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Article

The Impacts of Beaver Dams on Groundwater Regime and Habitat 6510

by
Ryszard Oleszczuk
1,
Sławomir Bajkowski
2,
Janusz Urbański
2,
Bogumiła Pawluśkiewicz
1,
Marcin J. Małuszyński
1,
Ilona Małuszyńska
1,
Jan Jadczyszyn
3 and
Edyta Hewelke
1,*
1
Institute of Environmental Engineering, Warsaw University of Life Sciences, 02-787 Warsaw, Poland
2
Institute of Civil Engineering, Warsaw University of Life Sciences, 02-787 Warsaw, Poland
3
Institute of Soil Science and Plant Cultivation—State Research Institute (IUNG-BIP), 24-100 Puławy, Poland
*
Author to whom correspondence should be addressed.
Land 2024, 13(11), 1902; https://doi.org/10.3390/land13111902
Submission received: 14 October 2024 / Revised: 4 November 2024 / Accepted: 12 November 2024 / Published: 13 November 2024
(This article belongs to the Special Issue Monitoring and Simulation of Wetland Ecological Processes (Second Edition))
Browse Figures
Versions Notes

Abstract

:
Changes in land usage, increasing climatic uncertainty, and dynamic development of the rate of natural population growth of the Eurasian beaver will lead to increasing benefits and disadvantages from beaver activity. During three growing seasons from 2020 to 2022, four cross-sections were marked on unused sub-irrigation systems with the periodic occurrence of beaver dams, located on organic soils in parts of the facility protected by the Habitats Directive (natural habitat 6510) in Central Poland. Periodic water table measurements in wells, the beds of adjacent ditches, and the riverbed were carried out. Identification of the states and structures of plant communities was done using the botanical-weight analysis of several samples with an area of 1 m2. Beaver dams increased water levels in the river, ditches, and groundwater depth in over 78% of events in 2020–2022 years. A large impact of precipitation on the hydraulic conditions in the meadow was observed. In the studied area, since a moderately moist habitat (6510) is protected within the Natura 2000 network, phenomena increasing soil moisture, in the absence of mowing of meadows and the occurrence of expansive herbaceous vegetation that tolerates increased moisture, may lead to the disappearance of these habitats, especially in the zone near the riverbed.

1. Introduction

The state of an area’s biocenoses, especially in protected areas, is closely dependent on habitat conditions, human economic activity, and other factors, e.g., the appearance of beavers and their activity. The most dynamic changes occur in the period when previously agricultural land is abandoned and beaver families appear at the same time. Beavers can profoundly modify ecosystems to meet their ecological needs, which is associated with significant hydrological, geomorphological, ecological, and social impacts [1,2,3,4,5]. The settlement of beavers [6] and their activity [7] cause environmental changes, particularly to water levels and retention in streams and ditches [8,9,10,11]. These changes also apply to neighbouring areas where agricultural or recreational activities are still carried out. According to research by Stefen et al. [12] and Wróbel [13], the largest populations of Eurasian beavers (Castor fiber) in Europe were observed in colder areas, mainly in Scandinavia, the Baltic countries, Russia, and Poland. Considering the actions and plans of various countries regarding the reintroduction of this species into their territories and the dynamic development of the rate of natural population growth, this requires observation and control [14,15]. Additionally, the environmental consequences of maintaining functions that support biodiversity due to beaver activity are unknown.
The activities of beaver families are most often associated with the destruction of trees. The very high environmental invasiveness of beavers results from their rapid adaptation to environmental conditions [16]. Beavers inhabit very vast and highly diversified areas in terms of nature and climate [17,18]. Their life and species resourcefulness results from their adaptation to living in aquatic and land environments thanks to their structure [19] and high food tolerance [20]. The ability to use the conditions created by the edge biotopes of streams and water reservoirs is also important for the invasion and settlement of new areas. The increase in the retention capacity of streams and lakes due to beaver activity is estimated to be 5% [21]. This is a significant value, especially since drought threats are increasing in the environment [22]. The arrival of beavers usually results in an increase in the amount of water stored.
The activity of beavers slows down and blocks the outflow of water in drainage systems with dense networks of ditches where maintenance works are no longer carried out [23]. This is particularly important for shallow drained peat soils located on sand because these soils, due to excessive drying, are subject to degradation, mineralization, and deterioration of physio-chemical properties. Their mineralization is accompanied by surface subsidence, increasing greenhouse gas emissions into the atmosphere, which leads to the disappearance of this type of soil in the natural environment [24,25,26]. The basic method of renaturalization of these areas is to block the outflow of surface water, which increases the groundwater table and soil moisture [27,28]. Typically, existing gravity systems of drainage and irrigation ditches and modified drainage systems equipped with damming devices are used for this purpose [29]. Currently, drainage systems, in addition to stabilizing the level of plant production, are credited with mitigating extreme climatic phenomena such as floods and droughts [30,31]. With increasing global warming in recent decades, the deficit of atmospheric precipitation during the growing season worsens the water–air relationships of soils [32]. Additionally, Liu et al. [33] indicated the limits of the soil’s available water capacity and water storage of peat following peatland drainage and rewetting connecting with the degradation soil processes. Larsen et al. [34] exposed that the large influence of beaver dams on river corridor processes and feedback is also fundamentally distinct from what would occur in the absence of beaver activities. Beaver dams, which transform hydrologic and biogeochemical cycles in riparian systems [35], overshadow climatic hydrologic extremes. Ecosystem services (ESs) provided by beaver activity [36] include water purification, moderation of extreme events, habitat and biodiversity provision, nutrient cycling, greenhouse gas sequestration, recreational hunting and fishing, water supply, and non-consumptive recreation. Additionally, a lot of effort is made in active and passive techniques of lowland meadow restoration depending on the local ecological context [37], with some uncertainty as to the effectiveness of the measures applied [38]. Against this background, with the effect of beaver dams on the targeted habitat, its conservation status and the local context are unclear and require recognition.
This study hypothesizes that the presence of beaver dams, as part of the seepage sub-irrigation system on shallow organic soils, changes the water regime and improves the habitat conditions in a site. The dynamics of changes in surface water levels on a section of the Mała River, and in two drainage ditches and groundwater in part of the facility protected by the Habitat Directive (Łąki Soleckie) in connection with the periodic occurrence of beaver dams in the river, are presented. The novelty is the presentation of the influence of beaver dams on the dynamics of changes in the layout and directions of groundwater filtration in the quarter. Changes in the conditions and resources of phytocoenoses in the study area caused by periodic changes in the water regime, in particular in natural habitat 6510, were also analysed in the selected two periods, i.e., before (2014–2015) and after the occurrence of beaver dams (2023–2024).

2. Materials and Methods

2.1. Research Facility

This research was carried out on a fragment of an unused sub-irrigation system located on organic soils in the Mała River valley in central Poland. The analysed area (Figure 1a,b) is part of the Łąki Soleckie facility (EPSG:2180: N: 52 02′17.187″, E: 21 05′48.759″), located in the Chojnowski Landscape Park, in a protected area, as part of the Natura network 2000 (PLH140055—Łąki Soleckie). The Special Habitat Protection Area covers the peaty valley of the Mała River, and the botanical composition of the fen includes low sedge and sedge-reed peats with a medium degree of decomposition [32]. Near the P4 measurement cross-section (Figure 1b), there is a mineral soil classified as gley soil, Stagnic Folic Gleysols–Arenic. In the remaining cross-sections towards the river, there is a shallow layer (up to 45 cm) of low sedge and reed sedge peat with a medium to strong degree of decomposition, classified as organic soil, Eutric Histic Glaysols (Drainic). Below the organic layer, there is a quaternary loose sand layer.
The protection area includes the peat-covered valley of the Mała River, which is a right-bank basin of the Jeziorka River. The Mała River’s catchment area is 72.8 km2. According to the hydrographic division, the research facility is located in the partial catchment area of the Mała River from the tributary from Wólka Dworska (right-bank tributary) to the tributary from Kawęczynek (right-bank tributary). The catchment area of the Mała River up to the cross-section of the Piaseczno–Góra Kalwaria road is 39.9 km2. The catchment area of the Mała River is located in an area characterized by an average unit runoff Sq = 3.5 l s−1 km2 and an average low runoff SNq = 0.75 l s−1km2. Flows for the Mała River catchment area in the Piaseczno–Góra Kalwaria road cross-section, calculated according to Bryła et al. [39] based on unit runoff maps included in the Hydrological Atlas [40], are average annual flow SQ = 0.14 m3s−1, and average low annual flow SNQ = 0.03 m3s−1. Ordinary flows of the Mała River in the Piaseczno–Góra Kalwaria road cross-section according to Kaca [41] are annual ordinary flow Q50% = 2.79 m3s−1, and summer ordinary flow QL50% = 1.89 m3s−1.
In the fen peat area, in the early 1970s, 62 drainage and irrigation ditches were made, part of the seepage sub-irrigation system for active agriculture production. In the early 2000s, agricultural production was discontinued, and recreational activities developed related to the operation of a nearby stud farm. Currently, this system is not used for irrigation [29]. In 2015, the activity of beavers was observed in this area, consisting of building dams in the bed of the Mała River.
A site located in the immediate range of three beaver dams was selected for analysis (Figure 1b). The D1 dam at km 8 + 350 existed in 2020, and the D2 dams at km 8 + 195 and D3 at km 8 + 045 existed in 2021–2022. The periods of occurrence of beaver dams D1, D2, and D3 are marked with horizontal lines. The analysed plot is located on the left bank of the Mała River and is located between the mouth of the R-29 ditch at km 8 + 395 and the mouth of the R-27 ditch at km 8 + 305. The spacing of the ditches is 90 m. There are four cross-sections, P1, P2, P3, and P4, perpendicular to the longitudinal axis of the section and the ditches, including measurement wells S1, S2, S3, and S4 located in the centre of the section and the beds of the adjacent ditches R-27 and R-29.
The slope from the top to the bottom of the cross-section of the terrain along the central axis of the plot is more diverse than along the edges of the ditches. The average slope of the terrain in the axis of the plot is 2.4‰, along the bank of the R-29 ditch it is 2.3‰, and along the R-27 ditch it is 2.2‰. The average slope of the bottom of the R-29 ditch is 2.3‰ and that of the R-27 ditch is 2.8‰. In the upper part of the plot, from its border to the P4 measurement section, there is sandy soil. In the remaining part of the plot, at the measurement sections P1, P2, and P3, there are degraded peats, meaning muck peats on sand up to a depth of 0.45 m.

2.2. Research Methodology

In the measurement periods from 1 April to 31 October in the years 2020–2022, measurements were made on the position of the water table in the Mała River, in ditches R-29 and R-27 and in wells S1, S2, S3, and S4. The rainfall amount from 2020–2022 was obtained from the meteorological station (A-Ster TPG 124 tipping bucket gauge) installed on the Solec peat fen. The rainfall totals in the analysed periods in individual years were: 2020: 524.2 mm, 2021: 385.5 mm, and 2022: 298.2 mm. To measure water levels in the Mała riverbed above and below the current beaver dam and in ditches, water gauges were installed, and groundwater measurements in wells were made using a hydrogeological whistle. In each analysed year, geodetic measurements of the soil surface and the bottom of ditches were made along sections P1, P2, P3, and P4.
The impact of the effects of beaver activity on the conservation status of habitat 6510 was analysed within the research area directly affected by the dam (Figure 1). On the designated plant patches, at the intersection of a straight line to the plot where constant monitoring of groundwater was carried out, the species composition of communities and their range were determined in 2014–2015 (in 10 points) and 2023–2024 (in 10 points). In accordance with the guidelines of the monitoring of natural habitat 6510 [42], phytosociological releves were taken in designated plant patches, what was the basis for further analyses. The phytosociological stability of the species, the structure, and functioning of communities were determined, and the value of the Ellenberg [43] indices was calculated. Ellenberg’s phytoindicators were used to determine the light conditions (L), humidity (F), and fertility (N) of the habitat.

3. Results and Discussion

3.1. Beaver Activity

Before the beavers’ appearance, the water level in the Mała riverbed in the summer was on average 0.30 m, and the ditch beds remained dry. Water retention in the Mała riverbed in the period without beaver dams on the section above the D1 dam cross-section was estimated at V1 = 157 m3, and on the section between the D1 and D2 dam cross-sections, V1–2 = 84 m3 (total 241 m3). After the construction of beaver dams, these volumes increased significantly [44]. The maximum retention of the system in 2020 was 1670 m3 (the riverbed retention of the Mała River was 1300 m3, the retention of the R-29 ditch was 270 m3, and the R-27 ditch was 100 m3). In 2021, the largest system retention was 2180 m3 (1700 m3 in the Mała riverbed, 270 m3 of water accumulated in the R-27 ditch, and 210 m3 in the R-29 ditch). The system retention in 2022 was 1650 m3 (1200 m3 accumulated in the Mała riverbed, the retention of the R-27 ditch was 250 m3, and the R-29 ditch was 200 m3). The maximum periodic backwater range of the water in the Mała River above the D1 beaver dam in 2020 was 650 m, and above the D2 beaver dam in 2021 and 2022, it was 800 m.
In 2020, there was a D1 beaver dam in the Mała riverbed, located halfway across the width of the analysed section, in the middle of the R-29 and R-27 ditches (Figure 1). This dam occluded the upper water in the Mała riverbed to a height of (70–80) cm in relation to the lower water (Figure 2). After 21 May 2020, as a result of beavers lifting the dam and heavy rainfall, the water table in the river continued to rise. Over the next three weeks, the water table in the river stabilized. After the damage of the D1 dam on 26 June 2020, the water in the riverbed gradually decreased. After one month, on 25 July 2020, the D1 dam was rebuilt, which resulted in water rising in the river to a height of 55 cm. The next dam removal took place on 10 August 2020, but beavers rebuilt it just two days later. The rebuilt beaver dam and intense rainfall resulted in an increase in the upper water table on the dam to a height of 30 cm compared to the lower water level. Once again, the dam was removed on 5 September 2020 and rebuilt by beavers two days later. Later, because of long-term and intense rainfall, the water levels in the riverbed increased. On 10 September 2020, another D2 beaver dam appeared, located at km 8 + 195 (Figure 1). The observed D1 dam existed until 22 September 2020, when it was removed once again, and the beavers did not rebuild it in this location. After the destruction of the D1 dam, the measurement sections in the river remained under the influence of the D2 dam. This resulted in the measured elevations of the upper and lower water tables in the cross-section of the observed D1 dam being the same (Figure 2).
In 2021, there was a D2 beaver dam in the Mała riverbed, located 105 m below the mouth of the R-27 ditch (Figure 1). Both analysed ditches were influenced by the water level of the upper D2 dam. The course of changes in the upper and lower water tables at the observed D2 dam were similar. Increased activity of beavers was noticed on 8 June 2021, when they raised the D2 dam, causing the upper water table to increase, while the lower water remained 60 cm lower. On 20 August 2021, there was a simultaneous increase in the elevations of the upper and lower water tables by 40 cm at the D2 dam, caused by the appearance of another beaver dam, D3, located 150 m below D2. The D3 dam was destroyed on 5 September 2021, which resulted in the water table decreasing in the Mała River (Figure 2). In 2022, from 1 April, there were two beaver dams, D2 and D3 (Figure 1), but on 10 April 2022, the D3 dam was destroyed. As a result, the water level in the Mała River decreased. From 5 May 2022, the elevation of the upper water table increased again as a result of the increase of the D2 dam, and from 5 June 2022, the elevation of the lower water table also increased, which was caused by the reconstruction of the D3 dam. Later in 2022, until the end of October, the water table remained unchanged (Figure 2).
It should be noted that the reconstruction and location of beaver dams was a reaction to human activity related to the removal of beaver structures. The dams were removed because high water levels made it impossible to conduct recreational activities related to nearby stud farms. Consequently, the locations of beaver dams in the third year of observation (2022) allowed more water to be retained in the riverbed, despite lower rainfall compared to previous years. This indicates that beaver-created dams modify natural flow regimes by increasing surface and groundwater retention, thereby moderating extreme events. According to Buckley et al. [45], a single beaver dam may modify the volume of flowing water by at least 3400 m3 per annum or more, depending on the characteristics of the ecosystem. Estimated global beaver ponds store 2.5–11 billion m3 of water [21]. Water storage in long-lasting dry periods occurring increasingly frequently is fundamental, and beavers may form a ‘nature-based solution’ to the land and water resource management problems society faces [46].

3.2. Groundwater Levels

The elevation of the groundwater level in the observation wells changed depending on the surface water levels in the adjacent ditches and the frequency and amount of precipitation (Figure 3). The water level in the ditches depended on the variability of the water level in the Mała River, which was influenced by the activity of beavers. In 2020, differences in water elevations in the R-29 and R-27 ditches resulted from the location of the mouth of the R-29 ditch above the D1 beaver dam, and the mouth of the R-27 ditch below this dam. After the D1 dam was removed on 22 September 2020, similar water table elevation values were observed in both ditches. In 2021–2022, the mouths of ditches R-29 and R-27 were within the backflow curve of the damming of the D2 dam. In 2021, the position of the water table in ditches in sections P1, P2, P3, and P4 was similar to the arrangement of the upper water table above the D2 dam (Figure 2 and Figure 3). In 2021, groundwater levels in all analysed cross-sections in the centre of the canopy were higher than in ditches R-29 and R-27, and increased because of precipitation. In 2021, in sections P2, P3, and P4 (located further from the river), the water table elevations in the R-29 ditch were approximately 10–30 cm higher than the elevations in the R-27 ditch. The level of the groundwater table in the centre of the plot (cross-sections P2, P3, and P4) may result from the infiltration of precipitation into the soil profile. In 2022, due to the presence of the D2 and D3 beaver dams, the upper water table in the Mała River remained at a stable level of 100.15–100.20 m.a.s.l. from the beginning of June (Figure 2). Therefore, the elevations of the ground and surface water tables in the ditches were at similar levels (Figure 3).
In cross-section P4 (Figure 3a), the groundwater table in well S4 located on mineral soil (Stagnic Folic Gleysols–Arenic) 280 m from the river was in the range of 99.80–100.60 m.a.s.l. Changes in position occurred rarely and were caused by intense rainfall in the third decade of June and the first half of October 2020. In this year, the water table in the R-29 ditch was 10–20 cm higher than the water table in the R-27 ditch. During the measurement period of 2021 until June 2022, the water table in the R-29 ditch was 30 cm higher than the water level in the R-27 ditch. This could be caused by the quick reaction of the sandy soil to periodic rainfall. After reconstruction of the D3 dam in 2022, the water table elevations in both ditches were at similar levels.
In cross-section P3 (Figure 3b), in the measurement periods of 2020–2022, the groundwater table in well S3 was in the range of 99.80–100.50 m.a.s.l. In 2022, after reconstruction of the D3 dam, the elevations of the groundwater table in the S3 well were 10–15 cm higher than the elevations of the water table in the ditches. In cross-section P2 (Figure 3c), the groundwater table in well S2 during the three-year measurement period was in the range of 99.65–100.40 m.a.s.l. and was higher compared to the P1 cross-section. In 2022, after the reconstruction of the D3 dam, the elevations of the groundwater table in the S2 well were higher than the elevations of the water table in the ditches by 10–15 cm. In cross-section P1 (Figure 3d), during the three-year measurement period, the groundwater table in well S1 located on organic soil 70 m from the river was in the range of 99.60–100.20 m.a.s.l. In 2021, the elevations of the water table in the R-29 ditch were similar to the elevations observed in the R-27 ditch. In 2022, the water table elevations in the S1 well and the surrounding R-29 and R-27 ditches remained at a similar level of 100.20 m.a.s.l. from 20 May to the end of October. This level was close to the elevation of the upper water table of the D2 dam in the Mała River.

3.3. Groundwater Flow

The dynamics of water flow under the influence of precipitation P (mm) and damming by beaver dams along sections P1–P4 varied greatly. The tested section under the influence of the beaver dam in location D1 in 2020 was fed with upper water from the R-29 ditch and lower water from the R-27 ditch. Forms of underground flow characteristics of porous soil media appeared in the canopy. By maintaining damming in the Mała River, beaver dams influenced the position of the water table in the R-29 and R-27 ditches and created levels that generated a phase of water inflow from the ditches into the section or a phase of its outflow from the section towards the ditches. In individual measurement sections, the elevations of the water table in the well were compared with the elevations in ditches R-29 and R-27, which allowed us to distinguish four forms of groundwater flow in the section (Figure 4):
F1—full irrigation phase, when the groundwater table in the wells in the centre of the plot was below the water table in both ditches (Figure 4a),
F2—high irrigation phase, when the groundwater table in the wells in the centre of the plot was above the high water table in both ditches (Figure 4b),
F3—up irrigation phase, when the groundwater table along the cross-sections was located below the water table in the upper ditch R-29, and above the water table in the lower ditch R-27 (Figure 4c),
F4—down irrigation phase, when the groundwater table along the cross-sections was located above the water table in the upper ditch R-29, and below the water table in the lower ditch R-27 (Figure 4d).
The groundwater elevations ZSi (m.a.s.l.) were determined in wells S1, S2, S3, and S4, and the related surface water elevations Zi(R-29) and Zi(R-27) (m.a.s.l.) were measured in each section in ditches R-29 and R-27. During three years of observation lasting a total of 642 days of the measurement period, 180 measurement series were performed in each of the four examined cross-sections, including measurements of the water table in ditches, groundwater in wells S1–S4, and observations of the process of creating and maintaining beaver dams (Table 1).
Identification of the occurrence of individual phases of filtration flow along the measurement cross-sections was performed for all 720 measurements. The F1 phase, reflecting the full irrigation of the quarter through both ditches, occurred only in seven measurement situations, most often five times in the P1 cross-section in 2022 after the location of the D3 dam stabilized (Figure 5).
Phase F2 occurred most often, as much as 78.33%, indicating the irrigation nature of high water levels of both ditches (Figure 5). Phase F2 (high irrigation phase) was the only form of flow that occurred in 2021 in cross-sections P1, P2, and P3, and in P4 it was also the form that occurred in the prevailing measurement period. Phase F3 appeared only during periods of heavy rainfall. Phase F2 also occurred most often in 2022 in sections P2, P3, and P4. During periods of rising water in the lower D2 dam caused by the construction of another D3 dam, phase F4 appeared.
Phase F3 is a system in which the R-29 ditch serves as an irrigation ditch, and the R-27 ditch serves as a drainage ditch to the Mała River below the D1 dam. Phase F3 (up irrigation phase) most often occurred for the D1 dam in a location along the length of the section. From the observed F3 phase (98 events), as many as 41 events, which is 5.69% of all events, occurred in 2020, when the beaver dam was in location D1. The P1 cross-section located closest to the Mała River was characterized by the greatest dynamics of changes in the position of the water table in the canopy. In cross-section P1, in 2020, phases F2 and F3 alternated, in 2021, only phase F2 was identified, and in 2022, all four phases occurred (Figure 5a).
All occurrences of phase F4 were observed in 2022, when water levels in the river and ditches were influenced by the upper water of the D2 dam, and the water level in the R-29 ditch was lower than in the R-27 ditch. Phase F4 reflects different flow conditions in ditches R-29 and R-27. They could result from different flow resistances caused by different developments of bed vegetation in both analysed ditches. These ditches are characterized by different slopes of the bottom and water table. The average slope of the bottom of ditch R-29 is 2.3‰, and that of ditch R-27 is greater at 2.8‰. At the same time, the average decline in the water table caused by the overgrowing of the riverbed in 2022 in the R-29 ditch was 0.145‰ and was greater than in the R-27 ditch (−0.052‰). A negative value indicates that in 2022, the R-27 ditch was supplied with water, both from rain and from the river, which occurred in 41 of 58 series. Beaver dams can increase surface and subsurface water storage, modify the reach scale partitioning of water budgets and altering low-flow hydrology.

3.4. Phytocoenoses of the Area

In the studied meadow site, the analysed natural habitat 6510 is the subject of protection, occupying the largest area (60 ha), and is represented by various moisture forms of the ryegrass meadow Arrhenathereum elatriolis. In the studied area in 2014–2015, the occurrence of 37 species was detected (Table 2). The number of species and their coverage in the plant community at the observation points varied and ranged from 9 to 18. The greatest phytosociological stability (V) was observed in the case of seven species. Two of them had a share of over 20%, i.e., Deschampsia caespitosa, a species of variable moisture habitats, and Holcus latantus, a species characteristic for drying and depleting organic soils. In 2023–2024, the number of species was similar to the period before the construction of beaver dams, and amounted to 35. Four species were still characterized by the highest phytosociological stability, but only one of them (D. caespitosa) was characterized by the coverage of over 32%. Veronica longifolia occurred much more frequently (V) and with greater coverage (over 20%) than before the construction of beaver dams.
The analysis of the Ellenberg ecological index value, describing the habitat humidity (F), indicates that the higher groundwater level did not change the category of the habitat humidity. The value of that indicator increased from 6.05 to 6.34. The habitat is still humid, close to the lower limit of the parameter qualifying humidity level (6–7). However, the characteristics of that indicator’s value at individual points of the transect shows its significant variation depending on the distance from the river. In the sites closer to the river, the F value was even above the value of 7 (7.56)—the wet habitat, and further away it was close to the value of 5.0 (5.17)—the moderately wet habitat. The average value of the trophism index (N) increased from 3.26 to 3.56, which may indicate the tendency of increasing soil fertility. Similarly to soil moisture, a high value of the standard deviation indicates large variation of this feature in the transect, especially in the period before beaver activity (from extremely poor to moderately fertile). Perfect conditions depend largely on the botanical composition of the community, turf cover, and soil environment conditions. In the period before the construction of the beaver dam, the average light index value (L) was equal to 5.46, which indicates a moderately shaded location. However, the range of differences between individual plant patches varied greatly, from 3.88 to 6.69. In the next period of research, the light conditions were more uniform and corresponded to moderate light conditions.
The structure and functioning of the natural habitat were described with eight required parameters. During the study period, the value and assessment of only one of them did not change—no invasive species of foreign origin were found (Table 3). The value of four parameters resulted in a change in their assessment, from FV to U1 and from U1 to U2. The fragmentation of the habitat was found due to increasing willow bushes. The layer of felt also increased. Currently, these parameters are rated as inadequate (U1). The botanical composition changed unfavorably, making it not typical for this habitat (U2). The coverage of characteristic species decreased, and the dominant species in the sward are still expansive species, and recently also herbaceous ones. The assessment of these parameters has not changed. However, it is still inadequate or bad.
The conservation task plan [47] assumed maintaining the conservation status of habitat 6510 at the U1 level. Due to the characteristics of the area (moist organic soils), the expansion of species of wet habitats due to the activity of beavers [44] and the increasing coverage of Deschampsia caespitosa, achieving this assumption does not seem possible. The increase in bush cover, Veronica longifolia cover, and layers of felt is also disturbing, as it indicates the abandonment of mowing the meadows.
However, taking into account climate change and the introduction of regular, earlier, and low mowing, beaver activity may provide additional support for the protection of ecosystems dependent on the groundwater level [48,49,50]. Maintaining water resources in organic soils is also important due to the ESs these ecosystems provide [4,36,51]. Improving the water balance is just one such ecosystem regulations, but as the authors point out, the positive or negative effects of beaver dams depend on the duration of their operation and the geomorphological conditions of the area [34,52]. In the study area, similarly to another region of central Poland [53], the beaver dam only raised the water level in the riverbed, but this may have a positive impact on water retention in the organic soil environment and reduce carbon dioxide emissions [28]. This will enable the implementation of the EU environmental policy in the field of peatland irrigation and climate protection. As in many other studies [54,55], our study also showed that beaver activity intensifies the processes of introducing marsh species, changing the structure of communities, especially coastal habitats of small rivers. In the studied area, due to the fact that a moderately moist habitat (6510) is protected within the Natura 2000 network, phenomena increasing soil moisture, in the absence of mowing of meadows and the occurrence of expansive herbaceous vegetation that tolerates increased moisture, may lead to the disappearance of these habitats, especially in the zone near the riverbed.

4. Conclusions

Maintaining water levels in facilities with beaver dams is very similar to the regulatory conditions implemented in drainage structures. The difference is that beaver dams can maintain damming year-round, while damming in regulatory structures is periodic and adapted to the production process. Water management using regulatory structures has a lower impact on marshy land, which enables the maintenance of a greater number of meadow plant species. The following conclusions were formulated from the conducted research and analysis of their results:
  • Water resources of the Mała River and adjacent ditches were closely related to the activity of beavers and atmospheric precipitation occurring in this area. For the beaver dam in location D1, in the beginning of 2020, the water levels above the dam were 1.0 m higher than below the dam (Figure 2), which resulted in water from the R-29 ditch irrigating the plot, while it was partially drained by the R-27 ditch (Year 2020 in Figure 3). For the locations of dams D2 and D3 in 2022, water levels in ditches R-29 and R-27 were similar (Year 2022 in Figure 3).
  • The activity of beavers was closely related to their annual life cycle and human activity consisting of periodic removal of rebuilt beaver dams. The dam in location D1 was destroyed four times, and the dam in location D3 twice. After the fourth destruction of the dam in location D1 in 2020, beavers refrained from rebuilding it again in this place (Figure 3).
  • Beaver activity influenced the dynamics of changes in groundwater levels in the plot by changing surface water levels in ditches adjacent to the plot. The greatest impact on these changes was at the location of the D1 beaver dam on the section of the river halfway between the R-27 and R-29 ditches, when the R-29 ditch was under the influence of the upper water of the D1 dam, and the R-27 ditch connected with the lower water (Figure 3).
  • The F2 phase occurred most often, in as many as 78.33% events, indicating the occurrence of high water levels in ditches and atmospheric precipitation. Phase F2 was the only form of groundwater system that occurred in 2021 in sections P1, P2, and P3 (Table 1 and Figure 5).
  • Due to the nature of habitat 6510 and local conditions, it is not possible to improve the conservation status of this natural habitat without taking remedial action.
Beaver-created dams modify natural flow regimes by increasing surface and groundwater retention, moderating extreme events. The novelty of our work is the analysis of the influence of beaver dams on the dynamics of changes in the layout and directions of groundwater filtration in the quarter, demonstrated by the proposed flow phases. Beaver dams kept water in the ditches at high levels, and the occurrence of the F2 (Figure 4b) phase indicates that the groundwater level in the centre of the site depended on direct precipitation for 78.33% (Table 1) of the research period. The results of this study support the argument of Orazi et al. [56] that beaver conservation is not a universal solution to the biodiversity crisis. However, it can certainly be part of a broader strategy to expand the range of ESs, especially in the storage of water and protected habitats. The implementation of alternatives such as network structures and conflict potential between different users requires detailed analysis in a larger number of case studies. The current condition of the habitats, the use of land in the surrounding area, and the implementation of supporting activities, e.g., the introduction of key species characteristic of the habitat, are key reference points.

Author Contributions

Conceptualization, R.O., S.B. and B.P.; methodology, R.O., J.U., M.J.M., J.J. and E.H.; investigation, R.O., J.U., B.P., M.J.M. and I.M.; writing—original draft preparation, R.O., S.B., J.U., B.P., M.J.M., J.J. and E.H.; writing—review and editing, E.H., R.O., S.B. and J.U. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The datasets used and analysed during the current study are available from the corresponding author on reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Land 13 01902 g001
Figure 1. Map of the research facility: (a) Special Habitat Protection Area (PLH140055—Łąki Soleckie); (b) analysed plot.
Figure 1. Map of the research facility: (a) Special Habitat Protection Area (PLH140055—Łąki Soleckie); (b) analysed plot.
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Figure 2. Upper and lower water levels in the Mała River in connection with precipitation and occurrences of beaver dams D1, D2, and D3.
Figure 2. Upper and lower water levels in the Mała River in connection with precipitation and occurrences of beaver dams D1, D2, and D3.
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Figure 3. Water levels in ditches and wells in the four cross-sections: (a) P4; (b) P3; (c) P2; (d) P1; against the background of precipitation (P) and beaver dams (D1, D2, D3).
Figure 3. Water levels in ditches and wells in the four cross-sections: (a) P4; (b) P3; (c) P2; (d) P1; against the background of precipitation (P) and beaver dams (D1, D2, D3).
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Figure 4. Phases of groundwater flow: (a) F1—full irrigation phase; (b) F2—high irrigation phase; (c) F3—up irrigation phase; (d) F4—down irrigation phase.
Figure 4. Phases of groundwater flow: (a) F1—full irrigation phase; (b) F2—high irrigation phase; (c) F3—up irrigation phase; (d) F4—down irrigation phase.
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Figure 5. Occurrence of groundwater flow phases F1—full irrigation phase (red square), F2—high irrigation phase (green), F3—up irrigation phase (blue), F4—down irrigation phase (red triangle) at the four cross-sections: (a) P1; (b) P2; (c) P3; (d) P4.
Figure 5. Occurrence of groundwater flow phases F1—full irrigation phase (red square), F2—high irrigation phase (green), F3—up irrigation phase (blue), F4—down irrigation phase (red triangle) at the four cross-sections: (a) P1; (b) P2; (c) P3; (d) P4.
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Table 1. Frequency of occurrence of four forms (phases) of groundwater flow in the section.
Table 1. Frequency of occurrence of four forms (phases) of groundwater flow in the section.
No.PhaseClassification CriterionNumber of Cross-SectionTotalFrequency
(%)
P1P2P3P4
1F1Zi(R-29) > ZSi and ZSi < Zi(R-27)510170.97
2F2Zi(R-29) < ZSi and ZSi > Zi(R-27)10814916414356478.33
3F3Zi(R-29) ≥ ZSi and ZSi > Zi(R-27)41197319813.61
4F4Zi(R-29) < ZSi and ZSi ≤ Zi(R-27)261195517.08
Table 2. Coverage and stability of species in the transect of habitat 6510 over the years 2014–2015 and 2023–2024.
Table 2. Coverage and stability of species in the transect of habitat 6510 over the years 2014–2015 and 2023–2024.
Species2014–20152023–2024
Coverage (%)StabilityCoverage (%)Stability
Deschampsia caespitosa (L.) P.B.24.6V31.9V
Holcus lanatus L.20.1V7.7V
Poa trivialis L.6.0V1.7III
Ranunculus repens L.5.2V0.0-
Festuca rubra L.12.3IV4.8V
Festuca pratensis Huds.6.2III8.3IV
Veronica longifolia L.5.8III21.3V
Plantago lanceolata L.3.2V3.7V
Anthoxanthum odoratum L.2.4V1.4V
Equisetum palustre L.2.4V0.0-
Veronica chamaedrys L.1.4V0.8II
Potentilla anserina L.1.0III1.4IV
Alopecurus pratensis L.0.2III0.2I
Urtica dioica L.2.4II0.1II
Juncus effusus L.1.2II2.0III
Carex hirta L.0.3II1.1I
Lythrum salicaria L.0.1I1.8IV
Festuca arundinacea Schreb.0.0-4.4III
Galium mollugo L.0.0-3.4III
Other species *5.2 4.0
Total100.0 100.0
Number of species in the transect (in a plant patch)37 (9–18)35 (10–17)
Phytoindicators:
Light conditions (L)5.46 ± 1.15SD
moderate shade		6.26 ± 0.50SD
moderate light
Habitat humidity (F)6.05 ± 0.74SD
humid		6.34 ± 0.84SD
humid
Habitat fertility (N)3.26 ± 0.97SD
poor		3.59 ± 0.68SD
moderately rich
* Species with medium cover below 1%: Arabidopsis arenosa (L.) Lawalrée, Arrhenatherum elatius L., Avenula pubescens (Huds.) Dumort., Carex vesicaria L., Cerastium holosteoides Fr. em. Hyl., Cirsium palustre (L.) Scop., Epilobium hirsutum L., Equisetum palustre L., Epilobium tetragonum L., Filipendula ulmaria, Galeopsis tetrahit L., Galium aparine L., Galium palustre L., Geum rivale, Juncus articulatus L., Lathyrus pratensis L., Linaria vulgaris, Lotus corniculatus L., Phalaris arundinacea L., Phragmites australis (Cav.) Trin. ex Steud Poa palustris L., Poa pratensis L., Ranunculus acris L., Rumex acetosa L., Rumex crispus L., Silene flos-cuculi (L.) Greuter and Burdet., Valeriana officinalis, Vicia hirsuta (L.) Gray.
Table 3. The specific structure and functions of habitat 6510 over the years 2014–2015 and 2023–2024.
Table 3. The specific structure and functions of habitat 6510 over the years 2014–2015 and 2023–2024.
ParameterParameter ValueParameter Evaluation
2014–20152023–20242014–20152023–2024
Spatial structure of habitat patchesuniform meadow surface,
no fragmentation		medium degree of fragmentation, due to the formation of bushesFVU1
Characteristic speciesFestuca rubra (“+” −45%) *, Plantago lanceolata (5–15%), Poa pratensis (“+” −10%),
Arrhenatherum elatius (+).		Festuca rubra (5–15%), Plantago lanceolata (5–10%),
Poa pratensis (<5%),
Galium mullugo (5–20%).		U1U1
Dominant speciesDeschampsia caespitose (5–70%), Holcus lanatus (10–60%)Deschampsia caespitose (5–60%) Veronica longifolia (5–70%)U2U2
Invasive alien specieslacklackFVFV
Expansive species of herbaceous plantsD. caespitose (as above), Urtica dioica (5–20%), Galium aprine (<1%).
Total in the transect < 50		Deschampsia caespitose (as above), Urtica dioica (+), Galium aprine (<5%)
Total in the transect < 50		U1U1
Expansion of shrubs and offshootscoverage < 1% on transectcoverage 1–5% on transectFVU1
Share of well-preserved habitat patchespatches not typical, medium richplant patches in the transect are poorly preservedU1U2
Felt<2 cm2–5 cmFVU1
* Percentage of species in the vegetation patch. FV—Favourable, U1—Inadequate, U2—Bad.
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MDPI and ACS Style

Oleszczuk, R.; Bajkowski, S.; Urbański, J.; Pawluśkiewicz, B.; Małuszyński, M.J.; Małuszyńska, I.; Jadczyszyn, J.; Hewelke, E. The Impacts of Beaver Dams on Groundwater Regime and Habitat 6510. Land 2024, 13, 1902. https://doi.org/10.3390/land13111902

AMA Style

Oleszczuk R, Bajkowski S, Urbański J, Pawluśkiewicz B, Małuszyński MJ, Małuszyńska I, Jadczyszyn J, Hewelke E. The Impacts of Beaver Dams on Groundwater Regime and Habitat 6510. Land. 2024; 13(11):1902. https://doi.org/10.3390/land13111902

Chicago/Turabian Style

Oleszczuk, Ryszard, Sławomir Bajkowski, Janusz Urbański, Bogumiła Pawluśkiewicz, Marcin J. Małuszyński, Ilona Małuszyńska, Jan Jadczyszyn, and Edyta Hewelke. 2024. "The Impacts of Beaver Dams on Groundwater Regime and Habitat 6510" Land 13, no. 11: 1902. https://doi.org/10.3390/land13111902

APA Style

Oleszczuk, R., Bajkowski, S., Urbański, J., Pawluśkiewicz, B., Małuszyński, M. J., Małuszyńska, I., Jadczyszyn, J., & Hewelke, E. (2024). The Impacts of Beaver Dams on Groundwater Regime and Habitat 6510. Land, 13(11), 1902. https://doi.org/10.3390/land13111902

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