Percentage land use in the watershed determines the water and sediment quality of 22 marshes in the Great Lakes basin

Abstract

Data from 22 Ontario marshes were used to test the hypothesis that distribution of forested, agricultural, and urban land in the watershed determines the water and sediment quality of Great Lakes wetlands. The first three components of the principal components analysis explained 82% of the overall variation. PC1 ordinated wetlands along a trophic gradient; species richness of submergent vegetation decreased with PC1 scores. PC2 reflected the content of inorganic solids and phosphorus in sediment and the ionic strength of the water. Both PC1 and PC2 scores were positively correlated with percent agricultural land, whereas PC1 scores were negatively correlated with forested land. Correlation between PC1 and agricultural land improved when best-management practices were considered. Accounting for common carp (Cyprinus carpio) disturbance did not confound the relationship between land use and water quality. PC3, driven by soluble reactive phosphorus and nitrate nitrogen concentration in the water, was not correlated with land use. Concentrations of polycyclic aromatic hydrocarbons and Metolachlor were correlated with urban and agricultural land, respectively, and may be useful as land use surrogates. Watershed management favouring the retention of forested land, or creation of buffer strips to trap agricultural runoff in the drainage basin, should help maintain aquatic plant diversity in coastal wetlands.

The accuracy of land cover-based wetland assessments is influenced by landscape extent

“…The relationship between biotic integrity and land cover is likely the result of multiple processes. For example, wetlands situated in disturbed landscapes suffer increased exposure to environmental stressors (Crosbie and Chow-Fraser 1999;Houlahan and Findlay 2004), increased nest predation (Phillips et al 2003), increased invasion by exotic species (Galatowitsch et al 2000), and reduced habitat connectivity, which has been associated with reduced richness of waterbirds (Guadagnin and Maltchik 2007). It is, therefore, not surprising that land cover surrounding a wetland is predictive of that wetland's biotic integrity as measured from plants and wetland-dependent songbirds and shorebirds.…”

Landscape Development Intensity Index

“…In summary, much attention has been given recently to the relationships between land use and the quality of ecological communities (see for example; Allan et al, 1997;Beaulac and Reckhow, 1982;Crosbie and Chow-Fraser, 1999;Ehrenfeld, 1983;Galatowitsch et al, 2000;Kirkman et al, 1996;Richards et al, 1996;Roth et al, 1996), the development of classification systems for watersheds (Habersack, 2000;Hawkins and Vinson, 2000), biological indicators of ecosystem health (Jones et al,2001;Patil, 2001), and indices of biological integrity for streams (Barbour et al, 1996;Karr and Chu, 2000;Gerritsen and White,1997). These efforts assume that human activities, which are tied to land uses, have effects on ecological functions, health, or integrity, yet there is a paucity of studies in the literature that have quantitatively evaluated the human disturbance gradient .…”

Development and use of the Wetland Fish Index to assess the quality of coastal wetlands in the Laurentian Great Lakes

“…There is well-documented evidence that land-use alteration in the watersheds of coastal wetlands can negatively affect their habitat quality (Crosbie and Chow-Fraser 1999;Lougheed et al 2001;Chow-Fraser 2006). Agricultural and urban development is generally accompanied by a high nutrient and sediment load to the wetlands, leading to high algal production and increased water turbidity.…”

“…An implicit assumption is that wetlands can be ranked according to the degree of anthropogenic disturbance, as indicated by water quality deterioration (i.e., increased nutrient concentrations; water turbidity, temperature, and conductivity; etc. Crosbie and Chow-Fraser 1999). Further, we assume that this degradation will be reflected in the species composition of the fish community, in a manner similar to that described in Lougheed and Chow-Fraser (2002) for zooplankton (Wetland Zooplankton Index).…”