WATERSHED URBANIZATION AND CHANGES IN FISH COMMUNITIES IN SOUTHEASTERN WISCONSIN STREAMS¹

Abstract

We compared watershed land‐use and fish community data between the 1970s and 1990s in 47 small streams in southeastern Wisconsin. Our goal was to quantify effects of increasing urbanization on stream fishes in what had been a predominantly agricultural region. In the 43 test watersheds, mean surface coverage by agricultural lands decreased from 54 percent to 43 percent and urban lands increased from 24 percent to 31 percent between 1970 and 1990. Agriculture dominated the four reference watersheds, but neither agriculture (65–59 percent) nor urban (4.4–4.8 percent) land‐uses changed significantly in those watersheds during the study period. From the 1970s to the 1990s the mean number of fish species for the test stream sites decreased 15 percent, fish density decreased 41 percent, and the index of biotic integrity (IBI) score dropped 32 percent. Fish community attributes at the four reference sites did not change significantly during the same period, although density was substantially lower in the 1990s. For both the 1970s and 1990s test sites, numbers of fish species and IBI scores were positively correlated with watershed percent agricultural land coverage and negatively correlated with watershed urban land uses, as indexed by percent effective connected imperviousness. Numbers of fish species per site and IBI scores were highly variable below 10 percent imperviousness, but consistently low above 10 percent. Sites that had less than 10 percent imperviousness and fewer than 10 fish species in the 1970s suffered the greatest relative increase in imperviousness and decline in species number over the study period. Our findings are consistent with previous studies that have found strong negative effects of urban land uses on stream ecosystems and a threshold of environmental damage at about 10 percent imperviousness. We conclude that although agricultural land uses often degrade stream fish communities, agricultural land impacts are generally less severe than those from urbanization on a per‐unit‐area basis.

Large‐scale relationships between basin and riparian land cover and the ecological status of European rivers

“…This was corroborated by the null effect of arable land in the direct linear regression (Table 7). Similarly, Wang et al (2000) More surprisingly, arable land appeared to have no effect in the French regional PLS models, even in the Tables Calcaires region where most basins are largely dedicated to crops. This was confirmed by the very small effect of arable land in the linear regression (dR 2 = 1.5%, Table 7).…”

A Gap Analysis and Comprehensive Conservation Strategy for Riverine Ecosystems of Missouri

“…August 2007have examined the effects of urban land cover on the ecological integrity of stream ecosystems (Klein 1979, Osborne and Wiley 1988, Limburg and Schmidt 1990, Booth 1991, Weaver and Garman 1994, Booth and Jackson 1997, Wang et al 2000. However, we were unable to find any thresholds in the literature dealing with the relations between percentage agriculture in the watershed and measures of ecological integrity.…”

Influence of environmental variables on stream fish fauna at multiple spatial scales

“…All these alterations drastically degrade stream ecosystems and lead to major changes in the biota even at relatively low levels of urbanization (Wang et al, 1997;, causing declines in fish diversity, abundance, and biotic integrity (Wang et al, 2000;. However, in this study we had few samples to evaluate rigorously the influence of urban land use on site variables.…”