(turloughs) in Ireland - Springer Link

Hydrobiologia (2012) 692:29–40 DOI 10.1007/s10750-012-1000-9

WETLAND SERVICES AND MANAGEMENT

The influence of flood duration on the surface soil properties and grazing management of karst wetlands (turloughs) in Ireland Sarah Kimberley • Owen Naughton • Paul Johnston • Laurence Gill • Steve Waldren

Received: 6 December 2010 / Accepted: 7 January 2012 / Published online: 7 February 2012 Ó Springer Science+Business Media B.V. 2012

Abstract Irish turloughs are hydrologically dynamic karst wetlands that are frequently used as marginal grazing land. We hypothesised that flood duration (FD) is a key driver of the spatial distribution of selected soil properties, and consequently turlough grazing practices. Six soil samples were collected during dry periods from eighteen turloughs between 2006 and 2008. Samples (n = 104) were analysed for pH, organic matter (OM) content, calcium carbonate content (CaCO3), sand/silt/clay content (INORG), total nitrogen (TN) and total phosphorus (TP). Data on flooding duration, flood frequency, grazing regime and vegetation type were collated for each soil sampling point. Multivariate and univariate statistical

Guest editor: Chris B. Joyce / Wetland services and management S. Kimberley (&) Centre for the Environment, School of Natural Sciences, University of Dublin, Trinity College, College Green, Dublin 2, Ireland e-mail: [email protected] O. Naughton P. Johnston L. Gill Department of Civil, Structural and Environmental Engineering, School of Engineering, University of Dublin, Trinity College, College Green, Dublin 2, Ireland S. Waldren Department of Botany, School of Natural Sciences, University of Dublin, Trinity College, College Green, Dublin 2, Ireland

analyses were used to examine the relationships between soil properties, grazing regime and flooding variables. There was a positive association between CaCO3, FD and sedge-dominated communities, whereas INORG had a positive association with grazing and grassland. There was a strong positive association between TN, TP, OM and soil depth rather than FD, and OM was found to be an efficient predictor of TN. Extended FDs in ephemeral karst wetlands are likely to increase the extent and degree of calcium carbonate accumulation in soils, thus, reducing the grazing potential of land. Keywords Irish turloughs Soil nutrient properties Land use Flood duration Flood frequency

Introduction Turloughs are a variant of karst wetland that flood intermittently from groundwater on an annual basis and lack a surface outflow (Working Group on Groundwater, 2004). Habitats with these particular characteristics have been reported in Wales (Campbell et al., 1992) and Slovenia (Sheehy Skeffington & Scott, 2008); however, the greatest global density of this ephemeral wetland type is found in the western region of Ireland. The main policy drivers of turlough conservation are the EU Habitats Directive (HD; 92/43/EEC) and the EU Water Framework Directive (WFD; 2000/60/EC). Turloughs are classified as

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priority habitats (Code 3180) under the HD, the focus of which is on maintaining the species and habitat diversity of the turlough landform and the achievement of a ‘favourable condition’. A first assessment of the conservation status of the turlough habitat for the HD reported an overall poor status, principally owing to an inadequate understanding of turlough structures and functions (NPWS, 2008). The WFD classifies turloughs, along with more commonly occurring fens, bogs and wet heaths, as groundwater-dependent terrestrial ecosystems. The WFD primarily focuses on the relationship between the turlough and the associated groundwater body, and requires the prevention of ‘significant damage’ (Kilroy et al., 2008). Fulfilling the management objectives of both the HD and WFD requires an improved understanding of turlough ecology prior to the development of indicators for assessment and monitoring of conservation status. In this context, a substantial research gap exists with respect to soils as a critical structural and functional component of the turlough habitat. Soils are both the medium in which many ecologically influential biogeochemical transformations take place (Kolka & Thompson, 2006) and the primary storage of nutrients for most wetland plants (Mitsch & Gosselink, 2000). An understanding of turlough soil property variation is important for informing the development of terrestrial phase assessment, monitoring strategies and soil-related ecological research. An understanding of the distribution of nutrient-related soil properties as influenced by flooding and land use factors is also critical for assessing the potential effects of future flooding regime or land use change on ecologically important turlough soil properties. Elucidating the drivers of soil property distribution in wetlands is challenging given the number of factors that affect soil properties. Wetland soil property heterogeneity is linked with differences in parent material, elevation, topography, erosional or depositional environment, vegetation, pedogenic effects and hydrology (Stolt et al., 2001). Turloughs are likely to exhibit a high degree of soil property heterogeneity as the turlough landform is recognised as highly variable with regards to size (\0.1 to [3 km2), depth, topography, groundwater connections and inundation patterns (Sheehy Skeffington et al., 2006). Flood frequency (FF) and flood duration (FD) have been identified as critical factors influencing soil property distribution in groundwater-dependent wetlands (Day

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Hydrobiologia (2012) 692:29–40

et al., 1998). More frequently flooded wetlands have been shown to have higher soil organic matter (OM) contents than less frequently flooded wetlands owing to reduced decomposition rates linked to prolonged anaerobic conditions (Bai et al., 2005). OM content influences the porosity, nutrient availability and cation exchange capacity of soils (Mitsch & Gosselink, 2000) and understanding the influences on soil OM is critical for understanding the productivity of turlough ecosystems. Carbonate accumulation is also common within turloughs. After floodwaters recede, the vegetation of turloughs is often covered with calcite crystals and in some turloughs tufaceous crusts cover bedrock outcrops (Coxon, 1994). Carbonate accumulation in turlough surface soils is likely to influence the soil pH. Soil pH is a critical functional component of soils as pH-controlled reactions alter the solubility, and therefore the availability, of nutrients (Plaster, 2003). Understanding the association between flooding factors, soil carbonate content and pH are important for understanding drivers of nutrient availability in turlough soils. Nitrogen (N) and phosphorus (P) are key productivity drivers in wetlands. Nitrogen is often the most limiting nutrient in flooded soils (Mitsch & Gosselink, 2000), making nitrogen dynamics in turloughs highly significant. P is also an important limiting chemical in wetlands and has been identified as a major limiting nutrient in bogs and freshwater marshes (Mitsch & Gosselink, 2000) and turlough floodwaters (Cunha Pereira et al., 2010). A positive association between FF and soil total P, total N and OM has been reported for wetlands (Bai et al., 2005). Biogeochemical cycling in turloughs is therefore potentially highly sensitive to changes in flooding regime resulting from climate change related increases in winter precipitation (McElwain & Sweeney, 2006) and potential new drainage schemes established in response to local community pressure. The ephemeral nature of turlough flooding facilitates the use of turloughs as marginal grazing land (Visser et al., 2007). Fields often radiate from a central commonage area, resulting in a mosaic of land parcels under different grazing regimes (Sheehy Skeffington & Gormally, 2007). The grazing practices within any turlough land parcel are influenced by the quality of grazing conditions, which are linked to soil conditions, and by the individual circumstances of the landowner. In relation to the latter point, turlough land abandonment is becoming increasingly common and many


turlough land parcels are now ungrazed owing to an increased focus on high-intensity agriculture (Visser et al., 2007). Variation in grazing activities is likely to affect a range of soil properties such as OM and nutrients. An improved understanding of the relationships between soil properties and grazing presence and absence is important for evaluating the implications of turlough land use changes on soil properties. Turlough soils are an important structural and functional element of turlough ecology yet they have rarely been the focus of research. Understanding the interrelationships of nutrient-related soil properties and flooding and land use factors is critical for developing an improved understanding of turlough ecological functioning. Our objective was to examine the relationships between flooding, land use and surface soil properties in turloughs.

Materials and methods Site selection Eighteen turloughs representing the geo-hydrological spectrum were chosen using best available hydrological criteria (Fig. 1). The geographical coordinates are provided for each turlough (Table 1). Fifteen of the sites are designated as candidate Special Areas of Conservation under the HD (92/43/EEC). Brierfield, Carrowreagh and Rathnalulleagh are solely designated as natural heritage areas under national legislation. Soil sampling and analyses Two surface soil samples were collected from the upper, middle and lower elevation zones of each turlough (n = 6) to a maximum depth of 20 cm. Vegetation communities are generally distributed in concentric zones within a turlough (Goodwillie, 2003) and were used to delimit the sampling zones. Samples were analysed for pH, OM content, calcium carbonate content (CaCO3), non-calcareous sand/silt/clay fraction (INORG), total nitrogen (TN), total phosphorus (TP). Estimations of pH were made on an approximately 1:2 (v:v) suspension of moist soil and doubledistilled water (Allen, 1989) using a Jenway 3030 calomel electrode. Prior to remaining analyses, samples were air-dried and passed through a 2 mm sieve. OM was measured as a percentage weight loss

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following ignition at 550°C (Allen, 1989). CaCO3 was estimated as a percentage weight loss following loss on ignition by further ignition at 1,000°C (Dean, 1974). INORG was calculated as the initial sample weight less OM and CaCO3 fractions. TN was measured according to Verado et al. (1990) using an ELEMENTAR analyser. TP was measured by nitric acid (69%) digestion (Kuo, 1996) using an MDS 2000 microwave digestor followed by ICP (inductively coupled plasma) analysis. Reference soil material was included during the TP digestion procedure which indicated an 85% P recovery. TP concentrations were consequently increased by 15%. Environmental variables The elevation of each soil sampling point was determined by applying the GPS-positions to digital elevation maps using GIS-software (ArcView, ESRI Inc., USA). The topographic GPS surveys were carried out using a Trimble R6 GPS system with a horizontal and vertical accuracy of 10 and 15 mm, respectively. Contour maps and depth–area relationships were computed for each turlough using SurferÒ version 8.6. The water depth in each turlough was continuously measured using Mini-DiverÒ DI501 and DI502 monitors (Schlumberger Water Services) placed in the bottom of each turlough. For each soil sampling point the duration and frequency of inundation was determined for the 2-year period from 1st January 2007 to 31st December 2008. The duration of the inundation is here characterised by the total number of flooded days or FD. The inundation frequency (FF) is the number of inundation events over the 2-year period. Land use was described as either grazed or ungrazed. Grazed land parcels are currently rotationally grazed whereas ungrazed land parcels are not rotationally grazed but may be sporadically grazed by horses, geese or wild goats. Vegetation at each sampling point was broadly classified into one of three vegetation categories, comprising grassland, sedge-dominated and aquatic community types (Sheehy Skeffington et al., 2006). Data analyses Turlough boundaries are undefined and one sample from each of four turloughs lay just outside the maximum recorded flood level for 2007 and 2008.

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Fig. 1 Geographical distribution of the 18 turloughs studied (abbreviations are explained in Table 1). Shaded areas correspond to areas of pure-bedded limestone (geological data from the Geological Survey of Ireland Database: http://www.gsi.ie/Mapping.html)

Table 1 Turlough names, site codes and locations (Fig. 1) Turlough

Site code

Irish national grid

Ardkill

ARD

127360 262500

Blackrock

BLA

149780 208130

Brierfield Caherglassan

BRI CAH

181600 276560 141235 206225

Caranavoodaun

CARA

145314 215421

Carrowreagh

CAW

178420 275080

Coolcam

COO

157420 271390

Croaghill

CRO

159631 270711

Garryland

GAR

141750 204050

Knockaunroe

KNO

131317 193982

Lisduff

LIS

184250 255500

L. Aleenaun

ALE

127740 195440

L. Coy

COY

149000 207500

L. Gealain

GEA

131502 194828

Rathnalulleagh

RAT

177710 273760

Skealoghan

SKE

124737 262878

Termon

TER

140941 197346

Turloughmore

TUR

134950 199480

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These samples were excluded from the data analysis as hydrological information could not be generated for these sampling points. The final data set therefore consisted of 104 samples. Descriptive data analyses were carried out using SPSS 16.0 (Norusis, 2008). Outlying values were checked and validated. Multivariate analysis We used non-metric multidimensional scaling (NMS) ordination to detect environmental gradients underlying variation of soil properties across turloughs. NMS avoids assumptions of linearity among variables and has the capacity to deal with a variety of variables with a minimum of distortions (McCune & Grace, 2002). Normality of soil property data (pH, OM, INORG, CaCO3, TN, TP) was checked using the Kolmogorov– Smirnov (n [ 50) test prior to analyses. TN and TP were log-transformed and OM, INORG and CaCO3 were arcsine-root transformed prior to NMS ordination. Soil properties were standardised using the Z transform prior to ordination to remove arbitrariness


in the units of measurement (Odeh et al., 1991). The NMS ordination was performed using the Euclidean distance measure and autopilot in the PC-ORD package version 5 (McCune & Mefford, 1999). Joint plots were used to illustrate the gradients of soil property variation across sites. Kendall tau rank correlation coefficients were used to examine the relationships between the environmental variables (soil depth, FD, FF, grazing and vegetation type) and the ordination axes. Vegetation categories were converted to binary variables prior to correlation with the ordination axes. The significance of Kendall tau correlation coefficients was tested using the asymptotic approximation for n [ 40 (Rohlf & Sokal, 1995). Univariate analyses Univariate analyses were used to further investigate the associations between soil properties and environmental variables. As data were non-normally distributed, Spearman rank-order correlation was used to examine associations between FD, FF and soil properties. Relationships between variables with highly significant (P B 0.001) associations (Zar, 1972) were investigated further using scatterplots. Univariate analyses were also used to investigate the effect of grazing regime (grazed/ungrazed) and vegetation type on soil TN and TP. Data normality was checked using either the Kolmogorov–Smirnov (n [ 50) or Shapiro Wilks (n \ 50) test prior to analyses and post transformation. The Mann–Whitney U test was used to compare TN and TP among grazing regimes as transformation did not yield even an approximately normal distribution. One-way analysis of variance (ANOVA) was used to compare TN and TP among vegetation types. Data were log-transformed prior to analysis. The Games Howell post hoc test and the Welch and Brown-Forsythe tests (Field, 2009) were used in the absence of homogeneity of variance among vegetation types to verify significant differences. These analyses were conducted using SPSS 16.0.

Results Summary statistics of the results (n = 104) are presented in Table 2. The TN concentrations of samples ranged from 3,600 to 34,300 mg kg-1, with

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a median value of 9,070 mg kg-1. TP concentrations ranged from 244 to 3,270 mg kg-1 (median = 1,019 mg kg-1). The pH status of turlough surface soils ranged from acidic (\5.5) to alkaline ([7.4). The majority of soils were circumneutral (5.5–7.4) and alkaline soils were more common than acidic soils. The two acidic soils were mineral in nature, rather than acidified peats, with INORG contents in excess of 70%. CaCO3 was the most positively skewed variable, with 13 samples with greater than 50% calcium carbonate content. CaCO3 in the main body of data ranged between 3.7 and 15.1%. The data set was approximately equally divided (median = 21.6%) between mineral (\20% OM) and organic soils ([20%). A wide range of INORG was also recorded (6.3–90.7%, median 61.5%). The NMS ordination of soil properties lead to a three dimensional solution with an acceptable final stress (6.6%) and instability (0.00778) after 200 iterations were run. The ordination extracted a high proportion (97.2%) of total variation in the data set, with 36.9% loaded on Axis 1, 9.7% loaded on Axis 2 and 50.6% loaded on Axis 3. The NMS therefore revealed two major gradients of variation. The two main axes (Axes 1 and 3) account for 87.5% of the variation and are presented in Fig. 2. Associations between environmental variables and NMS axis scores are presented in Table 3. The NMS ordination illustrates that soils are distributed as a continuum along the main axes. Axis 3 presents a pH/INORG gradient, the extremes of which are acidic mineral soils and calcareous alkaline soils. The biplot shows that INORG increases with increasing axis scores and both pH and CaCO3 increase with decreasing axis scores. Most samples from Caherglassan, Blackrock, Garryland, Coy, Rathnalluleagh, Carrowreagh and Turloughmore form a relatively distinct cluster towards the top of Axis 3. These turloughs have acidic soils with high proportions of sand/silt/clay. Distinctly alkaline samples from Termon, Ardkill, Lisduff, Aleenaun are located towards the extreme lower end of Axis 3. Along Axis 3, there is a significant positive association between grass and grazing and axis scores and a significant negative correlation between FD and sedge communities and axis scores (Table 3). Non-calcareous mineral soils are positively associated with grazed grassland and relatively shorter FDs whereas calcareous soils are associated with sedge-dominated vegetation and

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Table 2 Soil nutrient properties used in the study and their statistical characteristics (n = 104) Variable

Acronym

Unit

Min

Q1

Total nitrogen

TN

mg kg-1

3,600

6,350

9,070

16,019

34,300

Total phosphorus

TP

mg kg-1

244

628

1,019

1,373

3,270

pH Calcium carbonate

pH CaCO3

%

5.1 0.5

6.4 3.7

6.9 5.6

7.9 15.1

8.5 77.5

Organic matter

OM

%

6.9

15.2

21.6

40.4

82.3

Non-calcareous inorganic content

INORG

%

6.3

25.7

61.5

79.7

90.7

Median

Q3

Max

Fig. 2 NMS ordination of 104 samples in variable space with soil properties overlaid. Symbols indicate turlough site. 36.9% of the variation is loaded on Axis 1 and 50.6% of variation is loaded on Axis 3. Biplot vector cut-off is 0.6. The length of each biplot line is proportional to the r2 of the indicated variable with the axis; the direction indicates the direction of increasing values in the graph. TN total nitrogen (mg kg-1), TP total phosphorus (mg kg-1), INORG percentage noncalcareous inorganic content, OM organic matter, CaCO3 calcium carbonate

1.5

Axis 3

Q1 lower quartile, Q2 upper quartile

INORG

0.5

TP

-1.5

-0.5

0.5

TN OM

1.5 Axis 1

Turlough Sites Ardkill Blackrock Brierfield Caherglassan Caranavoodaun Carrowreagh Coolcam Croaghill Garryland Knockaunroe Lisduff L. Aleenaun L. Coy L. Gealain Rathnalluleagh Skealoghan Termon Turloughmore

-0.5

CaCO3 pH

-1.5

relatively longer FDs. Axis 1 represents an OM/ nutrient gradient. TN, TP, OM and soil depth are positively associated with each other and negatively associated with axis scores along Axis 1 (Table 3). Deep, peaty soils from Knockaunroe, Skealoghan and Croaghill are located at the extreme left of Axis 1 whereas very shallow alluvial mineral samples from Coolcam are located to the extreme right of the same axis. A correlation matrix of Spearman Rank coefficients is presented in Table 4, with highlighted values significant at the P B 0.001 level. CaCO3 and FD exhibited significant positive association (R = 0.445;

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P B 0.001), with samples comprised of more than 50% CaCO3 associated with FDs in excess of 350 days over the 2-year period (Fig. 3a). pH and CaCO3 were positively correlated with each other (R = 0.635; P B 0.001) and both were negatively associated with INORG (R = -0.484 and R = -0.723, respectively; P B 0.001 in both cases). The full range of turlough pH conditions were associated with soils comprised of less than 30% CaCO3, whereas soils with greater than 30% CaCO3 were all strongly alkaline (Fig. 3b). INORG steadily decreased as CaCO3 increased beyond 20% (Fig. 3c). OM and INORG exhibited a strong negative association


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Table 3 Kendall’s tau correlation coefficients between environmental variables and the NMS ordination axes (n = 104) (Fig. 2) Variable

Axis 1 tau

Flood duration

Axis 3 tau

0.068

Flood frequency

-0.257***

-0.073

0.143

Grazing

0.017

Grass

0.164

0.342*** 0.460***

Sedge

-0.147

-0.326***

Aquatic Soil depth (cm)

0.019 -0.280***

-0.138 -0.109

Flood duration: total number of days flooded (January 2007– December 2008), flood frequency: number of inundation events (January 2007–December 2008), grazing: grazing presence/ absence, grass: grass-dominated vegetation community, sedge: sedge-dominated vegetation community, aquatic: aquatic vegetation community *** P B 0.001

(R = -0.744; P B 0.001). There was a strong negative linear association between INORG and OM for soils with less than 20% CaCO3 (Fig. 3d). The relationships between CaCO3, OM and INORG in turloughs suggest that both the sand/silt/clay fraction and organic content steadily decrease as CaCO3 accumulates beyond 20% dry weight. INORG

decreases with increasing OM content in turlough soils with less than 20% CaCO3. Mineral turlough soils can be dominated by CaCO3 or the sand/silt/clay fraction. Both TN and TP exhibited significant positive correlation with OM (R = 0.896 and R = 0.428, respectively; P B 0.001 in both cases). 25% of soils in this study had TN concentrations greater than 16,019 mg kg-1, the majority of which had OM contents in excess of 40%. OM had a strong positive association with soil depth (R = 0.352). TN and OM had a strong linear association, with OM explaining 79% of variation of TN (Fig. 4a). TN also showed a significant negative association with INORG (R = -0.673; P B 0.001) which follows from the strong negative correlation between OM and INORG. All samples with greater than 50% CaCO3 were present within the cluster of outlying samples and a moderate linear association was observed between TN and INORG within the main body of data (Fig. 4b). TP had a weak association with OM (Fig. 4c). There was a significant positive association between TP and FF (R = 0.351; P B 0.001). A general increasing trend was observed between TP and FF (Fig. 4d), with low TP concentrations (\500 mg kg-1) associated with less than seven flood events.

Table 4 Spearman rank correlation matrix of associations between soil properties and hydrological variables (n = 104) Flood duration Flood duration

Flood frequency

TN (mg kg-1)

TP (mg kg-1)

pH

OM

INORG

Soil depth

1

Flood frequency

-0.134

TN (mg kg-1)

-0.061

TP (mg kg-1)

-0.084

1 -0.045 0.351***

1 0.489***

1

pH

0.350***

-0.237

0.041

-0.260

1

CaCO3

0.445***

-0.078

0.267

-0.018

0.635***

OM

0.010

-0.190

0.896***

-0.309

0.141

-0.673***

INORG

CaCO3

Soil depth

0.037

0.093 -1

0.254

0.428*** -0.017 0.353***

0.145

1 0.290

-0.484***

-0.723***

-0.040

-0.015

1 -0.744*** 0.352***

1 -0.253***

1

-1

TN total nitrogen (mg kg ), TP total phosphorus (mg kg ), OM percentage organic matter by loss on ignition, CaCO3 percentage calcium carbonate estimate by ignition, INORG percentage non-calcareous inorganic content, flood duration total number of days flooded (January 2007–December 2008), flood frequency number of inundation events (January 2007–December 2008), soil depth (cm) *** P B 0.001

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Fig. 3 Scatterplots of associations between a calcium carbonate (CaCO3) and flood duration (FD); b pH and calcium carbonate content (CaCO3); c inorganic content (INORG) and calcium carbonate (CaCO3) and d inorganic content (INORG) and organic matter (OM) (open circles [20% CaCO3; closed circles \20% CaCO3)

Fig. 4 Scatterplots of associations between a total nitrogen (TN) and organic matter (OM) and b total nitrogen (TN) and inorganic content (INORG) (open circles \50% calcium carbonate (closed circles [50% calcium carbonate); c total phosphorus (TP) and organic matter (OM) and d total phosphorus (TP) and flooding frequency (FF)

The median TN concentration was significantly higher (Fig. 5a) under the ungrazed regime than under the grazed regime (Mann–Whitney U = 716, P \ 0.05). Conversely, the median TP concentration was significantly higher (Fig. 5b) under the grazed regime than the ungrazed regime (Mann–Whitney U = 753, P \ 0.05). TN varied highly significantly

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among the three vegetation types (one-way ANOVA: log-transformed data, F2,101 = 10.065, P \ 0.001), with sedge having a higher mean TN concentration (13,693 mg kg-1) than grass (8,008 mg kg-1) (Fig. 6a). There was no significant difference in TP among the three vegetation types (Fig. 6b).


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Fig. 5 Variation in a median total nitrogen (TN) and b median total phosphorus (TP) among grazed (n = 76) and ungrazed (n = 28) regimes. Bars not sharing letters represent significant differences at P \ 0.05. Error bars represent the interquartile range

Fig. 6 Variation in mean a total nitrogen (TN) and b total phosphorus (TP) among grass-dominated (n = 42), sedgedominated (n = 43) and aquatic (n = 19) vegetation types.

Bars not sharing letters represent significant differences at P \ 0.001. Data shown are back transformed from log10 transformations. Error bars are ±1 standard error

Discussion

timing and duration of grazing activities at any site. This study found that FD also exerts a positive influence on the CaCO3 content of turlough soil. Similarly, Coxon (1987) found that marl (calcite deposition) accumulation in the sedimentary record was associated with a longer duration of flooding than sand/silt and silt/clay deposits. CaCO3 accumulation is likely to influence the vegetation communities and consequently the grazing potential of turlough land. CaCO3 in turloughs is also composed of shell marl in addition to calcite deposits from incoming floodwaters. Shell marl accumulation is also patchy, being restricted to residual pools, and turloughs which empty completely have a poor snail fauna (Donaldson et al., 1979). In this study, long durations of flooding did not necessarily result in CaCO3 accumulation, however, and floodwater alkalinity is a likely key determinant of turlough soil CaCO3 contents. Cunha Pereira et al. (2010) reported that mean seasonal turlough alkalinities range between 112 and 236 mg l-1 and such variation is likely to influence the spatial distribution of CaCO3 deposition. CaCO3 accumulation is also linked to flooding depth. Physical agitation of shallow alkaline turlough waters by wind action can speed the release of carbon dioxide to the atmosphere (Coxon,

The positive association between grazing, grassland and non-calcareous mineral soils identified by this study suggests that turloughs with mineral soils are relatively more intensively grazed than turloughs with calcareous soils. Turlough mineral soils are associated with relatively shorter FDs than calcareous turlough soils, supporting the assertion that management practices are influenced by the inherent grazing potential of a turlough and soil properties, which in turn are shaped by hydrological regime (Moran et al., 2008). Soil drainage is a major determinant of the grazing potential of land, with a relatively lower production capacity associated with wet soils (Lee, 1974). Turloughs may or may not contain free draining till subsoils (Coxon, 1987), the presence of which is likely to exert a positive influence on the sand/silt/clay content of turlough soils and consequently the grazing capacity of land. Debate persists as to whether till subsoils are the ‘cause’ rather than the ‘result’ of relatively shorter turlough FDs (Coxon, 1987). Less palatable sedge-dominated vegetation communities are associated with soils with higher soil moisture contents than grass/forb-dominated communities (Regan et al., 2007). FD also directly influences the

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1994) and patchy CaCO3 deposition may result. The pH status of soils was positively related to the accumulation of CaCO3 although the relationship was non-linear. The pH range identified in this study was broader than the range determined by Regan et al. (2007) across thirty turloughs (6.6–8.6), however, more acidic soils have been previously reported for turloughs (Kimberley & Waldren, 2005; Moran et al., 2008). An increase in soil pH related to the input of calcium cations from a mineral source is typical; however, organic content can influence this relationship, resulting in the occurrence of lower than expected pH, owing to the complexing of calcium cations to organic compounds or the release of organic anions (Glaser, 1987). pH conditions in turloughs are also potentially influenced by highly fluctuating moisture conditions as soil saturation can make the pH of both acidic and alkaline soils converge to 7 (Ponnamperuma, 1972). Evidently, alkaline (pH [ 7.4) turlough soils can have a wide range of CaCO3 contents and the pH status of turlough soils should not be used as an indicator of CaCO3 content. CaCO3 contents in excess of 30% reliably indicate alkaline pH conditions, however. Regional climate model predictions for Ireland (McGrath et al., 2005) predict increases in rainfall quantities and in the frequency of extreme precipitation events during winter months. These conditions would result in extended FDs in turloughs which may increase the extent and degree of calcium carbonate deposition and accumulation in turlough soils, potentially reducing the grazing potential of turlough land. Univariate analyses revealed that grazing regime and flooding frequency influence soil TP in turlough soils. TP presented a broad range of concentrations (400–1,600 mg kg-1) which is in accordance to other studies on wetlands (Xu et al., 2009). Many samples from this study lie within the agricultural range, reflecting the use of turloughs as marginal agricultural land. The higher TP of grazed areas may be attributed to nutrient inputs from grazing animals or historical fertiliser application. TP concentrations beyond the natural range ([1,200 mg kg-1) (Zaimes et al., 2008) were generally associated with grazed areas. Extensive data on inorganic and organic P fractions and stocking densities are required to adequately establish the effect of grazing on turlough soil P enrichment. High TP concentrations were associated with a wide number of inundation events whereas low TP concentrations (\500 mg kg-1) were associated with less

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than seven inundation events. Wetting and drying cycles influence soil P dynamics (Sah & Mikkelsen, 1986). Research integrating data on current and historical stocking densities and hydrological regimes is required to characterise the relative importance of grazing and FF on turlough soil TP content. pH or CaCO3 did not exert a significant effect on soil TP concentrations but they are likely to influence the spatial distribution of available P in turlough soils. P forms complexes with calcium at high pH and P availability diminishes as pH increases beyond 7.0 (Plaster, 2003). Research related to P availability in turlough soils should be a priority. Such research should be cognisant of the fact that the mineral fraction of turlough soils can be dominated by either INORG or CaCO3 derived from different sources. Turloughs soils were found to exhibit a wide range of TN concentrations. The TN content of soils is generally very diverse ranging from less than 0.1% to over 2% in highly organic soils (Haynes, 1986). OM was identified as an efficient predictor of TN in turlough soils. This supports the assertion than OM dynamics are tightly coupled to biogeochemical cycles of nitrogen in wetland soils. The higher TN of sedgedominated vegetation communities and ungrazed areas was likely owing to organic accumulation driven by higher lignin contents of Carex spp. and lack of herbage removal, respectively. The botanical origin of organic material is an important characteristic of organic soil (Wen, 1984) and sedge-dominated communities produce litter that is more difficult to decompose owing to higher concentrations of decay resistant compounds (Berendse et al., 1989). Intensive investigations of the effect of hydrological and grazing regime on plant communities in Skealoghan Turlough, Co. Mayo in western Ireland found that litter accumulation in soils decreased with increasing stocking rate owing to herbage removal by grazing animals (Moran et al., 2008). Turlough land abandonment is likely to result in an increase in both soil OM and soil TN concentrations. Results from this study indicate that land use, vegetation and soil depth are more important drivers of turlough soil TN than flooding factors. Highly organic turlough soils tend to be deep, reflecting the potential for peat accumulation in turloughs, and alluvial mineral soils are very shallow. The distribution of these soils is not apparently linked to flooding or land use factors and is more likely linked to differences in parent materials. Highly


alkaline turlough soils with CaCO3 contents in excess of 50% tend to have a narrow low range of TN concentrations possibly owing to sparse vegetation cover and reduced OM accumulation. In conclusion, turlough surface soil properties are highly variable and soil sampling for ecological research or conservation assessment should be cognisant of this variation. The results highlight the importance of determining the nature of the mineral fraction of turlough soils for soil classification purposes. Flooding, land use, vegetation, CaCO3, pH and INORG are significantly interrelated. Increases in turlough FD linked with climate change may result in increased CaCO3 contents in turlough soils which may influence P availability and vegetation community composition. More intensive research should focus on the effects of parent material on turlough soil inorganic content, and on elucidating the influence of different forms of CaCO3 on P availability. Another research priority should be long-term turlough hydrological monitoring which is essential for further evaluating the influences of flooding parameters on turlough soil property variation. Shifts in turlough land use arising from extended FDs, changes in agricultural policy or land abandonment are likely to influence the pools of nutrients available for vegetation. Soil nutrient assessments should not be incorporated into an EU HD monitoring programme for turloughs until the variability and environmental drivers of available forms of soil N and P are investigated. Acknowledgments This research was funded by the National Parks and Wildlife Service, Ireland. The authors thank Mr. Mark Kavanagh and Dr. Norman Allott for laboratory assistance. We also thank the farmers for allowing access to their turlough land. The authors also thank anonymous referees for very useful comments on the first submitted version.

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