Nutrients & Algae
Nitrogen and phosphorous containing compounds are natural and vital components of a healthy aquatic ecosystem. However, when released into the environment as a result of human activities, they can alter the finely balanced equilibrium of nutrients cycling through the ecosystem and drive the uncontrolled and unbalanced growth of aquatic plants and algae in a process called eutrophication. This can lead to severe problems for aquatic organisms, the ecological health of a waterbody and for humans who also depend on the water for drinking, recreational use or the production of food such as watercress and fish.
Sediment
Turbidity is a measure of the amount of sediment in the water. There are many factors that can cause turbidity to increase but the most common is the presence of soil and mineral sediments in the water column. These materials are often released following disturbance of the river or lake substrate, but they can also enter the water as a result of erosion and run-off from the land. Increased turbidity results in significant ecological impacts by blocking the penetration of light to aquatic plants, clogging the gills of fish and other organisms and by smothering benthic habitats. It can also increase the intensity and cost of treating water for drinking.
Microbes & Parasites
Microbial pollutants, derived from human and animal faecal matter, pose asignificant risk to human health, either when people come in contact with theriver or bathing waters and when contaminated water is abstracted for drinking water treatment. They can also have severe negative impacts on the ecological health of the river by increasing turbidity and reducing the levels of dissolved oxygen. The main mechanisms by which faecal material, parasites and faeces-derived substances enter the water course are from, direct ‘voiding’ into the water by livestock, leaching from manure and slurry stores and from consented and unconsented discharges of human sewage.
Pesticides
Chemicals used to kill and control ‘pest’ organisms are commonly referred to as ‘pesticides’. When used with care, they can deliver substantial benefits including; the availability of good quality, reasonably priced food and well managed urban environments. However, despite these benefits it is essential to note that large amounts of pesticides often miss their intended target and are lost into the environment where they can contaminate non-target species, air, water and sediments. By their very nature, pesticides can pose a significant threat to ecosystem health, biodiversity and human health if they are not used with appropriate care and consideration.

 
W A T E R   Q U A N T I T Y


Abstraction & Low Flows
The Test &Itchen supply much of Hampshire’s public waterneeds, including a large proportion of the Isle of Wight’srequirements. There are a number of significant surface water abstractions as well as groundwater abstractions from the chalk. The catchment also supports a large number of commercial fish farms and watercress growers who are dependant on reliable and abundant water supplies. Although the majority of abstraction is non-consumptive and returns water locally the overall impact of abstraction puts pressure on flows and can potentially lead to rivers not having enough water to support a healthy ecosystems.

        

Flooding
With changes in climate affecting rainfall patterns and larger areas of land being covered for development and thus losing their natural ability to drain water, flooding has become an increasingly apparent issue in the past couple of years. Flooding can be caused from surface water, groundwater and other watercourses and can be particularly severe when the different types of flooding combine.

 
Structure & Function
Chalk streams have been historically modified to suit a variety of human purposes such as agriculture, fisheries, flood risk management and the development of watercress bed and mills. The various modifications have altered the natural character of the river and led to systems being potentially over-widened, over deepened, impounded and disconnected with the floodplain.    

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Barriers to Fish 
In channel weirs and structures are generally linked to negative impacts on the physical and ecological condition of the river. In addition to altering the depth and velocity of flow, structures can also impact on the biological connectivity of the river by limiting fish and invertebrate passage.


Riparian Management
The Test and Itchen supports a thriving fisheries industry and the majority of the river is intensively managed to accommodate sport fisheries. Inappropriate vegetation management practices can impact on the diversity of riparian habitats, over widening of sections and the river's ability to restore it’s natural features.


Water temperature
Climate change models forecast that average summer air temperature will rise by between 2 and 4 degrees celsius. Rivers and the freshwater ecosystems they support are particularly sensitive to changes in climate and water temperature. For example a rise in water temperature above 22 degrees celsius for more than seven consecutive days can be lethal for brown trout.


Invasive Non-Native Species
Traditional chalk stream flora and fauna faces increasing pressure from a range of non-native invasive species that have taken hold within the catchment. These include Himalayan Balsam, American mink and most recently the American signal crayfish.

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