Budakoglu et al. investigated the distribution of, and contamination from, sulfur-isotopes related to the Baya Pb-Zn mine in Turkey [9], while Edraki et al. investigated the hydrochemistry, mineralogy and sulfur isotope geochemistry of acid mine drainage at the Mt.Morgan mine, Australia [10].
This study differs from those documented above, in that it reports the results of quantitative analysis of To-talS in a river, in which GeoS has been estimated quantitatively by analysis of Qs, Cs and AtdepS data.To date, there have been very few studies of quantitative analysis of S discharges from river basins [11].

Fundamental Concept of Our Research
We collected Qs and Cs data of river water and the At-depS (wet and dry) in a mountainous basin, to estimate fluxes of GeoS quantitatively, and analyzed the relationships among them.The relationship is relatively simple in mountainous basins when compared with lowland basins, as land use is generally more complicated in lowland basins and may include agricultural land, residential and industrial areas.
The S cycle in this study is based on the hypothesis that the TotalS (the product of Qs and Cs) is consist of AtdepS and GeoS in locations where there is little artificial disturbance (Figure 1).Among them, GeoS is a source of S from inside and AtdepS is an input of S from outside of the basin.The hypothesis contains the change in storage of S in the basin is negligible small due to At-depS without including GeoS, In other words, this study assumes a steady state, in which the effect of AtdepS in the study area remained constant during the study period.

Atomospheric
On the other hand, river basin usually has sedimentary rock layers, which sometimes contain S compounds.These layers will have been subject to long-term weathering, resulting in the release of into the river.SO  This research procedure consists of the three following steps: 1) Estimation of the total outflow of S (TotalS) from a test basin using Qs and Cs; 2) Estimation of AtdepS using 2 4 SO  atmospheric deposition data measured near the test basin; 3) Estimation of GeoS by subtracting the AtdepS from the TotalS.
To verify the relationships mentioned above, longterm data are required to 1) eliminate the short-term variation in stored S inside of the basin, and 2) minimize the influence of high flows through flooding periods on Cs concentrations.In other words, the S cycle is assumed to be in a dynamic steady state as follows: If AtdepS is deposited into a basin, the S will be distributed throughout the soil, water, grass, trees and wild animals.The forest (basin) will gradually become saturated with S, and the excess S from AtdepS will then flow out to the river.If this S cycle continues over a prolonged period, the flow of S in the forest will approach a steady state.Based on the above hypothesis, AtdepS data for a 16-year period (divided into yearly intervals) were analyzed.We applied the approach which has been taken in the nitrogen balance analysis already [12,13].Because the sulfur and nitrogen ions may behave in a similar manner, we applied the same procedure to sulfur analysis.

Research Site
The research site is located in the southern part of Ishikawa prefecture, Japan.The research river is the Tedori River which has an area of 809 km 2 , as shown in Figure 2. The source of the river is at Mount Hakusan, which has an altitude of 2702 m, and flows down a ravine between mountains to Nakajima point (at which point the basin area is 733 km 2 ), from where the river flows through an alluvial fan into the Sea of Japan.The alluvial area comprises developed fertile agricultural land and important industrial and residential areas, all of which are supported by surface water and groundwater from the Tedori River.
Plant cover in the basin varies according to the altitude.There is a mountainous belt (altitude 400 -1500 m), a semi-high mountain belt (1500 -2000 m) and a high mountain belt (>2000 m).The upstream area belongs to the high mountain belt, is dominated by the Hakusan National Park and is covered with low height pine trees.In the semi-high mountain belt there is high mountain grass, known as flower meadow.Betula Ermanii Chanisso and Abies Mariesii Mast are typical of this area, with the former tree more common in higher areas than the latter.In the mountainous area, there are mature high quality beech trees, while Quercus Crisoula Blume and Japan Marple are found in the lowland areas.Red pine trees are found on ridges and cedars are found in the valley areas of mountains [14][15][16].
The catchment is in an area of high precipitation, and the annual average precipitation recorded at Kanazawa is 2348 mm.Of this total, 1059 mm falls between April and September, while 1289 mm falls from October to May, including much snowfall.The average temperature is 14.9˚C, with an average maximum of 26.1˚C recorded in August and an average minimum of 4.0˚C recorded in January.

Investigation of AtdepS, Cs and Qs
The AtdepS was monitored weekly by the Ishikawa pre-fectural government over a 16 year period at the Taiyougaoka site, located at an altitude of 120 m and at a distance of 10 km from the study area [17].The samples were collected by a 20 cm diameter rain gauge.The S in AtdepS was analyzed by the ion chromatograph method.
In addition to wet deposition, there is dry deposition of S from the atmosphere, which was investigated only for years from 2003 to 2007 [18][19][20][21].To account for dry deposition in other years, the average of the dry deposition of S data collected was added to wet deposition of the other years because the ratio of dry deposition to wet deposition was very small.Furthermore, the AtdepS (wet deposit) was investigated at Torigoe, located close to the center of the study area, over 7-year period (1997 and 1999-2004) [17].When compared with the Taiyougaoka and Taiyougaoka data, similar trends are apparent; therefore we considered that the Taiyougaoka data was sufficiently reliable to be used for estimating the quantity of sulfur even though the observation site was located outside of the study area.
To assess the TotalS in the study area, Cs data (as  SO  was measured by the ion chromatograph method.The data were reported in an Annual Report by the Ishikawa Water Supply Office of the Tedori River [21]. The Qs was recorded at the Nakajima site, which is located in the lower reaches of the basin near the Hirose site (Figure 2).The Qs data were supplied by the Hokuriku Hydroelectric Company.The TotalS outflow from the basin was estimated by multiplying the Qs and Cs.

Altitude Correction for Qs and AtdepS
To estimate the TotalS at the above six sites, Qs and At-depS had to be corrected for Qs and AtdepS based on the altitude because both are strongly affected by basin height.Full details of how we analyzed the altitude dependence of Qs and AtdepS are available elsewhere [12,13], but brief details of the procedure are as follows: The altitude correction was conducted at 200 m intervals.To make the calculation simple, the weighted central height of the basin was obtained previously by the following formula.
Here, Hc(m) is the central altitude within the 200 m belt weighted area, Hi(m) is the central altitude of the each belt, Ai (ha) is the area of the belt, n is the number of belts and A (ha) is the total area of the test basin sites.
The Hc for relevant test sites is shown in Table 1.

Altitude Dependence of Qs
Qs in the Tedori River basin at Kanazawa was not recorded, but was estimated using precipitation minus evapotranspiration.The evapotranspiration was estimated by complementary relationship using the Penman equation.The result was obtained using 16 years data.
The relationship between the two sites is: Here, the unit of Qs is mm•year −1 .
The altitude dependence of Qs between sites at Kanazawa (Qs is 1603 mm•year −1 and Hc is 7 m) and Nakajima (Qs is 3299 mm•year −1 and Hc is 943 m) was determined by a straight line passing through the altitude and the Qs of two sites Figure 3.The following experimental formula was obtained: To estimate Qs at relevant sites, the experimental Formula (3) was rewritten by standardization with Nakajima site which have investigated Qs data.

 
0.000540 0.4908 Nakajima The relative Qs [Qs/Qs (Nakajima)] was shown in Ta- ble 1 for estimation of Qs at the relevant sites.

Altitude Dependence of AtdepS
The altitude dependence of AtdepS between Taiyougaoka and Sanpoiwa was based on the average of 7 years' data from June to October as shown in where, the unit of AtdepS is kg•ha −1 •year −1 ate AtdepS at relevant sites, the experimental Fo at any altitude Hc (m).
To estim rmula (6) was rewritten by standardization with Taiyougaoka site which have investigated AtdepS data.

Results
om Test Basin res of Qs, Cs and Total S as shown in Table 1 for estimation of AtdepS at relevant sites.
The basin ight of the center (Hc) of the relevant basins, the relative discharge based on Nakajima data calculated by Equation ( 4) and the relative AtdepS based on Taiyougaoka data calculated by Equation ( 7) at relevant sites are shown in Table 1.
Figure 5 shows the temporal and yearly change of T lS in unit area over the test period, which was divided into GeoS and AtdepS, ranged from 87.8 kg•ha −1 to 164.3 kg•ha −1 , with an average of 117.3 kg•ha −1 .GeoS ranged from 72.8 kg•ha −1 to 146.5 kg•ha −1 with an average of 99.1 kg•ha −1 and c.v of 20.1%.AtdepS ranged from 14.9 kg•ha −1 to 22.7 kg•ha −1 with an average of 18.2 kg•ha −1 and c.v of 11.4%.
Table 3 shows t d TotalS over the test period.Qs ranged from 130 mm to 431 mm, with an average of 254 mm (c.v is 38%).Cs ranged from 2.15 mg•l −1 to 5.25 mg•l −1 , with an average of 3.97 mg•l −1 .TotalS ranged from 387 ton to 1235 ton, with an average of 700 ton.Unit load ranged from 5.25 kg•ha −1 to 16.85 kg•ha −1 with an average of 9.55 kg•ha −1 (c.v is 31.7 %).
The TotalS load of the six sites with differen the study area are shown in Figure 6 dividing into GeoS and AtdepS, to which altitude correction had already been applied, by the relevant unit areas.The TotalS was based and TotalS at the Hirose site (Nakajima).on the observed Cs and the estimated Qs data from the Nakajima site.GeoS occupied large part of TotalS of relevant sites.TotalS shows variation between sites, but does not show any distinct trends as were observed in nitrogen concentrations, such as upstream sites having lower concentrations than downstream sites [12,13].The TotalS for the Kuwajima site are particularly high, probably attributable to geological factors.

Comparison of AtdepS and GeoS
Figure 7 shows the monthly changes in the average co s of AtdepS and peaks in the ile GeoS ncentrations of AtdepS and GeoS over the test period at the Hirose site.The GeoS concentration was about 5.46 times greater than the AtdepS concentration.The maximum AtdepS concentration occurred in the winter season because of seasonal wind from continental Asia, while the GeoS had its peak in summer, however the value for GeoS was relatively flat compared with that of AtdepS.Concentrations at the remaining five sites show similar patterns to those at the Hirose site.
Figure 8 shows the monthly change GeoS loads at the Hirose site.The AtdepS winter season for the same reason as Cs, wh peaks in summer, because rapid chemical reactions may be caused by the high temperature.The remaining five sites in the study area show the same patterns in TotalS similar to those at the Hirose site.
Table 5 shows the TotalS, the average load by unit area and the percentage of contributions from GeoS and irose site, the TotalS disharge was estimated at 8597 ton•year −1 , resulting in a unit load of 117.3 kg•ha −1 •year −1 , of which the AtdepS load was 18.2 kg•ha −1 •year −1 (15.5%) and the GeoS load was 99.1 kg•ha −1 •year −1 (84.5%).

SO  Locks
To help explain the reason for the large percentage of S from GeoS in TotalS, w this area (shown in Figure 9 [22]).
The upstream area of this basin contains a sedimentary rock layer named the "Tedori sedimentary layer group", which was formed during the Cretaceous period about 180 -110 million years ago.The S compounds fro Ogoya mine, which was in operation until 1971 and from which chalcopyrite was ex acted for about 100 years, is ed outside of the test basin.The sedimentary r r released SO  by oxidation because of the presence of a canyon in the Tedori River basin.
There are three oxidation processes that produce 2 4 SO  as following two forms [23]: (1) Oxidation process of pyrite (FeS 2 ) The first process rapidly progresses in the presence of sulfur and iron bacteria (Thiobacillus ferrooxidans or Ferrobacillus ferr xidans).The second process also rapidly progresses in the presence of bacteria (Thiobacilli co oo wi ntaining Thiobaccillus thiooxidans).The third reaction ll progress under acidic conditions, and as a result, (2) Oxidation of pyrite KFe SO OH  To investigate the difference of the sedimentary rock characteristics, we investigated the Cs concentrations in the rivers in the Hokuriku region, which has quite similar conditions for AtdepS as our study area.Kobayashi reported the presence of the 4 ion in many rivers throughout Japan [24].Table 6 gives information on the 4 To investigate the difference of the sedimentary rock characteristics, we investigated the Cs concentrations in the rivers in the Hokuriku region, which has quite similar conditions for AtdepS as our study area.Kobayashi reported the presence of the ion in many rivers throughout Japan [24].Table 6 gives information on the  SO  in the river water exceeds 2 -3 mg•l −1 which may be supplied by AtdepS in the Hokuriku region, the river will contain S that originates from sedimentary rocks such as pyrite.

Further Research
There were limited data available for Cs due to a lack of sampling, which is of particular concern because Cs is strongly dependent on Qs.Nitrogen concentrations were also strongly dependent on discharge; however, this was mainly due to changes in organic nitrogen concentrations, while inorganic nitrogen concentrations did not change significantly.Compared with nitrogen outflow, Cs may not change so remarkably because the inorganic nitrogen behavior will be comparable to that of sulfate.However, to rectify the Cs data shortage issue, data from as long a time period as possible will be used so as to ensure inclusion of data for a wide ra Therefore, more freque future for more reliable results.Further, this research was based on the hypothesis that the sulfur cycle was in a steady state, which is in turn based on an analogy of the nitrogen cycle, and verification of this hypothesis remains as a research issue for the future.

Conclusion
Based on the hypothesis that S in river water consists mainly of AtdepS and GeoS in mountainous basins, we carried out quantitative analysis of TotalS (the product of Cs and Qs) originating from AtdepS and GeoS.The Tedori River mountainous basin was chosen as a test basin, because 16 years of data for Cs, Qs and AtdepS were available.Furthermore, we also have experience of calculating the nitrogen balance for the same basin [19,20], thus, the procedure for which is comparable to that for the S analysis.
First,  [19,20].The GeoS load was strongly dependent on the individual site characteristics, and in particular the Kuwajima site showed a remarkably high GeoS load, which suggests that the sedimentary rock at this site has much higher pyrite content than at the other sites.
To help explain why GeoS was higher than AtdepS, we examined the geological map of the study basin and confirmed that the sedimentary rock layer was rich in the pyrite group.Finally, we examined the relationship between the characteristics of sedimentary rocks and GeoS in many rivers in the Hokuriku Region because the climate conditions for AtdepS in this area are quite uniform.From this examination it was clear that 2 4 SO  concentrations greater than about 10 mg•l −1 in river water were closely related to the sedimentary layer containing the pyrite group.In addition, we estimated that SO 4 2− conce −1 ntrations greater than 2 -3 mg•l in river water in the Hokuriku region would be influenced by GeoS.

Figure 2 .
Figure 2. The upland area of the Tedori river basin and the discharge (Qs) and total nitrogen concentration (Cs) monitoring sites.

2 4 SO
 ) was collected at the following six sites (Figure2): the Hirose site located near the Nakajima discharge observation site, the Tedori dam site located at the No. Hydroelectric Power Generation Station just downstream of the Tedori dam, and the Kamikawai site located downstream of the Dainichi dam.The Senami site is located at the water outlet of the Senami and the Ozo rivers because the basin was changed so that it flows into the Tedori dam.The Shiramine site is located in the upstream section of the Tedori River and the Kuwajima site is at the intake for the Kuwajima Hydroelectric Power Generation Station.Cs was sampled monthly from 1994 to 2003 and quarterly after 2004 (May, August, November, February), except at the Tedori dam site, where monthly sampling continued after 2004.

Figure 5 . 1 )Figure 6 .
Figure 5. Temporal change in TotalS by unit area at the Hirose site (Nakajima).

4. 1 .
Geological Features of the Study Catchment and Process of Production from Sedimentary e examined the geological map of layer seemed to have formed under the Sea of Japan at that time, and contained m the pyrite (FeS 2 ) group.In fact, the tr locat ock laye Hirose (Nakajima) site.AtdepS over 16 years.At the H c 2 4

Table 5 . TotalS, AtdepS and GeoS loads and unit area loads at Hirose site (Nakajima).
Formation of Jarosite and goethiteIn addition to the processes outlined in (1) and (2) above, the following process also occurs.

Table 6 . Sulfur concentration of river water in Hokuriku Region (Kobayashi 1971) [23].
TotalS was calculated using Qs and