Soil properties on sub-Antarctic Macquarie Island: Fundamental indicators of ecosystem function and potential change

Catena 177 (2019) 167–179

Contents lists available at ScienceDirect

Catena journal homepage: www.elsevier.com/locate/catena

Soil properties on sub-Antarctic Macquarie Island: Fundamental indicators of ecosystem function and potential change

T

Brian R. Wilsona,b, , Susan C. Wilsona, Brian Sindela, Laura K. Williamsa, Kirsten L. Hawkinga, Justine Shawc, Matthew Tighea, Quan Huad, Paul Kristiansena ⁎

a

School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia NSW Office of Environment and Heritage, PO Box U221, Armidale, NSW 2351, Australia c Centre for Biodiversity and Conservation Science, School of Biological Sciences, The University of Queensland, St Lucia, QLD 4072, Australia d Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia b

ARTICLE INFO

ABSTRACT

Keywords: Macquarie Island Birds Soil Nutrients Isotopes

We examined the nature and properties of soils on Australian sub-Antarctic Macquarie Island to determine key environmental factors driving their distribution, development and change. We provide the first classification of these soils using Australian and international (WRB) systems while combining elemental, stable and radio-isotope analysis to interpret processes of soil formation and key controlling environmental factors. Soil organic carbon (SOC) and total nitrogen (TN) concentrations across the island were influenced largely by elevation and topographic position with coastal soils and wetter depressions containing more SOC and TN compared with drier and higher elevation locations. Soils on the high, exposed plateau of the island contained low SOC and TN concentrations by comparison. Results suggested that soils of the coastal zone are subject to ongoing aggradation with significant inputs of nutrient, particularly extractable P (Ext P), from oceanic and especially avifauna sources. Nutrient subsidy was concentrated on coastal margins and the more sheltered eastern side of the island, diminishing significantly with increasing elevation and distance from the coast. Soils of the central plateau contained very low Ext P concentrations throughout the profile and appear to be relic if not degrading. Further comprehensive soil mapping, classification and monitoring across Macquarie Island will elucidate the important role that soils serve for healthy ecosystem function in these sub-Antarctic environments and provide early warning indicators of significant environmental change.

1. Introduction Island ecosystems are useful models to study the drivers of environmental evolution and change due to their isolation from other terrestrial systems and associated environmental factors. Sub-Antarctic islands of the Southern Ocean are particularly valuable in this respect being separated from other landmasses by thousands of kilometres of open-ocean (Bergstrom and Chown, 1999; Smith, 2002). Much work on the ecosystems of these islands has focused on the flora and fauna components of the ecosystem (e.g. Copson and Whinam, 2001; Bricher et al., 2013; Scott and Kirkpatrick, 2013; Bergstrom et al., 2015; Williams et al., 2016). Soils, however, may respond rapidly to environmental conditions, and can provide sensitive indicators of environmental processes (Greenslade, 2007; Yergeau et al., 2007). With strong evidence of rapidly changing climates in these environments (Smith, 2002; Bergstrom et al., 2015), a more detailed knowledge of

⁎

soils may offer early warning indicators of significant environmental change (Tarnocai and Bockheim, 2017). Although some recent work has considered the nature, formation and classification of soils of continental and maritime Antarctica (Michel et al., 2014; Bockheim et al., 2015; Schaefer et al., 2015), considerably less attention has focused on the ice-free, sub-Antarctic islands. Macquarie Island (54.30°S 158.57°E) is an Australian sub-Antarctic island approximately 1500 km south-southeast of Tasmania, half way between Australia and the Antarctic continent (Erskine et al., 1998; Varne et al., 2000) (Fig. 1). The island has a unique combination of an intense, maritime, sub-Antarctic climate with high winds, high precipitation (mist, rain, sleet and snow) and low temperatures all year round (Selkirk and Saffigna, 1990). The island has World Heritage listing for its abundant wildlife and its outstanding geological significance (Chown et al., 2001) being one of the few locations on earth where a variety of igneous rocks typical of oceanic crust are exposed at

Corresponding author. E-mail address: [email protected] (B.R. Wilson).

https://doi.org/10.1016/j.catena.2019.02.007 Received 2 October 2018; Received in revised form 14 January 2019; Accepted 7 February 2019 0341-8162/ © 2019 Elsevier B.V. All rights reserved.

Catena 177 (2019) 167–179

B.R. Wilson, et al.

Fig. 1. Location map of Macquarie Island and sample site locations.

the surface. This unique geology has led to the development of a distinctive assemblage of soils on the island that supports unique and diverse ecological communities. These soils, however, have received only limited scientific attention to date (e.g. Hallsworth and Costin, 1950; Taylor, 1955a). Very little is known about their development, distribution and nature, or their stability and vulnerability to a changing climate.

The profile characteristics and basic chemistry of a range of Macquarie Island soils were described briefly by Taylor (1955a) and classified according to the system of Glinka (1928) with modifications following Hallsworth and Costin (1950). At that time soils were classified as sand dune, highmoor peats, fen peats, bog peats and tundra soils (well-drained, poorly drained, vegetated and un-vegetated). No recent attempt has been made to classify the islands soils with respect to 168

Catena 177 (2019) 167–179

B.R. Wilson, et al.

the more recent and currently accepted classification systems such as the Australian Soil Classification (ASC) (Isbell, 2016) or the equivalent international system, the World Reference Base (WRB) (IUSS Working Group WRB, 2014). Key to the nature and condition of soils in this isolated environment is the nutrient and organic matter cycling on the island from internal (terrestrial) sources and external (oceanic) inputs. Macquarie Island is home to large, protected populations of marine mammals (principally seals), penguins and other seabirds that are known to augment nutrient cycles on the island (Erskine et al., 1998). There is evidence to suggest that these marine animals have inhabited the island for in excess of 8000 years (McEvey and Vestjens, 1973; Bergstrom, 1987) contributing excreta and other organic inputs throughout that time. The influence of marine mammals (e.g. Hindell and Burton, 1987; McMahon et al., 1999) and penguin colonies (Robertson, 1986) is evident around the coastal zone. Burrow-nesting and other seabirds are common on steep seaward facing slopes (Schulz et al., 2005) and these seabird colonies have continued to recover and expand since the Macquarie Island Pest Eradication Program (MIPEP) which aimed to remove exotic mammals (principally cats, rabbits, rats and mice) (Copson and Whinam, 2001; Springer, 2016). The consequence of pests and their management on soil nutrient quantity and spatial distribution is, however, unclear. Examination of the quantity and distribution of carbon (C), nitrogen (N) and phosphorus (P) in extant soils reveals much about soil development and current condition. Nutrient enrichment of soils by seabird and marine mammal inputs, particularly of N and P, has been reported widely in isolated island environments (e.g. Smith, 1979; Hawke et al., 1999; Ellis et al., 2006; Otero et al., 2015). Otero et al. (2018) demonstrated that seabirds are major global drivers of N and P cycles and estimated N and P excretion by oceanic seabirds combined in Australasia as a whole was in the order of 27 × 103 and 4.5 × 103 t yr−1 respectively while for the Antarctic and Southern Ocean region, they estimated quantities of 479 × 103 and 79 × 103 t yr−1 N and P respectively. On Macquarie Island, Erskine et al. (1998) estimated an input to the island ecosystem of > 3700 t yr−1 organic matter or 240 t N yr−1 derived from oceanic animal species (penguins and seals) alone. However, these latter estimates focused largely on rookery sites and did not account for other more widely distributed burrowing and nesting avian species and therefore omitted the broader spatial distribution of these materials across the island ecosystem. Seabirds contribute a significant input of material to island ecosystems but these nutrient inputs are unlikely to be uniform and the implications of heterogeneous geographical concentrations of inputs to island systems and the influence on soils remains uncertain. The source and distribution of oceanic/ornithogenic material can be traced in the ecosystem through the analysis of the enrichment or depletion of stable isotopes, principally δ15N and δ13C, in the system. This approach has been applied to detect nutrient subsidy on a range of island systems where patterns of 13C depletion and 15N enrichment of soils have been used to identify and quantify the predominantly oceanic origin of these elements (Bergstrom et al., 2002; Markwell and Daugherty, 2013; Hawke et al., 1999; Hawke and Clark, 2010; Callaham et al., 2012) and the subsequent redistribution of C and N through successive trophic levels (Erskine et al., 1998; Hawke and Clark, 2010; Hawke et al., 2013). Stable isotope analysis of C and N provides a sensitive index of the relative origin of nutrient subsidy to environments dependent upon external inputs. Radio-isotopes (mainly 14 C) have also been used to estimate the age, mean residence time and therefore the stability and rate of turnover of organic matter in soils (e.g. Rabbi et al., 2013; Mathieu et al., 2015; Hobley et al., 2017). These stable- and radio-isotopic techniques can elucidate the source of material and the rate of soil formation and provide knowledge of environmental process, stability and change. These techniques however, have rarely been applied in a sub-Antarctic environment (e.g. Erskine et al., 1998). The work reported here sought to i) provide a preliminary

classification of the soils on Macquarie Island using the ASC (to at least Great-Group level) and the WRB (to Supplementary Qualifier level); ii) examine the quantity and distribution of nutrient and organic matter in soils across the island through elemental analysis of soil organic carbon (SOC), soil total nitrogen (TN) and extractable phosphorus (Ext P); and iii) combine these analyses with stable-isotope (δ13C and δ15N) and radio-isotope 14C analysis to elucidate the nature, distribution and stability of soils in this unique environment to understand their vulnerability, especially in a changing climate. 2. Materials and methods 2.1. Site description Measuring approximately 34 km north-south and up to 5.5 km from west to east, Macquarie Island consists of a well-defined, narrow coastal terrace zone with a steep escarpment to an elongated plateau, between 250 and 410 m in elevation, running the length of the island. Macquarie Island lies on the boundary of the Australian/Indian and the Pacific tectonic plates and is still tectonically very active. The island represents an above sea-level exposure of oceanic crust of the Macquarie Ridge Complex (Varne et al., 2000) and is one of the few locations on earth where a variety of igneous rocks from the earth's mantle are exposed at the surface. These rocks have been dated to approximately 9 Ma (Quilty, 2007) and it is believed that the island emerged from the ocean as a result of tectonic uplift some 600 k–700 k years ago (Adamson et al., 1996). The north of the island is composed largely of rocks from deeper in the oceanic crust and include a variety of intrusive rocks (gabbro, peridotite, dolerite dyke swarms) and extrusive volcanic basalts and volcanic sediment. In the southern part of the island, near-surface rocks of the ocean floor dominate including pillow lavas and volcanic and pelagic sediments. The island has an intense, maritime sub-Antarctic climate with high winds predominantly from the southwest to northwest quadrant, high precipitation (rain, sleet and snow > 900 mm per annum) and cold temperatures (average 4.4 °C July to 8.8 °C January) all year round (Selkirk and Saffigna, 1990; Bureau of Meteorology, 2017). Vegetation communities on the island have been described by Taylor (1955a), Smith (1984) and Williams et al. (2016) and consist largely of tussock grasses and tall and short herb vegetation on lower elevation coastal slopes. Above an elevation of approximately 200 m, “feldmark” vegetation communities dominate. Feldmark (as described by Bergstrom and Selkirk, 1999) is typified by patchy vegetation communities interspersed with gravelly surfaces (typically > 50%) devoid of vegetation cover. These surfaces are believed to result from the extreme exposure of the sites and often retain periglacial patterning as described by Taylor (1955b) and share characteristics with similar “deflation lag surfaces” described in exposed island environments elsewhere (Ferreira and Wormell, 1971; Heindel et al., 2018; Nickling and Neuman, 1995; Wilson et al., 1999). 2.2. Sample collection Soil sampling on the island was undertaken within the University of New England's research program on Poa annua management (AAD4158) during the austral summer of 2014–2015 (Permit ES14363 – 2014-15) following a design that aimed to examine the range of key soil types and environments found on the Island (Fig. 1). Three transects were established across the northern and southern part of the island. These transects were located i) west from Sandy Bay, ii) northwest from Nuggets Point and iii) west from Waterfall Bay and were labelled: Sandy (S), Nuggets (N), and Waterfall (W) respectively (Fig. 1). Along each transect a number of soil cores were collected (Sandy = 9, Nuggets = 7, Waterfall = 11) with the aim of characterising the soils of a range of landforms and topographic environments across the island. No sites with obvious rookery or nesting activity were 169

Catena 177 (2019) 167–179

B.R. Wilson, et al.

Table 1 Study sites on Macquarie Island - ordered by transect and elevation. Site Sandy 1 Sandy 10 Sandy 8 Sandy 9 Sandy 7 Sandy 3 Sandy 6 Sandy 4 Sandy 5 Nuggets 11 Nuggets 12 Nuggets 13 Nuggets 14 Nuggets 19 Nuggets 17 Nuggets 18 Waterfall 1 Waterfall 2 Waterfall 14 Waterfall 3 Waterfall 10 Waterfall 8 Waterfall 7 Waterfall 9 Waterfall 4 Waterfall 6 Waterfall 5 a b

Code a

S1 S10 S8 S9 S7 S3a S6 S4a S5 N11 N12a N13 N14a N19 N17a N18 W1 W2 W14 W3 W10 W8 W7 W9 W4a W6 W5

b

Easting

492,021 494,604 494,575 494,538 494,438 492,023 494,397 492,823 493,397 495,812 495,589 495,590 495,165 493,954 494,466 494,299 491,688 491,600 491,597 491,116 489,563 489,724 489,825 489,637 490,782 490,014 490,139

b

Northing

3,954,697 3,953,567 3,953,598 3,953,524 3,953,630 3,954,653 3,953,637 3,954,128 3,953,878 3,957,545 3,957,720 3,957,719 3,958,291 3,959,151 3,958,809 3,958,899 3,940,868 3,940,952 3,941,032 3,940,867 3,940,899 3,940,842 3,940,754 3,940,853 3,940,685 3,940,735 3,940,762

Altitude (m)

Vegetation type

Topography

Soil type (after Taylor, 1955a)

6 11 15 19 20 24 28 134 141 15 24 73 133 224 255 282 22 74 87 206 220 232 235 246 270 279 301

Tall Tussock Tall Tussock Tall Tussock Tall Tussock Short Grassland Tall Tussock Short Grassland Short Grassland/Herbfield Short Grassland/Herbfield Tall Tussock Tall Tussock Short Grassland Short Grassland Short Grassland/Herbfield Short Grassland/Herbfield No vegetation Mire Short Grassland Short Grassland Short Grassland Short Grassland Feldmark No Vegetation No Vegetation No Vegetation No Vegetation No Vegetation

Beach Dune Beach Dune Coastal Footslope Stream Terrace Above Beach Flat on Lower Slope Coastal Footslope Flat on Mid-Slope Plateau Plateau Coastal Terrace Depression Creek Depression Creek Depression Mid-Slope Feldmark on Plateau Feldmark on Plateau Feldmark on Plateau Coastal Footslope Top of Escarpment Top of Escarpment Mid-Slope Feldmark on Plateau Feldmark on Plateau Feldmark on Plateau Feldmark on Plateau Feldmark on Plateau Feldmark on Plateau Feldmark on Plateau

Sand Dune Sand Dune Highmoor Peat Highmoor Peat Fen Peat Coastal Terrace Highmoor Peat Well Drained Tundra Poorly Drained Tundra Coastal Terrace Fen Peat Highmoor Peat Highmoor Peat Poorly Drained Tundra Poorly Drained Tundra Poorly Drained Tundra Fen Peat Highmoor Peat Highmoor Peat/Well drained Tundra Highmoor Peat Well Drained Tundra Well Drained Tundra Poorly Drained Tundra Well Drained Tundra Well Drained Tundra Poorly Drained Tundra Well Drained Tundra

Denotes sites selected for detailed analysis of profile form, soil properties with depth and Easting and Northing grid references based on UTM projection, Zone 57.

selected. The nature, elevation, vegetation type, topography and soil type (as per Taylor, 1955a) of each sample location were recorded (Table 1). At each of the sites selected, a corer (40 mm internal diameter) was used to collect soil samples to a maximum depth of 40 cm and each core was divided into a number of discrete and consistent depth increments (0–5, 5–10, 10–20, 20–30, 30–40 cm). Logistical limitations allowed only one core sample to be collected at each location. We acknowledge that this creates limitations in our analysis of local soil variability at each site. However, the aim of our investigation was to quantify landscape scale variation and provide a preliminary interpretation of soil nutrient and organic matter patterns across the island. Our sampling approach, while cognoscente of these limitations, nevertheless provides a representative range of samples from across this remote ecosystem. At some locations, rock or other sampling constraints meant that the deepest samples could not be recovered. Each soil sample was stored in dark conditions at 5 °C and transported to the University of New England for analysis.

14

C.

sieve and a sub-sample of each was then ground in a ball mill grinder to pass a < 200 μm sieve. SOC and TN concentrations were determined for each sample at the University of New England, Environmental Analysis Research Laboratory (UNE EARL) using a dry furnace combustion method on a Truspec CNS, LECO analyser (Truspec Corp, Michigan, USA) and expressed as a percentage dry weight, adjusted for 105 °C water content. The presence of carbonates in each sample was tested using hydrochloric acid (HCl), and samples containing carbonates were pre-treated using 2% phosphoric acid (H3PO4) prior to LECO analysis. Soil pH was determined by the glass electrode method using a 1:5 soil:water suspension. Extractable P (Colwell) was analysed at the NSW Office of Environment and Heritage Soils Laboratory, Yanco, NSW following Rayment and Lyons (2011). Briefly, air-dried soil samples (< 2 mm) were extracted using 0.5 M sodium bicarbonate (NaHCO3) (pH = 8.5) and samples were shaken in an end over end shaker for 16 h. The extract was filtered through 0.45 μm filter and the phosphate concentration measured by the molybdenum–blue colorimetric method using a flow injection analyser (Lachat QuickChem 8500 Flow Injection Analyser, Colorado, US). The δ13C and δ15N values for all samples were determined using a Sercon 20–22 (Cheshire, UK) continuous flow isotope ratio mass spectrometer (IRMS) connected to an ANCA-GSL sample preparation unit. Quality assurance for stable isotope analysis was achieved using internal soil standards analysed against certified soil materials (Elemental Microanalysis, Okehampton, UK). IRMS results have certified precision of ≤0.1 (carbon) and ≤0.3 (nitrogen). For each sample, the ratio of 13C to 12C was determined against a known Vienna Pee Dee Belemnite standard again at the UNE EARL. Isotope ratios were expressed using the “delta” notation (δ) of units per mil or parts per thousand (‰) (after Coplen, 2011) using the following calculation (Dalal et al., 2011).

2.3. Soil classification and analysis An initial analysis examined the surface (0-5 cm) concentrations of SOC, TN, Ext P (Colwell) and the δ13C, δ15N in the 27 soils sampled. Extractable P analysis was selected in preference to Total P because extractable P in the soil represents the form of the element that drives ecosystem function through plant growth, organic matter accumulation and cycling. Subsequently, a subset of seven sites (S1, S3, N12, N14, S4, N17, W4) were selected for preliminary soil classification and analysis of SOC, TN, Ext P across the whole core to 40 cm. These sites represented a range of elevation, soil type, site drainage and vegetation cover. These seven sites were subsequently analysed for radio-isotope 14 C with depth in the soil profiles. A preliminary classification was undertaken using detailed profile descriptions of the soil sample cores collected and augmented by profile descriptions provided in Taylor (1955a). All soil samples were dried at 40 °C and crushed to pass a < 2 mm

13C

(‰) =

R sample R standard

1 × 1000

where R is the molar ratio of the heavy to light isotopes (13C/12C) of the sample or standard (Ehleringer et al., 2000; Dalal et al., 2011). Values for δ 15N were also reported using per mil notation relative to the 170

Catena 177 (2019) 167–179

B.R. Wilson, et al.

isotope ratio of atmospheric N2. The 14C analysis of soil samples was undertaken at the Star Accelerator Mass Spectrometry (AMS) Facility at Australian Nuclear Science and Technology Organisation (ANSTO) (Fink et al., 2004). Preparation of the radiocarbon samples followed Hobley et al. (2017). In brief, samples after being pre-treated with 2 M HCl at 40 °C to remove carbonate were converted to carbon dioxide (CO2) at 900 °C, and were then graphitized in excess dihydrogen (H2) over an iron (Fe) catalyst to produce a graphite target for AMS analysis. A small portion of the graphite target was analysed for δ13C (again reported relative to Vienna Pee Dee Belemnite) using an elemental analyser – isotope ratio mass spectrometer (vario microcube EA, Elementar, Hanau, Germany, and IsoPrime Isotope Ratio Mass Spectrometer (IRMS), GV Instruments, Manchester, UK). Radiocarbon content of SOC samples, after correction for machine background, procedural blank and isotopic fractionation using measured δ13C, are reported as conventional radiocarbon ages (in years before present, yr BP, where 0 yr BP is 1950 CE).

concentrations of SOC, TN and Ext P in surface (0–5 cm) samples from all the 27 soil locations (Table 2). There were distinct differences in the quantity and distribution of SOC between the sites where elevation, topographic and drainage characteristics appeared to be primary drivers of SOC, TN and Ext P along the transects sampled (Fig. 2). Soils of the coastal sand dunes (S1, S10), designated Sand Dune soils by Taylor (1955a), were relatively low in both SOC and TN at 0–5 cm depth, ranging from 0.83 to 1.21% SOC and 0.09 to 0.10% TN, while Coastal Terrace soils had moderate SOC and TN (SOC 8.8–14.4%; TN 0.60–1.31%) at 0–5 cm (S3, N11). In surface soils on slopes of the coastal escarpment, higher SOC and TN concentrations were found, particularly in wet depressions and flats to an elevation of up to approximately 200 m (e.g. S8, S9, N12, N13, N14, W2, W3, W14) with SOC ranging from 31.8 to 53.3% and TN from 2.15 to 3.30%. These latter soils were broadly categorized by Taylor (1955a) as “Highmoor” and “Fen Peats”. The SOC and TN concentrations in surface soils (0-5 cm) on exposed higher elevation plateau surfaces (Feldmark) were lower compared with the escarpment slopes. Of these samples, S4, W10, W8, W9, and W4 showed an SOC range 1.0–7.2% and TN from 0.09 to 0.44% and represent soils referred to as “Well Drained Tundra” soils. Soils in the more poorly drained depressions of the Feldmark equating to the “Poorly Drained Tundra” soils referred to by Taylor (1955a) (S5, N19, N17, N18, W7, W6) showed a higher SOC range of 15.1–29.8% and TN range of 1.13–2.39%. Extractable phosphorus concentration in the surface (0–5 cm) soil again varied considerably between the sites sampled with a range of between 19 and 710 mg kg−1 (Table 2). Extractable P concentration was considerably higher in those sites at lower elevation (< 100 m approx.) coastal locations ranging from 50 to 710 mg kg−1 while for those sites above this elevation, Ext P ranged from only 19 to 166 mg kg−1. A plot of the distribution of soil surface (0–5 cm) Ext P concentration across the island (Fig. 2d) further illustrates that soil Ext P concentrations were generally higher in the near coastal zones and at lower elevation. There was a particularly high soil Ext P concentration at the N11 and the concentration of Ext P appeared to be considerably higher overall at sites on the eastern side of the island (Fig. 2d). Although the soil sampling locations were chosen somewhat

2.4. Statistical analysis Soil samples across Macquarie Island were collected along the three linear transects. Along these transects, we examined systematic change in soil SOC, TN, δ13C, δ15N and Ext P as a function of elevation using regression analysis applying a range of linear, polynomial and exponential curve functions. Where significant results were detected, exponential functions provided the best fit with the strength of relationship being determined by evaluation of R2 and probability values. Data relating to δ13C and δ15N were transformed prior to curve fitting using a simple arithmetic transformation (+30 for δ13C and +5 for δ15N) to account for negative values in the curve fitting procedure. All statistical analyses were undertaken in SPSS V6. 3. Results 3.1. Quantity and distribution of SOC, TN and Ext P The sample sites on the three transects across the island covered a range of soil types and environments. Initial analysis examined the Table 2 Surface (0-5 cm) soil properties at sampling sites across Macquarie Island.

Sandy 1 Sandy 10 Sandy 8 Sandy 9 Sandy 7 Sandy 3 Sandy 6 Sandy 4 Sandy 5 Nuggets 11 Nuggets 12 Nuggets 13 Nuggets 14 Nuggets 19 Nuggets 17 Nuggets 18 Waterfall 1 Waterfall 2 Waterfall 14 Waterfall 3 Waterfall 10 Waterfall 8 Waterfall 7 Waterfall 9 Waterfall 4 Waterfall 6 Waterfall 5

Altitude (m)

SOC%

δ13C (‰)

TN%

δ15N (‰)

Ext P (mg kg−1)

Soil type (after Taylor, 1955a)

6 11 15 19 20 24 28 134 141 15 24 73 133 224 255 282 22 74 87 206 220 232 235 246 270 279 301

1.21 0.83 52.21 53.29 50.12 8.79 50.01 2.38 29.51 14.43 33.77 42.66 36.60 20.69 46.40 48.29 43.13 43.22 31.79 37.82 0.98 7.20 15.07 2.24 6.26 29.81 4.89

−26.1 −26.4 −29.3 −26.6 −28.5 −27.5 −28.7 −26.9 −27.0 −28.0 −28.7 −29.3 −27.7 −26.2 −27.2 −27.1 −29.0 −27.7 −27.4 −27.9 −26.8 −26.2 −27.2 −27.19 −24.9 −26.7 −24.7

0.101 0.091 3.300 3.255 3.381 0.602 3.263 0.159 2.388 1.309 2.533 2.214 2.270 1.482 1.955 2.079 2.770 3.179 2.146 2.545 0.091 0.444 1.219 0.167 0.471 1.127 0.474

8.9 4.9 9.8 1.2 2.4 2.9 2.0 −2.3 −1.5 4.7 −2.9 −1.3 −1.4 −2.0 −3.4 −1.9 −0.1 2.3 0.5 −2.3 −0.3 −2.7 0.9 −2.714 −2.475 −3.660 −2.598

174 50 476 173 332 251 372 19 98 710 194 438 166 41 94 87 200 212 99 72 29 25 66 24 23 83 30

Sand Dune Sand Dune Highmoor Peat Highmoor Peat Fen Peat Coastal Terrace Highmoor Peat Well Drained Tundra Poorly Drained Tundra Coastal Terrace Fen Peat Highmoor Peat Highmoor Peat Poorly Drained Tundra Poorly Drained Tundra Poorly Drained Tundra Fen Peat Highmoor Peat Highmoor Peat/Well drained Tundra Highmoor Peat Well Drained Tundra Well Drained Tundra Poorly Drained Tundra Well Drained Tundra Well Drained Tundra Poorly Drained Tundra Well Drained Tundra

171

Catena 177 (2019) 167–179

B.R. Wilson, et al.

Fig. 2. SOC, TN, Ext P, δ13C and δ15N across Macquarie Island derived from three transects (dotted vertical line denotes watershed peak).

opportunistically, when the spatial distribution in these soil characteristics were explored by considering all three transects across Macquarie Island (Fig. 2a,b,c), the concentrations of SOC and TN (which were strongly correlated with each other, R2 > 0.9) clearly reflected the geographical distribution of samples. When this distribution of these elements was tested statistically using non-linear regression (Table 3), the correlation of SOC and TN with elevation on the island was not significant. However, soils on the eastern fall of the island appeared to have higher surface concentrations of SOC and TN overall. For soil Ext P there was a significant (P < 0.001) exponential decrease in this element with increasing elevation with larger concentrations of Ext P on the eastern side of the island. The spatial distribution of δ13C and δ15N was explored by combining the isotope analyses from all three transects across Macquarie

Table 3 Nature and statistical significance of non-linear regression analysis of SOC, TN, δ13C, δ15N and Ext P (0-5 cm) change with elevation, Macquarie Island. Property

Function

df

P value

R2

SOC (%) TN (%) δ13C (‰) δ15N (‰) Ext P (mg kg−1)

n.a. n.a. y = 1.69e0.0027x y = 7.61e-0.004x y = 264e-0.007x

25 25 25 25 25

n.s. n.s. 0.003 0.011 < 0.001

– – 0.33 0.54 0.55

n.a. = not applicable; n.s. = not significant.

172

Catena 177 (2019) 167–179

B.R. Wilson, et al.

Table 4 Soil profile descriptions for selected soils across Macquarie Island. Site

Sandy 1 (S1)

Sandy 3 (S3)

Nuggets 12 (N12)

Nuggets 14 (N14)

Grid Ref Altitude (m) Topography Vegetation Drainage Classification (Taylor, 1955a) Classification (ASC)

492,021 3,954,697 6 Beach Dune Tall Tussock Freely Drained Sand Dune

492,023 3,954,653 24 Coastal Footslope Tall Tussock Moderate Drainage Coastal Terrace

495,589 3,957,720 24 Creek Depression Tall Tussock Poorly Drained Fen Peat

495,165 3,958,291 133 Mid-Slope Short Grass Moderate Drainage Highmoor Peat

Arenic Rudosol

Arenic (?) Sapric Organosol

Hemic Organosol

Classification (WRB)

Arenosol (Aeolic)

Arenosol (Aeolic, Humic)

Description

0–40 cm

0–2 cm

Hemic/Sapric Histosol (Hyperorganic) 0–2 cm Fibric Peat Very Dark Brown (10YR 2/2) pH 4.5 Abundant fine/ medium fibrous roots. 2–22 cm Clear boundary to: Hemic Peat Very Dark Brown (10YR 2/2) pH 4.5 Common fine/ medium fibrous roots Clear boundary to: 22–40 cm Sapric Peat Black (10YR 2/1) pH 5.0 Common fine/ medium fibrous roots

Chernic-Leptic Sapric Tenosol (Organosol where surface organic layer exceeds 40 cm) Umbrisol (Hyperhumic) (Histosol where surface organic layer exceeds 10 cm) 0–6 cm Sapric Peat Black (7.5YR 2.5/1) pH 4.5 Abundant fine-medium fibrous roots No coarse fragments Diffuse boundary to: 6–11 cm Peaty Silty Loam Dark Brown (7.5YR 3/2) pH 5.0 Common fine fibrous roots Few coarse fragments Diffuse boundary to: 11–17 cm Peaty Gravelly Silty Loam Dark Brown (7.5YR 3/2) pH 5.0 Common coarse fragments (< 10 mm) Occasional fine fibrous roots 17–40 cm Diffuse boundary to: Peaty Silty Loam Dark Brown (7.5YR 3/3) pH 5.0 Common coarse fragments (< 10 mm) Few fine fibrous roots

Coarse Sand Very Dark Brown (10YR 2/2) pH 6.0 Colour and texture consistent through the profile. throughout profile Common medium fibrous roots. Abundant white (silicate) sand grains.

2–7 cm

7–40 cm

Peaty (Fibric) Sand Very Dark Brown (10YR2/2) pH 5.5 Common-abundant, fine-medium fibrous roots Gradual Boundary to: Peaty (Hemic) Sand Very Dark Brown (10YR2/2) pH 4.7 Common-abundant, fine-medium fibrous roots Gradual boundary to: Sapric Peat Very Dark Brown (10YR2/2) pH 6.0 Grading to Black (10YR2/1) Occasional medium fibrous roots

Island. Clear relationships for δ13C and δ15N were observed with elevation (Fig. 2a,e,f) and the values differed considerably across the sites sampled (δ13C: −24.7‰ to −29.2; δ15N: −3.7 to 9.8‰) (Table 2). For δ13C, lower (more negative) values (−27.0 to −29.3‰) were detected near to the coastal zones compared with both those more distant from the coast and at higher elevation in the interior of the island (−24.7 to −27.7‰). The δ15N values were much larger (up to +10‰) in soils of the coastal zones (−1.3 to 9.8‰) compared with much lower values (−3.7 to 0.9‰) for inland, higher elevation soils. Highly significant trends with elevation were detected. For δ13C a significant (P = 0.003) exponential increase in values (becoming less negative) was detected with increasing elevation (Table 3), while for δ15N a significant (P = 0.011) exponential decrease in 15N enrichment was found with increasing elevation.

this soil type (particularly the organic horizon “buried” beneath sand) suggests a dynamic, active depositional environment at this location. (See Table 4.) Poorly drained soils of depressions in the coastal fringe (N12) are undoubtedly Histosols (WRB) and Organosols (ASC) and these graded to more aerobic Umbrisols/Histosols (WRB) or Tenosols/Organosols (ASC) in better drained locations on the escarpment slopes (N14). These latter soils were described by Taylor (1955a) as Highmoor peats and their classification in both systems is dependent upon organic horizon depth and will therefore vary by location and drainage class. Soil profiles of the plateau (described by Taylor, 1955a as tundra soils) most closely match the criteria for Regosols (WRB) in well drained locations (S4, W4) while in more poorly drained locations (N17) where organic matter has been able to accumulate they are classified as Histosols (WRB). These latter soils equate to Organosols (ASC). In the ASC system, well drained soils are Tenosols where vegetation cover exists but Rudosols on un-vegetated feldmark locations (Table 4). The soil at site S1 was a sand dune and showed only limited soil development of SOC or TN accumulation. This soil did however, have a reasonably high but consistent Ext P concentration through the whole sampled profile. Other soils on the coastal zone of the island (S3 and N12) showed high concentrations of SOC down the profile (up to 48.7% at 40 cm depth at site S3) and TN (up to 3.5% at depth in soil N12) (Fig. 3). However, for each of these soils, both SOC and TN was relatively low at the surface and increased with increasing soil depth. For soil S3, there was also a high concentration of Ext P (251 mg kg−1 at the soil surface) again increasing to as much as 463 mg kg−1 at 35 cm depth in the soil profile. For N14, a soil on a mid-slope position on the coastal

3.2. Soil profile classification The classifications of the seven cores from across the island showed that the soil (S1) representative of the coastal zone was dominated by windblown sand with contemporary dune sands being classified as Arenic Rudosols (ASC) or Aeolic Arenosols (WRB) (Table 4). Neither classification system used provided an unequivocal classification of the coastal terrace soil (S3). However, given the high sand and organic matter content through the whole sampled profile, and the organic horizon at 7 cm depth in the profile, we believe this soil type most closely matched Humic Aeolic Arenosols using the WRB system. In the ASC system the soil matched most closely a Sapric Organosol. However, we propose a revised Subgroup category for this soil type of “Arenic” to reflect the high sand content throughout. The profile morphology of 173

Catena 177 (2019) 167–179

B.R. Wilson, et al.

Table 4 Soil profile descriptions for selected soils across Macquarie Island (cont). Site

Sandy 4 (S4)

Nuggets 17 (N17)

Waterfall 4 (W4)

Grid Ref Altitude (m) Topography Vegetation Drainage Classification (Taylor, 1955a) Classification (ASC) Classification (WRB)

492,823 3,954,128 134 Plateau Short Grassland/herbfield Well Drained Well Drained Tundra Soil

494,466 3,958,809 255 Feldmark on Plateau Short Grassland/herbfield Poorly Drained Poorly Drained Tundra Soil

490,782 3,940,685 270 Feldmark on plateau No vegetation Well drained Well Drained Tundra Soil

Brown-Orthic Tenosol Regosol (Humic)

Description

0–18 cm

Sapric Organosol Sapric Histosol (Hyperorganic) (possibly Cryosol where patterned ground evident) 0–4 cm Hemic Peat Very Dark Brown (7.5YR 2.5/2) pH 5.3 Abundant fine/medium fibrous roots. No coarse fragments. Diffuse boundary to: Hemic Peat 4–10 cm (7.5YR 2.5/2) pH 5.5 Common fine fibrous roots Diffuse boundary to: Sapric Peat (7.5YR 2.5/1) pH 5.8 10–40 cm Occasional fine/medium fibrous roots. No coarse fragments

Lithosolic Rudosol Regosol (Humic, Skeletic) (possibly Cryosol where patterned ground evident) 0–8 cm Peaty (Sapric) Sand/Gravel Very Dark Brown (7.5YR 2.5/2) pH 5.1 Abundant coarse fragments (5–15 mm) Diffuse boundary to: 8–40 cm Peaty (Sapric) Sand/Gravel Dark Brown (7.5YR 3/3) pH 5.2 Abundant coarse fragments (5–15 mm)

18–26 cm

26–40 cm

Peaty Sand Very Dark Brown (10YR 2/2) pH 5.5 Occasional fine, fibrous roots Abundant white (silicate) sand grains. Diffuse boundary to: Peaty Sand Very Dark Brown (10YR2/2) pH 5.4 Common white (silicate) sand grains. Diffuse boundary to: Peaty Sand Very Dark Brown (10YR 2/2) pH 6.1 Common-abundant coarse fragments (5–15 mm)

escarpment, concentrations of SOC, TN and Ext P were all high in the surface soil (36.6%, 2.3% and 166 mg kg−1 respectively) but diminished with depth and below 20 cm, showed no further change with increasing soil depth. Soils of the plateau (S4 and W4), collected on high elevation, feldmark sites, had comparatively lower concentrations of SOC (2–7%), TN (0.1–0.5%) and Ext P (19–23 mg kg−1) throughout the soil depth sampled and showed little change throughout the sampled profile, but at the poorly drained plateau site, N17, the SOC and TN concentration were somewhat higher. Even in this soil, however, Ext P (< 90 mg kg−1) remained consistently low by comparison with coastal soils.

elevation site N17 the average SOC ages were 745, 800 and 1545 yr BP in the 10–20, 20–30 and 30–40 cm layers respectively. Site S4 at an elevation of 134 m was a well-drained tundra soil with a limited quantity of soil carbon through the entire profile (1.60–4.98%). In this soil, the average age of SOC was in excess of 500 yr BP throughout the 0–20 cm, increasing to 690 and 2810 yr BP in the 20–30 and 30–40 cm layers respectively. At W4, a relatively low carbon (4.6–7.3%), tundra soil at approximately 244 m elevation, there was a radiocarbon age of 1190 yr BP in the surface (0–5 cm) soil increased to an average age of 2475 yr BP at 20–30 cm depth. 4. Discussion

3.3. Radiocarbon (14C) analysis

4.1. Quantity and distribution of SOC, TN and Ext P

The radiocarbon content of soils at various depths at the 7 sites analysed was converted to radiocarbon age (Table 5). Dune soils at site S1 had modern carbon throughout the profile sampled. Coastal sites (S3, N12), both at an elevation of approximately 24 m, displayed similar 14C patterns with depth in the soil, with modern carbon (younger than 1955 CE) dominating the surface soil layers and older carbon at depth. The site N12 was in a low-lying, wet, coastal creek depression and had a Fen Peat soil with large quantities of organic matter through the whole profile. This soil had modern carbon to at least 10–20 cm below surface which increased down profile to 440 yr BP (20–30 cm) and as much as 735 yr BP (30–40 cm). On the sandy, coastal terrace (site S3), there was a similar pattern of modern carbon to 20 cm with an average SOC age of 490 and 585 yr BP in the 20–30 and 30–40 cm layers, respectively. Sites N14 and N17 were at an elevation of 133 and 255 m respectively and both soils had large carbon concentrations, particularly in their surface layers that then diminished with soil depth. Each of these soils showed predominantly modern soil carbon in the 0–5 cm and 5–10 cm layers. Below this soil depth, the SOC age increased in both soils. In the N14 soil, average SOC age reached 350 yr BP and 775 yr BP in the 10–20 and 20–30 cm layers respectively, while at the higher

The quantity and distribution of SOC and TN in soils across the island appeared to be determined largely by elevation, topography and drainage, with larger SOC and TN concentrations on coastal terraces and on lower slopes and wet depressions of the coastal escarpment. Soils above 200 m elevation were typically lower in both SOC and TN albeit with slightly larger concentrations in wetter, more protected depressions. This distribution conforms with patterns identified by Taylor (1955a) and can be explained largely by the very extreme nature of the island's climate. The exposed nature of the higher elevation areas of the island, with low temperatures and low diurnal and annual variation and intense, largely westerly winds, significantly inhibits plant growth and soil development in these areas and therefore limits organic matter accumulation (Campbell and Claridge, 1992). With strong evidence of climate change (drying and warming) in these sub-Antarctic environments (e.g. Smith, 2002), the nutrient and organic matter status of these soils will be subject to significant long-term change, including the potential release of soil carbon into the atmosphere as carbon dioxide and methane (Tarnocai and Bockheim, 2017). Ongoing monitoring of the organic matter status would provide a valuable quantitative indicator to facilitate ecosystem change assessment across the 174

Catena 177 (2019) 167–179

B.R. Wilson, et al.

S1

S3

N12

N14

S4

N17

W4

Soil depth (cm)

0

-10

-20

-30

-40 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50

Soil carbon (%)

S1

S3

N12

N14

S4

N17

W4

Soil depth (cm)

0

-10

-20

-30

-40 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4

Total nitrogen (%)

S1

S3

N12

N14

S4

N17

W4

Soil depth (cm)

0 -10 -20 -30

0 10 0 20 0 30 0 40 0 50 0 0 10 0 20 0 30 0 40 0 50 0 0 10 0 20 0 30 0 40 0 50 0 0 10 0 20 0 30 0 40 0 50 0 0 10 0 20 0 30 0 40 0 50 0 0 10 0 20 0 30 0 40 0 50 0 0 10 0 20 0 30 0 40 0 50 0

-40

1

Extractable P (mg kg ) Fig. 3. SOC, TN and Ext P down the soil profile of selected sites on Macquarie Island.

island, especially given the correlation of SOC and TN. The severe environmental conditions encountered by plants on Macquarie Island, and the consequent limits for SOC and nutrient accumulation, are also likely to constrain the diversity and abundance of soil taxa on Macquarie Island. Resource and habitat limitations further constrain the development of soil biodiversity and their contribution to key soil functions (Yergeau et al., 2007; Powell et al., 2010). For example, Collembola, detritivores which play an important role in the decomposition of dead plant material and in nutrient cycling, had relatively low densities on Macquarie Island compared with those associated with other natural and agricultural vegetation types (Greenslade, 2007). Like SOC and TN, environmental variables such as elevation,

topography and drainage are also known to be correlated with soil microbial communities (Yergeau et al., 2007). Parent materials on Macquarie Island are derived largely form igneous materials and although few estimates of phosphorus content of rocks exist for this environment, generic data (e.g. Porder and Ramachandran, 2013) suggest that they are typically rich in mineral phosphorus (≥900 ppm) and provide a source of this element for soil development. Nevertheless, oceanic/ornithogenic inputs to island systems of this type are typically more significant determinants of differences in the nature and development of soils (e.g. Bancroft et al., 2005) and particularly soil nutrient status (e.g. Smith, 1979; Hawke et al., 1999; Ellis et al., 2006; Otero et al., 2015, 2018) creating significant 175

Catena 177 (2019) 167–179

B.R. Wilson, et al.

Table 5 Radiocarbon analysis of selected soils on Macquarie Island. Site

Sandy 1 (S1)

Sandy 3 (S3)

Nuggets 12 (N12)

Nuggets 14 (N14)

Sandy 4 (S4)

Nuggets 17 (N17)

Waterfall 4 (W4)

Alt (m)

6

24

24

133

134

255

270

Soil Depth

14

C Age

+/− 1σ

14

C Age

+/− 1σ

14

C Age

+/− 1σ

14

C Age

+/− 1σ

14

C Age

0-5 cm Modern – Modern – Modern – Modern – 550 5-10 cm Modern – Modern – Modern – Modern – 510 10-20 cm Modern – Modern – Modern – 350 30 505 20-30 cm Modern – 490 25 440 25 775 30 690 30-40 cm Modern – 585 25 735 25 n.d. – 2810 n.d. = not determined, insufficient sample; No value for +/− indicates > 100% modern carbon The term “14C age” used here does not represent a definite date of soil formation, but in a relative sense indicates that different chemical compounds with different degrees of stability (Krull et al., 2006).

enrichment of N and P. Extractable P values on Macquarie Island were comparable and often considerably larger than values reported in bird affected soils elsewhere (e.g. 31 to 175 mg kg−1 reported by Hawke et al., 1999) but there was a very clear spatial distribution in soil Ext P across the island with low elevation soils showing larger Ext P concentrations than those of higher elevations. These results suggest that soils near the coastal fringe are influenced more significantly by oceanic/seabird inputs. As an example, the large concentration of Ext P at N11 can be explained by its proximity to seabird activity and its use as a thoroughfare between the beach and a large penguin rookery 100 m upslope. Although we acknowledge a smaller number of samples on the western slopes and coastal zone compared with the east, our results suggested a pattern of higher SOC, TN and soil Ext P on the eastern side of the island. The dominant prevailing wind direction on Macquarie Island is from the west (Selkirk et al., 1990) making the eastern side of the island more sheltered. Our results suggest a more intense use and therefore nutrient input from avifauna on the east of the island. Changing distribution and numbers of avifauna on the island, particularly following successful pest eradication, coupled with climate change, has the potential to shift nutrient loads and modify soil processes, properties and ecology across the island. Stable isotopes of C and N have been used to determine the source and movement of external inputs through island ecosystems (e.g. Mizutani and Wada, 1988; Bergstrom et al., 2002; Markwell and Daugherty, 2013; Hawke et al., 1999, Hawke and Clark, 2010; Callaham et al., 2012; Zwolicki et al., 2013) where patterns of 13C depletion and 15N enrichment have both been used to detect the movement of material (principally from seabird guano) from external oceanic/ornithogenic sources to terrestrial ecosystems. Previous work (Mizutani and Wada, 1988; Hawke and Clark, 2010) suggests that carbon inputs from bird guano and associated material might be expected to result in a slight enrichment of 13C (i.e. less negative values) in affected soils. However, we found a very strong 13C depletion (i.e. more negative δ13C) associated with the coastal areas of Macquarie Island. The pattern might represent an altitudinal change in δ13C which has been observed elsewhere in Australia and internationally (e.g. Bird et al., 1994). However, the limited altitudinal range across Macquarie Island (~400 m max) would not support this explanation. A more plausible cause is a higher plant productivity in these nutrient enriched coastal zones with concomitant dilution of ornithogenic carbon in soils by plant material in soils. This result would tend to support the findings of Cocks et al. (1998) that 13C is not a particularly strong indicator of avian inputs to this island ecosystem. The 15N concentration in soils provides stronger evidence for the source of organic matter (oceanic or terrestrial). The atmosphere has a consistent and stable natural abundance of 15N but predators have a tendency to bioaccumulate 15N through the foodchain. Analysis of the enrichment of 15N relative to this atmospheric constant (δ15N) demonstrates the importance of organic matter contributions from

+/− 1σ

14

45 30 25 25 30

Modern Modern 745 800 1540

C Age

+/− 1σ

14 C Age

+/− 1σ

– – 25 20 20

1190 1470 2785 2745 n.d.

20 25 20 25 –

the measured value represents a composite of pools of

animals higher in the foodchain. Our results showed significantly elevated δ15N at coastal sites that decreased with distance inland and 15N values that were comparable with other authors (e.g. Erskine et al., 1998: −3.0 to +13.0‰; Hawke et al., 1999: +2.9 to +8.4‰). This we interpret to represent a change in the dominant inputs of organic matter from “oceanic” (guano derived from seabirds, seals etc.) in coastal environments to “terrestrial” derived organic matter in the higher, inland areas of the island. Erskine et al. (1998) suggested that significant quantities of volatilised ammonium from bird and mammal excrement, that are strongly depleted in 15N, might be transported and contribute to lower δ15N values at higher elevations. This process was particularly well expressed in δ15N of plant tissue. From our results, it is not possible to quantify the extent of this contribution to the N cycle but the low quantities of both C and N at higher elevations are consistent with a diminishing influence of biogenic N. These stable isotope analyses provide further evidence that the nutrient cycles in coastal soils on Macquarie Island are profoundly subsidised by oceanic and ornithogenic inputs. In the case of δ13C, and to a lesser extent δ15N, there was greater impact of these inputs on the eastern side of the island. At higher altitude near-centre of the island sites, this decreased with terrestrial inputs more dominant. This result further illustrates the need to monitor and understand links between fauna and soil condition on the island, so that change induced by climate and pest-eradication can be quantified. 4.2. Soil profile form and classification Soils on Macquarie Island were described and classified by Taylor (1955a) with no further pedological work being undertaken since that time. Our preliminary classification of the island's soils is the first attempt to match Taylor's descriptions to the current Australian Soil Classification (ASC) (Isbell, 2016) or equivalent international system, the World Reference Base (WRB) (IUSS Working Group WRB, 2014). Coastal dunes on the island match the diagnostic criteria of Arenic Rudosols (ASC) or Aeolic Arenosols (WRB) and are clearly composed of aeolian sand subject to contemporary geomorphic processes. These soils would however appear to grade inland on the coastal terrace, to more organic variants which, although classified as Humic Aeolic Arenosols (WRB), are poorly accommodated in the ASC system. In these circumstances, we propose that the soils most closely match Sapric Organosols (ASC) due to the presence of a humic horizon within the top 0.8 m of the profile but these require, as a minimum, an additional Subgroup category of Arenic to reflect the high sand content. The uncertainty of classification of both of these coastal sandy soils using ASC could however, be largely overcome with the introduction of a new order (Arenosols) in the classification system. We also conclude that the organic horizon “buried” beneath sand would suggest an aggrading nature for these soils as a result of continued sand deposition on these coastal zones. Buried soils are not well accommodated in the ASC and 176

Catena 177 (2019) 167–179

B.R. Wilson, et al.

require a further Subgroup category to reflect this. In more poorly drained locations on the coastal fringe and escarpment, Organosols (ASC) or Histosols (WRB) dominate with varying forms and depth of organic material. Such “peatlands” on Macquarie received a brief discussion in Whinam and Hope (2015) but this work related largely to vegetation community structure and less to the detailed morphology of these soils. In more freely drained, aerobic locations with a smaller accumulation of organic matter at the soil surface, Tenosols (ASC) or Umbrisols (WRB) might be a more appropriate classification but this distinction is determined by the depth of organic layers alone. However, Taylor (1955a) reported some soils of this category with surface organic matter horizons in excess of 150 cm and speculated some areas with peat layers that were even deeper. It is also possible that some of these soils match the Podosol (ASC) or Podzol (WRB) classification if deeper, mineral soil layers exist with humus or iron enrichment. However, we observed no such horizons in the soils we examined and such features were only hinted at by Taylor (1955a). Soils of the plateau on Macquarie Island are undoubtedly principally Rudosols (ASC) or Regosols (WRB) on poorly vegetated periglacial gravels (feldmark) while on more poorly drained locations, Organosols/ Tenosols (ASC) or Histosols (WRB) would appear to be more appropriate. On bare, feldmark surfaces, soils perhaps have “cryic” properties (e.g. Michel et al., 2014; Schaefer et al., 2015) where patterned ground and other periglacial features exist. In such cases, soils would be classed Cryosols (WRB) while the ASC has no current class to accommodate these. Although we observed no such features at our sample sites, soils with these characteristics undoubtedly occur at higher elevation, exposed sites on the island and were described briefly by Taylor (1955b). Our work also avoided areas of intense animal or bird use and it might be possible that further classification using “ornithogenic” descriptors (e.g. Schaefer et al., 2015) might be necessary in such locations. There is undoubtedly a need to map and classify soils on Macquarie Island to a greater level of detail to provide baseline information not only on the extent and distribution but to indicate the nature of soil forming processes and to detect any change in such processes. The concentrations of SOC, TN and Ext P in the soils examined to depth, conformed largely with the patterns of soil development across the island described by Taylor (1955a). However, soils of the coastal zone showed a marked increase in each of these elements with increasing soil depth. This provides further evidence that these soils are actively aggrading in this dynamic, sandy environment, with ongoing addition of new, fresh material (organic and inorganic) at the soil surface not unlike those of accretionary aeolian arctic paleoenvironments described by Gaglioti et al. (2018). In contrast, the soils of the high elevation plateau with low concentrations of SOC, TN and Ext P throughout the sampled profile implied a very limited input of fresh material and hence a stagnation or potential degradation of these soils as for other “deflation surfaces” reported elsewhere (Nickling and Neuman, 1995; Wilson et al., 1999). Only in topographic depressions with poor drainage were SOC, TN and Ext P concentrations more elevated in these high elevation environments and even here, soils were depauperate (particularly in Ext P) compared with soils of the lower elevation, coastal zones.

material is accumulating over an older underlying layer (e.g. Mathieu et al., 2015). In soils at higher elevation, highly exposed environments, with lower carbon content, average soil carbon age was in excess of 500 yr BP throughout the soil profile reaching as much as 2800 yr BP in the deeper soil layers, indicating soils with limited organic inputs and slow rates of organic matter turnover. This is suggestive of soils that are either static or declining from a soil formation perspective and these might be the most sensitive soils to environmental change with recent studies indicating the higher temperature sensitivity of older soil carbon (e.g. Davidson and Janssens, 2006; Zhou et al., 2018). Only those soils at high elevation occupying moist, more protected depressions with more complete vegetation cover had evidence of modern carbon accumulation. 4.4. Significance of soils on Macquarie Island The soils across Macquarie Island are critical to the functioning of the island's ecosystems and exhibit a range of features that reflect the dominant environmental factors and processes driving their development. Coastal zones of the island are clearly influenced by contemporary inputs and processes and are aggrading, while others at higher elevation and distance from the ocean are depauperate in nutrients with a slow rate of development or indeed, in some instances, evidence of degradation. The soils of this sub-Antarctic environment therefore provide a sensitive means to detect and predict fundamental changes in ecosystem processes in a changing environment. Mulder et al. (2011) discussed the issue of “legacy” effects on island ecosystems. For example, pre-human patterns of soils and nutrients on an environment such as Macquarie Island will undoubtedly have been significantly affected by human activity. On Macquarie Island the introduction of mammal predators is known to have enhanced erosion and resulted in a decline in bird population numbers and distribution. These effects set a background against which changes in ecosystem character might not follow predictable trajectories. For example, effects induced by potential future increases in bird populations and expansion of their distribution, resulting from the successful pest eradication program, might simply represent a reversion to pre-human conditions. Although it is not possible to fully quantify these historical legacy effects, our results nevertheless, provide a valuable baseline against which subsequent change in soils and their properties can be measured and considered in this context. In the work presented here, we have provided the first baseline soils data for Macquarie Island but more detailed assessment of the current soil resource and ongoing monitoring of soils in this unique environment is essential. This will determine not only the current distribution and nature of soils but detect the nature and rate of change of these soils under changing environmental conditions and provide early warning indicators of accelerating environmental change in this and similar fragile, sub-Antarctic environments. 5. Conclusions Soils sampled across Macquarie Island showed a range of characteristics driven principally by proximity to the coast, elevation and topography with three broad zones of soil development; the coastal zone, sites up to 200 m elevation and environments > 200 m elevation. Soils of the coastal zone and to a lesser degree of the coastal escarpment are clearly influenced by a nutrient subsidy provided by inputs from oceanic/ornithogenic sources and in this zone, contemporary, accretionary processes of soil formation are active. Although we acknowledge limited sample numbers, our preliminary examination of these soils would also suggest that the nutrient subsidy is of a larger magnitude on the eastern side of the island, most probably due to its relative shelter compared with the more exposed west. On the central plateau of the island above 200 m elevation, soils are depauperate (particularly in Ext P) and are exposed to the extreme climatic conditions that prevail

4.3. Radiocarbon (14C) analysis There was some considerable variation in the radiocarbon age of soils on Macquarie Island. Soils of the coastal dune sand (S1) had modern carbon throughout the profile indicating a fresh, dynamic coastal environment of relatively young age. In the low elevation, coastal areas (S3 and N12), soils had predominantly modern carbon in their surface layers again indicating contemporary carbon cycling. Only at depths of 20 cm did radiocarbon age increase, reaching a maximum average age of around 700 yr BP in the deepest of the soil layers examined in this coastal zone. This pattern further suggests an active, accretionary process of soil development at these sites where surface 177

Catena 177 (2019) 167–179

B.R. Wilson, et al.

and consequently, soil forming processes here are exceptionally slow if not in decline. For the first time, we have provided a preliminary classification of soils on the island following the currently accepted Australian Soil Classification (ASC) and World Reference Base (WRB) systems and have suggested some necessary, minor modifications to these classification schemes to accommodate the soils on the island. There is a clear need to more comprehensively map, classify and continue to monitor soil organic matter, nutrient status and condition through regular measurement and a structured monitoring program on Macquarie Island to generate fundamental information relating not only to the extent and distribution of these soils but also to indicate the nature of soil formation and environmental processes. Doing so will provide early warning indicators of significant environmental change in this and similar sub-Antarctic ecosystems.

plants on the inland mountains of Dronning Maud Land, Antarctica, using stable isotopes. Polar Biol. 20, 107–111. Coplen, 2011. Guidelines and recommended terms for expression of stable-isotope-ratio and gas-ratio measurement results. Rapid Commun. Mass Spectrom. 25, 2538–2560. Copson, G., Whinam, J., 2001. Review of ecological restoration programme on subantarctic Macquarie Island: pest management progress and future directions. Ecol. Manag. Restor. 2 (2), 129–138. Dalal, R.C., Strong, W.M., Cooper, J.E., King, A.J., 2011. Relationship between water use and nitrogen use efficiency discerned by 13C discrimination and 15N isotope ratio in bread wheat grown under no-till. Soil Tillage Res. 128, 110–118. Davidson, E.A., Janssens, I.A., 2006. Temperature sensitivity of soil carbon decomposition and feedbacks to climate change. Nature 440, 165–173. Ehleringer, J.R., Buchmann, N., Flanagan, L.B., 2000. Carbon isotope ratios in belowground carbon cycle processes. Ecol. Appl. 10 (2), 412–422. Ellis, J.C., Fariña, J.M., Witman, J.D., 2006. Nutrient transfer from sea to land: the case of gulls and cormorants in the Gulf of Maine. J. Anim. Ecol. 75 (2), 565–574. Erskine, P.D., Bergstrom, D.A., Schmidt, S., Stewart, G.R., Tweedie, C.E., Shaw, J.D., 1998. Sub-antarctic Macquarie Island - a model ecosystem for studying animal-derived nitrogen sources using 15N natural abundance. Oecologia 117, 187–193. Ferreira, R.E.C., Wormell, P., 1971. Fertiliser response of vegetation on ultra-basic terraces on Rhum. Trans. Bot. Soc. Edinb. 41, 149–154. Fink, D., Hotchkis, M., Hua, Q., Jacobsen, G., Smith, A.M., Zoppi, U., Child, D., Mifsud, C., van der Gaast, H., Williams, A., Williams, M., 2004. The ANTARES AMS facility at ANSTO. Nucl. Inst. Methods Phys. Res. B 223-224, 109–115. Gaglioti, B.V., Mann, D.H., Groves, P., Kuntz, M.L., Farquaharson, L.M., Reanier, R.E., Jones, B.M., Wooller, M.J., 2018. Aeolian stratigraphy describes ice-age paleoenvironments in unglaciated Arctic Alaska. Quat. Sci. Rev. 182, 175–190. Glinka, K.D., 1928. The Great Soil Groups of the World and their Development. Edwards Bros Inc. Ann Arbor, Michigan, US. Greenslade, P., 2007. The potential of Collembola to act as indicators of landscape stress in Australia. Aust. J. Exp. Agric. 47 (4), 424–434. Hallsworth, E.G., Costin, A.B., 1950. Soil classification. J. Aust. Inst. Agric. Sci. 16, 84–89. Hawke, D.J., Clark, J.M., 2010. Isotopic signatures (13C/12C; 15N/14N) of blue penguin burrow soil invertebrates: carbon sources and trophic relationships. N. Z. J. Zool. 37 (4), 313–321. Hawke, D.J., Holdaway, R.N., Causer, J.E., Ogden, S., 1999. Soil indicators of preEuropean seabird breeding in New Zealand at sites identified by predator deposits. Aust. J. Soil Sci. 37, 103–113. Hawke, D.J., Clark, J.M., Vallance, J.R., 2013. Breeding Westland petrels as providers of detrital carbon and nitrogen for soil arthropods: a stable isotope study. J. R. Soc. N. Z. 43 (1), 58–65. Heindel, R.C., Chipman, J.W., Dietrich, J.T., Virginia, R.A., 2018. Quantifying rates of soil deflation with structure-from-motion photogrammetry in west Greenland. Arct. Antarct. Alp. Res. 50 (1) (13 pages). Hindell, M.A., Burton, H.R., 1987. Past and present status of the southern elephant seal (Mirounga leonine) at Macquarie Island. J. Zool. 213 (2), 365–380. Hobley, E., Baldock, J., Hua, Q., Wilson, B.R., 2017. Land-use contrasts reveal instability of subsoil organic carbon. Glob. Chang. Biol. 23 (2), 955–965. Isbell, R.F., 2016. The Australian Soil Classification, 2nd edition. CSIRO Publishing, Melbourne, Australia. IUSS Working Group WRB, 2014. World Reference Base for Soil Resources 2014. International Soil Classification System for Naming Soils and Creating Legends for Soil Maps. World Soil Resources Reports Number 106. Food and Agriculture Organization, Rome. Krull, E.S., Bestland, E.A., Skjemstad, J.O., Parr, J.F., 2006. Geochemistry (δ13C, δ15N, 13C NMR) and residence times (14C and OSL) of soil organic matter from red-brown earths of South Australia: implications for soil genesis. Geoderma 132, 344–360. Markwell, T.J., Daugherty, C.H., 2013. Variability in δ15N, δ13C and Kjeldahl nitrogen of soils from islands with and without seabirds in the Marlborough Sounds, New Zealand. N. Z. J. Ecol. 27 (1), 25–30. Mathieu, J.A., Hatt, C., Balesdent, J., Parent, E., 2015. Deep soil carbon dynamics are driven more by soil type than by climate: a worldwide meta-analysis of radiocarbon profiles. Glob. Chang. Biol. 21, 4278–4292. McEvey, A.R., Vestjens, W.J.M., 1973. Fossil penguin bones from Macquarie Island, Southern Ocean. Proc. Roy. Soc. Victoria 86, 151–178. McMahon, C.R., Burton, H.R., Bester, M.N., 1999. First year survival of southern elephant seals, Mirounga leonine, at sub-Antarctic Macquarie Island. Polar Biol. 21 (5), 279–284. Michel, R.F.M., Schaefer, C.E.G.R., López-Martínez, J., Simas, F.N.B., Haus, N.W., Serrano, E., Bockheim, J.G., 2014. Soils and landforms from Fildes peninsula and Ardley Island, maritime Antarctica. Geomorphology 225, 76–86. Mizutani, H., Wada, E., 1988. Nitrogen and carbon isotope ratios in seabird rookeries and their ecological implications. Ecology 69 (2), 340–349. Mulder, C.P.H., Jones, H., Kameda, K., Palmborg, C., Schmidt, S., Ellis, J.C., Orrock, J.L., Wait, D.A., Wardle, D.A., Yang, L., Young, H., Croll, D., Vidal, E., 2011. Impacts of seabirds on plant and soil properties. In: Mulder, C.P.H., Anderson, W.B., Towns, D.R., Bellingham, P.J. (Eds.), Seabird Islands: Ecology, Invasion and Restoration. Oxford University Press, New York. Nickling, W.G., Neuman, C.M., 1995. Development of deflation lag surfaces. Sedimentology 42, 403–414. Otero, X.L., Tejada, O., Martín-Pastor, M., De La Peña, S., Ferreira, T.O., Pérez-Alberti, A., 2015. Phosphorus in seagull colonies and the effect on the habitats. The case of yellow-legged gulls (Larus michahellis) in the Atlantic Islands National Park (GaliciaNW Spain). Sci. Total Environ. 532, 383–397. Otero, X.L., De La Peña-Lastra, S., Pérez-Alberti, A., Ferreira, T.O., Huerta-Diaz, M.A., 2018. Seabird colonies as important global drivers in the nitrogen and phosphorus

Acknowledgements Funding and logistical support on Macquarie Island was provided by the Australian Antarctic Division and its Antarctic Science Program Grant AAS 4158. We thank the Tasmanian Parks and Wildlife Service for access to Macquarie Island and scientific permits. Thanks also to Leanne Lisle and Elizabeth Marshall of the UNE Environmental Analysis Laboratory and to NSW Office of Environment and Heritage Soil Health & Archive laboratory, Yanco, NSW (Kristen Clancy and Dr. Mano Veergathipillai). Cate MacGregor assisted with GIS and mapping. AMS 14 C analyses was funded by University of New England URS Seeding Grant 2014 (A13/4157) and financial support from the Australian Government supports the Centre for Accelerator Science at ANSTO through the National Collaborative Research Infrastructure Strategy (NCRIS). References Adamson, D.A., Selkirk, P.M., Price, D., Ward, N., Selkirk, J.M., 1996. Pleistocene uplift and palaeoenvironments of Macquarie Island: evidence from palaeo beaches and sedimentary deposits. Pap. Proc. R. Soc. Tasmania 130, 25–32. Bancroft, W.J., Garkaklis, M.J., Roberts, J.D., 2005. Burrow building in seabird colonies: a soil forming process in island ecosystems. Pedobiologia 49, 149–165. Bergstrom, D.M., 1987. Evidence from fossils for uplift during the Holocene in Green Gorge, Macquarie Island. Colloque sur les Écosystèmes Terrestres Subantarctiques (1986). vol. 58. Commiteé National Français pour les Recherches Antarctiques, Paris, France, pp. 73–82. Bergstrom, D.M., Chown, S.L., 1999. Life at the front: history, ecology and change on southern ocean islands. Trends Ecol. Evol. 14 (12), 472–477. Bergstrom, D.M., Selkirk, P.M., 1999. Bryophyte propagule banks in a Feldmark on Subantarctic Macquarie Island. Arct. Antarct. Alp. Res. 31 (2), 202–208. Bergstrom, D.M., Stewart, G.R., Selkirk, P.M., Schmidt, S., 2002. 15N natural abundance of fossil peat reflects the influence of animal-derived nitrogen on vegetation. Oecologia 130, 309–314. Bergstrom, D.M., Bricher, P.K., Raymond, B., Terauds, A., Doley, D., McGeoch, M.A., Whinam, J., Glen, M., Yuan, Z., Kiefer, K., Shaw, J.D., Bramley-Alves, J., Rudman, T., Mohammed, C., Lucieer, A., Visoiu, M., Jansen van Vuuren, B., Ball, C., 2015. Rapid collapse of a sub-Antarctic alpine ecosystem: the role of climate and pathogens. J. Appl. Ecol. 52 (3), 774–783. Bird, M.I., Haberle, S.G., Chivas, A.R., 1994. Effect of altitude on carbon-isotope composition of forest and grassland soils from Papua New Guinea. Glob. Biogeochem. Cycles 8 (1), 13–22. Bockheim, J.G., Lupachev, A.V., Blume, H.P., Bölter, M., Simas, F.N.B., McLeod, M., 2015. Distribution of soil taxa in Antarctica: a preliminary analysis. Geoderma 245-246, 104–111. Bricher, P.K., Lucieer, A., Shaw, J., Terauds, A., Bergstrom, D.M., 2013. Mapping subAntarctic cushion plants using random forests to combine very high resolution satellite imagery and terrain modelling. PLoS One 8 (8), e72093. Bureau of Meteorology, 2017. Climate statistics for Australian locations. http://www. bom.gov.au/climate/averages/tables/cw_300004.shtml, Accessed date: 27 September 2017. Callaham, M.A., Butt, K.R., Lowe, C.N., 2012. Stable isotope evidence for marine-derived avian inputs of nitrogen into soil, vegetation, and earthworms on the isle of Rum, Scotland, UK. Eur. J. Soil Biol. 52, 78–83. Campbell, I.B., Claridge, G.G.C., 1992. Chapter 8 - soils of cold climate regions. In: Martini, I.P., Chesworth, W. (Eds.), Developments in Earth Surface Processes. Weathering, Soils & Paleosols Elsevier, Amsterdam, pp. 183–201. Chown, S.L., Rodrigues, A.S.L., Gremmen, N.J.M., Gaston, K.J., 2001. World heritage status and conservation of Southern Ocean islands. Conserv. Biol. 15 (3), 550–557. Cocks, M.P., Balfour, D.A., Stock, W.D., 1998. On the uptake of ornithogenic products by

178

Catena 177 (2019) 167–179

B.R. Wilson, et al. cycles. Nat. Commun. (Dec. 2018), 1–8. Porder, S., Ramachandran, S., 2013. The phosphorus concentration of common rocks – a potential driver of ecosystem P status. Plant Soil 367 (1–2), 1–15. Powell, S.M., Bowman, J.P., Ferguson, S.H., Snape, I., 2010. The importance of soil characteristics to the structure of alkane-degrading bacterial communities on subAntarctic Macquarie Island. Soil Biol. Biochem. 42 (11), 2012–2021. Quilty, P.G., 2007. Origin and evolution of the sub-Antarctic islands: the foundation. Pap. Proc. R. Soc. Tasmania 141 (1), 35–58. Rabbi, S.M.F., Hua, Q., Daniel, H., Lockwood, P., Wilson, B.R., Young, I.M., 2013. Mean residence time of soil organic matter in aggregates under contrasting land uses based on radiocarbon measurements. Radiocarbon 55, 127–139. Rayment, G.E., Lyons, D.J., 2011. Soil Chemical Methods: Australasia. CSIRO Publishing, Collingwood, Australia. Robertson, G., 1986. Population size and breeding success of the Gentoo Penguin (Pygoscelis papua) at Macquarie Island. Aust. Wildl. Res. 13, 583–587. Schaefer, C.E.G.R., Pereira, T.T.C., Ker, J.C., Almeida, I.C.C., Simas, F.N.B., de Oliviera, F.S., Correa, G.R., Vieira, G., 2015. Soils and landforms at Hope Bay, Antarctic peninsula: formation, classification, distribution and relationships. Soil Sci. Soc. Am. J. 79, 175–184. Schulz, M., Robinson, S., Gales, R., 2005. Breeding of the Grey Petrel (Procellaria cinerea) on Macquarie Island: population size and nesting habitat. Emu - Austral Ornithol. 105 (4), 323–329. Scott, J.J., Kirkpatrick, J.B., 2013. Changes in the cover of plant species associated with climate change and grazing pressure on the Macquarie Island coastal slopes, 1980–2009. Polar Biol. 36, 127–136. Selkirk, J.M., Saffigna, L.J., 1990. Wind and water erosion of a peat and sand area on subantarctic Macquarie Island. Arct. Antarct. Alp. Res. 31 (4), 412–420. Selkirk, P.M., Seppelt, R.D., Selkirk, D.R., 1990. Sub-Antarctic Macquarie Island: Its Environment and Biology. Cambridge University Press, Cambridge, UK. Smith, R.V., 1979. The influence of seabird manuring on the phosphorus status of Marion Island (subantarctic) soils. Oecologia 41 (1), 123–126. Smith, R.I.L., 1984. Terrestrial plant ecology of the sub-Antarctic and Antarctic. In: Laws, R.M. (Ed.), Antarctic Ecology. Academic Press, London. Smith, V.R., 2002. Climate change in the sub-Antarctic: an illustration from Marion

Island. Climate Change 52, 345–357. Springer, K., 2016. Methodology and challenges of a complex multi-species eradication in the sub-Antarctic and immediate effects of invasive species removal. N. Z. J. Ecol. 40 (2), 273–278. Tarnocai, C., Bockheim, J.G., 2017. Soils of cold and permafrost-affected landscapes. In: Richardson, D., Castree, N., Goodchild, M.F., Kobayashi, A., Liu, W., Marston, R.A. (Eds.), International Encyclopedia of Geography: People, the Earth, Environment and Technology. John Wiley & Sons, Chichester, pp. 1–10. Taylor, B.W., 1955a. The flora, vegetation and soils of Macquarie Island. In: ANARE Reports. Series B, vol 2 Australian Antarctic Division, Department of External Affairs, Melbourne. Taylor, B.W., 1955b. Terrace formation on Macquarie Island. J. Ecol. 43 (1), 133–137. Varne, R., Brown, A.Y., Falloon, T., 2000. Macquarie island: its geology, structural history, and the timing and tectonic setting of its N-MORB to E-MORB magmatism. In: Dilek, Y., Moores, E.M., Elthon, D., Nicolas, A. (Eds.), Ophiolites and Oceanic Crust: New Insights from Field Studies and the Ocean Drilling Program. Special Paper 349 Geological Society of America, Boulder, Colorado, pp. 301–320. Whinam, J., Hope, G., 2015. The Peatlands of the Australasian Region. Stapfia 85, Zugleich Kataloge Neue Serie. 35. pp. 397–434. Williams, L.K., Kristiansen, P., Sindel, B.M., Wilson, S.C., Shaw, J.D., 2016. Quantifying the seed bank of an invasive grass in the sub-Antarctic: seed density, depth, persistence and viability. Biol. Invasions 18 (7), 2093–2106. Wilson, B.R., Longworth, D., Wormell, P., Ferreira, C., 1999. Fertiliser response of soils and vegetation on ultrabasic terraces on the Isle of Rum between 1965 and 1996. Bot. J. Scotl. 51 (1), 87–101. Yergeau, E., Bokhorst, S., Huiskes, A.H.L., Boschker, H.T.S., Aerts, R., Kowalchuk, G.A., 2007. Size and structure of bacterial, fungal and nematode communities along an Antarctic environmental gradient. FEMS Microbiol. Ecol. 59 (2), 436–451. Zhou, X., Xu, X., Zhou, G., Luo, Y., 2018. Temperature sensitivity of soil organic carbon decomposition increased with mean carbon residence time: field incubation and data assimilation. Glob. Chang. Biol. 24, 810–822. Zwolicki, A., Zmudczynska-Skarbek, K.M., Hisko, L., Stempniewicz, L., 2013. Guano deposition and nutrient enrichment in the vicinity of planktivorous and piscivorous seabird colonies in Spitsbergen. Polar Biol. 36, 363–372.

179