6.6 LOSS AND DEGRADATION OF RIPARIAN VEGETATION Loss and degradation of riparian vegetation are significant stressors on river and estuarine health in the Manning. Riparian vegetation was cleared extensively prior to the 1950s, and stock impact on the riparian zone remains a widespread. The estuary is severely modified due to substantial clearing of natural vegetation35. During the rapid assessment of the catchment (Swanson 2020), most estuarine sites were rated Poor or Fair, primarily due to the sparse distribution of riparian vegetation (mangroves, swamp oak). In freshwater catchments, the riparian zone was typically a narrow band (less than 10 metres wide) of River Oak, with exotic species dominating the shrub layer. Cleared shorelines are exposed to erosion from high rainfall events, high flows, wind waves, tides and boat wash. The subcatchments with the highest risk from loss of riparian vegetation are the Manning River, Upper Manning River, Myall Creek and Barnard River34. The Barnard River has the lowest riparian vegetation cover of any river in the MidCoast region, at 34%. This is reflected in MidCoast Water Services data, which shows the Barnard River contributes excessive levels of turbidity during high rainfall events and is also a significant contributor of nutrients (particularly nitrogen and phosphorus) at all flows. Impacts from loss of riparian vegetation include floodplain stripping and bank erosion, which have been identified as the largest contributors of sediment in the river36. Cleared hillslopes, poor groundcover and poor riparian vegetation are mobilising large amounts of sediment into the system, smothering micro-niches for fauna, reducing instream condition and causing turbidity with consequent impacts on aquatic fauna and flora. Nutrients are transported with sediment into waterways, causing algal blooms.
“My vision for the future is a stable catchment that’s well vegetated. Stock are managed and there is a healthy riparian buffer to filter run-off.” Noel Piercy, Member, Manning River ECMP Reference Group
Other impacts include declines in terrestrial and aquatic wildlife habitat and dispersion corridors, and socio–economic impacts such as shallowing of the estuary for boating and higher drinking water treatment costs. Stakeholders include: Hunter LLS, MCC, DPIE - Crown Lands, Forestry Corp, NPWS; Mid Coast 2 Tops Landcare; private property owners in rural and urban areas, MCC (Council owned land), general community (recreation and cultural purposes, cost-bearing) Related issues: Sediment and erosion; agricultural impacts; loss of biodiversity.
35: Swanson, 2020 36: Raine & Gardener, 1992
Manning River Estuary and Catchment Management Program (ECMP)
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