Understanding River Landscapes
Maintaining High Water Quality
Riparian management has an important role to play in maintaining high quality water for a range of purposes, including human consumption, irrigation for agriculture, stock watering, maintenance of wildlife and native fish populations, recreation, scenic values and cultural heritage.
Rivers can be contaminated by material from adjacent land. This can include soil particles (sediment), nutrients such as nitrogen and phosphorous, salt, plant material from crops, chemicals, and microbes. In rural regions, eroding soil and associated nutrients are the most important and widespread causes of reduced water quality. Some of the aspects of water quality that causes community concern is turbidity (created by suspended sediment carried by the water); algal blooms; and in some cases smell.
Under natural conditions, Australia's river landscapes experience naturally low loads of sediment and nutrient and much of our wildlife has adapted to these conditions. This can make native wildlife susceptible to increased contaminant loads and less able to compete with introduced specie. For example, many native fish are visual feeders and do not tolerate turbid waters, while exotic carp are well suited to turbid waters.
The diagram below shows the difference between a well managed and a poorly managed riparian areas. By clicking on the red cones you can explore some of the different elements that affect water quality.
<![CDATA[<table border='0' cellspacing='0' cellpadding='0'>
<tr valign='top'><td><img height="218" width="393" src="graphics/map2a_lib.gif" alt="Ephemeral Streams" border="0">
<p>Riparian management effects water quality by influencing the following processes:</p>
<ul>
<li><a href="#erosion">erosion</a>,
<li><a href="#buffering">buffering</a> land use,
<li><a href="#stockaccess">stock access</a>,
<li><a href="#shading">shading</a>
<li><a href="#nutrient">in-stream nutrient transformation</a>, and
<li><a href="#floodplainstreaminteractions">floodplain-stream interactions</a>
</ul>
<p><a name="erosion"> </a></p>
<h3>Erosion</h3>
<p><table border='0' cellpadding='0' cellspacing='0' align='none'><tr><td width="200"><a onClick="popImageWindow('brokenbankstabilisation.jpg');return false;" href="showimage.htm_9A127922"><img src='images/medium/brokenbankstabilisation.jpg' width='200' height='132' border='0' style='border:1px solid black;' alt="Bank Stabilisation, Broken River, VIC"></a><br><span class='photocaption'>Bank Stabilisation, Broken River, VIC<br><a onClick="popImageWindow('brokenbankstabilisation.jpg');return false;" href="showimage.htm_9A127922"><img src="graphics/zoom.gif" height="17" width="49" alt="Zoom Image" border="0" /></a></span></td></tr>
</table><p>Streambank erosion is a dynamic and natural process as streams meander across the landscape.
Since European settlement of Australia, however, in many places the rate of streambank erosion
has increased markedly. This is as a result of the extensive clearing of deep-rooted,
natural vegetation across catchments for agricultural and urban development.
In cleared catchments, rainfall moves off the land surface at a much faster rate.
This increased flow puts pressure on stream channels that can no longer contain flood peaks,
and bank erosion is one result. Access by stock, fire and the removal of riparian vegetation
from along streambanks increases the problem and weakens the ability of streambanks to
resist the erosive forces of increased flood flows.</p>
<p><a href="erosioncontrol.htm">Click for other benefits of erosion control.</a></p>
<p><a name="buffering"> </a></p>
<h3>Buffering</h3>
<p>The sediment and nutrient trapping effectiveness of riparian vegetation mean that well-located
strips can act as a buffer between land areas developed for agriculture or urban use, and
adjacent streams. Vegetation in riparian areas slow the overland movement of water and cause
sediment, attached nutrients and other contaminants to be deposited on land before they can reach
the stream channel.</p>
<p><a href="buffering.htm">Click for other benefits of buffering.</a></p>
<p><a name="stockaccess"> </a></p>
<h3>Stock Access</h3>
<p>Uncontrolled access by domestic stock to riparian land can lead to excessive run-off, bank erosion, loss of productive land, decline in important wildlife habitat, reduced water quality and damage to in-stream ecosystems. Unfortunately, domestic stock, particularly cattle, can favour riparian lands and, if not managed carefully, will spend much of their time along streambanks and in the water. The result is usually over grazing that erodes bank soils allowing weed invasions, and develops stock tracks that erode during heavy rain. This results in increased sediments and nutrients being washed into the stream. Inputs of animal dung and urine are important factors in reduced water quality for downstream users.</p>
<p><a href="stockaccess.htm">Click for more about the process of stock access.</a></p>
<p><a name="shading"> </a></p>
<h3>Shading</h3>
<p>Once natural riparian vegetation is widely cleared for agricultural or urban development, light intensity within the water column increases greatly. In steep landscapes where streams are narrow, the channel may be partly shaded by adjoining hills and the streambank itself. Where channels are less than about 10 metres in width they may be partly or completely shaded by adjoining shading vegetation. Recent research has shown that reduced light intensity prevents excessive growth of nuisance plants and algae, including toxic blue-green algae in river systems. The dim or patchy lighting resulting from undisturbed riparian vegetation also assists in providing habitats for both predators and prey within the stream.</p>
<p><a href="shading.htm">Click for other benefits of shading.</a></p>
<p><a name="nutrient"> </a></p>
<h3>In-stream nutrient losses</h3>
<p>Not all of the nutrient delivered to the stream from the surrounding land makes it through the
river system. Biological uptake along the way can result in significant losses of nitrogen to the
atmosphere by microbial organisms that live on the stream bed or other surfaces along the stream.
These losses can be important for maintaining high water quality downstream. The surfaces include woody
debris that is naturally a part of rivers, and sand and rock beds on the stream. Native riparian
vegetation directly supplies woody debris and provides the aquatic habitat suitable for microbial growth.
Increased loads of fine suspended sediment from riparian degradation upstream can smother these
environments removing the biofilms and their water filtering role (see
<a href="../publicat/guidemanual.htm">River and Riparian Management Technical Guideline 1</a> - '<i>Designing filter strips to trap sediment and attached nutrient</i>' - Ch 4</p>
<p><a href="instreamprocessing.htm">Click for more about in-stream processes.</a></p>
<p><a name="floodplainstreaminteractions"> </a></p>
<h3>Floodplain-stream interactions</h3>
<p>In lowland rivers, floodplains form extensive riparian landscapes.
These have a range of landforms including swamps, alluvial flats, levees, billabongs,
flood runners, and <font color='red'>anastomosing channels</font>, which support a diversity
of animal and plant life.
They are an ecosystem in their own right. The health of floodplains and the rivers that form them
is dependent on naturally varying flows of water, energy, <a class='glossaryitem' href="glossary.htm#Nutrients" onMouseover='showTerm(event,"Natural elements (usually nitrogen and phosphorus) that are essential for plant and animal growth.")' onmouseOut='hideTerm();'>nutrients</a>and organisms between the river and floodplain.</p>
<p><a href="floodplainstreaminteractions.htm">Click for other benefits of floodplain-stream interactions.</a></p>
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Shading | Buffering | Floodplain-stream interactions | In stream processing | Stock access | Erosion control For more information about water quality see:
Fact Sheet 3 - Improving Water Quality
or River and Riparian Management Technical Guideline 2 - 'Managing nutrients in floodplain wetlands and shallow lakes '
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