Stormwater - Riparian Vegetation Monitoring: Water Quality Monitoring Toolkit

Stormwater - Riparian Vegetation Monitoring

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General

Riparian vegetation is classified as vegetation that is found on the banks of a river or stream and is an integral component of the ecosystem. Riparian vegetation plays a
crucial role in maintaining bank stability and control of bed erosion in streams, which can be directly linked to water quality issues. IT can reduce the amount of sediment and associated pollutants entering the stream. Research suggests that stream and river banks that are sparsely vegetated erode at a much higher rate than those banks that are
densely vegetated. A well vegetated streambank is resistant to streambank erosion due to the extra stability provided by the roots and other plant material, and because it can reduce flow velocity at the edges of the stream. Riparian vegetation also plays a role in increasing biodiversity and serves to provide habitat for native fauna. Loss of riparian vegetation, through clearing, livestock grazing or recreational uses, means that these benefits are lost and the overall condition of the stream can decline. For this reason, riparian zone revegetation is an important aim of government agencies and many community groups.

Protocol

Riparian Zone Vegetation
Species and community survey and assessment

Riparian zone vegetation is assessed along the reach of each site. The structures of the vegetation communities are recorded using the methods and system described by Specht (Specht, R.L. (1970) Vegetation, In G.W. Leeper (ed) The Australian Environment CSIRO and Melbourne University Press, Melbourne), to ensure ease of cross-referencing with other public documents for the region.

Plant species are described by assessing the species composition of the commonly occurring species, with searches of microhabitats undertaken in the manner described by Cropper (Cropper, S., 1995, Management of Endangered Plants. CSIRO, Melbourne) for undertaking vegetation surveys. Data are recorded on standardised field data sheets.

The completion of surveys in Spring and Autumn enable the best possible identification of the range of environmental and noxious weeds which occur in riparian zones. Survey results can be both descriptive and management orientated. That is, in addition to providing a vegetation description in the standardised format, an assessment of threats, allowing management decisions to be made regarding weed control, can also been included.

The riparian vegetation assessment is based on:

the structure of the vegetation ( ground cover, shrubs, over story);
the width of the riparian zone in relation to that expected in the presettlement landscape;
the proportion of the vegetation that is native;
the extent and severity of riparian land clearing.

Weed mapping

Weeds are mapped using a quantitative approach. The % cover of weed invasion in each stratum of the plant community - canopy, mid-storey and ground cover is determined within a specified range and an index weighting then applied, to give a final weed class, which can be easily compared spatially and temporally. A detailed description of the steps undertaken to calculate the weed class within a specified area are listed below.

Step 1:
Visually dividing the vegetation community into logical sections.

Step 2:
Estimate the percentage of weeds compared to native species within each division. For each division, record the corresponding scale of 1-4. Refer to Table 1.

Table 1: Weed Cover Scale

Structural Division	Weed Cover %	Scale
	< 10%	1
Upper	10%-30%	2
	31%-60%	3
	> 60%	4
	< 10%	1
Middle	10%-30%	2
	31%-60%	3
	> 60%	4
	< 10%	1
Lower	11%-30%	2
	31%-60%	3
	> 60%	4

The scale should be recorded for each structural division as:
“Upper Scale / Middle Scale / Lower Scale”.

For example: “1 / 3 / 2’’

Step 3:
The weed class is calculated from the recorded scales of each division (Step 2), to give an overall rating.

This calculation takes into account the impact the weeds have on the vegetation community. Weeds in the upper division can strangle and destroy the dominant native species. Weeds in the middle division generally compete with native species whilst weeds in the lower division can significantly alter the ground conditions, preventing the regeneration of native species. Therefore a weighting factor is applied to each division to represent the relative impact on the vegetation community.

The equation:

Division	Scale	Weighting Factor
Upper		x 0.5	=	+
Middle		x 0.2	=	+
Lower		x 0.3	=	+
		4		Calculated Class (total)

To determine the Weed Class, round off the Calculated class to the nearest integer, (eg. <1.5 = 1, 1.5 or >1.5 = 2).

From; Aquatic Bio-indicator Survey for Hornsby Shire Council

Alternative method (less quantitative)

Riparian vegetation stress rating assessment criteria based on photography
Stress rating	Criteria for assessment and categorisation
Low stress	Greater than 50% of the photo showed a riparian buffer strip along the main stream that was (20m in width
Medium stress	Between 20 and 50% of the photo showed a riparian buffer strip along the main stream that was (20m in width
High stress	Less than 20% of the photo showed a riparian buffer strip along the main stream that was (20m in width
Cover of streambank and width of the riparian zone - A measure to identify the amount and extent of riparian vegetation coverIndigenous cover - A measure to identify the level of weed invasion in the riparian zone as well as the loss of native riparian vegetation due to grazing, planting of exotics and other pressures.Connectivity - A measure to assess the linkages between remnant patches of riparian vegetation and between the riparian vegetation and other remnants of indigenous vegetation in the landscapes.Structural integrity - A measure to assess the level of degradation of the riparian vegetation system, in terms of indigenous cover, width of cover, connectivity and diversity of canopy layers.