Arctic Salt Marsh Research Articles

Seasonal partitioning of resource use and constraints on the growth of soil microbes and a forage grass in a grazed Arctic salt-marsh

Seasonal growth responses of plants and soil microorganisms to additions of nitrogen (N), phosphorus (P) and carbon (C) were examined in goose-grazed and exclosed plots in an Arctic salt marsh. Plants showed strong growth responses to N and NP additions but not to P. Nitrogen levels in the shoots and roots of Puccinellia phryganodes declined as summer progressed. Microbial biomass was low in spring in spite of N and P additions, likely due to C limitation, but values rose in autumn, independent of nutrient treatment, as dissolved organic carbon (DOC) increased. Glucose addition (C source) elicited a transitory increase in microbial biomass. Multiple plant defoliations by geese had a negative effect on microbial biomass, in spite of the presence of DOC and added N and P, possibly because hypersalinity restricted growth. Plants appear to limit soil inputs of C in summer and compete effectively for resources in contrast to autumn, indicating a temporal partitioning of resources.

Vegetation loss alters soil nitrogen dynamics in an Arctic salt marsh

Summary Plant and microbial nitrogen (N) dynamics were examined in soils of an Arctic salt marsh beneath goose‐grazed swards and in degraded soils. The degraded soils are the outcome of intensive destructive foraging by geese, which results in vegetation loss and near‐irreversible changes in soil properties. The objective of the study was to determine whether vegetation loss led to a decline in microbial activity and a redistribution of N amongst the different soil N pools that potentially could adversely affect plant regrowth. In situ N allocation between plants, microbes and soil was determined based on injection of 15NH4Cl into soil cores; changes in isotopic ratios and N concentrations in the different pools were measured after 24 h. Degraded soils, in contrast to vegetated soils, were characterized by a decline in microbial biomass, reduced microbial 15N excess, reduced rates of gross N immobilization and an increased microbial residency time of 15N. In vegetated soils, both microbes and the forage grass, Puccinellia phryganodes, accumulated 15N such that little remained in the soil abiotic phase after 24 h, unlike in degraded soils. The decline in microbial activity in degraded soils may be linked to a low availability of soil carbon in the absence of plants and to deteriorating abiotic conditions, including the occurrence of hypersalinity in summer. Not all biotic processes respond similarly to the change in ecosystem state. Unlike vascular plant productivity and goose foraging which are absent in degraded soils, soil microbial activity is maintained, albeit at a lower level. In spite of this activity, the greater proportion of 15N in degraded soils is in the abiotic pool rather than in microbial biomass with an increased potential for soil N loss from leaching and soil erosion. Disturbance linked to herbivory often triggers catastrophic shifts in ecosystem properties resulting in vegetation loss and changes in soil biogeochemical cycling that are irreversible, at least on a decadal time scale, and lead to the loss of N and other nutrients required for plant growth. These results clearly illustrate that microbial activity does not compensate for the effects of plant removal on soil N retention.

Initiation and maintenance of vegetation mosaics in an Arctic salt marsh

Summary 1 Vegetation mosaics of grassland and exposed soil are often the outcome of intense herbivory and represent alternate stable states, although the vegetational and soil processes that both initiate and maintain the states in response to herbivory are poorly understood. 2 The vegetation mosaic resulting from grubbing by geese was examined on the intertidal flats at La Perouse Bay, Manitoba. Soil properties of the alternate states were measured in conjunction with the ability of transplanted tillers of Puccinellia phryganodes to grow in exposed soil and intact swards. Simulated grubbed patches (2.5–40 cm diameter) were prepared at three sites and the soil properties and inward clonal growth of the grass in each patch were examined during two growing seasons. 3 Where an organic layer was still present on exposed areas, soil properties were similar to those in the rooting zone beneath intact swards, except that soils were hyper-rather than hyposaline. Older exposed mineral soils, where the organic layer had been eroded, were similarly hypersaline, but were also low in soil moisture and total nitrogen, and compacted with a low infiltration rate. Transplanted tillers survived in intact swards, but few survived in any hypersaline soils. 4 Changes in soil properties over two seasons depended on size of experimentally created patches. Again, high salinities developed in soils of the larger patches, and there was a loss of nitrogen and soil moisture and an increase in bulk density with increasing patch size. Although inward clonal growth of P. phryganodes took place from plot perimeters, this is likely to be curtailed by high salinities in plots over 20 cm diameter. 5 As in tropical Africa, intense herbivory can lead to an alternate stable state in this Arctic salt marsh. Small patches of exposed soil are characterized by deteriorating soil conditions and the inability of vegetation to re-establish. As patches coalesce with continued herbivory, an ecological sere (the intertidal salt marsh) is lost.

Environmental gradients, plant distribution, and species richness in arctic salt marsh near Prudhoe Bay, Alaska

Spatial patterns of plant cover and species composition in arctic salt marsh and salt affected tundra near Prudhoe Bay, Alaska reflect gradients in elevation, soil conductivity, and soil concentrations of the ions prevalent in seawater. Soil conductivity and soil concentrations of Ca2+, Mg2+, Na+, K+, SO4= and Cl− were significantly related to site elevation, decreasing as elevation increased. Vascular plant species richness increased significantly as soil conductivity and soil ion concentrations decreased, and site elevation increased. Puccinellia phryganodes was the only species present in low elevation sites with low plant cover, high soil conductivity and high soil concentrations of Ca2+, Mg2+, Na+, K+, SO4= and Cl−. Mid-gradient sites were dominated by Carex subspathaceae. Plant cover at these sites was greater than at lower elevation sites, but bare ground was still present. Higher elevation sites had the lowest concentrations of soil ions and the lowest soil conductivities. These sites had little bare ground, contained as many as 16 species, and were dominated by Dupontia fischeri and Eriophorum angustifolium. Ordinations indicated that a complex topographic gradient related most closely to elevation and site distance from the coast best explains variation in the vegetation cover. Irregular deposition along the coastline partially or completely buried three sites in peat or sand up to 20 cm deep. Such rapid changes in plant cover and species composition contributes to the community patch mosaic typical of these marshes. Results suggest an individualistic response of plant species to the environmental gradients in salt marsh and salt affected tundra and are indicative of successional models developed in other marginal arctic environments.

The dynamics of nitrogen movement in an Arctic salt marsh in response to goose herbivory: a parameterized model with alternate stable states

Summary LPBN is a parameterized simulation model of flows of nitrogen (N) in an ecosystem of cyanobacteria, grass and grazers, based on the N dynamics of a grazed Puccinellia lawn in an intertidal marsh on Hudson Bay. This system shows two alternate stable states: (a) lawns that either support a foraging population of lesser snow geese, or are not grazed by geese; and (b) exposed saline sediments that support little or no vegetation. The model represents the flow of N from cyanobacterial fixation, the major N input into the system, to the geese that migrate in autumn; those that do not return represent the major N output from the system. We have modelled N fixation, the transformations of N in the soil, plant growth, lawn regeneration, and goose grazing and grubbing. The model simulates steady‐state flows of N similar to those observed in the field at zero and at moderate goose density, and it also simulates the transition to the state of zero plant biomass, a consequence of increased grubbing at high goose density. The simulated steady‐state flows are found to be more sensitive to changes in the parameters that describe N fixation and goose biology, than to similar changes in the parameters describing plant biology. Because the model shows the alternate stable states and the transition between them, with values for the state variables that are consistent with field data, we conclude that N dynamics are crucial in determining the stability of the real salt marsh‐goose system. The determining factor is the loss of the input of N from fixation when lawn area is reduced because the rate of goose grubbing exceeds that of plant re‐establishment.

Plant amino acid uptake, soluble N turnover and microbial N capture in soils of a grazed Arctic salt marsh

Summary The uptake of free amino acids by the grass Puccinellia phryganodes was investigated in soils of an Arctic coastal salt marsh, where low temperatures and high salinity limit inorganic nitrogen (N) availability, and the availability of soluble organic N relative to inorganic N is often high. Following the injection of 13C15N‐amino acid, 15N‐ammonium and 15N‐nitrate tracers into soils, rates of soluble nitrogen turnover and the incorporation of 13C and 15N into plant roots and shoots were assessed. Chloroform fumigation‐extraction was used to estimate the partitioning of labelled substrates into microbial biomass. Free amino acids turned over rapidly in the soil, with half‐lives ranging from 8.2 to 22.8 h for glycine and 8.9 to 25.2 h for leucine, compared with 5.6 to 14.7 h and 5.6 to 15.6 h for ammonium and nitrate, respectively. 15N from both organic and inorganic substrates was incorporated rapidly into plant tissue and the ratio of 13C/15N incorporation into plant tissue indicated that at least 5–11% of 13C15N‐glycine was absorbed intact. Microbial C and N per unit soil volume were 1.7 and 5.4 times higher, respectively, than corresponding values for plant C and N. Plant incorporation of 15N tracer was 56%, 83% and 68% of the comparable incorporation by soil microorganisms of glycine, ammonium and nitrate ions, respectively. These results indicate that P. phryganodes can absorb amino acids intact from the soil despite competition from soil microorganisms, and that free amino acids may contribute substantially to N uptake in this important forage grass utilized by lesser snow geese in the coastal marsh.

Foraging geese, vegetation loss and soil degradation in an Arctic salt marsh

Abstract.The North American mid‐continent population of Lesser snow geese (Chen caerulescens caerulescensL.) has increased by ca. 7% per year, largely as a result of geese feeding on agricultural crops in winter and on migration. We describe the long‐term effects of increasing numbers of geese at an arctic breeding ground (La Pérouse Bay, Manitoba) on intertidal salt‐marsh vegetation. Between 1985 and 1999 goose grubbing caused considerable loss of graminoid vegetation along transects in intertidal marshes. Loss of vegetation led to bare sediment with a plant cover of less than 2%. Changes in vegetation could not be described by simple linear, geometric or exponential functions; most losses occurred between 1988 and 1990 and losses were staggered in time between individual transects, some of which had all vegetation removed.Between 1979 and 1999 the standing crop in July in remaining intact heavily‐grazed swards ofPuccinellia phry‐ganodesandCarex subspathaceafell from 40–60 g m‐2to 20–30 g m‐2. Intense grazing on remaining patches of sward has restricted growth of these clonal forage plants and hypersalinity of bare sediments has precluded re‐establishment of vegetation. Between 1989 and 1993 numbers of faecal droppings in grazed plots reached maximum values of 15–22 droppings m‐2wk‐1. Since then peak values have remained at less than 13 droppings m‐2wk‐1. The loss of vegetation and changes in soil conditions have resulted in the establishment of an alternative stable state (hypersaline bare sediment).

Foraging geese, vegetation loss and soil degradation in an Arctic salt marsh

Foraging geese, vegetation loss and soil degradation in an Arctic salt marsh

Intertidal plant communities of an Arctic salt marsh: The influence of isostatic uplift and herbivory

Recently, the mid-continent population of lesser snow geese has increased at about 7% per year and increased numbers of geese have adversely affected the vegetation of intertidal communities on the shores of Hudson and James Bays. A quantitative description of plant communities was undertaken before they are modified or lost as a result of the direct and indirect effects of goose foraging. The region is undergoing isostatic uplift and salt marshes have developed on the extended, low elevation shorelines. The site chosen for the study was La Pérouse Bay, Manitoba, where there is a breeding colony of lesser snow geese. The plant assemblages recognised in intertidal zone, based on the use of Canonical Correspondence Analysis, were the Puccinellia-Carex community, the Festuca-Calamagrostis community (both of which were grazed and grubbed by geese), bare sediment, and the Hippuris-Myriophyllum assemblage characteristic of brackish aquatic habitats (rarely grazed by geese). The communities were primarily differentiated in terms of elevation, water depth, and area of plant cover. These communities are widespread elsewhere in intertidal areas adjacent to the Hudson Bay lowlands, but intensive goose foraging has led either to their loss or to fine-scale fragmentation with little likelihood of revegetation in the foreseeable future. This description of vegetation serves as a baseline against which further changes can be monitored and assessed.

Atmospheric Change and Biodiversity in the Arctic

The Canadian Arctic is characterized by a high variation in landform types and there are complex interactions between land, water and the atmosphere which dramatically affect the distribution of biota. Biodiversity depends upon the intensity, predictability and scale of these interactions. Observations, as well as predictions of large-scale climate models which include ocean circulation, reveal an anomalous cooling of northeastern Canada in recent decades, in contrast to the overall significant increase in average annual temperature in the Northern Hemisphere. Predictions from models are necessary to forecast the change in the treeline in the 21st century which may lead to a major loss of tundra. The rate of change in vegetation in response to climate change is poorly understood. The treeline in central Canada, for example, is showing infilling with trees, and in some locations, northerly movement of the boundary. The presence of sea ice in Hudson Bay and other coastal areas is a major factor affecting interactions between the marine and terrestrial ecosystems. Loss of ice and therefore hunting of seals by polar bears will reduce bear and arctic fox populations within the region. In turn, this is likely to have significant effects on their herbivorous prey populations and forage plants. Further, the undersurface of sea ice is a major site for the growth of algae and marine invertebrates which in turn act as food for the marine food web. A rise in sea-level may flood coastal saltmarsh communities leading to changes in plant assemblages and a decline in foraging by geese and other consumers. The anomalous cooling in the eastern Arctic, primarily in late winter and early spring, has interrupted northern migration of breeding populations of geese and ducks and led to increased damage to vegetation in southern arctic saltmarshes as a result of foraging. It is likely that there has been a significant loss of invertebrates in those areas where the vegetation has been destroyed. Warming will have major effects on permafrost distribution and on ground-ice resulting in a major destabilization of slopes and slumping of soil, and disruption of tundra plant communities. Disruption of peat and moss surfaces lead to loss of insulation, an increase in active-layer depth and changes in drainage and plant assemblages. Increases of UV-B radiation will strongly affect vulnerable populations of both plants and animals. The indigenous peoples will face major changes in life style, edibility of food and health standards, if there is a significant warming trend. The great need is for information which is sensitive to the changes and will assist in developing an understanding of the complex interactions of the arctic biota, human populations and the physical environment.

A Positive Feedback: Herbivory, Plant Growth, Salinity, and the Desertification of an Arctic Salt-Marsh

1 A 2-year study is described which suggests that a positive feedback process results in the destruction of salt-marsh swards and the exposure of bare sediments at La Perouse Bay, Manitoba, Canada. Lesser snow geese initiate the process by grubbing for roots and rhizomes of salt-marsh graminoids (Puccinellia phryganodes and Carex subspathacea) in spring. The increased rates of evaporation from sediments beneath disturbed or destroyed swards in summer result in high soil salinities that adversely affect the growth of the remaining grazed plants. 2 Above-ground biomass and soil salinity differed between sites in the salt marsh. Soil salinity was inversely related to above-ground biomass and shoot density of Puccinellia phryganodes. Increased biomass led to reduced soil salinity at sites where exclosures were erected. 3 Plant growth, measured as the rate of leaf births on Puccinellia shoots, was reduced by high soil salinities at sites where exclosures were erected. 4 Leaf demography of transplanted experimental plants of Puccinellia differed in 1992, but not 1991, between plants transplanted into sites with different amounts of above-ground biomass. Leaf births and deaths were highest for plants grown in sites where above-ground biomass was high and lowest for plants transplanted into bare sites. Grazing had no effect on leaf demography in 1991 and only marginally increased the rate of leaf deaths in 1992. 5 Growth of transplanted individuals of Carex subspathacea was similarly highest at sites where the standing crop of Puccinellia and Carex was high and was lowest in bare sites. 6 Algal crusts, which formed on bare or poorly vegetated sites, also reduced the growth of Puccinellia plants. 7 The effects of this deleterious positive feedback on plant growth are discussed in relation to changes occurring in the lesser snow goose colonies at La Perouse Bay and elsewhere.

The Effect of Salinity on the Leaf and Shoot Demography of Two Arctic Forage Species

1 Two important graminoid forage species, Puccinellia phryganodes and Carex subspathacea, which are eaten by lesser snow geese, are widespread in arctic coastal salt marshes. Extensive grubbing of these plants by geese has led to increased soil salinity which may restrict their regrowth, particularly for the sedge which grows in less saline sites. 2 The effects of salinity on leaf and shoot birth and death rates and on mortality of plants of the two species were therefore examined when pot-grown plants of Puccinellia were exposed to different salinities under field conditions at La Perouse Bay, Manitoba. A similar experiment on Puccinellia was also conducted in a growth chamber. 3 Leaf death rates increased with salinity and approached or exceeded leaf births at the highest salinities (40-80 g L` dissolved salts containing sodium at a concentration between 568 mol m-3 and 1136 mol m-3). The salinities at which these changes were evident depended on the species and the growing conditions. When birth and death rates of leaves and plant deaths were compared, Puccinellia phryganodes was less saltsensitive than Carex subspathacea. 4 As salinity increased, the decline in numbers of leaf births on axillary shoots and attached tillers of plants of Puccinellia and Carex was faster than the decline in leaf births on main shoots. 5 The growth responses of the two species to salinity are discussed in relation to the foraging activities of the geese and the long-term changes occurring in salt marshes on the coast of Hudson Bay.

Mosaics of vegetation and soil salinity: a consequence of goose foraging in an arctic salt marsh

Grubbing of roots and rhizomes of salt-marsh graminoids by lesser snow geese at La Pérouse Bay, Manitoba, on the Hudson Bay coast, has resulted in a vegetational mosaic. Bare sites, devoid of vegetation, occur adjacent to intact swards (high biomass sites). At some sites destruction of swards is incomplete (low biomass sites). In 1991 and 1992, highest soil salinities occurred in midsummer; surface sediments were flushed of salts by meltwater in spring and by tides in autumn. By late July, in both years, the soil was hypersaline in low biomass and bare sites, unlike that in the high biomass sites. The highest soil salinities were recorded in bare sites, especially in large bare patches. Aboveground plant biomass (g∙m−2) was a much better predictor of the salinity of soil water than the water content or redox potential of soil. Evaporative loss of water from tubes buried in sediments was higher in bare sites compared with that in vegetated sites. Differences in evaporation between sites led to large differences in the salinity of soil water but only small differences in soil water content. The upward movement of salts from buried Tyrell Sea sediments appears responsible for the development of hypersaline conditions. Key words: grubbing, goose grazing, plant biomass, sodium, soil water, hypersalinity.

Leaf and Shoot Demography of an Arctic Stoloniferous Grass, Puccinellia Phryganodes, in Response to Grazing

(1) Swards ( < 2 5 cm in height) of Puccinellia phryganodes are heavily grazed by lesser snow geese (Chen caerulescens caerulescens) on intertidal flats on the shores of Hudson Bay. This paper describes the morphological changes that account for the increased net primary production due to grazing. (2) Demographic techniques were used in 1983 to monitor the births and deaths of leaves and shoots in grazed and ungrazed swards (exclosures) between mid-June ('spring melt') and early September (before 'freeze-up'). (3) Overall, the mean number of axillary shoots produced per main shoot of Puccinellia was significantly higher in grazed plots (2 03) than that in ungrazed plots (1 47). Shoots remained alive beyond one growing season. (4) There was no significant difference in the mean number of leaves produced per main shoot by plants from grazed and ungrazed swards. Leaf births per axillary shoot were significantly greater in grazed plots compared with ungrazed plots. Overall 64% of all leaves produced between June and September were grazed or partially grazed. (5) Within-season cumulative deaths were 6 9 and 6 0 leaves per main shoot and 2 2 and 1 1 leaves per axillary shoot, respectively, in grazed and ungrazed plots. Life expectancies for leaves exserted between June and early August were as follows: partially grazed leaves 24 9-30 2 days, ungrazed leaves in grazed plots 27 5-34 4 days, leaves in ungrazed plots 32 7-42 5 days. This indicates a rapid turnover of leaves in this arctic salt marsh. Leaves produced late in the season survived the winter but died in early summer of the following year. (6) These results are compared with those of Carex subspathacea, the other important forage species. In C. subspathacea the greater net primary production in response to grazing is achieved by the growth of existing shoots and not by the production of new shoots.

The Leaf and Shoot Demography of Grazed and Ungrazed Plants of Carex Subspathacea

(1) Dense swards of aerial shoots (< 2 5 cm in height) of Carex subspathacea are heavily grazed by lesser snow geese on intertidal flats on the shores of Hudson Bay. This paper describes the morphological changes in plants which account for the greater net primary production when these swards are grazed. (2) Demographic techniques have been used to monitor the births and deaths of leaves and shoots in grazed and ungrazed swards. Between mid-June ('spring thaw') and early September 1984 (just prior to 'freeze-up'), shoots in grazed plots produced an average of 8 2 new leaves, compared with an average of 5 7 leaves per shoot in ungrazed plots. This difference accounted for the greater net annual primary production in grazed swards. (3) Within-season deaths of leaves totalled 8 0 and 5 7 leaves per shoot, respectively, in grazed and ungrazed plots. Life expectancies were as follows: grazed leaves, 33 3 days; ungrazed leaves in grazed plots, 34 2 days; leaves in ungrazed plots 45 1-472 days. This indicates a very rapid turnover of leaves in this arctic salt marsh where the growing season is about 110 days. Some leaves produced late in the season survived the winter but died in early summer of the following year. (4) No differences were detected in the number of new shoots in grazed and ungrazed swards, in contrast to a higher significant within-season mortality of shoots in grazed plots. Turnover of shoots is very slow compared with leaves. Shoots remain alive beyond one growing season. (5) The geese graze selectively. Only 20%/, of shoots in grazed plots were removed and only 30% of leaves were removed completely, although between 420% and 56%/o of leaves were grazed. Meristems are inot destroyed and the continuous production of leaves occurs throughout the season. (6) The growth responses of the sedge to grazing are probably dependent on goose faeces which provide a source of soluble nitrogen in the nitrogen-deficient habitat.

The Effects of Grazing by Lesser Snow Geese on the Vegetation of a Sub- Arctic Salt Marsh

Les resultats obtenus dans un marais domine par Puccinellia phryganodes et Carex subspathacea a La Perouse Bay (Canada) suggerent que le pâturage stimule la production primaire en accelerant le cycle de l'azote

Genetic variation within and between populations of the asexual plant Puccinellia × phryganodes

Puccinellia × phryganodes (Trin.) Scriber and Merr is widely distributed in Arctic salt marshes. In North America the species, which is capable of extensive clonal growth, appears to be a sterile triploid (2n = 21); seed set has never been observed. Consequently it was predicted that the level of genetic variation would be low, both within and between populations. Examination of electrophoretic mobilities of isozymes of 12 enzyme systems in plants from three widely separated populations in Arctic Canada indicated a high level of variability both within and between the populations. The unexpected discovery of significant amounts of genetic variability suggests that sexual processes occur in this species.

The vegetational zonation of the East Pen Island salt marshes, Hudson Bay

The extensive salt marshes at East Pen Island in Hudson Bay are described in quantitative terms and the well-marked sequence of species is characterized. The lower marsh is dominated by Puccinellia phryganodes and Carex subspathacea, with Hippurus vulgaris and Senecio congestus abundant in the salt pans. The midmarsh has well-developed swards of Dupontia fisheri and Celamagrostis neglecta, which give way to stands of Carex aquatilis in a well-developed freshwater marsh below the first beach ridge. The results are compared with other arctic salt marshes, and the development of a wide freshwater marsh in the upper zone of the salt marsh is described. This feature is perhaps unique to the Hudson Bay marshes and is a function of meltwater runoff from the surface of the permafrost table. This results in the high, standing water table at the top of the marsh, which is maintained by the permafrost table of the salt marsh itself.A transit survey of the marsh relates the quadrat samples to a high-tide datum point and allows interpretation of the vegetation sequence in terms of saltwater inundation. The depth of the active layer of the salt marsh is also described.