Comparison of mineral and organic phosphorus forms in regulated and restored section of a small lowland river (NE Poland)

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ECOHYD-72; No. of Pages 11 Ecohydrology & Hydrobiology xxx (2015) xxx–xxx

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Comparison of mineral and organic phosphorus forms in regulated and restored section of a small lowland river (NE Poland) Piotr Zielin´ski *, Elz˙bieta Jekatierynczuk-Rudczyk Department of Environmental Protection, Institute of Biology, University of Białystok, Ciołkowskiego 1J, 15-245 Białystok, Poland

A R T I C L E I N F O

A B S T R A C T

Article history: Received 17 December 2014 Accepted 9 February 2015 Available online xxx

A two-year study on water quality changes with particular concern about forms of phosphorus in two sections (regulated and restored) of a small lowland river in northeastern Poland, was carried out. Analyses were performed 7 years after restoration treatment. A clear, significant differences in water quality between the two investigated sections were observed. In the case of different phosphorus (P) forms: soluble reactive phosphorus (SRP), dissolved hydrolysable phosphorus (DHP), total dissolved phosphorus (TDP) and total phosphorus (TP), concentrations were by about 40% lower within restored than in regulated river section. There has been a significant influence of hydrometeorological conditions on P concentrations in the river. Contrary to the assumptions, concentrations of all P forms, with the exception of DHP, were lower in more humid period than in year characterized by smaller precipitation sum, and minor differences between two compared sections of the river were noted. These decreases of P forms concentrations were not only induced by dilution effect. Better catchment hydration (even degraded/ regulated one) prevents rapid transport of P to the surface waters. Numerous relationships between P concentrations and other water quality parameters were found (e.g. with Cl , NO2 , NO3 , NH4+, Na+ and K+). The comparative study on the regulated and restored river sections confirms that the preservation or construction of riparian land/water buffer zones can be recommended to reduce P forms concentrations in lowland rivers. Even small-scale restoration efforts in the estuary sections of rivers may be important factor improving the quality of water leaving degraded catchment. ß 2015 European Regional Centre for Ecohydrology of Polish Academy of Sciences. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved.

Keywords: River restoration Phosphorus Water quality Hydrology Precipitation

1. Introduction Freshwater ecosystems have long been affected by numerous types of human interventions that have a negative impact on their water quality and ecological state (Søndergaard and Jeppesen, 2007). Most changes in a catchment on agricultural areas were land reclamations

* Corresponding author. Tel.: +48 857388397. E-mail address: [email protected] (P. Zielin´ski).

and regulation of small rivers carried out on a large scale (especially in the 60s and 70s in Poland). As a consequence, these treatments significantly changed hydromorphological features of rivers by reducing their ecological status (Zielin´ski et al., 2012a,b). Hydromorphological degradation of rivers and streams is one of the most severe limitations to improving the water quality in many parts of the world (Søndergaard and Jeppesen, 2007; Schirmer et al., 2014). However, in recent years, there has been a lot of efforts to improve the condition of many types of water, especially running waters, due to restoration projects. A number of

http://dx.doi.org/10.1016/j.ecohyd.2015.02.002 1642-3593/ß 2015 European Regional Centre for Ecohydrology of Polish Academy of Sciences. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved.

Please cite this article in press as: Zielin´ski, P., Jekatierynczuk-Rudczyk, E., Comparison of mineral and organic phosphorus forms in regulated and restored section of a small lowland river (NE Poland). Ecohydrol. Hydrobiol. (2015), http://dx.doi.org/10.1016/j.ecohyd.2015.02.002

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studies on the effectiveness of restoration focused on the improvement of the ecological status taking into account aquatic invertebrates (Jenkins and Boulton, 2007), macrophytes (Pedersen et al., 2007), fish (Grift et al., 2001), and birds (Poudevigne et al., 2002), while issues related to water quality were undertaken to a lesser extent (Meyer et al., 2013; Zielin´ski and Jekatierynczuk-Rudczyk, 2014). This issue is very important from the point of view of the Water Framework Directive (WFD), that is defined to gain at least a good ecological status of surface water by 2015. Of the major plant nutrients, phosphorus (P) is typically in shortest supply in rivers and other freshwaters so generally has the greatest potential to limit plant growth. P is derived to the river system from a range of sources, varying in its bioavailability from source to source (Mainstone and Parr, 2002). The total load of P to the river can be broadly divided into point source inputs and diffuse inputs. Most watersheds have a range of P sources, with varying composition of timing of P delivery, from highly episodic event-driven P delivery (diffuse sources), to nearcontinuous P inputs (point sources) (Stamm et al., 2013). Catchment export of P is a function of land use, population densities, agricultural practices and urban development (Carpenter et al., 1998). The other important factors influencing P export, retention and transformation in river catchment are hydrology and hydro-meteorology. The travel time of water in streams governs the time of exposure of stream P to key transformation sites, the sedimentation rate of organic and inorganic particulates, hyporheic flow, oxidation at the soil and sediment water interface and diffusion into interstitial waters (Bostro¨m et al., 1988; Kerr et al., 2011). Riverine buffer zones efficiently reduce P content occurring as a result of diffuse pollution through several mechanisms e.g. assimilation of inorganic forms by microbiological activity (Parn et al., 2012) or building-up the P into the biomass. River restoration projects and restoration of degraded buffer zones comprise one of the most effective management measures for non-point source pollution control according to Ecohydrology principles (Zalewski, 2000; Izydorczyk et al., 2013). Analyses of P forms in rivers, its spatial and seasonal variability, were investigated repeatedly by scientists (Carpenter et al., 1998; Jarvie et al., 2005; Royer et al., 2006; Fink and Mitsch, 2007; Jarvie et al., 2013; Meyer et al., 2013; Stamm et al., 2013). However, there is no comprehensive analysis of different P forms in the river subjected to restoration treatment in the context of the effectiveness of these measures particularly in relation to the watershed hydration. Considering the current state of knowledge, we hypothesize that better hydration of catchment accelerates restoration effects, improving water quality including the decrease of reactive P forms in restored river. The aim of this study was to compare the concentrations of different P forms in two sections (regulated (RG) and restored (RS)) of small, lowland river. Another analyzed aspect was the influence of the hydration status of the catchment and different hydro-meteorological conditions (dry and wet period) on the concentrations of P forms in both: regulated and restored parts of the investigated river.

2. Materials and methods 2.1. Study area The Rudnia River is a right tributary of the Narew River which is main and the largest lotic system in north-eastern Poland. The Rudnia River has a total length of 23.2 km and its catchment covers the area of 88.6 km2. The catchment inclination is very low (1.2%), being typical of this region. Mean flow in the river mouth profile during the study period was 0.2 m3 s 1, which contributes to a low specific discharge (about 2.4 dm3 s 1 km 2). In the 1970s the Rudnia River was intensively regulated, mainly in the upper and middle sections. In the ending part of Rudnia River, the natural channel (going parallel to Narew River) was shortened by 250 m long artificial canal leading water directly to Narew River (Fig. 1). A cut-off, 4 km long, river channel fragment has been remained for over 25 years, and held role as an oxbow lake. In 1998–1999, the NorthPodlasie Association for Birds Protection (N-PABP) commissioned a project designed to restore the cut-off river section of Rudnia River. As a result of this project, the natural course of lower river section was restored by damming the artificial canal built in the 70s and unblocking overgrown old river bed. The Rudnia River catchment is dominated by agriculturally used lands in 70%. More than a half of this areas are covered with arable lands (58%), meadows and pastures (41%) and orchards (1%). The afforestation coefficient within the catchment reaches 21%. The fallow lands cover 9% of the Rudnia River catchment with domination dense and dispersed rural areas as well as urban development–Zabłudo´w town. The type of agricultural management can be described as extensive. Significant source of the pollutions for investigated river is Zabłudo´w town with less than 2500 inhabitants. Rudnia River catchment soils are developed from fluvioglacial formations of Warta glaciation (sand, gravel, clay). In the river valley, especially in the restored part, the soil cover was formed on Holocene peat. Regulated part of the Rudnia River represents intensively canalized river with fascine bundles and small weirs. Most of the bends were straightened out and branches cut off from the main stream. This part of the river built and farming in the floodplain area were intensified. This has brought a degradation of the natural freshwater habitats. The restored part of the river kept its more natural character with meandering riverbed, oxbow lakes and wetlands in the floodplain. In this part of Rudnia River ecotone wetlands are broad and play an important role as buffer zones. 2.2. Hydrological features of Rudnia River in 2006–2007 During the study period, the average flow rate within the estuary section of Rudnia River was 0.54 m3 s 1, and at the measurement point Trzes´cianka (site no. 4) 0.52 m3 s 1 (Fig. 2). The flow rate of the Rudnia River in Trzes´cianka profile changed during the study period from 0.012 m3 s 1 in August 2006 to 8.80 m3 s 1 in March 2007. Minimum flow rates in 2006 were recorded in summer amounting to 0.01–0.03 m3 s 1, while in 2007 to 0.07 m3 s 1, which occurred in July. In contrast to 2006, there were high water

Please cite this article in press as: Zielin´ski, P., Jekatierynczuk-Rudczyk, E., Comparison of mineral and organic phosphorus forms in regulated and restored section of a small lowland river (NE Poland). Ecohydrol. Hydrobiol. (2015), http://dx.doi.org/10.1016/j.ecohyd.2015.02.002

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Fig. 1. Location of the Rudnia River catchment and distribution of sampling stations. (a) Restored section of Rudnia River; BR – artificial canal connecting Rudnia River with Narew River before restoration.

levels and flow rates in the winter months of 2007, which greatly contributed to improved hydration of the valley. In 2006, considerably smaller river flow rates were observed than in 2007, which were at the estuary of Rudnia River to Narew River 0.25 m3 s 1 and 0.82 m3 s 1, respectively. Differences in the river flow rate in subsequent hydrological years were determined by variable sum of precipitation and their distribution throughout the year (Fig. 3). In both years of study, the highest rainfall was recorded in summer. Annual sum of precipitation in 2006 was lower by more than 100 mm than in 2007. Higher amount of precipitation in winter 2007 significantly improved the hydration of Rudnia River valley making the potential for floods in summer. The flow rate in the RG and RS sections was similar, but the water flow rate was significantly different. In the RG section, water flow rate ranged from 20 to 80 cm s 1, while in the RS section, only

from 10 to 30 cm s 1. The water flow rate accurately reflects the nature (rate) of water circulation in meliorated rivers and close to the natural ones. Changes in water flow rate are derived from the reduction in the altitude difference along the course of the studied river. 2.3. Methods Samples were collected on a monthly basis for two years (from February 2006 to December 2007) for all sites. Nine measurement sites were situated along the continuum of the Rudnia River (sampling sites: 1–5 regulated (RG), 6–9 restored (RS) channel). In addition, water samples were taken from Narew River 100 meters below the mouth of the Rudnia River (Fig. 1). Hydrochemical and hydrological investigations have been carried out every month. The water quality of the transit Narew River was considered as

Please cite this article in press as: Zielin´ski, P., Jekatierynczuk-Rudczyk, E., Comparison of mineral and organic phosphorus forms in regulated and restored section of a small lowland river (NE Poland). Ecohydrol. Hydrobiol. (2015), http://dx.doi.org/10.1016/j.ecohyd.2015.02.002

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Precipitaon [mm]

250 200 150 100 50 0

J

F M A M J

J

A S O N D J

F M A M J

J

A S O N D

2007

2006

Fig. 2. Monthly sum of precipitation in 2006 and 2007 at Zabłudo´w gauge station (data obtained from the Institute of Meteorology and Water Management).

10.00 9.00 8.00

Q [m3 s-1]

7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00

1

101

201

301

Days

401

501

601

701

Fig. 3. Changes in actual discharge of Rudnia River in 2006 and 2007 on the site no. 4 (Trzes´cianka; data obtained from the Institute of Meteorology and Water Management).

a good example of typical riverine state for investigated region. Measurements of physical parameters (temperature, electrolytic conductivity (EC), pH, dissolved oxygen concentration and saturation) were carried out using Hydrolab Data Sonde (Hydrolab Corp., Austin, TX) directly in the field. Main hydrochemical parameters were determined within c. 24 h of sampling, to avoid significant sample deterioration on storage using standard methods described by Hermanowicz et al. (1999) and APHA (2001). Bicarbonate (HCO3 ) content was measured by titration with 0.01 N hydrochloric acid using methyl orange as indicator. Calcium (Ca2+) and magnesium (Mg2+) ions were determined by titration with EDTA. Sodium (Na+) and potassium (K+) ions concentrations were measured by flame photometry. Chloride ions (Cl ) were determined spectrophotometrically using mercury thiocyanate method. Iron ions (Fe2+/3+) concentration was

measured spectrophotometrically with 1,10-phenanthroline method. Sulfate ions (SO42 ) were analyzed with turbidimetric method. For P determinations the following measurements were made: soluble reactive P (SRP) in the less than 0.45 mm fraction. Total dissolved P (TDP) as the combination of SRP and dissolved hydrolysable P (DHP). DHP is the organic P form and polymeric P formin the <0.45 mm fraction released by peroxodisulphate UV digestion on filtered sample. Total P (TP) was the combination of TDP and particulate P (PP). Non-reactive phosphorus (NRP) was calculated as the difference between TP and SRP concentrations. The SRP, TDP and TP fractions were determined spectrophotometrically with phosphomolibdenum blue method of Murphy and Riley (1962) as modified by Neal et al. (2000) other fractions were calculated. Investigated nitrogen (N) forms were analyzed spectrophotometrically, using reagents by Riedel de Ha¨en, according to following methods: NH4+ – indofenol

Please cite this article in press as: Zielin´ski, P., Jekatierynczuk-Rudczyk, E., Comparison of mineral and organic phosphorus forms in regulated and restored section of a small lowland river (NE Poland). Ecohydrol. Hydrobiol. (2015), http://dx.doi.org/10.1016/j.ecohyd.2015.02.002

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blue method, NO2 – with sulfanilic acid by the chromotropic acid method, NO3 – with N-(1-naphthyl)ethylenediamine with the zinc catalyst method. Total nitrogen (TN) was determined using the Kjeldahl analyzer (Tecator 2300, Sweden) by the titration method. Total inorganic nitrogen concentration (TIN) was calculated as the sum of NH4+–N, NO2 –N, and NO3 –N. Total organic nitrogen (TON) was calculated by subtracting the ammonium from the total Kjeldahl nitrogen (TKN) amounts. TN was considered as a sum of TKN and nitrate and nitrite. Water color was measured spectrophotometrically according to Hongve and A˚kesson (1996) method. Chlorophyll a concentration was determined by the spectrophotometric method with ethanol extraction. Samples were filtered on GF/C filters and extracted with boiling 90% ethanol (Nusch, 1980). The collected hydrological, meteorological and physicochemical data were subject to statistical analysis according to the methodology described by Griffiths (2008). Statistical comparisons between means to analyze the existing differences among the investigated sites and periods were carried out using one-way ANOVA followed by Duncan’s multiple range-test. The statistical significance of difference was taken as p  0.05. The differentiation of the distribution of main analyzed parameters was described with the coefficient of variation (CV), defined as the ratio of the standard variation from a given sample to its arithmetic mean and expressed as a percent value (Subrahmanya Nairy and Aruna Rao, 2003). The Spearman rank correlation test was employed for further interpretations of results with the significance level of p  0.05 or

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less. All of the statistical calculations were performed using the Statgraphics v. 5.0 software package (Statistical Graphics Corporation). Probability level of p  0.05 or less was considered as significant. Hydro-meteorological data come from the Institute of Meteorology and Water Management (IMWM), Białystok Division. 3. Results Hydrochemical results obtained in this research indicate considerable differences in water quality between the analyzed sections of Rudnia River. Statistically significant differences were found for many parameters such as: temperature, EC, Ca2+, Mg2+, Cl , SO42 , chlorophyll a, different forms of P and N (Table 1). Rudnia River was characterized by statistically different concentrations of most determinants in comparison to hydrochemical background for the region – Narew River (Table 1). 3.1. Comparison of P forms in regulated and restored sections of Rudnia River The average value of SRP concentration for Rudnia River water throughout the study period was 91 mg dm 3, and the concentration of TP was more than twice as high (201 mg dm 3). The most variable form of P within the whole study period was PP, the average concentration of which was 65 mg dm 3 and the coefficient of variation (CV) amounted 155%. Results for the entire study indicate that the concentration of SRP in the RS section of the Rudnia River was over 40% lower than in the RG section (Table 1).

Table 1 Hydrochemical characteristics of Rudnia River and Narew River in 2006 and 2007 years; (EC–electrical conductivity, SRP–soluble reactive phosphorus, TP– total phosphorus, TDP–total dissolved phosphorus, PP–particulate phosphorus, NRP–non-reactive phosphorus, DHP - dissolved hydrolysable phosphorus, TN–total nitrogen, TON–total organic nitrogen, TIN–total inorganic nitrogen). Statistically significant differences at p < 0.05. Parameter

Temperature pH EC Oxygen saturation HCO3 Ca2+ Mg2+ Cl SO42 Fe2+ SRP TP TDP PP NRP DHP TN TON TIN NO3 –N NO2 –N NH4+–N Water color Chlorophyll a

8C

mS cm

1

% mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mg dm 3 mgPt dm mg dm 3

3

Regulated part of Rudnia (a) n = 115

Restored part of Rudnia (b) n = 92

Narew River (c) n = (23)

Statistically significant differences

Average

Range

Average

Range

Average

Range

9.46 7.54 507 78.6 324 94.6 12.5 22.9 43 321 106 219 164 64 112 52 3451 2123 1347 583 19 259 62.2 12.4

0.1–20.9 6.04–8.25 348–623 26.9–128 223–629 43.6–127 1.03–48.1 13.4–41.7 18.2–64.4 134–753 1–674 70–950 28–748 0.3–690 16–699 2–283 994–8128 215–7045 356–3815 32–2142 3–47 72–988 17.2–142 6.20–23.8

11.56 7.57 467 74.1 318 88.2 10.1 18.9 37.7 295 60 159 97 66 99 35 3016 2204 860 896 31 420 56.5 11.1

0.1–22.1 6.84–8.28 368–594 27.9–153 195–565 38.9–127.1 0.36–27.4 12.2–28.3 18.3–54.9 102–695 1–185 45–994 26–217 1–842 16–901 1–113 834–5344 251–4655 180–2319 79–2097 8–307 71–2114 18.4–130 5.70–30.2

10.71 7.60 387 79.1 295 83.1 10.4 17 31.3 375 52 165 96 77 113 41 2698 1845 819 500 20 299 63.2 14.6

0.1–22 6.79–9.60 288–474 31.0–143 195–453 35.4–123 2.43–23.4 7.82–26.3 10.6–51.7 123–772 4–103 49–743 19–168 7–591 29–673 3–94 1182–4157 338–3439 229–1879 64–1540 7–49 94–672 21.1–132 5.82–29.1

a–b a–b, a–c, b–c

a–b, a–b a–b, a–b, a–c a–b, a–b a–b,

b–c b–c a–c, b–c b–c b–c

a–b a–b, a–c, b–c a–b, b–c a–b, b–c a–b a–b a–b, a–c, b–c

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Fig. 4. Changes in mean concentrations (SE-standard error) of soluble reactive phosphorus (SRP) and total phosphorus (TP) in 2006 (drier period– indicated with d) and in 2007 (wetter period – indicated with w) on sampling stations along Rudnia River. SRP concentrations are presented as a part of TP.

In addition, the SRP concentration in the RS section was much less variable (lower CV) than the SRP concentration obtained for the RG section (58% and 84% respectively). In the case of other forms of P: DHP, TDP, NRP, and TP, levels achieved in the RS were lower than in the RG section (Table 1). Statistically significant differences were observed for SRP, DHP, TDP, and TP. Only in the case of PP, concentrations in both parts of the studied Rudnia River remained at the same level (Table 1). The lowest values of the CV in both RG and RS sections were noted for TDP (62% and 46% respectively). Concentrations of basic P forms were characterized by spatial variability along the Rudnia River continuum (Fig. 4). At the sampling station no. 2, both SRP and TP were on average twice as high as on other measurement points. In the following 4 sampling stations, a gradual decrease in the concentrations of SRP and TP was observed. In the RS section (stations 6–9), a slight increase in TP concentration along the river was observed again (Fig. 4). In the RG part of Rudnia River, the SRP contribution in TP was the highest (nearly 50% in average) while in the RS section, PP was the dominant form of P (more than 40%). In both types of river channel, DHP represented similar proportions (approximately 20%) of TP (Fig. 5). Participation of different P forms (SRP, DHP, and PP) in the TP along the RG section of Rudnia River was very similar, and SRP constituted approximately 40%, DHP approximately 20%, and PP approximately 30% (Fig. 5). At RS part of Rudnia, these proportions were changeable along the river continuum in favor of the non-reactive fractions, for which the proportion of PP even doubled to 40–50% (Fig. 5). 3.2. Comparison of different hydro-meteorological conditions in Rudnia River catchment Substantial differences in the moisture content of Rudnia River catchment (Fig. 2) were reflected in the concentrations of P forms on both analyzed sections of the

Fig. 5. Share of phosphorus forms in the total phosphorus pool along the Rudnia River continuum (average results from 2006 to 2007; RG – stations 1–5, RS – stations 6–9); SRP, soluble reactive phosphorus; DHP, dissolved hydrolysable phosphorus; PP, particulate phosphorus.

river between 2006 characterized by lower precipitation and 2007 that was definitely more humid (Fig. 6). In general there has been noted a higher concentration of P forms in 2006 than in 2007, with the exception of DHP. However statistically significant differences between these hydro-meteorologically distinct years were found only in the RG section for SRP, DHP, PP, and TP (Fig. 6). Comparing P loads for both years (dry and wet) SRP loads did not differ statistically (1.33 tons yr 1 and 1.30 tons yr 1 respectively) but TP loads were different (2.18 tons yr 1 and 3.57 tons yr 1 respectively). When comparing concentrations of the same P forms at the RG and RS sections in a year

Fig. 6. Mean concentrations (SE) of phosphorus forms: soluble reactive phosphorus (SRP), total dissolved phosphorus (TDP), dissolved hydrolysable phosphorus (DHP), particulate phosphorus (PP) and total phosphorus (TP) in both studied Rudnia River sections in 2006 (drier period – indicated with d) and in 2007 (wetter period–indicated with w). Bold asterisk indicate statistically significant differences between regulated (RG) and restored (RS). Designations: a* – difference between P concentration in 2006 and 2007 on RG section; b* – difference between P concentration in 2006 and 2007 on RS section.

Please cite this article in press as: Zielin´ski, P., Jekatierynczuk-Rudczyk, E., Comparison of mineral and organic phosphorus forms in regulated and restored section of a small lowland river (NE Poland). Ecohydrol. Hydrobiol. (2015), http://dx.doi.org/10.1016/j.ecohyd.2015.02.002

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with lower rainfall, the statistically significant differences were noted for SRP, TDP, and TP. In the following year characterized by greater sum of precipitation (2007), such differences between the studied sections of Rudnia River were found for: SRP, TDP, DHP, and TP (Fig. 6). In 2006, the lower water levels in the RG part of Rudnia River adversely affected the concentrations of TDP (r = 0.65; p < 0.05), NRP (r = 0.31; p < 0.05), DHP (r = 0.32; p < 0.05), PP (r = 0.30; p < 0.05). Within the RS section, the dependence between P forms concentrations and water level was reflected differently. Positive correlations were found for: TP (r = 0.73; p < 0.05), NRP (r = 0.69; p < 0.05), PP (r = 0.56; p < 0.05), and DHP (r = 0.52; p < 0.05) and negative correlation was found for TDP concentration (r = 0.95; p < 0.05). Much less dependences were observed in the wet year (2007). At the RG part (at sampling station no. 4), high water levels shaped the concentrations of SRP (r = 0.50; p < 0.05) and TDP (r = 0.42; p < 0.05). A positive correlation was noted for the water level and PP concentration (r = 0.50; p < 0.05). Much less impact of the hydrological conditions were found in RS section of the river in 2007. At (at sampling station no. 6), the water level negatively affected the PP concentration (r = 0.67; p < 0.05) and positively – the DHP (r = 0.31; p < 0.05). Each analyzed year was characterized by different relationships between P forms concentrations and other water quality parameters. In 2006, the largest number of dependencies was found in the RG section. In the case of SRP values, positive dependencies were recorded with concentrations of Cl , NO2 , NO3 , NH4+, Na+ and K+ (Table 2). In the case of TP and TDP, the positive

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dependencies were recorded, with concentrations of Cl , NO2 , NO3 , NH4+, Na+ and K+ (Table 2). Much less dependencies in the same year were recorded in the RS section, where in addition to the concentrations of Cl , Na+, K+, significant relationships with the water color and temperature, SO42 or EC, were also determined. During the wet season, number of detected dependencies was much smaller. In the RG part of Rudnia River, the SRP concentration positively correlated only with two other hydrochemical parameters (water color and chlorophyll a concentration), while others were characterized by negative relationships (Mg2+, Cl , NO3 ). In the RG section, very strong correlations with concentrations of N+, K+, and NO2 were found for TP, TDP, DHP, and NRP. 4. Discussion Rudnia River in comparison to other rivers of the region may be counted to those with a slightly higher content of the most water quality determinants including concentrations of P forms, except PP (Table 1). Narew River is a good example of hydrochemically referential water course for the investigated area (Zielin´ski and Jekatierynczuk-Rudczyk, 2014). Observed difference in water quality of Rudnia River are mainly due to presence of Zabłudo´w town with 2.5 thousand inhabitants in the upper part of the catchment, and still low attention to agricultural best management practices in the region. The most of Rudnia River catchment is mainly agriculturally used in form of extensive fields, meadows, and pastures. The geological structure of the basin (domination of sandy, gravel and sandy-clay fractions) favors easy and quick migration of

Table 2 Statistically significant dependencies (Spearman’s linear correlation coefficient) between phosphorus forms and water quality features in restored and regulated part of Rudnia River in 2006 and 2007;(EC – electrical conductivity, TP – total phosphorus, DP – dissolved phosphorus, SRP – soluble reactive phosphorus, TN – total nitrogen, TON – total organic nitrogen, TIN – total inorganic nitrogen). Parameters

2006

2007

Regulated part TP Temperature pH EC Oxygen saturation HCO3 Ca2+ Mg2+ Na+ K+ Cl SO42 Fe2+ Water color TN TON TIN NO3 –N NO2 –N NH4+–N Chlorophyll a

DP

Restored part SRP

TP

DP 0.55***

Regulated part SRP 0.43***

TP

DP

0.43***

0.39***

Restored part SRP

TP

DP

SRP 0.45***

0.37***

0.37***

0.52*** 0.35***

0.36*** 0.35***

0.39*** 0.38*** 0.48***

0.40* 0.34*

0.50*** 0.77*** 0.59***

0.52** 0.86*** 0.58***

0.51** 0.88*** 0.66***

0.43* 0.55** 0.56*** 0.48***

0.52***

0.47***

0.41**

0.68*** 0.53*** 0.52*** 0.63***

0.65*** 0.56*** 0.78*** 0.53***

0.63*** 0.49*** 0.75*** 0.55***

0.62** 0.47*** 0.48***

0.36*** 0.45***

0.39*** 0.39* 0.68***

0.37*** 0.62** 0.68**

0.42**

0.45*** 0.60** 0.36** 0.40***

0.52***

0.55***

0.37* 0.61***

0.56***

0.49*** 0.63*** 0.44***

0.47*** 0.60*** 0.45***

0.42***

* Significant at the 0.05 probability level. ** Significant at the 0.01 probability level. *** Significant at the 0.005 probability level.

Please cite this article in press as: Zielin´ski, P., Jekatierynczuk-Rudczyk, E., Comparison of mineral and organic phosphorus forms in regulated and restored section of a small lowland river (NE Poland). Ecohydrol. Hydrobiol. (2015), http://dx.doi.org/10.1016/j.ecohyd.2015.02.002

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different ions, including PO43 , into surface waters. The obtained results showed that SRP was the dominant fraction of TP in RG part (Table 1). Obtained positive correlations between SRP and other easy migrating ions (Cl , NO2 , NO3 , NH4+, Na+, K+) confirm the specificity of the Rudnia catchment structure. Smith et al. (2003) have indicated that SRP is the dominant form of P exported from farmlands, dominated with meadows and pastures, what was confirmed also by our study. One of the most common forms of the investigated area use is cattle grazing, and Podlasie region is considered an important producer of milk in Poland. The studies by Jarvie et al. (2006) demonstrated the significance for P pollution of even small settlements (and their associated point source inputs) within largely agricultural and rural catchments. This type of catchment use is represented by Rudnia River. Diffuse sources of P, particularly from agriculture, are a major contributor to P pool in riverine ecosystem, where it can be utilized by benthic algae and rooted plants (Mainstone and Parr, 2002) but only if the ecological status of the river is on the higher level. Ecological status of Rudnia River was definitely better in the lower (restored) part of the river, therefore self-cleaning process of the river increases the efficiency. In RS section the majority of analyzed parameters decrease their concentration and the number of parameters that differ significantly compared to the reference river was reduced (Table 1). Another important feature of Rudnia River is elevated Ca2+ content, typical for glacial origin catchment. There is slight but significant difference in Ca2+ concentration between investigated river sections (Table 1) which could be induced with riverbed deepening in RG part. This feature probably favors the co-precipitation of P with calcite along the Rudnia River continuum. This phenomenon has been in detail documented for hardwater rivers and lakes (House, 1990) and is primarily driven by intensity of photosynthesis (Neal, 2002; House, 2003). The other results of P monitoring on the Rudnia River are discussed in relation to the two main objectives of the study: (i) comparison of P forms in both RG and RS sections of Rudnia River regarding spatial distribution of P forms along the river continuum; (ii) functioning of the restored rural river system in different (dry/wet) hydro-meteorological states. 4.1. Comparison of P forms in regulated and restored sections of Rudnia River Significant differences in concentrations of P forms, except from NRP and PP, found in our study between RG and RS sections (Table 1) indicate numerous complex processes governing the transport of P into the river. Intensity of biogeochemical cycling (either riparian or instream) plays a significant role in controlling nutrient chemistry in the rural headwater stream systems (Jarvie et al., 2008). However, anthropogenic transformation of the catchment and the river bed (as it is in the case of Rudnia River) can considerably disrupt the natural biogeochemical processes in the catchment and consequently speed up the penetration of P to surface waters. Such disturbances and effects of channel straightening as

well as disappearing the valley wetlands significantly affected the P balance in Rudnia River catchment, where concentrations of SRP, DHP, TDP, and TP were nearly twice as high as in the restored section (Table 1, Figs. 4 and 5). River regulations and reduced flooding of lowland areas along rivers negatively influence the retention of nutrients (Søndergaard and Jeppesen, 2007). According to Mainstone and Parr (2002) pragmatic management targets for lowland riverine SRP vary between 0.02 and 0.1 mg dm 3. In the RG section of Rudnia River, the upper limit has been exceeded, and the SRP values periodically exceed 6 times this value (Table 1). In Great Britain introduction of agricultural best management practices, P stripping in wastewater treatment plants or the ban of P in detergents have been implemented for decades and have had variable successes in achieving control of eutrophication (Jarvie et al., 2013). Admittedly, whereas in Poland, there was a significant improvement referring to the use of P compounds in detergents, the agricultural best management practices are applied rather in large commodity farms. The two-year analyses indicate that another effective way to reduce the level of P in the river water can be to carry out the restoration treatments aimed at increasing the participation of wetlands in the catchment as well as a significant slowdown in the water outflow from the catchment and water flow rate in the river (Table 1, Figs. 4 and 5). Restoration by allowing water to spill back onto the original floodplain can be a way of increasing retention of P (Kronvang et al., 2007). In Rudnia River, about 5 km fragment of restored catchment area with extensive low peat bogs has enough positive impact on phosphorus budget and its use (Fig. 5). In the RS section percentage of NRP forms in TP has changed clearly favoring PP and PO form (Fig. 5). Riparian wetlands allow seasonal floodwaters to deposit sediments and chemicals into the wetlands and for the water to then seep back into the stream (Mitsch and Day, 2006). Wetlands usually are a net sink for P during snow-melt, most spring floods, and on an annual basis but during some of the flood pulses they will export P (Bowes et al., 2003; Fink and Mitsch, 2007). This is confirmed by the results collected in the RS section, where P export in the form of PP occurs. A comparative study in the RG and RS sections confirms that the preservation or construction of riparian land/water buffer zones (ecotones) is widely recommended to reduce the negative impact of nutrients present in the catchment on freshwater ecosystems (Zielin´ski and Jekatierynczuk-Rudczyk, 2010; Passeport et al., 2013). Higher rates of SRP uptake in restored part of the Rudnia River (‘‘self-cleansing’’) may result from higher rates of primary production confirmed with high macrophyte cover rate and Mean Trophic Rank (MTR) score (Zielin´ski et al., 2012b) and can be linked to longer water residence time (Jarvie et al., 2008) which is affected by considerable slowdown of water flow rate within that river section. The two-years study revealed a clear impact of the river restoration on the change in the structure of P along the river continuum within the TP pool (Figs. 4 and 5). First of all, a strong uptake of P by both the abundant vegetation growing in the riverbed as well as in periodically irrigated

Please cite this article in press as: Zielin´ski, P., Jekatierynczuk-Rudczyk, E., Comparison of mineral and organic phosphorus forms in regulated and restored section of a small lowland river (NE Poland). Ecohydrol. Hydrobiol. (2015), http://dx.doi.org/10.1016/j.ecohyd.2015.02.002

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floodplain, and the simultaneous increase in the NRP share resulting from a constant supply of PP into the water mainly due to plant debris, in the RS section (Fig. 5). Gradual increase in the concentration of TP in the RS section (Fig. 4) can be attributed to the higher presence of mineral-organic complexes transported from fertile (SRP enrichment) peat bogs areas of the RS valley, similar relation was observed previously in lowland river by Zielin´ski et al. (2003). These changes are related to humiceutrophication processes occurring in waters with high content of humic organic matter. Greater variability of P forms found in the RG section results from a direct influence of agricultural land on the water quality in the valley (no buffer zones). In the RS section, an importance of extensive buffer zones for less volatile P forms in the river water, can be observed. 4.2. Functioning of the restored rural river system in different hydro-meteorological states After a comparative analysis of the study results, a larger P mobilization in wetter 2007 than in 2006 was not observed in Rudnia River (Figs. 4 and 6), although PalmerFelgate et al. (2008) reported an increased SRP export during elevated water levels. Probably in such a small river as Rudnia, increased supply of P is of pulsating and shortlived character, and their recording during regular monthly surveys is difficult to grasp. However our results confirm reports by Bowes et al. (2003), and Royer et al. (2006), who recorded the highest SRP concentrations during low water flow rates. Within analyzed period, all forms of P, except DHP, were characterized by smaller concentrations in 2007 than in 2006 (Fig. 6). The largest differences in SRP and TP concentrations between dry and wet period were observed in RG part (Fig. 4). SRP loads for dry and wet year did not differ statistically therefore these decreases of P forms concentrations could not only be induced by dilution effect. RS section does not react much on changes in hydration conditions (has a sufficient moisture level), which is important difference between the two studied sections and is reflected in obtained results (Figs. 4 and 6). The catchment hydration improves the buffer properties of transitional zone mainly in the regulated part of the river and it is likely to reduce the direct impact of groundwater on water quality in the river. Higher water level activates an intensive biogeochemical processes and development of riparian vegetation – an important element that reduces the P concentrations. However P enrichment in rivers (in this case in drier period) can degrade the plant community by altering the competitive balance between different aquatic plant species, including both higher plants and algae (Mainstone and Parr, 2002). Therefore, Zielin´ski et al. (2012b) has observed a significant difference between the number of macrophyte species and MTR indicator in both sections of the Rudnia River. Perhaps, this type of lowland river as Rudnia with very low slope and fine bottom sediments may be temporarily an important source of pulse P supply. The fine organicmineral sediments and low velocities create ideal conditions for the accumulation of P and the potential for

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subsequent biological utilization (Mainstone and Parr, 2002). Similar phenomena were observed by McDowell and Sharpley (2001) and Jarvie et al. (2005) in studies on other lowland rivers. Within any given basin, the importance attached to controlling point and diffuse sources will vary depending on population density, land use intensity and the nature of the river (Mainstone and Parr, 2002). Small and medium rivers are not resistant in hydrochemical terms to flow decreases what has environmental consequences for transport of nutrients, organic matter and finally on riverine habitats (Zielin´ski et al., 2009). In 2006, the largest number of dependencies was found in the RG section, and many of them confirms the anthropogenic origin of P forms (positive dependencies with Cl , NO2 , NO3 , NH4+, Na+ and K+, Table 2). Under better moisture conditions in the catchment (2007), P compounds were probably complexed with mineral and organic formations constituting the catchment area, which was confirmed by smaller number of relationships between P forms and other hydro-chemical parameters (Table 2). It can be assumed that even the anthropogenically transformed catchments still retain a high capacity to reduce P under conditions of a complete hydration of the surface layers. Reassuming, river restoration helps to improve water quality, reduce effectively nutrients concentrations including P. Better hydration of restored catchment accelerates improvement of water quality including decrease of mineral and reactive P forms. However effective way to restore streams should also enclose information campaigns to farmers and other catchment residences on best management practices (Søndergaard and Jeppesen, 2007). The collected data can help to predict hydrochemical processes occurring in restored lowland rivers. Our data clearly show that undertaken even small restoration actions can reduce P concentrations in degraded fluvial ecosystems. 5. Conclusions

1. The restored section of the Rudnia River is characterized by lower phosphorus forms concentration (SRP, TDP, DHP and TP). 2. The restored section of investigated river is characterized by altered distribution of phosphorus compounds with shift from mineral, reactive phosphates to PP dominated system as compared to the regulated section. 3. Lower concentrations of P forms in restored section of the investigated river indicate a significant role of active buffer zones. Buffer zones activity can be modified with the catchment moisture even in regulated part. 4. Higher precipitation (estimated on yearly basis) causes reduction of phosphorus content (SRP, TP, DHP and PP) in the river water. 5. Restoration of rivers in agricultural areas can improve the quality of water, including reduction of P forms, but it should be combined with the parallel implementation of good agricultural practices.

Please cite this article in press as: Zielin´ski, P., Jekatierynczuk-Rudczyk, E., Comparison of mineral and organic phosphorus forms in regulated and restored section of a small lowland river (NE Poland). Ecohydrol. Hydrobiol. (2015), http://dx.doi.org/10.1016/j.ecohyd.2015.02.002

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Zielin´ski, P., Szoszkiewicz, K., Soko´ł, M., 2012b. Effects of lowland stream restoration on the hydromorphology and macrophyte communities. In: International Symposium on Aquatic Plants, Poznan´. Zielin´ski, P., Jekatierynczuk-Rudczyk, E., 2014. Comparison of mineral and organic nitrogen forms in regulated and restored sections of a small lowland river. Environ. Prot. Eng. 40, 33–46.

Please cite this article in press as: Zielin´ski, P., Jekatierynczuk-Rudczyk, E., Comparison of mineral and organic phosphorus forms in regulated and restored section of a small lowland river (NE Poland). Ecohydrol. Hydrobiol. (2015), http://dx.doi.org/10.1016/j.ecohyd.2015.02.002