Primary determinants of macrophyte community structure in 62 marshes across the Great Lakes basin: latitude, land use, and water quality effects

Abstract

We collected water quality, land use, and aquatic macrophyte information from 62 coastal and inland wetlands in the Great Lakes basin and found that species richness and community structure of macrophytes were a function of geographic location and water quality. For inland wetlands, the primary source of water quality degradation was inputs of nutrients and sediment associated with altered land use, whereas for coastal wetlands, water quality was also influenced by exposure and mixing with the respective Great Lakes. Wetlands within the subbasins of the less developed, more exposed upper Great Lakes had unique physical and ecological characteristics compared with the more developed, less sheltered wetlands of the lower Great Lakes and those located inland. Turbid, nutrient-rich wetlands were characterized by a fringe of emergent vegetation, with a few sparsely distributed submergent plant species. High-quality wetlands had clearer water and lower nutrient levels and contained a mix of emergent and floating-leaf taxa with a diverse and dense submergent plant community. Certain macrophyte taxa were identified as intolerant of turbid, nutrient-rich conditions (e.g., Pontederia cordata, Najas flaxilis), while others were tolerant of a wide range of conditions (e.g., Typha spp., Potamogeton pectinatus) occurring in both degraded and pristine wetlands.

Relating Effect and Response Traits in Submersed Aquatic Macrophytes

“…Shallow water systems are at great risk of being impacted by a variety of environmental stressors owing to their location in watersheds . Longterm changes in macrophyte communities have indeed been documented throughout the world (Brush andHilgartner 2000, Sand-Jensen et al 2000) and have been associated most often with changes in water quality (Sand-Jensen et al 2000, Lougheed et al 2001 and changes in hydrology (Keddy and Reznicek 1986). The current study decreased water level of the mesocosms to the point that aboveground structures desiccated.…”

“…Indeed, Barrat-Segretain (2001) showed that reestablishment of submersed aquatic plants after a disturbance either occurred through resprouting of underground plant parts or by vegetative fragments, each strategy related to high below-or aboveground biomass, respectively. Species-specific responses to environmental stress and simultaneous effects on ecosystem processes are poorly understood for freshwater submersed aquatic plants, even though this group of species shows strong responses to changes in the environment (Roelofs 1983, Lougheed et al 2001) and is recognized for its important effects on ecosystem processes (Carpenter and Lodge 1986). Here, I show that four common submersed aquatic macrophyte species differ in their effects on ecosystem properties and their response to environmental stress (temporary water draw-down).…”

Development and Use of a Zooplankton Index of Wetland Quality in the Laurentian Great Lakes Basin

“…3; r 2 ϭ 0.32, P Ͻ 0.0001), leveling off at ϳ10 species of submergent plants and a WZI value of 4. This is not unexpected, given the significant relationship between submergent plants species richness and wetland water quality (Crosbie and Chow-Fraser 1999;Lougheed et al 2001).…”

“…Second, zooplankton taxa often have different preferences for trophic state Bertilsson 1989, Berzins andPejler 1989) , and therefore species replacement will also occur with water quality degradation. Finally, since the species richness of submersed macrophytes declines as marshes become eutrophic and degraded (Crosbie and Chow-Fraser 1999;Lougheed et al 2001), we hypothesize that the zooplankton community should reflect changes in the plant community as we proceed along the trophic-degradation gradient.…”

The Impact of Agricultural Land Use Change on Lake Water Quality: Evidence from Iowa

“…Another technique used in the literature is to use simple univariate regressions of land use on water quality (see, e.g. Lougheed, 2001). Limiting the model to one period, or not controlling for other factors that can affect water quality can potentially bias the coefficients of interest.…”