Redundancy Analysis (RDA) shows a similar pattern to PCA, indicating that the environmental descriptors latitude, longitude, depth and graminoid salt marsh (shown with dashed vector lines) describe the variation in the water chemistry data well. The relationship between the environmental descriptors and water chemistry data can be interpreted by the alignment of the vectors. The diagram shows that the major variation in the pond ionic concentration is found to increase eastward and northward in the park, while DOC (the second greatest source of variation among the ponds) is found to decrease with increasing latitude and also slightly decrease from west to east in the park. The only significant vegetation descriptor, Graminoid Willow Salt Marsh (GWSM), captures variation independent of latitude and longitude and is associated with higher DIC and specific conductance. 

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Context 1

... Figure 4). Depth, latitude, longitude and GWSM vegetation were the only environmental descriptors that showed a significant relationship with water chemistry. In general, the ponds studied were dilute, oligotrophic, with circumneutral to slightly alkaline pH measurements. Riley (1982) documented a trend of increasing pH with latitude for wetlands in the Hudson Bay lowlands south of our study area. Consistent with this, the mean pH of our more northerly sites was even higher than that measured by Riley (1982). DOC was relatively high in these ponds (range 4.8 Á 16 mg/L) although not as high as has been observed in other peat-dominated areas from this latitude (mean 0 16 mg × L ( 1 , McEachern et al. , 2000). The higher DOC values observed by McEachern et al . (2000) may be due to the higher drainage area to lake area ratio of their lakes and a higher proportion of forested catchment. Similar to Eilers et al. (1992) we found that none of the ponds in our study area were acidic, despite relatively high concentrations of DOC, much of which is likely from acidophilic bryophytes such as Sphagnum . Organic acid production in the catchments is apparently insufficient to overcome alkalinity production from watershed weathering and in situ alkalinity generation within the ponds. Although weak thermal stratification was observed in those ponds sampled on warm still days, energy from strong coastal winds seemed sufficient to overcome stratification, which was not observed in ponds sampled on windy days. Given the similarity of ponds sampled on different days, it is likely that all of the ponds are polymictic throughout the ice-free period. On windy days considerable amounts of suspended sediment were observed in the water column of the ponds and thus the entire water column is likely in almost continuous contact with the sediment during the ice-free period. TN:TP ratios were generally high (range by mass 0 11 Á 128, mean 0 62, range by molar ratio 0 25 Á 283, mean 0 133) in these ponds and indicates they are likely phosphorus rather than nitrogen limited (Downing and McCauley, 1992). The high TN:TP ratio’s observed from our shallow ponds are consistent with research from Alexander et al. (1989) which demonstrated that water in shallow ponds from Alaska is essentially always in contact with sediment, which serves as a nitrogen source and thus the ponds tend to be phosphorus limited. The specific conductance of our samples spanned a much larger gradient than previously observed in the Saqvaqjuac research lakes located near Hudson Bay to the Northwest of our sites. Specific conductance of our samples ranged from 45 to 2451 m S × cm ( 1 , whereas the lakes observed in Saqvaqjuac spanned 40 Á 100 m S × cm ( 1 . These differences are likely due to some of our sites being more proximate to Hudson Bay. The ionic composition of most ponds was similar to that of seawater, although the salinity was often much more dilute (Figure 2). Many of the ponds have only recently been elevated from the sea and some likely still receive significant amounts of sea spray, the molar ratio of Na:Cl in the ponds (0.62 5 x 5 1.29, mean 0 0.92) spanned that of seawater (0.86). In general, both Na ' and Cl ( , had elevated levels in ponds more proximate to Hudson Bay (Figure 4). The stability of ionic composition amongst all the ponds regardless of concentration is consistent with a dominance of surface rather than groundwater influ- ences on most ponds. Pond water chemistry was not strongly related to catchment vegetation as identified by Landsat classification (Brook and Kenkel, 2002). The only vegetation characteristic that showed a significant relationship to the water chemistry data was Grami- noid Willow Salt Marsh. GWSM habitat is only found immediately adjacent to the coast, and only Pond 18 had GWSM as a significant component (17%) of the catchments vegetation. Ponds 16 and 18 had much higher salinity than the rest of the ponds and ordinate together in the PCA. However, Pond 18 differs from Pond 16 in that it also has much higher alkalinity. Thus, for this data set, Pond 18 has the unusual combination of high alkalinity and high salinity, and it is likely this combination of features that GWSM is able to uniquely describe. Our dataset does not have sufficient redundancy to say whether this is a general characteristic of ponds with significant amounts of GWSM in the catchment. In other northern areas, a strong relationship has been observed between DOC and the extent of forest development in the catchment (e.g., Pienitz et al ., 1997a, 1997b; Ruhland et al ., 2003). Surprisingly, Landsat-based measures of arboreal vegetation such as Willow Birch Shrub Fen, Sedge Larch Fen, Sphagnum Spruce Bog and Lichen Spruce Bog were not significantly related to pond water chemistry. However, latitude and longitude were significantly related to the variation in the water chemistry data. Wapusk National Park does have increasing forest development as ...

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... Figure 4). Depth, latitude, longitude and GWSM vegetation were the only environmental descriptors that showed a significant relationship with water chemistry. In general, the ponds studied were dilute, oligotrophic, with circumneutral to slightly alkaline pH measurements. Riley (1982) documented a trend of increasing pH with latitude for wetlands in the Hudson Bay lowlands south of our study area. Consistent with this, the mean pH of our more northerly sites was even higher than that measured by Riley (1982). DOC was relatively high in these ponds (range 4.8 Á 16 mg/L) although not as high as has been observed in other peat-dominated areas from this latitude (mean 0 16 mg × L ( 1 , McEachern et al. , 2000). The higher DOC values observed by McEachern et al . (2000) may be due to the higher drainage area to lake area ratio of their lakes and a higher proportion of forested catchment. Similar to Eilers et al. (1992) we found that none of the ponds in our study area were acidic, despite relatively high concentrations of DOC, much of which is likely from acidophilic bryophytes such as Sphagnum . Organic acid production in the catchments is apparently insufficient to overcome alkalinity production from watershed weathering and in situ alkalinity generation within the ponds. Although weak thermal stratification was observed in those ponds sampled on warm still days, energy from strong coastal winds seemed sufficient to overcome stratification, which was not observed in ponds sampled on windy days. Given the similarity of ponds sampled on different days, it is likely that all of the ponds are polymictic throughout the ice-free period. On windy days considerable amounts of suspended sediment were observed in the water column of the ponds and thus the entire water column is likely in almost continuous contact with the sediment during the ice-free period. TN:TP ratios were generally high (range by mass 0 11 Á 128, mean 0 62, range by molar ratio 0 25 Á 283, mean 0 133) in these ponds and indicates they are likely phosphorus rather than nitrogen limited (Downing and McCauley, 1992). The high TN:TP ratio’s observed from our shallow ponds are consistent with research from Alexander et al. (1989) which demonstrated that water in shallow ponds from Alaska is essentially always in contact with sediment, which serves as a nitrogen source and thus the ponds tend to be phosphorus limited. The specific conductance of our samples spanned a much larger gradient than previously observed in the Saqvaqjuac research lakes located near Hudson Bay to the Northwest of our sites. Specific conductance of our samples ranged from 45 to 2451 m S × cm ( 1 , whereas the lakes observed in Saqvaqjuac spanned 40 Á 100 m S × cm ( 1 . These differences are likely due to some of our sites being more proximate to Hudson Bay. The ionic composition of most ponds was similar to that of seawater, although the salinity was often much more dilute (Figure 2). Many of the ponds have only recently been elevated from the sea and some likely still receive significant amounts of sea spray, the molar ratio of Na:Cl in the ponds (0.62 5 x 5 1.29, mean 0 0.92) spanned that of seawater (0.86). In general, both Na ' and Cl ( , had elevated levels in ponds more proximate to Hudson Bay (Figure 4). The stability of ionic composition amongst all the ponds regardless of concentration is consistent with a dominance of surface rather than groundwater influ- ences on most ponds. Pond water chemistry was not strongly related to catchment vegetation as identified by Landsat classification (Brook and Kenkel, 2002). The only vegetation characteristic that showed a significant relationship to the water chemistry data was Grami- noid Willow Salt Marsh. GWSM habitat is only found immediately adjacent to the coast, and only Pond 18 had GWSM as a significant component (17%) of the catchments vegetation. Ponds 16 and 18 had much higher salinity than the rest of the ponds and ordinate together in the PCA. However, Pond 18 differs from Pond 16 in that it also has much higher alkalinity. Thus, for this data set, Pond 18 has the unusual combination of high alkalinity and high salinity, and it is likely this combination of features that GWSM is able to uniquely describe. Our dataset does not have sufficient redundancy to say whether this is a general characteristic of ponds with significant amounts of GWSM in the catchment. In other northern areas, a strong relationship has been observed between DOC and the extent of forest development in the catchment (e.g., Pienitz et al ., 1997a, 1997b; Ruhland et al ., 2003). Surprisingly, Landsat-based measures of arboreal vegetation such as Willow Birch Shrub Fen, Sedge Larch Fen, Sphagnum Spruce Bog and Lichen Spruce Bog were not significantly related to pond water chemistry. However, latitude and longitude were significantly related to the variation in the water chemistry data. Wapusk National Park does have increasing forest development as you move south and west in the park. Correspondingly, the RDA analysis shows increasing DOC with decreasing latitude and increasing longitude. It is unclear why latitude and longitude would be better metrics for tree cover than the Landsat derived vegetation measures. The shallow depth (Z max B 2 m) of all the sampled waterbodies makes it likely that they all freeze completely in winter and are thus ponds. Anecdotal evidence from sediment coring that was conducted at the same time as water sampling supports this hypothesis. In shallow ponds where contact with the corer could be maintained it was obvious that core length was limited due to striking a permafrost layer. In deeper ponds it was difficult to ascertain with confidence if permafrost was present, but the short length of the retrieved cores indicates that permafrost may exist in ponds as deep as 2.5 m. Bello and Smith (1990) reported the potential for permafrost (pond completely frozen to bottom) for a lake 60 km south of our study sites. Changes in climate and ultraviolet radiation levels in the Arctic may have far-reaching impacts on northern aquatic ecosystems in ways that are difficult to project (Wrona et al. , 2006). Climatically mitigated changes in evapotranspiration, rainfall, permafrost, fire frequency and tree line all have the potential to alter aquatic conditions within Wapusk National Park. Without site-specific climatic models it is difficult to ascertain what the rate, magnitude or combined effect of these changes may be. Our data show that the dominant limnological patterns in the park are a strong gradient in ionic concentration driven by proximity to the coast and isostatic rebound; conservation of ionic ratios likely due to permafrost isolating the ponds from groundwater; and a latitudinal and longitudinal gradient in DOC related to forest cover. The dominant limnological patterns we have described point to areas where changes in the park are likely to be detected by future monitoring. As demonstrated by Welch and Legault (1986), the delivery of solutes to waterbodies in the permafrost setting bordering Hudson Bay is strongly affected by the timing and magnitude of runoff. Climate change is likely to cause increased solute delivery to these waterbodies. In particular, increases in summer rainfall once the active layer has become well-developed results in high solute output from the watershed (Welch and Legault, 1986). Currently much of the melt occurs before the ponds are ice free so much of the solute is lost in runoff. However, ponds may retain most of the nutrients delivered to them if they become ice free at the time of melt. Permafrost isolates ponds from interactions with groundwater so future climate induced disruption to permafrost may alter the stable ionic composition that ponds currently exhibit. The northeast to southwest trend in DOC levels is the second greatest variation seen in the water chemistry in this study. Any environmental change that alters northern tree line may alter the distribution of DOC and associated diversity of aquatic environments found in the park. Changes in water budgets may also strongly affect the ponds of the Hudson Bay lowlands. Predictions of climate warming impacts include reduce overland flow during the key ...