Cattle exclusion over the short-term impacted instream deposited sediment and aquatic macroinvertebrate communities
Significantly greater mean masses of deposited sediment were observed at pressure points (relative to control points) prior to fencing, however, following fencing there was no difference between control and pressure points, despite a general increase in background levels of deposited sediment. Patch scale deposits of fine sediment (as assessed here) reflect stream bank erosion in the immediate upstream vicinity of the affected site (Larsen et al., 2009). Habitat assessment results here did not highlight any improvement in bank stability following exclusion of cattle access, although increased ground cover in riparian areas was observed. Reductions in the extent of bare ground following cattle exclusion via fencing were also observed in Alberta, Canada by (Miller et al., 2010a) and in the north of Ireland by Rice et al. (2021) and were linked to improved water quality (Miller et al., 2010a). These authors also found no improvement in stream bank stability following four years of cattle exclusion but did suggest that increased ground cover could also contribute to reduced rates of stream bank erosion. Collins et al. (2010) concluded that stream bank erosion was significantly reduced in all of six catchments studied in the UK following fencing and eight years of exclusion, leading to reduced siltation of salmonid spawning gravels. Hansen and Budy (2011) however did observe significant improvement in stream bank stability after only one to two years of exclusion of cattle via fencing in Utah. The time-frame of the current study may have been too short to allow for improvements in bank stability following fencing.
Elevated levels of deposited sediment have been shown to drive changes in macroinvertebrate communities affected by cattle access (Braccia and Voshell, 2006; Conroy et al. 2018). The results here have highlighted the elimination of pre-fencing disparities in masses of deposited sediment between control and pressure points as a result of one year of exclusion via fencing. Additionally, reductions in multivariate dispersions (macroinvertebrate data) between control and pressure samples following fencing have been highlighted at several sites. Warwick and Clarke (1993) found that multivariate dispersion among marine community samples collected from impacted areas may be greater than from un-impacted areas, thus, here, higher dispersion among (control and pressure) samples prior to fencing compared to post-fencing may indicate reduced community stress following restoration via fencing. Other authors (see White et al., 2017) have shown increases in the magnitude of multivariate dispersion following restoration of streams and instream habitats due to improved habitat heterogeneity. It should be noted however that multivariate dispersions in the current study were measured across the gradient of impact (i.e. upstream and downstream of cattle access points) and thus reductions in dispersion here represent a convergence of communities towards control conditions following the removal of the cattle access impact. Results for EPT richness and total richness also suggested that improvements in ecological quality had occurred following one year of cattle exclusion at certain sites.