Benthic Macroinvertebrate Responses to Increasing Levels of Cattle Grazing in Blue Ridge Mountain Streams, Virginia, USA

Abstract

The relationship between benthic macroinvertebrate assemblages and cattle density was assessed from fall 2002 through spring 2004 in five small streams that represented a gradient of cattle grazing intensity. All study stream reaches were in pasture with no woody riparian vegetation, but varied in the intensity of cattle grazing (0 cattle ha(-1) at site 1 to 2.85 cattle ha(-1) at site 5). Regression analysis indicated highly significant and strong macroinvertebrate metric responses to cattle density during most sampling periods. The majority of metrics responded negatively to increased grazing, while a few (total taxa richness, number of sensitive taxa, and % collector filterers) increased along the gradient before declining at the most heavily grazed sites. Total number of sensitive taxa and % Coleoptera had the strongest relationship with cattle density throughout the study period. During some sampling periods, nearly 80% of the variation in these metrics was explained by cattle density. The elmid beetle, Oulimnius, had a particularly strong negative response to the grazing gradient. Study site groupings based on taxa composition, using detrended correspondence analysis (DCA), indicated that benthic samples collected from the reference site and light rotational grazing site were more similar in macroinvertebrate taxa composition than samples collected from the intermediate grazing and heavy grazing sites. Our findings demonstrate that biological integrity, as measured by benthic macroinvertebrate metrics and assemblage composition, is highly related to cattle density in small streams in the Blue Ridge mountains, Virginia, USA. This suggests that the degree of agricultural intensity should be given consideration in stream assessments, as well as land use planning and regulatory decisions.

Stream Macroinvertebrates and Habitat Below and Above Two Wilderness Fords Used by Mules, Horses, and Hikers in Yosemite National Park

“…Other belowabove differences appeared only in late season. Summer use, perhaps compounded by low flows (Fritz et al 1999), may have affected these measures, but lack of trail activity and periphyton dieback during winter, along with spring flushing flows, may have facilitated annual recovery (Fritz et al 1999, Braccia andVoshell 2007, see also Gard 2002) such that early season differences were not present. Some late-season responses might also be indicative of longer-term impacts that only became detectable with population increases during late summer (see also .…”

“…Most related work has focused on disturbance distributed along one or more stream reaches (e.g., Braccia andVoshell 2007, Herbst et al 2012). However, stream crossings on formal trails used by hikers and stock are localized disturbances focused at fords and habitat immediately downstream (Miller et al 2010).…”

“…Humans and equines (Cole 1995, Cole et al 2004, Holmquist et al 2014, Ostoja et al 2014) have generally, though not exclusively, negative effects on wetland vegetation and fauna. Similarly, there may be negative effects on stream macrofauna immediately downstream of fords, but it is also possible that limited increases in particulate organics, periphyton, and habitat heterogeneity could enhance diversity in these oligotrophic streams without negatively affecting sensitive taxa (Braccia and Voshell 2007).…”

Mollusc communities of lowland rivers and oxbow lakes in agricultural areas with anthropogenically elevated nutrient concentration

“…The values of some metrics, e.g. the total taxa richness, number of sensitive taxa, % collector filterers or % Coleoptera respond negatively to increase in the cattle grazing (BraccIa & VosheLL 2007). Among macroinvertebrates, freshwater molluscs, which are hololimnic organisms that are present in the waters throughout their whole life cycle, are especially vulnerable to water pollution.…”

Impacto del uso del suelo agropecuario sobre macroinvertebrados acuáticos en pequeñas quebradas de la cuenca del río La Vieja (Valle del Cauca, Colombia)

“…Los sedimentos se acumulan en el fondo de la quebrada uniformizando el canal y cubriendo los espacios entre piedras que sirven de hábitat para organismos como peces y macroinvertebrados (Nakamura & Yamada, 2005;Braccia & Voshell, 2006;Chará et al, 2009;Giraldo et al, 2011). Otros estudios también han encontrado mayor cantidad de sedimentos en quebradas con pasturas, que en quebradas protegidas (HeartsillScalley & Aide, 2003).…”