3. Results

3.1 Short-term study

3.1.1 Sediment mass and organic matter content: GLAS sites

Mean deposited sediment levels in the pre-fencing period ranged from 19.96± 5.29 gm-2 (SE) at the GLAS site 11 control point to 538.15± 473.74 gm-2 (SE) at the GLAS site 3 pressure point. In the post fencing period, mean deposited sediment levels ranged from 40.48± 11.94 gm-2 (SE) at the GLAS site 7 control point to 458.76± 197.88 gm-2 (SE) at the GLAS site 1 control point.
PERMDISP analysis detected a marginally significant difference in homogeneity of dispersions among samples for levels of deposited sediment mass (z scores) at sampling points prior to fencing compared to sampling points following fencing (F15,188= P=0.06*), but none in relation to %OM. No reductions were found, however a pattern of reductions in dispersions (z scores) following fencing was observed at several sites (Figure 3).
A significant interaction effect was identified between Fencing and Treatment in relation to deposited sediment mass (F1,28= 5.17, P=0.03). Pairwise results demonstrated significantly greater masses of deposited sediment at pressure points compared to control points, prior to fencing (t1,14=2.38, P=0.04) but no significant difference following fencing. It should be noted however, that there was also a significant increase in levels of deposited sediment at control points in year 2 compared to year 1 (t1,14=3.09, P=0.01) (Figure 4).
There were no significant effects in relation to %OM data for either PERMDISP or PERMANOVA analyses.

3.1.2 Macroinvertebrate

A significant difference was detected in the magnitude of multivariate dispersions among samples (across control and pressure points) between pre-fencing and post-fencing periods (F15,176=3.81, P=0.01). Pairwise comparisons indicated that at Site 1 (t1,10=2.34, P=0.04) and Site 3 (t1,10=3.58, P=0.01) (both on the Blacklion stream) the magnitude of multivariate dispersion between samples was significantly less following fencing. Additionally, a marginally significant decrease in sample dispersions was found in relation to Site 4 (t1,10=2.07, P=0.06) (Figure 5).
Principle coordinate ordination (PCO) plots demonstrate (in most cases) closer grouping of macroinvertebrate data between control and pressure points post fencing (Figure 6).
SIMPER analysis highlighted twelve taxa that consistently contributed to dissimilarities between the Treatment/Fencing levels (Table 1).A. fluviatilis, R. semicolorata, S. pallipes and Agapetussp. had higher abundance at control points than at pressures points in the pre-sampling period (Pre-Pressure v Pre-Control) and greater in the post-fencing period compared to the pre-fencing period at both control (Pre-Control v Post-Control) and pressure (Pre-Pressure v Post-Pressure) points. The grazing riffle beetles, Elmis aenea and Limnius volckmari occurred in higher abundance at pressure points following fencing. Three taxa (B. rhodani/atlaniticus , Simuliidae and Chironomidae) were less abundant in the post-fencing period at both control and pressure points, and less abundant at control points in both the pre-fencing and post-fencing periods.
In terms of the univariate metrics, there was a significant interaction effect (Fencing/Treatment x Site ) in relation to total richness (F21,157=5.10, P=0.01) and EPT richness (F21,157=5.96, P=0.01). Pairwise results highlighted significantly higher values at the pre-fencing control point relative to the pre-fencing pressure point at Site 3 (t1,10=5.17, P=0.01), Site 6 (t1,10=2.63, P=0.04) and Site 7 (t1,10=4.15, P=0.01), while at Site 1 total richness values were greater at the pressure point (t1,10=3.92, P=0.01) (Figure 7). Following fencing none of these significant differences in total richness persisted and there were significant increases in total richness at the pressure points following fencing compared to prior to fencing at Site 2 (t1,10=4.13, P=0.01), Site 3 (t1,10=6.29, P=0.01) and Site 6 (t1,10=2.79, P=0.03)
In relation to EPT richness (Figure 8), there were higher values at the control points relative to the pressure points at Site 3 (t1,10=6.76, P=0.01) and Site 7 (t1,10=3.80, P=0.01) in the pre-fencing period. At Site 1, EPT richness values were greater at the pressure point in the pre-fencing period (t1,10=3.39, P=0.02). Here again, none of these differences persisted following fencing and there were also significant increases in EPT richness at pressure points following fencing at Site 2 (t1,10=5.26, P=0.01) and Site 3 (t1,10=5.26, P=0.01).

3.1.3 Habitat assessment: short-term study

Univariate PERMANOVA analysis of habitat index scores (THI and RHI) did not highlight any difference between pre- and post-fencing periods. Multivariate analysis of habitat score sub-indices and stream substrate cover, geomorphic unit representation, physico-chemical measurements and stream dimensions, similarly did not detect any differences. However, RHI scores (available in supplementary information) did show an increase at pressure points following fencing, but RHI scores were typically higher at control points.
In relation to the univariate analyses, the ground coversub-index of the RHI and THI was the only habitat parameter that showed a difference between pre- and post-fencing periods. A significantFencing and Treatment interaction was observed (F1,28=6.44, P=0.02) and pairwise results highlighted a significantly (t1,14=2.65, P = 0.05) higher metric value at post-fencing pressure points (9.75 ±0.66 SE) compared to pre-fencing pressure points (7±0.2.65 SE). Significant main term Treatmenteffects with no Fencing interaction were detected for longitudinal connectivity (F1,28=9.29, P=0.01), canopy cover (F1,28=7.58, P=0.01) and shrub layer cover (F1,28=8.82, P=0.01). For each of these RHI sub-indices, mean values at control points were greater than for those at pressure points.

3.2 Long term study

There was a significant interaction between the factors Fencingand Catchment in relation to community structure data in the Milltown Lake catchment (F1,11=2.78, P = 0.02). Significant differences were detected in community structure in both the fenced (t1,6=3.09, P=0.01) and the control (t1,5=2.51, P = 0.01) catchments between pre- and post-fencing periods. Pairwise results also showed that prior to fencing there was a significant difference in community structure between the ‘to be fenced’ catchment and control catchment (t1,11=2.31, P = 0.01) that did not persist following the fencing period.
Ordination based on principle components (PCO) illustrated a clear separation between pre- and post-fencing sites in the fenced catchment along the first PCO axes which accounted for 34.8% of total variation in the community structure (Figure 9). There is also a separation between pre-and post-fencing samples in the control catchment, although this appears not to be as pronounced as in the fenced catchment.
SIMPER analysis on the fenced catchment data showed that increased abundances of Simuliidae, Ancylus fluviatilis, Glossomatidae, Elmidae and Baetidae, and reduced abundance of Asellidae, in the post fencing period accounted for 41% of the dissimilarity in community structure between the pre- and post-fencing period. In the control catchment 48% of the dissimilarity in community structure between the two periods was due to increased abundances of Gammaridae and Simuliidae in the post-fencing period, and reduced abundances of Baetidae,Hydropsyche siltalai and Elmidae.
In relation to univariate metrics, there was a significant interaction effect (Fencing x Catchment ) for % ephemeropteran abundance (%E) (F1,11=19.62, P=0.01) and EPT abundance (F1,11=14.69, P=0.01). Pairwise results for both, showed significant differences in values between pre- and post-fencing periods in both the fenced and control catchments. In the fenced catchment values for both metrics generally increased following fencing while in the control catchment values for both generally decreased (Figure 10).