Historical changes in herbaceous wetland distribution induced by hydrological conditions in Lake Saint-Pierre (St. Lawrence River, Quebec, Canada)

Abstract

Historical changes in the distribution of herbaceous wetland plant associations were inferred from the hydrological regime of Lake Saint-Pierre, a 312 km 2 broadening of the St. Lawrence River (Quebec, Canada), to assess the cumulative effects of human interventions and climatic variability. Relative abundance index (height · percent cover) of wetland plants in 630 field quadrats sampled at 13 sites (1999)(2000)(2001)(2002) were used to derive a model predicting the occurrence of nine herbaceous plant classes with a 71% (24-84%) accuracy. Wetland types included seasonally dry (meadows), mudflats and wet (low marshes and submerged) assemblages. Over the 1961-2002 period, the total surface area of Lake Saint-Pierre herbaceous wetlands ranged between 11 (in 1972) and 128 (in 2001) km 2 and was negatively correlated (Spearman r ¼ )0.86, p < 0.0001) to average water level during the current growing season. Within-season variability and level conditions over the previous season defined 5 marsh assemblages characterized by different species composition, relative abundance and diversity. Significant hydrological variables included quadrat elevation, water depth, number of days flooded and depth variability experienced over the current and/or previous growth seasons. The hydrological model suggests that for a given level, wetland plant assemblages differed markedly whether the multi-year sequence of water levels was rising or falling. Lake Saint-Pierre alternated between three broad-scale wetland configurations, dominated by meadows and open marsh with floating-leaved vegetation (in the 1960s), scattered tall Scirpus marshes (in the 1970s and early 1980s) and closed marsh with aggressive emergents (since 1996). The strong response of Lake Saint-Pierre wetlands to hydrological conditions in the current and previous growth seasons underlines their vulnerability to future water level variations resulting from regulation and climate variability.

Wet meadows of the alliance Molinion and their environmental gradients in Slovenia

“…Linkage between water regime, composition and distribution of herbaceous wetland plant communities has been documented many times (Wierda et al 1997;Jarolímek et al 2000;Wheeler & Proctor 2000;Wassen et al 2002;Hudon et al 2005;Schröder et al 2005).…”

“…But the vegetation variation is most efficiently explained by the following non-colinear variables (Tables 3, 4): pH, mean annual precipitation and temperature, de Martonne index of humidity, plant-available P and silt content. Forward selection of variables was used to avoid the co-linearity as suggested by Hudon et al (2005). These variables enable the segregation of the relevés in CCA ordination (Fig.…”

The Impact of “Man-Made Hydrological Drought” on Plant Species Abundance in the Low-Flow Channel Downstream from the Matawin Dam, Quebec

“…This goal is based on the following hypothesis: the high interannual variability of streamflow during the growing season downstream from the Taureau reservoir leads to decrease in the abundance of obligate wetland species on sand bars in the low-flow channel of the river. It should be mentioned that several studies have looked at the effects of water level variability in the St. Lawrence River on vegetation in aquatic settings in Quebec [21][22][23][24][25][26][27]. However, as shown by [27], the interannual variability of water levels in the St. Lawrence is very low due to flow regulation by dams and locks.…”

A unifying approach for evaluating the condition of wetland plant communities and identifying related stressors

“…CART can select from among a large number of variables, both numerical and categorical, those that are most important in determining the outcome variable to be explained (Urban 2002). CART analyses have been used to predict seasonal-wetland abundance based on land type (Palik et al 2003), relate coastal urbanization to Phragmites australis abundance and foliar nitrogen (King et al 2007), model historical changes in herbaceous wetland plant communities on the St. Lawrence River (Hudon et al 2005), and evaluate nonlinear responses of wetland biota to generalized stressor gradients (Brazner et al 2007a, Lougheed et al 2007.…”